中山杉应压木的物理性质与拉伸性能

Physical and tensile properties of compression wood of Taxodium hybrid ‘Zhongshanshan’

中山杉(Taxodium hybrid ‘Zhongshanshan’)作为一种速生树种,更易产生应压木,对其木材加工利用产生不利影响。以中山杉应压木为研究对象,对同一年轮应压木和对应木区域木材的密度、干缩率、微纤丝角、单根管胞拉伸性能及木薄片顺纹拉伸性能进行了系统分析,以揭示中山杉应压木物理与力学性能之间的内在关系。研究结果表明:中山杉应压木的微纤丝角显著增大,使得物理性质与力学性能出现较大的变化。其中,中山杉应压木的绝干、基本密度均显著大于对应木,和管胞截面积的变化一致;中山杉应压木和对应木的微纤丝角平均值分别为38.02°和30.01°;受微纤丝角增大的影响,应压木径向和弦向绝干干缩率分别为1.54%和2.96%,体积绝干干缩率为12.06%,均较对应木有所减小,而纵向绝干干缩率为5.97%,较对应木有所增大。应压木单根管胞以及应压木木薄片的抗拉强度较对应木均显著减小,其中微纤丝角的变化显著影响了木薄片的顺纹抗拉强度。综上所述,中山杉应压木的微纤丝角对其干缩率存在较大的影响,与对应木相比其对纵向干缩率影响最大,同时,微纤丝角的变化显著影响了其顺纹拉伸性能。

As a fast-growing wood species, Taxodium hybrid ‘Zhongshanshan’ compression wood is easily formed due to its growth condition, which adversely affects wood processing and utilization. In this study, the compression wood of Taxodium hybrid ‘Zhongshanshan’ was taken as the raw material, and the density, shrinkage rate, microfibril angle, single tracheid tensile strength and strength parallel to grain of wood veneer of compression wood and opposite wood of Taxodium hybrid ‘Zhongshanshan’ were systematically analyzed to reveal the immanence relationship between the physical and mechanical properties of the compression wood of Taxodium hybrid ‘Zhongshanshan’. The results showed that the microfibril angle of the compression wood increased significantly, which made the physical pro-perties and mechanical properties change greatly. The oven-dry density and basic density of compression wood of Taxo-dium hybrid ‘Zhongshanshan’ were significantly higher than those of the opposite wood, which was consistent with the change of tracheid cross-sectional area. The average microfibril angle of compression wood and opposite wood of Taxodium hybrid ‘Zhongshanshan’ were 38.02° and 30.01°, respectively. Affected by the increase of microfibril angle, the radial and tangential oven-dry shrinkage rates of the compression wood of Taxodium hybrid ‘Zhongshanshan’ were 1.54% and 2.96%, respectively, and the oven-dry volume shrinkage rate was 12.06%, which was lower than that of the opposite wood, while the longitudinal oven-dry shrinkage rate was 5.97%, which was higher than that of the opposite wood. The single tracheid tensile strength and strength parallel to grain of wood veneer of compression wood of Taxodium hybrid ‘Zhongshanshan’ was significantly lower than that of the opposite wood, and the change of microfibril angle significantly affected the strength parallel to grain of wood veneers. In summary, the microfibril angle of compression wood of Taxodium hybrid ‘Zhongshanshan’ had a great influence on its shrinkage rate, among which the effect on the longitudinal shrinkage was the most significant. Compared with the compression wood of Taxodium hybrid ‘Zhongshanshan’, the microfibril angle had the greatest influence on the longitudinal shrinkage. At the same time, the change of microfibril angle significantly affected its tensile properties along grain.