Preparation Of Functionalized Boron Nitride Nanosheets And Their Polymer Composites

Owing to its unique two-dimensional structure,excellent mechanical strength,thermal conductivity,electrical insulation,chemical and thermal stability,the h-BN has broad potential applications in enhancing the performance of polymer.In this thesis we studied the preparation of boron nitride nanosheets(BNNS)and effects of boron nitride nanosheets on properties of polyvinyl alcohol,natural rubber and polyacrylamide hydrogel polymer composites.The main contents including the following aspects:1.Functionalized BNNS were successfully synthesized by high temperature and ultrasonic treatment.The structure and morphology of nanosheets were characterized by FTIR,XRD,TEM and Laman.The results showed that this method can be used to prepare BNNS with complete crystal structure,large size and few layers.There are a large number of hydroxyl groups on the nanosheets that can allow for further functionalization of BNNS.2.Using functionalized BNNS and polyvinyl alcohol(PVA)as raw materials,a series of BNNS/PVA composites with different loadings of BNNS were prepared by solution blending method.The composites were investigated by FTIR,XRD,scanning electron microscopy(SEM),differential scanning calorimetry(DSC),thermogravimetric analysis(TGA),tensile test and dynamic mechanical analysis(DMA).The nanosheets were found to be dispersed in the polymer matrix well and the thermal properties of the polymer can be improved by the addition of BNNS.The results of tensile tests and DMA showed that with 1wt% BNNS added,tensile strength and storage modulus were increased by 87.5 % and 43 % compared to the neat samples,indicating that the BNNS can behave as an effective filler for polymers.3.A series of BNNS / natural rubber(NR)composites with different loadings of BNNS were prepared by latex mixing and co-coagulation methods.The XRD,SEM,DMA,tensile and thermal conductivity of the composites were tested and analyzed.The results indicate that the addition of boron nitride nanosheets,mechanical strength of the composites improved significantly.In this experiment,co-coagulation process would afford a network morphology.This skeleton structure provided more pathways for heat transfer,contributing to the improvement of composite materials' thermal conductivity.Incorporation 5 wt% of BNNS,the thermal conductivity of rubber can reach 0.192 W m-1K-1 higher than that of neat samples(0.152 W m-1K-1).4.Polyacrylamide(PAM),sodium alginate(SA),BNNS as raw materials,different types(PAM,BNNS/PAM,SA/PAM,and BNNS/SA/PAM)hydrogel were prepared.The structure and properties were investigated by FTIR,SEM,DSC,tensile and swelling test.The results suggested that the structure of the ternary nanocomposites hydrogel is more compact than that of the PAM hydrogel.It was found that the tensile strength and thermal properties of the hydrogel can be improved obviously by BNNS and the new ionic crosslinking network,the maximum degradation temperature of the ternary nanocomposites hydrogel can be increased by 12 ?,and tensile strength increased by 963.6%.