Preparation Of Heat-resistant ABS And PLA Materials

As one of the most important indicators of engineering materials, the heat resistance of polymers is not only involed in material processing, but also closely related to the product applicability. In this dissertation, we developed a new synthetic route of N-phenylmaleimide-styrene-maleic anhydride (NSM), which is a heat-resistant moditifer of acrylonitriie-butadiene-styrene (ABS), and the heat-resistant ABS was prepared by blending. Meanwhile, for the heat-resistance defect of biodegradable polylactide (PLA), a sreies of stereoblock PLAs (sb-PLAs) were prepared by chemical copolymerization to develop the high-performance PLA materials.First of all, the heat-resistant copolymer of NSM was synthesized in xylene at125℃, using di-tert-butyl diperoxyterephthalate as an initiator. The characteristic of NSM was analyzed by Fourier transform infrared (FTIR), nuclear magnetic resonance (’H-NMR,13C-NMR), gel permeation chromatography (GPC) and elemental analysis (EA). The13C-NMR results showed that the NSM possessed random sequence distribution; this was also supported by the differential scanning calorimetry (DSC) experiment in which a single glass-transition temperature (Tg) of202.3℃was observed. The thermal stability and degradation mechanism of NSM were investigated by thermogravimetric analysis (TGA). Using the Kissinger equation and Ozawa equation, a nucleation controlling mechanism was proved with an apparent activation energy of144KJ/mol. Therefore, the NSM showed greater thermal stability due to the existence of five-member planar ring and strong polar carbonyl structures. It had no weight loss below290℃. This temperature is much higher than the processing temperature of ABS, which is about220℃-240℃in most cases.Futher, the NSM random copolymer was treated as a novel heat-resistant modifier and was blended with the general-grade ABS to prepare high-performance heat-resistant ABS materials. The NSM showed good compatibility with the ABS matrix. The impact fracture surface morphology results revealed that, cayitation and cavity coalescence played an important role in material toughening, which may cause a downward trend of impact strength with the contents of NSM increased. The effects of NSM contents on the thermal, mechanical and rheological properties of ABS blends were investigated. With the increasing contents of NSM, the Vicat softening point (VST), tensile strength, flexural strength, flexural modulus and Rockwell hardness of the ABS/NSM blends were all significantly enhanced, whereas the impact strength decreased, as predicted. The rheological behavior of the blends was examined with a capillary rheometer. For all the ABS/NSM samples, pseudoplastic characteristics were observed and their viscosity increased with increasing NSM contents. However, they still held excellent processing property, and are suitable for injection molding.The key issue that restricts the development of PLA materials is their poor heat resistant properties. Therefore, we focused our research on the synthesis, structure and characterization of stereoblock PLA (sb-PLA) subsequently, hoping to upgrade the performance of PLA by stereocomplex technique. The triarm poly(propylene oxide)-poly(D-lactide)(PPO-PDLA) copolymer was prepared by ring-opening polymerization (ROP) of D-lactide (DLA) with low unsaturated poly(propylene oxide) triols (PPO) as an initiator. The terminal hydroxyls of the prepolymer were activated by Stannous octanoate (Sn(Oct)2). Then a series of novel triarm poly(propylene oxide)-poly(D-lactide)-poly(Z-lactide)(PPO-PDLA-PLLA) block copolymers were synthesized by ROP of Z-lactide (LLA) with functioned PPO-PDLA prepolymer as a macroinitiator. FTIR, NMR and GPC results confirmed the configuration of triarm PPO-PDLA-PLLA block copolymers with high isotacticity, and the number average molecular weight (Mn) of the samples could be greater than105. The block structure of copolymer chain could be readily adjusted in terms of LLA units and molecular weight of PPO-PDLA prepolymer. DSC and wide-angle X-ray diffraction (WAXD) demonstrated that the stereocomplex PLAs (sc-PLAs) were formed between intermolecular PLLA and PDLA blocks without the PLLA crystallization process. The melting temperature (Tm) of sc-PLA crystal was about200°C, which was much higher than that of pure PLLA. These results show that the triarm PPO-PDLA-PLLA block copolymers could be promising as a heat-resistant PLA material.