Commercial Polymer Blends

CHAPTER 15

COMMERCIAL POLYMER BLENDS

M. K. AKKAPEDDI

Honeywell Inc., EAS R & T, Morristown, USA

15.1 Abstract

In this chapter, an overview of the commercially important blends is presented with a particular emphasis on the rationale for their commercial development, the compatibilization principles, their key mechanical properties and their current applications and markets. To facilitate the discussion, the commercial polymer blends have been classifi ed into twelve major groups depending on the type of the resin family they are based on, viz. (i) polyolefi n, (ii) styrenic, (iii) vinyl, (iv) acrylic, (v) elastomeric, (vi) polyamide, (vii) polycarbonate, (viii) poly(oxymethylene), (ix) polyphenyleneether, (x) thermoplastic polyester, (xi) specialty polymers, and (xii) thermoset blends. Within each major category, the individual polymer blends of industrial signifi cance have been described with relevant data. Since the discussion is limited only to those blends that are actually produced and used on a commercial scale, the relevant cost and performance factors that contribute to the commercial viability and success of various types of blends have been outlined. In comparing the different blends, the specifi c advantages of each type, as well as any potential overlap in performance with other type of blends have also been discussed. The fundamental advantage of polymer blends viz. their ability to combine cost-effectively the unique features of individual resins, is particularly illustrated in the discussion of crystalline/amorphous polymer blends, such as the polyamide and the polyester blends. Key to the success of many commercial blends, however, is in the selection of intrinsically complementing systems or in the development of effective compatibilization method. The use of reactive compatibilization techniques in commercial polymer blends has also been illustrated under the appropriate sections such as the polyamide blends. In many commercial blends, rubber toughening plays an important and integral part of the blend design. Combining high impact strength with other useful properties such as heat and solvent resistance can signifi cantly enhance the commercial value of a blend. Hence, the nature of the impact modifi ers used and the role of morphology on properties have been discussed under the appropriate cases of commercial blends. The chapter concludes with an outline of the potential trends in the commercial polymer development.

15.2 Introduction 6. Blends can be formulated, optimized and commercialized generally at a much faster rate Polymer blends have gained signifi cant com- (from concept to commercialization) than new mercial growth in the last two decades outpacing polymers, provided there are no major techni- the growth rate of existing polymers by at least cal hurdles for the compatibility development 2 to 5%. The current worldwide market volume between the components. for polymer blends and alloys is estimated to be 7. The development of an effective compatibiliza- more than 700,000 metric ton/y, with an average tion technology, whenever needed, allows the growth rate of 6 to 7%. Although this pace of resin supplier to establish a proprietary and growth slightly slackened during the ‘90’s, the competitively advantageous position. demand for polymer blends is expected to be 8. Blends offer useful and economic means of maintained due to the possibility of adjusting upgrading recycled and off-specifi cation polymers. the cost-performance balance and tailoring the technology to make products for specifi c end-use The terms “polymer blends” and “polymer applications [Utracki, 1998]. A combination of alloys” are defi ned in Chapters 1 and 2 of this the following important factors contribute to the Handbook. In the trade literature, they have been continued commercial interest in the polymer used interchangeably. In the context of current blends: discussion, we will treat all of them simply as 1. The blending of commercially available poly- polymer blends, except specifying, where pos- mers is a more cost-effective method of devel- sible, the origin of the technological compat- oping a new product that meets the customer or ibility between the components in each type market requirements, as opposed to developing of blend. Table 15.1 lists the commercially avail- a totally new polymer what generally involves able polymer blends according to their primary prohibitively high research, development and structural categories (Figure 15.1). capital costs. 2. Polymer blends can fi ll the cost-performance 15.2.1 Compatibilization Mechanisms in gaps in the existing commercial polymers. Commercial Polymer Blends Several properties can be uniquely combined in a blend that a single resin often cannot To be useful, most commercial polymer blends provide. In some cases, synergistic improve- are either designed or selected to have some ments in properties such as toughness and heat degree of the technological compatibility between resistance are achievable. the components to resist delamination and loss 3. Polymer blending can be done at a relatively in ductility. Compatibility is defi ned here as the low cost using an extruder. Production of new ability for the polymer components to co-exist polymers, on the other hand, requires capital- either as molecularly miscible or as morphologi- intensive plants and reactors that must operate cally distinct phases, but interfacially stabilized, on a reasonably large scale for reasons of without a tendency for delamination. economics. The technological compatibility in polymer 4. The fl exibility of extruder blending enables blends can result from any of the following custom production of different blends in a wide mechanisms: range of production volumes. Polymerization 1. Thermodynamic miscibility between the com- plants are generally not as fl exible and not ponents such as in the case of polystyrene (PS) economical for small volume production. and poly(2,6-dimethyl 1,4-phenylene ether) 5. Polymer blends provide an avenue for diversi- (PPE) blends. fying and expanding the product line for resin 2. Segmental miscibility between the compo- producers and suppliers, without signifi cant nents, even when they are phase separated, investment risks. imparting a low interfacial tension and an Commercial Polymer Blends 1025

Table 15.1. Commercial polymer blends

Blend Producer Trade Name Compatibilization Blend Type Mechanism(a)

Polyolefi n Blends Elastomeric Polyolefi n blends PP/EPDM Monsanto Santoprene® None (b); Dynamic Crystalline/ Amorphous Novacor Sarlink 3000® Vulcanization (c) PP/NBR Advanced Elastomer Geolast® Grafting/Dynamic Crystalline/ Amorphous Systems Vulcanization PP/EPDM/NBR Japan Synthetic Rubber Dynafl ex P® Grafting/Dynamic Crystalline/ Amorphous Vulcanization PP/PBD Monsanto Vyram® None; Dynamic Crystalline/ Amorphous Novacor Sarlink 1000® Vulcanization PP/Butyl Novacor Sarlink 2000® None; Dynamic Crystalline/ Amorphous Advanced Elastomer Systems TPE-3000® Trefsin® Vulcanization Ethylene DuPont Alcryn® Partial miscibility(d) Amorphous/ Amorphous terpolymer/PVC

Thermoplastic Polyoleﬁ n blends (TPO) PP/EP or EPDM BP Performance None Crystalline/ Amorphous polymers; Bayer; D&S International; Ferro; Himont Hoechst; ISR; Mitsubishi Petrochem; Republic Polymers; A. Schulman; Teknor Apex; Tonen and others HDPE/Polyisobutylene Paxon Polymer Co. Pax-Plus 3200® None Crystalline/ Amorphous

Styrenic blends ABS blends ABS/PC Monsanto Triax 2122® Partial miscibility Amorphous/ Amorphous General Electric Cycoloy EHA® Mobay Bayblend® ABS/PBT General Electric Cycovin® - - Monsanto Triax 4000® Daicel (Japan) ABS/PA Monsanto Triax 1000® Grafting(R) Amorphous/ Crystalline ABS/PVC General Electric Cycovin® Partial miscibility Amorphous/ Amorphous ABS/SMI Denka (Japan) Malecca K® Partial miscibility Amorphous/ Amorphous 1026 M. K. Akkapeddi

Table 15.1. continued

Blend Producer Trade Name Compatibilization Blend Type Mechanism(a)

SAN blends AES (SAN/AES blend) Dow Rovel® Miscibility Amorphous/ Amorphous SAN/PVC Vista Suprel® Partial Miscibility Amorphous/ Amorphous

Vinyl blends PVC/PMMA Polycast Royalite® Partial Miscibility Amorphous/ Amorphous PVC/Nitrile rubber B.F. Goodrich Hycar® Miscibility occurs with Amorphous/ Amorphous Showa Denka Denka LCS® NBR containing Polysar, etc. Krynac® >25% AN PVC/polyurethane D & S International Vythene® None Amorphous/ Amorphous

Acrylic blends PMMA/PV DFRexham Fluorex® Miscibility Crystalline/ Amorphous PMMA/PVC Kleerdex Kydex® Partial miscibility Amorphous/ Amorphous PMMA/acrylic core Rohm & Haas Plexiglas® Miscibility Amorphous/ Amorphous shell elastomer CYRO Cyrex® Miscibility

Elastomeric blends EPDM/PP Advanced Elastomer Systems Santoprene® Dynamic Vulcanization Amorphous/ Amorphous Novacor Sarlink® NBR/PP Advanced Elastomer Systems Geolast® Dynamic Vulcanization Amorphous/ Amorphous Novacor Sarlink® Dynamic Vulcanization Amorphous/ Amorphous Butyl rubber/PP Novacor Trefsin® Dynamic Vulcanization Amorphous/ Amorphous PBD/PP Novacor Vyram® Dynamic Vulcanization Amorphous/ Amorphous

Polyamide blends PA/ABS Monsanto Triax 1000® Graft-coupling(e) Crystalline/ Amorphous PA/Acrylic rubber DuPont Zytel FN® Grafting/controlled Crystalline/ Amorphous crosslinking PA/Elastomer DuPont Zytel ST® Graft-coupling Crystalline/ Amorphous Zytel Z408® Polar interactions(f) AlliedSignal Capron® 8350, 8351 EMS-American A28®, BT40X® Grilon PA/ Polypropylene D&S Int. Dexlon®, Dexpro® Grafting Crystalline/ Crystalline PA/Polyarylate Unitika X-9® Crystalline/ Amorphous Commercial Polymer Blends 1027

Table 15.1. continued

Blend Producer Trade Name Compatibilization Blend Type Mechanism(a)

PPE blends PPE/HIPS General Electric Noryl® Miscibility Amorphous/ Amorphous PPE/PS Gepax® PPE/PA-66 (and 6) General Electric Noryl GTX® Grafting Crystalline/ Amorphous AlliedSignal Dimension® Grafting BASF Ultranyl® Grafting PPE/PBT General Electric Gemax® Polycarbonate as Crystalline/ Amorphous compatibilizing additive Polycarbonate blends ABS/PC Dow Pulse® Partial miscibility Amorphous/ Amorphous AES/PC Dow Rovel 747® Partial miscibility Amorphous/ Amorphous ASA/PC BASF Terblend S® Partial miscibility Amorphous/ Amorphous PC/Styrene-Acrylic Novacor Chemicals SD 9000® Partial miscibility Amorphous/ Amorphous CYRO Cyrex® Partial miscibility PC/SMI Denka (Japan) Malecca® Partial miscibility Amorphous/ Amorphous PBT/PC General Electric Xenoy® Partial miscibility Crystalline/ Amorphous Dow Sabre 1628® Mobay Makroblend® PET/PC Mobay Makroblend UT® Partial miscibility Crystalline/ Amorphous General Electric Xenoy 2230® Polysar Petsar PD 8100® Eastman Ektar EA-001® Dow Chemical Sabre 1647, 1664® PA/PC Dexter Plastics Dexcarb 500® Compatibilizing additive Crystalline/ Amorphous

Polyester blends PBT/PC General Electric Valox 508®, 553® Partial Miscibility Crystalline/ Amorphous PBT/PET General Electric Valox 815®, 830® Miscibility Crystalline/ Crystalline Hoechst Celanese Celanex 5200®, 5300® PBT/ASA BASF (Germany) Ultrablend S® PC additive (?) Crystalline/ Amorphous PBT/Acrylic Hoechst Celanese Vandar® None Crystalline/ Amorphous PBT/Elastomer General Electric Valox 357®, 430®, 780® - Crystalline/ Amorphous PBT/SMI Denka (Japan) Malecca® - Crystalline/ Amorphous Copolyester/PBT Hoechst Celanese Riteﬂ ex® Miscibility Crystalline/ Amorphous DuPont Bexloy V® PCTG/PC Eastman Ektar DA® Miscibility Amorphous/ Amorphous 1028 M. K. Akkapeddi

Table 15.1. continued

Blend Producer Trade Name Compatibilization Blend Type Mechanism(a)

Specialty Resin blends Polysulfone/ABS Amoco Mindel A® Phenoxy resin or Amorphous/ Amorphous compatibilizer Polysulfone/PET Amoco Mindel B® Phenoxy resin or Crystalline/ Amorphous compatibilizer Polyarylate/PET Unitika V-8000® Partial Miscibility Crystalline/ Amorphous Polyetherimide/PC General Electric Ultem UT350® Partial Miscibility Amorphous/ Amorphous PBT/Acrylic Hoechst Celanese Vandar® None Crystalline/ Amorphous

Notes: (a) Compatibilization mechanisms are deﬁ ned here as the underlying principles responsible for the blend’s desirable properties, delamination resistance and morphology stability. (b) No compatibilizer used. Low interfacial tension between the components is responsible for the inherent compatibility in these systems. (c) Crosslinking of the dispersed phase via dynamic vulcanization (see 16.6) stabilize the blend morphology. (d) Partial miscibility between the components leads to self-compatibilization even though these systems are phase separated.

Experimentally, these blends exhibit two Tg’s, but different from the pure components due to a small amount of mutual miscibility. (e) Grafting involves direct chemical reaction between the components during melt mixing, generating a graft copolymer as the compatibilizer. (f) Ionic or chelate complex forming interactions between the components at the interface, may lead to compatibilization.

Figure 15.1. Price/performance proﬁ le of commercial polymers. Commercial Polymer Blends 1029

adequate level of interfacial adhesion, e.g., in effectively reduce the interfacial tension between ABS/polycarbonate, PBT/polycarbonate, PVC/ the components to achieve useful levels of ductil- nitrile rubber blends. ity and delamination resistance, while at the 3. Compatibilizing effects of interfacial agents same time stabilizing the morphology against such as block or graft copolymers that reduce processing effects. Interfacial compatibilization in the interfacial tension, stabilize the morphol- commercial polymer blends is generally achieved ogy, and strengthen adhesion at the interface. through reactive extrusion in which the block or graft copolymer compatibilizer is generated in- Although complete miscibility between poly- situ at the interface. The end groups or pendant mers is generally rare, when this does happen, it groups in some commercial polymers such as provides a unique opportunity to tailor the blend polyamides (amine or carboxyl), polyesters (car- properties by simply adjusting the blend ratio. boxyl or hydroxyl) and styrene-maleic anhydride The immense commercial success of PPE blends copolymers (anhydride group) are useful for this with high impact polystyrene (HIPS) is primarily purpose. In most other cases, the polymer back- attributed to the miscibility between PPE and bones must appropriately be modifi ed to include PS, that enabled one to combine the low cost, reactive functionalities by graft reactions with easy processability features of HIPS with the high small molecules (e.g., maleation of polyolefi ns performance (high heat resistance and strength) with maleic anhydride) or through copolymeriza- features of PPE. There was also some synergistic tion techniques. improvement of the toughness due to the improved The recent advances in reactive extrusion tech- ductility of the blend matrix resulting in improved nology, involving reactive modifi cation of poly- rubber toughening effi ciency. Simple melt mix- mers and/or reactive blending to form graft or ing in extruder type compounding equipment is block copolymer compatibilized blends in an adequate to make an alloy from such miscible extruder, have resulted in several successful com- polymers. mercial blends of otherwise highly immiscible Even in the phase separated blends, where polymer pairs, such as polyamide/olefi nic elasto- some degree of partial miscibility or compat- mer, polyamide/polyolefi n and polyamide/PPE ibility exists between the components, simple blends. In many cases, the reactive modifi cation melt blending in an intensive shear mixer is of the base polymers and the subsequent reactive adequate for making a well dispersed, reasonably blending can be combined into a one-step, sequen- stable blend product with useful combination of tial operation in a twin-screw extruder, making properties, such as polypropylene/ethylene-propyl- this an economically attractive process. Reactive ene rubber blend, ABS/polycarbonate blend, etc. compatibilization is still an emerging technology The self-compatibilizing nature of these blends for the development of useful blends from other- stems from partial miscibility and the mutual wise highly immiscible polymers, and particularly interpenetration of polymer chains at the interface. those of crystalline polymers. Specifi c examples Slight modifi cations of the polymer backbone of reactive modifi cation and reactive blending are often employed, particularly in the case of will be discussed later in individual cases. Further styrenic and ABS resins to induce partial miscibil- details on compatibilization strategies can be ity with other resins. found in chapters 4 Interphase and Compati- Compatibilization of the highly immiscible bilization by Addition of a Comptabilizer and commercial polymer pairs has thus far been a 5 Reactive Comptabilization of Polymer Blends technically more challenging task for the polymer of this book. blend technologists in the industry. Signifi cant progress has, however, been made in recent years in utilizing compatibilizers based on graft or block copolymer or other interfacial agents that 1030 M. K. Akkapeddi

15.2.2 Rationale for Polymer Blends Many commercial polymer blends often include an elastomer, to improve the impact strength of Commercial polymer blends belong to one of the the blend under conditions of stress concentra- following three categories: tion (notched Izod impact strength) and to lower 1. Blends of amorphous/amorphous polymers the ductile-brittle transition temperature of the 2. Blends of crystalline/amorphous polymers blend. The elastomeric dispersions are judi- 3. Blends of crystalline/crystalline polymers ciously employed either in the matrix phase, in the dispersed polymer phase, or in both phases, While the specifi c advantages of each type of depending upon the requirement and the fracture the blends will be discussed later in detail for the behavior of the blend. As a general rule, the more individual cases, the general motivations for mak- brittle component in a given polymer blend has a ing commercial polymer blends may be any of the greater need for rubber toughening. following factors: However, an overwhelming factor in determin- • lower cost ing the impact strength of an immiscible or par- • improved heat resistance tially miscible blend is the degree and effi ciency • improved toughness of interfacial compatibilization that either is • improved solvent resistance inherent in or has been designed into the blend • improved moisture resistance system. If the interfacial adhesion or compatibili- • improved dimensional stability zation is poor, the elastomer dispersion alone will • improved processability not improve the toughness. Further details on the • improved weatherability role of compatibilization and rubber toughening • improved fl ame resistance effects in polymer blends will be discussed later • improved esthetics and appearance, etc. with specifi c commercial examples. Combining

Figure 15.2. Notched Izod impact strength vs. DTUL (in °C at 1.82 MPa) of various commercial blends. Commercial Polymer Blends 1031

Figure 15.3. Notched Izod impact strength vs. DTUL (in °C at 0.45 MPa) of various commercial polymer blends. a high level of impact strength with a high level downstream feeding purposes. For example, the of heat resistance and/or chemical resistance has twin-screw extruders can be readily adapted to been the primary thrust of most commercial poly- combine both the polymer modifi cation and polymer blends (Figures 15.2., and 15.3). mer-polymer grafting steps of a reactive blending process into a single-pass, multi-stage reactive Polymer blend processing extrusion process. Most commercial polymer blends are produced The polymer that needs to be functionalized is by melt mixing in continuous compounding equip- fed at the throat of a co-rotating twin-screw extruder ment such as single-screw or twin-screw extruders and melt-mixed with a suitable grafting agent and and kneader-extruders. Twin-screw extruders are catalyst in the initial zones. After vacuum venting becoming more popular because of their greater to remove the unreacted and volatile materials, the versatility and production effi ciency. Owing to ‘functionalized polymer’ melt is then mixed with their segmented barrel and screw designs, twin- the second polymer and other components (impact screw extruders offer the advantage of multiple modifi er, fi llers, additives, etc.) added through the processing zones. The degree of shear mixing, down stream feed ports. The temperature and the residence time, and the temperature in each of shearing conditions in these latter zones of the these zones can be varied at will by simply chang- extruder are controlled to promote intimate mixings. ing the order and/or the type of the screw ele- Polymer-polymer grafting, compatibilization and ments and kneading blocks, and using separately the morphology development in the blend occurs at controlled heaters. this stage of extrusion. Thus all the sequences of the Twin-screw extruders also offer the choice of complex blending process can be accomplished in an multiple ports for liquid injection, venting and economically viable one-step, extruder process. 1032 M. K. Akkapeddi

Many commercial blends are often not as 15.3 Polyolefi n Blends complex as above and can be made by simple melt blending without a compatibilizer because Polyolefi ns (PO) constitute the largest single of partial miscibility between the components. group among all the commercial thermoplastics, However, even in these cases, good intimate considering the worldwide volume of usage. The mixing (dispersive and distributive) between the polyolefi n family comprises of (a) polyethylenes components is necessary to ascertain a morpho- of various types, viz. high density polyethylene logically stable, good quality product. Although (HDPE), low density polyethylene (LDPE), lin- twin-screw extruders are preferred for polymer ear low density polyethylene (LLDPE); (b) poly- blending, many single screw extruders, with mix- propylene (PP); (c) ethylene-propylene copoly- ing devices, are also employed, for the reason mers, block and random, ranging from tough of their low cost. Further discussion on the com- thermoplastic to rubbery types; (d) ethylene pounding procedure can be found in Chapter 9 copolymers with various comonomers such as Compounding Polymer Blends, in this Handbook. ethyl acrylate, acrylic acid, methacrylic acid and Although commercial twin-screw extruders the ionomers; (e) specialty polyolefi ns such as can be as large as 300 mm size, capable of poly(4-methyl,1-pentene), poly(1-butene), etc. compounding up to 40 ton/hr, the actual type Among these, HDPE, LDPE and LLDPE and and size of the equipment used depends on the polypropylene are the four most widely used, type of the polymer blend and the production commodity type polymers with a current total volume. Normally, for engineering polymer blends, consumption in USA of nearly 13 Mton/y [Greek, twin-screw extruders of about D = 90 mm size 1991; Anonym., 1993]. (L/D ≅ 30 to 40) and capable of compounding at Because of the wide range of properties avail- 700 to 1000 kg/hr, are used. For blending PVC able within PO’s, generally there has not been or elastomer blends other types of compounding any major need to blend polyolefi ns with other equipment are used, e.g. Farrell continuous mixer types of polymers. Furthermore, the immiscibility (FCM), Buss co-kneader, or a batch mixer, such of the commodity polyolefi ns with other types as Banbury. of polymers has also been a major reason for The technological details on commercial poly- the lack of commercial interest in such blends, mer blends are kept proprietary by the manu- although with the advent of reactive modifi cation facturers, particularly with respect to the exact and grafting chemistry, signifi cant progress has compositions of the commercial grades and the been made in recent years in compatibilizing processes used to make them. Even when the such dissimilar polymer systems as PA/PO blends patent literature is available for a given type of [Ide and Hasegawa, 1974; Epstein, 1979; Hobbs polymer blend, often one cannot infer the actual et al., 1983]. compositions and processes used for the commer- Blending within the family of PO has, however, cial blends. Hence, in reviewing the technology of been more common [Plochocki, 1978]. Although commercial polymer blends, certain assumptions they are usually immiscible with each other, there and generalizations have to be made regarding the exists some degree of mutual compatibility between compositional effects on the properties of some them. The similarity of their hydrocarbon back- commercial blends, where the literature informa- bones and the closeness of their solubility parame- tion is lacking. However, in the following sec- ters, although not adequate for miscibility, accounts tions, all relevant technological principles behind for a relatively low degree of interfacial tension. the various commercial blends have been outlined For example, the solubility parameters of polyeth- along with a discussion of their key properties, ylene, polyisobutylene, ethylene-propylene rubber differentiating values and applications based on and polypropylene are estimated to be 16.0, 15.4, a reasonable evaluation of the literature available 15.5, and 17.0 J1/2cm3/2 respectively, all very close to to date. each other [Van Krevelen 1990]. Similarly, the inter- Commercial Polymer Blends 1033 facial tension coeffi cients between PE or PP and EP- HDPE, the toughness, puncture resistance and elastomers are quite small (typically ca. 0.1 MN/m) heat sealability of the HDPE fi lms could be [Shih, 1990; Wu, 1989]. Hence polyolefi n blends improved. It is estimated that in the USA over have been made by simple melt mixing without a 30% of PE consumed in fi lms, is usually blended compatibilizer since the early days of polyolefi n with LLDPE [Kosoff, 1987]. commercialization. Generally, crystalline polyolefi ns such as 15.3.1.2 Toughened HDPE HDPE and polypropylene have been blended (HDPE/polyisobutylene blends) with low modulus/elastomeric polyolefi ns such as LDPE, EP-rubber or polyisobutylene, in order HDPE is a highly crystalline polymer with a good to improve the toughness. Hence toughened PO combination of stiffness, strength and toughness, have traditionally constituted the major volume suitable for most packaging applications. How- of polyolefi n blends used commercially. Most of ever, for more demanding applications such as the toughened PO blends are simple mechanical industrial bagging, an increased toughness, punc- mixtures of PO’s and olefi nic elastomers melt ture resistance and environmental stress crack blended in an extruder without a compatibilizer. resistance was needed. This could be achieved However, recent advances in polymerization by blending an elastomeric polyolefi n such as technology has allowed the production of tough- polyisobutylene (PIB, e.g., Vistanex®, Exxon). ened polypropylenes, through sequential poly- The dart impact and tear strength of the fi lm merization of ethylene-propylene copolymer in are improved signifi cantly with the elastomer PP matrix leading to blends with some block or dispersion [Anonym., 1974] (Figure 15.4). Some graft copolymer exhibiting somewhat improved commercial grades of HDPE (Paxon 3200 series) modulus/toughness balance [Galli and Haylock, utilize this technology [Haartman, et al., 1970]. 1991]. Another recent development in polyolefi n Although HDPE and PIB are not miscible, they blends is the technology of dynamic vulcaniza- have some degree of interfacial compatibility. The tion by which an elastomer is dispersed and fact that their solubility parameters are quite close cured in the matrix of the thermoplastic poly- δ = 16.0 vs. 15.4) leads to low interfacial tension propylene [Coran, 1987]. Since the latter type coeffi cient. The dispersability of the elastomer blends have the characteristics of thermoplastic can be optimized by controlling the molecular elastomers, they will be discussed under the weight, rheological parameters and the mixing elastomer blends section in Part 15.7. conditions in the extruder blending process. With the advent of new tougher versions of LLDPE 15.3.1 Blends Based on Polyethylenes designed for blown fi lm applications, further growth of HDPE/butyl rubber blends may how- 15.3.1.1 Polyethylene Blends (LLDPE/LDPE or ever be limited. HDPE Blends) 15.3.1.3 Polyethylene/polystyrene Blends Over 60% of the LDPE and LLDPE produced are used in fi lm applications. Because of the A blend of PS in HDPE (interpenetrating net- continuous nature of the fi lm extrusion, tradition- work) is commercially sold as expandable beads ally this process has been more amenable for (Arcel®, ARCO; Neopolen® S, BASF) for mak- blending different types of polyolefi ns to achieve ing cellular foams [Kosoff, 1987]. Although specifi c improvements in fi lm properties. For PS and polyethylene are immiscible, closed-cell example, by blending 30% LLDPE with LDPE, foams made from this immiscible pair appear thinner gage fi lms with improved tensile and to combine the rigidity of PS with the solvent tear strengths could be produced [Forger, 1982]. resistance and abrasion resistance of HDPE. Similarly, by blending about 30% LLDPE with Hydrogenated styrene-butadiene-styrene block 1034 M. K. Akkapeddi

Figure 15.4. Dart impact and tear strength of fi lms (0.1 mm) made from HDPE/polyisobutylene blends [Anon., 1974]. copolymers are known to compatibilize the PE/PS By proper choice of the molecular weight, melt blends. However there are no commercially rheology of the PA and processing conditions, a signifi cant applications for such compatibilized platelet like dispersion of the PA in HDPE matrix blends. could be achieved [Subramanian, 1985]. Since PA is a good barrier to hydrocarbons and many organic 15.3.1.4 Polyethylene/polyamide Blends solvents, the platelets in HDPE provide the desired permeation resistance to solvents that HDPE lacks. A graft copolymer compatibilized blend of PA- On the other hand, polyethylene matrix provides 66/PA-6 (75/25) copolymer with HDPE was com- the toughness, moisture resistance and low cost mercially offered as a barrier resin for making per- advantages compared to PA. The blend was desig- meation resistant solvent containers (Selar®RB, nated as a ‘laminar barrier’ blend. DuPont) [Subramanian, 1984]. Before melt blend- The PA/PE ‘grafted blend’ was offered com- ing with the PA, the PE backbone must be modi- mercially as a concentrate (Selar® RB) to be fi ed by grafting with such reagents as maleic melt blended with HDPE to a fi nal PA/HDPE anhydride [Steinkamp, 1976]. A graft-coupling ratio ≅ 15/85 for subsequent blow molding reaction between the PA and the maleated poly- into containers such as gasoline tanks, solvent ethylene, involving an amine/anhydride addition containers, etc. This laminar barrier blend of reaction leads to the graft copolymer formation HDPE and PA was reported to provide up to 100 at the interface, which reduces the interfacial fold improvement in the barrier to permeation of tension and stabilizes the PA dispersion in the such organic solvents as toluene, relative to pure HDPE matrix. HDPE, or a similar blend composition containing PA as a uniform spherical dispersion. Commercial Polymer Blends 1035

The commercial potential of the PA/HDPE typically < 2 J (at -30°C) and its notched Izod laminar barrier blend technology has not been impact strength is < 40 J/m at room temperature, fully established yet. A potential problem could both signifi cantly lower than that of polyethylene. be the high sensitivity of the morphology to the This brittleness of polypropylene is related to the process conditions, which could lead to a lack of spherulitic morphology and the intrinsic tendency reproducibility in achieving the desired platelet of PP for crazing followed by unstable craze morphology. The advent and rapid commercial growth and crack propagation under conditions succes of coextrusion blow molding may also be of stress concentration and/or low temperatures another factor limiting the blend’s market penetra- [Kinloch and Young, 1983; Friedrich, 1983]. tion. Coextrusion assures a more uniform barrier Commercial impact modifi ed PP were devel- layer of PA that can be relied upon for permeation oped during the early 1970’s by melt blending resistance. Surface fl uorination of polyethylene, about 5 to 25 wt% ethylene-propylene rubbers to improve the resistance to permeation of oxygen (EP or EPDM) with the polypropylene homopoly- and solvents, was also a commercially competing mer via extruder compounding [Holzar, 1966]. technology. Some LDPE or HDPE is often used to assist the dispersability of the EP rubber and enhance the 15.3.2 Blends Based on Polypropylene impact/modulus balance of the product [D’Orazio, 1982]. For the toughening of PP, EP rubbers 15.3.2.1 Impact Modifi ed Polypropylene meet the normal criteria for impact modifi ers. (PP/EPR blends) Toughening of rigid polymers generally requires the formation of fi ne rubber dispersions with good Polypropylene is a very large volume thermoplastic adhesion to the matrix and thus providing multiple with an annual consumption of nearly 4 Mton/y in sites for crazing and localized shear yielding as the USA alone. It is used in a variety of applications mechanisms for the impact energy dissipation. such as fi bers, fi lms and molded parts. Commercial Although not miscible, there exists a reasonable polypropylene homopolymer is produced by the level of compatibility between EP rubbers and the stereospecifi c polymerization of propylene in the polypropylene matrix due to their similarity in the presence of Ziegler-Natta type catalysts, which hydrocarbon type structures and the closeness of gives an isotactic polymer of high crystallinity. solubility parameters which leads to low interfacial Due to this crystallinity and a reasonably high tension and an adequate level of interfacial adhe- melting point (165°C), isotactic polypropylene sion [Krause, 1972]. Hence a small particle size exhibits a useful combination of properties such as dispersion of EP rubber is readily achievable good stiffness, strength, heat and solvent resistance. by adjusting the molecular weights and melt vis- The hydrocarbon nature of the backbone imparts cosity ratio of EPR to PP and through the proper it excellent hydrolytic and dimensional stability. In choice of mixing conditions [Yeh and Bisley, 1985; addition to these properties, polypropylene’s low Rifi , 1987]. The control of the rubber-phase density, 900 kg/m3, and relatively low cost makes morphology in polypropylene also depends on it an attractive candidate for many applications the rubber composition (ethylene/propylene ratio), and often competing with even the higher priced crystallinity, compounding and processing meth- engineering thermoplastics. ods, as well as rheological properties. A slight The crystallinity of isotactic polypropylene crosslinking of EPDM rubber leads to better mor- homopolymer, PP, however, leads to its well phology stability during high shear fl ow conditions known brittle behavior at low temperatures or such as injection molding [Dao, 1982; 1984]. when impacted under conditions of stress concen- Commercial impact modifi ed PP based on such tration, i.e., in the presence of sharp notches. blends exhibit excellent notched Izod impact For example, the low temperature drop weight strengths ranging from 80 J/m to 800 J/m and (Gardner) impact strength of unmodifi ed PP is moduli ranging from 1000 to 1700 MPa. Because 1036 M. K. Akkapeddi of the large number of commercial suppliers and of the reactor-made blend products is usually grades, no attempt will be made to describe the better than that of extruder-made blends. properties of any specifi c type of commercial Conventional extruder compounding process impact modifi ed PP blends, except to generalize for making impact modifi ed PP and thermoplastic the trends in the impact/modulus behavior with polyolefi n blends (TPOs) is still widely used to respect to the content and the nature of the EP date, particularly by the independent compound- rubber. ers because of the versatility of this process In general, for best impact modifi cation, the for making a variety of specialized products hav- ethylene-propylene copolymer must have > 30% ing a wide-range of performance characteristics. propylene and show essentially no crystallinity Compounding additive packages for improved [Rifi , 1987]. The size and distribution of the heat stability, weatherability and paintability, is EP rubber particles in the polypropylene matrix readily feasible in the extruder blending process. depend on the molecular weights and the melt Colors, pigments and fi llers can also be blended in viscosity ratio between the two polymers, as well during the compounding of the PP/EPR blends. as the mixing conditions [Speri and Patrick, 1975; Impact modifi ed polypropylene is used for injec- Jang et al., 1985]. Particle size must be < 3 µm tion molding automotive, consumer and appliance and preferably be < 1 µm for optimum impact parts. For example, the medium impact PP is strengths. Melt index ratio of PP/EPR, MI ≅ 10 widely used for automotive interior trim. High to 60 was found to give acceptable dispersion impact PP is used for battery cases, fender and size. The volume fraction and the particle size truck liners. Impact PP is also used extensively in distribution of the rubber dispersion affect the the houseware and appliance markets. modulus, impact strength and melt fl ow of the blend signifi cantly. 15.3.2.2 Thermoplastic Polyolefi n Blends Although historically, commercial impact mod- (TPOs) ifi ed PP has been produced by extruder compounding, more recent advances made in the Thermoplastic polyolefi n blends (TPOs), also catalyst and polymerization technology allowed sometimes referred to as thermoplastic polyolefi n the production of these blends via an “in-situ” elastomers (TPE’s) or olefi nic TPE’s, are blends process in the reactors [Rifi , 1987; Galli and Hay- of olefi nic thermoplastics (primarily polypropyl- lock, 1991]. By using a “super-active” catalyst ene) with elastomers with properties ranging from and a gas phase, fl uidized-bed reactor technology, fl exible elastomers to tough rigid materials, each the ethylene/propylene copolymer is allowed to specifi cally formulated to meet the needs of a polymerize and grow within the polypropylene particular application [Srinivasan, 1991; Spencer, homopolymer particle, polymerized earlier in 1990]. Essentially they are not much different the same reactor without isolation. The reactor from the impact modifi ed polypropylenes, except technology could be tailored to produce a wide that higher levels of EP rubber (up to 60%) may choice of products ranging from impact modifi ed be used for additional low temperature impact polypropylene to thermoplastic elastomer type strength. In some cases, the dispersed rubber may PP/EPR blends (TPOs) by a judicious choice of also be partially crosslinked during the mixing the reaction conditions and the component feed without losing the thermoplastic character of ratios. The particle size of EPR in reactor TPOs the matrix. However, the dynamically vulcanized is reported to be much smaller and hence more elastomeric alloys with high rubber content are effi cient in impact modifi cation. considered as a separate class of materials and Impact vs. modulus balance of the extruder- hence will be discussed separately under elasto- compounded blends of PP/EPR is illustrated in mer blends. Figure 15.5. While the fl exural modulus values are Most TPO alloys are compounded in the comparable, the low temperature impact strength extruders whereby additional components such Commercial Polymer Blends 1037

Figure 15.5. Effect of EPR content on the modulus and the low temperature impact strength of Polypropylene/EPR blends [Rifi et al., 1987]. as fi llers, stabilizers and adhesion promoters may Lower cost and recyclability are the primary also be employed. For improved paint adhesion reasons for the rapid growth of TPOs in bumper without primers, the blends may contain maleic applications, relative to SMC, polyurethane RIM anhydride or acrylic acid grafted polyolefi ns. and steel. Typical properties of TPOs used in bum- Commercially important TPOs may have fl ex- per applications [Evans, 1991]: ural moduli ranging from 20 to 2000 MPa and service temperatures ranging from -40 to 130°C. They are noted for their excellent toughness, high Density (kg/m3) 930 notched Izod impact strengths, and reasonable Flexural Modulus (MPa) level of chemical resistance. The largest market at -30°C 2380 for TPO is in the automotive area because of at 22°C 700 the material’s low cost, low specifi c gravity, low at 70°C 175 temperature toughness and weatherability. TPOs Tensile yield strength (MPa) 13.5 with molded-in color are used for bumper fascias, Elongation at break (%) 400 grilles, air dams, side moldings, etc. Under-the- Hardness (Shore D) 60 hood applications include ducting, protective Instrumented Impact (-30°C) 19 shielding and sound abatement systems. (Energy at Max. load, J) (with ductile failure) The current annual consumption of TPO blends Notched Izod No break in transportation alone is 50 Mton/y in the USA and is projected to grow at >10%/yr [Spencer, 1990]. The use of TPOs in automotive bumper covers is expected to grow even more at an annual rate of about 30% [Evans and Mosier, 1991]. 1038 M. K. Akkapeddi

Reactor TPOs, reportedly offering better com- ness and heat resistance (Surlyn® HP, DuPont). bination of toughness and stiffness, are gaining Key to this technology appears to be the selection increasing penetration into the automotive market, of a suitable surfactant that must be added in in both the soft bumper fascia applications as small amounts (0.3%) to aid the dispersability of well as other rigid applications replacing the more glass fi bers, yet retain high toughness [Murphy, expensive engineering resins. 1986]. The blend is reported to have an interpenetrating 15.3.2.3 Elastomeric Polyolefi n Blends network (IPN) type morphology, with the ionomer as the continuous phase. An unusual feature of this Thermoplastic elastomer blends comprising fully blend is the high notched Izod impact strength of cured elastomer dispersions in a matrix of ther- >1000 J/m at 23°C and >760 J/m at -29°C, even in moplastic polyolefi n such as PP, have been com- the presence of 15% of chopped glass fi ber. In the mercial for some time. These blends have been absence of the surfactant additive, the blend with made by the technology of dynamic vulcanization the same level of glass fi ber showed somewhat [Speri and Patrick, 1975]. The process consists of poorer impact properties, e.g., notched Izod of melt mixing and dispersing a high volume fraction < 500 J/m at -29°C and elongation at break of of an elastomer such as EPDM rubber or nitrile < 3%. In the presence of the surfactant additive, rubber (NBR) into a thermoplastic matrix such as an ionomer/polyolefi n blend reinforced with 15% PP, using a compatibilizer if necessary, and then glass (Surlyn® HP) exhibits a fl exural modulus selectively crosslinking the dispersed elastomer of 1600 MPa, a high notched Izod of > 1000 J/m during the extrusion, with specifi c curing agents. and a moderate DTUL of 82°C (at 0.45 MPa). The resulting elastomeric blends display the typical These properties were claimed to be good enough properties of cured rubbers such as high elastic to enable this blend to compete with the impact recovery, low compression or tension set, yet modifi ed polyamides in some applications. process like thermoplastics, due to the presence of PP thermoplastic matrix. Commercial, elastomeric 15.3.4 Reactor-made Polypropylene/ polyolefi n blends produced the dynamic vulcaniza- Non-olefi nic Polymer alloys tion include EPDM/polypropylene blend (Santo- prene®); Nitrile/polypropylene blend (Geolast®); A new class of ‘reactor-made’ alloys or ‘in-situ’ Butyl rubber/polypropylene (Trefsin®). The tech- graft copolymer compatibilized blends of poly- nology and properties of these blends will be propylene with other amorphous, non-olefi nic discussed in Part 15.7 Elastomeric blends. polymers have been commercially introduced by Montell recently under the trade name of Hival- 15.3.3 Ionomer/polyolefi n Blends loy® [DeNicola, 1994]. The commercial Hivalloy G series consisting of polypropylene/polystyrene Commercial ionomers are ethylene-methacrylic alloys were fi rst launched on a pilot scale in the acid copolymers and terpolymers in which the mid-1994 and later fully commercialized in 1996. carboxylic acid moiety is partially neutralized Their Hivalloy W series are developmental grades with sodium or zinc, to promote interchain ionic of polypropylene/ acrylic alloys, while the Hivalloy bonding. Ionomers exhibit excellent low tempera- T series are experimental grades of polypropylene/ ture toughness, chemical resistance and adhesion. styrene-maleic anhydride (SMA) copolymer alloys. However they lack in stiffness and heat resistance. All these reactor-made PP alloys are produced Hence ionomer blends with polyolefi ns such as by Montell’s proprietary ‘Catalloy’ or ‘reactor polyethylene have been developed which, upon granule’ technology [Galli and Haylock, 1991; reinforcing with suitable fi llers, seem to give a Galli et al., 1994], which is a multi-stage, multi- unique combination of high strength, excellent monomer polymerization process. low temperature toughness, and moderate stiff- The fundamental basis for the reactor granule Commercial Polymer Blends 1039 technology starts with the formation of a highly properties, as well as better chemical resistance porous polypropylene particle fi rst by the polym- and a lower specifi c gravity. The higher Tg of erization of propylene monomer using a ‘super- the amorphous, non-olefi nic polymer dispersion active’, third-generation, Ziegler-Natta initiator (PS, Acrylic, SMA) is expected to reinforce the system which consists of a MgCl2-supported, PP matrix yielding a somewhat higher stiffness, electron donor-modifi ed TiCl4/AlR3 catalyst in a strength and heat distortion temperature, while the very high surface area, spherical particle shape high crystalline melting point, ductility, chemical (‘Spheripol’ process). A unique feature of this resistance and high melt fl ow characteristics of catalyst system is the high uniform porosity PP are maintained. The following is a summary that is maintained during the polymerization in of the properties and applications of the two com- the growing PP particles. As the polymerization mercially signifi cant reactor alloys viz., PP/PS takes place, a growing skin of PP polymer is and PP/acrylic polymer alloys. formed from the active sites on the surface of the expanding initiator particle. Proper control 15.3.4.1 Commercial, Polypropylene/ of the morphological structure of the initiator Polystyrene (PP/PS) reactor alloys particles and the polymerization process results in the formation of highly porous, lattice-structured A series of reactor alloys of PP and PS are available PP granules. from Montell under the Hivalloy G trade name, These highly porous PP granules or beads are in the unreinforced, rubber toughened and glass- then used as the ‘reactor bed’ for subsequent reinforced forms. Typical properties are illustrated polymerization of one or more non-olefi nic mono- in Table 15.2. A key feature of these PP/PS alloys is mers such as styrene and methyl methacrylate. the impact strength/stiffness envelope that report- Since the latter polymerization is generally free edly exceeds the performance of conventional radical, it results in the simultaneous formation of PP and approach in some aspects with those of the non-olefi nic polymer as well as its graft copo- other engineering resins such as acetals, PC/ABS, lymer with PP uniformly distributed in micron- PC/PBT. Depending on the PS content in the scale domains within the individual PP granules. blend, the fl exural modulus and DTUL increase This ‘in-situ’ generated graft copolymer then predictably above that of PP while maintaining effectively compatibilizes and stabilizes the PP a high level of ductility and ultimate elongation. blend morphology during subsequent melt pro- The notched Izod impact toughness could be cessing such as injection molding. The blends raised to a ‘no-break’ level particularly with the exhibit typical multi-phase morphology behavior incorporation of some ethylene-propylene (EP) or with the non-olefi nic polymer generally forming styrene-ethylene/butylene-styrene block copolymer the fi ne dispersed phase in the continuous PP (SEBS) elastomeric modifi er. Compounding vary- matrix phase [DeNicola, 1992]. The PP matrix ing levels of glass fi bers and reinforcing mineral may contain additional rubber particle (EPR type) fi llers provides the desired balance of stiffness and dispersions for impact toughening of the blend. toughness in these PP/PS alloys. The reinforced The mechanical properties of these reactor- grades reportedly exhibit improved stiffness and made alloys offer a balance of stiffness and tough- creep resistance compared to PP alone and may ness not generally attainable through the simple compete against reinforced polyamides and poly- melt blending of the same polymer systems, esters, particularly in applications that do not primarily due to the effective graft copolymer require high temperature performance. compatibilization and good interfacial adhesion Typical applications in development with these between the component phases. The Hivalloy PP/PS alloys include automotive bumper beams, reactor blends have been positioned by Montell pillars, sporting and recreational equipment, sledge to compete against ABS alloys and other low-end hammer handles and other consumer tools & engineering resins based on on some comparable appliance components. The lighter weight (lower 1040 M. K. Akkapeddi

Table 15.2. Properties of some commercial, ‘reactor-made’ polypropylene/polystyrene and polypropylene/acrylic polymer alloys

Blend Type PP/PS PP/PS/EP PP/PS, PP/PMMA PP/PMMA 35 wt% GF

ASTM UNITS Hivalloy Hivalloy Hivalloy Hivalloy Hivalloy PROPERTY Method G120 G170 GXPA072 WXPA018 WXPA012 Montell Montell Montell Montell Montell

PHYSICAL Density D792 kg/m3 0.94 0.92 1.2 0.98 0.95 Mold Shrinkage D955 % 1.3 1.2 0.3 1.4 1.4 Water Absorption, 24 h D570 % <0.2 <0.2 <0.05 <0.05

MECHANICAL Flexural Modulus D790A MPa (kpsi) 1520 (220) 1200 (170) 7580 (1100) 1930 (280) 1380 (200) Flexural Strength D790A MPa (kpsi) 43 (6.2) 33 (4.8) 165 (24) 54 (7.9) 39 (5.7) Tensile Strength at Yield D638 MPa (kpsi) 33 (4.8) 27 (3.9) 113 (16.4) 36 (5.2) 30 (4.3) Elongation at Break D638 % 45 200 2.5 20 180 Rockwell Hardness D785 R 114 90

IMPACT Izod Impact, Notched D256 J/m (ft-lb/in) at 23°C 135 (2.5) No break 107 (2.0) 59 (1.1) 160 (3.0) Instrumented Impact D3763 J (ft-lb) Total Energy, at 23°C 36(27) 40 44 (32) Total Energy, at -20°C 47

THERMAL Heat Deﬂ ection Temp. D648 °C at 0.45 MPa 93 88 160 96 90 at 1.82 MPa 60 55 150 63 57

density) to stiffness & toughness balance of these surface appearance and colorability in addition alloys compared to the PC alloys is claimed to be to a good stiffness/ toughness combination. In a key advantage in these applications. comparative SAE J1960 exterior weathering tests, PP/acrylic alloy showed superior color & gloss 15.3.4.2 Commercial, Polypropylene/ Acrylic retention compared to ASA and PC/PBT [Sher- (PP/PMMA) Reactor Alloys man, 1997; Hivalloy Data sheets, 1997]. The UV resistance of the blend must originate from the A series of reactor alloys based on polypropylene acrylic polymer, which may be enriched on the and methyl methacrylate copolymer have been surface of the part. The attractive refractive index commercialized by Montell under the Hivalloy of the blend also makes it easy to color with W series. Typical properties of such an alloy molded-in colors. are shown in Table 15.2. These alloys have Typical applications in use or development been claimed to exhibit excellent weatherability, with the PP/ acrylic polymer reactor alloys include Commercial Polymer Blends 1041 automotive exterior mirror housings, interior trim fl exibility and resilience and hence been referred and handles, truck wheel fenders, marine/ outdoor to as polyolefi n elastomers (POE). As a result of recreational equipment, building and construction the controlled long-chain branching in otherwise applications such as the outer layer for siding etc. linear polymers, the processability of these resins The apparent outstanding weatherability, good is claimed to be signifi cantly enhanced compared colorability and mechanical properties of these to the standard LLDPE and EPR materials. Envi- alloys are positioned to compete against the well ronmental stress crack resistance of metallocene established engineering resins such as ABS, ASA, polyolefi n is also claimed to be signifi cantly better. PC/ABS and PC/PBT. A wide range of densities (860 to 930 kg/m3), fl exural modulus (10 to 100 MPa), melting points 15.3.5 Metallocene Polyolefi n Blends (60-120°C) and melt fl ow index (0.5 to 125) is available in the commercial metallocene-based Recent progress made in the development of novel ethylene copolymers. metallocene catalyst systems for polyolefi n polym- Thermoplastic polyolefi n (TPO) blends of erizations represents a true technological break- metallocene-based polyolefi n elastomers (POE) through with wide ramifi cations in the plastics with polypropylenes are beginning to gain com- industry [Wigotsky, 1995; Schut, 1996; Zamora, mercial signifi cance because of the improved 1997]. As the latest generation catalysts, the metal- melt fl ow and toughness compared to the conven- locenes differ from the traditional Ziegler-Natta tional TPOs based on PP/ EPR or EPDM blends catalysts in that they have well defi ned single [Toensmeier, 1994]. In comparative tests with catalytic sites and well understood molecular struc- 70/30 PP/elastomer blends, the blends with POE tures. Typically they consist of a transition metal maintained ductile behavior at -29°C even with such as zirconium sandwiched between suitably high melt fl ow index PP (MFI = 35), while substituted cyclopentadienyl ring structures to form the corresponding EPR based blends were brittle a sterically hindered or ‘constrained geometry’ with PP of MFI = 20. In addition, they showed metal catalyst site. With these new generation of improved knit-line strengths. Because of their catalysts, a wide variety of monomers can be high shear-thinning and melt elasticity, plastomers polymerized or copolymerized in high effi ciency and POEs disperse well in PP matrix yielding but more importantly various parameters such fi ne particle dispersions leading to the better as comonomer distribution, polymer molecular properties. TPOs are the fast growing segment of weight, molecular weight distribution, molecular thermoplastics market in the ‘90s with more than architecture, stereospecifi city, degree of linearity 10% growth rate/yr. Typical applications of these or branching can be independently and precisely TPOs include automotive bumper fascias, interior controlled. While the range of the new metallocene instrument panel skins, air-bag doors, etc. based polymers includes such specialty polymers Blends of metallocene polyolefi n elastomer/ as cyclo-olefi n copolymers (COC), syndiotactic plastomer materials compounded with EPDM polystyrene, ethylene/styrene copolymers, which (typically 70/30) are fi nding several extrusion are still in the developmental stage, commercially applications such as fl exible hoses, cords and wire the most prominent candidates are the ethylene/ jacketing because of much higher extrusion rates α-olefi n copolymers such as ethylene/butylene or and better heat aging characteristics than EPDM hexene copolymers (Exxon’s Exact) or ethylene/ [Sherman, 1997]. Blends of POEs with ethylene- 1-octene copolymers (Dow’s Engage and Affi n- vinyl acetate copolymers are used as cushioning ity). Depending on the comonomer content these in sports shoes because improved resiliency and copolymers have been classifi ed as plastomers or durability. Blends of POE with PVC are employed elastomers. At comonomer levels of > 25%, the in some extruded profi les for refrigerator gaskets, copolymers exhibit the characteristics of thermo- window and garage door seals. Other applications plastic elastomers such as high softness, toughness, of POE blends include soft-touch handles for 1042 M. K. Akkapeddi hand-held tools and for automotive noise, vibra- moderate heat resistance, have become more tion and harshness (NVH) dampening. As the widely accepted in many molding and extrusion metallocene olefi n copolymers become increas- applications. HIPS and ABS may themselves be ingly more cost-effective, the application of their considered as blends, since they normally contain corresponding blends are expected to proliferate. 5% polybutadiene rubber as a discrete phase, dispersed as 0.1-5 µm size particles in the matrix of polystyrene or SAN copolymer [Echte, 1989]. 15.4 Styrenic Blends However, the rubber phase in these resins is incorporated during the free radical polymeriza- Styrenic resins, a family of commercially signifi - tion of styrene or S-AN monomer mixture via cant polymers and copolymers derived from sty- a mass, suspension or emulsion polymerization rene, rank among the major volume thermoplastic process that results in the graft-coupling of the materials used, with an annual consumption of rubber phase to the matrix phase. In the context of nearly 4 Mton/y in the USA alone [Greek, 1991]. the current discussion on blends, HIPS and ABS Their low cost, ease of processability and good are considered not blends, but more impact modi- balance of properties account for widespread use. fi ed resin systems made in a reactor, although Commercial styrenic resins may be classifi ed into several grades of ABS are produced routinely the following types: by captively melt blending with SAN to adjust 1. Polystyrene (PS) and high impact polystyrene the rubber levels to the desired property specifi - (HIPS) cations. HIPS and ABS are themselves used, 2. Styrene-acrylonitrile copolymer (SAN) and its however, as components for blending with other impact modifi ed versions, viz., ABS (polybu- thermoplastic resins to make new blends with tadiene rubber grafted SAN), ASA (acrylate desired combination of properties. rubber grafted SAN), AES (EPDM rubber The general motivation for blending styrenic grafted SAN) resins with other polymers, particularly with 3. Styrene-maleic anhydride copolymer (SMA) the higher priced engineering resins, such as and terpolymers with methyl methacrylate polycarbonate or polyphenylene ether, is primarily (SMA-MMA) and acrylonitrile (SMA-AN) to lower the cost and improve the processability 4. Styrene-methyl methacrylate copolymer of the latter resins. As far as styrenic resins are (S-MMA) concerned, some of the reasons for blending stem 5. Styrene-butadiene block copolymers [di, tri from the need to improve their property defi cien-

and radial block (S-B)n] cies, viz. solvent resistance, impact strength, heat resistance and fl ame resistance. Among these, polystyrene is the lowest cost, commodity type resin followed by SAN, SMA 15.4.1 Polystyrene and High Impact and the other copolymers. All the styrenic resins Polystyrene (HIPS) Based Blends are essentially amorphous polymers with glass transition temperatures ranging from about 100 to Because of its inherent brittleness, polystyrene 130°C, and heat distortion temperatures ranging homopolymer itself has limited application in from about 80 to 120°C, depending upon the blends. However, its impact modifi ed version, comonomer and impact modifi er content. viz., HIPS, is more widely used. HIPS itself is Although the unmodifi ed styrenics, viz. poly- a reactor-made multiphase system with 5 to 13% styrene, SAN and SMA copolymers, exhibit good polybutadiene (‘cis’-rich) dispersed as discrete clarity, strength and rigidity, they are invariably particles in the polystyrene phase, with an opti- brittle for many applications. Hence the rubber mum particle size of mean diameter of 2.5 µm. modifi ed styrenics such as HIPS and ABS, which The rubber in HIPS is chemically grafted to some combine a good level of impact strength with extent to the polystyrene. The effective volume of Commercial Polymer Blends 1043 the rubber dispersion is actually increased through PPE is the acronym used for poly (2,6-dimethyl the occlusion of some polystyrene. To optimize 1,4-phenylene ether), a high Tg (205 to 210°C) the impact strength, the rubber particle size ( 2.5 polymer produced by the oxidative coupling µm) and the distribution is normally controlled polymerization of 2,6-dimethyl phenol [Hay, by the agitation and the proper choice of other 1959; 1976]. Sometimes a minor amount of process conditions during the polymerization. The 2,3,6 trimethyl phenol is used as comonomer. property improvements in HIPS, viz., increased Although PPE exhibits a good level of ductility impact strength and ductility, are accompanied by and toughness along with a high heat distortion the loss in clarity and a decrease in the tensile temperature, its high softening temperature and strength and modulus compared to the unmodifi ed high melt viscosity precluded it from being used polystyrene. as a commercial molding resin, by itself. How- ever, the discovery that blending PPE with high 15.4.1.1 Blends of Polystyrene with S-B Block impact styrene could lead to improved process- Copolymers ability and impact properties resulted in the successful commercialization of these blends [Cizek, In order to improve the toughness, yet maintain 1968]. By simply adjusting the blend ratio, a a suffi cient level of clarity in the polystyrene wide spectrum of blend products with the desired homopolymer, it is often melt blended with some combinations of DTUL, impact strength, pro- styrene-butadiene block copolymers containing cessability and cost balance could be produced. 40% styrene blocks. Such polystyrene blends This versatility of tailor-making the blends for are commercially employed in the blow molding, various levels of performance led to their rapid sheet extrusion and thermoforming applications commercial success. [Traugott, 1985]. Both the multiblock type (Fire- Key to this success, however, was the observed stone Synthetic Rubber and Latex Company’s miscibility between the PPE and the PS phases Stereon® resins) and the radial block type resulting in a single phase matrix with a single (Phillips Petroleum Company’s K-resins) S-B glass transition temperature that can be varied at block copolymers are used for blending. These will with the blend ratio. This thermodynamic blends are normally made by the fabricator, miscibility between PPE and PS was established e.g., during the sheet extrusion or blow molding by various characterization techniques viz. glass [Salay, 1991]. Some commercial precompounded transition temperature [Schulz and Gendron, 1972; grades of blends are also available. Typical appli- Fried et al., 1978], electron microscopy [Kambour cations include thermoformed food packaging et al., 1980], small angle X-ray scattering and containers, blister packs, shrink-wrap fi lms, etc. calorimetric methods [Weeks et al., 1977], the latter showing a negative heat of mixing over 15.4.1.2 Polystyrene or HIPS Blends with the entire composition range. The presence of Poly(phenylene ether) (PPE/HIPS polybutadiene rubber particle dispersions in such blends) a homogeneous matrix was found to lead to signifi cant synergistic enhancement of the tough- Blends of polyphenylene ether (PPE, also known ness of the blend, due to both the crazing and as PPO®) with HIPS are, by far, the most success- shear yield mechanisms of toughening [Bucknall, ful of all the commercial blends. Currently, more 1977; Yee, 1977]. The particle size and the than 100 kton/y of PPE/HIPS blends are produced amount of rubber, however, affect the impact, in the USA [Levy, 1991] almost exclusively modulus and tensile properties of the blend. by General Electric company, which originally Commercial PPE/HIPS blends generally span introduced this blend commercially in 1964 under a range of blend ratios from, 25/75 to 60/40 of the trade name, Noryl®. There are now other PPE/HIPS. Typical properties of commercial PPE/ producers of this blend in Europe and Japan. HIPS blends are shown in Table 15.3. Depending 1044 M. K. Akkapeddi upon the PPE content, the heat distortion tem- effi ciency of rubber toughening increases as the perature can vary from 90°C to about 150°C. PPE content in the blend increases. Shear yielding The melt rheology and fl ow characteristics again process also contributes to the overall toughening depend predominantly on the ratio of PPE to effect, in addition to the usual craze-toughening HIPS, with the molecular weights of PPE and mechanism. In blends containing 50% PPE, HIPS also playing an important role [Schmidt, shear yielding is the dominant mode of energy 1979; Priest and Porter, 1972]. All the blends dissipation [Yee, 1977]. Unlike the case of poly- exhibit good ductility and impact strength. The styrene, the blend needs smaller size ( 2 µm) notched Izod values range from 250 to 500 J/m. rubber particles for optimum impact strength The rubber particles in HIPS contribute to the properties [Bucknall, 1972]. For higher impact enhanced toughness of the blend. Since PPE strength, additional blending of styrene-butadi- is inherently more ductile than polystyrene, the ene-styrene (S-B-S) block copolymer type elasto-

Table 15.3. Key properties of commercial PPE/HIPS blends

ASTM NORYL NORYL NORYL NORYL PROPERTY TEST UNITS SPN410 SPN420 731 N300 METHOD GEC GEC GEC GEC

PHYSICAL Density D792 kg/m3 1,060 1,070 1,060 1,060 Mold Shrinkage D955 % 0.6 0.6 0.6 0.6 Water Absorption, 24 hrs. D570 % 0.07 0.07 0.07 0.06

MECHANICAL Flexural Modulus D790 MPa (kpsi) 1830(265) 2140(310) 2530(360) 2400(350) Flexural Strength D790 MPa (kpsi) 51(7.8) 59(8.6) 95(13.5) 104(15) Tensile Strength at Yield D638 MPa (kpsi) 36(5.2) 44(6.4) 67(9.6) 76(11) Elongation at Break D638 % 82 60 60 20

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 375(7) 295(5.5) 270(5) 272(5) at -40°C 190(3.5) 133(2.5) 130(2.5) 130(2.5)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 121 137 157 at 1.82 MPa 96 110 129 149

ELECTRICAL Dielectric Strength D149 K/V/mm 21.6 21.6 Dielectric Constant at 1 KHZ D150 2.7 2.7 2.6 2.6 Dissipation Factor at 1 KHZ D150 0.001 0.001 Volume Resistivity D257 ohm-m 1.0E+15 1.0E+15 1.0E+15 1.0E+15 Commercial Polymer Blends 1045 mers and their hydrogenated derivatives, S-EB-S, 15.4.2 ABS Blends are often employed. The ratio of PPE to PS in the blends can be determined from the ratio of the Among the styrenic resins, ABS enjoys a unique IR peaks at 854 cm-1 and 700 cm-1 respectively position of being considered an engineering ther- [White, 1983]. The rubber particle size is deter- moplastic because of its key performance char- mined by transmission electron microscopy using acteristics, viz. high impact strength, solvent osmium tetroxide staining [Bucknall, 1977]. resistance and moderate heat resistance. Due to Most of the PPE/HIPS blends are utilized by its relatively low cost, ABS can bridge the gap the injection molding process, although in recent between the commodity plastics and the higher years, blow molding and extrusion/thermoforming priced engineering thermoplastics. Nearly 700 applications are also increasingly practiced. Low kton/y of ABS is produced currently in the USA moisture absorption and the good melt stability with an estimated 20 kton/y metric tons used in of PPE/HIPS blends along with their broad range the blends and alloys [Greek, 1991]. of melt viscosities enable the fabricators a wide ABS itself is a two-phase polymer system with choice of processing conditions. PPE/HIPS blends a fi nely dispersed polybutadiene rubber phase are used in a wide range of applications in (0.1 to 1 µm) embedded in a continuous matrix of the automotive, business equipment, appliance, SAN copolymer. The rubber phase is chemically electrical/electronic and industrial markets. grafted to the SAN during the polymerization of Automotive applications include instrument ABS. As mentioned earlier, ABS is commercially panel frames, interior trim, glove boxes, fuse produced by the free radical polymerization of boxes, connectors, wheel covers, mirror housings, styrene/acrylonitrile monomer mixture (usually etc. Flame retarded grades are used for business 3:1 wt. ratio) in the presence of polybutadiene machine housings which are also often foamed (of high ‘cis’ content) which is added as a solution to reduce the specifi c gravity and blow molded (ca. 10%) in the mass polymerization process or to reduce processing costs. Appliance parts and as a latex seed during the emulsion polymeriza- housings include those for refrigerators, washers, tion (30-60% rubber) [Ku, 1985]. The emulsion dryers, dishwashers, power tools, etc. The blends grade ABS is usually blended with virgin SAN exhibit extremely low moisture absorption and copolymer to produce an ABS with a desired level good electrical properties suitable for electrical of rubber (10 to 25%). The impact strength, modu- and electronic applications such as TV cabinets, lus, tensile strength, processability and surface connectors, electrical junction boxes, housings, gloss of ABS depend on the rubber content and relays, and bobbins. The low moisture absorption its particle size and distribution that is determined and excellent hydrolysis resistance of PPE/HIPS by the polymerization process and its conditions. blends coupled with their high dimensional stabil- The high rubber ABS (25 to 50% rubber) grades ity makes them suitable for water meters and can be made only by emulsion process and pump housings, plumbing parts and a variety of such resins (e.g., ‘Blendex’ grades from General fl uid handling equipment parts. Some developing Electric Co.) are often employed for compounding applications include such construction applica- with other more economic thermoplastic resins tions as roofi ng panels, insulation, fl ooring sub- such as polyvinylchloride (PVC) for impact modi- strates, etc. The high heat distortion temperature fi cation [Dotson and Niznik, 1991]. The bulk of PPE/HIPS led to its evaluation in microwave polymerization process (continuous or suspen- packaging. In applications requiring clarity, blends sion) produces low-gloss, medium impact grades of PPE and crystal PS (Gepax®, GE) have also of ABS. been evaluated. Trays and packages that can be While the standard ABS resins, containing safely heated in microwave ovens have been 10 to 25% polybutadiene rubber, indeed have a made from such blends. wide range of useful engineering properties, it is possible to extend further and improve these 1046 M. K. Akkapeddi properties for certain niche applications via blend- retardant characteristics (self-extinguishing, V-O ing with other polymers. For example, blending ratings of UL-94) at a reasonable cost (Table 15.4). with PVC can improve the fl ame retardancy of Such ABS/PVC blends have been used in appli-

ABS at a low cost. Blending with such higher Tg, ance and business machine housings, TV cabinets, engineering resins as polycarbonate and polysul- electrical and electronic component manufacture. fone can improve the heat distortion temperatures. Although the low cost, fl ame retardancy advantag- On the other hand, use of ABS in blends with es of ABS/PVC blend are attractive, the thermal other resins can bring the advantages of low instability of PVC poses processing problems cost, improved impact strength and processability. requiring careful control of processing conditions These will be discussed with the following exam- and temperature. In the injection molding markets, ples of blends. the processing disadvantages of ABS/PVC blend are limiting its growth, while improved versions 15.4.2.1 ABS/PVC Blends of fl ame retardant grades of ABS, ABS/PC and PPE/HIPS blends are steadily gaining competitive Incorporation of 10 to 40 wt% ABS into PVC advantage due to their superior processability. improves its impact strength, processability and hot tear strength. Commercially ABS/PVC blends 15.4.2.2 ABS-Polycarbonate Blends are available from several sources, but more often these blends are made in-situ by the fabri- Blends of ABS and polycarbonate (PC) were cators of sheet or profi le extrusions. High rubber, commercially introduced by Borg-Warner Co. low modulus grades of ABS made by emulsion (now part of GEC) several years ago [McDougle, polymerization are often used for the impact 1967; Grabowski, 1964]. After an initial sluggish modifi cation of PVC. Because of the thermal growth, these blends have now gained increased degradation problem of PVC, blending is done acceptance by resin fabricators and end users. typically in Banbury type mixers. The blend Currently more than 50 Kton/y of ABS/PC blends exhibits signifi cantly improved notched Izod are consumed in USA, Western Europe and Japan impact strength (1000 J/m) over PVC. Although [SRI, 1992]. There are many suppliers of ABS/PC PVC is immiscible with ABS, the interfacial blends, primarily by those involved in producing tension between the SAN phase and PVC is low the polycarbonate and/or ABS. enough to allow enough compatibility. The rub- ABS/PC blend is an essentially immiscible ber particles, of course, are responsible for the blend [Echte, 1989; Suarez et al., 1984; Kim enhancement of toughness. The primary applica- and Burns, 1988] with three distinct phases, viz. tion of this type of ABS/PVC blend, particularly the PC phase, the SAN copolymer phase and in Western Europe, is in the manufacture of the grafted polybutadiene rubber phase dispersed foil for vacuum thermoforming automotive and within the SAN phase (as in the ABS to begin mass-transit interiors. The fabricators blend the with). Depending upon the blend ratio, the con- powders of PVC and ABS and use the blend tinuous phase can either be the ABS (or more captively for the foil manufacture. Similar blends correctly the SAN phase) or the PC phase. of PVC with MBS and ASA as impact modifi ers In spite of the immiscible nature, the blends are also used. These will be discussed in Part exhibit good toughness, particularly in the region 15.5.1 PVC/impact modifi er blends. of 30-65 vol% PC [Weber and Page, 1986]. Pre-compounded blends of ABS and PVC have A primary reason for the good properties and also been commercially available for molding delamination resistance in ABS/PC blends is and extrusion applications as low cost alter- partial miscibility between the PC and SAN natives to fl ame retarded grades of ABS and phases, which leads to low interfacial tension PPE/HIPS blends. Commercial ABS/PVC blends and high interfacial adhesion, particularly when offer high impact strength coupled with fl ame- the SAN contains 25% acrylonitrile [Keitz et Commercial Polymer Blends 1047

Table 15.4. Properties of some commercial styrenic/PVC blends

Blend Type ABS/PVC ASA/PVC SMA/PVC

ASTM CYCOVIN KANEKA GELOY TRIAX PROPERTY TEST UNITS KAF ENPLEX GY1220 CBE METHOD B.F. Goodrich Kanegafuchi GEC Monsanto

PHYSICAL Density D792 kg/m3 1,200 1,200 1,200 1,200 Mold Shrinkage D955 % 0.4 0.4 0.5 Water Absorption, 24 hrs. D570 % 0.09 0.09 0.1

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2310(330) 2740(390) 2140(310) 2800(400) Flexural Strength D790 MPa (kpsi) 67(9.6) 61(8.7) 60(8.5) Tensile Strength at Yield D638 MPa (kpsi) 40(5.8) 44(6.3) 46(6.6) 41(6.1) Elongation at Break D638 % 20 20 25 Rockwell Hardness D785 R100 R105 R96 R106

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 570(10) 201(3.7) 1080(20) 320(6) at -40°C 107(2)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 80 85 at 1.82 MPa 79 71 76 76 Flammability Rating UL94 V-0 V-0 V-0 V-0

al., 1984]. The partial miscibility between PC but not in the notched Izod impact strength and SAN has been demonstrated by the small (Table 15.5). But as the polycarbonate level in yet fi nite increases in the Tg of SAN phase and the blend increases (particularly at PC 50%), similar decreases in the Tg of PC phase [Kim the notched Izod impact strength improves sig- and Burns, 1988; Morbitzer et al., 1985]. The nifi cantly, even at low temperatures. The ductile- polymer-polymer interaction parameter (χ) for brittle transition temperature in the latter blends is this blend was calculated to be slightly positive shifted to signifi cantly lower temperature [Weber (χ = 0.03). Some interpenetration of the chains at and Paige, 1985], even compared to polycarbon- the phase boundary is responsible for the increase ate alone. The high dimensional stability, the in the interfacial strength. excellent impact toughness at low temperatures, Properties of ABS/PC blend depend on the low gloss and easy processability features of blend ratio. Blends containing major amounts of ABS/PC blends have led to their application ABS (e.g., Cycoloy EHA) show improvements in automotive interior instrument panels and, more in DTUL and tensile properties relative to ABS, recently, in exterior body panels, wheel covers, etc. 1048 M. K. Akkapeddi

Table 15.5. Properties of commercial grades of ABS/polycarbonate vs. polycarbonate

Blend Type ABS/PC PC

ASTM CYCOLOY BAYBLEND PULSE TRIAX LEXAN PROPERTY TEST UNITS EHA T65MN 710 2153 141 METHOD GEC Miles Dow Monsanto GEC

PHYSICAL Density D792 kg/m3 1,090 1,120 1,120 1,130 1,200 Mold Shrinkage D955 % 0.5 0.6 0.6 0.7 0.6 Water Absorption, 24 hrs. D570 % 0.2 0.15 0.15

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2550(370) 2100(305) 2412(350) 2390(340) 2300(340) Flexural Strength D790 MPa (kpsi) 75(10.9) 83(12) 87(12.4) 97(14) Tensile Strength at Yield D638 MPa (kpsi) 45.5(6.6) 50(7.2) 48(7) 52(7.5) 60(9) Tensile Strength at Break D638 MPa (kpsi) 45(6.5) 45(6.5) 70(10) Elongation at Break D638 % 40 80 60 56 130 Rockwell Hardness D785 R111 R118 R110 R113 R118

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 370(6.9) 534(10) 534(10) 800(13) 694(13) at -29°C 320(6) 481(9) 250(4.6)* 100(2) Instrumented Impact, Energy D3763 J (ft-lb) at 23°C 47(35) 45(33) 57(42) 62(46) at -29°C 47(35) 40(30) 57(42)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 104 124 118 115 140 at 1.82 MPa 95 104 102 97 130 Vicat Softening Point D1525 °C 113 121 128 154 ELECTRICAL Dielectric Strength D149 K/V/mm 14 19.8 Dielectric Constant at 1 KHZ D150 3.3 2.9 Dissipation Factor at 1KHZ D150 0.03 0.03 Volume Resistivity D257 ohm-m 5.0E+13 9.5E+14

* at -40°C

ABS/PC is also used in business machine hous- rate (ca. 10%) is expected for the ABS/PC ings, snow throwers, snowmobiles and other such blends because of their balance of high impact equipment housings. A continued high growth and heat resistance properties and moderate cost. Commercial Polymer Blends 1049

15.4.2.3 ABS/Polyamide Blends The advantages of blending ABS with PA are primarily reduced moisture sensitivity, improved Blends of ABS with commercial polyamides such toughness and reduced shrinkage and warpage. as polyamide-6 and -66 are highly incompatible Typically the blends exhibit high impact strengths due to their dissimilar polarity. Such simple with the notched Izod values of > 600 J/m and blends of ABS and PA exhibit poor delamination better solvent resistance and heat resistance than resistance and have no practical value. Recent ABS (Table 15.6). Comparative properties of efforts to improve the compatibility led to several ABS/polyamide blends and other polyamide different approaches. blends will be discussed in Part 15.8.1 Polyamide/ In one approach, modifi cation of ABS through Elastomer blends. ABS/PA blends are relatively copolymerization of acrylamide was reported to new and have not yet developed a signifi cant improve the compatibility between ABS and PA-6, market growth. presumably through hydrogen bonding interaction [Grant, 1988]. 15.4.2.4 ABS/Thermoplastic Polyurethane In another approach, the SAN backbone of Blends (ABS/TPU) ABS was modifi ed through copolymerization with maleic anhydride. This modifi cation introduced A recent commercial blend of ABS contains controlled amounts of an anhydride functionality thermoplastic polyurethane elastomer as the main on ABS, which upon subsequent melt blending blend component. The blend was introduced in with a PA reacts to form a graft copolymer of 1990 by Dow Chemical Co., under the trade name SAN and PA which effectively compatibilizes Prevail®. These blends characteristically exhibit the blend. Commercial blends of ABS with PA-6 low modulus (340 to 1000 MPa) and high impact and PA-66, introduced by Monsanto under the strength at low temperatures, e.g. notched Izod trade name of Triax® 1000, utilize this reactive values of 370 to 1500 J/m at -29°C. The TPU compatibilization technology [Lavengood et al., component of the blend imparts high toughness 1987]. In another technique of reactive compatibi- and also allows paintability without a primer. lization, commercial grades of ABS were directly ABS component imparts heat resistance (for paint modifi ed by reactive extrusion with maleic anhy- ovens) and good tensile strength in the blend. dride or fumaric acid and then melt blended The blend is projected to fi nd applications in the with PA-6 and optionally adding small amounts automotive markets, particularly as paintable, soft of functionalized EP rubber [Akkapeddi et al., bumper fascias. Typical properties of commercial 1990]. ABS/TPU blends are shown in Table 15.6. Key to the successful compatibilization involves the formation of a graft copolymer of SAN and 15.4.3 Acrylic-Styrene-Acrylonitrile (ASA) PA at the interface, which reduces the interfacial Terpolymer Based Blends tension and improves the interfacial adhesion. Blends with stable, dispersed morphology are Acrylic-Styrene-Acrylonitrile (ASA) resins, com- achievable. They exhibit high delamination resis- mercialized initially by BASF and subsequently tance and toughness. by GEC and others, are normally produced by Since PA-6 and PA-66 are crystalline polyam- the graft copolymerization of styrene-acrylonitrile ides with high melting points, it is desirable to copolymer (SAN) onto an acrylic rubber (usually keep them as the continuous phases and ABS as polybutylacrylate) via emulsion polymerization. the dispersed phase, for better heat and solvent The properties of ASA polymers are similar to resistance. The phase morphology of the blend, those of ABS, exhibiting high impact strength, of course, depends upon the blend ratio and the good chemical and heat resistance. However, relative viscosity of the individual components. unlike the ABS resins, the ASA resins exhibit outstanding weatherability, lasting at least 10 1050 M. K. Akkapeddi

Table 15.6. Comparison of various commercial blends of ABS

Blend Type ABS/PVC ABS/PC ABS/TPU ABS/PA-6 ABS/PBT

ASTM CYCOVIN PULSE PREVAIL TRIAX CYCLOLIN PROPERTY TEST UNITS K25 710 3150 1120 GCM 1900 METHOD B.F. Goodrich Dow Dow Monsanto GEC

PHYSICAL Density D792 kg/m3 1,200 1,120 1,090 1,060 1,120 Mold Shrinkage D955 % 0.4 0.6 0.6 0.9 Water Absorption, 24 hrs. D570 % 0.09 0.15 0.1

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2310(330) 2412(350) 1034(150) 2070(300) 1800(260) Flexural Strength D790 MPa (kpsi) 67(9.6) 83(12) 72(10.5) Tensile Strength at Yield D638 MPa (kpsi) 40(5.8) 48(7) 28(4) 46(6.6) 41(6) Elongation at Break D638 % 20 60 180 270 Rockwell Hardness D785 R100 R110 D71 R99 R103

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 640(12) 534(10) NB 850(16) 587(11) at -29°C 481(9) 374(7) 108(2) Drop Weight Impact J (ft-lb) at 23°C 57(42) 52(38) >45(33) at -29°C 57(42) 64(48) 44(33)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 83 118 78 92 93 at 1.82 MPa 79 102 63 78 74 CHEMICAL RESISTANCE Fair Fair Good Excellent Excellent

times longer than ABS. The butadiene rubber in pellets for extrusion or injection molding applica- ABS is subject to oxidative degradation by the tions. Compared to ABS, the ASA resins are combined effect of atmospheric oxygen and solar relatively more expensive, hence used only for radiation. Hence ABS gradually loses its impact specialty applications requiring outdoor weather- strength upon exposure to sunlight. On the other ability and aging resistance. hand, ASA polymers retain their impact strength upon outdoor exposure signifi cantly better than 15.4.3.1 ASA/PVC Blends ABS, due to the saturated nature of the acrylic elastomer phase. ASA resins are generally pro- Most of the ASA produced is used for blending duced as powders for easy blending with other with a lower cost PVC resin by the end users. resins such as PVC. ASA is also supplied as The fabricator blends powders of ASA and PVC Commercial Polymer Blends 1051 in the desired ratio using conventional PVC strength and outstanding weatherability of ASA processing equipment such as Banbury mixers. resins, specialty blends based on ASA are being The blend is used in profi le extrusions and coex- developed recently for exterior automotive appli- trusions. Applications for ASA/PVC blend include cations. Blending polycarbonate with ASA enhanc- siding, mobile home skirts, window profi les, es the notched impact strength and DTUL, while vending machine trim, automotive exterior trim, maintaining the weatherability characteristics of etc. The blend has signifi cantly better impact ASA. Black, pigmented parts such as automotive strength, better heat distortion temperature and mirror housings, trim, cowl vents, grilles, etc., better color retention than PVC. The blend has cost are some of the target applications for this blend. advantages over the neat ASA. Typical properties It must be remembered that the properties and of ASA/PVC blends are described in Table 15.7. morphology of ASA/PC would be similar to ABS/PC blends, except for the added feature of 15.4.3.2 ASA/PC Blends outdoor weatherability of ASA. Typical properties of ASA/PC are shown in Table 15.7. In order to take advantage of the high impact Owing to the relatively recent nature of this

Table 15.7. Properties of some commercial ASA blends

Blend Type ASA/PVC ASA/PC

ASTM GELOY SUPREL GELOY TERBLEND S PROPERTY TEST UNITS 1220 9301 XP4001 KR2861 METHOD GEC Vista GEC BASF

PHYSICAL Density D792 kg/m3 1,200 1,200 1,110 1,150 Mold Shrinkage D955 % 0.45 Water Absorption, 24 hrs. D570 % 0.1 0.29 0.3

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2140(310) 2760(400) 1910(295) 2250(320) Flexural Strength D790 MPa (kpsi) 60(8.5) 68(9.7) 61(11.2) Tensile Strength at Yield D638 MPa (kpsi) 46(6.6) 43(6.3) 48(7) 53(7.5) Elongation at Break D638 % 25 70 100 Rockwell Hardness D785 R96 R106 R99 R109

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 1080(20) 425(6) 700(13) 610(11.2) at -40°C 107(2) 190(3.5)

THERMAL Heat Defl ection Temp D648 °C at 0.45 MPa 85 110 127 at 1.82 MPa 76 76 99 108 1052 M. K. Akkapeddi technology, little has been published regarding of SMA-MMA terpolymers with ABS (Cadon®, the characterization of this blend. Market volume Monsanto). These blends exhibit higher DTUL/ for this blend has also been thus far, relatively impact balance compared to ABS (Table 15.8) small. Competition from lower cost ABS/PC and reportedly offer processing and cost advantages blend will limit the use of ASA/PC blend to over PPE/HIPS and ABS/PC blends [Kosoff, niche applications requiring weatherability and 1987]. Applications for these blends are also in UV resistance. similar markets, e.g. automotive interior, appliance, and business machine housings. 15.4.4 Styrene-Maleic Anhydride (SMA) SMA copolymers and terpolymers have also Copolymer and Terpolymer Based been used for blending with PVC to improve the Blends heat distortion temperature and processability of PVC. These blends also contain a rubbery compo- Commercial SMA resins (Dylark®, ARCO; nent for impact modifi cation that is usually a high Stapron®-S, DSM) are amorphous, random copo- rubber ABS or a polymethyl methacrylate grafted lymers of styrene and maleic anhydride (10 to styrene-butadiene rubber (MBS). For improved 30%) that exhibit higher glass transition tempera- weatherability, acrylic rubber modifi ed PVC has tures (20 to 60°C higher) and higher heat distor- been used for blending with SMA copolymers tion temperatures than polystyrene. The maleic and terpolymers (Table 15.4). The market for anhydride comonomer imparts rigidity to the SMA/PVC blends is still relatively low in volume styrenic backbone raising its Tg by 2°C with each with only a few applications such as in business 1 wt% increase in the maleic anhydride content. machine housings as a low cost replacement for In addition, the maleic anhydride comonomer fl ame retarded ABS. imparts higher polarity to the styrenic backbone A commercial blend of SMA and polycarbon- and hence, increasing the modulus, strength, ate (Arloy®, ARCO) was offered for some time, solvent resistance and adhesion to reinforcing but recently it was discontinued. The polarity fi llers and glass fi bers [Wambach, 1991]. The of SMA copolymer may account for the good polarity and the reactivity of the SMA resins have degree of compatibility between the two resins. also been utilized for the compatibilization of its The blend contained the polybutadiene rubber blends with other polymers. normally used in SMA resins for impact strength. Unmodifi ed SMA resins are quite brittle, like It exhibited good low temperature impact strength the PS and hence they are invariably toughened (Table 15.8) and in many properties was similar by incorporating suitable rubber dispersions, either to ABS/PC blend. by grafting of a polybutadiene rubber during the A commercial blend of SMA and polybutylene polymerizations in a manner similar to the HIPS terephthalate (Table 15.8) was also offered for technology, or by blending with styrene-butadiene applications requiring solvent resistance, which the multiblock copolymer type elastomers. Rubber crystalline PBT provided. This blend lacked ade- toughened SMA resins (Table 15.8) exhibit some- quate compatibility and hence its impact strength what higher heat distortion temperatures than HIPS is relatively poor. or ABS, yet have an equivalent toughness. Hence Some imidized derivatives of SMA resins, such elastomer modifi ed SMA copolymers fi nd containing N-phenyl maleimide units in place of good application niches in automotive interior maleic anhydride comonomer units have been instrument panels, headliners, and in some appli- offered commercially (Denki Kagaku, Japan) as ance and business machine housing applications. blend components to modify the heat distortion Terpolymers of SMA containing small amounts temperature of styrenics (HIPS and ABS). Blends of methyl methacrylate comonomer were found of such resins with ABS have been commercial- to exhibit good miscibility with SAN [Hall, 1982], ized in Japan (Malecca®, Denki Kagaku). hence this technology was used to develop blends Commercial Polymer Blends 1053

Table 15.8. Properties of some commercial blends of SMA copolymer resins

Blend Type SMA/S-B SMA/PC SMA/PBT SMA-MMA/ ABS

ASTM DYLARK ARLOY DYLARK CADON PROPERTY TEST UNITS 250 1000 DPN 520 127 METHOD Arco Arco Arco Monsanto

PHYSICAL Density D792 kg/m3 1,060 1,130 1,160 1,070 Mold Shrinkage D955 % 0.6 0.7 0.5 0.6 Water Absorption, 24 hrs. D570 % 0.12 0.2 0.3

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2390(340) 2200(330) 2760(400) 2410(350) Flexural Strength D790 MPa (kpsi) 62(8.9) 80(12) 105(15) 67(9.5) Tensile Strength at Break D638 MPa (kpsi) 35(5) 45(6.6) 50(7.3) 35(5) Elongation at Break D638 % 25 80 21 40

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 180(3.4) 640(12) 38(0.7) 218(4) at -40°C 320(6)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 120 at 1.82 MPa 113 108 89 112 Vicat Softening Point D1525 °C 118 138

15.5 Vinyl Resin Blends include (a) general inertness to many chemicals and aqueous fl uids, (b) good dimensional stability, Polyvinylchloride (PVC) is commercially the (c) good electrical properties, (d) inherent fl ame most signifi cant member of the family of vinyl resistance and (e) good weatherability. These resins. The other important members of this group attributes led to its widespread use in building are chlorinated-PVC (CPVC) and polyvinylidene construction, wire/cable and packaging markets. chloride (PVDC). PVC is one of the most widely PVC, however, suffers from an inherent sus- used, commodity type thermoplastics with an ceptibility to thermal degradation and hence must annual consumption of over 5 Mton/y in the USA. invariably be processed with heat stabilizers The excellent versatility of PVC is attributed and careful control of processing temperature. to its blending capability with a variety of plas- The other important drawbacks of PVC are: its ticizers, additives and fi llers to yield products brittleness in the absence of a plasticizer (low ranging from very fl exible to very rigid types. notched Izod impact strength) and its low heat In addition, PVC has a low cost advantage and distortion temperature (ca. 60°C) originating from a reasonably good balance of properties, which its low glass transition temperature and essentially 1054 M. K. Akkapeddi amorphous character. Hence the primary motiva- particle size of the elastomer phase [Shaw, 1982; tions for blending PVC with other polymers in Shur and Ranby, 1976; Walsh and McKeown, rigid applications have been to improve its impact 1990]. For high impact strength the particle size strength (notched Izod), DTUL and processabil- should be > 0.1 µm but < 1 µm. The good degree ity. In fl exible, plasticizer-free (free from low of compatibility or miscibility between PVC and molecular type materials) applications, PVC is PMMA or SAN phase also plays an important role blended with low modulus polymeric modifi ers in the toughening effect. Hence a notched Izod (as polymeric plasticizers). Impact modifi ed and impact strength of > 1000 J/m is readily achieved fl exibilized PVC blends together constitute a with these impact modifi ers. ABS, MBS and major fraction of PVC used commercially. acrylic impact modifi ers are available as powders, and are usually blended with PVC powder in 15.5.1 PVC/Impact Modifi er Blends high shear intensive mixers prior to fabrication of sheet or profi le extrusion [Forger, 1977]. Pre- In rigid PVC applications (pipes, building and compounded grades of PVC are also sold com- construction) PVC is compounded with impact mercially by all the major producers of PVC. modifi ers, usually up to 10-15%, to improve the When the particle size of the rubber is > 0.2 µm, notched Izod impact strength without sacrifi cing the toughened PVC is opaque. tensile strength and modulus. Various commer- Clear impact modifi ers for PVC are controlled cial impact modifi ers effective in toughening the particle size grades of MBS, acrylic core shell PVC are illustrated in Table 15.9. These are gener- rubbers, or ABS. They offer the impact strength ally core-shell type rubbers with a controlled par- improvement as well as maintenance of suffi cient ticle size, rubbery core (polybutadiene, styrene- optical clarity in the PVC blend. These impact butadiene rubber or poly-n-butylacrylate) grafted modifi ers are designed to match the refractive to a styrene-acrylonitrile (SAN) or styrene-methyl index of PVC. Controlled particle size (100-300 methacrylate (S-MMA) copolymer or PMMA as nm) and suffi cient compatibility or solubility of a rigid outer shell. These are generally made the rigid SAN, S-MMA or PMMA phase with by emulsion polymerization of the corresponding the PVC account for the clarity of the blends. monomers using a pre-made rubber latex as seed Some grades of MBS have been designed to have or core. The shell (rigid polymer) content in MBS cluster-like structures [Saito, 1973], in which and acrylic core rubbers is usually 20-30% and the individual rubber particles of small diameter about 30-50% in ‘high rubber’ ABS. (50-70 µm) are held together by a styrene-meth- The toughening effect of ABS, MBS and acryl- ylmethacrylate graft copolymer or terpolymer. ic modifi ers is undoubtedly due to the controlled When blended with PVC, these rubber particles

Table 15.9. Effect of various types of commercial impact modiﬁ ers for rigid PVC

Modiﬁ er Advantages Notched Izod (J/m) (Modiﬁ er level 0, 3, 5, and 12%)

‘High rubber’ ABS (PBD 50%) Impact, Processability 53 69 203 972 Methacrylate-butadiene-styrene Clarity, Impact strength 53 64 240 1335 (‘MBS’) (PMMA-g-SBR) Processability Acrylate core-shell rubbers (PMMA-g-BuA) Weatherability, 53 69 192 1041 Clarity Impact, Processability Chlorinated polyethylene (CPE) Weatherability, Impact 54 90 235 1225 Commercial Polymer Blends 1055 are small enough to offer transparency to the Ethylene-vinylacetate blends with PVC have blend, but the clusters of these particles in PVC been widely used in Europe as permanent “poly- matrix are large enough to cause craze toughen- meric plasticizers” for PVC. Low cost and good ing. Typical applications for clear impact modi- weatherability of these blends permitted their use fi ed PVC blends are in clear, calendered sheet in window profi les, cable jacketing and other or fi lm for packaging and for blown bottles. outdoor applications. Ethylene vinylacetate copo- Acrylic impact modifi ers based on poly(n-butyl lymer with 65-75% vinyl acetate content is quite acrylate) or poly(2-ethyl hexyl acrylate) rubbery miscible with PVC exhibiting a single Tg for cores offer improved weatherability to PVC due the blend [Hammer, 1971; Ranby, 1975; Rellick to their saturated backbone. These blends are used and Runt, 1985]. Two phases are apparent when for outdoor applications such as siding, window the vinylacetate is 45%. Vinylchloride grafted profi les, etc. ethylene-vinyl acetate copolymers have also been Chlorinated polyethylene (CPE) fl exibilizes used for blending with PVC. and toughens PVC more by a miscibility mecha- In PVC/nitrile rubber blends, PVC is added nism especially when the chlorine content is more as an ozone resistant additive. In these ther- above 42% [Donbe and Walsh, 1979]. However, moplastically processable blends, PVC is fl exibil- partial miscibility occurring at chlorine levels ized enough to be used for ‘soft’ goods, wire of 36% leads to higher toughening effects. CPE jacketing, hoses, gaskets and seals. When the offers also weatherability advantage, which is the NBR contains > 25% acrylonitrile, it becomes major reason for its commercial use. miscible with PVC and at 20% acrylonitrile level, it is fairly compatible due to partial misci- 15.5.2 PVC/Flexible Modifi er Blends bility [Matso et al., 1969].

In addition to chlorinated polyethylene, three 15.5.3 PVC/Styrenic Blends other major types of modifi ers are blended commercially with PVC in order to fl exibilize the PVC has been blended with some styrenic resins composition. Usually 30-60% modifi er levels are primarily to achieve some degree of fl ame retar- employed. These fl exibilizing modifi ers usually dant characteristics and cost benefi ts. ABS, SMA, have some degree of miscibility with PVC. A and rubber modifi ed SMA, SMA-MMA copoly- list of the commercial fl exibilizing modifi ers and mers have been used commercially for blending their advantages are shown in Table 15.10. with PVC. These have been discussed under the styrenic blends and illustrated in Table 15.4.

Table 15.10. Effect of various types of fl exibilizing modifi ers for PVC (Modifi er levels: 30 to 60%)

Modiﬁ er Advantages Applications

Ethylene-vinyl acetate (EVAc) Low smoke generation; Weatherability Construction (windows), sheet/fi lm, cable jacketing Thermoplastic polyurethane (TPU) Oil and chemical resistance; Shoes, gaskets, seals, tubing, fi lm Low temperature toughness Butadiene-acrylonitrile rubber (NBR): Cable jacketing, hoses, belting, High nitrile type Oil and chemical resistance seals, gaskets, shoe soles, etc. Low nitrile type Low temperature fl exibility 1056 M. K. Akkapeddi

15.5.4 PVC/PMMA Blends thermoforming applications as well as in several molding applications in which these properties PVC blends with polymethylmethacrylate (PMMA) are well utilized. have been commercialized (e.g. Kydex®, Kleerdex Since most of the applications of the PMMA Co.) as extruded sheets for thermoforming appli- type acrylic resins are based on their high cations such as chairs, seats, trays, etc. Ease of degree of transparency and UV resistance char- thermoformability, toughness, resistance to cleaning acteristics, there has been little commercial inter- solvents, and the fl ame retardancy characteristics of est or motivation in developing acrylic blends. the blends have been the primary features leading This is understandable because unless there is to its use. The good level of compatibility between complete, molecular level miscibility between PMMA and PVC is mainly responsible for the the components, it is not possible to maintain a toughness characteristics of the blend [Walsh and high degree clarity in the blends. Nevertheless, Cheng, 1984; Tremblay and Prud’homme, 1984; several examples of commercial blends of acrylic Jager et al., 1983]. Notched Izod impact strength resins are known. These will be discussed under of > 600 J/m has been reported, although it is separate headings. likely that some acrylic rubber modifi er may have been used. The inherent fl ame retardancy and low 15.6.1 Impact Modifi ed Acrylic Resins smoke-generation characteristics of PVC/PMMA blends meet the aircraft fi re safety standards. Since the homopolymer PMMA as well as the This factor coupled with the low cost, high tough- MMA-rich copolymers are quite brittle, exhibit- ness and easy processing features of the blend ing low elongation to break ( 5%) and low led to its use in aircraft components such as notched Izod impact strength (typically 15 J/m), toilet shrouds, fl oor pans, air diffusers, emergency there was a need to blend suitable impact modi- respirator enclosures, etc. fi ers that would improve the ductility and impact strength of these resins without sacrifi cing the transparency, rigidity and weatherability charac- 15.6 Acrylic Blends teristics. Two general types of impact modifi ed acrylic Commercial acrylic resins comprise a broad resins have been developed commercially, viz. (a) array of polymers and copolymers derived from weatherable, impact modifi ed, transparent acrylic esters of acrylic acid and methacrylic acid. resins for outdoor use in signs and automobiles; They range from the homopolymer of methyl- (b) non-weatherable impact modifi ed, transparent methacrylate to a variety of copolymers includ- acrylic resins for medical and food packaging appli- ing both the thermoplastic and thermoset type cations. The weatherable grades of acrylics are and ranging from hard and stiff type to soft made by blending ‘all acrylic’ core-shell rubbers and elastomeric types. The most common of the viz., PMMA grafted, crosslinked poly(n-butyl thermoplastic acrylic resins are the polymethyl- acrylate) type rubbers (Paraloid®, Rohm Haas). methacrylate homopolymer (PMMA) and the The non-weatherable grades are made by blend- copolymers containing predominantly methyl ing polymethyl-methacrylate-g-butadiene/styrene methacrylate but with small amounts of methyl (‘MBS’) type core-shell rubbers. In both cases, or ethyl acrylate, acrylonitrile or styrene como- due to the small particle size of these core-shell nomers added for improved toughness. The com- rubbers ( 100 nm) and the miscibility of the shell mercial PMMA-based acrylic resins are rigid, (PMMA) with the PMMA matrix, the refractive amorphous polymers (Tg’s ranging from 85 to index could be matched and the transparency 105°C) particularly noted for their exceptional could be completely maintained. The rubber par- clarity and UV resistance. They are therefore ticles were found to promote localized shear widely used for glazing, extruded sheet and banding in the matrix and hence, the ductility Commercial Polymer Blends 1057

and toughness of the matrix improves [Hooley usually blended captively by the manufacturers et al., 1981; Bucknall et al., 1984; Wrotecki et of the acrylic resins. The base resin in a typical al., 1991] weatherable grade (Plexiglas DR, Rohm and Haas) Commercial impact modiﬁ ed acrylic resins could be a methylmethacrylate copolymer with (Table 15.11) exhibit 5 to 10 fold improvement ethylacrylate and styrene, while the rubber addi- in the notched Izod impact strength and the tive (ca. 10%) could be an emulsion polymerized, ultimate tensile elongation compared to the neat PMMA grafted, crosslinked poly(n-butylacrylate) PMMA resin. These impact modiﬁ ed acrylics are rubber of controlled particle size ( 200 nm).

Table 15.11. Commercial acrylic/impact modiﬁ er blends vs. acrylic

Blend Type ACRYLIC/IMPACT MODIFIER ACRYLIC

ASTM PLEXIGLAS PLEXIGLAS PROPERTY TEST UNITS XT 375 DR VO44 METHOD Cyro Rohm & Haas Rohm & Haas

PHYSICAL Density D792 kg/m3 1,120 1,150 1,190 Mold Shrinkage D955 % 0.7 0.5 0.4 Water Absorption, 24 hrs. D570 % 0.3 0.4 0.3

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2450(350) 1900(270) 3160(450) Flexural Strength D790 MPa (kpsi) 77(11) 72(10.3) 120(17) Tensile Strength at Yield D638 MPa (kpsi) 49(7) 39(5.5) 72(10.2) Elongation at Break D638 % 28 35 5 Rockwell Hardness D785 M45 M45 M96

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 108(2) 60(1.1) 12(0.2) at -40°C

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 86 93 at 1.82 MPa 85 79 92

ELECTRICAL Dielectric Strength D149 KV/mm Dielectric Constant at 1 MHZ D150 2.8 2.2 2.2 Dissipation Factor at 1MHZ D150 0.02 0.03 0.03 Volume Resistivity D257 ohm-m 1.0E+15 1.0E+15 1058 M. K. Akkapeddi

The non-weatherable impact modifi ed acrylic automotive parts. A 50 µm fi lm of the blend is (XT, CYRO) typically consists of a MMA/S/AN laminated to PVC fi lm which is then laminated to copolymer with MBS (ca. 10%) rubber particle metal, followed by the fi nal fabrication (stamping, dispersions. rolling) of the automotive parts such as rocker Generally, the weatherable impact modifi ed panels, hubcaps, pillar posts, door edge guards, acrylic resin has better color and transparency etc. The fi lm is pigmented to a solid or colored retention than the non-weatherable grade but metallic look matching the body. The role of the latter shows better toughness. The weather- PVDF in this blend is to offer chemical and able grades are used for making outdoor signs, weather resistance to the fi nal surface fi nish on automotive headlight lenses, lighting fi xtures, the part. glazing, etc. The non-weatherable, high impact acrylics are used for medical devices, medical and food packaging, refrigerator trays, etc. Poly- 15.7 Elastomeric Blends carbonate is a competitive threat to the impact modifi ed acrylic resin markets. Currently over The blending of different types of rubbers and 30 Mton/y of acrylic/impact modifi ed blends are then curing into the fi nal fabricated parts such used in the USA. as automotive tires has long been known in the rubber industry and will not be discussed here. 15.6.2 PVC/Acrylic Blends This discussion will deal with the commercial blends containing a high volume fraction of a Since PVC is known to be quite miscible with rubbery polymer and minor amounts of a rigid, PMMA (miscibility with an LCST behavior) amorphous or crystalline thermoplastic. A major [Jager et al., 1983] and is also low in cost, some motivation for developing such blends was to blends of PVC and PMMA have been used in combine the elastomeric character of the rubber sheet extrusion and thermoforming applications. component with the melt processability of the However, the acrylic PVC compositions commer- thermoplastic. Hence blending has been an alter- cially used are invariably contain an acrylic core- native and somewhat lower cost approach to shell rubber (PMMA-g-n-BuA or MBS type) to making thermoplastic elastomers compared to the get high toughness), with some PMMA, to reduce block copolymer approach. the cost/impact performance balance. The role Vulcanized rubbers are distinguished by their of PVC in these blends is to reduce cost and impart characteristically low modulus, high extensibility some degree of fl ame-retardancy. The acrylics and high elastic recovery, i.e., by their ability to defi nitely help in the processability of PVC. return to the original dimensions after stretching These blends have already been discussed under to high strain levels and then releasing the applied PVC heading. stress. The elasticity behavior in vulcanized rubbers is related to the crosslinking between the 15.6.3 PVDF/Acrylic Blends polymer chains. However in the thermoplastic elastomers, the elasticity originates from the pseu- Polyvinylidenefl uoride (PVDF) and polymethyl- do-crosslinks formed by the rigid phase, which methacrylate have been known to be a thermo- is either the hard segment of the block copoly- dynamically miscible blend exhibiting a single mer, or the rigid inclusion having high gloss

Tg, an indication of a single phase behavior transition temperature, or crystalline polymer [Bernstein et al., 1977; Mijovic et al., 1982]. A phase, blended into the elastomer as a ﬁ ne disper- commercial PVDF/PMMA blend ﬁ lm (Fluorex® sion. A, Rexham Corp.) produced captively by solvent casting is used in specialty applications, such as a protective and decorative overlaminated for Commercial Polymer Blends 1059

15.7.1 Nitrile Rubber/PVC Blends Ingredients and Machinery for Rubber,” published annually by Bill Communications, Inc. Currently, Blends of butadiene-acrylonitrile copolymer rubber the PVC/nitrile rubber blends worldwide con- (nitrile rubber or NBR) and PVC are among the sumption is estimated to be 30 kton/y. oldest known examples of commercial elastomer/ Nitrile rubbers are known for their oil and thermoplastic blends. The shortage of natural rub- chemical resistance and addition of PVC improves ber during World War II stimulated research in the ozone resistance. Use of carboxylated NBR is the USA on the compounding and modiﬁ cation of believed to obviate the necessity of vulcanization. synthetic polymers to produce rubber-like materi- Nitrile rubber/PVC blends have reached a als. An outcome of this research was the com- mature stage in their commercial usage. They face mercial introduction of NBR/PVC blends by B.F. increasing competition from other thermoplastic Goodrich in 1947 under the trade name of Geon® elastomers such as the dynamically vulcanized Polyblends [Pittenger and Cohan, 1947]. The blend blends of PP/EPDM and PP/NBR (Santoprene® showed improved ozone resistance and melt pro- and Geolast®, Monsanto-Advanced Elastomer cessability compared to the nitrile rubber (Table Systems). 15.12). Butadiene-acrylonitrile copolymer rubbers 15.7.2 Dynamically Vulcanized, Alloys of PP containing > 25% acrylonitrile exhibit good and Elastomers miscibility with PVC as evidenced by single

Tg behavior of the blend [Zakrzewski, 1973; Another type of thermoplastic elastomer blend, Matsuo et al., 1969], although high resolution which is gaining signifi cant commercial interest electron microscopy indicated some degree of is the “dynamically vulcanized” blends of fully microheterogeneity with a very fi ne dispersion cured elastomers in a thermoplastic matrix [Coran, size (< 10 nm) [Matsuo, 1968]. This high degree 1987]. Dynamically vulcanized alloys are pro- of miscibility, or partial miscibility, between the duced by melt blending a high volume fraction components accounts for the blend’s high com- of an elastomer with a thermoplastic in a high patibility and improved mechanical properties. intensity mixer, with a compatibilizer if necessary, Commercial nitrile rubber/PVC blends are used that a fi ne dispersion of the elastomer is achieved. in both not-vulcanized and vulcanized forms. The elastomer is then fully cured during the melt A descriptive list of commercially available nitrile mixing through the use of selective crosslinking rubber/PVC blends can be found under a variety agents. Since the elastomer is fully cured the of trademarks in the Nitrile Elastomers section blend achieves high rubber elasticity character, of “The Blue Book, Materials, Compounding but since the thermoplastic still remains as an

Table 15.12. Typical properties of nitrile rubber/PVC blends

Property NBR/PVC (70/30) NBR/PVC (55/45) NBR

Hardness 73A 82A 63A Modulus (MPa) at 100% 4.6 7.5 2 at 300% elongation 12 13.5 10 Tensile strength (MPa) 17 15.8 22 Elongation at break (%) 530 460 600 Compression set (%) (22 hr, 100°C) 48 64 37 1060 M. K. Akkapeddi uncrosslinked matrix, the blend can be melt pro- polypropylene blends containing up to 30% EPR cessed like a thermoplastic. In order to distinguish have already been discussed under polyolefi n from the simple blends of an elastomer and blends. Blends containing high content of an thermoplastic, the dynamically vulcanized blends uncured or partially cured EPDM in polypropyl- have been classifi ed as “elastomeric thermoplastic ene have been known [Kresege, 1978]. However, alloys” (ETA) [Wallace, 1992]. the advantage of fully cured EPDM/PP blends Dynamically vulcanized, elastomeric thermo- made by selective crosslinking of the rubber plastic alloys display properties as good as or phase during the melt mixing has not been com- even better than the block copolymers, viz. a high mercially realized until recently (Santoprene®, degree of rubber elasticity yet good melt process- AES; Sarlink® 3000, Polysar). The technology ability. The main advantages of the fully cured, [Coran et al, 1978; 1980], involved an acceler- elastomeric thermoplastic alloys over the uncured ated sulfur cure of the EPDM rubber ( 70%) thermoplastic/elastomer blends are: (1) improved in the presence of polypropylene ( 30%) while tensile strength and elongation, (2) reduced perma- melt compounding under high shear mixing con- nent set (compression or tension), (3) improved ditions. The curing agents typically consisted fl exural fatigue resistance, (4) improved chemical of zinc oxide (5 phr), sulfur (2 phr), tetramethyl- resistance, (5) better morphology stability during thiuram disulfi de (1 phr), and 2-benzothiazolyl melt processing, (6) recyclability (regrind reuse), disulfi de (0.5 phr). The particle size of cured (7) improved melt strength. The dynamically vulca- EPDM dispersions was typically < 2 µm. nized blends are very elastomeric in their properties, Increasing the crosslink density of the elasto- yet readily melt processable in the conventional mer dispersion results in improvements of the injection molding, blow molding, and extrusion strength and tension set of the blend. The differ- processing techniques. ence between the earlier commercial grades of Commercially important elastomeric thermo- partially cured EPDM/PP blends (TPR, Uniroyal) plastic alloys are dynamically vulcanized blends and the more recent commercial grades of com- of polypropylene with high volume fractions of pletely cured EPDM/PP blend is in the improved EPDM, polybutadiene rubber, nitrile rubber, and elastomeric properties, viz. reduced compression butyl rubber (Santoprene®, Vyram®, Geolast® and tension set and improved fl exural fatigue. and Trefsin®) all currently sold by Advanced More important, the chemical resistance and Elastomer Systems, a joint venture of Mon- resistance to oil swelling is improved. Typical santo and Exxon. Another recent member of properties of commercial dynamically vulcanized the commercial dynamically cured elastomeric EPDM/PP blend (Santoprene®) are shown in thermoplastic alloys is the blend of PVC and Table 15.13. a crosslinked ethylene copolymer (Alcryn®, Nearly all of the dynamically vulcanized DuPont). The current consumption of all the EPDM/PP blend’s (Santoprene®) growth has elastomeric thermoplastic alloys in the USA been at the expense of thermosetting rubbers is over 23 kton/y, with the EPDM/PP blend due to the blend’s easy melt processability and (Santoprene®) assuming about 90% of the recyclability. Much of this growth has been market share. in automotive applications such as rack and pinion steering boots, seat belt sleeves, and air 15.7.2.1 Dynamically Vulcanized EPDM/PP ducts. EPDM/PP blend has also been used in Blends window and door glazing seals, weather stripping and extrusion applications in the electrical/ Owing to adequate level of compatibility between electronic industry. polypropylene and ethylene-propylene copolymers, simple blends of these two polymers have been known for a long time. Impact modifi ed Commercial Polymer Blends 1061

Table 15.13. Key properties of commercial thermoplastic elastomer blends based on polypropylene/elastomer dynamic vulcanizates

Properties ASTM PP/EPDM PP/PBD PP/NBR PP/Butyl Method (Santoprene®) (Vyram®) (Geolast®) (Trefsin®)

Speciﬁ c Gravity (g/mL) D792 0.98 1.04 1.0 1.2 Shore Hardness D2240 73A 70A 70A 70A 100% Modulus (MPa) D412 3.2 3.7 3.3 5.2 Tensile Strength (MPa) D421 8.3 7.6 6.2 7.6 Elongation at Break (%) D624 375 380 265 250 Tear Strength (KN/m) D624 28 31 33 26 Tension Set (%) D412 14 16 10 12 Compression Set (%) D395 24 32 29 52 Brittlenss Temp. (oC) D746 -63 -58 -40 60 Flexural Fatigue1 >3.4 Oil Swelling2 32 32 10

Notes 1In megacycles to fail; 2As vol% in ASTM oil #3, after 70h at 100°C.

15.7.2.2 Polybutadiene Rubber/PP, nitrile rubber and a small amount of maleic anhy- Dynamically Vulcanized Blends dride grafted polypropylene (maleated PP) with the (Vyram®, AES) high molecular weight polypropylene and then intimately mixing all the components together. A This class of blends was introduced in 1989, as graft coupling reaction presumably takes place a lower cost alternative to EPDM/PP blend. Its between the ATBN and maleated PP. The result- heat-aging resistance and use temperature limits ing poly(butadiene/acrylonitrile)-g-polypropyl- are, however, inferior to the EPDM/PP blends. ene copolymer compatibilizes and reduces the interfacial tension between the nitrile rubber and 15.7.2.3 Nitrile Rubber/PP, Dynamically polypropylene phases. Vulcanized Blends (Geolast®, AES) Typically a 50/50 blend of nitrile rubber and polypropylene is melt mixed with 5% maleated The oil resistance and chemical resistance of PP and 1% ATBN respectively and then cured nitrile rubber is generally superior to that of with SnCl2 (0.5%). The resistance to hot oil EPDM rubbers. However, the highly polar swell (72 hr, 100°C) of NBR/PP blend is signiﬁ - nature of acrylonitrile comonomer is responsible cantly better than that of EPDM/PP blend. Typical for the high incompatibility between nitrile rub- properties of the commercial dynamically cured ber and polypropylene. The dispersability and NBR/PP blend (Geolast®) are compared with the stability of nitrile rubber dispersions in the other such blends in Table 15.13. polypropylene matrix are poor. Hence a reactive Commercial applications for this blend include compatibilization technology was used [Coran seals and gaskets in the automotive oil, fuel and and Patel, 1983]. It consisted of blending a small brake systems. Other automotive uses include air amount of a low molecular weight amine-termi- ducts, boots, connectors, etc. Geolast® is also used nated butadiene-acrylonitrile copolymer (ATBN, in gasoline powered lawn and garden equipment, B.F. Goodrich) with the high molecular weight power tools and other industrial applications. 1062 M. K. Akkapeddi

15.7.2.4 Butyl rubber/PP Dynamically comonomer units. For example, when the vinyl Vulcanized Blends acetate content is high (e.g., > 65 wt%) the copolymer forms completely miscible blends with The dynamically cured, butyl rubber/polypro- PVC [Hammer, 1971; Rellick and Runt, 1985]. pylene blends were fi rst developed by Gessler At lower levels, the blends are partially miscible. et al. using phenolic type crosslinking agents. Similarly ethylene-methyl acrylate and ethyl-butyl Commercial dynamic vulcanizates are based on acrylate copolymers form miscible to partially halobutyl rubbers and polypropylene cured by miscible blends with PVC [Kalfoglou, 1983]. zinc oxide type curatives. [Hazelton and Puydak, Ethylene copolymers, which exhibit partial 1987; Kay and Ouhadi, 1991; Anon., 1988]. miscibility, can be expected to be dispersed into The blend containing a high volume fraction of fi ne particles in a matrix of PVC by simple butyl rubber dispersion in polypropylene exhibits melt mixing, because of the self-compatibilizing high elastomeric properties but retains good ther- nature of the blends. If a suitable third comono- moplastic processability. In addition, this blend mer is also present in these copolymers, which exhibits the following advantages: contains a reactive functionality suitable for (i) Low permeability to air and moisture crosslinking, one can use selective crosslinking (ii) High energy absorption and consequently techniques through dynamic vulcanization pro- high vibration damping characteristics cess to achieve high volume fraction dispersions (iii) Resistance to thermal and UV aging and of cured ethylene copolymers in the thermoplas- weathering tic matrix of PVC. This principle has been com- (iv) Excellent resistance to common organic fl uids. mercially employed in developing thermoplastic elastomer blends of PVC with such ethylene Typical applications are in medical stoppers, terpolymers as ethylene-n-butylacrylate-carbon bladders and packaging seals. Other automotive monoxide (E-BA-CO) and ethylene-vinylace- and non-automotive applications are expected. tate-carbon monoxide (E-VAc-CO) terpolymer systems. Due to the presence of the carbonyl 15.7.3 Elastomeric Thermoplastic Alloys of moiety in their backbone, these ethylene terpoly- PVC and Ethylene Terpolymers mers can be crosslinked selectively through the use of peroxide/bis maleimides or diamine type Recently blends of certain types of ethylene ter- curatives or through electron beam or gamma polymers with PVC, which have been dynamical- radiation techniques [Loomis and Statz, 1986]. ly vulcanized into highly elastomeric yet thermo- In a typical formulation, an ethylene-n-butyl- plastically processable blends, have been offered acrylate-carbon monoxide (60/30/10) terpolymer commercially (Alcryn®, DuPont). The principle (60 wt%) is melt compounded with plasticized behind this technology appears to be the selec- PVC (40 wt%) in a twin-screw extruder and the tion of proper types of ethylene copolymers ethylene terpolymer dispersion cured in situ dur- and terpolymers which exhibit high degree of ing the mixing by catalytic amounts of a suitable miscibility with PVC and which can selectively peroxide (0.3%) and a bismaleimide crosslink be crosslinked in-situ, during the melt mixing promoter (0.2%). The extruded pellets of the with specifi c curing agents [Loomis and Statz, elastomeric blend can be used in conventional 1986]. It has been known that PVC forms miscible melt fabrication processes such as profi le extru- or partially miscible blends with certain types sion, extrusion coating, milling and calendering of ethylene copolymers such as ethylene-vinyl of sheets, injection and/or compression molding. acetate (EVAc), ethylene-methyl acrylate (EMA) Commercial elastomeric blends of such ethylene and ethylene-butyl acrylate (EBA) copolymers terpolymers and PVC have been reported to have [Krause, 1989]. The degree of miscibility depends the following advantages: (i) outstanding weather- on the structure and ratio of ethylene to the ability and ozone resistance, (ii) excellent oil Commercial Polymer Blends 1063 resistance, (iii) good low temperature toughness, their outstanding solvent resistance and mechani- (iv) good melt processability and recyclability. cal properties. In Table 15.14, the typical properties of a com- Commercial polyamides are generally of two mercial elastomeric blend of ethylene terpolymer type (a) those derived from diamines and dicarbox- and PVC (Alcryn®) are compared with similar ylic acids and (b) those derived from amino acids elastomeric blends. or lactams as monomers. The major characteristics Commercial elastomeric blends of ethylene of these two types of polyamides are similar since terpolymer/PVC system (Alcryn®) are used in these are determined largely by the hydrogen outdoor weather stripping, seals and gaskets, bonding structure of the amide groups. However, coated fabrics, pond linings and a variety of other within these two types, a wide variety of PA are extruded and molded goods for automotive and known, varying in their melting points and mois- industrial applications. ture absorption characteristic, depending on their structure. Among these, PA-66, a polyamide made by polycondensation of hexamethylene diamine 15.8 Polyamide Blends and adipic acid and PA-6, a polyamide made by the ring opening polymerization of caprolactam, are Commercial polyamides, frequently referred to as the two major nylon engineering thermoplastics nylons, are crystalline engineering thermoplastics produced commercially. Because of their wide- exhibiting high performance characteristics such spread use in fi ber, plastic and fi lms, both PA-66 as high melting points, high mechanical strength, and PA-6 are produced on a large scale with an ductility, and excellent resistance to solvents, estimated total volume globally to be > 4.5 Mton/y, fatigue and abrasion. Nylon is a generic term 18% of which is used for non-fi ber applications used for all synthetic polyamides in which the [SRI, 1992]. In 1993, an estimated 355 kton/y recurring amide groups (-CONH-) are part of the of PA will be used in the USA for molding main polymer chain. These amide groups impart applications. PA blends consumed in the USA are strong hydrogen bonding capability and crystal- currently about 30 kton/y. linity in the polyamides, PA, which account for

Table 15.14. Comparison of the typical properties of the dynamically vulcanized ethylene terpolymer/PVC blends vs. similar elastomeric blends based on polypropylene

Property Ethylene terpolymer / EPDM/PP NBR/PP PVC (Alcryn® 2070) (Santoprene® 101-73) (Geolast® 701)

Density (kg/m3) 1,140 980 1,000 Shore Hardness 73A 70A 68A Tensile Strength (MPa) 8.9 7.6 6.2 Elongation at Break (%) 680 470 480 Tension Set (%) 9 14 16 Compression Set (%) (at 100°C) 65 33 28 Brittleness Temperature (°C) -78 -65 -40 Hot Oil Resistance Excellent Fair Excellent Weatherability (Ozone & UV Resistance) Excellent Excellent Poor 1064 M. K. Akkapeddi

There are a number of other specialty poly- polymer candidates commercially used for blend- amides produced from a combination of other ing with PA and the major reasons for blending diamines and dicarboxylic acids and/or lactams them are listed in Tables 15.15 and 15.16. The graft of varying number of carbon atoms. PA-11 and copolymer compatibilization technique requires PA-12 with 11 and 12 methylene units between the other polymer component to be already “func- each repeat amide group are relatively low melt- tionalized”, i.e., modifi ed with functionalities ing point (170°C), but exhibit excellent ductility such as anhydride or epoxide groups, which are and moisture resistance. reactive towards the amine or carboxyl end groups Among the newer class of polyamides are of PA respectively. During the melt blending, the the high melting (ca. 300°C) PA-4,6 and PA-6T reaction between the functionalized polymers and copolymers with 6 or 66 or 6T monomer units. polyamides leads to graft copolymer formation Because of the high level of crystallinity at the interface, which essentially compatibilizes and high melting points, PA’s generally exhibit and stabilizes the blend against delamination. high heat distortion temperature at low loads even in unfi lled form, and when reinforced 15.8.1 Polyamide/Elastomer Blends with glass fi bers, exhibit high heat distortion (Impact modifi ed polyamides) temperatures at high loads. Most of the commercial polyamides exhibit a common set of Commercial polyamides such as PA-6 and PA-66 property advantages attributable to their crystal- are generally regarded as tough and ductile mate- line nature and hydrogen bonding character. rials since they exhibit high tensile elongation The advantages offered by the crystalline polyam- to break and high drop weight impact strengths. ides (PA-6, PA-66) in blends with other polymers, They become even tougher after equilibration are: excellent solvent resistance (e.g., gasoline, with ambient humidity, due to the plasticization oils, paint solvents, etc.), heat resistance and effect of the absorbed water. However, under melt fl ow characteristics. On the other hand, the conditions of stress concentration such as in the primary motivation to blend other thermoplastic presence of sharp notches or cracks, polyamides polymers with polyamides, is for reducing the exhibit brittle failure. This property, commonly moisture sensitivity of PA and improving its evaluated as notched Izod or Charpy impact tests, dimensional stability and toughness. indicates that unmodifi ed polyamides exhibit Because of their highly polar and hydrogen relatively low energies for crack propagation. bonded structure of the backbone, as a general To overcome this defi ciency, polyamides have rule polyamides are immiscible with most of the been blended with several types of impact modi- commercially known polymer systems. In addi- fi ers that are typically elastomeric or low modulus tion, the high degree of interfacial tension [Wu, type olefi nic polymers. However, the inherent 1989] between polyamides and other classes of immiscibility of polyamides with other polymers polymers leads to highly phase separated blends such as olefi nic rubbers necessitated the develop- with poor delamination resistance. Hence simple ment of proper compatibilization techniques to blends of PA with other commercial polymers reduce the interfacial tension and improve the generally do not have any practical value. dispersability of the rubber for effective impact Signifi cant progress has been made in recent modifi cation. years in developing techniques for compatibil- The technology for impact modifi cation of izing polyamide blends, particularly utilizing the polyamides has evolved signifi cantly over a peri- reactivity of polyamide end groups in forming od of several years through improved methods ionic or covalently linked bonds with other poly- of compatibilization and particularly through mers at the blend interface. Several commercial reactive blending techniques [Kray and Bellet, blends are based on such reactive compatibiliza- 1968; Murch, 1974; Epstein, 1979; Mason and tion technology. Some of the more important Tuller, 1983]. Several commercially successful Commercial Polymer Blends 1065

Table 15.15. Effect of various blend components on the properties of polyamides

Blend Component Reasons for blending Compatibilization method

Elastomers (functionalized EPR, * Improve notched Izod impact strength Graft-coupling reaction acrylate rubbers, etc.) * Shift ductile brittle transition to lower temperatures Ethylene copolymers, ionomers * Improve toughness and fl exibility Polar interaction * Lower modulus Polyolefi ns (HDPE, LDPE, PP) * Lower cost Graft-coupling reaction * Improve dimensional stability with humidity ABS * Toughness Graft-coupling reaction * Reduce moisture sensitivity (better strength and stiffness retention) Polyphenylene ether, PPE * Improve DTUL (at 1.83MPa), unfi lled Graft-coupling reaction * Improve strength and creep resistance * Reduce moisture sensitivity (better strength and stiffness retention with humidity) Polycarbonate (PC) * Improve DTUL (at 1.83MPa), unfi lled Maleated-PP, * Lower mold shrinkage polyether amide elastomer * Reduce moisture sensitivity Silicon IPN * Improve lubricity and wear None (IPN cured in situ) * Reduce shrinkage and warp Amorphous polyamide * Improve oxygen barrier at high humidity levels None (miscibility)

(High Tg, barrier)

Table 15.16. Comparative rating of performance characteristics of polyamideswith other key blend components

PA-6, PA-66 Polypropylene ABS PPE

Melting/softening temperature High Moderate Moderate Very High Glass transition temperature Low Low Moderate High Melt processability Excellent Excellent Excellent Poor Moisture absorption High None Low None Moisture sensitivity (properties, dimensions) High None None None Drop weight impact strength High Moderate High Moderate Notched Izod impact Low Low High Low Tensile strength High (dry) Moderate Moderate High Moderate (wet) Creep resistance Good Low Moderate Excellent Solvent resistance Hydrocarbons, oils Excellent Moderate Moderate Poor Paint solvents (MEK, toluene) Excellent Moderate Moderate Poor Alcohols, glycols Poor Excellent Excellent Excellent Hydrolysis resistance (in acidic or basic aqueous fl uids) Poor Excellent Moderate Excellent 1066 M. K. Akkapeddi impact modifi ed polyamides are based on blends There are several other routes to compatibil- of polyamides with (a) reactive elastomers such izing polyamide/elastomer blends for the purpose as maleic anhydride-grafted (“maleated”) EPDM, of impact modifi cation such as through the use EP and styrene-ethylene/butylene-styrene block of anhydride modifi ed ABS rubbers [Baer, 1988], copolymer rubbers, and (b) functional ethylene anhydride modifi ed S-EB-S block [Gelles et al., copolymers such as ethylene-ethyl acrylate, eth- 1988] copolymers, carboxylated core-shell rub- ylene-acrylic acid, ethylene-ethylacrylate-maleic bers (MBS or acrylic type) [Liu, 1988] and anhydride and ethylene-methacrylic acid iono- acylcaprolactam grafted EP rubbers [Akkapeddi mers. Compatibilization of an olefi nic rubber and Haylock, 1989]. dispersion in a polyamide melt blend is achiev- The outstanding impact toughness of the com- able through a direct chemical coupling reaction mercial impact modifi ed polyamides is attributed between the polymers at the interface such as to the small particle size of rubber dispersion and through the addition reaction between the amine their good degree of adhesion to the polyamide end groups of polyamide and the anhydride func- matrix. Typical morphologies of compatibilized tionality of a maleated EP rubber. polyamide/elastomer blends are shown in Figure The graft copolymer formed in situ via this 15.6. In all of these blends the rubber particle size reaction during the melt blending process effec- is much smaller than would be obtained with a tively compatibilizes the blend by reducing the typical unmodifi ed EPR phase. interfacial tension and increasing the adhesion at The toughening mechanism is believed to the phase boundary. Due to the graft copolymer’s involve the internal cavitation and debonding of capability to act as an interfacial agent, the the rubber which induces localized shear yielding dispersability of the rubber in the polyamide of the polyamide matrix as the primary energy matrix improves considerably, resulting in well dissipation processes [Borggreve and Gaymans, stabilized, reduced particle size ( 1µm), rubber 1989; Ramsteiner and Heckmann, 1985; Borg- dispersions and thereby substantially increasing greve et al., 1988] occurring during the impact the toughness. DuPont’s commercially successful deformation. Rubber particle size, distribution and ‘super-tough’ nylon, Zytel® ST801 is based on interparticle distance [Wu, 1988] are some of the such a reactive blending technology using PA-66 key parameters that have been correlated to the and a maleated EPDM rubber [Epstein, 1979]. impact toughness. The ductile-brittle transition of Commercial ‘super-tough’ PA-66 exhibits an the polyamide blend is shifted to low temperature, excellent notched Izod impact strength ( 900 J/m) both by choosing a low Tg rubber, as well as that is remarkably insensitive to part thickness controlling the rubber particle size ( 1 µm) and and notch radius. volume fraction. At an equivalent content of the Impact modifi cation of PA-6 has also been compatibilized rubber, PA-6 tends to show higher achieved by blending with such ethylene copoly- impact strength at low temperatures than PA-66. mers as ethylene-ethylacrylate, ethylene-acrylic Commercial impact modifi ed polyamides typi- acid and ethylene-methacrylic acid copolymer cally contain 10 to 25% of the reactive or com- based zinc ionomers. It is believed that favorable, patible elastomer to maximize the toughening associative interactions involving some type of effi ciency while retaining a high level of tensile complexation between the amine end groups of strength and DTUL. Commercial impact modifi ed polyamide and the zinc carboxylate groups of PA blends (Table 15.17) indeed offer a unique the ionomer are responsible for the high compat- combination of high notched Izod impact and ibility and toughening effi ciency of ionomers. drop weight impact strengths, coupled with a Some commercial impact modifi ed PA-6 blends good balance of modulus, tensile strength, heat, (Capron® 8253 and 8350, AlliedSignal) are based solvent and abrasion resistance characteristics. either on ethylene copolymer or ionomer type These properties are suitable for many engineer- tougheners [Mason and Tuller, 1983]. ing and metal replacement applications. Because Commercial Polymer Blends 1067

constitute the largest fraction of PA blends used commercially. Some PA/elastomer blends containing a combination of different types of impact modifi ers and elastomers have been specifi cally designed for low volume, specialty extrusion applications (tubing and profi les). Generally, these blends contain higher levels of these elastomers or impact modifying polymers than the impact modifi ed polyamides. Often the rubbers are used in combination with plasticizers to achieve a fl exible, low modulus blend product that still retains much of the polyamide advantages, viz. heat resistance and solvent resistance, particularly permeation resistance to such automotive fl uids as gasoline, refrigerants (CFC, HCFC), etc. These blends are often formulated to suit a specifi c customer or application requirement. The demand for such polyamide based fl exible blends seems to be growing. Recently a fl exible polyamide blend [Saltman and Varnell, 1988; Saltman, 1992] containing < 50% PA-6 or PA-66 and >50% acrylic elastomers has been introduced by DuPont (Zytel® FN) as a plasticizer-free, low modulus composition with good low-temperature toughness, resistance to thermal aging and solvents (particularly to fl uorocarbon refrigerants) (Table 15.17). Figure 15.6. Morphology of typical Polyamide/impact Although the fl exible polyamide blends contain modifi er blends — TEM., Phosphotungstic acid stain, < 50% polyamide, the PA phase is continuous top — PA-6/ethylene copolymer/ionomer blend (21,000X); and the major elastomeric phase (> 50%) is kept bottom — PA-6/maleated EPR (3:1) blend (30,000X). as dispersion. It is believed that the morphology can be controlled by modifying the viscosity of the elastomer phase during the blending through of their good melt fl ow characteristics most of controlled and selective grafting reactions. By the impact modifi ed polyamides are processed using two mutually miscible (or compatible), by injection molding, although recently blow co-reactive elastomers, a high viscosity ratio molding applications are also emerging. between the elastomer and polyamide phases can Typical automotive applications include gas be maintained preventing phase inversion even cap covers, fan blades, shrouds for cooling sys- when the total volume fraction of elastomer phase tems, gears, fasteners, clips, emission control is higher than that of polyamide. For example, canisters, oil pans, shields, etc. Toughened poly- by using an ethylene-butylacrylate-methacrylic amides are also used in sports and recreational acid ionomer in combination with an ethylene- equipment, lawn and power tool housings and butylacrylate-glycidyl methacrylate (E-BA-GMA) components where impact strength, heat and terpolymer, a grafting or cross-linking reaction chemical resistance are the primary criteria for between the two elastomers via the carboxy/ their choice. With an estimated consumption of epoxide addition reaction is expected to take 25 Mton/y in the USA, impact modifi ed PAs place, during the melt blending with polyamide. 1068 M. K. Akkapeddi

Table 15.17. Properties of some commercial polyamide/elastomer blends

Blend Type PA-66 BASED PA-6 BASED

ASTM ZYTEL ZYTEL ZYTEL CAPRON CAPRON PROPERTY TEST UNITS 408 ST801 FN716 8253 8351 METHOD Du Pont Du Pont Du Pont AlliedSignal AlliedSignal

PHYSICAL Density D792 kg/m3 1,090 1,080 1,030 1,090 1,070 Mold Shrinkage D955 % 1.5 1.5 1.2 1.3 Water Absorption, 24 hrs. D570 % 1.2 1.2 0.5 1.5 1.1

MECHANICAL Flexural Modulus D790 MPa (kpsi) 1960(285) 1690(245) 690(100) 2200(320) 1800(240) Flexural Strength D790 MPa (kpsi) 80(12) 68(9.8) 85(12.5) 65(9.5) Tensile Strength at Yield D638 MPa (kpsi) 62(9) 52(7.5) 30(4.3) 65(9.5) 55(8) Elongation at Break D638 % 80 40 250 150 200 Rockwell Hardness D785 R115 R112 D59 R78 R82

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 240 937(17) NB 135(2.5) 990(18) at -40°C 220(4) 270(5) 70(1.3) 265(5) Drop Weight Impact D3029 J (ft-lb) at 23°C 170(125) 135(100) 200(150) at -40°C 170(125) 100(75) 200(150)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 230 216 176 170 at 1.82 MPa 73 71 60 60 Vicat Softening Point D1525 °C 216 210 210

* Elastromers are functionalized EPR or ethylene copolymers

This would cause an increase in the melt viscosity ber blend dispersion morphology of PA appears to of the elastomer phase relative to polyamide, translate into a signifi cant improvement of impact thus preventing a phase inversion [Saltman, 1992; strength and elongation at break after heat-aging Ohme, 1991]. At the same time, the compatibility at 150°C for 14 days. Because of the saturated between the ionomer and polyamide as well and polar nature of the rubber and the continuous as some degree of reactive compatibilization matrix of polyamide, the blend retains a high between E-BA-GMA and polyamide (through degree of solvent resistance in addition to its carboxy/epoxide or amine/epoxide reactions) may aging resistance. Since fl exible polyamide blends lead to the stabilization of the dispersions. are relatively new, their uses are still emerging. The key advantage of this stabilized, high rub- Typical applications are expected to be in the Commercial Polymer Blends 1069 extrusion and blow molding areas, e.g., tubing are in 50/50 to 60/40 ratio. Since both polyamide and hoses; ducts and air-intake systems; oil and and PP are crystalline polymers, one would expect grease seals, etc. notch sensitivity and brittleness under impact loading conditions, despite the compatibilization. 15.8.2 Polyamide/Polypropylene Blends Accordingly, the polyamide/PP blends show about the same low notched Izod impact strengths as Polyamide and polypropylene are both crystalline the individual components. However, using PP polymers, but are signifi cantly different in their copolymers, or an atactic PP of low crystallinity or structure and polarity. Hence they are immiscible. by using a PP impact modifi ed with EPR, higher The primary motivations for blending polypro- notched Izod impact strength in the polyamide/PP pylene with polyamide appear to be based on blends can be achieved. All other properties such some cost advantages and some improvements in as modulus, strength and DTUL are intermediate dimensional stability in the presence of moisture. between the individual components, as expected. Although compatibilization of polyamide and Polyamide/PP blends exhibit a signifi cantly polypropylene via grafting with a maleic anhy- slower rate of moisture absorption compared to the dride modifi ed polypropylene was known for a polyamides due to the presence of the moisture long time [Ide and Hasegawa, 1974], commercial resistant polypropylene phase. The morphology of interest in such polyamide/polypropylene blends PA/PP blend depends on the molecular weights of has not developed until recently [Girard, 1990; polyamide and PP (especially after functionaliza- Moody, 1992]. tion and blending) as well as the degree of grafting. It is known that polypropylene can be modifi ed Typically, commercial polyamide/PP blends show by a free radical catalyzed grafting reaction with nylon as the continuous phase and polypropylene maleic anhydride (maleation) in the melt phase as the dispersed phase. The morphology, however, under extruder processing conditions. The reaction seems somewhat sensitive to the fl ow induced involves hydrogen abstraction from polypropylene shear effects during the injection molding. backbone followed by chain scission. The polypro- Commercialization of polyamide/PP blends is pylene chain fragments with secondary radical still at an early stage. One of the commercial or unsaturated chain ends undergo an addition sources in the USA (D&S International) offered reaction with maleic anhydride forming a modi- two kinds of polyamide/PP blends, one rich in fi ed polypropylene with anhydride functionality PP (DexPro®) and the other rich in polyamide bound to the polymer chains. The process involves (Dexlon®). The blend’s improved dimensional some chain degradation that must be controlled stability over polyamide has led to some applica- by amount of peroxide used and the temperature tions in automotive, lawn and power tool markets. and mixing conditions used. Typically, about The relative advantages of polyamide/PP blends 0.5% maleic anhydride can be grafted to PP. vs. polyamide, PP and other blends have not been Similarly, other unsaturated anhydrides can be clearly identifi ed and further market and applica- used to modify PP. tion development is actively under investigation Melt blending of PA-6 (or 66) with such an with several companies. anhydride functionalized polypropylene causes a fast graft copolymer reaction between the poly- 15.8.3 Polyamide/ABS Blends amide and PP at the interface, which subsequently compatibilizes the blend. Some commercial As indicated in Table 15.15, the advantages of polyamide/polypropylene blends may utilize such blending ABS with PA are primarily in impact types of reactive compatibilization techniques. strength and moisture resistance. Since ABS is an Properties of commercial PA/PP blends, both amorphous polymer, its heat resistance is limited unfi lled and glass fi lled grades, are shown in by the Tg of the SAN phase, thus the blend would Tables 15.18 and 15.19. Typically, these blends be expected to exhibit lower heat resistance than 1070 M. K. Akkapeddi

Table 15.18. Properties of some commercial polyamide/polypropylene blends vs. polypropylene

Blend Type PA-6/PP PA-66/PP PP

ASTM ORGALLOY AKULOY RM DEXLON PROFAX PROPERTY TEST UNITS R6000 NY-75 602 6523 METHOD Atochem DSM D&S Int. Himont

PHYSICAL Density D792 kg/m3 1,030 1,030 1,090 900 Mold Shrinkage D955 % 0.79 0.9 1.25 Water Absorption, 24 hrs. D570 % 0.4 0.4 1.1 0

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2050(300) 2140(310) 1725(250) 1610(230) Flexural Strength D790 MPa (kpsi) 68(9.9) 76(11) Tensile Strength at Yield D638 MPa (kpsi) 43(6.2) 48(7) 48(7) 35(5) Elongation at Break D638 % 300 150 90 200

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 90(1.6) 77(1.4) 850(16) 52(0.95)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 140 152 216 91 at 1.82 MPa 60 65 65 53

polyamide. However, by keeping the polyamide SAN backbone of ABS in suffi cient concentration as a continuous phase and ABS as the dispersion caused compatibilization with PA-6 when melt blends with high softening point (due to the blended, presumably due to favorable hydrogen high melting point of polyamide) high HDT can bonding interactions [Grant, 1985]. be achieved. In addition, a polyamide matrix In another approach, a small amount of maleic would be advantageous for maintaining solvent anhydride was copolymerized with styrene and resistance in the blend. acrylonitrile during the preparation of ABS by Simple blends of ABS and PA are highly emulsion polymerization. The ‘anhydride modi- immiscible and hence are of little practical value. fi ed’ ABS was then melt blended with polyamide Compatibilization of ABS with polyamide was to form a compatibilized ABS/PA blend [Laven- accomplished by several methods, most of which good et al., 1986, 1987; Howe and Wolkowicz, involving structural modifi cation of ABS. In one 1987]. Obviously, a reaction between the anhy- approach, ABS was modifi ed by copolymeriza- dride functionality of ABS and the amine end tion with acrylamide, during the preparation of group of polyamide leads to an in situ graft ABS by the standard emulsion polymerization. copolymer responsible for compatibilizing this The introduction of polar acrylamide units on the blend. Monsanto’s ABS/PA blends (Triax® 1000 Commercial Polymer Blends 1071

Table 15.19. Properties of 30% glass reinforced polyamide/polypropylene blends vs. 30% glass reinforced polypropylene

Blend Type PA-6/PP PA-66/PP PP

ASTM AKULOY RM MCX-Q DEXLON AKULOY RM COMALLOY PROPERTY TEST UNITS J-75/30 QA5030 633HI M-2040 130 METHOD DSM Mitsui D&S Int. DSM Comalloy

PHYSICAL Density D792 kg/m3 1,260 1,300 1,400 1,280 1,130 Mold Shrinkage D955 % 0.3 0.4 Water Absorption, 24 hrs. D570 % 0.35 0.4 0.5 0

MECHANICAL Flexural Modulus D790 MPa (kpsi) 7600(1100) 7500(1090) 7600(1100) 8100(1170) 5340(760) Flexural Strength D790 MPa (kpsi) 160(23) 190(27.5) 190(27.5) Tensile Strength at Yield D638 MPa (kpsi) 120(17.5) 130(19) 162(23.5) 135(19.5) 70(10) Elongation at Break D638 % 4 4 3 4 3

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 90(1.6) 100(1.8) 133(2.5) 115(2.1) 82(1.5)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 151 at 1.82 MPa 165 190 199 242 143

series) are based on this reactive compatibilization improved impact strength (Figure 15.7) and a fi ne technology. The polybutadiene rubber content of dispersion morphology (Figure 15.8). Undoubt- the ABS used for this blend technology is about edly the chemical coupling between the phases via 40%, signifi cantly higher than the standard grade the amine/anhydride reaction, is responsible for ABS (10-20% PBD). Because of the high rubber the observed compatibilization. A small amount content and the compatibilization chemistry, the (5 wt%) of maleated EP rubber preblended with blends exhibit excellent notched Izod impact the maleated ABS led to substantial improvement strengths (Table 15.20). in the notched Izod impact strength of the fi nal Standard grade ABS (20% PBD) could also ABS/PA-6 blend. It was postulated that migration be directly modifi ed by grafting an anhydride of the maleated EPR to the vicinity of SAN/PA-6 functionality via reactive extrusion with maleic boundary and subsequent graft copolymer reac- anhydride in the presence of a trace amount of tion with nylon led to substantial toughening of peroxide initiator [Akkapeddi et al., 1990]. Such the interphase region [Akkapeddi et al., 1993]. an extruder ‘maleated ABS’ upon subsequent melt At present, only Monsanto is commercially blending with an amine terminated PA-6, gave a offering ABS/PA blends. These are based on PA-6 compatibilized ABS/PA-6 blend with signifi cantly (Triax 1120) or PA-66,6 copolymer (Triax 1125). 1072 M. K. Akkapeddi

Table 15.20. Properties of some commercial grades of polyamide/ABS blends

Blend Type ABS/PA-6 and ABS/PA-66,6

ASTM TRIAX TRIAX TRIAX TRIAX PROPERTY TEST UNITS 1120 1125 1180 1315 METHOD 15% GF

PHYSICAL Density D792 kg/m3 1,060 1,060 1,060 1,160 Mold Shrinkage D955 % 0.9 0.9 0.9 0.3 Water Absorption, 24 hrs. D570 % 0.1 0.1 0.1

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2070(300) 2140(310) 1930(280) 4275(620) Tensile Strength at Break D638 MPa (kpsi) 46(6.6) 47(6.8) 51(7.4) 79(11.5) Elongation at Break D638 % 270 270 330 2 Rockwell Hardness D785 R95 R99 R101

IMPACT Izod Impact, No Notch D256 J/m(ft-lb/in) NB NB NB 520(9.4) Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 850(16) 850(16) 1030(19) 115(2.1) at -40°C 100(1.9) Drop Weight Impact D3029 J (ft-lb) at 23°C >45(>33) >45(>33) >45(>33) at -40°C 44(33) 6(4.4) >45(>33)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 92 94 93 188 at 1.82 MPa 104 Vicat Softening Point D1525 °C 197 180 210 Coefﬁ cient of D676 m/m/°C 1.7E-04 1.7E-04 Thermal Expansion U.L. Thermal Index UL 746B °C 60 60

ELECTRICAL Dielectric Strength D149 K/V/mm 16.7 17.7 Dielectric Constant at 1 KHZ D150 3.8 4.5 Dissipation Factor at 1KHZ D150 0.014 0.05 Volume Resistivity D257 ohm-m 9.7E+13 6.4E+13 Arc Resistance D495 sec 108 105 Commercial Polymer Blends 1073

Figure 15.7. Instrumented Impact behavior of ABS/PA-6 Figure 15.8. Morphology of ABS/PA-6 blends (TEM, (50/50) blends; top — uncompatibilized blend, bottom — phosphotungstic acid); top — Uncompatibilized blend (5000X), compatibilized blend [Akkapeddi et al., 1993]. bottom — Compatibilized blend (10,000X) [Akkapeddi, 1993].

Commercial ABS/PA-6 blend exhibits excellent at the Tg of ABS(SAN), and hence the blend notched Izod impact ( 850 J/m) at room tempera- exhibits lower DTUL at 0.45 MPa than the impact ture and good drop weight impact (> 40 J) at modifi ed polyamide. The latter are polyamide rich -40°C. These impact properties are equivalent (75%) and hence maintain a higher level of heat to the impact modifi ed polyamide (Table 15.20). resistance due to their crystallinity. Commercial However, the DTUL (0.45 MPa) of ABS/PA blends ABS/PA blends compete for the same type of are relatively low compared to those of impact applications as the impact modifi ed polyamide, modifi ed nylons. The key difference being that in primarily in areas where impact strength and ABS/polyamide blends, due to the signifi cant level chemical resistance are required. Presumably due of ABS, a substantial drop in the modulus occurs to their lower heat resistance and slightly inferior 1074 M. K. Akkapeddi low-temperature notched Izod impact strengths, between PPE and polyamides. Several compatibil- their market growth has been somewhat slower izer additives have been claimed in the early than that of impact modifi ed polyamide. However, patent literature [Ueno and Maruyama, 1982], ABS/PA blends exhibit somewhat better dimen- which included the use of liquid diene rubbers, sional stability and lower warpage characteristics epoxides and unsaturated compounds containing than impact modifi ed polyamide, which led to acid, anhydride, amino, imino or hydroxyl groups. some applications in electronic devices like calcu- Since polyamides have reactive end groups (amine lators, key pads, battery packs, etc. and carboxyl) it is quite conceivable that the compatibilizing additives may react fi rst with poly- 15.8.4 PPE/Polyamide Blends amide if all the components are blended together all at once, inhibiting any actual coupling reaction Poly (2,6-dimethyl-1,4-phenylene ether) PPE is a between PPE and polyamide. The latter is more high-Tg, amorphous polymer [Hay, 1976]. It was desirable for the effective compatibilization of the originally developed by General Electric Co., blend. Hence subsequent investigators focused fi rst which until recently has been the sole producer on functionalizing PPE with a grafting agent such of this polymer [Hay, 1967]. PPE is generally of that suitable functional groups are attached to the homopolymer type, although a copolymer with PPE backbone [Jalbert and Grant, 1987; Akkapeddi minor amounts of 2,3,6 trimethyl phenol is also et al., 1988]. Although functionalization of PPE produced. Although PPE exhibits high mechani- is possible through solution-phase end-capping cal strength, DTUL and ductility, it is generally reaction with trimellitic anhydride acid chloride diffi cult to process as a molding resin due to its [Aycock and Ting, 1986], one would prefer to use high softening temperature (T 300°C), high melt melt-phase grafting reactions via reactive extrusion viscosity and tendency for thermo-oxidative deg- techniques for reasons of economics. radation at the high melt processing temperatures Melt phase reaction of PPE with unsaturated (330°C). The discovery that PPE can form highly functional reagents such as maleic anhydride, compatible (miscible) blends with polystyrene led fumaric acid, acrylic acid and their derivatives, to the development of PPE/HIPS blends [Cizek, glycidyl methacrylate and other unsaturated com- 1969] that have been the commercially most pounds were investigated. This functionalization successful to date. The properties of PPE/HIPS reaction could be done in extruders and the blends are suitable for many applications. How- functionalized PPE could be isolated and charac- ever, they lack adequate chemical resistance. terized. The functionalization step introduced a In order to improve chemical resistance, blends reactive functional group on the PPE chain, that of PPE with crystalline polymers such as polyam- upon subsequent melt blending with polyamide ides have been the subject of much investigation. would react with the amine or carboxyl end Simple blends of PPE and polyamides are highly groups of nylon forming a graft copolymer of incompatible, generally leading to brittle and PPE and polyamide at the interface. Since the readily delaminating products of low value. Hence block and graft copolymers are the best interfacial considerable attention has been paid in recent agents for a blend, the dispersability of PPE in years to develop technology for effective compati- polyamide improves due to decreased interfacial bilization and impact modifi cation of these blends. tension, and consequently, the tensile properties The exact compositions, the nature of grafting (strength, elongation) and toughness of the blend agents or compatibilizers used and the impact improve considerably. The structure of maleated modifi ers used in commercial PPE/PA blends are PPE and the characterization of the graft copoly- still kept proprietary, although many patents have mer was reported [Glans, 1991; Akkapeddi, 1993; been issued. Campbell, 1990]. Research efforts have been focused largely Functionalization of PPE with maleic anhy- on the methods of improving the compatibility dride or fumaric acid could be done by melt Commercial Polymer Blends 1075

Figure 15.9. Ultimate elongation and melt ﬂ ow behavior of reactively compatibilized PPE/PA-6/impact Modiﬁ er (50/40/10) blends — Effect of amine terminated PA-6 [Akkapeddi, et al., 1993].

blending (ca. 300°C) in an extruder. This anhydride functionalized PPE could either be isolated and reextruded with PA-6 or melt blended in a single-pass through down stream addition of the Figure 15.10. Morphology of PPE/PA-6 (60/40) blends polyamide in a twin-screw extruder. In either case, (TEM, phosphotungstic acid stain); top — Uncompatibilized pre-functionalization of PPE is a necessary and blend (10,000X), bottom — Compatibilized blend (20,000X). an important step in order to optimize the selective grafting reaction between PPE and polyamide, and prevent any premature reaction between polyamide and the maleic anhydride or fumaric tron microscopy of compatibilized PPE/PA-6 blend acid. The graft-coupling reaction itself is an (Figure 15.10) indicates fi nely dispersed PPE in addition reaction between the amine end group a PA matrix. of polyamide and the anhydride group of the The heat distortion temperature of the PPE/PA functionalized PPE. It was also found that the blend at high loads (1.8 MPa) increases with compatibilization effi ciency increased when a the amount of PPE in the blend (Figure 15.11) PA-6 rich in amine end groups (‘amine terminated [Akkapeddi and VanBuskirk, unpublished results]. polyamide’) was used [Akkapeddi, 1992 and However, because of the crystallinity of the 1993]. The tensile elongation to break increased polyamide matrix, the heat distortion temperature considerably, as did also the melt viscosity, the at low loads (0.4 MPa) is relatively less sensitive latter indicative of increased polymer-polymer to the PPE content and is largely determined by grafting reaction (Figure 15.9). Transmission elec- the polyamide. This is one signifi cant difference 1076 M. K. Akkapeddi

Figure 15.11. Effect of PPE Content on the DTUL of PPE/PA-6 vs. PPE/HIPS blends. between blends of crystalline/amorphous polymers or reactive type), its content and manner in which (PA-6/PPE) vs. blends of amorphous/amorphous it is added determine the effi ciency of notched (PS/PPE) polymers. In the PPE/polyamide blends, Izod impact strength improvement and the low the crystalline PA phase is invariably the continu- temperature ductility. Hydrogenated styrene-buta- ous phase, because of the large melt viscosity diene-styrene block copolymer (S-EB-S) rubbers difference between PPE and PA. have been used as impact modifi ers in PPE/PA-66 Although the binary blends of PPE and polyblends [Grant et al., 1988] since they are expected amides exhibit good ductility (tensile elongation to be compatible and readily dispersible in the and drop weight impact) after the reactive com- PPE phase. Preblending a functionalized rubber patibilization, the notched Izod impact strengths (such as a maleic anhydride modifi ed EP rubber) are still relatively low. This is to be expected since into the functionalized PPE, followed by melt the individual resin components, viz. PA-6 (or blending with the polyamide, generally gave better PA-66) and PPE, exhibit low notched Izod impact impact strength improvement in PPE/PA-6 blends strengths (< 70 J/m). Hence commercial PPE/PA [Akkapeddi et al., 1988 and 1992]. An impact blends invariably include an impact modifi er modifi ed PPE/PA blend developed by Hüls in component, the exact composition and content of Europe, contained polyoctenylene as impact mod- which is kept proprietary and varied from grade ifi er [Droescher, 1988]. to grade. Commercial PPE/polyamide blends typically Commercial impact modifi ed PPE/PA blends contain 40-60% polyamide and 0-10% of the exhibit notched Izod impact strengths ranging impact modifi er, each grade being formulated for from 175 to 500 J/m at room temperature. They specifi c types of applications. Typical properties of also differ in their ductile brittle transition tem- some commercial unfi lled and glass-fi lled PPE/PA perature and low temperature impact behavior. blends are illustrated in Tables 15.21 and 15.22. The type of nylon used (PA-6 or PA-66 or In general, PPE/polyamide blends offer a unique copolymer type), its end group concentrations combination of high heat resistance (DTUL and and molecular weight, and more importantly, continuous use temperatures), high impact strength, the nature of the rubber modifi er used (compatible hygro-thermal dimensional stability and ease of Commercial Polymer Blends 1077

Table 15.21. Properties of some commercial PPE/polyamide blends

Blend Type PPE/PA-66 PPE/PA-6

ASTM NORYL NORYL NORYL DIMENSION DIMENSION TEST PROPERTY METHOD UNITS GTX910 GTX901 GTX625 D9000 D9300 GEC GEC GEC AlliedSignal AlliedSignal

PHYSICAL Density D792 kg/m3 1,100 1,100 1,100 1,080 1,090 Mold Shrinkage D955 % 1.4 1.4 1.5 1.6 1.6 Water Absorption, 24 hrs. D570 % 0.5 0.3 0.3 0.5 0.5

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2135(310) 2000(290) 2000(290) 1900(275) 2340(339) Flexural Strength D790 MPa (kpsi) 76(11) 76(11) 83(12) 70(10.5) 96(14) Tensile Strength at Yield D638 MPa (kpsi) 60(8.6) 54(7.8) 56(8) 56(8) 70(10.2) Elongation at Break D638 % 60 50 50 50 75

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 220(4) 175(3.3) 477(9) 550(10) 190(3.5) at -40°C 137(2.5) 125(2.4) 156(3) 275(5) 80(1.5) Drop Weight Impact D3029 J (ft-lb) at 23°C 100(75) 136(100) at -40°C 34(25) Instrumented Impact, D3763 J (ft-lb) Energy at 23°C 50(38) 38(28) 45(33)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 193 160 177 185 180 at 1.82 MPa 143 121 132 121 112 Vicat Softening Point D1525 °C 232 215 210 210

processability. In addition, the blends exhibit better PPE/PA blends have found many applications chemical resistance compared to other high heat, in the automotive area, such as in fenders, hatch- amorphous engineering resins such as PPE/HIPS backs, wheel covers and mirror housings. Because blend and polycarbonate (Table 15.23) [Akkapeddi of their high heat resistance, exterior automotive et al., unpublished results]. body parts made from PPE/PA blends can be painted “on-line,” attached to the metal frame in 1078 M. K. Akkapeddi

Table 15.22. Properties of 30% glass reinforced PPE/PA blends vs. PPE/PS blend

Blend Type PPE/PA-6 PPE/PA-66 PPE/PS

ASTM DIMENSION NORYL NORYL PROPERTY TEST UNITS D9130 GTX830 GFN3 METHOD AlliedSignal GEC GEC

PHYSICAL Density D792 kg/m3 1,330 1,330 1,270 Mold Shrinkage D955 % 0.5 0.5 0.2 Water Absorption, 24 hrs. D570 % 0.2 0.2 0.06

MECHANICAL Flexural Modulus D790 MPa (kpsi) 7720(1120) 7655(1100) 7730(1120) Flexural Strength D790 MPa (kpsi) 235(32.5) 224(32) 140(20) Tensile Strength at Yield D638 MPa (kpsi) 160(23) 160(23) 119(17) Elongation at Break D638 % 3.7 3.7 5 Compressive Strength D695 MPa (kpsi) 77(11.2) 76(11) 125(18)

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 115(2.1) 105(2) 125(2.3)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 215 252 158 at 1.82 MPa 205 235 148 Vicat Softening Point D1525 °C 215 249 158

the existing automotive paint oven temperatures gives somewhat higher impact strength to the of ca. 180 to 200°C. The parts retain good tough- blend at any given blend ratio. Although other ness required in these applications. PPE/PA blends specialty polyamides such as PA-12 and PA-4,6 have also been used in many industrial and non- have also been investigated in PPE blends, they automotive markets such as pumps, water meter have not gained commercial signifi cance due to housings, lawn and garden tractor hoods, mono- their higher cost. fi laments, etc. The annual growth for PPE/PA blends is predicted to be about 10%. The cost of 15.8.5 Polyamide/Polycarbonate Blends PPE/PA blends can, in principle, be lowered by the addition of some polystyrene or HIPS into Polycarbonate has been blended with commercial the PPE phase, taking advantage of their mutual polyamides (PA-66 and PA-6), in order to improve miscibility. However, this results in some sacrifi ce its poor solvent resistance while maintaining a in DTUL. Most of the commercial PPE/PA blends reasonable level of heat resistance and toughness. are based either on PA-66, that gives slightly However, simple blends of polycarbonate and higher heat resistance to the blend or PA-6, which polyamides are highly incompatible and hence Commercial Polymer Blends 1079

Table 15.23. Comparison of the chemical resistance of PA-6, PPE/PA-6, PE/HIPS and PC(a) (% change in properties(b))

Solvent PA-6 PPE/PA-6 PPE/HIPS Polycarbonate

Y.S. E b Y.S. Eb Y.S. Eb Y.S. E b

Water -40 200 0 0 0 -30 0 -75 Antifreeze -20 200 0 0 0 -70 Stress Cracked (50% aqueous glycol) Gasoline 0 200 0 100 Stress Cracked -80 -100 Gasohol -50 300 -50 0 Dissolved Stress Cracked (15% Methanol) Brake fl uid 0 21 10 -25 -80 -100 Stress Cracked Transmission fl uid 0 -25 0 0 Stress Cracked 0 0 Power steering fl uid 0 -50 0 0 Stress Cracked Stress Cracked Motor oil 10 -50 0 0 Stress Cracked Stress Cracked Trichloroethylene 0 200 -70 100 Dissolved Stress Cracked

(a) Tensile bars, 3 mm thickness, tested at 6% strain after one week immersion in a solvent. (b) % change in properties, increase (+) or decrease (-) relative to the dry as molded properties in air; Y.S. = Yield Stress;

Eb = elongation at break.

not useful. Several different additives such as ity, resistance to paint solvents and automotive phenoxy resins, polyester amide elastomers in fl uids, and a relatively low mold shrinkage may combination with maleated polyolefi ns, poly- have been some of the reasons for their consider- etheramide block copolymers, and polyamide- ation. However, polyamide/polycarbonate blends polyacrylate block copolymers have been used as have not yet gained any signifi cant commercial compatibilizers and impact modifi ers. However, volumes. These blends must face signifi cant com- polyamide/polycarbonate blends have not been petition from PPE/polyamide blends, since the lat- commercialized to any signifi cant extent yet. ter offer higher heat resistance viz., higher DTULs The commercial grades of polyamide/poly- at both low and high loads, while also offering carbonate blend (Dexcarb®) exhibit high notched an equivalent or better toughness and solvent Izod impact strength comparable to that of impact resistance. Polyamide/polycarbonate blends must modifi ed polyamides and polycarbonate (Table also face stiff competition from impact modifi ed 15.24). It is believed that an elastomeric impact PA’s that offer higher impact strengths at low modifi er was included in these compositions. Patent temperatures and higher DTULs at low loads. claims the use of a polyetheramide and a maleated polypropylene or EPR as the compatibilizing/ 15.8.6 Polyamide/Silicone Blends impact modifying additives [Perron, 1988]. The commercial grades contain varying amounts of PC, A commercial blend consisting of a thermoplastic PA-66 (or 6) and the impact modifi er. polyamide (PA-6 or PA-66) and 5-25 wt% of Polyamide/polycarbonate blends have been a crosslinkable silicone, which forms a semi- evaluated for exterior automotive applications interpenetrating network (semi-IPN) upon curing, such as bumper beams. Their dimensional stabil- has been offered under the trade name of Rim- 1080 M. K. Akkapeddi

Table 15.24. Comparison of different types of commercial polycarbonate blends

Blend Type PC/ABS PC/S-MMA PC/PBT PC/N6

ASTM PULSE SD9101 XENOY DEXCARB PROPERTY TEST UNITS 710 5220 507 METHOD Dow Novacor GEC D&S Int.

PHYSICAL Density D792 kg/m3 1,120 1,150 1,250 1,100 Mold Shrinkage D955 % 0.6 1.6 Water Absorption, 24 hrs. D570 % 0.15 0.14

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2275(330) 2490(361) 1900(275) 1725(250) Flexural Strength D790 MPa (kpsi) 83(12) Tensile Strength at Yield D638 MPa (kpsi) 45(6.5) 56(8.2) 45(6.5) 41(6) Elongation at Break D638 % 80 125 175 100

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 534(10) 1015(19) 850(16) 908(17) at -40°C 481(9)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 106 127 at 1.82 MPa 102 92 99 102

CHEMICAL RESISTANCE Fair Fair Good Excellent

plast® (Petrarch, div. of Hüls) [Arkles, 1985]. with some sacrifi ce in strength and elongation. The blends are produced by extruding the poly- Some applications in medical tubing and indus- amide with a vinyl terminated, polydimethyl- trial uses have been projected. No signifi cant siloxane and silicone hydride terminated dimethyl market for this technology has yet been devel- siloxane in the presence of a platinum catalyst. oped, primarily because of the high cost of this The siloxanes react with one another forming blend system. cured silicone thermoset in the thermoplastic matrix phase of the polyamide. 15.8.7 Polyamide/Polyamide Blends At the low concentrations 5-10 % silicone, the blend is reported to retain much of its Blends of PA-66 with some aliphatic-aromatic thermoplasticity and processability. This silicone polyamides of higher Tg such as poly (hexamethyl- semi-IPN reportedly improves the lubricity, wear ene isophthalamide) (PA-6I) have been evaluated and biocompatibility of polyamide as well as as fi bers, in order to achieve improved modulus reducing the shrinkage and warpage although and heat resistance in PA-66 tire yarn and con- Commercial Polymer Blends 1081 sequently reduce the tire fl at-spotting tendency (Figure 15.12), presumably due to a good degree [Zimmerman et al., 1973]. Although the rate of of miscibility. These commercial PA-6/amorphous amide interchange in these polyamide/polyamide polyamide blends have been developed particu- blends was found to be quite slow (< 3% inter- larly for applications in fl exible food packaging change based on the aromatic polyamide), the markets and hence captively produced as fi lms. formation of some block copolymer was not ruled out. Nevertheless, the observed improvements in the modulus and Tg were primarily attributable to some degree of compatibility or miscibility between the components of the blend. There have been several other research investigations on the compatibility and phase behavior of polyamide/ polyamide blends [e.g., Takanayagi et al.,1980; Ellis, 1990; Hirakawa et al., 1985]. However, no commercially signifi cant polyamide/polyamide blends have been developed until recently. There has been some commercial interest particularly in the blends of PA-6 with aliphatic-aromatic polyamides exhibiting good oxygen barrier properties suitable for food packaging applications. Certain types of aliphatic-aromatic random copolyamides such as those derived from the polymerization of (a) hexamethylene diamine and isophthalic/terephthalic acids (6I/6T) or (b) m-xylylenediamine, isophthalic/terephthalic acids and caprolactam (MXDI/T,6), exhibit high glass transition temperature, amorphous character and a high barrier to oxygen permeation [Akkapeddi and Gervasi, 1989]. The oxygen barrier property of these amorphous polyamides is retained even Figure 15.12. Oxygen permeability and water vapor under high humidities because of their high Tg’s. transmission rate (WVT) behavior of PA-6/Amorphous PA-6I/6T In contrast, semicrystalline polyamides such as blends at 95% RH. PA-6 and PA-66 characteristically exhibit low Tg (ca. 50°C) that becomes even lower after moisture absorption. As a consequence, the permeability of oxygen in PA-6 and PA-66 increases with Similarly there has been some commercial humidity. There are several amorphous polyam- activity in the blends of poly(m-xylylene adip- ides commercially available that exhibit good amide) (MXD6) with PA-6 and PET. MXD6, oxygen barrier properties, suitable for packaging produced by Mitsuibishi Gas Chemical Co., in applications e.g., Selar(R) PA (duPont), Novamid(R) Japan, has been used both as a molding resin (Mitsubishi Chemical). (Reny®) as well as an oxygen barrier fi lm resin To improve the oxygen barrier properties of particularly in multi-layer coextrusions [Harada,

PA-6 (and PA-66), high Tg, barrier type amor- 1988]. In blends of MXD6 with aliphatic polyam- phous polyamides such as PA-6I/6T (Selar® PA) ides, interchange reactions were found to play a have been blended [Krizan et al., 1989; Blatz, major role in the observed phase homogenization 1989]. These blends exhibit improved barrier to during melt-mixing, particularly at long residence oxygen permeation even at high relative humidity time [Takada and Paul, 1992]. 1082 M. K. Akkapeddi

15.9 Polycarbonate Blends in the neat polymer which can be overcome by blending with other polymers or additives. Some Commercial polycarbonate is an amorphous engi- deﬁ ciencies of polycarbonate are: neering thermoplastic characterized by a high 1. high notch sensitivity and part thickness sensi- glass transition temperature (ca. 150°C) and an tivity in impact strength (Figure 15.12); excellent balance of properties such as high 2. lack of an adequate low temperature notched toughness, clarity, heat resistance, dimensional Izod impact strength; stability, good electrical and ignition-resistance 3. lack of an adequate solvent resistance and characteristics. Because of this outstanding com- stress crack resistance (Table 15.23); bination of properties, polycarbonate has become 4. limited long-term hydrolytic stability at elevated one of the most successful of engineering thermo- temperatures; plastics with an estimated global consumption of 5. relatively high melt viscosity compared to each over 595 kton/y [Kircher, 1990]. crystalline polymers as PA-6, PBT, etc. Standard polycarbonate, (PC), is made from bisphenol A and phosgene via an interfacial Hence the development of polycarbonate blends polymerization process. The polymer backbone was primarily market driven, with a motivation has an aromatic polycarbonate structure with to extend the applications of polycarbonate into a recurring carbonate, moiety which, uniquely areas where improved chemical resistance and accounts for the outstanding toughness of the processability are required while still retaining polycarbonate and the rigid aromatic unit contrib- high impact strength. In the development of all utes to its high glass transition temperature. the polycarbonate blends the common goal was Although a large number of applications of to maintain a very high level of impact strength polycarbonate have been based on its unique com- while improving the properties and cost balance bination of high impact strength, heat resistance (Table 15.24). and clarity there are still a few property deﬁ ciencies Commercial blends of polycarbonate and the major reasons for their development are listed as follows:

Blend Reasons for blending

1. Impact modiﬁ ed polycarbonates * Improve notch sensitivity (PC/LDPE, PC/elastomer, etc.) * Improve low temperature toughness * Improve thermal-aging resistance 2. ABS/Polycarbonate * Improve low temperature toughness * Improve processability * Lower cost 3. Styrenic/PC blends * Improve processability * Weatherability 4. Thermoplastic polyester/polycarbonate * Improve solvent resistance (PBT/PC, PET/PC) * Improve processability 5. Polyamide/PC blend * Improve solvent resistance 6. Polyetherimide/PC blend (PEI/PC) * Lower cost, improved processability Commercial Polymer Blends 1083

15.9.1 Impact Modiﬁ ed Polycarbonates notched Izod impact strength at low temperatures is low, e.g., 100 J/m at -30°C. Another important Although polycarbonate is exceptional among deﬁ ciency of polycarbonate is the sensitivity of engineering resins in exhibiting an outstanding its notched impact strength to part thickness and level of toughness, its ductile-brittle transition notch radius. The notched Izod impact strength of depends on the temperature, notch sharpness, polycarbonate is reduced from 900 J/m to about sample thickness and thermal aging effects. 100 J/m when the thickness is increased from A sharp ductile-brittle transition [Carhart, 1985] 3.2 to 6.4 mm [Jones, 1985] These effects are for polycarbonate occurs at 0-10°C, hence its due to the changes in the deformation behavior at

Table 15.25. Properties of commercial impact modiﬁ ed polycarbonate vs. polycarbonate

Blend Type PC/LDPE PC/ELASTOMER PC

ASTM MAKROLON MAKROLON MAKROLON PROPERTY TEST UNITS T7700 T7855 2800 METHOD Miles Miles Miles

PHYSICAL Density D792 kg/m3 1,190 1,190 Mold Shrinkage D955 % 0.6 Water Absorption, 24 hrs. D570 % 0.15

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2200(320) 2200(320) 2275(330) Flexural Strength D790 MPa (kpsi) 86(12.5) 86(12.5) 86(12.5) Tensile Strength at Yield D638 MPa (kpsi) 59(8.5) 62(9) 62(9)

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 740(14) 800(15) 908(17) at -40°C 510(9.5) 640(12) 117(2.4)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 134 138 at 1.82 MPa 132 127 131 Vicat Softening Point D1525 °C 150 143 157

ELECTRICAL Dielectric Strength D149 KV/mm 16 16 16 Dielectric Constant at 1 MHZ D150 3 3 3 Dissipation Factor at 1MHZ D150 0.01 0.01 0.01 Volume Resistivity D257 ohm-m 1.0E+15 1.0E+15 1.0E+15 Arc Resistance D495 sec 100 100 120 1084 M. K. Akkapeddi the crack tip from shear yielding (plane stress) to crazing and unstable crack propagation. By blending small amounts of elastomeric or low modulus polymers, the impact strength of polycarbonate could be readily improved, largely by modifying the crack tip plastic deformation. The rubber particles facilitate the localized matrix yielding through internal cavitation and debonding mechanisms. Polycarbonate modifi ed with small amount of low density polyethylene (ca. 5%) exhibits substantially improved notched Izod (> 500 J/m) in thick sections (6.4 mm) [Dobkowski, 1988; Dobrescu and Cobzaru, 1978; Gardlund, 1984]. Some commercial impact modifi ed grades of PC (Table 15.25) are based on this technology [Freitag et al., 1985]. GE’s Lexan EM (energy Figure 15.13. Effect of sample thickness on the notched management) grades are believed to contain 5-8% impact strength of unmodifi ed (I) vs. impact modifi ed (II) of a polyolefi n [Kosoff, 1985]. Addition of poly- polycarbonates [Freitag et al., 1985]. ethylene is also reported to improve the stress crack resistance [Freitag et al., 1985]. In order to improve both the thickness sensitivity and low temperature sensitivity of the impact strength, polycarbonate has been blended with a variety of low Tg, elastomeric impact modifi ers. More important among these are the core-shell rubbers like PMMA-g-polybutadiene, PMMA-g-SBR (MBS), PMMA-g-n-butylacrylate (acrylic core-shell), all normally composed of 0.1µm crosslinked rubbery core particles. These modifi ers improve both the thick-section (6.4 mm) and low temperature notched Izod impact properties of polycarbonate [Witman, 1981; Neuray and Ott, 1981; Bussink et al., 1977] (Figures 15.13 and 15.14). The blends are of course opaque. Impact modifi ed polycarbonate also shows better retention of impact strength with heat-aging. Commercial impact modifi ed (elastomer blend- Figure 15.14. Low temperature impact strength of unmodifi ed (I) vs. impact modifi ed PC (II) [Freitag et al., 1985]. ed) polycarbonates are used for the production of protective headgear, sporting goods, bobbins for textile industry and automotive components 14.9.2 ABS/Polycarbonate Blends requiring high toughness. Impact modifi ed PC has to compete with the more solvent resistant Since their introduction in 1967, ABS/polycar- impact modifi ed PBT/PC, PET/PC blends and bonate blends [Grabowski, 1964] have enjoyed polyamides in some of the applications. a dramatic growth in market volume. They are by far the largest volume polycarbonate blends Commercial Polymer Blends 1085

Figure 15.15. Ductile brittle transition temperature of ABS/PC Blends vs. ABS and PC [Freitag et al., 1985]. used with the global consumption approaching phase. The rubber particles are primarily located 100 kton/y by 1996. The growth rate of ABS/PC in the SAN phase. Typical properties of some of blends is estimated to be > 12%, which is faster the commercial ABS/PC blends are illustrated in than that of polycarbonate or ABS. The major Table 15.5. The blends containing higher levels reason for the success of ABS/PC blends is their of polycarbonate exhibit better low temperature overall better cost/performance balance relative impact strengths. to PC and impact modifi ed PC. Particularly note- ABS/PC blends are used in a variety of auto- worthy is their unique, synergistic improvement motive components such as instrument panels, in the low-temperature notched impact strength fl aps for glove compartments, dashboards, clad- [Morbitzer et al., 1983], which is better than ding for steering wheel columns, ventilation ports, the individual components (Figure 15.15). The spoilers, wheel covers and protective side trims. partial miscibility between the SAN and the Flame retardant ABS/PC blends are used in polycar-bonate phases, the intrinsic ductility of offi ce equipment and business machine housings. polycarbonate matrix, and the presence of small Chlorine or bromine-free fl ame retardant ABS/ particle size polybutadiene dispersions are the PC compositions contain organophosphate/PTFE key factors contributing to the low temperature powder dispersions [Freitag et al., 1991]. ABS/PC toughness of the blend. blends have been used in automotive exterior A discussion of the ABS/PC blends comparing body panels for GM’s Saturn models. The assem- with other ABS blend, may be found under bly line for this car was equipped to handle the the ABS blends section. The properties of the new water-borne paint systems, which cure at ABS/PC blends, primarily the DTUL and impact lower temperatures than the normal ‘E-coat’ paint strength, are determined by the ratio of ABS to ovens. Due to their excellent low temperature polycarbonate. The morphology is also dictated toughness, dimensional stability and cost advan- by the blend ratio. In blends containing 50% tages, ABS/PC blends are replacing some of the polycarbonate, the continuous phase is formed PPE/HIPS applications and are also competing by the polycarbonate with ABS as the dispersed against some polyamide applications. However, 1086 M. K. Akkapeddi they cannot compete with the impact modifi ed and PC are miscible, exhibiting a lower critical polyamides and the PPE/PA blends in all those solution temperature behavior (LCST ≅ 180°C). applications which require higher heat and chemi- S-MMA/PC blends are relatively new and their cal resistance such as automotive fuel emission advantages, if any, over ABS/PC blends have not canisters, fasteners, connectors and exterior parts been clearly identifi ed. They will, no doubt, be like fenders, etc. more expensive than the ABS/PC blends but will have better UV resistance. 15.9.3 Styrenic/Polycarbonate Blends ASA/PC blends. ASA polymers are similar Blends of polycarbonate with other styrenic resins to ABS except that the polybutadiene rubber are relatively new and therefore their current mar- phase in the SAN copolymer matrix is substituted ket volume is low. They have been developed by the more weatherable acrylic-rubber, viz., primarily to upgrade the performance of such the crosslinked n-butyl acrylate rubber particles styrenic resins as styrenic-maleic anhydride (SMA), grafted with SAN copolymer. The weatherability styrene-methyl methacrylate (S-MMA), acrylic-sty- advantages of ASA polymers can be extended also rene-acylonitrile (ASA) resins primarily for impact into the polycarbonate blends, [Sakano, 1980] strength and to some extent for DTUL improvement as long as suffi cient ASA is used in the blend (Tables 15.7, 15.8 and 15.23). These blends unique- ( 50%). ASA/PC blends fi nd niche applications ly combine high notched Izod impact strengths in exterior automotive parts such as cowl vents, (ranging from 500 J/m to > 1000 J/m) with better grills, mirror housings, trim, etc., where the parts UV resistance or weatherability than ABS. can be pigmented (black or color) instead of being painted, unlike the case of ABS/PC. Since the SMA/PC blend. This blend (Arloy®, Arco) con- withdrawal of EPDM-g-SAN copolymer (AES, tained SMA grafted with polybutadiene as the Rovel®, Dow) from the market, ASA and ASA impact modifi er. The properties of SMA/PC blend blends have assumed increased commercial sig- were similar to ABS/PC blend with slightly higher nifi cance in outdoor, weatherable applications. heat distortion temperatures (107 to 117°C) but comparable impact strength (> 500 J/m). How- AES/PC blends. AES polymers are similar ever, it was discontinued from the market due to to ABS except that the polybutadiene rubber is unfavorable economics relative to ABS/PC blend. replaced with EPDM rubber, which is grafted to The partial miscibility between the styrene-maleic the SAN copolymer. The saturated backbone of the anhydride and polycarbonate accounts for the rubber makes the AES or EPDM-g-SAN (Rovel®, adequate compatibility of this blend as evidenced Dow) more weatherable. Blends of AES/PC are by the high level of tensile and impact strengths. similar to ABS/PC with the same level of high impact strength and good DTUL but with the S-MMA/PC blend. This blend (Novacor® added advantage of weatherability. The compat- SD-9101) was reported to have better fl ow, surface ibility between the SAN phase of the AES and the fi nish and scratch resistance than PC/polyester polycarbonate is governed by the same principle blends and an equivalent level of impact tough- of partial miscibility. Since the withdrawal of AES ness (Table 15.24). It is believed that these from the market, other suppliers with ASA based formulations also include some acrylic rubber blends are actively following this market. (core-shell type) for impact modifi cation. One would expect a suffi cient level of partial miscibil- 15.9.4 Thermoplastic polyester/PC Blends ity for self-compatibilization between the styrene- (PBT/PC, PET/PC, PCTG/PC) methyl methacrylate copolymer (S-MMA) and the polycarbonate especially at high MMA content of The second most important class of commercial the copolymer, since the binary blends of PMMA polycarbonate blends is derived by blending with Commercial Polymer Blends 1087 commercial thermoplastic polyesters such as poly- PBT/polycarbonate blend, fi rst introduced in butylene terephthalate (PBT) and polyethylene 1980 by General Electric (Xenoy®) has enjoyed terephthalate (PET). Both PBT and PET are crys- a fast growth in automotive applications, particu- tallizable polymers and hence offer the expected larly for bumpers. The blend was developed chemical resistance advantages of the crystalline to meet the low temperature impact strength, polymers in blends with polycarbonate. Among the dimensional stability and paintability require- thermoplastic polyester/polycarbonate blends, the ments of rigid bumper fascias [Bertolucci and PBT/PC blend has the major commercial volume, Delany, 1983], which accounted for the bulk of followed by the PET/PC blend. A copolymer of the current market volume for the PBT/PC blend 1,4-cyclohexanedimethanol, ethylene glycol and (estimated 25 kton/y in the USA). The develop- terephthalic acid (PCTG) forms a miscible blend ment of commercial PET/PC blends followed with polycarbonate. PCTG/PC blend is commer- shortly after the initial success of PBT/PC blends. cially offered by Eastman Kodak (Ektar®) for Currently there are several commercial blends specialty applications. of both PBT/PC and PET/PC blends available,

Table 15.26. Properties of some commercial grades of PBT/polycarbonate blends

ASTM XENOY XENOY XENOY SABRE PROPERTY TEST UNITS 1102 5220 6120 1628 METHOD GEC GEC GEC Dow

PHYSICAL Density D792 kg/m3 1,200 1,210 1,250 1,200 Mold Shrinkage D955 % 0.9 0.9 1.6 0.7 Water Absorption, 24 hrs. D570 % 0.08 0.12 0.14 0.1

MECHANICAL Flexural Modulus D790 MPa (kpsi) 1964(285) 2040(296) 1900(275) 2136(310) Flexural Strength D790 MPa (kpsi) 82(11.9) 85(12.3) 72(10.5) 81(11.7) Tensile Strength at Break D638 MPa (kpsi) 54(7.9) 53(7.7) 45(6.5) 56(8.1) Elongation at Break D638 % 150 120 175 160

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 800(15) 710(13) 850(16) 800(15) at -40°C 640(13) 300(5.6) 534(10) Drop Weight Impact D3029 J (ft-lb) at 23°C 54(40) 54(40) 54(40)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 110 106 121 119 at 1.82 MPa 91 99 57 83 1088 M. K. Akkapeddi

Table 15.27. Properties of some commercial PET/polycarbonate blends

ASTM MAKROBLEND SABRE IMPACT PROPERTY TEST UNITS UT1018 1647 METHOD Miles Dow AlliedSignal

PHYSICAL Density D792 kg/m3 1,220 1,220 1,180 Mold Shrinkage D955 % 0.8 0.1 1.1 Water Absorption, 24 hrs. D570 % 0.16 0.16 0.15

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2070(300) 1930(280) 1590(230) Flexural Strength D790 MPa (kpsi) 75(10.9) 77(11.1) 60(8.7) Tensile Strength at Yield D638 MPa (kpsi) 48(7) 51(7.4) 44(6.4) Elongation at Break D638 % 160 130 185

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 970(18) 750(14) 800(15) at -40°C 700(13) 214(4) 140(2.6) Drop Weight Impact D3029 J (ft-lb) at 23°C 135(175) 100(135) Instrumented Impact, Energy D3763 J (ft-lb) at 23°C 20(27) 26(35) 22(30)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 115 119 110 at 1.82 MPa 88 81 80

and their properties are compared in Tables 15.26 rubber ( 50% acrylate rubber) have also been and 15.27. used. The presence of such a rubber component All the commercial PBT/PC and PET/PC is defi nitely needed to obtain high notched Izod blends also contain typically 10-20 wt% of impact strengths ( 500 J/m) in these blends. an additional elastomeric impact modifi er. The The binary blends of polycarbonate with poly- exact nature and the content of the impact modi- butylene terephthalate (PBT/PC) or polyethylene fi er is kept proprietary and often forms the basis terephthalate (PET/PC) are now known to be for a particular blend patent. Typically core-shell essentially phase separated blend systems exhibit- rubbers such as polymethylmethacrylate grafted ing two glass transition temperatures in each case, butadiene-styrene rubber (MBS) or an all acrylic one for the polycarbonate-rich phase, and another core-shell rubber such as poly (MMA-g-n-BuA) for the polyester-rich phase. [Murff et al., 1984; are used [Nakamura, 1975; Chung, 1985]. ABS Huang and Wang, 1986; Wahrmund et al., 1978]. (with high polybutadiene content 50%) or ASA The evaluation of the amorphous phase miscibility Commercial Polymer Blends 1089 in these blends was often complicated by the The transesterifi cation reactions in PBT/PC potential of a transesterifi cation reaction between melt blends could be suppressed by using organo- the two polymers during the melt blending, which phosphites and phosphonates which probably may in principle lead to a block copolymer and function by deactivating the titanium or antimony eventually to a random copolymer with a single type polymerization catalyst residues present in phase, single glass transition temperature behavior PBT [Golovoy et al., 1989]. Even in the presence [Deveux et al., 1982; Hobbs et al., 1987; Porter of phosphite stabilizers, PBT/PC blends showed and Want, 1992]. Sometimes different conclusions dual phase behavior. However, a partial miscibil- have appeared in the literature regarding the phase ity was evident since the Tg of PC phase was still behavior of PET/PC and PBT/PC blends, because reduced from the normal 150°C to about 140°C. different methods were used to prepare the blends. This partial miscibility between PBT and PC which occurs even in the absence of an exchange 15.9.4.1 Polybutylene Terephthalate/ reaction is responsible for the good compatibility Polycarbonate Blends (PBT/PC) and interfacial strength of the blend.

Early investigations of the melt blends of PBT 15.9.4.2 Polyethylene Terephthalate/ and PC showed two glass transition temperatures Polycarbonate Blend (PET/PC) indicative of two amorphous phases [Murff et al.,

1984]. However the Tg’s did not correspond to Early work on the PET/PC blends indicated that those of pure components and in addition, there in blends containing > 70% PET, PC was miscible was a slight depression in the melting point of and in blends with < 70% PET, the components PBT. A melt-phase reaction was hypothesized to separated into two phases. Subsequent investiga- take place. Subsequent studies showed that the tions concluded that the blend was essentially melt phase transesterifi cation reaction between immiscible over the entire composition range. The PBT and PC can indeed take place, at these high transesterifi cation reaction between PET and PC in temperatures (T 260°C), as followed by NMR the melt phase was found to be slower than in the spectral changes as a function of melt residence case of PBT at 270°C. However, when the reaction time [Deveux et al., 1982]. The presence of does occur, the newly formed ethylene carbonate titanium catalyst normally present in PBT also linkages, -CH2-CH2O-CO-O- in the polymer chain catalyzed this reaction. appear to degrade more rapidly than the butylene Although NMR and IR techniques were used carbonate units generated with PBT. The divergent in characterizing these interchange reactions, these conclusions in the literature on the phase behavior techniques are often insuffi cient to detect small of PET/PC blend are undoubtedly caused by the changes in the structure that occurs when only differing degrees of transesterifi cation reaction one or few interchanges per chain take place. For occurring under the conditions of melt mixing example, NMR can detect only gross structural (temperature, time) and the amount of catalyst changes that take place after long reaction times residues [Goddard et al., 1986]. ( 30 min at 250°C). Blends made by solution Under the normal extrusion blending condi- technique or by normal extruder melt blending tions PET/PC blend forms a 2-phase blend mor- process under short residence time exhibited a two phology. The melt residence times are short phase structure [Hanrahan et al., 1985; Dekkers et enough such that the interchange reaction does not al., 1990]. However, the Tg of the PC phase in the occur, and the PC can be quantitatively extracted melt blended product was usually lower (by 20°C) out with methylene chloride. From the observed than the PC phase of solution blended product or glass transitions of the PET-rich phase and PC- neat PC. This was attributed to the effect of a small, rich phase, measured by DSC or DMA, the blend although not readily detectable level of interchange can be classifi ed as partially miscible with an esti- reaction in the melt blended product. mated interaction parameter of slightly positive 1090 M. K. Akkapeddi

χ ( 12 = 0.04). From the measured Tg’s, it appears that more PET dissolves in PC phase than PC does in the PET-rich phase [Kim and Burns, 1990]. Nevertheless, the existence of a partial miscibility, even in the absence of transesterifi cation accounts for the self-compatibilization effect in the blend. Mutual interpenetration of the components at the phase boundary accounts for the high interfacial strength. The binary blends of PET/PC and PBT/PC exhibit good ductility and tensile strengths but the notched Izod impact strengths are still low at all the blend compositions containing 80% PC. This is a signifi cant difference from ABS/PC blends, in which the grafted polybutadiene rubber particles of ABS phase contribute to the toughness at all the ABS/PC blend ratios. Hence commercial PBT/PC and PET/PC blends, by necessity, include a proper level of an effective impact modifi er, Figure 15.16 Morphology of PET/PC/MBS core-shell elastomer (40/40/20) blends - TEM; RuO4 stain; 15000X usually a core-shell rubber of small particle size, [Akkapeddi et al., 1993]. such as MBS, ABS, etc. It has been shown that during the melt blending, these rubber particles preferentially migrate to the PC phase due to the known compatibility of the PMMA or SAN Injection molded PET/PC blends, on the other component of these rubbers (shell structure) with hand, generally lead to an essentially amorphous the polycarbonate [Dekkers et al., 1990]. Hence PET phase. Short term annealing at elevated the blend morphology indicates that the rubber temperatures (120-150°C) causes this PET phase particles are predominantly located in the PC to crystallize and leads to some loss in ductility phase (Figure 15.16). especially when the polycarbonate content in the Commercial PBT/PC and PET/PC blends con- blend is 30% [Akkapeddi et al., unpublished tain about 15-20 % of such core-shell rubber impact results]. modifi ers for maximum toughness, i.e., notched Long term thermal aging of PBT/PC blends is Izod impact strengths of typically 700 J/m known to lead to severe embrittlement [Bertillson which is maintained even at low temperature et al., 1988]. Phase segregation, secondary crys- (Tables 15.26 and 15.27). The ratio of PBT/PC or tallization and changes in the amorphous phase PET/PC is usually kept between 50/50 to 40/60 free volume with aging are some of the key factors to optimize the ductility in the blend, while still attributable to the embrittlement phenomenon. maintaining a continuous or co-continuous phase Embrittlement of PET/PC blends upon heat-aging of the polyester. A continuous phase of PBT is even more likely to occur due to the more brittle or PET with PC as dispersed phase, would be nature of crystalline PET phase. Recent work preferred for solvent resistance. has focused on the use of reactive rubber toughen- The crystallization of PBT and PET in these ers to improve the embrittlement resistance of blends is somewhat suppressed by the partial PET/PC blends upon heat-aging [Akkapeddi and miscibility of the PC. However, since PBT crys- Mason, 1991; Akkapeddi et al., 1993]. tallizes intrinsically faster than PET, blends of The excellent low temperature toughness and PBT and polycarbonate after injection molding solvent resistance of PBT/PC and PET/PC blends show a crystalline PBT phase in their morphology. have found good application in automotive exte- Commercial Polymer Blends 1091 rior parts such as bumper beams and fascias generally showed excellent surface fi nish and (mainly PBT/PC), air dams, rocker panels, wheel hence molded-in-color could be used. covers, and mirror housings. Non-automotive applications included instrument housings, lawn- 15.9.5 Polyamide/Polycarbonate Blends mower chutes, snow blower components, etc. With the increasing competition from low cost Unlike the thermoplastic polyesters (PBT and paintable thermoplastic polyolefi ns (TPO’s) in the PET), the commercial polyamides such as PA-6 automotive bumper and fascia markets, further or PA-66 are more polar and hence highly immis- growth for PBT/PC and PET/PC blends may be cible with polycarbonate. Hence simple blends limited in this area. Hence these blends must of polyamide and polycarbonate are expected to fi nd other applications where their dimensional delaminate readily, unless a suitable compatibiliz- stability, chemical resistance, high toughness and er is used. Because of the lack of an effi cient com- moderate DTUL (T 100°C) are considered patibilization technique, blends of PA-6 (or PA-66) suitable. with polycarbonate have not yet reached a commercial signifi cance, although there are several 15.9.4.3 Poly(1,4-cyclohexanedimethylene- patents claiming improvement in properties. terephthalate) Copolymer/ At present, there is only one commercial Polycarbonate Blend (PCTG/PC) source of the polyamide/polycarbonate blends (Dexcarb®, Dexter Corp.). According to their The commercial copolyester derived from 1,4-cyclo- patent, the blend was compatibilized by using hexane dimethanol, ethylene glycol and terephthal- a combination of a polyesteramide elastomer ic acid (PCTG, Ektar® DN003, Eastman Kodak) and a maleated olefi nic polymer, such as male- is an amorphous polymer exhibiting excellent ated polypropylene or EP rubber [Perron, 1984; toughness (notched Izod impact strength of 800 1988]. However the degree or the effi ciency of J/m), high clarity and good chemical resistance compatibilization achieved is unknown, since the characteristics. However, it has a relatively low added components are not known to be miscible glass transition temperature (ca. 85°C) and a low or compatible with the polycarbonate. Neverthe- heat distortion temperature (ca. 66°C at 1.8 MPa). less, the data sheet indicated good properties Hence a commercial blend of PCTG and poly- including a high notched Izod impact strength of carbonate was developed, which maintained the > 700 J/m (Table 15.24). high toughness of both components (notched At the present time, the commercial volume of Izod import strength 800 J/m), yet had a polyamide/PC blend is small due perhaps to its useful combination of DTUL (ca. 95°C) and unfavorable cost/performance balance. The product chemical resistance. More importantly, the blend has to compete with the more established impact maintained a high degree of clarity because of the modifi ed polyamide and PPE/PA blends, which thermodynamic miscibility between the PCTG offer higher DTUL/impact strength balance. and polycarbonate, although some transesterifi cation cannot be ruled out. The miscibility was 15.9.6 Polyetherimide/PC Blends (PEI/PC) confi rmed by a single Tg, single phase behavior of the blend [Mohn et al., 1979; Smith et al., 1981]. Polyetherimide (Ultem® 1000, GEC) is a high per- Commercial PCTG/PC blends (Ektar® DA formance engineering thermoplastic with high heat series, Eastman Kodak) have been used in lawn distortion temperature (> 200°C), high mechani- and garden equipment, fl oor care appliance parts, cal strength and inherent fl ame-retardancy charac- sterilizable medical equipment, etc., where their teristics. Recently blends of polyetherimide with combination of clarity, toughness, chemical resis- polycarbonate have been commercially offered tance, heat resistance, UV and gamma radiation as thermoformable sheets and as molding com- resistance have been well utilized. Molded parts pounds (Table 15.28). The primary reason for 1092 M. K. Akkapeddi

Table 15.28. Properties of commercial polytherimide/polycarbonate vs. polytherimide and polycarbonate

Blend Type PEI/PC PEI PC

ASTM ULTEM ULTEM ULTEM LEXAN PROPERTY TEST UNITS LTX100A LTX100B 1000 141 METHOD GEC GEC GEC GEC

PHYSICAL Density D792 kg/m3 1,310 1,310 1,270 1,200 Mold Shrinkage D955 % 0.07 0.07 0.07 0.06

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2900(420) 3380(490) 3370(480) 2390(340) Tensile Strength at Yield D638 MPa (kpsi) 93(13.5 99(14.3) 106(15) 63(9) Elongation at Break D638 % 90 80 60 110

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 53(1.0) 48(0.9) 54(1.0) 820(15) Drop Weight Impact D3029 J (ft-lb) at 23°C 36(27) 36(27)

THERMAL Heat Deﬂ ection Temp D648 °C at 1.82 MPa 185 193 210 132

blending polycarbonate appears to be to lower blends of PEI and PC will continue to be used the cost of the PEI while retaining a high level only for specialty niche applications in low to of heat resistance. The blend has about the same moderate volumes. impact strength as the polyetherimide, although not as good as polycarbonate [Mellinger, 1985]. However, the DTUL and chemical resistance of 15.10 Polyoxymethylene Blends the blend is better than that of polycarbonate. Extrusion grade, PEI/PC blend was developed Polyoxymethylene polymers, POM, commonly for aircraft applications to meet the federal avia- known as polyacetals or ‘Acetal’ resins are linear tion standards for low fl ammability, smoke and thermoplastic polymers containing predominantly toxic gas generation [Skeist, 1991]. PEI/PC ther- the -CH2-O- repeat unit in their backbone. There moformable sheet is used for the fabrication of are two types of acetal resins available com- transport aircraft window housings, air ducts, mercially: (1) homopolymers made by the polym- consoles and other components. PEI/PC sheet erization of formaldehyde, followed by endcap- is also used as high temperature paint mask ping, (2) copolymers derived from the ring open- in the automotive industry. PEI/PC molding com- ing polymerization of trioxane (a cyclic trimer pounds have also been evaluated for microwave- of formaldehyde), and a small amount of a como- able cookware. Due to the high cost of PEI, nomer such as ethylene oxide. Acetal resins are Commercial Polymer Blends 1093 highly crystalline polymers with melting points deformation process. of 160-175°C and heat distortion temperatures of Typical properties of commercial impact modi- 110-125°C at 1.82 MPa, unfi lled. Due to highly fi ed POM resins are shown in Table 15.29. With crystalline nature, POM resins exhibit excellent the increase in the impact strength of these blends, rigidity, hardness and resistance to creep, fatigue there is a corresponding decrease in the modulus, and chemical attack. They also exhibit low wear strength and DTUL relative to the neat POM and friction, high dimensional stability and good resin. Impact modifi ed POM blends are still low electrical properties. Because of their excellent volume in usage relative to unmodifi ed POM. mechanical properties and moderate cost, acetal About 80% of the impact modifi ed POMs are resins are among the more widely used engineer- used in the automotive area in typical applications ing resins with an estimated current global con- such as electrical switches, fuel system compo- sumption of over 370 kton/y. nents, gears and hardware. Industrial applications Owing to their high crystallinity, POM resins include cams, gears, valves, impellers, pumps and are not miscible with any of the commercially a variety of plumbing and appliance parts. available polymers. Unmodifi ed POM resins tend to be brittle, particularly when notched. Due to their lack of reactivity, POMs are generally not 15.11 Polyphenyleneether (PPE) Blends amenable to any chemical modifi cation by post- reactions with grafting agents. Hence there are PPE is the generic name for the homopolymer, very few commercial blends based on POM res- poly(2,6-dimethyl,1,4-phenylene ether) derived ins, with the exception of impact modifi ed POMs from the oxidative coupling polymerization of that are simple blends containing elastomeric/ 2,6-dimethyl phenol [Hay, 1976]. Developed in impact modifi ers. In order to improve the notched the early 1960’s, the polymer had many desirable

Izod impact strength, several types of impact properties such as a high Tg (205°C) and DTUL modifi ers have been employed, which included (174°C at 1.8 MPa), high strength and dimen- core-shell rubbers of acrylic type [Kusumgar, sional stability, moisture and hydrolysis resistance 1987] polymethylmethacrylate-g-styrene/butadiene and inherent fl ame retardancy. However, because [Schuette et al., 1986] or polymethylmethacrylate- its extremely high melt viscosity dictated melt g-polybutadiene type [Burg, 1985]. Some com- processing temperatures of well above 300°C, at mercial medium impact grades with notched Izod which the polymer tends to degrade or crosslink impact strengths of 100-150 J/m, may contain in the presence of air, its use as a molding resin such impact modifi ers. by itself was severely limited. A commercial grade of high impact (notched Hence there was a major motivation for blend- Izod > 900 J/m) POM resin (Delrin® 100 ST, ing PPE with other thermoplastic polymers, to DuPont) is believed to be a blend of POM take advantage of its high performance properties with 30 wt% of a thermoplastic poly(ester- and yet combine some useful melt processability urethane) elastomer derived from poly(1,4-butane features. Several blends of PPE have been inves- adipate) diol and methylene-bis-(4,4’-diphenyl tigated stemming from the initial success of diisocyanate) (MDI) [Flexman, 1989]. This blend PPE/polystyrene blends. Table 15.30 lists some is reported to have a co-continuous or semi-inter- of the currently commercial blends of PPE of penetrating network of the elastomer in a matrix different types, comparing their key properties. of the polyacetal [Flexman, 1990]. The toughening effect in such a blend of IPN type morphology 15.11.1 PPE/PS or HIPS Blends was interpreted to occur partly through a rubber band mechanism by which the fracture energy is Since the early discovery of miscibility between absorbed. The bands of rubbery domains were the low-cost polystyrene and PPE, several com- believed to span the crack and participate in the mercial grades of PPE/HIPS have been developed 1094 M. K. Akkapeddi

Table 15.29. Properties of commercial acetal/elastomer blends vs. acetal

Blend Type POM/TPU POM/RUBBER POM

ASTM DELRIN DELRIN ULTRAFORM DELRIN PROPERTY TEST UNITS 500T 100ST N2640X 500 METHOD Dupont Dupont BASF Dupont

PHYSICAL Density D792 kg/m3 1,390 1,340 1,360 1,420 Water Absorption, 24 hrs. D570 % 0.3 0.4 0.25 0.25

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2410(350) 1240(180) 1690(240) 2880(410) Flexural Strength D790 MPa (kpsi) 69(10) 40(5.8) 100(14.3) Tensile Strength at Yield D638 MPa (kpsi) 58(8.4) 45(6.5) 48(6.8) 70(10) Elongation at Break D638 % 260 260 70 40 Rockwell Hardness D785 R119 R108

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 112(2.1) 908(17) 152(2.8) 76(1.4)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 169 145 155 172 at 1.82 MPa 100 90 85 136 Coefﬁ cient of Thermal Expansion D676 m/m/°C 1.1E-04 1.2E-04 1.9E-04 1.0E-04

ELECTRICAL Dielectric Strength D149 KV/mm 15.8 18.9 19.6 Dielectric Constant at 1 MHZ D150 3.6 4.1 4.2 3.7 Dissipation Factor at 1MHZ D150 0.007 0.009 0.005 Volume Resistivity D257 ohm-m 2.0E+12 2.3E+12 1.0E+12 1.0E+13 Arc Resistance D495 sec 120 120

which offer a wide choice of heat resistance PPE/HIPS blends ﬁ lled the price-performance (DTUL), impact strength and melt processability gap between the styrenic resins (HIPS, ABS) [Cizek, 1969; Fried et al., 1978]. This versatility and the engineering resins such as polycarbonate, of PPE/HIPS blends led to their unparalleled polyarylate and polysulfones. The technology and commercial success, accounting for nearly 50% applications of PPE/HIPS blends have already of market volume of all engineering polymers been discussed under the styrenic resin blends commercial blends. section (Table 15.3). Commercial Polymer Blends 1095

Table 15.30. Comparison of different types of commercial PPE blends

Blend Type PPE/HIPS PPE/PA-6,6 PPE/PA-6 PPE/PBT

ASTM NORYL NORYL DIMENSION GEMAX PROPERTY TEST UNITS 731 GTX910 D9000 MX4315 METHOD GE GE AlliedSignal GE

PHYSICAL Density D792 kg/m3 1,060 1,100 1,080 1,150 Mold Shrinkage D955 % 0.6 1.4 1.6 Water Absorption, 24 hrs. D570 % 0.07 0.5 0.5 Water Absorption % 2.8 2.9 at Saturation

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2530(360) 2135(310) 1900(275) 1860(270) Flexural Strength D790 MPa (kpsi) 95(13.5) 76(11) 70(10.5) 69(10) Tensile Strength at Yield D638 MPa (kpsi) 60(8.6) 60(8.6) 56(8) 42(6.1) Elongation at Break D638 % 60 60 50 40

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 270(5) 220(4) 550(10) 640(12) at -40°C 130(2.5) 137(2.5) 275(5) 130(2.5)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 137 193 185 152 at 1.82 MPa 129 143 121 93 Vicat Softening Point D1525 °C 140 232 210

CHEMICAL RESISTANCE Poor Excellent Excellent Good

15.11.2 PPE/PA Blends fi ed PPE/PA blends have already been discussed under polyamide blends [see 15.8.4]. Commercial Commercial PPE/PA blends were developed by PPE/PA blends are based primarily on the lower the motivation to combine the high heat resistance cost polyamide (PA-6 and PA-66) and most often characteristics of PPE with the chemical resis- include a rubbery impact modifi er as the third tance characteristics of the crystalline polyamide blend component, added for a desired level of polymers (PA-66 and PA-6). Because of the inher- toughness (Table 15.21). ent incompatibility between PPE and polyamides, The unique difference between PPE/PA blends suitable methods of compatibilization and tough- and PPE/HIPS blends is illustrated by (a) the dif- ening have not been developed until recently. ferences in DTUL at 0.45 MPa and the DTUL at The technology of compatibilized, impact-modi- 1.82 MPa in glass reinforced compositions (b) the 1096 M. K. Akkapeddi difference in their relative sensitivity or resistance partial miscibility and therefore contributes to the to chemicals, e.g., some common solvents and over-all toughness. It has also been reported that automotive fl uids (Table 15.23). These differences polycarbonate encapsulates the PPE dispersions arise from the facts that (a) polyamide is a crystal- in the PBT matrix, and consequently improves the line polymer unlike HIPS which is amorphous compatibility of the blend [Hobbs et al., 1992]. and (b) due to the large melt viscosity difference The addition of PC to PPE/PET or PBT blends between polyamide and PPE at the normal blend indeed leads to some sacrifi ce in heat resistance ratios, the polyamide forms the continuous phase. and some loss in tensile and impact performance Hence in the molded parts, the polyamide surface during thermal cycling or reprocessing. offers resistance to solvent permeation, and high Although General Electric Co. announced the softening temperature. In PPE/HIPS blends due properties of a developmental grade of PPE/PBT to the single phase amorphous character of the blend (Gemax®), no commercial grades are matrix, the solvent resistance is limited and the available as yet. The typical properties of the heat resistance is limited by the Tg of the blend. developmental (semi-commercial) grades of PPE/ Because of these differences, PPE/PA blends have PBT are illustrated in Table 15.30. found signifi cant application niches. 15.11.4 PPE/Polyolefi n Blends 15.11.3 PPE/Polyester Blends Several approaches to compatibilizing PPE blends Thermoplastic polyesters, PET and PBT also with commercial polyolefi ns (polypropylene, etc.) offer the advantages of easy melt processability have been reported in the literature [Lee, 1990; and good solvent resistance owing to their semi- Kirkpatrick, 1989]. However, no commercial crystalline nature. In addition, PET and PBT are blends of PPE/polyolefi ns have been offered to relatively moisture insensitive under ambient con- date. Compatibilization and impact modifi cation ditions, unlike the polyamides (PA-6 and PA-66) of PPE/polypropylene can be achieved by choos- which can absorb signifi cant levels of moisture. ing a selected type of styrene-ethylene/butylene- Moisture absorption in polyamides leads to sig- styrene block copolymer and PPE of low molecu- nifi cant growth in dimensions and loss in modulus lar weight [Akkapeddi and VanBuskirk, 1992]. and strength. Although PPE/PA blends exhibit lower moisture and dimensional growth than the 15.11.5 PPE/PPS Blends standard polyamides, they are still not suitable for many exterior automotive applications such as Some developmental blends of PPE and PPS door (PA-6 and 66) panels and many electrical [Noryl® APS4300 GEC] have been reported to and electronic applications where their moisture be in the test marketing phase [Gabrielle, 1992]. absorption and dimensional growth are still unac- These alloys have been made from specially func- ceptable. tionalized versions of each resin and proprietary Several research investigations have been made compatibilizers. The addition of the amorphous to compatibilize PET or PBT with PPE both by PPE was reported to improve the ductility of PPS reactive and non-reactive routes of compatibiliza- while reducing the fl ash and shrinkage during tion [Brown et al., 1990 and 1991; Akkapeddi and molding. The blends were primarily developed in VanBuskirk, 1992]. Compatibilized binary blends glass fi ber reinforced forms. of PPE/polyesters still lacked adequate toughness and invariably required the addition of rubbery 15.11.6 PPE/Epoxy Blends impact modifi ers (reactive or compatible type) and polycarbonate. The addition of polycarbon- PPE has been blended with commercial epoxy ate presumably suppresses the crystallization of formulations [Chao et al., 1993] presumably to the thermoplastic PET or PBT phase, due to its improve dielectric properties (lower dielectric Commercial Polymer Blends 1097 constant), toughness and moisture resistance of tion promoters, PET molding compounds are the cured epoxy resins. These formulations have gradually gaining acceptance as injection molding been evaluated with fi berglass reinforcements for resins [Deyrup, 1982; Legras, 1986; Kozielski, the printed circuit boards and other electronic 1988]. On the other hand, polybutylene tere- applications. In one formulation of epoxy resin phthalate (PBT) produced in much smaller vol- (Epon 825, Shell) cured with aluminum alkoxide, ume than PET is more widely accepted as an incorporation of ca. 30% PPE increased the tensile injection moldable engineering plastic due to elongation at break for the epoxy thermoset from its faster crystallization rate [Pratt and Hobbs, < 2 % to 17%. The heat distortion temperature 1976]. Hence PBT is more commonly employed was increased from 60 to 195°C. The dissolution in the formulation of blends also. PBT has gener- of PPE in the epoxy raised its viscosity from 0.2 ally been preferred over PET in the engineering to 400 Pa.s [Anon., 1991]. plastics industry because of its superior processability, faster crystallization rate, shorter molding cycles and better properties (DTUL/impact bal- 15.12 Thermoplastic Polyester Blends ance) in the molded parts, particularly in the unfi lled form. Nevertheless, PET is also used Polyethylene terephthalate (PET) and polybutyl- primarily in glass or mineral reinforced form along ene terephthalate (PBT) are two of the most with nucleators and crystallization promoters. important members of a family of commercial The primary motivations for blending the ther- thermoplastic polyesters. Other members of this moplastic polyesters with other polymers are: family include specialty polyesters such as PET (a) to improve the solvent resistance and process- copolymers (PETG) and poly(1,4-cyclohexanedi- ability of amorphous polymers such as PC, styren- methylene terephthalate) (PCT). Commercially ics, PPE, etc., (b) to reduce the mold shrinkage important PET and PBT resins are known for of polyesters associated with their crystallization, their high crystalline melting points (265°C and (c) to increase the DTUL of unfi lled polyesters, 225°C), good mechanical properties and solvent (d) to improve toughness. resistance characteristics. Between the two, PET The largest volume polyester blend sold com- is the largest volume commercial polyester with mercially is the PBT/polycarbonate blend. PET/ an estimated global consumption of in excess of PC blend is also gaining commercial importance 8 Mton/y in fi ber applications and in excess of because it is similar to PBT/PC blend in properties 1 Mton/y in thermoplastic applications such as in and moldability but has some cost advantages. the injection blow molding of bottles and contain- Unlike neat, unfi lled PET that is diffi cult to ers and, extrusion of fi lm and thermoformable injection mold due to its slow crystallization rate sheets [SRI, 1992]. The dramatic growth in the (long mold cycle times with hot molds and amor- use of PET for soft drink bottles and in other phous parts with cold molds), PET/PC blends can packaging applications has also spurred consider- be molded readily using the normal hot molds able activity in the recycling of PET. Hence PET (ca. 80 to 100°C) and fast mold cycles. The pres- is a relatively low cost polymer both because of ence of PC helps retain high stiffness and strength large scale economics as well as its availability in the part at the mold temperatures, to enable the as a recycled material, thus providing a cost demolding of distortion-free parts. The properties incentive for blending with other polymers. and applications of PET/PC blends have already However, due to the slow rate of crystalliza- been discussed under the polycarbonate blend tion, PET has not been used in injection molding section. Other commercial blends of PET and applications until recently [Burke and Newcombe, PBT are discussed as below. 1982; Hecht and Ford, 1985]. Through the use of specifi c types of nucleators (e.g., sodium stearate, sodium ionomers) and other crystalliza- 1098 M. K. Akkapeddi

15.12.1 PBT/PET Blends resistance to unstable crack propagation is low. Impact modifi cation of PBT was investigated These blends take advantage of the low cost of through the use of several elastomeric modifi ers. PET and the rapid crystallization rate of PBT. Commercial PBT/elastomer blends are of two Despite their large difference in the crystallization types viz. (a) high impact strength type, (b) low rates PET and PBT form stable blends without modulus, highly fl exible types. the need for compatibilizating agent. This was Commercial impact modifi ed PBT grades gen- attributed to the amorphous phase miscibility erally contain 20 to 30 wt% of controlled particle between the two components [Escala and Stein, size (< 0.3 µm), core-shell rubber modifi ers 1979; Mondragon et al., 1989]. X-ray, DSC and [Neurey and Ott, 1981; Farnham and Goldman, IR studies indicated that the two components 1978; Binsack, 1985]. Typical impact modifi ers form separate crystalline phases and a single are: PMMA-g-SBR (MBS), PMMA-g-poly(n-BuA) amorphous phase with a single Tg. Some trans- (acrylic core-shell rubbers), SAN-g-PBD (high esterifi cation was detected in the melt by NMR, rubber ABS) or SAN-g-poly(n-BuA) (high rub- especially at long melt residence times ( 6 ber ASA). Commercial impact modifi ed PBT min) [Mondragon et al., 1989]. The extent of grades (Table 15.31) exhibit notched Izod impact transesterifi cation under the fast extruder blending strengths in excess of 500 J/m, while retaining a operation is however expected to be low. good level of modulus, strength and DTUL. In Commercial grades of PET/PBT blends are these blends, the dispersion of rubber particles generally glass fi ber reinforced (15-30 wt%). promotes multiple sites for crazing and localized Compared to the glass reinforced PBT and PET, shear yielding in the PBT matrix, thus providing the heat distortion temperatures of the blends mechanisms for energy dissipation during impact at 1.8 MPa are actually lower indicating the deformation and hence offering high resistance to lower level of net crystallinity in the blend, an crack propagation [Hourston et al., 1991]. effect possibly caused either by miscibility or A commercial blend of PBT with high rubber transesterifi cation. The primary reason for devel- ABS as impact modifi er (Pocan S1506, Bayer) oping these blends appears to be the improve- has been used in Europe for automotive bumpers, ment of surface appearance and gloss in the mirror housings and other exterior parts [Kosoff, injection molded parts compared to those made 1987]. The blend was reported to exhibit good from the individual resins. There is also some heat sag resistance at 135°C and maintain high cost advantage over PBT. notched Izod impact strength > 700 J/m even at PBT/PET blends are used for making visible -29°C (Table 15.31). Substitution of ABS with parts of both large and small appliances that need ASA (SAN-grafted to crosslinked poly(n-butylac- the appeal of smooth and glossy surface along rylate) rubber particles gives a more weatherable, with high stiffness, strength, and DTUL. There are impact modifi ed PBT (Ultradur KR4071, BASF). also other electrical and automotive applications. A commercial PBT blend containing ca. 25 wt% Compared to the neat PBT molding resins, the of MBS type impact modifi er (Vandar® 2100, market for the blend is still relatively small. Hoechst Celanese) has been used in such exterior automotive applications as under body rivets, fuel 15.12.2 PBT/Elastomer Blends line clips, etc. PBT/elastomer blends display a unique com- Unmodifi ed PBT is a fairly ductile material exhib- bination of high impact strength, dimensional iting high elongation at break, even after crystal- stability due to their non-hygroscopic nature, lization. However, as to be expected of all rigid excellent resistance to automotive fl uids such as semi-crystalline polymers, molded parts of PBT gasoline, oils, paint solvent, aqueous salt solu- show low notched Izod impact strength indicating tions and good heat resistance. In addition, their that under conditions of stress concentration, the easy processability (low melt viscosities) lends Commercial Polymer Blends 1099

Table 15.31. Properties of commercial PBT/elastomer blends

ASTM VALOX VANDAR TORAY PBT POCAN PROPERTY TEST UNITS 357 2100 5207X11 S1506 METHOD GEC Celanese Toray Albis Corp

PHYSICAL Density D792 kg/m3 1,290 1,210 1,200 1,200 Mold Shrinkage D955 % 1.2 1.8 2.6 1.8 Water Absorption, 24 hrs. D570 % 0.08 0.1 0.08 0.1

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2100(300) 1930(280) 1660(235) 1540(220) Flexural Strength D790 MPa (kpsi) 84(12) 61(8.7) 54(7.7) Tensile Strength at Break D638 MPa (kpsi) 37(5.3) 43(6.3) 37(5.3) 38(5.4) Elongation at Break D638 % 200 150 250 100

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 540(10) >800(15) 770(14) >900(18) at -40°C 160(3)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 98 82 at 1.82 MPa 48 50 58

themselves to the fabrication of both small and high degree of rubbery elasticity, yet they process large parts. High mold shrinkage and tendency to like thermoplastics and hence appropriately are warp are some of the drawbacks resulting from called thermoplastic elastomers [Adams and Hoe- the crystallization phenomenon, which need to be schele, 1987]. addressed by proper design of the tools and the Because the hard segments crystallize like PBT, molding process. these thermoplastic elastomers exhibit high heat resistance with Vicat softening points typically in 15.12.3 PBT/Copoly(ether-ester) the range of about 180°C. The hard segment crystal- Elastomer Blends linity also imparts a good level of solvent resistance

in these materials. The low Tg of the soft segment Commercial copoly(ether-ester) elastomers (e.g., is responsible for the ﬂ exibility, resilience and low- Hytrel®, DuPont; Lomod®, GEC) are segmented temperature toughness characteristics. Although the block copolymers containing a polyether soft poly(ether-ester) block copolymers have been used segment such as poly(tetramethylene oxide) and in many niche applications requiring high perfor- a hard segment that is chemically identical to mance thermoplastic elastomer characteristics, their polybutylene terephthalate. When the soft seg- high cost has been a drawback in extending to ment is 50%, these block copolymers exhibit larger volume applications. 1100 M. K. Akkapeddi

To reduce the cost, these elastomers have been of crystallization of PET. Unfi lled PET and PET/ diluted with some PBT homopolymer. Because of elastomer blends are not easy to injection mold the chemical similarity between the hard segment under normal mold temperatures (ca. 80-100°C) of the copoly(ether-ester) elastomers and the PBT, in fast molding cycles. The parts tend to stick to they form fairly compatible blends. When the the mold and distort. Use of cold molds allows hard segment content in the copoly(ether-ester) is molding of amorphous PET parts (1-2 mm) lack- > 80 wt%, it was found to be completely miscible ing heat resistance (DTUL). Upon annealing at with PBT, showing a single Tg, amorphous phase elevated temperatures (ca. 150°C), one can devel- and co-crystallization of the PBT segments of op crystallinity in PET parts, but they become the elastomer with PBT homopolymer. As the brittle even in the presence of a modifi er. Lack of hard segment content was lowered to 60%, proper adhesion between the rubber and the PET the blend exhibited incomplete miscibility, with after crystallization, in general, seems to be the two Tg’s for two amorphous phases and also two reason for this embrittlement. separate crystalline phases. [Runt et al., 1989]. Use of reactive tougheners such as ethylene- Nevertheless, a partial miscibility was indicated glycidyl methacrylate copolymers [Iida, 1981] due to changes in the Tg observed in DSC and and ethylene-n-butyl methacrylate-glycidyl meth- dielectric relaxation spectra. The partial miscibil- acrylate terpolymer [Deyrup, 1988], leads to sig- ity and low interfacial tension between the phases nifi cantly improved toughness which is retained makes the blend very compatible. even after annealing [Akkapeddi and VanBus- Commercial PBT/copoly(ether-ester) blends are kirk, 1993]. However, at present no commercial generally richer ( 50%) in the copoly(ether-ester) PET/elastomer blends are offered in the unfi lled elastomer content. These blends were designed form. The compositions such as those described for the automotive, fl exible bumper fascia market above may be nucleated and glass fi lled. An (Bexloy® V, DuPont). Typical properties of these ethylene copolymer rubber modifi ed, glass fi lled blends are shown in Table 15.32. Typically they PET (Rynite® SST) with improved notched Izod exhibit low moduli ( 800 MPa), high elongation impact strength and elongation is commercially and toughness. The purpose of PBT in the blend available. A glass fi lled PBT, impact modifi ed with is to lower the cost and improve the heat sag SAN-g-poly(n-BuA) core-shell rubbers (ASA) resistance required for paint oven capability. is also available commercially (Ultrablend®S, PBT/copoly(ether-ester) elastomer blend mold- BASF). Because of the superior weatherability ed parts exhibit excellent surface fi nish and good of ASA rubber vs. other rubbers such as ABS, paint adhesion without the need for primers. MBS, etc., the PBT/ASA blend is likely to fi nd About 3 kton/y of this blend is being used for applications in the exterior automotive applica- painted, fl exible bumper fascias in selected luxury tions. Mirror housings, door handles, roof racks, model cars in the USA. Because of the excellent are typical exterior, automotive applications. surface esthetics of the blend, molded-in colors Some grades of glass/mineral reinforced, impact are also being evaluated to reduce the painting modifi ed PET molding resins have also been costs. Lower levels ( 20%) of copoly(ether-ester) developed specifi cally for automotive exterior elastomers have also been blended with PBT for body panel applications (Bexloy®K, DuPont). high impact strength molding resin applications This specifi c formulation was reported to with- (Celanex®, Hoechst-Celanese). stand automotive on-line “E-coat” paint oven temperatures (ca. 200°C) as well as give low 15.12.4 Glass Reinforced, Impact Modifi ed PET warpage and smooth surface fi nish in the molded (and PBT) parts. A combination of glass fi ber or glass beads and/or mica is believed to be used for reinforce- PET/Elastomer blends have not been commercial- ment. The impact modifi er is more likely a reac- ized in the unfi lled form, due to the slow rate tive toughener of the ethylene-n-butylacrylate Commercial Polymer Blends 1101

Table 15.32. Commercial PBT/polyester elastomer blends vs. PBT and polyester elastomer

Blend Type PBT/POLYESTER ELASTOMER POLYESTER PBT ELASTOMER

ASTM BEXLOY LOMOD RITEFLEX HYTREL CELANEX PROPERTY TEST UNITS V978 A-1220 BP 5526 1400 METHOD Dupont GE H. Celanese Dupont H. Celanese

PHYSICAL Density D792 kg/m3 1,200 1,200 1,180 1,200 1,300 Mold Shrinkage D955 % 1.2 Water Absorption, 24 hrs. D570 % 0.25 0.32 0.5 0.08

MECHANICAL Flexural Modulus D790 MPa (kpsi) 760(110) 828(120) 760(110) 211(30) 2300(330) Flexural Strength D790 MPa (kpsi) 84(12) Tensile Strength at Yield D638 MPa (kpsi) 33(4.8) 25(3.6) 10(1.5) 56(8) Tensile Strength at Break D638 MPa (kpsi) 41(5.8) 56(8) Elongation at Break D638 % 400 200 200 560 50 Shore D Hardness D59 D67 D55 M72

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C NB NB NB NB 32(0.6) at -29°C 187(3.5) 203(3.8)

THERMAL Heat Deﬂ ection Temp D648 °C at 0.45 MPa 111 101 at 1.82 MPa 44 49 54 Vicat Softening Point D1525 °C 176 180 210

glycidyl methacrylate terpolymer type or an ion- still relatively low compared to the more widely omeric type ethylene-butylacrylate-methacrylic used engineering thermoplastics and commodity acid terpolymer. thermoplastics. Specialty polymers may be of two

types viz., (a) high Tg, amorphous engineering thermoplastics such as polysulfones, polyarylates, 15.13 Specialty Polymer Blends polyetherimide, polyamideimide, polyimides; (b) high melting, crystalline thermoplastics such as In the plastics industry, specialty polymers are polyphenylene sulfi de, liquid-crystalline polyes- generally considered as high performance, high ters (LCP’s), polyetherketones (PEEK, PEK). priced resins whose current market volume is Both categories of polymers can be classifi ed 1102 M. K. Akkapeddi as high temperature polymers with long term such as polycarbonate and polyestercarbonates. service capability at T 150°C and more often Hence the polysulfones have been used primarily at T 200°C, as defi ned by U.L. temperature in specialty niche applications such as steam index; i.e., temperature at which 50% tensile sterilizable medical equipment, cookware, appli- strength is retained after 10,000 hours of heat- ance parts, etc. These unique advantages of poly- aging. A common structural feature of all these sulfones in having transparency coupled with high temperature polymers is their essentially all hydrolytic stability and heat resistance, would aromatic backbone structures. be lost if other polymers are blended. Hence The high temperature, specialty polymers pos- there has been very little incentive for blends of sess certain common property advantages such as: polysulfone. In addition, the cost factor has also

(i) high Tg and/or Tm, (ii) inherent fl ame retardancy, been a deterrent. The only commercial blends of (iii) high thermo-oxidative stability, (iv) high polysulfone are those containing ABS or PET (Min- continuous use temperatures, (v) high mechanical del®, Amoco), which together make up for about rigidity and strengths, (vi) high dimensional sta- 1 kton/y of current market volume in the USA. bility (to moisture and temperature) and creep resistance. 15.13.1.1 Polysulfone/ABS Blend The crystalline polymers such as PPS, LCP, PEEK offer the additional advantages of high The primary reasons for developing this blend solvent resistance. Due to the inherently high cost appear to be: (a) to improve the toughness, of the specialty polymers, very few blends have particularly the notched Izod impact strength been developed for commercial applications. The (b) processability (c) plateability of polysulfone. only driving force for the development of even Since ABS is a low cost, tough, plateable resin, the few blends of specialty polymers has been it meets the requirements. However, ABS and the desire to reduce the cost of the base resins polysulfone lack adequate compatibility, which by blending with lower cost engineering plastics, manifests itself in poor weld-line strength and although this invariably results in a lower DTUL. surface appearance in the molded parts. Various Nevertheless, a few commercial blends of spe- types of compatibilizing additives such as phe- cialty polymers exist and their properties will be noxy resins, styrene-maleic anhydride copolymers discussed below: have been claimed to improve the weld line strength of the polysulfone/ABS blends [Robe- 15.13.1 Polysulfone Blends son, 1985]. Commercial polysulfone/ABS blend (Mindel(R) A) is composed of PSO, high heat α Polysulfones are aromatic high Tg, amorphous ABS (based on -methylstyrene) a phenoxy resin polymers having a sulfone and an aromatic ether compatibilizer and MBS core-shell rubber as linkage in the recurring units of their backbone. impact modifi er. Owing to this structure of their polymer backbones, The plateability and hydrolytic stability advan- they display unique resistance to hydrolysis. tages of polysulfone/ABS blends have been The two commercially signifi cant polysulfones utilized to make selected appliance, plumbing, are (a) the polysulfone derived from bisphenol A, and sterilizable equipment parts, replacing poly- which is simply referred to as polysulfone (PSO; carbonate. Polysulfone/ABS blend has also been Udel®, Amoco) and (b) the polyethersulfone (PES; evaluated for plateable components of electrical Victrex®, ICI). The current world-wide consump- and electronic parts, circuit boards and con- tion of all polysulfones is estimated to be less nectors. However, the lack of adequate heat than 19 kton/y about 70% of which belong to resistance (DTUL lower than polysulfone) for the polysulfone (PSO). The hydrolytic stability of vapor phase solderability limited its use only polysulfones appears to be their unique advantage in conjunction with other high heat resins as over other high heat, transparent thermoplastics laminates. Commercial Polymer Blends 1103

15.13.1.2 Polysulfone/PET Blend polyarylates is estimated below 2 kton/y. Rela- tively few blends of polyarylate have been com- Polysulfone has been blended with PET for the mercialized because by blending other polymers purposes of cost reduction and improvement in results in the loss of the clarity and DTUL solvent stress-crack resistance. The blend was advantages of the polyarylate. The only com- developed primarily in the glass reinforced forms mercially signifi cant blend of polyarylate appears for applications in electrical and electronic mar- to be a blend with PET (U 8000, Unitika; Ardel® kets (Mindel® B, Amoco). However the DTUL, D-240, Amoco). fl exural strength and impact strength of the com- Polyarylate/PET blends prepared by solution or mercial polysulfone/PET blend appears to be melt blending under short residence times at T lower than those of PET at comparable levels 280°C with or without an added ester interchange of glass reinforcement (Table 15.33). Lack of inhibitor such as triphenylphosphite, are essentially an adequate compatibility between PET and poly- phase-separated, exhibiting two glass transition sulfone and a net reduction in the crystallinity temperatures, one each for a PET phase and a account for the lower properties. However, below polyarylate-rich phase. From the observed glass the Tg of polysulfone, e.g., at T 150°C, the transition temperatures, one can conclude that it dimensional stability (modulus retention) should is a partially miscible blend in which more PET be somewhat better than that of glass fi lled PET, dissolves in the polyarylate phase than polyarylate which loses some of its initial modulus above does in PET. The interaction parameter has been χ ≅ its Tg of ca. 75°C. Other advantages of glass- estimated to be slightly positive ( 12 0.1) [Chung fi lled PSO/PET blend include lower warpage and and Akkapeddi, 1993]. shrinkage, better fl ame resistance than glass-fi lled The miscibility between polyarylate and PET PET or PBT. PSO/PET blends have also been may be further driven by transesterifi cation reac- reported to exhibit superior hydrolysis resistance tion within the melt phase, which occurs slowly relative to PET or PBT. at T 280°C but more rapidly at T 300°C [Robeson, 1985; Eguiazabal et al., 1991]. In any 15.13.2 Polyarylate Blends case, polyarylate can readily form transparent blends when the PET content is 30% and Commercial polyarylate is an aromatic polyester the melt blending done above 300°C. Hence by of high glass transition temperature (ca. 180°C) adjusting the melt blending conditions, PET can derived from bisphenol A and a mixture of tere- be used to lower the cost and improve the chemi- phthalic and isophthalic acids. It is a transparent, cal resistance of polyarylate while maintaining rigid and tough thermoplastic of high heat distor- an adequate level of transparency. The heat dis- tion temperature (174°C). Polyarylates face com- tortion temperature is, of course, sacrifi ced to petition from the more established polycarbonate some extent. Except for some improved chemical and its higher heat analogues, viz. polyester resistance, processability and cost the blend does carbonates; as well as the polysulfone that is not seem to offer any compelling advantages over superior in hydrolic stability. Although polyary- polyarylate and hence its applications appear to late has been commercially available for many be quite limited. years, its market growth has been slow due to its high cost/performance balance. Nevertheless, 15.13.3 Polyetherimide Blends polyarylate’s transparency, UV/weather resistance and high heat distortion temperature properties Commercial polyetherimide (PEI Ultem®, GEC) have found specialty niche applications in auto- is an amorphous, high performance thermoplastic motive taillights, refl ectors, etc. Polyarylates have with its repeat unit structure containing both the also been used in electrical/electronic connector rigid aromatic imide units and the somewhat more applications. Current world-wide production of fl exible aromatic ether units. 1104 M. K. Akkapeddi

Table 15.33. Commercial polysulfone blends vs. polysulfone and PET

Blend Type PSF/ABS PSF/PET PSF PET ASTM MINDEL MINDEL UDEL PETRA PROPERTY TEST UNITS A670 B322* P1700 130* METHOD Amoco Amoco Amoco AlliedSignal

PHYSICAL Density D792 kg/m3 1,130 1,470 1,240 1,550 Mold Shrinkage D955 % 0.66 0.25 0.7 0.3 Water Absorption, 24 hrs. D570 % 0.25 0.14 0.3 0.05

MECHANICAL Flexural Modulus D790 MPa (kpsi) 2220(316) 7030(1000) 2740(390) 9130(1300) Flexural Strength D790 MPa (kpsi) 84(12) 162(23) 108(15.4) 240(34) Tensile Strength at Yield D638 MPa (kpsi) 51(7.2) 105(15) 72(10) 154(22) Tensile Strength at Break D638 MPa (kpsi) 44(6.2) 105(15) 154(22) Elongation at Break D638 % 75 2 75 2

IMPACT Izod Impact, Notched D256 J/m(ft-lb/in) at 23°C 380(7) 54(1) 71(1.3) 98(1.8)

THERMAL Heat Deﬂ ection Temp D648 °C at 1.82 MPa 149 160 173 225

ELECTRICAL Dielectric Strength D149 KV/mm Dielectric Constant at 1 MHZ D150 3.7 3.5 Dissipation Factor at 1 MHZ D150 0.009 0.02

* 30% Glass ﬁ lled

Owing to the unique structure of its backbone, However, its relatively high cost has limited its polyetherimide exhibits high glass transition tem- market volume.

perature (Tg = 215°C), high mechanical strength Very few blends of PEI have been commercial- and rigidity, yet has a good degree of ductility and ized because blending a lower cost polymer melt processability. Its highly aromatic backbone generally compromises the performance of the structure also imparts an inherent fl ame retar- base resin. Nevertheless, some PEI/PC blends dancy and low smoke generation characteristics in have been introduced as thermoformable sheets the polymer. Because of these high performance (Ultem® 1668, GEC) for aircraft interior applica- characteristics, PEI fi nds specialty niche applications, to meet the processability and the low tions in the automotive under-the-hood, aero- fl ammability/low smoke generation requirements space, electronic and medical equipment markets. (Table 15.28). Other applications in the automo- Commercial Polymer Blends 1105 tive and the industrial markets have also been used by itself, PPS is generally compounded with found for this blend, the details of which have reinforcing fi llers. Glass reinforced PPS exhibits already been discussed under the polycarbonate high heat distortion temperature (HDT ≅ 265°C) blends section. and high continuous use temperature (U.L. index Polyetherimide was found to be miscible with of ca. 200°C). polyetheretherketone (PEEK) exhibiting a single Owing to its unique combination of proper-

Tg. Since PEEK is a semicrystalline polymer ties, PPS is experiencing a recent growth in with a Tg of ca. 150°C, the blend should have the market interest with several producers and a higher Tg (intermediate between that of PEEK suppliers entering this business. Although current and PEI) and yet possess some solvent resistance worldwide consumption of PPS is still relatively characteristics of PEEK. The blend may have low (below 7 kton/y based on the neat resin) some advantages in fi lm and composite applica- steadily improving cost and supply position of tions, but no commercial application of this blend PPS may increase its usage in the future. Since have been developed to date. most PPS is used in the glass or mineral reinforced form, blending other polymers generally 15.13.4 Polyimide/Poly(tetrafl uoroethylene) has no benefi ts. In addition, the chemical inertness Blends of PPS and the crystallization tendency do not promote any degree of compatibility with other High performance polyimides (Vespel®, Dupont) polymers. and polyamide-imide (Torlon®, Amoco) molding The only commercial blend of PPS currently compounds are often mixed with polytetrafl uoro- being used is the blend of PPS with PTFE. How- ethylene (PTFE) to fabricate a variety of low- ever in these formulations, PTFE is simply added friction bearings, bushings and seals used in as a lubricating fi ller. These products (Dianippon automotive, aerospace and industrial markets. Ink, Japan) are used for making low-friction gears The role of PTFE in these formations is simply (for fl oppy disc drives), bearings, relays and other to function as a lubricating fi ller. Hence these moving parts. may not be considered as real blends. The PTFE Since a major weakness of PPS is its brittle- particles are inert and not bonded to the poly- ness, some attempts have been made to improve imide matrix in the molded part. Because of this its toughness by blending with other suitable heterogeneity, higher amounts of PTFE can not polymers. A commercial impact modifi ed PPS be tolerated in the polyimide compounds, due (Toray) is believed to consist of a blend of PPS to undesirable loss in tensile strength. Generally with ethylene-glycidylmethacrylate polymer. A only about 10% PTFE is used, often in conjunc- grafting reaction is expected to occur if the PPS tion with additional lubricants such as graphite has active end groups such as -SH or -S-Na+, and/or molybdenum sulfi de. which can in principle react with the epoxy group of the ethylene/GMA copolymer. 15.13.5 Polyphenylenesulfi de Blends Recently a PPS blend with liquid crystalline polyesters (LCP) has also been offered com- Polyphenylenesulfi de (PPS) is an aromatic semi- mercially in 40% glass fi lled form (Vectra® crystalline polymer with a recurring sulfi de link- V140, Hoechst-Celanese). The liquid crystalline age in the backbone. Due to the highly aromatic polyester used in this blend is a copolyester of nature of its structure, PPS is inherently fl ame p-hydroxybenzoic acid and 2-hydroxy-6-naph- retardant and also exhibits an outstanding level thoic acid. The melting point of this LCP and of chemical resistance. PPS is high melting (Tm= of PPS closely match, i.e., Tm = 285 to 290°C. 285°C), yet its low melt viscosity allows easy Since there is no compatibility or reaction processing and high loading of glass or mineral between the two components, LCP/PPS blend fi llers. Since unfi lled PPS is too brittle to be is considered to be a simple mechanical blend. 1106 M. K. Akkapeddi

The purpose of blending PPS seems to be simply investigated by many researchers, but their high to lower the cost of LCP without sacrifi cing the cost has precluded the successful commercializa- high heat distortion temperature and high melt tion of any such blends. fl ow (Table 15.34). The commercial LCP/PPS blend is designed for injection molding complex electronic parts, 15.14 Thermoset Blend Systems chip carriers, sockets and coil bobbins. It is very likely that due to its low melt viscosity, LCP Thermoset systems are, by defi nition, three- still forms the continuous phase, while PPS may dimensional polymer networks formed by thermal simply be present as a dispersed fi ller along with radiation or chemically induced polymerization the glass fi bers. Very little information about this and crosslinking (curing) reactions of multi- blend has been published. functional monomers or prepolymers. Since a There has been some commercial development thermosetting resin solidifi es upon curing and activity in the blends of PPS with PPE, in which cannot be remelted or reprocessed, it is a neces- the PPE is claimed to improve the ductility of sary to mix all the required ingredients including PPS, e.g., with an elongation at break of 8% the reinforcing fi llers or fi bers, modifi ers, stabi- in a 40% glass fi ber reinforced blend [Gabriele, lizers and additives during the initial monomeric 1992]. The contribution of high ductility, high or prepolymer stage before being fabricating into DTUL of 270oC and good processability (low the fi nal shape by curing. The mixing is facili- mold shrinkage and fl ash), appears to make this tated by the low viscosity of the system. Among blend to be a signifi cant improvement over glass- the most widely used commercial thermosets fi lled PPS. However, no further details on the are: (a) unsaturated polyesters, (b) phenolics, commercial usefulness of this blend have been (c) epoxies, (d) vinyl esters, (e) polyurethanes, reported to date. (d) polyimides, etc. Many commercial thermosets are quite often 15.13.6 Liquid Crystalline Polyester Blends used as complex mixtures of several co-reacting monomers and prepolymers, specifi cally formu- Although liquid crystalline polyesters (LCP’s) are lated to suit a given end-use application. For interesting polymers exhibiting high mechanical example, in coating and adhesive applications, strength and modulus due to a high degree of self- often mixtures of different epoxies, differing in orientation, no commercial blends of LCP (except chemical structure and/or molecular weights, are with PPS) are available. LCP blends have been used as required. Even two different thermoset-

Table 15.34. Typical properties of LCP/PPS blend (Vectra® V140, Hoechst-Celanese) (40 wt% glass ﬁ ber reinforced)

Density (kg/m3) 1,670 Water absorption, 24 hr (%) 0.02 Flexural Modulus (MPa) 16,550 Flexural Strength (MPa) 248 Tensile Strength (MPa) 165 Tensile Elongation (%) 1.4 DTUL (°C, 1.8 MPa) 265 Dielectric Constant (at 1kHz) 3.7 Dielectric Strength (kV/mm) 23.6 Commercial Polymer Blends 1107 ting monomers may be mixed such as in the melamine prepolymer/epoxy resin; carboxyl ter- case of single-package epoxy-phenolic molding minated unsaturated polyester/epoxy thermosets. compounds [Fry et al., 1985]. However, even The graft or copolymer network reaction involves these hybrid thermoset systems are not usually the reaction between the phenolic-OH or an amine considered as blends. Since the molecular weights or a carboxyl and the epoxide group. of the epoxy and novolaks are low and during Some examples of what may be considered as curing they become integral parts of the polymer actual thermoset/thermoset blends are the epoxy and network through co-reaction, the system may be bismaleimide thermosets modifi ed with aromatic called a co-reacted thermoset. dicyanate esters such as bisphenol A dicyanate. Although it is sometimes hard to distinguish Aromatic cyanates crosslink by cyclotrimerization some thermoset blends from co-reacting thermo- to form a network of triazine ethers. sets, thermoset blends can be ideally classifi ed Crosslinked cyanate ester systems typically as follows: exhibit higher glass transition temperatures ° A) Thermoset-thermoset blends and interpen- (Tg 250 C), lower moisture absorption and etrating networks (IPN’s) lower dielectric constants than conventional epoxy B) Thermoset-thermoplastic blends and semi- thermosets. Hence by mixing dicyanates or their interpenetrating networks (Semi-IPN) corresponding prepolymers with epoxy resins, C) Rubber modifi ed thermosets and then co-curing, the desired level of property improvements can be achieved. Such hybrid ther- An interpenetrating network (IPN) is defi ned mosets have been used in printed circuit board as a combination of two polymer networks, at manufacture. least one of which is in the presence of the other. Similar hybrid thermosets consisting of bisma- The distinction between interpenetrating network leimide resins mixed with bisphenol A dicyanate and blend may often be based on morphology ester have been commercially available (BT resin, and the degree of phase separation. If there Mitsubishi gas chemical). The presence of cross- is a suffi cient degree of molecular interaction, linked triazine ether network in the matrix of the phase separation tendency is suppressed and bismaleimide crosslinked network is believed a true molecularly or morphologically uniform to improve the toughness, reduce the moisture interpenetrating network can be achieved. Very sensitivity and improve the dielectric properties few systems can form truly homogeneous blend of the bismaleimide thermoset without a sacrifi ce networks and, in reality, some microheterogeneity in heat resistance. is invariably observed. Compatible IPN’s gener- In a majority of cases, the thermoset/thermoset ally form < 5 nm size domains and incompatible blends are actually formulated by the fabricator or IPN’s or blends form domain size > 30 nm. the end user during the fabrication and processing of such materials as composite prepregs, 15.14.1 Thermoset/Thermoset Blends printed circuit boards, laminates and adhesives. The formulations and compositions are often kept As previously mentioned, several commercial proprietary and are designed to meet their own hybrid thermosets are known to be co-reacting individual requirements. thermosets, i.e. when the mixture of two different thermosetting monomers or prepolymers is cured, 15.14.2 Thermoset/Thermoplastic Blends there is a simultaneous graft or co-reaction between the components along with the crosslink- 15.14.2.1 Low-profi le/low-shrinkage Additives ing reactions. These systems may therefore be for Unsaturated Polyesters considered as co-polymerizing thermosets and not as true blends. Examples of such systems are: phe- Unsaturated polyesters account for nearly 75% of nolic novolak/epoxy resin (or epoxy novolaks); the reinforced thermosetting composite volume 1108 M. K. Akkapeddi of usage [Atkins, 1978]. Unsaturated polyesters Thermoplastic additives in SMC and BMC are derived from the polycondensation of glycols accounted for nearly 8 kton/y consumption in the such as propylene glycol and maleic anhydride USA [Skeist, 1992]. A primary requirement for with some phthalic anhydride added to control the the polymer additive is that it must be amorphous degree of unsaturation. This unsaturated polyester with a low to moderate Tg and fairly soluble or prepolymer is further mixed with styrene mono- dispersible in the resin matrix initially, but capable mer (ca. 40%) and glass fi ber reinforcements of phase separation during the polymerization. and then polymerized via a radical initiator and heat to the fi nal thermoset network. Reinforced 15.14.2.2 PPE/epoxy Blends unsaturated polyesters are generally processed as sheet molding compound (SMC) or bulk molding Poly(2,6-dimethyl 1,4-phenylene ether) (PPE) compound (BMC). In the SMC process, the resin, is a high Tg (215°C) ductile polymer with a low fi llers, glass fi bers, catalyst and other additives are dielectric constant and extremely low moisture mixed together and cast into a sheet sandwiched absorption. Epoxy thermosets exhibit a very good by polyethylene fi lm. The sheet is then cured by combination of useful properties such as good compression molding in a matched-die mold to adhesion, low-shrinkage, high electrical resistiv- the required part shapes such as automotive exte- ity and good thermal properties. The brittleness rior body panels. and the moisture sensitivity of epoxies can be Although parts fabricated from reinforced improved by blending a thermoplastic additive polyester thermosets exhibit excellent rigidity, such as PPE. In addition, since PPE has a high strength and toughness, the high shrinkage asso- Tg, the thermal properties are not sacrifi ced, but ciated with the polymerization of the matrix improved. Furthermore, the dielectric constant causes sink marks and depressions in the surface is lowered. Such blends have been used in glass where ribs or bosses are located. Hence for parts reinforced composite form for laminates and printed requiring close tolerance and surface appearance circuit boards. such as automotive body panels, SMC based on In a typical formulation of epoxy resin (Epon unsaturated polyester could not be used for a long 825, Shell) cured with aluminum alkoxide, time, until it was found that addition of some incorporation of 30% PPE increased the elonga- thermoplastics to the formulation helped reduce the tion at break from <2% to >17%. The heat distor- shrinkage and produce smooth class “A” surface. tion temperature increased from 160 to 195°C. Polyvinylacetate (PVAc) and vinyl acetate- The dissolution of PPE in epoxy formulation- acrylic copolymers (VAc-A), thermoplastic poly- raised its viscosity at 200°C from 0.2 to 4 Pas urethanes, polyethylene, polystyrene and polycap- [Anonym., 1991]. rolactone are some of the candidates for low-profi le shrinkage additives to SMC and BMC. PVAc and 15.14.2.3 Thermoplastic/silicone Semi-IPNs VAc copolymers are the most widely used thermoplastic additives. Typically a low-profi le SMC Although the dynamically vulcanized blends recipe contains about 15% unsaturated polyester such as EPDM/PP (Santoprene®) and NBR/PP resin, 8% thermoplastic additive, 50% calcium (Geolast®) have sometimes been referred in the carbonate and 27% glass fi ber. literature as semi-IPNs, we considered them as It is believed that during the curing the thermo- blends of crosslinked elastomer dispersions in plastic forms a separate phase, which counteracts a thermoplastic matrix and as such treated them the curing shrinkage in the matrix initially by under the elastomer blends. There is yet another thermal expansion and subsequently by void class of thermoplastic/thermoset blend system formation. Almost all of the SMC used in the in which a minor amount of the crosslinkable automotive industry is based on low profi le, low- monomer(s) is allowed to polymerize in the shrinkage additives. thermoplastic matrix forming a loose network. Commercial Polymer Blends 1109

Examples of such systems are silicone semi- The commercial volume for silicone IPNs is, IPNs in thermoplastics that have been recently however, still very small. commercialized (Rimplast®, Petrarch, div. of Hüls) [Anonym., 1983]. 15.14.3 Rubber Toughened Thermosets The silicone semi-IPNs consist of mixing a hydride-containing silicone prepolymer and a Most commercial rigid thermosets of high Tg vinyl functionalized silicone polymer into a ther- exhibit brittleness and low tensile elongation moplastic matrix such as PA, PBT, thermoplastic because of the inherent nature of crosslinked polyurethane (TPU) or styrene-ethylene/butylene- network structures. Addition of rubbery disper- styrene (S-EB-S) block copolymer elastomer. sions into the thermoset matrix should improve The two silicone prepolymers co-react in the the ductility and impact strength of the matrix thermoplastic matrix during melt extrusion and by promoting the absorption of strain energy injection molding to form a partially crosslinked through multiple crazing and shear deformation network within the thermoplastic matrix. sites in the matrix. However, dispersion of high The crosslinking reaction may be catalyzed molecular weight rubbers into the monomeric or by a small amount of suitable organometallic prepolymer mixtures of the thermosetting resin catalysts. The blends typically contain ca. 5-20% matrix is usually diffi cult due to a viscosity mis- silicone. Injection molded or extruded parts are match and a lack of solubility or compatibility. further heat-treated to complete the curing reac- Hence a low molecular weight, reactive elas- tions. There is, of course, a signifi cant level of tomer is normally used for impact modifi cation phase separation. In the thermoplastic molding of thermosets. The low molecular weight of the compounds such as glass-fi lled PA and PBT, addi- rubbery prepolymer aids its easy dissolution or tion of the silicone semi-IPN in small amounts dispersability in the thermosetting resin. The reac- (ca. 5-10%) is reported to reduce the mold shrink- tive functionality couples the rubber covalently to age, improve mold release, and increase wear and the growing polymer network during the curing friction resistance. Polyamide-silicone blends have reaction. Hence the rubber toughened thermosets already been discussed under PA blends section. may also be considered as co-reacted thermosets Elastomeric silicone IPN with TPU and S-EB-S and not true blends. thermoplastic elastomer matrices have found some Rubber toughened epoxy resins are the well medical applications [Carew and Deisher, 1989]. known examples of impact modifi ed thermosets The silicone contributes to the excellent release utilizing reactive rubbery prepolymers. Epoxy characteristics and to the bio-compatibility. resins can be toughened or fl exibilized by any Typical applications include medical tubing, cath- one of the following types of oligomeric reactive eters, implants, diaphragms, seals, gaskets, etc. elastomers:

Oligomeric Elastomer Reactive functionality

Polypropylene glycol diglycidyl ether [Riew, 1976] Epoxide end groups Polyaminoamides (condensation products of polyamines Amine groups and ‘dimer’ acids) [McAdams, 1985] Liquid polysulﬁ des [McAdams, 1985] Thiol groups Aliphatic polyesters [Drake, 1983] Carboxyl and -OH groups Liquids, butadiene-acrylonitrile copolymers Amine or carboxyl end groups (Hycar® ATBN or CTBN, B.F. Goodrich) [McGerry, 1968; Drake, 1975] 1110 M. K. Akkapeddi

These oligomeric reactive rubbers co-react ity targets. with the epoxy resins through their correspond- 3. Improved technology for obtaining reproduc- ing reactive end groups thus incorporating rub- ible and stable morphologies under commercial bery blocks into the crosslinked epoxy network. extrusion and molding conditions. For impact modifi cation usually 10 wt% of the 4. Better understanding of the correlations between reactive rubber is used. For fl exibilizing the rheology, morphology and mechanical proper- thermoset higher levels (up to 50 %) are needed. ties to help optimize polymer blend design. The type and the amount of the oligomeric 5. Development of effi cient toughening technol- rubber used depends upon the degree of tough- ogy (impact strength, fracture toughness and ness and fl exibility required in the product. ductile/brittle transition temperature). The rubbery segments must phase separate after 6. Improving the long-term service life and per- curing into discrete domains for effective impact formance of polymer blends (thermal aging/ modifi cation without sacrifi cing the glass transi- embrittlement resistance, creep and fatigue tion temperature or heat resistance of the matrix. resistance, weatherability, etc.). Generally, 1-5 µm size rubber particles promote 7. Developing cost-effective processing (com- craze formation while shear deformation is pro- pounding and post-fabrication) technology. moted by rubber particles of < 0.5 µm. Systems 8. Improving the recyclability and reprocessabil- possessing both small and large particles, i.e., ity aspects of polymer blends, particularly with bimodal distribution, provide maximum tough- respect to the retention of properties after ness [Riew, 1976]. Elastomer modifi ed epoxy multiple processing histories, to increase the resins are primarily used in composites, struc- effi ciency of regrind use. tural adhesives and electronics applications. 9. Development of cost-effective technology for polymer blends that can continue to bridge the performance gaps between the commodity, 15.15 Conclusions engineering and specialty polymers.

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