EFFECT OF MOLECULAR-WEIGHT AND CRYSTALLINITY ON POLY(LACTIC ACID) MECHANICAL-PROPERTIES

Several samples of poly(lactic acid) with different molecular weights and tacticity have been prepared, and some PLLA injection moulded spec imens have been annealed to promote their crystallization. From the ch aracterization data, poly(L-lactide) showed more interesting mechanica l properties than poly(D,L-lactide), and its behavior significantly im proves with crystallization. In fact, annealed specimens possess highe r values of tensional and flexural modulus of elasticity, Izod impact strength, and heat resistance. The plateau region of flexural strength as a function of molecular weights appears around M(upsilon) = 35,000 for PDLLA and amorphous PLLA and at higher molecular weight, around M (upsilon) = 55,000, for crystalline PLLA. The study of temperature eff ect shows that at 56 degrees C only crystalline PLLA still exhibits us eful mechanical properties. (C) 1996 John Wiley & Sons, Inc.