Preparation Of Bnnss By Liquid Phase Exfoliation And Its Application In Thermally Conductive Polymers

With the development of graphene research,hexagonal boron nitride nanosheets(BNNSs)were aroused widespread concerns due to their excellent physical and chemical properties and extensive application prospects.The efficient preparation method of BNNSs is the premise and foundation of the application of BNNSs.In this paper,the liquid phase shearing method is used to prepare the hydroxylated BNNSs dispersion in the aqueous phase.The high-speed dispersing homogenizer and rotating packed bed are used as the exfoliation equipment.The surfactant and ball mill pretreatment are used to strengthen dispersibility in water.The main contents are as follows:1 h-BN powder was exfoliated in aqueous solution by using high-speed dispersion homogenizer as the exfoliation device and sodium dodecyl sulfate(SDS)as the surfactant.The effects of process conditions were studied on the concentration of BNNSs supernatant,such as exfoliation speed,exfoliation time,initial concentration of h-BN and SDS.Under better experimental conditions,the concentration of BNNSs dispersion was 0.88 mg/mL.The average lateral dimension of BNNSs was 236 nm,and the thickness was less than 10 layers.XPS,infrared spectroscopy,and EDS line scan analysis showed that the liquid phase shear exfoliation method in aqueous solution could be used to complete hydroxyl functionalization at the edge of BNNSs while preparing BNNSs.2 Nano-composite films were prepared by using hydroxyl functionalized BNNSs(OH-BNNSs)prepared by high-speed dispersion homogenizer and BNNSs prepared by ultrasonic method as fillers.We have studied the effect of different hydroxylated BNNSs on the thermal conductivity of composite films and different mass concentrations of OH-BNNSs on the mechanical properties and thermal conductivity of the composite film.The results show that the in-plane thermal diffusivity of OH-BNNSs-PVA film reaches 9.031 mm2/s when the amount of OH-BNNSs added is 50 wt%,which is 40 times the in-plane thermal diffusion the pure PVA film and 1.6 times the in-plane thermal diffusivity of the PVA composites filled by BNNSs prepared from ultrasonic exfoliation.In addition,OH-BNNSs can greatly improve the thermal stability and rigidity of the composite film,and reduce the toughness of the composite film.3 h-BN powder was exfoliated in aqueous solution by using rotating packed bed as the exfoliation device and polyvinyl alcohol(PVA)as the surfactant.The effects of process conditions were studied on the concentration of BNNSs supernatant,such as exfoliation speed,exfoliation time,initial concentration of PVA.Under better experimental conditions,the concentration of BNNSs dispersion was 0.28 mg/mL.The average lateral dimension of BNNSs was 390 nm,and the thickness was less than 10 layers.Similarly,this method could also realize hydroxyl functionalization at the edge of BNNSs.4 Using h-BN powder and easily decomposed ammonium salt as raw materials,h-BN was pre-treated by ball milling for 6 h,and then the added ammonium salt was removed at a high temperature of 900?.The results show that ball milling can decompose ammonium salt and promote the bonding of-NH2 group to h-BN.Pre-treated h-BN powder was exfoliated in aqueous solution by using rotating packed bed as the exfoliation device.Under better experimental conditions,the concentration of BNNSs dispersion was 1.7 mg/mL,and the yield was 8.5%.According to the test results,the hydroxyl functionalization also occurred during the liquid phase shear exfoliation process.