Poly(L-lactide): 7. Enzymatic hydrolysis of free and restricted amorphous regions in poly(L-lactide) films with different crystallinities and a fixed crystalline thickness

Poly(L-lactide) (PLLA) films having different initial crystallinities (x(c)) (0-57%) and a fixed crystalline thickness were prepared by annealing the melt at a fixed temperature for different times. Their enzymatic hydrolysis was investigated in the presence of Proteinase K(R). The rate of weight loss decreased rapidly and slowly with an increase in the initial x(c) for x(c) below and above 33%, respectively, where the free and the restricted amorphous regions, respectively, are the major amorphous components in the PLLA films. This is ascribed to the higher hydrolysis-resistance of the PLLA chains in the restricted amorphous region than that in the free amorphous region. Gel permeation chromatography (GPC) results revealed that in the restricted amorphous region the folding chains an much more hydrolysis-resistant than the tie chains and the chains with free ends. The increased x(c) during the enzymatic hydrolysis is due to the preferential hydrolysis and removal of the amorphous regions, but not to the crystallization of the amorphous regions. (C) 2001 Elsevier Science Ltd. All rights reserved.