Properties of phase change assisted preparation of low density polyethylene/expanded graphite composites
Aiming at the difficulty of exfoliating and dispersing layered fillers in polymer matrix,water is introduced into the layers of the layered fillers and frozen into ice.The volume of water with the same mass increases from liquid to solid,which increases the layer spacing of the fillers.In the process of melt blending,the ice between the layers of the fillers is rapidly trans-formed into water vapor under the action of high temperature and instantaneous high pressure is generated,thus achieving in-situ stripping of the layered fillers.Based on this principle,a new process for preparing low density polyethylene(PE-LD)/expanded graphite(EG)composites with phase transition assisted melt blending was proposed.The effects of the new method on the micro-morphology,crystalline properties and thermal conductivity of the composites were investigated.The scanning electron microscope images of the phase change assistant PE-LD/EG composites show thinner sheet stack structure and lower(002)diffraction peak intensity,which indicate the phase transition effect can effectively promote the in-situ exfoliation of EG.Dynamic scanning calorim-etry results indicate that the exfoliated EG layers can be used as heterogeneous nucleation point to promote the crystallization of PE-LD,the crystallinity of the composite was increased from 23.47%to 28.44%.The thermal conductivity test results show that the thermal conductivity of PE-LD/EG composite increases with the increase of EG content,and the thermal conductivity of the phase change assisted composite is higher than that of the conventional melt blend preparation,with a maximum value of 0.715 W/(m·K).EG in PE-LD/EG composite prepared by introducing phase change assistant effect has higher stripping degree and better dispersion effect,which helps to form a thermal conductivity path between EG sheets and improve the thermal conductivity of the composites.
phase transitionin-situ exfoliationexpanded graphitelow density polyethylenethermal conductivity
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