Miscibility and phase structure of binary blends of poly(L-lactide) and poly(vinyl alcohol)

Blend films of poly(L-lactide) (PLLA) and poly(vinyl alcohol) (PVA) were ob tained by evaporation of hexafluoroisopropanol solutions of both components . The component interaction, crystallization behavior, and miscibility of t hese blends were studied by solid-state NMR and other conventional methods, such as Fourier transform infrared (FTIR) spectra, differential scanning c alorimetry (DSC), and wide-angle X-ray diffraction (WAXD). The existence of two series of isolated and constant glass-transition temperatures (T-g's) independent of the blend composition indicates that PLLA and PVA are immisc ible in the amorphous region. However, the DSC data still demonstrates that some degree of compatibility related to blend composition exists in both P LLA/atactic-PVA (a-PVA) and PLLA/syndiotactic-PVA (s-PVA) blend systems. Fu rthermore, the formation of interpolymer hydrogen bonding in the amorphous region, which is regarded as the driving force leading to some degree of co mponent compatibility in these immiscible systems, is confirmed by FTIR and further analyzed by C-13 solid-state NMR analyses, especially for the blen ds with low PLLA contents. Although the crystallization kinetics of one com ponent (especially PVA) were affected by another component, WAXD measuremen t shows that these blends still possess two isolated crystalline PLLA and P VA phases other than the so-called cocrystalline phase. 13C solid-state NMR analysis excludes the interpolymer hydrogen bonding in the crystalline reg ion. The mechanical properties (tensile strength and elongation at break) o f blend films are consistent with the immiscible but somewhat compatible na ture of these blends. (C) 2001 John Wiley & Sons, Inc.