Preparation And Thermal Conductivity Of Composite Poly(vinylidene Fluoride)-based Thermal Conductive Materials

Compared to metallic materials for the use of heat exchanger,polymeric materials enjoy superior advantages such as corrosion resistance,low density,fouling resistance and facile processing.The defects of metal materials could be supplemented by polymers,with great potential in the application of heat exchanger.Poly?vinylidene fluoride??PVDF?is semi-crystalline thermoplastic polymer with excellent corrosion resistance,thermal and electrochemical stability.In this paper,the PVDF composites filled with different fillers were prepared and studied.The graphene was doped in PVDF matrix for preparing GE/PVDF composite membranes.In addition,electric field was applied for graphene alignment during membrane formation.The structure and properties of the composite membranes before and after alignment were characterized and analyzed.The results showed that after the alignment with electrical field,the arrangement of graphene was orderly in the matrix.The tensile strength and thermal conductivity of composite membranes were significant improved with the addition of graphene.This tendency was further enhanced by the application of electric field.When graphene content was 20 wt%,the thermal conductivity of the composite membrane was increased by 212%than that of pure PVDF and it was further enhanced to 226%after applying electric field.The MWCNTs/GE/PVDF composite membrane was prepared with the hybrid filling of one-dimensional MWCNTs and two-dimensional GE in PVDF matrix.The synergistic effects of MWCNTs and GE on the mechanical properties and thermal conductivity of MWCNTs/GE/PVDF composite membrane were investigated.After the introduction of MWCNTs,the accumulation and stacking of GE was effectively suppressed.The synergistic effect of MWCNTs and GE improved the mechanical and thermal properties of PVDF composite membrane.When the content of MWCNTs/GE was 10 wt%,the thermal conductivity of the composite membrane achieved a value of 0.5214 W/?m·K?,which was 189.7%higher than that of pure PVDF.The thermal conductivity of composite membrane was increased by 28.2%after the introduction of MWCNTs,compared to composite membrane with the same content of GE.The a-MWCNTs were prepared by treating MWCNTs with H₂SO₄/HNO₃.The a-MWCNT/GE/PVDF was prepared by hybrid addition of a-MWCNTs and GE into PVDF matrix.The dispersibility of carbon nanotubes?a-MWCNTs?was significantly improved after acidification.The coiling was greatly reduced.Significantly improved dispersibility and homogeneity could be obtained in a-MWCNTs/GE/PVDF composite membrane,compared to that of in p-MWCNTs/GE/PVDF composite membrane.The improved dispersion resulted in elevated thermal stability,enhanced tensile strength and increased thermal conductivity.When the content of a-MWCNTs/GE reached 10 wt%,the thermal conductivity of the composite membrane achieved a value of 0.6277 W/?m·K?,which was 248.72%higher than that of pure PVDF.The a-MWCNTs was further modified with vinyl triethoxysilane coupling agent.Then s-MWCNTs/GE/PVDF composite membrane was prepared by hybrid addition of s-MWCNTs and GE in PVDF matrix.There was a better dispersibility of s-MWCNTs than a-MWCNTs,as well as smaller entanglement of carbon nanotubes.The s-MWCNTs suspension in NMP exhibited long-term stability.The SEM images indicated better dispersibility and improved compatibility of s-MWCNTs/GE in PVDF matrix.When the content of s-MWCNTs/GE reached 10 wt%,the maximum thermal conductivity of 1.46 W/?m·K?could be achieved.It was 711.11%higher than that of pure PVDF.