CRYSTALLIZATION BEHAVIOR OF POLY(L-LACTIDE)

The crystallization characteristics of poly(L-lactide) (PLLA) films of different molecular weights have been studied by differential scannin g calorimetry, optical microscopy and a depolarized-light intensity (d .l.i.) method. In non-isothermal crystallization modes from the isotro pic melt, the crystallinity of PLLA films increased remarkably with a decrease in the cooling rate, accompanied by a kind of annealing effec t. Overall isothermal crystallization rates of the polymer determined by d.l.i. in the range from 90 degrees C to 140 degrees C indicated th e maximum value at 105 degrees C. This temperature is lower than that (120 degrees C) at which the maximum spherullite growth rate is observ ed. The PLLA polymer exhibited an Avrami exponent n = 4 in the isother mal d.l.i. experiments over the whole temperature range examined. Mole cular parameters governing the isothermal crystallization behaviour ha ve been estimated by the application of secondary nucleation theory. ( C) 1998 Elsevier Science Ltd. All rights reserved.