In Vitro Hydrolysis of Blends from Enantiomeric Poly(lactide)s. 3. Homocrystallized and Amorphous Blend Films

Abstract

Homocrystallized and amorphous enantiomeric blend films were prepared from the melt of high molecular weight poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) (1:1) by crystallization and quenching, respectively. A phosphate-buffered solution was used to investigate effects of homocrystallinity via in vitro hydrolysis as well as crystallization process during the hydrolysis, which was performed for a period of 24 months at 37 °C and pH 7.4. Results derived from gravimetry, gel permeation chromatography, and tensile testing showed that hydrolyzability was higher for the homocrystallized film than for the amorphous film. Thus, probable mechanisms are proposed for the enhanced hydrolysis of the homocrystallized blend film compared with that of the amorphous blend film. The hydrolysis rate constant (k) values of the homocrystallized and amorphous films estimated from the changes in number-average molecular weight (M_n) were 5.00 × 10^-3 and 3.32 × 10^-3 day^-1, respectively. Moreover, hydrolyzability of equimolar enantiomeric poly(lactic acid) blends can be altered in the k range of 0.73 × 10^-3 and 5.00 × 10^-3 day^-1 by varying their crystalline species, crystallinity, or molecular weights.