| As a kind of high-performance polyolefin prepared through copolymerization, impact polypropylene copolymer (IPC) has attracted great attention, and many researches concerning composition, structure and properties of which have been carried out. In general, IPC synthesized by means of two-step polymerization is a multi-component/multi-phase system which supplies good rigid-toughness balance. For multi-phase polymer materials, their ultimate properties are determined by the structure in condensed state directly. Moreover, evolution of phase morphology occurred during processing certainly affect this structure. Hence, studies on the phase morphology and crystallization behavior of IPC during thermal treatment are significant to optimize the performance and regulate the processing technic.In this thesis, the influences of two main processing factors affecting phase 'structure and crystallization behavior, i.e., thermal treatment and shearing were studied, and the aggregation structure and morphology evolution during annealing were discussed in detail.The evolution of phase morphology for IPC was observed by scanning electron microscope (SEM) and phase contrast optical microscopic (PCM). An entirely different architecture of IPC melt could be found after being annealed. The 'core-shell' structure of dispersed phase is destroyed completely, and the sizes of the dispersed domains increase obviously by 5 to 10 times after being annealed at 200℃for 200 min. Through examining the coarsening of phase morphology, we find that the co-continuous structure and an abnormal'sea-island'structure successively appear with the increase of annealing time. The original matrix, PP component, turns to be dispersed phase, while the copolymer components, the continuous phase, implying appearance of a special phase inversion induced by melt-state annealing. Moreover, PP component becomes matrix and the copolymer components form the dispersed phase again when IPC solidifies, which is believed to be another'phase inversion'. These changes are ascribed to the large tension force induced by solidification in phase interface and the great difference in content between components. Contrarily, the coarsening rate of phase domain of iPP/EPR with same proportion is much smaller under thermal treatment, which is ascribed to the compatibilization of EbP component existing in IPC. The morphology of IPC/HDPE blend was investigated. The results show that HDPE component mainly intrudes into the'core'of dispersed phase—PE-rich EbP component and become new'core'together with EbP. This proved indirectly that the dispersed phase of IPC is composed of EbP and EPR, and the'core-shell' structure is endowed with certain thermodynamic stability.The crystal morphology of IPC samples after being annealed was investigated. It is seen that the crystal of IPC is still spherulite and only the perfection is affected by the degree of phase separation. Moreover, spherulite morphology become clear, large amorphous phase domains appear in the spherulite and crystal is imperfect because of phase coarsening. In general, increase of annealing time results in the decrease of the overall crystallization rates and nucleation densities of IPC sample, however, the spherulite radial growth rates keep almost constant. It is suggested that annealing in the molten-state mainly affects the nucleation ability of IPC, due to the coarsened phase structure and decreased interface area.Furthermore, the phase morphology and rheological behavior of IPC samples exposed to different shearing histories were investigated. The results reveal that there exists an optimal shearing range which results in the best distribution of dispersed phase and formation of network-like structure. The influence of shearing time and rate on crystallization behavior is just opposite. The increase of shearing time promotes crystallization; however, increase of shearing rate reduces the crystallization ability of IPC. |
PDF Full Text Request