Glass transition temperature of chitosan and miscibility of chitosan/poly(N-vinyl pyrrolidone) blends

There are a few communications concerning the relaxation temperature corresponding to the glass transition temperature of chitosan. We succeeded in observing the Tg of chitosan (to be ca. 203°C) by the direct and careful measurement of differential scanning calorimetry (DSC), which had been assumed not to be sensitive enough to detect it. In addition to this observation, the dynamic mechanical analysis (DMA) measurement in the second heating run showed the α-relaxation at the same temperature as the glass transition temperature observed in DSC. The peak in the tan δ curve appeared at about 150°C in the first heating run as if it were the α-relaxation and might be due to the secondary molecular motion when the chitosan molecules were in the pseudo-stable state. Chitosan was blended with poly(N-vinyl pyrrolidone) in acetic acid solution and this solution was cast to prepare the blend film. The miscibility and the phase structure in the binary blend films were studied using DSC measurements and the wide-angle X-ray diffraction (WAXD) method. The glass transition temperature of the binary blend films decreased with increase of PVP content and the relation obeyed Fox's theory. This implies that the blend system of chitosan and PVP is able to form a miscible phase. It was supported by WAXD observations of the binary blend films.