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Physical Properties of Poly(Lactic Acid) and Starch Composites with Various Blending Ratios¹

¹Contribution 00-224-J from the Kansas Agricultural Experiment Stn, Manhattan, KS 66506. ²Department of Grain Science and Industry, Kansas State University, Manhattan, KS 66506. ³Corresponding author. Phone: 785-532-4077. Fax: 785-532-7010. E-mail: xss@ksu.edu

Two-phase polymer blends of poly(lactic acid) (PLA) and corn or wheat starches at various ratios were prepared by using a laboratory-scale twin-screw extruder and compression molding. The blends were characterized for thermal transitions, mechanical properties, and water absorption. Starch and PLA were immiscible polymers, and the thermal behavior of PLA was not affected by starch. Crystallinity of the blends decreased in some degree as starch content increased 20–40%. Tensile strength and elongation of the blends decreased as starch content increased, but modulus increased as starch content increased up to 70%. As starch content increased to >60%, the PLA phase became discontinuous, and water absorption of the blends increased sharply. Blends made from wheat starch gave slightly better mechanical properties than those made from corn starch, and no differences in other properties were observed.