Examining Functionalized Butyl Rubber

P014_RPN_20150112.qxp 1/7/2015 3:27 PM Page 1

14 Rubber & Plastics News ● January 12, 2015 www.rubbernews.com Technical Examining functionalized butyl rubber By Kevin Kulbaba, An expected increase in the plateau Dana Adkinson and Jon Bielby Executive summary modulus, GN, is observed for the butyl Lanxess Inc. ionomer as ionic aggregates act as phys- Many industrial rubber applications are X_Butyl I4545P is a new butyl-based material that has been developed by ical crosslinks. subjected to cyclical stress or deforma- Lanxess and contains a persistent ionic charge attached to the butyl backbone. In Here, GN is estimated from the G’ at tions, which can cause cracks to initiate addition to the properties of traditional butyl rubber (impermeability and low the frequency of the G” minima. The GN and propagate, leading to failure of the temperature flexibility), this new butyl ionomer displays many unique physical of 3.0x105 Pa obtained for BIIR-h is sim- rubber article. The fatigue process in- and dynamic properties, including excellent green strength, improved polymer- ilar to that of reported values for poly- volves the formation of cracks due to natu- filler interaction and the formation of stable pellets. isobutylene between 2.9x105 Pa to rally occurring flaws or the aging process. Incorporation of the butyl ionomer in an bromobutyl inner liner compound for- 3.2x105 Pa,15-17 while the butyl ionomer As minimizing the propagation of mulation has been shown to provide improved green strength leading to greater was found to be 3.8 x10.5 cracks is critical for many applications dimensional stability needed during extrusion and calendering processes. This increase in modulus is useful in in their service life, improving fatigue is The final cured article shows significant improved crack growth resistance and butyl applications where an increase in a major challenge for dynamically adhesion to carcass compounds without impacting the other compound properties. elasticity is desired or where greater co- loaded rubber products. Such properties may lead to longer lasting tire inner liners, which can be of bene- hesive strength is required, such as for Many types of polymers, fillers, and vul- fit for off-the-road tire manufacturing and retreading operations. adhesives. canization systems are used in rubber ap- Another difference in the butyl plications (all of which are known to influ- ionomer rheology is seen in the decrease ence fatigue behavior)1-2 in order to achieve melt viscosity and relaxation time. The interactions allow for improved green in the mid-frequency (10-2 to 101 rad/s) a wide range of mechanical properties. solubility behavior and the glass transi- strength and polymer-filler interactions as G”, which is normally identified with the Ionomers are polymers that contain a tion temperature also can be affected by well as the formation of stable pellets.10-14 relaxation of the non-functionalized small amount of covalently bound ionic ionic associations.3-8 In Fig. 1, the butyl ionomer is charac- polymer chain through reptation, con- functionality dispersed in a nonpolar ma- Relaxation of the ionic groups is terized through its rheological properties tour length fluctuations and constraint trix. They are an important class of poly- thought to proceed through a mechanism and is evaluated in a halobutyl-based release mechanisms as described by the mers as ionic interactions produce large of “ion hopping” where ion pairs hop to an- rubber compound to demonstrate the per- tube model.18-20 changes in physical, mechanical and rhe- other aggregate, allowing the stress of the formance attributes of this new material. Conversely, for the butyl ionomer, re- ological properties compared with poly- polymer chain segment containing the ion laxation after the entanglement time, Te, mers that do not contain ionic groups.3-8 group to relax.7-9 Raw polymer characterization (Rouse time of the chain segment be- Ionomers are microphase-separated Butyl ionomer is a new class of butyl Fig. 2 displays the storage (G’) and tween entanglements) proceeded through materials, where the ionic groups aggre- polymer that has been developed by the loss (G”) modulus mastercurves of high the “hopping” of ionic aggregates to re- gate into domains, which act as re- generation of permanent ionic groups Mw brominated butyl rubber (BIIR-h) duce the stress as well as relaxation versible crosslinks, strongly influencing bound to the polymer backbone. and butyl ionomer at a reference tem- through reptation.7,21,22 the polymer behavior. In addition to the properties of tradition- perature of 20°C. A maximum in G” was detected for the The ionic clusters affect the viscoelastic al butyl rubber polymers (impermeability Time-temperature-superposition was butyl ionomer at approximately 10 rad/s response with an increase in modulus, and low temperature flexibility), the ionic successful for the ionomer due to the and is attributed to the relaxation of ion- large difference between the entangle- ic aggregates, with T representing the ment and ionic relaxation times. A small average duration of an ion pair multi- Fig. 2. G’ (solid symbols) and G” (open symbols) mastercurves at a reference tem- amount of ionic functionality (0.4 mol plet. The “ion hopping” relaxation mech- perature of 20°C. percent) gave rise to large changes in anism subsequently hindered reptation the polymer’s viscoelastic properties. and imparted a much greater terminal

Fig. 1. BIIR-based phosphonium ionomers.

The authors Kevin Kulbaba is the technical marketing manager for NAF- TA-focused butyl rubber at Lanxess Inc., located in London, Ontario. His work focuses on business development for butyl rubber materials and applications. Kulbaba has more than 17 years of experience in the field of polymer science, including 12 years with elastomers and rubber compounding. He studied chemistry at the University of Western Ontario and obtained his doctorate in inorganic polymer chemistry at the University of Toronto. Fig. 3. Temperature dependence of the shift factors. Kulbaba is a member of the Canadian Society of Chemistry, American Chemical Society and the On- Kulbaba tario Rubber Group. Dana Adkinson is a senior research scientist at the Research and Development Center for Lanxess in London. She focuses on the development of new butyl-based materials geared to- ward expanding the application scope of butyl rubber. She received her doctorate in chemistry from the Universi- ty of Western Ontario in 2005. Her work has resulted in more than 12 patent applications. Jon Bielby is a senior research scientist at the Global Research and Development Cen- Adkinson ter for the Butyl Rubber Business unit of Lanxess in London. He leads the physical and dynamic material research laboratory in support of the development of new butyl-based materials, fo- cusing on expanding the application scope of butyl rubber. He received his degree in physics from the University of Waterloo in 1996 and accepted a position at Lanxess (then Bayer) in 2000. Bielby P015_RPN_20150112.qxp 1/7/2015 3:29 PM Page 1

www.rubbernews.com Rubber & Plastics News ● January 12, 2015 15 Technical

relaxation time or disentanglement fore, creep testing was employed to de- cal properties for the blend compounds. inner liner with repeated heat cycles. time, Td, on the polymer to such an ex- termine the terminal response, with the Table II outlines the change in Mooney Crack propagation was determined tent that it is not measurable in the ex- zero shear viscosity being calculated: viscosity and Mooney scorch of the using a DeMattia flex tester on samples perimental window. halobutyl blend compounds relative to the that were aged for one week at 100°C. This indicates that the butyl ionomer control. The 10 percent increase in Mooney The results show that the rate of crack may be more difficult to handle than viscosity can be attributed to improved propagation for the BB-ION10 blend BIIR-h in certain industrial processes. filler dispersion and the presence of low was comparable to the control formula- The temperature dependence of the concentrations of ionic aggregates at such tion while the crack propagation for the experimental shift factors, aT, used to where JN(t) is the Newtonian creep com- temperatures. BB-ION20 compound was enhanced (re- construct the viscoelastic mastercurves pliance.27 Table II also highlights the change in fer to Fig. 6). obeyed the Williams, Landel and Ferry Fig. 5 displays the shear creep curves green strength relative to the mill shrink- Since the physical crosslinks due to equation:15,23 of BIIR-h and butyl ionomer. The creep age of the compounds. the ionic interactions are reversible, the response validated the impact of only a Significantly, the blends shows a 40-90 incorporation of the butyl ionomer into small amount of ionic content towards percent improvement in green strength the polymer matrix appears to impart the rheological properties as the creep of (peak stress) with no negative impact on self-healing properties, whereby the ion- the butyl ionomer is greatly reduced. the mill shrinkage, thereby resulting in ic aggregates break and re-form. The zero shear viscosity was found to an enhancement in dimensional stability Thus, a substantial reduction in the While polyisobutylene is known for its increase by more than a decade from of an uncured compound without signifi- fatigue properties of the cured rubber weak temperature dependency,24-26 the 3.6x108 Pa-s for BIIR to 4.2x109 Pa-s for cantly increased nerve, which is desir- article could be realized once again with shift factors were influenced strongly by butyl ionomer. Lower Mw brominated able for extrusion or calendering opera- the addition of low levels of the butyl 8 ionic functionality as the temperature butyl rubber (BIIR-l), with a ␩0 of 1.82x10 tions. ionomer. dependence was greatest for butyl Pa-s is also shown in the figure for com- Table III compares the resulting ten- ionomer at higher temperatures in comparison. sile properties of the BB-ION10 and BB- Conclusions parison to the reference. Whereas the long relaxation time may ION20 blends relative to the BB-CTRL The physical and rheological behavior The greater temperature dependence be an issue with some processing condi- compound. The higher modulus for the of Lanxess X_Butyl I4565P (butyl is due to the large separation in ion hop- tions, a small amount of butyl ionomer resulting butyl ionomer blend com- ionomer) was compared with brominat- ping and entanglement relaxation may show improvements in others, with pounds shows significant reinforcement ed butyl rubber. The butyl ionomer was mechanisms. The shift factors are plot- its enhanced melt strength and reduced relative to the control. found to have an increased plateau mod- ted against temperature in Fig. 3. cold flow. This effect may be attributed to im- ulus, which would be beneficial for cohe- A vertical shift of the modulus was proved filler dispersion resulting in a sive strength in adhesives and a longer performed according to the expres- Inner liner compounds higher degree of reinforcement in the relaxation time that may be a process- sion;27,23 Rubber compounds outlined in Table cured article. ing issue if utilized in high phr levels in I were mixed on the laboratory scale us- There is no impact on the permeation the compound. ing a 1.5-liter internal mixer, refined on properties when butyl ionomer is incor- Viscoelastic shift factors showed a a cold 10x20” two roll mill where the cu- porated into the carbon black filled tire greater temperature dependence of the ratives were incorporated into the com- inner liner formulation. butyl ionomer due to a relaxation of the withwith pound. The final batch was then sheeted As expected, the barrier properties in- ionic aggregates at higher tempera- out from which test specimens were cut. herent to the butyl rubber base polymer tures, which can be taken advantage of A standard tire inner liner formula- are maintained for the butyl ionomer in melt processing. tion using commercially available bro- blends. There was a slight increase in Also, creep testing exhibited an im- mobutyl rubber was used as a control tear strength observed. provement in cold flow resistance for formulation (BB-CTRL) to compare the The ionic aggregates act as reversible butyl ionomer. Fig. 4 shows the temperature depend- effect of blending bromobutyl with incre- physical crosslinks, which may be in- The butyl ionomer has been evaluated ency of butyl ionomer compared with mental amounts of the butyl ionomer creasing the energy required to initiate in a standard tire inner liner compound BIIR-h. The effect of the relaxation of (BB-ION10 and BB-ION20). a crack. This effect is diminished in the formulation based on 100 phr of bro- the ionic network is clearly seen as the There is no impact on the final state butyl ionomer blend compounds, but mobutyl. The green strength of the butyl butyl ionomer has a significantly higher of cure or on the rate of cure when the nonetheless is still observable. ionomer blend compounds was signifi- elastic modulus at lower temperatures, butyl ionomer is incorporated into the There is however, a significant in- cantly higher than the control but with but has a similar modulus at 120°C. compound (refer to Table II). crease in adhesion to an NR/BR carcass negligible change in the mill shrinkage The reduction of the elastic modulus The presence of residual allylic bro- compound. It is difficult to assign the ex- of the compound. with increasing temperature compared mide groups and isoprene groups in the act mechanism of this increased adhe- This effect allows for improved shape with BIIR-h is due both to ionic relax- butyl ionomer allows the polymeric mod- sion; however the increased polarity of retention of the uncured compound duration and the difference in Mw as BIIR- ifier to be cured into the network with- the butyl matrix in the butyl ionomer ing processing, which is desirable for ex- h is a higher Mw polymer. out reducing the effective chemical blend compound may be a contributing trusion and calendering operations. These temperature dependent proper- crosslink density of the cured article. factor. The cured compounds showed im- ties can be exploited to improve the pro- As mentioned previously, the ionic ag- When the cured samples are subse- provements in reinforcement (modulus) cessing behavior of the butyl ionomer. gregates depicted in Fig. 1 can impart quently aged (100°C for one week), there and reduced compound hardening dur- Viscous flow (G’ slope = 2, G’’ slope = significant changes in the physical and is a slight reduction in modulus relative ing heat aging. 1) was not observed within the experi- dynamic properties of a polymer. The to the control compound. Such an effect Most significantly an increase in the mental window of the mastercurves for properties inherent to the butyl ionomer would be of benefit during retreading op- flex fatigue resistance and adhesion to a either of the polymers studied. There- translate directly into improved physi- erations to prevent hardening of the tire See Butyl, page 16

Fig. 4. Temperature dependence of the modulus. Fig. 5. Creep compliance of at 20°C. P016_RPN_20150112.qxp 1/7/2015 3:30 PM Page 1

16 Rubber & Plastics News ● January 12, 2015 www.rubbernews.com Products

Dow Automotive Systems has new Dow Automotive additive polyol nicates alerts in real-time; mobilizes re- that might damage the equipment, launched Specflex Activ, the first viable with high and specifically balanced cat- sources based on standard operating pro- Henkel said, yet is flexible enough to al- amine emission-free polyurethane foam alytic activity. This formulation allows cedures; automatically escalates issues; low free movement of the hydraulic leg. formulation for interior applications. foam manufacturers to eliminate cata- views resources assigned to the escalation Loctite MR5898 foaming polyurethane This technology enables automotive seat lysts and amine emissions when manu- and the status; and captures and exports replaces precut foam inserts that allow pad foamers to meet the most stringent facturing polyurethane foam. data including actual response time, esca- debris to get into cavities through gaps industry requirements, Dow Automotive For more information, go to www.dow- lation rates and machine-level problems. between inserts and equipment edges. said, such as the German original equip- automotive.com. SyncAlert software is part of the Syn- This self-extinguishing, low-odor foam is ment manufacturer specifications in- chrono Demand-Driven Manufacturing intended for use underground and in con- cluding ultra-low emissions. Synchrono L.L.C. has launched Platform. For more information, includ- fined spaces. The two-part formula be- Traditional polyurethane foams require SyncAlert, a real-time notification and ing a video of the Platform, go to gins to foam a few minutes after mixing, amine catalysts to promote reaction be- escalation software that enables manu- www.synchrono.com. Henkel said, and becomes tack-free with- tween polyols and water with the iso- facturing teams to quickly notify the in minutes of pouring. The flexible cured cyanate component (the gelling and blow- right resource about problems and en- Henkel Corp. has introduced Loctite foam can be cut or trimmed using a ser- ing reactions), Dow Automotive said. able a rapid response, while tracking the MR5898 foaming polyurethane for hy- rated blade, the company said. Previously, these added catalysts have results and minimizing costly downtime. draulic roof support equipment used in Use of Loctite MR5898 foaming contributed to amine emission issues with SyncAlert is an add-on designed to longwall mining. polyurethane ensures proper functioning polyurethane foams and negatively im- run in tandem with SyncOperations, a Loctite MR5898 foaming polyurethane of equipment, reduces downtime and pre- pact physical and mechanical properties. workflow engine and data historian for is a pour-in-place foam material de- vents costly component replacement, Specflex Activ has been tested and vali- smart monitoring and synchronization, signed to bond to pockets and hydraulic Henkel said. The foaming polyurethane dated in an industrial setting by Faurecia, and SyncView software, a visual factory cylinders. By foaming up to fill cavities product is available in kit sizes. one of the leaders in automotive seating. information system. and adhering to edges, this foam blocks For additional information, visit The Specflex Activ product includes a Features of SyncAlert include: Commu- out debris, particulates, teeth or tools www.henkelna.com/mining. Technical

inner liner compound, incorporation of 3. Earnest, T.R.; MacKnight, W.J. Journal of Poly- 15. Ferry, J.D. Viscoelastic Properties of Polymers, 10-25 phr of the butyl ionomer has mer Science, Polymer Physics Edition, 1978, 16:143. 3rd ed.; Wiley: New York (1980). 4. Eisenberg, A.; King, M. Ion containing Polymers: 16. Fetters, L.J. et al. Macromolecules, 24, 3136 Butyl shown similar advantages with other Physical Properties and Structure. New York: Acad- (1991). polymers, including regular butyl, emic Press, 1977. 16. Santangelo, P.G. et al. Macromolecules, 32, 1972 Continued from page 15 chlorobutyl, natural rubber, EPDM, 5. Makowski, H.S. et al. Ions in Polymers. Washing- (1999). carcass compound were observed for the SBS and blends thereof, allowing for the ton: Adi Eisenberg, 1980. 18. de Gennes, P.G. J. Chem. Phys., 55, 572 (1971). 6. Tant, M.; Wilkes, G.J. Macromolecules, 1988, 19. Doi, M.; Edwards, S.F. The Theory of Polymer BB-ION blend compounds, which should use of this novel polymer in both current C28: 1. Dynamics; Clarendon: Oxford (1986); Likhtman, provide advantages for off-road tire ap- butyl applications as well as new appli- 7. Lieber, L. et al. Macromolecules, 1991, 24:4701. A.E.; McLeish, C.B. Macromolecules, 35, 6332 plications where delamination and cations. 8. Vanhoorne, P.; Register, R.A. Macromolecules, (2002). cracking can occur under high stresses. 1996, 29: 598. 20. Kim, J. et al. Macromolecules, 27, 6347 (1994). 9. Tierney, N.K.; Register, R.A. Macromolecules, 21. Colby, R.H., et al. Phys. Rev. Lett., 81, 3876 These effects were observed without References 2002, 35: 2358. (1998). any detriment to the air retention or 1. Lake, G.J.; Lindley P.B. Rubber Journal, 1964, 10. Parent, J.S. et al. Journal of Polymer Science, 22. Williams, M.L., et al., J. Am. Chem. Soc., 77, tear strength of the final cured articles. 11:30. Part A: Polymer Chemistry, 2005, 43:5671. 3701 (1955). In addition to the bromobutyl-based 2. Mars, W.V,; Fatemi, A. Journal of Rubber Chem- 11. Parent, J.S. et al. Polymer, 2004, 45:8091. 23. Plazek, D.J. et al. Macromolecules, 25, 4920 istry and Technology, 2004, 77:391. 12. Parent, J.S. et al. Macromolecules, 2004, 37: (1992). 7477. 24. Ngai, K.L., Plazek, D.J., Rubber Chem. Tech. 13. Parent, J.S. et al. (to Lanxess Inc.) U.S. Patent Rubber Rev., 68, 376 (1995). Table I: Tire inner liner formulations. 7,238,736, July 3, 2007. 25. Kunal, K. et al., J. Poly. Sci: Part B: Poly. Phys., 14. Adkinson, D.K. et al. (to Lanxess Inc.) Interna- 46, 1390 (2008). tional Patent Application No. PCT/CA10/000158, 26. Ninomiya, K.J., J. Phys. Chem., 67, 1152 (1963). 2010.

Table II: Compound properties for tire inner liner.

Fig 6. Comparison of aged (168 h @ 100°C) flex fatigue properties of tire inner liner compounds.

Table III: Selected properties for tire inner liner.