Study On Preparation And Thermal Conductivity Of Liquid Crystal Epoxy Resin Filled With Nanocellulose/BNNSs

With excellent dielectric properties,mechanical properties,chemical resistance and heat resistance,epoxy resin is widely used in electrical engineering.With the development of power systems to high voltage and large capacity,the heat within the unit volume of the equipment increases dramatically,causing insulation degradation of the epoxy resin.Therefore,it requires epoxy resin to have good thermal conductivity and heat resistance.In this paper,a novel epoxy resin composite with good thermal conductivity was developed.The hydrophobicity,mechanical properties,thermal conductivity and insulation properties were investigated.The main contents of the paper are as follows:(1)A preparation method of thermal conductive liquid crystal epoxy resin filled with CNF/BNNSs was studied.Biphenyl liquid crystal epoxy resin was used as a matrix,BNNSs as thermal conductive fillers,and cellulose nanofibers were used to increase the dispersibility of BNNSs and to construct the thermal conductive path.The effect of curing temperature on the microstructure of liquid crystal epoxy resin composite was discussed.It was found that the liquid crystallinity appeared between 106.8°C and 168.3°C.When the curing temperature were 120 °C and 150 °C,the anisotropic liquid crystal epoxy resin can be obtained.While the isotropic epoxy resin was obtained when the curing temperature was higher than 168.3°C.The addition of cellulose nanofibers can increase the dispersion of boron nitride in epoxy resin.(2)The hydrophobic properties,mechanical properties and insulation properties of liquid crystal epoxy resin filled with CNF/BNNSs were investigated.The static contact angle of the thermal conductive epoxy resin composite was measured,and the tensile strength,impact strength and dielectric properties were evaluated.The microscopic morphology of the surface of epoxy resin composite was observed.The results show that liquid crystal epoxy resin composites have good hydrophobicity,mechanical properties and insulation properties,and CNF/BNNSs can improve the toughness of the liquid crystal epoxy resin.(3)The effect of the content of CNF/BNNSs on the thermal conductivity,thermal stability and dynamic mechanical analysis of liquid crystal epoxy resin composites were studied.The thermal conduction mechanism of the liquid crystal epoxy resin was analyzed.The results show that with the increase of CNF/BNNSs,the thermal conductivity and thermal stability of the liquid crystal epoxy resin are improved.Compared to BNNSs,the addition of CNF/BNNSs can increase the thermal conductivity more significantly.(4)The AC breakdown voltage and partial discharge voltage of liquid crystal epoxy resin composites were measured.The effect of CNF/BNNSs content on pulsed electro-acoustic was studied.The results show that CNF/BNNSs can restrain the occurrence of thermal breakdown.The breakdown voltage and partial discharge voltage can be increased effectively when the CNF/BNNSs content is low.The results of above research show that the CNF/BNNSs filled liquid crystal epoxy composites have good thermal conductivity.CNF/BNNSs are easy to form heat conductive paths in liquid crystal epoxy resin,which can significantly improve the thermal conductivity of composite.As a result,it restrains the occurrence of thermal breakdown,providing excellent thermal conductivity,mechanical performances and insulation performance of epoxy resin composites.