This paper presents systematic and improved methodologies to characterize the surface and fracture of elementary hemp fibres by Field Emission Scanning Microscope (FE-SEM), determine the Microfibril Angles (MFA) by an...This paper presents systematic and improved methodologies to characterize the surface and fracture of elementary hemp fibres by Field Emission Scanning Microscope (FE-SEM), determine the Microfibril Angles (MFA) by an advanced microscopy technology and examine the crystallinity by X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR). The results showed that 1) There existed various deformations/defects in elementary hemp fibres, showing four types of deformations, namely kink bands, dislocations, nodes and slip planes. The crack on the surface of elementary fibres was the initial breaking point under stress;2) Under tension the primary wall and secondary wall of hemp fibres showed different deformation and breaking behaviour. The crack initiated in a weak point of primary wall and subsequently propagated along radial direction from S1 to S2 layers;3) The average MFA for the broken regions of S2 layer was 6.16? compared to 2.65? for the normal hemp fibres and the breaking of hemp fibres occurred at the points where had the biggest MFA;4) The average MFA was 2.65? for S2 layer and 80.35? for S1 layer;5) the Crystallinity Index (CI) determined by XRD and FTIR was very similar, showing the lattice parameters of the hemp fibres tested a = 6.97 ?, b = 6.26 ?, c = 11.88 ? and γ = 97.21?, and the ratio of 1423 to 896 cm-1 was found more suitable for CI evaluation for hemp fibres.展开更多
To improve the mechanical properties of fast-growing Chinese fir(Cunnighamia lanceolate),expand its range of application,increase its value,and avoid the environmental pollution caused by impregnation with synthetic r...To improve the mechanical properties of fast-growing Chinese fir(Cunnighamia lanceolate),expand its range of application,increase its value,and avoid the environmental pollution caused by impregnation with synthetic resin,Chinese fir was impregnated with a shellac solution.Since the shellac solution was difficult to penetrate into fast-growing Chinese fir,so microwave pretreatment was used to irradiate the wood to improve the permeability.This study investigated the effects of four factors,including the content of moisture in the wood before it was microwaved,the chamber pressure of microwave,the time of microwaving and the vacuum impregnation on the mechanical properties of Chinese fir wood.When the moisture content of wood before microwave was approximately 50%–60%,after microwaving and impregnation,the ultimate strength in static bending(modulus of rupture[MOR])and strength in compression perpendicular to the grain(SCPG)of the wood increased significantly.A microwave time of 100 seconds was more effective at improving the MOR and SCPG of the wood.If the wood was microwaved for too short or long period of time,the microwave pretreatment was not effective.When the samples were immersed in shellac for a longer period,the MOR and SCPG of Chinese fir gradually increased,but when the wood was impregnated for more than 12 hours,the increases were not significant.After the shellac penetrated the Chinese fir wood,it spread on the inner wall surface of tracheid to form a shellac film and easily formed plug-like deposits in microcapillaries.The use of Fourier-transform infrared spectroscopy,scanning electron microscopy and scanning electron microscopy-energy dispersion x-ray indicated that the microwave pretreatment can destroy the pit membranes on tracheids and facilitate the ability of shellac to penetrate the channel.展开更多
文摘This paper presents systematic and improved methodologies to characterize the surface and fracture of elementary hemp fibres by Field Emission Scanning Microscope (FE-SEM), determine the Microfibril Angles (MFA) by an advanced microscopy technology and examine the crystallinity by X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR). The results showed that 1) There existed various deformations/defects in elementary hemp fibres, showing four types of deformations, namely kink bands, dislocations, nodes and slip planes. The crack on the surface of elementary fibres was the initial breaking point under stress;2) Under tension the primary wall and secondary wall of hemp fibres showed different deformation and breaking behaviour. The crack initiated in a weak point of primary wall and subsequently propagated along radial direction from S1 to S2 layers;3) The average MFA for the broken regions of S2 layer was 6.16? compared to 2.65? for the normal hemp fibres and the breaking of hemp fibres occurred at the points where had the biggest MFA;4) The average MFA was 2.65? for S2 layer and 80.35? for S1 layer;5) the Crystallinity Index (CI) determined by XRD and FTIR was very similar, showing the lattice parameters of the hemp fibres tested a = 6.97 ?, b = 6.26 ?, c = 11.88 ? and γ = 97.21?, and the ratio of 1423 to 896 cm-1 was found more suitable for CI evaluation for hemp fibres.
基金the 2018 Forestry Science and Technology Research Project by Forestry Department of Fujian Province(No.2018-26)Science and Technology Innovation Special Fund Project of Fujian Agriculture and Forestry University(CXZX2019111S)+1 种基金National Natural Science Foundation of China(31971593,32071688)the Natural Science Foundation of Fujian Province Department of Science and Technology(2019J01386).
文摘To improve the mechanical properties of fast-growing Chinese fir(Cunnighamia lanceolate),expand its range of application,increase its value,and avoid the environmental pollution caused by impregnation with synthetic resin,Chinese fir was impregnated with a shellac solution.Since the shellac solution was difficult to penetrate into fast-growing Chinese fir,so microwave pretreatment was used to irradiate the wood to improve the permeability.This study investigated the effects of four factors,including the content of moisture in the wood before it was microwaved,the chamber pressure of microwave,the time of microwaving and the vacuum impregnation on the mechanical properties of Chinese fir wood.When the moisture content of wood before microwave was approximately 50%–60%,after microwaving and impregnation,the ultimate strength in static bending(modulus of rupture[MOR])and strength in compression perpendicular to the grain(SCPG)of the wood increased significantly.A microwave time of 100 seconds was more effective at improving the MOR and SCPG of the wood.If the wood was microwaved for too short or long period of time,the microwave pretreatment was not effective.When the samples were immersed in shellac for a longer period,the MOR and SCPG of Chinese fir gradually increased,but when the wood was impregnated for more than 12 hours,the increases were not significant.After the shellac penetrated the Chinese fir wood,it spread on the inner wall surface of tracheid to form a shellac film and easily formed plug-like deposits in microcapillaries.The use of Fourier-transform infrared spectroscopy,scanning electron microscopy and scanning electron microscopy-energy dispersion x-ray indicated that the microwave pretreatment can destroy the pit membranes on tracheids and facilitate the ability of shellac to penetrate the channel.
