Study On The Preparation And Properties Of Thermal Conductive Fillers/Nylon 6 (Or Epoxy) Composites

With the development of miniaturization and high performance of electronic devices,it is difficult to eliminate the heat generated during operation.Packaging materials with high thermal conductivity are needed to eliminate the heat and ensure the working life and reliability of the devices.Traditional packaging materials such as metal and ceramic have brilliant strength and thermal conductivity.However,they are dense and difficult in machining.The poor insulation of metal may lead to the safety problems such as electric leakage.Due to the advantages of low density,good insulation and easy processing,polymer composites have gradually replaced traditional metals and ceramics as new packaging materials.However,the intrinsic thermal conductivity of polymer is low.It is important to develop polymer composites with high thermal conductivity to meet the demands of electronic devices.In this thesis,thermal conductivity and insulating polymer composites were prepared by different methods according to different application scenarios and requirements.The effects of filler combination,surface modification and preparation method on the thermal conductivity and mechanical properties of polymer composites were explored.(1)MgO-BN-GF/PA6 composites were prepared by the reaction of modified fillers to form a heat conduction network in the extrusion process.MgO and BN were treated with KH550 and GF was treated with KH560.The surface modification of the fillers was investigated by Fourier infrared spectroscopy(FT-IR)and X-ray photoelectron spectroscopy(XPS).Fifteen kinds of thermal conductive and insulating composites were prepared by melt blending of filler and PA6 by adjusting the filler treatment method and filler addition ratio.The effects of the reaction of amino and epoxy groups on the distribution of fillers during extrusion were studied by scanning electron microscopy(SEM)and X-ray energy dispersive spectroscopy(EDS).The effects of surface modification and filler content on thermal conductivity,bending properties,tensile properties and notch impact properties of the composites were studied.Compared with the non reactive extrusion process,the reactive extrusion process could improve the thermal conductivity of the composite.The thermal conductivity increased from 1.872 W/(m·K)to 2.121 W/(m·K)at 50 wt%filler.Besides,the composites had excellent mechanical properties.(2)Based on the reaction between amino group of KH550 and epoxy group of KH560,KH550 modified magnesium oxide whisker(MgOW)and KH560 modified BN were connected to prepare three kinds of MgOW@BN hybrid fillers with different proportions.Twelve groups of composites were prepared by mixing different amounts of MgOW@BN hybrid fillers with epoxy resin.The micro morphologies of MgOW and BN were observed by SEM.The modification of the filler was studied by FT-IR and XPS.The composites with different fillers were studied by FT-IR,XPS and SEM.The results showed that MgOW and BN in the hybrid filler were closely connected,which was beneficial to the construction of heat conduction network.The thermal conductivity of composite M@B3-20 with 20 wt%filler MgOW@BN-3 content increased to 0.489 W/(m·K)(220%of pure epoxy resin).When the mass ratio of MgOW-KH550 to BN-KH560 was 1:1 and the total filler filling content was 20 wt%,the thermal conductivity could be increased through hybrid treatment from 0.410 W/(m·K)to 0.465 W/(m·K).The bending test showed that when the filler content was higher than 15 wt%,the bending performance of the epoxy composite treated with hybrid fillers was higher than that of the epoxy resin composite without hybrid treatment.(3)Three dimensional porous BN(BN-PVA-foam)was prepared by removing NH4HCO3 as sacrificial phase in the mixture of BN-PVA and NH4HCO3.BN-PVAfoam was pyrolyzed to prepare BN-C-foam.Nine groups of BN foams were prepared by adjusting the ratio of NH4HCO3 to BN,and the composites were prepared by immersing them in epoxy resin.The microstructure of BN,BN foam and epoxy composites were characterized by SEM and TEM.The test of thermal conductivity showed that the thermal conductivity of composites could be greatly improved by introducing three-dimensional porous BN foam.At the same BN filling content,the thermal conductivity showed the order of EP-BN-foam>EP-BN-PVA-foam>EP-BN-Cfoam.The introduction of PVA increased the contact thermal resistance of BN,and the pyrolysis process destroyed the integrity of three-dimensional porous BN.The changes of surface temperature of composites during heating were recorded by infrared camera,and the results were consistent with the thermal conductivity.The thermal conductivity of the composites strengthened with BN foam increased to 6.201 W/(m·K)when the filling volume was 43 vol%BN.