Variation Of Mechanical Properties And Structure Of Wood-based Carbon Fiber Treated By Boric Acid

In this study,wood-based carbon fibers made from lignin and wood powder were prepared through processes of liquefaction,melt-spinning,curing,modifying by boric acid and carbonization.The effect of carbonization temperature and boric acid concentration on tensile strength and modulus of wood-based carbon fibers were investigated.To clarify the relationship between microstructures and mechanical properties of wood carbon fibers modified by boric acid,the mechanism of boron on the mechanical properties of wood carbon fibers was explored through morphological observation,Raman,XPS and so on.The main results are as follows:1.The tensile strength and modulus of lignin-based carbon fiber(LCF)increased with the increasing carbonization temperature and the concentration of boric acid solution.The LCF treated with 11%boric acid and carbonized at 900? had the best mechanical property.The tensile strength and modulus were 513.67MPa and 68.72GPa,respectively.2.The tensile strength and modulus of carbon fiber made from wood powder(WCF)increased with the increasing carbonization temperature.The WCF treated with 8%boric acid and carbonized at 900? had the best mechanical property.The tensile strength and modulus were 468.39MPa and 58.64GPa,respectively.3.According to the Raman spectra and XRD analysis,with the increasing of carbonization temperature and the boric acid impregnation,the R-value and intensity of D band decreased,while the intensity of G band increased,which corresponded to the vibrational modes of the ideal carbon lattice,indicating that the increase of carbonization temperature and boric acid solution modification were beneficial to improve the order of graphite crystal layers.In addition,the distance of graphite layer d002 decreased,the crystallite size Lc and La increased,the ratio of Lc and d002 gradually increased in the range of 1?2.4.The residual boron oxide(B2O3),which was generated through boric acid(H3BO3)decomposition,would cause oxidation and etching on the fiber surface during the process of thermal decomposition,leading to fiber surface defect,and further mechanical property reduction of carbon fiber.After impregnating with boric acid,the d002 of LCF decreased slightly,but the La increased obviously from 0.7616 to 1.0543.Besides,the d002 of WCF decreased from 0.4524 to 0.4288.Hence,boron would give priority to substitute the carbon atoms which possessed high activity in amorphous region,and then prevented the defects causing by carbon atoms escape and promoted the perfection of microcrystalline structure.The mechanical property of wood-based carbon fiber was improved simultaneously by boric acid modification.