长江滩地不同品系杨树木材纤维形态、微纤丝角和结晶度变异研究

The Variation of Fiber Form, Microfibril Angle and Crystallinity of Different Strains of Poplar Wood in the Flood Land along the Lower Yangtze River, China

为杨树选种育种及利用提供理论依据,并为长江滩地综合治理和开发优选树种,对5个品系杨树木材构造、纤维形态、微纤丝角和结晶度进行了比较研究。结果表明:5个品系杨树木材之间的粗视构造和显微构造无显著差异。纤维长度为967.5—1118.5μm,分布频率1000μm以上者占53—89%,长宽比为35.9—43.7μm,壁腔比为0.48—0.79,柔性系数为0.56—0.67,次生壁S_2层微纤丝角为19.59°—25.46°,纤维素相对结晶度为52.36—57.72%。5个品系杨树木材均适宜作制浆造纸原料,尤以Ⅰ—63杨为最佳。Ⅰ—63杨、Ⅰ—69杨和Ⅰ—72杨速生丰产,可作为长江滩地造林的优良树种。

Most of the poplar trees planted in the flood land along the middle and lower Yangtze River in early 1980s using clones grew well with a high growth rate. This study, as a part of the study on tackling various problems in flood land of Yangtze River in a comprehensive approach, will provide theoritical bases for the selecting, breeding and cultivating of poplar clones and the utilization of poplar wood in forest industry. The five strains of poplars are as follows: 1-214 poplar (Populus×euramericana cv. I-214), 1-72 poplar (P. ×euramerican cv. I-72/58), I-63 poplar (P. deltoides cv. I-63/51), I-69 poplar (P. deltoides cv. I-69/55), and I-Jialong poplar (P. nigra cv. Blanc de Garonne), All of the experimental wood samples were collected from seven-year old artificial stands in Xinzhou Forest Farm of Anqing, China, with 14—27cm in DBH (diameter at breast height). Five individual trees for each of above five strains of poplars were sampled for the purpose of studies of the anatomical and physico-mechanical properties of the wood. The conventional method was used to measure the wood fiber form. The wood samples were cut into small chips and ground into powder respectively in order to determine microfibril angle on the S_2 layer of secondary cell wall and the relative crytallity of cellulose by X-ray diffraction analysis, All wood samiples came from the same height of 1.3m. Almost all of the characteristics examined both from gross and minute structures indicated that there is no significant differences among the five poplars except that the annual ring is wider in I-63 poplar, I-69 poplar and I-72 poplar, which show that those three poplars grew faster than the others. Wood fibers account for around 50 percent of its total tissue in hardwood. The wood fiber length, length-width ratio and cell wall-cavity ratio are the important factors in determining the paper strength and quality. Hardwood fiber length is usually shorter than or even only 1/3 that of softwood. The length-width ratio is also smaller in hardwood than in softwood, but the wallcavity ratio on hardwood is the same or larger than that of softwood. The wood fiber length, width, cell wall thickness and wall-cavity ratio are summarized. The average fiber length is between 0.9-1.2μm, which is belong to middle length(0.9-1.6μm)specified by International Association of Wood Anatimists (IAWA), but it is belong to long fiber length in China. The Figure result, indicated that the fiber length increased as the increases of an nual ring. The differences among the five poplars are not significant. The frequency distributions of the fiber length of the five poplars from pith to outer annual ring. The pertion of the fibers with the length over 1000μm is 53-89%. The length-width ratios(35.9-43.7) and compliance coefficients (0.56-0.73) are relatively large. The wood of these five poplar can be used as good raw materials for paler-pulp. The microfibril angle on the S_2 layer of secondary wall is a fundamental property of cell wall. It has a big effect on wood properties and size stability(Harris and Melan 1965). The smaller the fibril angle, the greater the strength of wood; the smaller the deformation of wood, the better the properties of wood. The average fibril angles on the S_2 layer of the cell wall of five poplar wood range from 25.94°-20.58°, and decrease from the pith outwards. The trend is similar to the results by Nagai et al. (1984) Who studied the wood properties of poplar, beech, chestnut and zelkove. Cellulose exists in the wood Cell wall as filiform. There are crystalline regions and amorphou regions in microfibrils Of cellulose. The percentage Which crystalline regions make up in the total cellulose is called the cellulose crystallinity. The fiber tension strength, modulus of elasticity, hardness, density and the size stability will increase as increasing crystallinity. The water preservation and elongation of fiber will decrease as increasing crystallinity. The relative cryastallinity of cellulose is also related to wood fiber length an