Toughening of polylactide by blending with various elastomeric materials

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2014
Meyva, Yelda
The purpose of the first part of this thesis was to investigate influences of three different ethylene copolymers on the toughness and other properties of very brittle biopolymer PLA (polylactide). For this aim, PLA was melt blended by twin-screw extruder with various amounts of ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA) and ethylene-n-butyl acrylate-glycidyl methacrylate (EBA-GMA). SEM and DSC analyses indicated that these ethylene copolymers were thermodynamically immiscible with phase separation in the form of 1-5 micron sized round domains in the PLA matrix. Rubber toughening mechanisms of EVA, EMA and EBA-GMA were very effective to improve ductility and toughness of PLA significantly. Depending on the type and content of the ethylene copolymers, the highest increases in % elongation at break, Charpy impact toughness and GIC fracture toughness values of PLA were as much as 160%, 320% and 158%, respectively. Although there were no detrimental effects of using EVA, EMA and EBA-GMA on the thermal properties of PLA, they resulted in certain level of reductions in stiffness, strength and hardness values. The purpose of the second part of thesis was again to improve toughness of inherently very brittle PLA without sacrificing other mechanical and thermal properties, so that PLA could be used also in engineering applications. For this purpose, PLA was blended with two different thermoplastic elastomers; TPU (thermoplastic polyurethane) and BioTPE (biomass based thermoplastic polyester) in various amounts. SEM analysis again indicated that TPU and BioTPE were immiscible forming fine and uniform round domains in the PLA matrix. It was revealed that rubber toughening mechanisms of TPU and BioTPE were much more effective, e.g. using only 10 phr of one of them increased Charpy impact toughness of PLA more than 300%, while increases in KIC and GIC fracture toughness values were as much as 35% and 130%, respectively. Other mechanical tests (tension, flexure, hardness) and thermal analyses (DSC, TGA, DMA) indicated that there was no significant detrimental effects of using 10 phr TPU and BioTPE on the other mechanical and thermal properties of PLA. The purpose of the third part of this thesis was to investigate the effects of using maleic anhydride (MA) compatibilization on the toughness and other properties of PLA blended with TPU and BioTPE. MA grafting on the PLA backbone (PLA-g-MA) was prepared separately by reactive extrusion and added during melt blending of PLA/thermoplastic elastomers. IR spectroscopy revealed that MA graft might interact with the functional groups present in the hard segments of TPU and BioTPE domains via primary chemical interactions, so that higher level of compatibilization could be obtained. SEM studies indicated that PLA-g-MA compatibilization also decreased the size of elastomeric domains leading to higher level of surface area for more interfacial interactions. Toughness tests revealed that Charpy impact toughness and fracture toughness (KIC and GIC) of inherently brittle PLA increased enormously when the blends were compatibilized with PLA-g-MA. For instance, GIC fracture toughness of PLA increased as much as 166%. It was also observed that PLA-g-MA compatibilization resulted in no detrimental effects on the other mechanical and thermal properties of PLA blends.

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Citation Formats
Y. Meyva, “Toughening of polylactide by blending with various elastomeric materials,” M.S. - Master of Science, Middle East Technical University, 2014.