Research On Online Characterizing Crystallization Of Complex Polymer Systems

Understanding the process of crystallization or vulcanization of polymers is important for controlling the molding process parameters and manufacturing of excellent products. The characterization method of crystallization or vulcanization of polymer was studied in this thesis. The main work and conculsions are as follows.(1) The process of non-isothermal crystallization of HDPE/PP was detected by ultrasonic device systematically. An equation between velocity and temperature was generated. The curves of crystallinity calculated by ultrasonic velocity were translated by Jeziorny model. The values of Avrami index were between 3-4 and the semi-crystallization time decreased with increasing of pressure. The number of peak on melting and crystallization curves of DSC changed from single to double when the cooling rate changed from 10?/min to 5?/min. The tensile strength and impact strength increased firstly and then dropped with increasing of HDPE while there was a maximum at 50% of HDPE.(2) The process of non-isothermal crystallization of PP/CaCO3 was detected by ultrasonic device systematically. An equation of velocity related with temperature and CaCO3 content was established. Crystallinity calculated by ultrasonic velocity was translated by Jeziorny method. The value of Avrami index was between 3-4 and the semi-crystallization time decreased firstly and then increased with increasing loads of CaCO3 while there was a maxmuum at 5% of CaC03. The melting and crystallization curves of DSC showed CaCO3 decreased the melt temperature and increased the crystallization temperature firstly and then decreased. The tensile strength dropped with increasing of CaCO3 and the impact strength increased firstly and then dropped with increasing of HDPE while there was a maximum at 20% of CaCO3.(3) The process of vulcanization of NBR/HDPE mixture was detect-ed by such rheological methods, as rubber processing analyzer. The fite-d results of torque during scorch progress showed HDPE reduced the v-ulcanization rate. The curve of storage modulus-strain showed Payne eff-ect. The main function of storage modulus with strain and HDPE load by Kraus model. DSC curves showed NBR decreased the melt temperat-ure of HDPE while lifted the crystallization temperature slightly. The v-alues of Avrami index was between 1-2 while the semi-crystallization t-ime of HDPE in vulcanizated mixture, HDPE and unvulcanized mixture reduced in turn. The capillary rhemometry showed the mixture was ps-eudoplastic while DMA and mechanical properties showed that HDPE i-ncreased thermal deformation resistance, hardness and tear strength of NBR in contrast with decreasing the glass transition temperature and the tensile strength.(4) The vulcanization process of NBR/HDPE was monitored by rotorless rheometer and PVT with ultrasonic probes. An equation between velocity and time that described process of crosslinking was proposed. The PVT of mixtures was analyzed by Tait equation showing that the isothermal compressibility decreased while the compression coefficient of thermal expansion increased with the increasing load of HDPE. The relationship between velocity and specific volume was got by linear fitting and Tait fitting on the basis of the experimental data. The linear fitting was better than Tait fitting.The formed online quantitative characterization of rubber vulcanization and polymer crystallization can be further widened and deepened for other polymer thermodynamics. This suggests its significance in material modification and molding process optimization for engineering applications.