Poly(L-lactide): V. Effects of storage in swelling solvents on physical properties and structure of poly(L-lactide)

The effects of storage at 25 degreesC in swelling solvents having different solubility parameter (delta (s)) values of 16.8-26.0 J(0.5) cm(-1.5) on th e physical properties and structure of as-cast poly(L-lactide) (PLLA) films was investigated by the degree of swelling (DS), differential scanning cal orimetry (DSC), and tensile tests. It was found that PLLA film shows durabi ty to swelling solvents having delta (s) values much lower or higher than t he value range of 19-20.5 J(0.5) cm(-1.5) and that the polymer solubility p arameter (delta (p)) for PLLA is in the value range of 19-20.5 J(0.5) cm(-1 .5). The decrease in the glass transition temperature (T-g) and tensile pro perties and the increase in melting temperature (T-m) and crystallinity (x( c)) were larger for PLLA films swollen in solvents having a high DS at 7 da ys (DS7days). The slight increase in T-m and x(c) for PLLA films after, swe lling in solvents with high DS7days values was due to the crystallization o f PLLA that occurred during swelling, while the small increase in T-g and e longation at break (epsilon (B)) for PLLA films after immersion in the solv ents having low DS7days values was ascribed to stabilized chain packing in the amorphous region. The T-g, epsilon (B), and Young's modulus of the PLLL A films after swelling in the solvents varied in the ranges of 47-57 degree sC, 4-8%, and 55-77 kg/mm(2), depending on their DS7days or delta (s) value s. (C) 2000 John Wiley & Sons, Inc.