Study On Wood Microfibril Angle And Its Relation With Wood Mechanical Properties

Wood microfibril angle is one of the most important properties in all wood properties. The variation of wood microfibril angle has an important influence with the anatomical, physical, mechanical and the chemical properties of wood. Studying on wood microfibril angle and its variation can provide the scientific basis for predicting wood characteristic in the early age; can provide the technical parameters for seed selection and breeding, the gene improvement , felling and thinning intensity of plantation; can propel the development of the cell wall mechanics, the micromechanics and the fiber composite materials.With the science and technology development, more and more new techniques emerge quickly for measuring the wood microfibril angle. In this research, four techniques were used for measuring and analyzing the wood microfibril angle of Chinese Fir, and the influences of wood microfibril angle were analyzed on macroscopic and microscopic mechanical propertie.The main results of this dissertation are as follows:1.The wood microfibril angle and its variation of Chinese Fir were obtained by using X-ray diffraction, pit aperture observing, polarized light microscope and the near infrared spectrum technique separately, and the detailed comparison were also gained for the four techniques:(1)X-ray diffraction technique were suitable for the variation research of massive samples, because for its faster measuring speed and good represent- ation. The polarized light technique were suitable for a few samples in the laboratory, because for its low measuring speed and the low cost of instrume- nt.The measuring speed was fast with Pit aperture techni- que, and the cost of instrument was not high, but the variability of the results was the biggest. The difference were not significant of average wood microfibril angle obtained by the three techniques.(2)The near infrared spectrum technique and the X-ray diffraction technique were also called nondestructive testing technique, and the model seted up by the two techniques was very good and was convenient for online analysis. Because the difference were little about microfibril angle obtained by other three methods, therefore, every group values gained by one of the four techniques can all be seemed as true values of the near-infrared spectrum technique to predict the wood microfibril angle.2 The effect of wood microfibril angle on microscopic mechanical properties (1)In the normal space tensile, the average density of wood microtome section of Chinese Fir was 0.3434g/cm3, the average wood microfibril angle was 12.06°, the average longitudinal module of elasticity(L MOE) was 2431Mpa, and the longitudinal tensile strength was 44.96Mpa.(2)In the normal space tensile,the influence of average microfibril angle on D333A wood microtome section occupyed the leading role, but the density occupyed the leading role to D1123A and D1223A wood microtome section. Both average microfibril angle and the density together accounted for the variation of longitudinal mechanical properties in wood microtome section.(3)In the normal space tensile,after controling the influence of density, the variation of microfibril angle had a decisive effect on L MOE and longitudinal tensile strength of D333A wood microtome section; the Correlation coefficient between microfibril angle and L MOE became significant at 0.05 level for D1123A wood microtome section; the Correlation coefficients were all unsignificant between microfibril angle and L MOE and between microfibril angle and longitu- dinal tensile strength to D1223A wood microtome section.(4)In the Zero-span tension,the average longitudinal tensile strength of tested Chinese Fir tracheid was 357.39Mpa.The 6mm width samples were the best for testing tracheid longitudinal tensile strength of Chinese Fir.3 The effect of wood microfibril angle on macroscopic mechanical properties(1)The average density of tested Chinese Fir was 0.3991g/cm3,the average module of elasticity(MOE) was 12.38Mpa,the average module of rapture(MOR) was 75.22Mpa,the average wood microfibril angle was between 10.25°and 30.55°,and its average value was 12.49°.(2)For the samples of sapwood and low altitude, the density had a biggest influence on MOE and MOR, the density/MFA was ranked the second, the MFA was the third.(3)For the samples of heartwood and high altitude, the density had a biggest influence on MOE, the density/MFA was ranked the second, the MFA was the third; but for MOR, the density/MFA had a biggest influence, the density was ranked the second, the MFA was the third.(4)For the samples of sapwood and low altitude, the density had a biggest influence on MOE; but for the samples of heartwood and high altitude, the density/MFA had a biggest influence on MOR, especially, the Correlation coefficients between MFA and MOE became more and more significant, from the lowest value -0.177 to -0.478.(5)For all the samples, after controlling the influence of density, the Correlation coefficients became more significant between MFA and MOE, and the Correlation coefficient also became inverse correlation from noncorrelation between MFA and MOR, these showed that the MFA played an important role on the variation of the MOE and MOR.(6)For the samples of heartwood, after controlling the influence of density, the Correlation coefficients increased to -0.814 between MFA and MOE, and the Correlation coefficients also became bigger between MFA and MOR, these also showed that the variation of MFA could bring the variation of the MOE and MOR.(7)When prodicting the MOE and MOR, we had better consider the density and MFA together, so as to gain better results than consider the density only. angle of Chinese Fir...