Preparation of Maleic Anhydride Grafted Poly(Trimethylene Terephthalate) (PTT-G-MA) by Reactive Extrusion Processing

Journal of Manufacturing and Materials Processing

Article Preparation of Maleic Anhydride Grafted Poly(trimethylene terephthalate) (PTT-g-MA) by Reactive Extrusion Processing

Natália F. Braga 1,* , Henrique M. Zaggo 1, Thaís L. A. Montanheiro 2 and Fabio R. Passador 1 1 Laboratório de Tecnologia de Polímeros e Biopolímeros, Universidade Federal de São Paulo - UNIFESP, São José dos Campos, SP 12231-280, Brazil; [email protected] (H.M.Z.); [email protected] (F.R.P.) 2 Laboratório de Plasmas e Processos, Divisão de Ciências Fundamentais, Instituto Tecnológico de Aeronáutica – ITA, São José dos Campos, SP 12228-900, Brazil; [email protected] * Correspondence: [email protected]

Received: 5 March 2019; Accepted: 29 April 2019; Published: 4 May 2019

Abstract: Maleic anhydride (MA) grafted with poly(trimethylene terephthalate) (PTT)—abbreviated as PTT-g-MA—can be used as a compatibilizing agent to improve the compatibility and dispersion of nanofillers and a dispersed polymer phase into PTT matrix. This work suggests the preparation of PTT-g-MA using a mixture of PTT, MA, and benzoyl peroxide (BPO) by a reactive extrusion process. PTT-g-MA was characterized to confirm the grafting reaction of maleic anhydride on PTT chains by Fourier transform infrared (FTIR) spectroscopy. Thermal properties (differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)) and rheological analysis (parallel plates rheology) were used to prove the changes that occurred after the graphitization reaction. The reactive processing route allowed the production of the compatibilizing agent (PTT-g-MA) with good thermal properties and with lower viscosity compared to neat PTT, and this could be an alternative for the compatibilization of polymer blends, as example for PTT/ABS (acrylonitrile butadiene styrene) blends and nanocomposites based on PTT matrix.

Keywords: poly(trimethylene terephthalate); maleic anhydride; compatibilizing agent

1. Introduction Polymeric blends and nanocomposites have been developed over the years with the aim of creating new materials with desirable features. One of the biggest challenges in this field is the weak interfacial adhesion and poor dispersion of the dispersed phase and/or the filler in the polymeric matrix phase. The low physical attraction forces across the immiscible phase boundaries usually cause immiscible blend systems with weak interfacial adhesion, which have poor mechanical properties. The compatibility between the components has great importance and influence on the final properties of polymer blends and nanocomposites, and the interfacial region that occurs strains transfer from the matrix to the reinforcement agent [1]. The number of immiscible blends is extensive due to the low entropy of mixing two polymers as a result of their long chain structure, and phase separation can occur. This problem has been mitigated since the 1960s with the introduction of small quantities of an additive, known as a compatibilizing agent [2]. The compatibilizing agent is commonly used to improve the compatibility of immiscible polymeric blends. Compatibility is promoted by the presence of functional groups which undergo interaction [3]. These agents graft polymers by reactive reactions, typically using maleic anhydride (MA) or acrylic acid (AA). The introduction of MA has overcome the disadvantage of the low polymer surface energy, improving their surface hydrophilicity and adhesion with polar polymers, inorganic filler, and glass fibers [4].

J. Manuf. Mater. Process. 2019, 3, 37; doi:10.3390/jmmp3020037 www.mdpi.com/journal/jmmp J. Manuf. Mater. Process. 2019, 3, 37 2 of 11

The compatibilizing agent acts as an organic surfactant, and it is located on the interface between two incompatible polymer phases, where it reduces interfacial tension and promotes adhesion between the phases. The compatibilizer plays an important role in controlling the dispersed phase size in a blend produced in a conventional melt process [3], as the phase becomes smaller and more uniform, there is an increase in the blend stability and, consequently, there is an increase in the mechanical properties. A variety of substances can be used as compatibilizers for polymer blends, but it is necessary to have structural characteristics of both polymers. For example, block and graft copolymers are commonly used as compatibilizing agents in small percentages in polymer blends, while functionalized polymers are also used as compatibilizing agents [5]. Some works can be found in the literature proposing the use of MA grafting thermoplastic polymers. Montanheiro et al. [1] prepared a compatibilizer by grafting maleic anhydride to poly(hydroxybutyrate-co-hydroxyvalerate) chains by reactive processing using mechanical mixing, as an alternative way to produce polymers with low molecular weight without prejudicing their thermal properties. Hezavehi et al. [6] studied the properties of polypropylene and poly(trimethylene terephthalate) (PP/PTT) blends using maleic anhydride grafted polypropylene (MAPP) as compatibilizer, and the results showed improved adhesion between the phases with the addition of the compatibilizer. Passador et al. [7] studied the influence of two compatibilizers: high-density polyethylene grafted maleic anhydride (HDPE-g-MA), low-linear-density polyethylene grafted maleic anhydride (LLDPE-g-MA), and a mixture of HDPE-g-MA and LLDPE-g-MA on the properties of HDPE/LLDPE/organoclay nanocomposites. The compatibilized nanocomposites with LLDPE-g-MA or a mixture of 50/50 wt% of HDPE-g-MA and LLDPE-g-MA better exhibited the nanoclay’s dispersion and distribution with stronger interactions between the matrix and the nanoclay. Xue et al. [8] studied the crystallization behavior of poly(trimethylene terephthalate)/polypropylene (PTT/PP) blends with the addition of polypropylene grafted maleic anhydride (PP-g-MA) as compatibilizer. The shift of PTT’s crystallization temperature was larger than that of the PP, suggesting that the addition of PP-g-MA had a greater effect on PTT’s crystallization than on PP due to the reaction between MA and PTT. The current work suggests the development of a new compatibilizing agent, poly(trimethylene terephthalate) grafted maleic anhydride (PTT-g-MA), obtained by a reactive extrusion process. Poly(trimethylene terephthalate) is a polyester belonging to the PET (poly(ethylene terephthalate)) and PBT (poly(butylene terephthalate)) family, but with different physical properties. Due to the odd-numbered methylene groups in its chain, PTT has higher elastic recovery than PET and PBT [9]. PTT can be blended with other polymers in order to develop materials with properties better than those of the original polymers, enhancing the final properties of the material. For instance, Huang [10] prepared PTT/polystyrene (PS) blends, and noted an improvement in tensile strength of the blends compatibilized with styrene-glycidyl methacrylate (SG), which can be attributed to improvement in the interfacial adhesion. There are few reports in the literature about the melting grafting of PTT-g-MA. Wang and Sun [11] prepared PTT-g-MA from melt reaction to improve the compatibility of blends of cellulose acetate butyrate (CAB) and PTT. The reactive melt mixing was conducted by mixing PTT, MA, and initiator (2,5-dimethyl-2,5-di(tert-butylperoxy) hexane at 240 ◦C for 5 min at a speed of 100 rpm. They concluded that this compatibilizing agent significantly reduced the phases’ sizes, generating strong interfacial interactions and improved mechanical properties. Wu and Liao [12] prepared a mixture of phenol/tetrachloroethane solution (60:40 v/v), MA, and benzoyl peroxide in four equal portions at 2-min intervals to molten PTT to allow grafting to take place. The authors used PTT-g-MA to improve the compatibility and dispersibility of multi-walled carbon nanotubes (MWCNT) within PTT matrix. In this work, a new route is proposed to obtain PTT-g-MA by reactive extrusion using MA, with benzoyl peroxide as the initiator. Thus, in a single extrusion step, it was possible to obtain a compatibilizing agent with low viscosity and without loss of the thermal properties. The effectiveness of the obtained compatibilizing agent was verified in a PTT/ABS (acrylonitrile butadiene styrene) blend through the analysis of morphology. J. Manuf. Mater. Process. 2019, 3, 37 3 of 11

2. Materials and Methods

2.1. Materials Poly(trimethylene terephthalate) (PTT), with speciﬁcation Corterra 200, was supplied by Shell Chemicals (Montreal, Canada) with a density of 1.35 g/cm3. Maleic anhydride (MA) with 99% purity was supplied by Sigma-Aldrich (Saint Louis, MO. USA), and the benzoyl peroxide (BPO) initiator was supplied by Dinâmica Química Contemporânea (Indaiatuba, Brazil). Both components were of commercial grade and were used as received. Acrylonitrile butadiene styrene (ABS), with speciﬁcation MG38 - CYCOLAC, was supplied by SABIC Innovative Plastics (Al Jubail, Saudi Arabia) with a density of 1.04 g/cm3.

2.2. Reactive Extrusion of PTT-g-MA

Before the reactive processing, PTT was dried at 80 ◦C for at least 12 h in a vacuum oven to minimize the hydrolytic degradation during processing. The grafting reaction of MA into PTT chains was carried out by reactive extrusion in a co-rotational twin-screw extruder, AX Plásticos, model AX16:40DR (L/D = 40, D = 16 mm), with a temperature proﬁle of 230/235/235/240/240 ◦C from the ﬁrst section to the die, operating at a screw rotation speed of 100 rpm and feeding of 30 rpm. PTT-g-MA was produced with the addition of 96 wt% of PTT, 2 wt% of MA, and 2 wt% of BPO, which was used as the initiator. All components were thoroughly mixed in a bag before extrusion. The extrudate was pelletized and then dried (80 ◦C for at least 12 h in a vacuum oven) before analysis. The PTT was processed under the same conditions to compare the analyses, and it was labeled as extruded PTT for the polymer after the extrusion process, and neat PTT for the polymer before the extrusion process.

2.3. Characterization of the PTT-g-MA

2.3.1. FTIR Spectroscopy The chemical structures of the MA, PTT, and PTT-g-MA were analyzed by Fourier transform infrared (FTIR) spectroscopy. The samples were analyzed using the PerkinElmer Frontier with a 1 universal attenuated total reﬂectance (UATR) sensor accessory in the scan range 550–4000 cm− .

2.3.2. Rheological Characterization The rheological behavior of neat PTT (before extrusion process), extruded PTT (after the extrusion process), and PTT-g-MA was evaluated through viscosity tests as a function of the shear rate (permanent regime) in an inert nitrogen atmosphere at a temperature of 230 ◦C using a controlled-voltage AR G2 rheometer from TA Instruments. The test geometry was parallel plate, with a plate diameter of 25 mm and a distance between the plates of 1 mm. The deformation applied in each test was deﬁned according to the material, ensuring that the tests were conducted in their regions of linear viscoelastic behavior.

2.3.3. Diﬀerential Scanning Calorimetry (DSC) The thermal properties of neat PTT, extruded PTT, and PTT-g-MA such as glass transition temperature (Tg), melting temperature™, and crystallization temperature (Tc) were analyzed by DSC. ® The DSC tests were performed using Netzsch 204 F1 Phoenix equipment under N2 atmosphere. Approximately 10 mg of each sample was sealed in an aluminum DSC pan and heated at 10 ◦C/min under nitrogen atmosphere from 30 to 250 ◦C kept for 3 min to eliminate the heat history and then cooled to 0 ◦C. The samples were reheated to 250 ◦C. The crystallinity degree (Xc) was calculated using Equation (1): ∆Hm Xc (%) = 100, (1) W ∆H◦ · · J. Manuf. Mater. Process. 2019, 3, 37 4 of 11

J. Manuf. Mater. Process. 2019, 3, x FOR PEER REVIEW 4 of 13 where ∆Hm is the total melting enthalpy, W is the weight fraction of PTT in the sample, and ∆H◦ is the heat2.3.4. of Thermogravimetric fusion of 100% crystalline Analysis PTT, (TGA) which was taken as 146 J/g [13].

2.3.4.The Thermogravimetric thermal behaviors Analysis of neat (TGA) PTT, extruded PTT, and PTT-g-MA were analyzed by thermogravimetric analysis (TGA) using Netzsch 209 F1 Iris® equipment. Samples were heated from The thermal behaviors of neat PTT,extruded PTT,and PTT-g-MA were analyzed by thermogravimetric room temperature to 800 °C with a heating rate of 10 °C min−1, under nitrogen atmosphere. analysis (TGA) using Netzsch 209 F1 Iris®equipment. Samples were heated from room temperature to 1 8002.3.5.◦C Verification with a heating of the rate effectiveness of 10 ◦C min of− the, under PTT-g-MA nitrogen in atmosphere.the phase formation of the PTT/ABS blend 2.3.5. Verification of the effectiveness of the PTT-g-MA in the phase formation of the PTT/ABS blend The PTT/ABS (60/40) and PTT/PTT-g-MA/ABS (57/3/40) blends were prepared in a co-rotational The PTT/ABS (60/40) and PTT/PTT-g-MA/ABS (57/3/40) blends were prepared in a co-rotational twin-screw extruder, AX Plásticos, model AX16:40DR (L/D = 40, D = 16 mm), with temperature profile twin-screw extruder, AX Plásticos, model AX16:40DR (L/D = 40, D = 16 mm), with temperature profile of 230/235/240/240/240 °C from the first section to the die, operating at screw rotation speed of 120 of 230/235/240/240/240 ◦C from the first section to the die, operating at screw rotation speed of 120 rpm rpm and feeding of 30 rpm. Samples were prepared in a mini injector (Thermo Scientific Haake and feeding of 30 rpm. Samples were prepared in a mini injector (Thermo Scientific Haake MiniLab) MiniLab) with an average temperature of 260 °C. The fracture surfaces of the blends were coated with with an average temperature of 260 ◦C. The fracture surfaces of the blends were coated with a thin a thin layer of gold and were analyzed by scanning electron microscopy (SEM) FEI Nova NanoSEM layer of gold and were analyzed by scanning electron microscopy (SEM) FEI Nova NanoSEM 450, 450, operating at 2 kV. operating at 2 kV.

3.3. ResultsResults andand DiscussionDiscussion

3.1.3.1. GraftingGrafting MechanismMechanism BetweenBetween PTTPTT andand MAMA FigureFigure1 1 illustrates illustrates the the reaction reaction mechanism mechanism proposed proposed for for MA MA grafting grafting PTT PTT chains. chains. The The grafting grafting reactionreaction ofof PTTPTT occursoccurs inin threethree stages:stages: (1)(1) BenzoylBenzoyl peroxideperoxide (BPO)(BPO) breaksbreaks intointo twotwo alkoxyalkoxy radicalsradicals uponupon heating.heating. (2)(2) TheThe radicalradical thenthen extractsextracts hydrogenhydrogen atomsatoms fromfrom thethe backbonebackbone ofof thethe moltenmolten polymerpolymer toto generategenerate the the macromolecular macromolecular radicals—alkyl radicals—alkyl radical. radical. (3) (3) The The alkyl alkyl radical radical initiates initiates the the grafting grafting of the of vinylthe vinyl groups groups of maleic of maleic anhydride anhydride (MA), producing(MA), producing the compatibilizer the compatibilizer PTT-g-MA PTT- [11g].-MA These [11]. reaction These stepsreaction occur steps simultaneously occur simultaneously in the extruder. in the extruder The reactions. The reactions start at thestart feed at the zone, feed supported zone, supported by the temperatureby the temperature of the equipment of the equipment and by theand friction by the offr theiction particles of the (viscousparticles heating)(viscous andheating) continue and throughcontinue the through plastiﬁcation the plastification zone. zone.

Figure 1. Reaction mechanism of maleic anhydride (MA) in poly(trimethylene terephthalate) (PTT) Figure 1. Reaction mechanism of maleic anhydride (MA) in poly(trimethylene terephthalate) (PTT) chains in the presence of benzoyl peroxide (BPO). PTT-g-MA: MA grafted with PTT. chains in the presence of benzoyl peroxide (BPO). PTT-g-MA: MA grafted with PTT.

3.2. FTIR Spectroscopy

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J. Manuf. Mater. Process. 2019, 3, x FOR PEER REVIEW 5 of 13 3.2. FTIR Spectroscopy In order to confirm the grafting of MA onto PTT chains, the samples were characterized by FTIR spectroscopy,In order as tothis conﬁrm technique the graftingenables the of MA determi ontonation PTT chains, of the themolecular samples composition were characterized and structure by FTIR of solid,spectroscopy, liquid, and as this even technique gaseous enables samples the [14]. determination The spectra of in the the molecular region of composition 550–4000 cm and−1 of structure MA, 1 extrudedof solid, PTT, liquid, and andPTT- eveng-MA gaseous are shown samples in Figure [14]. 2, The even spectra as a zoomed-in in the region view of of 550–4000 the region cm between− of MA, 1600extruded and 1900 PTT, cm and−1, allowing PTT-g-MA the are identification shown in Figure of the2, evenpeaks as resulting a zoomed-in from view the grafting of the region reaction. between It 1 was1600 observed and 1900 that cm all− ,the allowing characteristic the identiﬁcation bands of extruded of the peaks PTT resulting could also from be the observed grafting in reaction. the PTT- Itg was- MAobserved spectrum. that The all intense the characteristic band at 1710 bands cm−1 ofwas extruded related PTTto the could stretch also of be the observed carbonyl in group the PTT- (C=O)g-MA 1 characteristicspectrum. of The PTT. intense Vibrational band at bands 1710 cmof −PTTwas are related associated to the with stretch the terephthalate of the carbonyl ring group and (Cthe= O) trimethylenecharacteristic group of PTT.[15]. VibrationalThe band at bands1245 cm of−1 PTT was areattributed associated to the with ester the group, terephthalate whereas ring the band and the 1 at 2958trimethylene cm−1 was group attributed [15]. to The aromatic band at CH 1245 groups, cm− was both attributed resulting tofrom the the ester terephthalate group, whereas groups the band[16]. at 1 The2958 wavenumber cm− was attributedat 723 cm− to1 corresponds aromatic CH to groups, coupled both vibration resulting of fromthe carbonyl the terephthalate out-of-plane groups ring [16 ]. 1 deformationThe wavenumber of the phenyl at 723 group cm− [17].corresponds to coupled vibration of the carbonyl out-of-plane ring deformation of the phenyl group [17].

Figure 2. FTIR spectra of maleic anhydride, PTT-g-MA, and extruded PTT (left) and zoom at region Figure 2. FTIR spectra of maleic1 anhydride, PTT-g-MA, and extruded PTT (left) and zoom at region between 1900–1600 cm− (right). between 1900 – 1600 cm-1 (right). It is expected that the reactions between OH, COOH, and ester groups from MA modified the PTT chainsIt is expected [18]. In this that way, the thereactions MA grafting between on OH, PTT COOH, chains was and confirmed ester groups by thefrom appearance MA modified of two the new PTT chains [18]. In this way, the MA grafting on PTT chains was1 confirmed by the appearance of two absorption bands in the region between 1600 and 1900 cm− , highlighted in Figure2. The two new new absorption bands in the region between 16001 and 1900 cm−1, highlighted in Figure 2. The two bands, one at 1844 and the other at 1793 cm− , are related to the symmetric and asymmetric stretching −1 newof bands, the carbonyl one at groups 1844 and from the the other grafted at 1793 MA, presentcm , are in related the PTT- tog -MAthe symmetric structure [11and,12 asymmetric]. A new band stretching of the1 carbonyl groups from the grafted MA, present in the PTT-g-MA structure [11,12]. A at 900 cm− was also observed on the PTT-g-MA spectrum, indicating the stretching of anhydride −1 newCO band [19] at and 900 confirming cm was thealso reaction observed between on the PTT PTT- andg-MA MA. spectrum, indicating the stretching of anhydride CO [19] and confirming the reaction between PTT and MA. 3.3. Rheological analysis 3.3. Rheological analysis The rheological analysis was measured in order to characterize the melt viscoelasticity of PTT beforeThe rheological and after extrusion analysis process was measured (neat PTT in and order extruded to characterize PTT, respectively), the melt viscoelasticity and PTT-g-MA. of Figure PTT 3 beforeshows and the after viscosity extrusion dependence process (neat concerning PTT and theextruded shear PTT, rate ofrespectively), the samples and at 230PTT-◦C.g-MA. The Figure neat PTT 3 showspresented the viscosity initial viscosity dependence (η0) value concerning around the 446 shea Pa.sr wlilerate of extruded the samples PTT showedat 230 °C.η0 Thearound neat 370 PTT Pa.s 0 0 1 presentedand PTT- initialg-MA viscosity around (η 330) value Pa.s. around The η0 446was Pa.s measured wlile extruded at the shear PTT rateshowed of 0.01 η around s− . The 370 value Pa.s of 0 −1 0 andη 0PTT-cang be-MA correlated around 330 with Pa.s. the The molar η was mass measured of the material, at the shear since rate smaller of 0.01 molar s . The masses value are of related η can to be lowercorrelated melt with viscosity. the molar It is noted mass that of the the material, extrusion since process smaller decreases molar the massesη0 of extruded are related PTT, to relatedlower to meltchain viscosity. breaking, It is however,noted that this the changeextrusion isnot process significant. decreases Comparing the η0 of extruded PTT-g-MA PTT, with related neat PTT, to chain a more breaking,significant however, decrease this can change be observed, is not which significant. may be Comparing related to chain PTT- breakingg-MA with during neat processing, PTT, a more as well significantas breaking decrease of chains canresulting be observed, from which graphitization may be reactions,related to sincechain this breaking process during is an exothermic processing, process as welland as canbreaking increase of chains the local resulting temperature, from graphitization contributing to reactions, the breaking since of this chains. process However, is an exothermic the viscosity processof neat and PTT can and increase extruded the PTT local are temperature, nearly unchanged contributing with increasing to the breaking shear rate, of chains. showing However, characteristics the viscosityof a Newtonian of neat PTT fluid. and Extruded extruded PTT PTT had are a nearly lower viscosity,unchanged comparing with increasing to PTT beforeshear extrusion,rate, showing due to characteristics of a Newtonian fluid. Extruded PTT had a lower viscosity, comparing to PTT before extrusion, due to chain breakage during the processing. It can also be observed that at low shear rate

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J. Manuf. Mater. Process. 2019, 3, x FOR PEER REVIEW 6 of 13 chain breakage during the processing. It can also be observed that at low shear rate range, the viscosity range,of PTT- theg-MA viscosity did not of change, PTT-g-MA while did at highernot change, shear while rate, the at viscosityhigher shear decreases rate, the sharply viscosity with decreases increasing sharplyshearing with rate, increasing exhibiting shearing pseudoplastic rate, exhibiting behavior, i.e.,pseudoplastic viscosity decreases behavior, gradually i.e., viscosity with increasingdecreases graduallyshear rate, with due toincreasing the disentanglements shear rate, due between to the thedisentanglements molecular chains, between occurred the duringmolecular the reactivechains, occurredprocessing. during This featurethe reactive can be processing. essential for This the compatibilizationfeature can be essential process. for Since the thiscompatibilization compatibilizer process.agent has Since a lower this viscositycompatibilizer in the melt,agent it has may a interact lower viscosity more intensively in the melt, with theit may other interact components more intensivelyof the mixture with during the other processing. components However, of the mixtur it is necessarye during to processing. know the thermalHowever, parameters, it is necessary so that to knowpremature the thermal degradation parameters, of this so component that premature does not degradation occur. of this component does not occur.

Figure 3. Viscosity curve as a function of the shear rate obtained by deformational rheometry of PTT, Figureextruded 3. Viscosity PTT and curve PTT-g-MA. as a function of the shear rate obtained by deformational rheometry of PTT, extruded PTT and PTT-g-MA. 3.4. Thermal Analysis: DSC and TGA 3.4. ThermalThe thermal Analysis: properties DSC and of TGA neat PTT, extruded PTT, and PTT-g-MA were analyzed by DSC. The first heating,The thermal cooling, properties and the second of neat heating PTT, extruded scans are PTT, shown and inPTT- Figureg-MA4 a–c,were respectively. analyzed by TheDSC. glass The firsttransition heating, temperature cooling, and (Tg), the second melting heating temperature scans are (Tm), shown melting in Figure enthalpy 4 a,b,c, respectively. (∆Hm), crystallization The glass transitiontemperature temperature (Tc), and the (Tg), degree melting of crystallinity temperature (Xc) (Tm), are described melting inenthalpy Table1. (ΔHm), crystallization temperatureIn Figure (Tc),4a it and is observed the degree that of neither crystallinity the extrusion (Xc) are process described nor in the Table incorporation 1. of MA changed the TmIn Figure of neat 4a PTT, it is which observed was aroundthat neither 227 ◦ C.the The extrusion Tg of PTT process is diffi norcult the to detectincorporation by heating of MA PTT changedwith a linear the Tm heating of neat rate PTT, [20 which,21], and was it around depends 227 on °C. the The polymer’s Tg of PTT crystallinity. is difficult Into thisdetect work, by heating careful PTTanalysis with showed a linear that heating the Tg rate was [20,21], obtained and only it de bypends the first on heating the polymer’s scan (Figure crys4tallinity.a). The Tg In ofthis neat work, PTT carefulwas 67.2 analysis◦C. Tg showed was not that evident the Tg for was extruded obtained PTT only or PTT-by theg-MA first heating using the scan DSC (Figure technique. 4a). The Because Tg of neatTg corresponds PTT was 67.2 to °C. variations Tg was in not the evident heat capacity for extruded due to PTT chain or mobility, PTT-g-MA it can using be concludedthe DSC technique. that after Becauseextrusion Tg processing, corresponds the to heat variations capacity in became the heat smaller capacity compared due to tochain neat mobility, PTT [22]. it Moreover, can be concluded the chain thatelasticity after isextrusion an important processing, factor thatthe influencesheat capacity in thebecame Tg—once smaller there compared are large to side neat groups PTT in[22]. the Moreover,backbone ofthe the chain polymer, elasticity the chainis an elasticityimportant of fact theor polymer that influences decreases in [23the]. Tg—once there are large side groupsFrom thein the cooling backbone scans of inthe Figure polymer,4b, itthe can chain be observedelasticity of that the the polymer addition decreases of MA [23]. into PTT chainsFrom decreased the cooling the scans Tc from in Figure 180 ◦C 4b, in it extruded can be ob PTTserved to 173that◦ theC in addition the PTT- ofg MA-MA into compatibilizer. PTT chains decreasedThe crystallization the Tc from peak 180 for °C extruded in extruded PTT PTT was to narrower 173 °C thanin the those PTT- ofg-MA neat compatibilizer. PTT or PTT-g -MA,The crystallizationindicating the peak formation for extruded of crystals PTT with was more narrower homogeneous than those size of neat distribution PTT or PTT- and allowingg-MA, indicating polymer thecrystal formation organization. of crystals Zhang with et more al. [24 homogeneous] compared raw size PTT distribution resin to kneaded and allowing PTT and polymer observed crystal that organization.Tc values became Zhang higher et al. [24] and compared the crystallization raw PTT re peaksin to became kneaded much PTT narrower,and observed meaning that Tc that values the becamecrystallization higher and rate the of PTTcrystallization was great peak improved became through much narrower, the extrusion meaning process. that Thisthe crystallization behavior was rate of PTT was great improved through the extrusion process. This behavior was confirmed by the degree of crystallinity, which considerably increased compared to the neat and extruded PTT. Tm showed no significant changes during the second heating scan (Figure 4c), and it was not possible to observe the Tg. The glass transition temperature is defined as the temperature at which

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J. Manuf. Mater. Process. 2019, 3, x FOR PEER REVIEW 8 of 13 conﬁrmed by the degree of crystallinity, which considerably increased compared to the neat and extruded PTT.

Figure 4. DSC thermograms for neat PTT, extruded PTT, and PTT-g-MA: (a) ﬁrst heating, (b) cooling, and (c) second heating.

Figure 4. DSC thermograms for neat PTT, extruded PTT, and PTT-g-MA: (a) first heating, (b) cooling, and (c) second heating.

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Table 1. Thermal properties obtained by DSC analysis.

First Heating

Sample Tg (◦C) Tm1 (◦C) ∆Hm1 (J/g) Xc1 (%) Neat PTT 67.2 227 64.3 44.1 Extruded PTT - 227 55.4 37.9 PTT-g-MA - 227 59.5 42.4 Cooling

Sample Tc (◦C) Neat PTT 170 Extruded PTT 180 PTT-g-MA 173 Second Heating

Sample Tm2 (◦C) ∆Hm2 (J/g) Xc2 (%) Neat PTT 228 64.0 43.8 Extruded PTT 227 60.6 41.5 PTT-g-MA 227 64.2 45.8

Tm showed no significant changes during the second heating scan (Figure4c), and it was not possible to observe the Tg. The glass transition temperature is defined as the temperature at which the amorphous phase becomes mobile, and a change in the heat capacity is observed with this event. In the second heating, it was not possible to determine the Tg, probably due to an extensive broadening of the change in baseline, meaning that the amorphous phase was smaller in this case compared to the first heating scan. This behavior was justified, because there was previous controlled chain crystallization in the cooling scan [22]. PTT is a typical semicrystalline polymer, and grafting reaction may cause changes in its structure. It is possible to observe that MA did not inhibit the crystal formation process, but increased the degree of crystallinity in the second heating, as observed in Table1.X c1 and Xc2 for neat PTT were very close. However, the Xc2 was higher than Xc1 for both extruded PTT and PTT-g-MA because, during the controlled cooling in the DSC analysis, the polymer chain was able to organize and form more crystals. Xc1 reflects the crystals formed during the material processing with no controlled cooling rate. The thermal properties of neat PTT, extruded PTT, and PTT-g-MA were also analyzed by TGA. Figure5 shows that the samples had similar thermal decomposition patterns, and the thermal degradation occurred in a single-step process. The values of initial degradation temperature (Tonset), the degradation temperature of 10% and 50% of weight loss, and the maximum weight-loss rate temperature (Tmax) obtained from the first derivative of the curve are shown in Table2. Extruded PTT polymer underwent thermal degradation, Tonset, at 387 ◦C, the neat PTT at 388 ◦C, and PTT-g-MA at 378 ◦C. Grafting MA into PTT chains did not vary the degradation pattern, since T10% and T50% underwent minor shifts but remained very close for PTT-g-MA, neat PTT, and extruded PTT. The Tmax values were also almost the same for all of them, indicating that MA did not change the maximum weight loss degradation behavior of extruded PTT. In general, it can be said that the addition of MA did not alter the thermal stability of PTT polymer. Thus, the compatibilizing agent was not degraded during its processing, according to the TGA curves.

Table 2. Initial thermal degradation temperature (Tonset), temperatures at weight loss of 10% and50%, and maximum weight loss rate temperature (Tmax).

Sample Tonset (◦C) T10% (◦C) T50% (◦C) Tmax (◦C) Extruded PTT 387 385 409 407 Neat PTT 388 389 411 408 PTT-g-MA 378 379 405 405 J. Manuf. Mater. Process. 2019, 3, x FOR PEER REVIEW 10 of 13

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Figure 5. Thermal degradation behavior of neat PTT, extruded PTT, and PTT-g-MA.

3.5. EﬀectivenessFigure of PTT-g-MA 5. Thermal as degradation a Compatibilizer behavior for of PTT ne/atABS PTT, Blend extruded PTT, and PTT-g-MA.

FigureTable6 2. shows Initial thermal the e ff ectdegradation of adding temperature PTT-g-MA (T inonset the), temperatures PTT/ABS blend. at weight To loss show of the10% evidenceand50%, of the enhancementand maximum properties weight loss of rate PTT temperature using PTT- (Tgmax-MA,). we prepared a PTT/ABS (60/40) blend and a PTT/PTT-g-MA/ABS (57/3/40) blend using the extrusion process. The addition of a compatibilizer in an incompatible blendSample usually resultsTonset in (°C) finer andT10% more (°C) stable T50% morphology,(°C) Tmax (°C) better processability, and improved mechanicalExtruded properties. PTT Through387 SEM385 analysis of409 the fracture407 surface, it was possible to note that the morphologiesNeat PTT of the blends388 with and389 without the411 compatibilizing 408 agent were quite different. In Figure6aPTT- it is possibleg-MA to observe378 the379 presence of405 ABS domains405 in the PTT matrix. The domains are marked in the image for better visualization. The domain consisted of a matrix of3.5. styrene Rheological acrylonitrile Analysis (SAN) and polybutadiene (PB) dispersed in the SAN matrix. As seen in FigureThe6b, the rheological addition ofanalysis 3 wt% was of PTT- conductedg-MA in in the order system to characterize reduced the particlethe melt size viscoelasticity of these domains. of PTT Thebefore compatibilizer and after the acted extrusion on the process morphological (neat PTT formation and extruded of the PTT, PTT respectively),/ABS blends. and During to characterize the melt mixing,PTT-g-MA. the flow Figure of the 6 shows extruder the made viscosity the compatibilizing dependence co agentncerning go tothe the shea extremityr rate of of the the samples PTT, causing at 230 a°C. gradient The neat in the PTT interfacial presented tension an initial along viscosity the surface (η0) value of the around ABS phase, 446 Pa.s, favoring extruded the “tip PTT streaming” showed η0 mechanism.around 370 Pa.s, In this while way, PTT- theg ABS-MA phaseshowed coalescence η0 around was330 Pa.s. suppressed, The η0 was and measured this was at caused the shear by the rate immobilizationof 0.01 s−1. The ofvalue the of interface η0 can be due correlated to the interfacial with the tensionmolar mass gradient of the or material, elastic repulsion since smaller resulting molar frommasses the are compression related to oflower the melt chains viscosity. of the compatibilizer. It is noted that Asthea extrusio result,n there process was decreased a decrease the in theη0 of sizeextruded of the secondPTT, related phase to (ABS). chain It breaking, is thus possible but this to change conclude was that not the significant. compatibilizing Comparing agent PTT- actedg-MA in thewith suppression neat PTT, ofa ABSmore phase significant coalescence decrease during was theobserved, melt processing, which may reducing be related the phaseto chain size breaking of the ABSduring in the processing, PTT/PTT- gas-MA well/ABS as breaking (57/3/40) of blend. chains Thus, resulting with thesefrom results,graphitization it is possible reactions, to check since the this effprocessectiveness is an of exothermic PTT-g-MA process as a compatibilizing and can increase agent the for local the temperature, PTT/ABS blends. contributing to the breaking of chains. However, the viscosities of neat PTT and extruded PTT were nearly unchanged with increasing shear rate, showing the characteristics of a Newtonian fluid. Extruded PTT had a lower viscosity compared to PTT before extrusion due to chain breakage during the processing. It was also observed that the viscosity of PTT-g-MA did not change at low shear rates, while the viscosity decreased sharply with increased shearing rate at higher shear rates, exhibiting pseudoplastic behavior (i.e., viscosity decreased gradually with increasing shear rate due to the disentanglements

J. Manuf. Mater. Process. 2019, 3, x FOR PEER REVIEW 11 of 13 between the molecular chains occurring during the reactive processing). This feature could be essential for the compatibilization process. Since this compatibilizer has a lower viscosity in the melt, it may interact more intensively with the other components of the mixture during processing. However, it is necessary to know the thermal parameters so that premature degradation of this component does not occur.

3.6. Effectiveness of PTT-g-MA as a Compatibilizer for PTT/ABS Blend Figure 6 shows the effect of adding PTT-g-MA in the PTT/ABS blend. To show the evidence of the enhancement properties of PTT using PTT-g-MA, we prepared a PTT/ABS (60/40) blend and a PTT/PTT-g-MA/ABS (57/3/40) blend using the extrusion process. The addition of a compatibilizer in an incompatible blend usually results in finer and more stable morphology, better processability, and improved mechanical properties. Through SEM analysis of the fracture surface, it was possible to note that the morphologies of the blends with and without the compatibilizing agent were quite different. In Figure 6a it is possible to observe the presence of ABS domains in the PTT matrix. The domains are marked in the image for better visualization. The domain consisted of a matrix of styrene acrylonitrile (SAN) and polybutadiene (PB) dispersed in the SAN matrix. As seen in Figure 6b, the addition of 3 wt% of PTT-g-MA in the system reduced the particle size of these domains. The compatibilizer acted on the morphological formation of the PTT/ABS blends. During the melt mixing, the flow of the extruder made the compatibilizing agent go to the extremity of the PTT, causing a gradient in the interfacial tension along the surface of the ABS phase, favoring the “tip streaming” mechanism. In this way, the ABS phase coalescence was suppressed, and this was caused by the immobilization of the interface due to the interfacial tension gradient or elastic repulsion resulting from the compression of the chains of the compatibilizer. As a result, there was a decrease in the size of the second phase (ABS). It is thus possible to conclude that the compatibilizing agent acted in the suppression of ABS phase coalescence during the melt processing, reducing the phase size of the ABS in the PTT/PTT-g-MA/ABS (57/3/40) blend. Thus, with these results, it is possible to check the J. Manuf. Mater. Process. 2019, 3, 37 10 of 11 effectiveness of PTT-g-MA as a compatibilizing agent for the PTT/ABS blends.

Figure 6. SEM images of PTT/ABS blends (A) without and (B) with compatibilizing agent. Figure 6. SEM images of PTT/ABS blends (A) without and (B) with compatibilizing agent. 4. Conclusions 4. ConclusionThis paper proposed a new route to produce a compatibilizing agent by grafting maleic anhydride (MA)This into poly(trimethylenepaper proposed terephthalate)a new route (PTT)to produce chains bya compatibilizing reactive processing. agent The by poly(trimethylene grafting maleic terephthalate)anhydride (MA) grafted into maleic poly(trimethylene anhydride (PTT- terephthalg-MA) showedate) (PTT) lower chains viscosity by comparedreactive processing. to neat PTT andThe extrudedpoly(trimethylene PTT, and theterephthalate) thermal analysis grafted results maleic showed anhydride that MA (PTT- didg not-MA) have showed a significant lower impact viscosity on thecompared thermal to degradation neat PTT and of PTT. extruded Thus, PTT, the PTT- andg -MAthe thermal showed analysis good thermal results and showed rheological that MA properties, did not makinghave a significant it an excellent impact candidate on the for thermal use as degradation a compatibilizer of PTT. in polymer Thus, the blends PTT- andg-MA nanocomposites showed good usingthermal PTT and as rheological a polymer properties, matrix. The making effectiveness it an excellent of this compatibilizercandidate for use was as tested a compatibilizer on PTT/ABS in blends,polymer where blends the and addition nanocomposites of PTT-g-MA using decreased PTT as thea polymer size of thematrix. ABS The phase effectiveness compared of to thethis non-compatibilizedcompatibilizer was tested blend. on PTT/ABS blends, where the addition of PTT-g-MA decreased the size of the ABS phase compared to the non-compatibilized blend. Author Contributions: Conceptualization, N.F.B., H.M.Z., T.L.A.M. and F.R.P.; Data curation, N.F.B., H.M.Z., T.L.A.M. and F.R.P.; Methodology, N.F.B., H.M.Z., T.L.A.M. and F.R.P.; Supervision, F.R.P.; Validation, F.R.P.; Visualization, F.R.P.; Writing—original draft, N.F.B., T.L.A.M. and F.R.P.; Writing—review & editing, N.F.B., T.L.A.M. and F.R.P. Funding: The authors would like to thank the Brazilian Funding Institutions CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil - 001), CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico – Process 405675/2018-6 and 310196/2018-3), and FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo - Process 2016/19978-9 and 2017/24873-4) for financial support. And NSF grant #1126100. Acknowledgments: The authors would like to thank the SEM images which was performed in part at the Biosciences Electron Microscopy Facility of the University of Connecticut (USA). Conflicts of Interest: The authors declare no conflict of interest.

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