Preparation And Properties Of Poly(Vinylidene Fluoride)-Based Thermal Conductive Composites

With the development of science and technology and the needs of industrial applications,higher requirements are imposed on polymer composites.It is expected to have excellent comprehensive properties such as low cost,easy processing,excellent mechanical properties,corrosion resistance,high thermal conductivity,and electrical insulation etc..In this paper,carbon nanotubes(CNTs),copper nanosphere(Cu),and boron nitride nanosheets(BNNS)were applied as the thermally conductive fillers to fabricate the PVDF-based composites.The thermal conductivity and mechanical properties of PVDF composites were systematically studied.The modified PVDF composite membrane was prepared into a hollow fiber heat exchanger to explore its potential application value in the field of the heat transfer and desalination separation.The main research methods and the conclusions are as follows:Polyhedral oligomeric silsesquioxane(POSS)functionalized CNT was used to fabricate the CNT-POSS/PVDF composite membranes with high thermal conductivity.The surface modification of POSS promoted the dispersibility of CNT-POSS in PVDF matrix and enlarged the contact area between the fillers.Furthermore,the introduction of POSS nanoparticles into CNT-PVDF composites could improve their thermal stability,mechanical and thermal conductivity.Compared with pure PVDF membrane(0.15 W/(m·K)),15 wt%CNT-POSS/PVDF composite membrane possessed an extremely high thermal conductivity of 1.12 W/(m·K).Dopamine modifyied the Cu and PVDF matrix was applied to improve the interface compatibility between metal and polymer matrix,and then the synergy effect of CNT to build an interconnected heat conduction network was used to prepare the CNT-Cu/PVDF composite membrane.CNT filled the holes between Cu and PVDF matrix and reduced the distance the interface thermal resistance.With the filler loading of 30 wt%Cu and 5 wt%CNT,the thermal conductivity and tensile strength of PVDF composite membrane reached to 1.44 W/(m·K)and 95 MPa,which were860%and 78%higher than pure PVDF.PVDF composite membranes filled by SiO₂/CNT and BNNS were converted from electrical conductive to insulation properties by adjusting the proportion of fillers to meet the needs of the appliment of thermally conductive and insulating polymer materials in the field of electronic packaging.SiO₂ and BNNS suppressed the high electrical conductivity of CNT through space barrier effect.Meanwhile,the synergistic effect of nano-fillers with different morphologies improved the connectivity of the thermal network.The thermal conductivity and tensile strength of10 wt%BN-20 wt%(c-CNT/SiO₂)-PVDF composite were 1.23 W/(m·K)and 62.2MPa,respectively.The modified PVDF was prepared into a hollow fiber heat exchange tube by the melt stretching method.The heat transfer performance of PVDF hollow fiber heat exchanger in tube and shell style without phase change(liquid-liquid),single-phase change(steam-liquid)and two-phase change were tested in the experiment.The results showed that the phase change process could significantly improve the heat transfer performance of the heat exchanger,and the condensation heat transfer data was appled to fit prediction model of condensation heat transfer coefficient of hollow fiber heat exchanger.In two-phase change heat transfer process,the overall heat transfer coefficient and thermal efficiency of the hollow fiber heat exchanger reached up to1168 W/(m²·K)and 92%.