The Preparation And Study Of Dicumyl Peroxide Crosslinked Polyethylene

Polyethylene(PE) is one of the five general plastics,which shows excellent electric insulation,low temperature tolerance,easy processing. PE has been the most widely used plastics in(?)hin film,foam,pipe material,insulated material and etc.However,PE has some disadvantages,i.e.,low melting point,poor creep behavior,which greatly limit its application.Recently,proper modifications of PE attract great attention in both application and theoretical studies.Crosslinkage of PE will improve its tensile strength,impact strength,anticreepy property,high temperature resistance and etc.with little effect on its original capabilities.Therefore,the study on the crosslink modification of PE has particular important significance.In this work,dicumyl peroxide(DCP) was chosen as a crosslinker and the diffusion of DCP into the PE chip at the temperature below the PE melting point has been studied.The crosslinking process of PE intiated by DCP was carried under the temperature above 160℃.Generally,the work of this thesis is summarized as follows:1.Blending method was used to make DCP diffuse into PE chips.The same DCP/PE ratio samples with various diffusion times were prepared.The results of differential scanning calorimetry(DSC) characterization showed that the amount of DCP diffused into PE chips increased with the increase of time.The Fick model was adopted to theoretically describe the DCP diffusion process,showing that the diffusion process in this work is accord with zero-order diffusion equation.2.The thermal decomposition process of DCP inside PE was studied by DSC.Arrhenius equation was used to depict the thermal decomposition kinetics and the results manifested that the decomposition accord with first-order reaction kinetics.Frequency factor(lnA) was about 35-40 and the apparent activation energy(E) was about 150-160 kJ/mol.According to the relationship between reaction degree and reaction time,a method to control the reaction process of DCP crosslink PE was also proposed.3.DSC characterization was applied to study the non-isothermal crystallization kinetics and crystal behavior of DCP crosslinked PE. The results showed that crystallization rate of modified PE significantly decreased.Avrami index(n) is between 3.2 and 4.2, implying the coexistence of homogeneous nucleation and heterogeneous nucleation during the crystallization process in pure PE and crosslinked PE.The constant of crystallization rate(Z_c) is larger than that of pure PE and the same trend of n was also observed.4.The results of dynamic mechanical analysis(DMA) measurement indicated that storage modulus of crosslinked FE was larger than that of pure PE.Theαrelaxation peak shifted towards lower temperature and the peak profile became wide,indicating that the addition of DCP lead to the multiple movement of PE chains and destruction of its crystal regularity.Furthermore,the decrease tendencies of the melting point and melting enthalpy of PE/DCP illustrated that the crosslink effect brought by DCP did hinder the arrangement of PE molecules into the crystal lattice,thus decreased the matrix crystallinity.