Study On The Performance Of Nanocomposites Based On Cellulose Nanofibrils And Functionalized Boron Nitride Nanosheet

In this study,cellulose nanofibrils(CNFs)prepared by mechanical grinding was respectively post-treated by high pressure homogenization,endoglucanase and a combination of endoglucanase and homogenization,and then the cellulose nanopaper(CNP)with different post-treated CNFs were prepared by vacuum-assisted filtration.Next,the undried CNP was mercerized with different concentrations of NaOH solution to tune the content of cellulose?in CNP.After then,the functionalized hexagonal boron nitride nanosheet(f-BNNS)was prepared by mechanochemical exfoliation h-BN under xylose assisting ball milling.At last,the composite based on CNFs and f-BNNS was prepared.At the same time,the CNFs/f-BNNS composite with best comprehensive performance were mercerized by different concentration of NaOH solution to further enhance the performance of the composites.The main conclusions are as follows:(1)Compared with the GCNFs prepared by mechanical grinding only,the size uniformity of CNFs was significantly improved by post-treatments,but excessive post-treatment resulted in the decrease of polymerization degree and crystallinity of CNFs.Besides,the optical properties,mechanical properties,thermal dimensional stability and oxygen barrier properties of CNP prepared with the post-treated CNFs had been significantly improved.Especially for the GHCNF-f samples,its optical transparency(46.97%),tensile strength(148.29MPa),elongation at break(12.54%),thermal stability(6.91 ppm·K^-1)and oxygen barrier property(29.96 m L/m²·day)all were kept well.(2)Through mercerizing treatment of undried CNP,the CNPs with different cellulose II crystalline structure content were successfully prepared.When the alkali treatment concentration was?15 wt.%,the proportion of cellulose II crystal structure in CNP was?85%.The mercerized CNP showed dense structure and smooth surface,but excessive mercerization resulted in the crystallinity of the cellulose in CNP to decrease from 65.7%to 46.2%.Among them,the CNP treated with 15 wt.%NaOH solution showed the best comprehensive properties,including tensile strength of 143.2 MPa,toughness of 17.2 MJ·m^-3,wet strength of 45.6 MPa,optical transparency of 88.44%,and initial thermal degradation temperature of 323.9?.(3)The f-BNNS with hydroxyl group,amino group and xylose was prepared by mechanochemical exfoliation h-BN under xylose assisting ball milling.A composite with anisotropic thermal conductivity and flexibility was prepared by combining CNFs and different amounts of f-BNNS.When the f-BNNS dosage was 30 wt.%,the composite of 0.3-BNNS-CNP with best performance was obtained,which in-plane thermal conductivity was 12.68 W/m K,the tensile strength was 117.63 MPa,and the elongation at break was 2.88%.(4)The 0.3-BNNS-CNP sample was mercerized by different degree of mercerization,and the sample's toughness and thermal conductivity were significantly enhanced.Compared with the sample of 0.3-BNNS-CNP,the sample(0.3-BNNS-CNP-12.5)mercerized by 12.5 wt.%NaOH solution showed the best comprehensive performance,and its in-plane thermal conductivity and toughness were increased by 16.3%and 321.8%,respectively.The composite of 0.3-BNNS-CNP-12.5 with excellent anisotropic thermal conductivity and flexibility has the potential to be used as a heat dissipation material in next-generation flexible electronic devices.