Water Vapor Permeability of Poly(L-lactide)/Poly(D-lactide) Stereocomplexes

PLLA/PDLA blend films with only stereocomplex crystallites as a crystalline species together with pure PLLA and PDLA films with only homo-crystallites as a crystalline species were prepared, and the effects of enantiomeric polymer blending, crystalline species, and crystallinity on the water vapor permeability were investigated. The WVT coefficient P of PLLA/PDLA blend films was 14-23% lower than that of pure PLLA and PDLA films in the crystallinity X(c) range of 0-30%. Amorphous PLLA/PDLA blend films have a much lower P than pure PLLA and PDLA films. The dependence of P on Xc for blend films was stronger for X(c) = 0-30% than for X(c) = 30-100%. This dependence is discussed using the Nielsen model and the concept of restricted (or restrained) and free amorphous regions.