Water vapor permeability of poly(lactide)s: Effects of molecular characteristics and crystallinity

Amorphous-made poly((L)-lactide) [i.e., poly((L)-lactic acid) (PLLA)], POIY((L)-lactide-co-(D)-lactide)[P(LLA-DLA)](77/23), and P(LLA-DLA)(50/50) films and PLLA films with different crystallinity (X-C) values were prepared, and the effects of molecular weight, D-lactide unit content (tacticity and optical purity), and crystallinity of poly(lactide) [i.e., poly(lactic acid) (PLA)] on the water vapor permeability was investigated. The changes in number-average molecular weight (M,,) of PLLA films in the range of 9 X 10(4)-5 X 10(5) g mol(-1) and (D)-lactide unit content of PLA films in the range of 0-50% have insignificant effects on their water vapor transmission rate (WVTR). In contrast, the WVTR of PLLA films decreased monotonically with increasing X-C from 0 to 20%, while leveled off for X-C exceeding 30%. This is probably due to the higher resistance of "restricted" amorphous regions to water vapor permeation compared with that of the "free" amorphous regions. The free and restricted amorphous regions are major amorphous components of PLLA films for X-C ranges of 0-20% and exceeding 30%, respectively, resulting in the aforementioned dependence of WVTR on X-C. (c) 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2245-2252, 2006