| With the development of new design concept, the progress of modern molding technology and the growth of awareness for energy conservation and environmental protection, plastic materials are gradually to play their potential and advantage. On the one hand, the plastic green manufacturing technology begins to become a modern nanufacturing concept and molding mode. On the other hand, developing new and competitive polymers and their composites with high-performance, high-function and low cost is impending, especially for their applications in the functional and structural fields.RHCM injection process is a new green manufacturing technology in which the mold cavity surface is demanded to have high-glossiness, ripid cooling and heating is needed and the injection cycle is started as the temperature of cavity surface is up to the glass transition temperature of molded polymer. Because the parts with high surface glossiness and without weld line can be injected by RHCM process, so that the injected plastic parts no longer need any spraying, glaring or other post processing, and RHCM process has received rapid development and wide application in many fields. However, its unique process characteristics also puts forward higher requirement to the performance of molded resin. For example, under the high-temperature injection molding, the additives with small molecular weight are very easy to decompose, and their modification effect is weakened; the decomposition and floating of additives with small molecular weight cause poor surface quality of molded plastic parts; the crystallization process of crystalline polymers become more complicated, etc. In addition, though the performance of existing polymers and their composites have received a great deal of optimization, the indexes for strength and rigidity are not still able to meet the requirement of materials performance needed in functional and structural fields, and it is urgent for us to develop new alternative materials with low cost, more excellent comprehensive performance and more outstanding needed characteristics.Focusing on the above problems, this studies were carried out based on RHCM injection and melt blending processes, and selected the widely applied amorphous composites-PC/ABS and semi-crystalline resin-PP as the research objects, meanwhile, the micro and macro material characterization methods were employed, the specific work are as follows:(1) This paper studied the sensitivity level of PC/ABS composities to weld line of plastic parts with the increase of ABS content, deeply analysed the effect law of fiber initial length, addition content and feed way on the length distributions of glass fibers in plastic parts, and analysed and revealed their action effect and mechanism on the mechanical and thermal properties of composites.(2) Standard test specimens with flame-retarded short glass fiber reinforced PC/ABS materials were fabricated under the RHCM condition by selecting a potassium perfluorobutane sulfonate (PPFBS) flame retardant specially used for PC, FR2025, and two kinds of aryl phosphorus halogen-free flame retardants, UN707 and PX-220. The flame retardancy effect of the above different flame retardants and some common fillers on the studied systems was compared. Meanwhile, the thermal properties, mechanical properties and surface quality of flame-retarded fiber reinforced composites were studied. Finally, PC/ABS composite with high-strength and high flame retardancy which is in accordance with industry demand was obtained.(3) Under RHCM process conditions, Effects of mold cavity surface temperature in the filling process on the crystallization status of PP on the different thickness layers of injected plastic parts were investigated, the inner relationship between the surface quality of plastic parts, crystallinity and residual stress was revealed, and effects of common fillers on the surface glossiness and shrinkage of PP plastic parts were studied.(4) Effects and action mechanism of high-temperature annealing process parameters, such as annealing temperature, annealing duration and cooling speed, on the microstructure evolution of PP on different thickness layers, and the surface quality and mechanical properties of PP plastic parts were investigated and revealed.(5) The a nucleation agent, RHCM mold temperature, annealing process, compatibilizers and SiO2 nanoparticles were selected as research objects, and their effects and action mechanicsm on strength and rigidity of PP resin and its composites were investigated from the viewing angle of crystallinity, crystallization evolution, interfacial compatibility and physical action of nanoparticles to interface.Through the above researches, a PC/ABS composite meeting flame retardancy requirement of VO level under RHCM high-temperature injectin process and a large amount of glass fibers was obtained, the technical advantages of gas phase flame retardancy mechanism in fiber reinforced system was discovered, and the improvement action and negative effects of flame retardants on the mechanical properties and surface quality of the fiber reinforced PC/ABS composites were revealed. Meanwhile, the action mechanism and law of RHCM high-temperature injection and high-temprature process on improving crystallization state of PP resin were got, the optimal injection mold temperature and annealing parameters which are benefit of PP materials with excellent comprehensive performance were obtained, and the inner relationship between RHCM injection process, high-temprature parameters, crystallization state of resin and surface quality of plastic parts. In addition, the different effects and action mechanism of crystallinity, crystallization evolution, imterfacial compatibility and interfacial characterization on the strength and rigidity of PP materials were analysed and obtained, the modification methods and action conditions of nano-SiO2 for improving the radial compressive stress and shear modulus of imterface were revealed, and a PP composite with high-strength and high-rigidity was obtained. Finally, the valuable theoretical guidance and modification experience for developing high-performance amorphous and crystalline polymers and their composites being suitable for RHCM process were provided. |
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