Study On The Crystallinity Mechanism And Nanocrystal Effect

On the basis of retriving of the relative literatures, the crystallization behavior of PVC were summarized in this paper. It was concluded that the crystallinity can be improved by modification on the base of the crystallization bahavior of PVC. The high crystallinity PVC was crashed in the jet-mil and the size of crystal reduced. Then the nanocrystalline PVC was prepared. The properties of nanocrystalline PVC were tested and the theory was used to explain it.The effect of different heat treatment factor on PVC crystallinity was studied firstly in this paper. The research result indicated that heat treatment time and heat treatment temperature had effect on PVC crystallinity. The ideal heat treatment time was about 2 hours and the maximum crystallinity appeared at 130掳C. The heat treatment temperature followed a linear relationship with Tm. Furthermore Tm was about higher 20 掳C than heat treatment temperature.In this paper, the crystallinity of PVC modified by homemade nucleating agent and heat treatment was increased. The maximum crystallinity reached 12%.The crystal PVC was crashed by jet-mill to prepare nanocrystal PVC. The crash, degradation and the change of morphology and crystalline structure changes of PVC was studied by FTIR, SEM, DSC, TEM. The self-plasticization and self-reinforcement of nanocrystal PVC was studied, too. The results showed that there was anomalistic crystal whose size reached nanometer grade in fine PVC; it's about 80nm. The crystal structure was damaged by jet-milling, which induced the melting point of nanocrystal PVC decreased from 210"C to 128掳C. The nanocrystal PVC induced the decrease.of plasicizing time and equilibrium torque and the increase of maximal torque, which showed that the nanocrystal PVC had self-plasticization in PVC composites. At the same time, the impact and tensile strength enhanced adding nanocrystal PVC.Scanning electron microscopy was utilized to observe the structure of nanocrystalline PVC. The sheet structure of PVC was found in the rupture partical of PVC. The nanocrystalline PVC formed through jet-mill crashing. Different crashcondition had effect on particle morphology and melting point and crystallinity and particle size distribution.The physics model was established to deduce the relationship of different classifying gear speeds and melting point on the base of the broken theory and the broken process of PVC. It explained that the melting point of nanocrystalline PVC was low. Therefore the effect of nanocrystal was proved in theory.