Crystallization Of Polycarbonate Induced By Synergistic Action Of Zero-And One-Dimensional Carbon Nano-Materials At High Pressure

With excellent optical properties, high impact resistance, and high glass transition temperature (Tg=150℃), polycarbonate (PC) has been widely used as an engineering polymer of high performance. The bulk crystallization of the PC is extremely slow because of an inherent rigid nature of the molecular backbone. This makes it an ideal subject for the investigation of polymer crystallization. The research on the crystallization behaviors of PC can enlarge its application area and deepen the understanding about the nature of polymer crystallization.Nanostructured materials are effective nucleating agents for crystallizable polymers. Also, it is known that an appropriate pressure treatment can increase the crystallization rate of such aromatic polymers. Fullerenes, such as C60, and carbon nanotubes (CNT) are representative zero-and one-dimensional nanostructured carbonaceous fillers, respectively. In addition to serving as a nucleating agent to decrease the crystallization active energy in the polymer-based composite system, such zero-or one-dimensional carbon material was found recently to be a promising material in promoting the formation of new polymeric structures at high pressure.Herein, well dispersed binary PC/CNT and ternary PC/CNT/C60composites were prepared respectively by a physical and mechanical route, and then crystallized in a piston-cylinder high-pressure apparatus by varying temperature, pressure and crystallization time. The as crystallized composite samples were investigated using wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The main results are as follows:1. By means of the combination of mechanical and melt blending, PC/CNT and PC/CNT/C60composites were prepared, respectively. For a PC/CNT (93/7, wtw/wt) composite, transmission electron microscopy (TEM) disclosed an overall good dispersion of CNT in PC matrix. However, large CNT aggregations, with size around several hundreds of nanometers, were still observed in the binary composite sample when CNT loading was increaded to10wt.-%. For a PC/CNT/C60composite sample, with simultaneous introduction of1.0wt.-%C60and5.0wt.-%CNTs, well dispersed nano-scale aggregations of both C60and CNT were achived in PC matrix, as revealed by TEM. Therefore, the PC/CNT (93/7, wtw/wt) and PC/CNT/C60(94/5/1, wt/wt/wt) composites were selected for the following high pressure experiments by varying temperature, pressure and crystallization time.2. Crystallization of PC induced by CNT at high pressure. XRD indicated that no new crystal form of the polymer was crystallized in the presence of the CNT at high pressure. DSC showed that both the crystallinity and melting temperature of PC/CNT samples increased with the increase of crystallization temperature, which reached a maximum value under the condition of300℃. The optimum pressure for the crystallization of PC/CNT samples was found to be200MPa. Further increasing pressure resulted in the increase of supercooling degree, and both the crystallinity and melting point of PC/CNT samples decreased. It was also shown that crystallization time has a significant influence for the high-pressure crystallization of such PC/CNT composites. The crystallinity for a sample crystallized for just3h attained a value of3.71%. When crystallization time was increased to18h, it reached39.03%. SEM showed that the PC/CNT nanocomposites mainly generated a dendritic crystal structure under high pressure. This was possibly due to the intertwining effect of CNT in PC matrix. Under high temperature and high pressure, the synergistic induction of these intertwined CNT may lead to the growth of such dendritic crystalline structure in the composite samples. Some other crystalline morphology formed in the pressure-crystallized PC/CNT samples, including spherulites, honeycomb-like porous crystals, and spike-like crystals, were also revealed by SEM.3. Crystallization of PC induced by synergistic action of C60and CNT at high pressuue. XRD suggested that the simultaneous introduction of C60and CNTs still did not alter the crystalline form of the polymer at high pressure. DSC results showed that the optimum pressure and temperature for the crystallization of the ternary PC/CNT/C60composites were200MPa and300℃, respectively. By increasing crystallization time to24h, a sample was crystallized with crystallinity and melting point respectively up to27.70%and238.65℃was finally crystallized under such optimum conditions. The synergistic induction of C60and CNT generated a wide variety of crystal morphologies of PC in the high-pressure crystallized ternary composites, such as dendritic crystals, open porous structured crystals, spherulites, three-dimensional reticular woven crystals, and so on. Moreover, as disclosed by SEM, the synergistic action of zero-dimensional C60and one-dimensional CNT promoted the large scacle growth of necklace-like nanocables with crystalline PC as sheaths, which further assembled into a three dimensional interpenetrating crystalline network with unique structures.