Thermal and mechanical properties of poly(lactic acid) and starch blends with various plasticizers
2001
Ke, T. | Sun, X.
Poly(lactic acid) (PLA) has potential for use in disposable and biodegradable plastics. Blending starch with PLA would increase biodegradability and reduce costs. However, the brittleness of the starch/PLA blend is a major drawback for many applications. The objective of this study was to characterize thermal and mechanical properties of PLA/starch blends with addition of six plasticizers at various levels. Three groups of plasticizers were used: (1) acetyl triethyl citrate (AC) and triethyl citrate (TC); (2) poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) of low molecular weight and containing an ether group that might interact with PLA; and (3) glycerol and sorbitol, which are miscible with starch. The PLA and cornstarch were blended at a 60:40 weight ratio by using a lab-scale twin-screw extruder with addition of these plasticizers ranging from 5% to 25%. The thermal transition temperatures (glass transition, crystallization, and melting) of the extruded PLA/starch blends decreased as AC, TC, and PEG contents increased. The PPG almost had no effect on the transition temperatures of the blends. Cold crystallization and melting temperatures of PLA increased slightly with increasing sorbitol content. Glycerol reduced the cold crystallization and melting temperatures but had no effect on the glass transition temperature. Starch formed a continuous phase in the presence of 25% sorbitol or 15%, 20%, or 25% glycerol. The TC and PEG enhanced the crystallization of PLA. The annealed samples containing glycerol had the highest crystallinity. As concentration of AC, TC, PEG, PPG, and glycerol increased, tensile strength and Young's Modulus of the extruded and molded blends decreased, and elongation increased in comparison to the blend without plasticizers.
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