Structure and mechanical properties of polymer blends incorporating ...
10.1002/spepro.003402
Structure and mechanical properties of polymer blends incorporating waste PET Soheila Lashgari, Ahmad Arefazar, Somayeh Lashgari, and Somayyeh Mohammadian Gezaz
Adding a compatibilizer to blends of acrylonitrile-butadiene-styrene terpolymer and recycled engineering plastic results in better mixing as well as products with enhanced properties. The blending of immiscible (nonmixing) polymers such as polycarbonate and acrylonitrile butadiene styrene—used widely in the automobile industry—is an economically attractive route to developing a mixture that retains the desirable properties of both components. In general, the polymers are selected based on advantageous properties such as toughness, chemical resistance, and heat stability. However, the so-called mixing rule, which calculates the properties of blends based on a linear average, generally does not hold for immiscible polymers because the components form a two-phase structure, such as, part crystal and part amorphous. Consequently, melt blending usually involves adding a third component as an interfacial agent to bridge the materials, in the same way that soap bridges water and oil.1 Recycled post-consumer plastics offer a particularly attractive option for blending with other polymers to enhance their physical and mechanical properties. Polyethylene terephthalate (PET), for example, is an engineering plastic that is ubiquitous in soft-drink bottles, packaging, electronics, and many other applications. Accordingly, reusing PET is an industrial priority owing to environmental pressure and the substantial amount of energy required to produce it. Here, we report blends based on waste PET (W-PET) and acrylonitrile butadiene styrene (ABS) terpolymer,2 which is used as an impact modifier for thermoplastics such as polyvinylchloride,3 polycarbonate,4–6 and polyamide 6.7 ABS is a tough, nonpolar thermoplastic styrenic terpolymer, while PET is an oil-resistant semicrystalline polyester. Blending the chemical polarity, crystallinity, and toughness of these materials poses a major scientific challenge. PET/ABS has substantial commercial significance, especially when it is formed from W-PET and can replace the expensive polymer
Figure 1. Scanning electron microscope images for selected polymerblend samples. Experimental run numbers (a) 8, (b) 2, (c) 10, and (d) 1. MA: Maleic anhydride. phABS: Parts by weight per hundred parts of acrylonitrile butadiene styrene. phr: Parts per hundred parts of resin. dN : Average particle size. blends commonly used in industrial applications. However, reports of this material in the literature are scant.8–10 We prepared our W-PET blends with varying amounts of ABS content. To compatibilize the polymer phases, we attached maleic Continued on next page
10.1002/spepro.003402 Page 2/4
Table 1. Materials used in this study. W-PET: Waste PET. DCP: Dicumyl peroxide. PS: Polystyrene. AN: Acrylonitrile. PBD: Polybutadiene rubber. Tm : Temperature of melting. Material ABS W-PET Antioxidant MA DCP
Grade SV 0157 Bottle Irganox 1010 – –
Supplier Tabriz Petrochemical, Iran Texpet, Korea Ciba-Geigy, Switzerland Merck, Germany Merck, Germany
Comment 57wt% PS 25wt% AN 18wt% PBD – Tm : 110–125ı C Tm : 53ı C Tm : 40ı C
Process Blending Blending Blending Grafting Grafting
Table 2. Material concentrations used for grafting of ABS. Code A1 A2 A3 A4 A5 B1 B2 B3 B4
Weight parts (phABS) ABS MA DCP 100 3 0 100 3 0.1 100 3 0.2 100 3 0.3 100 3 0.4 100 1.5 0.2 100 3 0.2 100 4.5 0.2 100 6 0.2
Degree of grafting (wt%) 0.08 1.11 1.38 1.37 1.35 0.74 1.38 1.95 2.43
anhydride (MA) groups onto ABS through a chemical grafting process. We chose the response surface methodology (RSM) Box-Behnken experimental design to test the effects of all input variables and their interactions on the response functions. We analyzed the experimental data using Mini Tab v.13.2 software. Finally, we selected three variables to investigate: blend composition, the MA level used in the grafting procedure to prepare ABS-g-MA (where g means ‘grafted’), and rotor (screw) speed. Table 1 provides details of the materials used to generate the samples, including recycled W-PET pellets, ABS terpolymer, antioxidant, MA, and dicumyl peroxide (DCP), which was used as an initiator in grafting. We prepared a number of different formulations of ABSg-MA (see Table 2). The experimental design called for 15 separate experimental runs (see Table 3). The blends were prepared using an internal mixer at 260ı C. We began by incorporating PET and the antioxidant, and after 2min, added the ABS-g-MA to the mixture. After another 5min, mixing was stopped, and the sample was left to solidify in a dry place. We examined the structure of the blends using a scanning electron microscope (XL300, Philips), and measured the impact strength of notched samples (1/8in) with a Zwick impact tester according to ASTM (American Society for Testing and Materials) Standard D256.
Figure 2. Response surface methodology graphs of impact strength versus screw speed and compatibilizer content for ABS levels of (a) 5, (b) 17.5, (c) 30phr. Figure 1 shows micrographs of selected samples containing different amounts of ABS (or ABS-g-MA). As expected, increasing ABS content from 5 to 30phr (parts per hundred parts of resin) clearly increases Continued on next page
10.1002/spepro.003402 Page 3/4
Table 3. Box-Behnken experimental design. Run order 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
W-PET (phr) 70 95 82.5 82.5 82.5 70 82.5 95 95 70 82.5 70 82.5 82.5 95
ABS (phr) 30 5 17.5 17.5 17.5 30 17.5 5 5 30 17.5 30 17.5 17.5 5
MA (phABS) 6 6 0 6 3 3 0 0 3 0 3 3 3 6 3
Speed (rpm) 50 50 30 30 50 70 70 50 70 50 50 30 50 70 30
*MA added in the ABS phase of the grafting process. Note: To prevent oxidation and degradation of samples during the process, 0.1phr Irganox was added to all formulations.
Table 4. Statistical information and equation model. R2 : Relative predictive power of the model.
Property (unit) Impact strength (J/m)
ABS
MA
Speed
ABS2
MA2
ABS speed A8
MA speed A9
Const.
A5
Speed2 ABS MA A6 A7
A1
A2
A3
A4
A10
R2 (%)
2.1950
31.1768 0.6337
–
–3.9148
–
–
–
–25.77
98.7
0.5666
Adjusted R2 (%) 98
Impact strength = A1 (ABS) + A2 (MA) + A3 (speed) + A4 (ABS2 / + A5 (MA2 / + A6 (speed2 / + A7 (ABS MA) + A8 (ABS speed) + A9 (MA speed) + A10 ABS: 5–30phr. MA: 0–6phABS. Speed: 30–70rpm.
the number of domains, or dispersed particle phases. Introducing ABSg-MA decreases the average particle size from 7.2 to 1.7m and from 8.3 to 3.5m for 30 and 5phr, respectively. We attribute the reduction to strong interaction (compatibility) of the two phases (dispersed and matrix) owing to formation of graft copolymer between them. In contrast, in compatibilized W-PET/ABS-g-MA blends, interfacial interaction is probably due to the formation of graft copolymer between the carboxyl group of MA and hydroxyl groups of W-PET. Table 4 presents the relevant statistics and the equation model we derived using the RSM. The calculated R2 value (relative predictive power for impact strength) is in the acceptable range of 90.7–99.7%.
This result suggests a good fit between the experimental data and the model. Figure 2 shows RSM graphs of impact strength versus rotor speed and MA content for three levels of ABS. As expected, samples with more ABS content have higher impact strength. But impact strength also increases with MA content, which means ABS-g-MA is more advantageous than neat ABS owing to bond formation between the functional groups of W-PET and ABS-g-MA. Because the average size of dispersed particles reduces with increasing MA, they distribute stress more effectively. In addition, strong interfacial adhesion easily Continued on next page
10.1002/spepro.003402 Page 4/4
Somayyeh Mohammadian Gezaz Shahre Rey Branch Islamic Azad University Tehran, Iran References
Figure 3. Comparison of the impact strength of compatibilized and uncompatibilized blends with mixing rule.
transfers the stress field from the PET matrix to the dispersed ABS-gMA phase. Consequently, impact strength also rises as the MA concentration increases.7, 11 Figure 3 shows impact strength versus blend composition together with the same results calculated using the mixing rule. The impact strength of all the compatibilized blends deviates positively from the mixing rule, while that of uncompatibilized blends is lower. In summary, we have described our efforts to investigate various preparations of W-PET/ABS blends. Using ABS-g-MA instead of neat ABS resulted in more uniform particle size distribution and finer average particle size. High impact strength values proved the good fit of experimental data with the RSM, confirming the reliability of our model. Our experiments showed that mechanical properties were strongly affected by the composition of the blend, MA content, and processing speed. As a next step, we plan to prepare and investigate recycled PET blended with ethylene vinyl acetate, which has a higher impact strength than ABS.
1. L. A. Utracki, Polymer Alloys and Blends Thermodynamics and Rheology, Hanser Munich, 1989. 2. S. Lashgari, A. A. Azar, S. Lashgari, and S. M. Gezaz, Properties of wastepoly(ethylene terephthalate)/acrylonitrile butadiene styrene blends compatibilized with maleated acrylonitrile butadiene styrene, J. Vinyl Addit. Technol. 16, pp. 246–253, 2010. 3. N. Belhaneche-Bensemra and A. Bedda, Study of the properties of PVC/ABS blends, Macromol. Symp 176, p. 145, 2001. 4. F. Elmaghor, L. Zhang, R. Fan, and H. Li, Recycling of polycarbonate by blending with maleic anhydride grafted ABS, Polymer 45, p. 6719, 2004. 5. S. Balakrishnan and N. R. Neelakantan, Mechanical properties of blends of polycarbonate with unmodified and maleic anhydride grafted ABS, Polym. Int. 45, p. 347, 1998. 6. X. Zhang, Y. Chen, Y. Zhang, Z. Peng, Y. Zhang, and W. Zhou, Effects of ABS-g-MAH on mechanical properties and compatibility of ABS/PC alloy, J. Appl. Polym. Sci. 81, p. 831, 2001. 7. S. M. Gezaz, I. Ghasemi, and A. Oromiehie, Study of the properties of compatibilized ABS/PA6 blends using response surface methodology, J. Vinyl. Addit. Technol. 15, p. 191, 2009. 8. N. K. Kalfoglou, D. S. Skafidas, and J. K. Kallitsis, Blends of poly(ethylene terephthalate) with unmodified and maleic anhydride grafted acrylonitrile-butadiene-styrene terpolymer, Polymer 37, p. 3387, 1996. 9. W. D. Cook, T. Zhang, G. Moad, G. Van Deipen, F. Cser, B. Fox, and M. O’Shea, Morphology-property relationships in ABS/PET blends. I. Compositional effects, J. Appl. Polym. Sci. 62, p. 1699, 1996. 10. W. D. Cook, G. Moad, B. Fox, G. Van Deipen, T. Zhang, F. Cser, and L. McCarthy, Morphology-property relationships in ABS/PET blends. II. Influence of processing conditions on structure and properties, J. Appl. Polym. Sci. 62, p. 1709, 1996. 11. S. Balakrishnan, N. R. Neelakantan, and S. N. Jaisankar, Effect of functionality levels and compatibility of polycarbonate blends with maleic anhydride grafted ABS, J. Appl. Polym. Sci. 74, p. 2102, 1999.
Author Information Soheila Lashgari, Ahmad Arefazar, and Somayeh Lashgari Polymer Engineering Department, Amirkabir University of Technology Tehran, Iran Soheila Lashgari received her BS and MS in polymer engineering from Amirkabir University of Technology. She currently works in private industry as an assistant technology manager on polymer projects.
c 2011 Society of Plastics Engineers (SPE)
Structure and mechanical properties of polymer blends incorporating waste PET Soheila Lashgari, Ahmad Arefazar, Somayeh Lashgari, and Somayyeh Mohammadian Gezaz
Adding a compatibilizer to blends of acrylonitrile-butadiene-styrene terpolymer and recycled engineering plastic results in better mixing as well as products with enhanced properties. The blending of immiscible (nonmixing) polymers such as polycarbonate and acrylonitrile butadiene styrene—used widely in the automobile industry—is an economically attractive route to developing a mixture that retains the desirable properties of both components. In general, the polymers are selected based on advantageous properties such as toughness, chemical resistance, and heat stability. However, the so-called mixing rule, which calculates the properties of blends based on a linear average, generally does not hold for immiscible polymers because the components form a two-phase structure, such as, part crystal and part amorphous. Consequently, melt blending usually involves adding a third component as an interfacial agent to bridge the materials, in the same way that soap bridges water and oil.1 Recycled post-consumer plastics offer a particularly attractive option for blending with other polymers to enhance their physical and mechanical properties. Polyethylene terephthalate (PET), for example, is an engineering plastic that is ubiquitous in soft-drink bottles, packaging, electronics, and many other applications. Accordingly, reusing PET is an industrial priority owing to environmental pressure and the substantial amount of energy required to produce it. Here, we report blends based on waste PET (W-PET) and acrylonitrile butadiene styrene (ABS) terpolymer,2 which is used as an impact modifier for thermoplastics such as polyvinylchloride,3 polycarbonate,4–6 and polyamide 6.7 ABS is a tough, nonpolar thermoplastic styrenic terpolymer, while PET is an oil-resistant semicrystalline polyester. Blending the chemical polarity, crystallinity, and toughness of these materials poses a major scientific challenge. PET/ABS has substantial commercial significance, especially when it is formed from W-PET and can replace the expensive polymer
Figure 1. Scanning electron microscope images for selected polymerblend samples. Experimental run numbers (a) 8, (b) 2, (c) 10, and (d) 1. MA: Maleic anhydride. phABS: Parts by weight per hundred parts of acrylonitrile butadiene styrene. phr: Parts per hundred parts of resin. dN : Average particle size. blends commonly used in industrial applications. However, reports of this material in the literature are scant.8–10 We prepared our W-PET blends with varying amounts of ABS content. To compatibilize the polymer phases, we attached maleic Continued on next page
10.1002/spepro.003402 Page 2/4
Table 1. Materials used in this study. W-PET: Waste PET. DCP: Dicumyl peroxide. PS: Polystyrene. AN: Acrylonitrile. PBD: Polybutadiene rubber. Tm : Temperature of melting. Material ABS W-PET Antioxidant MA DCP
Grade SV 0157 Bottle Irganox 1010 – –
Supplier Tabriz Petrochemical, Iran Texpet, Korea Ciba-Geigy, Switzerland Merck, Germany Merck, Germany
Comment 57wt% PS 25wt% AN 18wt% PBD – Tm : 110–125ı C Tm : 53ı C Tm : 40ı C
Process Blending Blending Blending Grafting Grafting
Table 2. Material concentrations used for grafting of ABS. Code A1 A2 A3 A4 A5 B1 B2 B3 B4
Weight parts (phABS) ABS MA DCP 100 3 0 100 3 0.1 100 3 0.2 100 3 0.3 100 3 0.4 100 1.5 0.2 100 3 0.2 100 4.5 0.2 100 6 0.2
Degree of grafting (wt%) 0.08 1.11 1.38 1.37 1.35 0.74 1.38 1.95 2.43
anhydride (MA) groups onto ABS through a chemical grafting process. We chose the response surface methodology (RSM) Box-Behnken experimental design to test the effects of all input variables and their interactions on the response functions. We analyzed the experimental data using Mini Tab v.13.2 software. Finally, we selected three variables to investigate: blend composition, the MA level used in the grafting procedure to prepare ABS-g-MA (where g means ‘grafted’), and rotor (screw) speed. Table 1 provides details of the materials used to generate the samples, including recycled W-PET pellets, ABS terpolymer, antioxidant, MA, and dicumyl peroxide (DCP), which was used as an initiator in grafting. We prepared a number of different formulations of ABSg-MA (see Table 2). The experimental design called for 15 separate experimental runs (see Table 3). The blends were prepared using an internal mixer at 260ı C. We began by incorporating PET and the antioxidant, and after 2min, added the ABS-g-MA to the mixture. After another 5min, mixing was stopped, and the sample was left to solidify in a dry place. We examined the structure of the blends using a scanning electron microscope (XL300, Philips), and measured the impact strength of notched samples (1/8in) with a Zwick impact tester according to ASTM (American Society for Testing and Materials) Standard D256.
Figure 2. Response surface methodology graphs of impact strength versus screw speed and compatibilizer content for ABS levels of (a) 5, (b) 17.5, (c) 30phr. Figure 1 shows micrographs of selected samples containing different amounts of ABS (or ABS-g-MA). As expected, increasing ABS content from 5 to 30phr (parts per hundred parts of resin) clearly increases Continued on next page
10.1002/spepro.003402 Page 3/4
Table 3. Box-Behnken experimental design. Run order 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
W-PET (phr) 70 95 82.5 82.5 82.5 70 82.5 95 95 70 82.5 70 82.5 82.5 95
ABS (phr) 30 5 17.5 17.5 17.5 30 17.5 5 5 30 17.5 30 17.5 17.5 5
MA (phABS) 6 6 0 6 3 3 0 0 3 0 3 3 3 6 3
Speed (rpm) 50 50 30 30 50 70 70 50 70 50 50 30 50 70 30
*MA added in the ABS phase of the grafting process. Note: To prevent oxidation and degradation of samples during the process, 0.1phr Irganox was added to all formulations.
Table 4. Statistical information and equation model. R2 : Relative predictive power of the model.
Property (unit) Impact strength (J/m)
ABS
MA
Speed
ABS2
MA2
ABS speed A8
MA speed A9
Const.
A5
Speed2 ABS MA A6 A7
A1
A2
A3
A4
A10
R2 (%)
2.1950
31.1768 0.6337
–
–3.9148
–
–
–
–25.77
98.7
0.5666
Adjusted R2 (%) 98
Impact strength = A1 (ABS) + A2 (MA) + A3 (speed) + A4 (ABS2 / + A5 (MA2 / + A6 (speed2 / + A7 (ABS MA) + A8 (ABS speed) + A9 (MA speed) + A10 ABS: 5–30phr. MA: 0–6phABS. Speed: 30–70rpm.
the number of domains, or dispersed particle phases. Introducing ABSg-MA decreases the average particle size from 7.2 to 1.7m and from 8.3 to 3.5m for 30 and 5phr, respectively. We attribute the reduction to strong interaction (compatibility) of the two phases (dispersed and matrix) owing to formation of graft copolymer between them. In contrast, in compatibilized W-PET/ABS-g-MA blends, interfacial interaction is probably due to the formation of graft copolymer between the carboxyl group of MA and hydroxyl groups of W-PET. Table 4 presents the relevant statistics and the equation model we derived using the RSM. The calculated R2 value (relative predictive power for impact strength) is in the acceptable range of 90.7–99.7%.
This result suggests a good fit between the experimental data and the model. Figure 2 shows RSM graphs of impact strength versus rotor speed and MA content for three levels of ABS. As expected, samples with more ABS content have higher impact strength. But impact strength also increases with MA content, which means ABS-g-MA is more advantageous than neat ABS owing to bond formation between the functional groups of W-PET and ABS-g-MA. Because the average size of dispersed particles reduces with increasing MA, they distribute stress more effectively. In addition, strong interfacial adhesion easily Continued on next page
10.1002/spepro.003402 Page 4/4
Somayyeh Mohammadian Gezaz Shahre Rey Branch Islamic Azad University Tehran, Iran References
Figure 3. Comparison of the impact strength of compatibilized and uncompatibilized blends with mixing rule.
transfers the stress field from the PET matrix to the dispersed ABS-gMA phase. Consequently, impact strength also rises as the MA concentration increases.7, 11 Figure 3 shows impact strength versus blend composition together with the same results calculated using the mixing rule. The impact strength of all the compatibilized blends deviates positively from the mixing rule, while that of uncompatibilized blends is lower. In summary, we have described our efforts to investigate various preparations of W-PET/ABS blends. Using ABS-g-MA instead of neat ABS resulted in more uniform particle size distribution and finer average particle size. High impact strength values proved the good fit of experimental data with the RSM, confirming the reliability of our model. Our experiments showed that mechanical properties were strongly affected by the composition of the blend, MA content, and processing speed. As a next step, we plan to prepare and investigate recycled PET blended with ethylene vinyl acetate, which has a higher impact strength than ABS.
1. L. A. Utracki, Polymer Alloys and Blends Thermodynamics and Rheology, Hanser Munich, 1989. 2. S. Lashgari, A. A. Azar, S. Lashgari, and S. M. Gezaz, Properties of wastepoly(ethylene terephthalate)/acrylonitrile butadiene styrene blends compatibilized with maleated acrylonitrile butadiene styrene, J. Vinyl Addit. Technol. 16, pp. 246–253, 2010. 3. N. Belhaneche-Bensemra and A. Bedda, Study of the properties of PVC/ABS blends, Macromol. Symp 176, p. 145, 2001. 4. F. Elmaghor, L. Zhang, R. Fan, and H. Li, Recycling of polycarbonate by blending with maleic anhydride grafted ABS, Polymer 45, p. 6719, 2004. 5. S. Balakrishnan and N. R. Neelakantan, Mechanical properties of blends of polycarbonate with unmodified and maleic anhydride grafted ABS, Polym. Int. 45, p. 347, 1998. 6. X. Zhang, Y. Chen, Y. Zhang, Z. Peng, Y. Zhang, and W. Zhou, Effects of ABS-g-MAH on mechanical properties and compatibility of ABS/PC alloy, J. Appl. Polym. Sci. 81, p. 831, 2001. 7. S. M. Gezaz, I. Ghasemi, and A. Oromiehie, Study of the properties of compatibilized ABS/PA6 blends using response surface methodology, J. Vinyl. Addit. Technol. 15, p. 191, 2009. 8. N. K. Kalfoglou, D. S. Skafidas, and J. K. Kallitsis, Blends of poly(ethylene terephthalate) with unmodified and maleic anhydride grafted acrylonitrile-butadiene-styrene terpolymer, Polymer 37, p. 3387, 1996. 9. W. D. Cook, T. Zhang, G. Moad, G. Van Deipen, F. Cser, B. Fox, and M. O’Shea, Morphology-property relationships in ABS/PET blends. I. Compositional effects, J. Appl. Polym. Sci. 62, p. 1699, 1996. 10. W. D. Cook, G. Moad, B. Fox, G. Van Deipen, T. Zhang, F. Cser, and L. McCarthy, Morphology-property relationships in ABS/PET blends. II. Influence of processing conditions on structure and properties, J. Appl. Polym. Sci. 62, p. 1709, 1996. 11. S. Balakrishnan, N. R. Neelakantan, and S. N. Jaisankar, Effect of functionality levels and compatibility of polycarbonate blends with maleic anhydride grafted ABS, J. Appl. Polym. Sci. 74, p. 2102, 1999.
Author Information Soheila Lashgari, Ahmad Arefazar, and Somayeh Lashgari Polymer Engineering Department, Amirkabir University of Technology Tehran, Iran Soheila Lashgari received her BS and MS in polymer engineering from Amirkabir University of Technology. She currently works in private industry as an assistant technology manager on polymer projects.
c 2011 Society of Plastics Engineers (SPE)
