Post-Consumer Polyethylene Terephthalate and Polyamide 66 Blends and Corresponding Short Glass Fiber Reinforced Composites

Home , Polyamide

Post-consumer Polyethylene Terephthalate and Polyamide 66 Blends and Corresponding Short Glass Fiber Reinforced Composites

Marcus Vinicius Novelloa, Lilian Gasparelli Carreiraa, Leonardo Bresciani Cantob*

aInstitute of Macromolecules – IMA, Federal University of Rio de Janeiro – UFRJ, CEP 21941-598, Rio de Janeiro, RJ, Brazil bMaterials Engineering Department – DEMa, Federal University of São Carlos – UFSCar, CEP 13565-905, São Carlos, SP, Brazil

Received: March 14, 2014; Revised: August 2, 2014

Blends of bottle-grade post-consumer polyethylene terephthalate (PET) and virgin polyamide 66 (PA66), over the complete composition range, and corresponding short glass fiber (SGF) reinforced composites were investigated. These materials were compounded in a twin-screw extruder and injection molded as standard specimens. Morphological investigation of the composites revealed that the short glass fibers have a good size distribution and are homogenously dispersed within a polymeric matrix. The PET/PA66/SGF composites showed good mechanical performance in flexural, tensile and impact tests demonstrating that the addition of SGFs to PET/PA66 blends is an interesting approach to obtaining new thermoplastic composites. In addition, this represents a potential application for post-consumer PET, an abundant and cheap material, in the well-established market of PA66/SGF composites, which are widely used in technical parts requiring high mechanical and thermal properties.

Keywords: PET, PA66, nylon 66, short glass fiber, composite, blend

1. Introduction Polymer blends reinforced with short glass fibers (SGFs) Likewise, polyamide 66 (PA66) has been compounded have received considerable attention from academic and with SGFs to produce thermoplastic composites that are industrial researchers in recent years because these materials widely used in technical parts requiring high mechanical can combine the properties of both blends and composites. and thermal properties13,14. Success in attaining the target properties of these materials The aim of this study was to prepare blends of is dependent on several morphological aspects including bottle-grade post-consumer PET and virgin polyamide the polymer blend morphology, the glass fiber size and 66 (PA66), over the complete composition range, as well distribution within the polymer blend and the adhesion as composites of these blends reinforced with 30 wt% of 1 between the glass fiber and the polymeric matrix . SGFs (PET/PA66/SGF). The microstructure, thermal and The blending of bottle-grade post-consumer mechanical properties of the samples obtained were then polyethylene terephthalate (PET) with suitable polymers investigated. The use of post-consumer PET in PET/PA66/ and/or compounding with SGFs can be used to attain SGF composites is an interesting approach to incorporate improved properties of the post-consumer PET and broaden this abundant and cheap material into the well-established the possibilities for its use as an engineering thermoplastic. market of PA66/SGF composites. Cheng et al.2 studied SGF-reinforcement in blends of post-consumer PET and ethylene-butyl acrylate-glycidyl methacrylate (EBA-GMA) copolymer and of post-consumer 2. Experimental PET and maleic anhydride grafted polyethylene-octene elastomer (POE-MAH). Karsli et al.3 investigated the effects 2.1 Materials of SGF-reinforcement on the properties of post-consumer The PET was supplied as bottle-grade flakes by the polyethylene terephthalate/poly(ethylene naphthalate) company Repet (Brazil) and had an intrinsic viscosity (PET/PEN) blends. Composites of post-consumer PET of 0.74 dL g–1 (ASTM D 4603[15]). The PET flakes were with SGFs has been used to improve the mechanical and agglutinated prior to extrusion, converting them into free- 4-7 thermo-mechanical properties of post-consumer PET . flowing semi-crystallized granules with a bulk density of The blending of post-consumer PET with engineering 0.44 g cm–3. 8 thermoplastics, such as poly(butylene terephthalate) (PBT) ,  9 10-12 The PA66 was commercial grade (Radilon A 27D) polycarbonate (PC) and polyamide 66 (PA66) , is another and supplied in pellet form by the company Radici Plastics strategy that has been used to improve the properties of (Brazil). post-consumer PET. The short glass fibers (SGFs) used were commercial *e-mail: [email protected] grade (EC10 4.5 952) E-glass fibers with nominal diameter 1286 Novello et al. Materials Research

of 10 μm containing an epoxysilane surface treatment and following processing conditions: barrel temperature profile were supplied by the company Vetrotex (Brazil) in the form 230°C-265°C-270°C-275°C-285°C, mold temperature of chopped roving of 4.5 mm length. 50°C, flow rate 25 cm3 s–1, holding pressure 500 bar for 7 s 2.2 Processing and mold cooling time 30 s. All materials were dried in a vacuum oven at 80oC 2.3 Characterization for 24 h prior to the processing steps. PET/PA66 blends The relative viscosities of the polymers PET and PA66 and PET/PA66/SGF composites were compounded in a were estimated in the mixing chamber (Rheomix 600p with TEK TRIL DCT20 intermeshing co-rotating twin-screw roller rotors) of a HAAKE torque rheometer. The analysis extruder, with L/D = 36 and D = 20 mm. The barrel temperature was set at 275oC and the screw speed was was performed at a chamber temperature of 275°C and rotor 300 rpm. The screw configuration, along with the material speed of 100 rpm for 10 min. feed locations in the extruder, is shown in Figure 1. The Glass fiber lengths in the injection-molded PET/PA66/ screw profile is comprised of two sets of kneading blocks SGF composites were determined from digital optical in between conveying sections. The set of kneading blocks images recorded using a Nikon model Coolpix 5400 digital upstream was designed to melt and blend the PET and PA66 camera, coupled with an Olympus model SZH 10 optical polymers, whereas the functions of the set of kneading microscope. The images were analyzed using Image J blocks downstream were to disperse and distribute the software to estimate the glass fiber lengths in the molded short glass fibers in the molten polymers. The PET and the composites. Approximately 400 fibers were examined for PA66 granules were tumbled and fed by a volumetric feeder each sample. The glass fibers were recovered by burning off positioned above the main hopper. Short glass fibers were the PET/PA66 in an oven at 600°C for 3 hours. The number fed by a volumetric feeder coupled to a side twin screw average length (l ), the weight average length (l ) and the feeder located before the second set of kneading blocks. The n w polydispersity index (P) of the glass fibers were calculated total feed rate was 4.0 kg h–1 and the screw torque level was according to Equations 1, 2 and 3, respectively, where n is at around 50% under these conditions. i N Table 1 shows the composition of the materials the number of glass fibers with lengthl i and ∑ nNi = is the processed in this study. PET/PA66 blends (100/0, 72/25, total number of glass fibers. i=1 50/50, 25/75 and 0/100 by weight) and composites of these PET/PA66 blends with 30 wt% of SGFs were prepared. N ∑ nlii⋅ Specimens for mechanical tests (ASTM standard bars) l = i=1 n N (1) were injection-molded from the extruded pellets using an ∑ ni ARBURG ALLROUNDER 270S 400-170 machine under the i=1

Figure 1. Screw profile and the feed locations of the twin-screw extruder.

Table 1. Composition of the PET/PA66 blends and PET/PA66/SGF composites.

Material PET content (wt%) PA66 content (wt%) SGF content (wt%) PET 100 — — PET/PA66 75/25 75 25 — PET/PA66 50/50 50 50 — PET/PA66 25/75 25 75 — PA66 — 100 — PET/SGF 70/30 70 — 30 PET/PA66 75/25 with 30% SGF 52.5 17.5 30 PET/PA66 50/50 with 30% SGF 35 35 30 PET/PA66 25/75 with 30% SGF 17.5 52.5 30 PA66/SGF 70/30 — 70 30 2014; 17(5) PET/PA66 Blends and Corresponding Short Glass Fiber Reinforced Composites 1287

N at 23°C and 50% relative humidity for 48 hours prior to the 2 ∑ nlii⋅ tests, which were all conducted under the same ambient l = i=1 w N (2) conditions. Each mechanical test value was calculated from ∑ nlii⋅ the average value of five independent measurements. The i=1 standard deviations of each value were calculated and are l shown as error bars in the plots. P = w (3) ln 3. Results and Discussion The critical glass fiber aspect ratio(l/d) c for the effective reinforcement of polymer matrices is given by Equation 3.1 Microstructure 4, where l is the fiber length, d is the fiber diameter, σ is f The glass fiber length distributions in the molded the tensile strength of the fiber and intτ is the fiber-matrix interfacial shear strength16: PET/PA66/SGF composites are shown as histograms in Figure 2. The values for the average glass fiber lengths l σ f ln (Equation 1) and lw (Equation 2) and the polydispersity c = (4) d 2τint index P (Equation 3) can be seen in the histograms. For all of the composites, similar fiber length distribution patterns The value of τint can be approximated to the value of were observed, the ranges being 158 μm to 182 μm for the the shear stress of the polymer matrix by assuming that ln values, 214 μm to 230 μm for the lw values and 1.22 to there is perfect adhesion between the fiber and the polymer. 1.36 for the P values. Therefore, the experimental values of Taking into account that the shear stress values for the PET ln and lw for the glass fibers in the composites under study and PA66 are around 45 MPa and considering a typical (Figure 4) are similar to or higher than the critical value value for the fiber strength of 1500 MPa, it follows that the (170 μm according to the calculations using Equation 4) critical fiber aspect ratio is 17, and thus the critical fiber required for the effective mechanical reinforcement. length is 170 μm (fiber diameter is 10 μm), for the effective Figure 3 shows typical SEM micrographs of cryo- reinforcement of PET/PA66 blends. fractured surfaces of the molded PET/PA66/SGF composites, The microstructures of the injection-molded PET/PA66/ verifying a homogeneous distribution of the glass fibers in SGF composites and PET/PA66 blends were examined by the polymer matrices. Another important observation is scanning electron microscopy (SEM) using a Philips XL30 that the glass fibers are mostly oriented perpendicular FEG instrument at an accelerating voltage of 10 kV. The to the fractured surface, that is, parallel to the direction samples were taken from the core of the injection molded of mold filling. Injection-molded short glass fiber filled bars and cryo-fractured perpendicular to the mold filling. thermoplastic composites exhibit a complex distribution These fractured samples were used to observe the glass of fiber orientations along the part thickness, often forming fiber distributions in the PET/PA66/SGF composites. To layers, caused by a complex interaction between melt assess the blend morphology, the fractured surfaces of the properties and molding conditions. As the melt fills the PET/PA66 75/25 blend and the respective SGF composite mould there is fountain flow which initially orients the were further cryo-polished using a diamond knife and then fibers and polymer chains perpendicular to the main flow etched in 85% formic acid to remove the PA66 phase. The direction. This causes the melt to be deposited on the mold surfaces of all samples were sputter coated with gold prior wall with the alignment direction parallel to the mold flow to SEM examination. direction. Here it solidifies rapidly and this alignment is The melting events of the PET and PA66 in the retained in the solid part. Further behind the melt front, shear PET/PA66 blends and PET/PA66/SGF composites were flow dominates and produces fairly uniform levels of fiber determined by differential scanning calorimetry (DSC) alignment. In the very centre of the melt the rate of shear is using a TA Instruments model Q100 calorimeter. Samples low and the transverse fiber alignment present at the gate is (∼ 9 mg) were taken from the core of the injection-molded retained. The final morphology is therefore characterized by o –1 bars and heated from 20°C to 300°C at 20 C min under the skin layer with small oriented fibers and the core region –1 N2 atmosphere (50 mL min ). The melting enthalpies for with low orientation, along with a transition shear zone with the 100% crystalline PET and PA66 were considered to be high orientation between these two layers, which is simply –1 –1 17 140 J g and 196 J g , respectively . called skin-core morphology21. The micrographs show some The tensile properties of the PET/PA66 blends and PET/ holes which are due to the fiber pullout during the cryogenic PA66/SGF composites were determined according to ASTM fracture and can thus be disregarded in the evaluation of D 638[18] on type I specimens (narrow section: 57 x 12.7 x the adhesion between the fibers and the polymer matrices. 3.2 mm) using a EMIC DL 2000 universal testing machine In general, the composite microstructures verify the –1 at a crosshead speed of 5 mm min . Flexural properties efficiency of the mixing in the twin-screw extruder and (three point bending) were determined according to ASTM injection molding, which led to an appropriate degree of D 790[19] on specimens (127 x 12.7 x 3.2 mm) using a EMIC DL 2000 universal testing machine at a crosshead speed dispersion and a homogeneous distribution of the glass of 1 mm min–1. The Izod impact strength of specimens fibers in the polymeric matrices. (63 x 12.7 x 3.2 mm) with standard notch (angle of 45o, Another aspect to be considered is the interface between 2.5 mm in depth, radius of curvature at the apex of 0.25 the glass fiber and the polymeric matrix of the composite. mm) was determined according to ASTM D 256 [20] using a The glass fiber used has epoxy pendant groups on the CEAST Resil pendulum. The specimens were conditioned surface which can react with the carboxyl end groups of 1288 Novello et al. Materials Research

Figure 2. Histograms of the glass fiber lengths in the PET/PA66/SGF composites. a) PET with 30% SGF; (b) PET/PA66 75/25 with 30% SGF; (c) PET/PA66 50/50 with 30% SGF; (d) PET/PA66 25/75 with 30% SGF and (e) PA66 with 30% SGF. both PET and PA66 chains during compounding. This leads holes in the micrographs because of the etching in formic to coupling reactions between the fiber and the polymeric acid. The phase morphology of the PET/PA66 75/25 blend matrix, regardless of the continuous phase in the polymer is comprised of PA66 domains with average size of 0.5 μm blend matrix, which ensure good interfacial adhesion in dispersed in a continuous PET phase (Figure 4a). This blend the composites. morphology is preserved in the corresponding composite Figure 4 shows typical SEM micrographs of cryo- (Figure 4b). The good dispersion achieved for the PET/PA66 polished surfaces of a PET/PA66 75/25 blend (Figure 4a) and blend morphology even without a compatibilizer is assign the corresponding SGF composite (Figure 4b), highlighting to the rheological characteristics of the polymers. The low the blend morphology. The PA66 domains appear as dark interfacial tension between the PET and PA66 in the melt 2014; 17(5) PET/PA66 Blends and Corresponding Short Glass Fiber Reinforced Composites 1289

Figure 3. SEM micrographs of the PET/PA66/SGF composites. (a) PET with 30% SGF; (b) PET/PA66 75/25 with 30% SGF; (c) PET/ PA66 50/50 with 30% SGF; (d) PET/PA66 25/75 with 30% SGF and (e) PA66 with 30% SGF. Magnification: 100. Scale bar: 200 μm. state, which was estimated to be 0.82 mN/m at 275°C using The morphological aspects mentioned above are the Wu equation22, together with the low PA66/PET viscosity essential for ensuring an effective stress transfer from the ratio, which was measured to be 1.8 in the mixing chamber PET/PA66 matrix to the glass fibers as the composites are of a torque rheometer at 275°C, are favorable conditions mechanically overloaded. for the blend dispersion during the compounding in the molten state. Furthermore, Retolaza et al.10 have shown 3.2 Thermal properties that ester-amide interchange reactions are allowed to occur The results for the differential scanning calorimetry during melt mixing even in the absence of a catalyst, leading (DSC) employed to evaluate the overall crystallization of to the formation of interfacial compatibilizer agents in the the polymers in the injection molded PET/PA66 blends and PA66/PET blend. PET/PA66/SGF composites are shown in Figure 5. 1290 Novello et al. Materials Research

Figure 4. SEM micrographs of (a) PET/PA66 75/25 (magnification: 2,000; scale bar: 10 μm) and (b) PET/PA66 75/25 with 30% SGF (magnification: 4,000; scale bar: 5 μm). Samples were etched in formic acid to remove the A66P phase.

Figure 5. DSC curves (1st heating) (a) and melting enthalpies (b) of the polymers in the PET/PA66 blends and PET/PA66/SGF composites.

Figure 5a shows the DSC curves for the blends and the cold crystallization of PET and normalized in relation composites. The melting of the neat PET and PA66 is to the glass fiber content in the case of the composites. represented by endothermic peaks at 249°C and 263°C, For the blend-based materials, the overall crystallization respectively. The melting events for the blend-based was considered instead of the individual crystallization materials appear as double peaks in the DSC curves since of the polymers. The melting enthalpies of the molded the melting temperatures of the individual polymers are materials, calculated according to the procedure described very close. The materials containing PET additionally show above, are shown in Figure 5b. The neat PET showed the a cold crystallization event in the temperature range of 113 lowest value for the degree of crystallization (15%) of to 124°C, indicating that the PET did not fully crystallize the materials investigated and the neat PA66 showed the during the injection molding process. highest value (35%). This is because the crystallization rate To estimate the degree of crystallization of the polymers of PA66 is much higher than that of PET; in fact, the low in the molded materials the melt enthalpies (area below crystallization rate of bottle-grade post-consumer PET23 the melting peaks) were subtracted from the enthalpy of is one of the major obstacles in relation to its use as an 2014; 17(5) PET/PA66 Blends and Corresponding Short Glass Fiber Reinforced Composites 1291

engineering thermoplastic. The melting enthalpies of the PET/PA66 blends shows a synergistic effect in relation to the neat polymers, indicating that the PA66, with a higher crystallization temperature (Tc ≈ 230°C), provides nucleation o 10 sites facilitating the crystallization of the PET (Tc ≈ 190 C) . The glass fibers were observed to act as a nucleating agent for the crystallization of the neat polymers. This effect is more significant for the PET composite, which have a lower crystallization rate; the degree of crystallinity of the PET was increased from 15 to 26% with the incorporation of glass fibers whereas for the PA66 this increase was lower (34 to 38%). The overall crystallization of the blends in the PET/ PA66/SGF composites follows the additive rule in relation to the PET/SGF and PA66/SGF. 3.3 Mechanical properties The flexural modulus values for the PET/PA66 blends Figure 6. Flexural modulus of PET/PA66 blends and PET/PA66/ and PET/PA66/SGF composites are shown in Figure 6. SGF composites. The modulus values almost adhere to the additive rule with a slightly positive deviation, values ranging from 2.6 to 3.4 GPa for the blends and from 10.0 to 10.5 GPa for the composites. Since the modulus represents an almost elastic property, it is not dependent on the strength of the interfaces between polymer-polymer and polymer-fiber. Because the PET and PA66 have similar modulus values this property is not dependent on the polymer blend composition, but only on the glass fiber length, orientation and distribution in the polymer matrix. The degree of reinforcement in the PET/PA66/SGF composites was evaluated through a comparative analysis between the experimental modulus values and the theoretical values obtained using the Halpin-Tsai model24. According to the Halpin-Tsai model, the modulus for a fiber-reinforced polymer composite can be expressed in terms of the corresponding properties of the polymer matrix and the fiber phase together with their proportion and the fiber geometry, Figure 7. Relative modulus of PET/PA66/SGF composites along with the values predicted using the Halpin-Tsai model. using Equations 5 and 6:

1+ξ⋅η⋅φ Ec ( f ) Er = = (5) Em (1−η⋅φf ) blends (Figure 6) and the modulus of the glass fiber was assumed to be 70 GPa. The relative modulus represents the improvement in this property for the composite (EEfm−1) η= (6) in relation to the polymeric matrix. The experimental EE+ξ ( fm ) relative modulus values for the composites range between 3 and 4, which is very close to the maximum theoretical In Equations 5 and 6, E is the relative modulus, E , E r c m value for composites in which the fibers are oriented and E are, respectively, the moduli for the composite, matrix f longitudinally in relation to the applied strain, indicating and fiber and ϕf is the fiber volume fraction. The factor ξ is an empirical constant that describes the influence of the a high level of glass fiber orientation and reinforcement fiber geometry. For oriented short fibers with aspect ratios in the composites. higher than the critical value (l/d) (Equation 4), the factor ξ Figure 8 shows the tensile stress-strain curves for PET/ c PA66 blends (Figure 8a) and PET/PA66/SGF composites equals 2.(l/d)c for fibers oriented parallel to the stress/strain and it has a value of 2 for fibers oriented perpendicular to (Figure 8a). the stress/strain. Therefore, the modulus is at the maximum The tensile strength values for the PET/PA66 blends and when the fibers are oriented parallel to tensile direction and PET/PA66/SGF composites are shown in Figure 9. The PET/ minimum when the fibers are oriented perpendicularly. PA66 blends show a negative deviation from the additive The relative modulus values for the PET/PA66/ rule. Since the tensile strength involves plastic deformation SGF composites are shown in Figure 7 along with the of the polymeric matrix it becomes dependent on the phase theoretical values obtained according to the Halpin-Tsai morphology and thus the blend composition. The tensile model (Equations 5 and 6). The matrix modulus values for strength value for the PA66-rich blend (PET/PA66 25/75) composites were assumed to be those of the corresponding was found to be between those for the neat polymers, while 1292 Novello et al. Materials Research

Figure 8. Tensile stress-strain curves of (a) PET/PA66 blends and (b) PET/PA66/SGF composites.

for the PET-rich blend (PET/PA66 75/25) and the blend with symmetric composition (PET/PA66 50/50) the tensile strength values were lower than those of the neat polymers. In contrast, the tensile strength values for the PET/PA66/ SGF composites almost follow the additive rule with a slightly negative deviation, with values ranging from 129 to 155 MPa. These values are around twice those for the neat polymers, indicating, once again, the effective reinforcement of the polymer matrices with the addition of glass fibers. The glass fibers, with lengths exceeding the dimensions of the PET and PA66 phases, act as bridges binding the PET and PA66 phases and preventing premature failure in the interfacial region of the blends when the composites are overloaded. The notched Izod impact strength values for the PET/ PA66 blends and PET/PA66/SGF composites are shown in Figure 9. Tensile strength of PET/PA66 blends and PET/PA66/ Figure 10. In general, the composites showed higher impact SGF composites. strength values (68-85 J m-1) than the blends (26-42 J m–1). This is a consequence of energy dissipation mechanisms, such as fiber debonding, pullout, bridging and fracture, which induce plastic deformation of polymeric matrix before failure. Bridging and fiber fracture are likely to occur as a consequence of the presence of a population of fibers which are longer than the critical length for effective reinforcement, while debonding and fiber pullout occur due to the presence of fibers which are shorter than this critical length value. The impact strength values for the PA66-rich blend (PET/PA66 25/75) and the respective composite (PET/ PA66 25/75 30 wt% SGF) follow the additive rule. On the other hand, for the PET-rich blend (PET/PA66 75/25) and the blend with symmetric composition (PET/PA66 50/50) the impact strength values were similar to that for the neat PET (26 J m–1), which, in turn, is lower than the value for the neat PA66 (46 J m–1). Similar behavior was observed for the respective PET/PA66/SGF composites. It is worth mentioning that the values for the mechanical Figure 10. Notched Izod impact strength of PET/PA66 blends and properties of the PET/PA66/SGF composites are consistent PET/PA66/SGF composites. with values reported in the literature for short glass fiber 2014; 17(5) PET/PA66 Blends and Corresponding Short Glass Fiber Reinforced Composites 1293

reinforced composites based on post-consumer PET4-7 and composites based on polymeric matrices with a PET PA6613,14. content of 50% or higher showed a negative deviation The mechanical properties of the PET/PA66/SGF from the additive rule, whereas these properties were composites reported herein (Figures 6 to 10) attest to the consistent with the additive rule for the composite with effective reinforcement of the PET/PA66 matrices through a PA66-rich blend matrix. There was evidence that PA66 the incorporation of glass fibers, which is in agreement and SGFs act as nucleating agents for PET, reducing the with the good dispersion of the blends (Figure 4), the limitations associated with the use of post-consumer PET in homogeneous distribution, high level of orientation engineering applications. In summary, the use of PET/PA66/ (Figure 3) and optimized dispersion (Figure 2) of the glass SGF composites is an interesting strategy for obtaining fibers within the polymeric matrices. new thermoplastic composites with good mechanical performance. In addition, this represents a promising 4. Conclusions alternative for the application of post-consumer PET, an Composites comprised of bottle-grade post-consumer abundant and cheap material, in the well-established market polyethylene terephthalate and virgin polyamide 66 (PET/ of PA66/SGF composites, which are widely used in technical PA66) blends and corresponding short glass fiber reinforced parts with engineering properties. composites (PET/PA66/SGF) were investigated. In general, they showed good mechanical performance in flexural, Acknowledgments tensile and impact tests. A high level of reinforcement was achieved in the composites, which was confirmed The authors are grateful to CNPq-Brazil for the by comparison of the experimental modulus values with scholarship awarded to M.V. Novello and to CAPES-Brazil theoretical ones obtained using the Halpin-Tsai equation. and FAPERJ-Brazil for the scholarship awarded to L. G. The tensile strength and notched impact strength of the Carreira.

References of postconsumer poly(ethylene terephthalate). Journal of Applied Polymer Science. 2010; 115(2):928-934. http://dx.doi. 1. Kocsis JK. Reinforced polymer blends. In: Paul DR and org/10.1002/app.30647. Bucknall CB, editors. Polymer blends. New York: John Wiley and Sons; 2000. p. 395-428. v. 2: Performance. 9. Tang X, Guo W, Yin G, Li B and Wu C. Reactive extrusion of recycled poly(ethylene terephthalate) with polycarbonate by 2. Cheng H, Tian M and Zhang L. Toughening of recycled addition of chain extender. Journal of Applied Polymer Science. poly(ethylene terephthalate)/glass fiber blends with ethylene- butyl acrylate-glycidyl methacrylate copolymer and maleic 2007; 104(4):2602-2607. http://dx.doi.org/10.1002/app.24410. anhydride grafted polyethylene-octene rubber. Journal of 10. Retolaza A, Eguiazábal JI and Nazábal J. Structure and Applied Polymer Science. 2008; 109(5):2795-2801. http:// mechanical properties of polyamide-6,6/poly(ethylene dx.doi.org/10.1002/app.27564. terephthalate) blends. Polymer Engineering and Science. 2004; 3. Karsli NG, Yesil S and Aytac A. Effect of short fiber 44(8):1405-1413. http://dx.doi.org/10.1002/pen.20136. reinforcement on the properties of recycled poly(ethylene 11. Khoshnevis H and Zadhoush A. The influence of epoxy resin terephthalate)/poly(ethylene naphthalate) blends. Materials on the morphological and rheological properties of PET/PA66 & Design. 2013; 46:867-872. http://dx.doi.org/10.1016/j. blend. Rheologica Acta. 2012; 51(5):467-480. http://dx.doi. matdes.2012.11.009. org/10.1007/s00397-011-0615-5. 4. Mondadori NML, Nunes RCR, Zattera AJ, Oliveira RVB 12. Khoshnevis H and Zadhoush A. Investigation of the effect and Canto LB. Relationship between processing method and of SSP in stabilizing the structure of condensation polymer microstructural and mechanical properties of poly(ethylene blends via rheological measurements. Rheologica Acta. 2011; terephthalate)/short glass fiber composites. Journal of Applied 50(2):131-140. http://dx.doi.org/10.1007/s00397-010-0528-8. Polymer Science. 2008; 109(5):3266-3274. http://dx.doi. 13. Gasparin AL, Corso LL, Tentardini EK, Nunes RCR, org/10.1002/app.28459. Forte MMC and Oliveira RVB. Polyamide Worm Gear: 5. Mondadori NML, Nunes RCR, Canto LB and Zattera AJ. Manufacturing and Performance. Materials Research. Composites of Recycled PET Reinforced with Short Glass 2012; 15(3):483-489. http://dx.doi.org/10.1590/S1516- Fiber. Journal of Thermoplastic Composite Materials. 2012; 14392012005000056. 25(6):747-764. http://dx.doi.org/10.1177/0892705711412816. 14. Javangula S, Ghorashi B and Draucker CC. Mixing of glass fiber 6. Arencon D and Velasco JI. The influence of injection-molding to nylon 6-6. Journal of Materials Science. 1999; 34(20):5143- variables and nucleating additives on thermal and mechanical 5151. http://dx.doi.org/10.1023/A:1004777520458. properties of short glass fiber/PET composites. Journal of Thermoplastic Composite Materials. 2002; 15(4):317-336. 15. American Society for Testing and Materials - ASTM. ASTM http://dx.doi.org/10.1177/0892705702015004456 D4603: standard test method for determining inherent viscosity of Poly(Ethylene Terephthalate) (PET) by glass capillary 7. Pegoretti A and Penati A. Recycled poly(ethylene terephthalate) viscometer. West Conshohocken; 2011. and its short glass fibres composites: effects of hygrothermal aging on the thermo-mechanical behavior. Polymer. 16. Kelly A and Tyson WR. Tensile properties of fibre-reinforced 2004; 45(23):7995-8004. http://dx.doi.org/10.1016/j. metals: cooper/tungsten and copper/molybdenum. Journal of polymer.2004.09.034. the Mechanics and Physics of Solids. 1965; 13(6):329-350. 8. Baxi RN, Pathak SU and Peshwe DR. Mechanical, thermal, http://dx.doi.org/10.1016/0022-5096(65)90035-9. and structural characterization of poly(ethylene terephthalate) 17. Brandrup J, Immergut EH and Grulke EA. Polymer Handbook. and poly(butylene terephthalate) blend systems by the addition New York: John Wiley and Sons; 1999. 1294 Novello et al. Materials Research

18. American Society for Testing and Materials - ASTM. ASTM Composites Science and Technology. 1999; 59(16):2315-2328. D638: standard test method for tensile properties of plastics. http://dx.doi.org/10.1016/S0266-3538(99)00083-4. West Conshohocken; 2010. 22. Wu S. Calculation of interfacial tension in polymer systems. 19. American Society for Testing and Materials - ASTM. ASTM Journal of Polymer Science. 1971; 34(1):19-30. http://dx.doi. D790: standard test methods for flexural properties of org/10.1002/polc.5070340105. unreinforced and reinforced plastics and electrical insulating 23. Viana JC, Alves NM and Mano JF. Morphology and mechanical materials. West Conshohocken; 2010. properties of injection molded poly(ethylene terephthalate). 20. American Society for Testing and Materials - ASTM. ASTM Polymer Engineering and Science. 2004; 44(12):2174-2184. D256: standard test methods for determining the izod pendulum http://dx.doi.org/10.1002/pen.20245. impact resistance of plastics. West Conshohocken; 2010. 24. Halpin JC and Kardos JL. The Halpin-Tsai Equations: A 21. Thomason JL. The influence of fibre properties of the Review. Polymer Engineering and Science. 1976; 16(5):344- performance of glass-fibre-reinforced polyamide 6,6. 352. http://dx.doi.org/10.1002/pen.760160512.