Miscibility and phase structure of binary blends of polylactide and poly(vinylpyrrolidone)

The miscibility, crystallization behavior, and component interactions of two binary blends, poly(L-lactide) (L-PLA)/poly(vinylpyrrolidone) (PVP) and poly(D,L-lactide) (DL-PLA)/PVP, were studied with differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy. The composition-dependent changes of the glass-transition temperature (T,,) and degree of crystallinity (X,) of the L-PLA phase indicated that L-PLA and PVP were immiscible over the composition range investigated. However, the sharp decrease of X, with increasing PVP content in the second heating run demonstrated that the cold crystallization process of L-PLA was remarkably restricted by PVP. In DL-PLA/PVP blends, the existence of two series of isolated T-g's indicated that DL-PLA and PVP were phase-separated, but evidence showed that there was some degree of interaction at the interface of the two phase, especially for the blends with low DL-PLA contents. FTIR measurements showed that there was no appreciable change in the spectra of L-PLA/PVP with respect to the coaddition of each component spectrum, implying the immiscibility of the two polymers. In contrast to L-PLA, the intermolecular interaction between DL-PLA and PVP was detected by FTIR; this was evidenced by the observation of a high-frequency shift of the C=O stretching vibration band of PVP with increasing DL-PLA content, which suggested some degree of miscibility. (C) 2003 Wiley Periodicals, Inc.