Making a Rapid Completion of Crystallization for Bisphenol A Polycarbonate by a Double-Layer Film Method

Bisphenol A polycarbonate (PC) is difficult to crystallize. In this study, it was found that PC could rapidly accomplish melt crystallization only within 8 min by laying poly(ethylene glycol) (PEG) film on it. Polarized optical microscope (POM) was applied to trace the growth of spherulites of PC in PEG/PC double-layer films during isothermal crystallization in a wide range of temperatures, which were above the melting temperature for PEG. The dependence of spherulitic growth rate (G) on isothermal crystallization temperature (T-c) followed a "bell-shape" curve, just like some other semicrystalline polymers did. A PEG film was laid on a PC film at 250 degrees C for 5 mm to obtain a PEG/PC double-layer film, which was subsequently quenched to different T-c's for observation on its crystallization process by using POM. It was surprising to observe that the spherulitic growth rate of PC was significantly improved and the crystallization time was obviously shortened. The miscibility for PEG/PC blends was evaluated by applying differential scanning calorimetry (DSC), which played a crucial role in the crystallization accelerating effect. This method provides an operative way to surmount the particular disadvantages of PC, such as very slow crystallization rate and harsh conditions that PC needs to crystallize in the film processing.