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 Xc 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 Xc = 0–30% than for Xc = 30–100%. This dependence is discussed using the Nielsen model and the concept of “restricted” (or “restrained”) and “free” amorphous regions. The water vapor permeability of PLLA or PDLA could be effectively reduced (by 14–23%) by equimolar polymer blending of PLLA and PDLA. Interestingly, the higher barrier property of PLLA/PDLA blends was observed even when they were amorphous. The effect of stereocomplex crystallinity of PLLA/PDLA blends on the WVP was investigated in detail, together with that of homo‐crystallinity of pure PLLA and PDLA.