The Study On Cross-linking Behavior And Crystallization Behavior Of High-density Polyethylene

In this paper, the peroxide crosslinking behavior of high density polyethylene (PE-HD) was studied. The effect of dicumyl peroxide (DCP) content on gel fraction of PE-HD was investigated. The optimum crosslinking condition was selected. The gel fraction of PE-HD increased with the increment of DCP content. The increase rate of gel fraction leveled down when the DCP content was over1.5%. The gel fraction reached73.9%with the DCP content of3.0%. DCP was completely decomposed and the cross-linking reaction was completed at the temperature of170℃with the cross-linking time of30min.The effect of DCP content on crystallization behavior of PE-HD were studied by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that the melting temperature and the crystallization temperature decreased with the increasing of DCP content. The crystallization degree and the grain size decreased. But DCP content showed no effect on the crystal structure.The isothermal crystallization and non-isothermal crystallization behavior of cross-linked high-density polyethylen was studied by means of differential scanning calorimetry(DSC).Its crystallization kinetics was studied respectively by Avrami method,Gupta method,Jeziorny method and Mo method. The results showed that in the isothermal crystallization process, with the increase of crystallization temperature the crystallization rate was slower, and the growth of crystal was three-dimensional mode of heterogeneous nucleations. In the non-isothermal crystallization process, with the increase of cooling rate the crystallization rate of cross-linked high-density polyethylen was improved. Cross-linked high-density polyethylen produced secondary crystallization. The nucleation mechanism and growth mode was changed by cooling rate of cross-linked high-density polyethylen.At primary crystallization stage,the growth of cross-linked high-density polyethylen was three-dimensional mode of homogeneous nucleations when the cooling rate is slower. The growth of cross-linked high-density polyethylen was three-dimensional mode of heterogeneous nucleations when the cooling rate is improved to30℃/min.In the secondary crystallization stage,the growth of cross-linked high-density polyethylen was one-dimensional mode when the cooling rate is slower. The growth of cross-linked high-density polyethylen was two-dimensional mode of heterogeneous nucleations when the cooling rate is improved to30℃/min.The crystal morphology in the isothermal crystallization and non-isothermal crystallization process was studied by Polarized Optical Microscope. The crystal morphology of cross-linked high-density polyethylen was investigated. The results showed that the crystal size after heat treatment was much bigger than before. The crystal of high-density polyethylen appear extinction concentric rings under conditions of high temperature. The crystal size of PE-HD was reduced with the increment of DCP content and the crystal structure more incomplete.