【作者】 曹双平；

【导师】 王戈；

【作者基本信息】 中国林业科学研究院 ， 木材科学与技术， 2010， 硕士

【摘要】 植物单根纤维力学性能测量是当今木材科学领域的一项前沿技术,是在细胞水平上对单个的管胞或纤维直接进行轴向拉伸的技术。单根纤维尺寸微小,测量困难,被认为是一项国际性的难题。竹木单根纤维力学研究是引导竹木材等生物质材料力学性质研究走向深入的手段,可以将生物质材料力学研究从宏观提升到细胞水平,实现从微观层面研究材料宏观力学特性及其影响因素,对于最终把握竹木材力学性质的本质起源有重要意义;可以满足在竹木纤维基高分子复合材料研究中,对作为增强相的竹木纤维力学性能数据的迫切需求,为纤维选择性利用提供科学依据,指导产品制造工艺设计与改进,促进产品性能的优化。还能为人工林竹木材材性的基因改良提供量化的目标和指标,具有重要的现实和理论意义。单根纤维力学性能测试在国内属开创性课题,本研究在总结了前人研究的基础上,进行了单根纤维微拉伸力学性能测试技术的研究。在此基础上,研究了不同竹龄(2、4、6年生)毛竹中部靠近竹青的竹肉部分的单根纤维、30年生杉木幼龄材(第5年轮)、成熟材(第25年轮)晚材管胞力学性能,测量指标包括断裂载荷、横截面面积、拉伸强度、弹性模量、断裂伸长率;对比研究了不同植物(毛竹、杉木、苎麻、洋麻)单根纤维力学性能;研究了不同测试环境湿度(40%、70%、90%)下,不同纤维(毛竹、杉木、苎麻、芳纶)力学性能对湿度的敏感性;探索性的研究了不同处理洋麻单根纤维的力学性能。通过研究取得主要结论如下:1、毛竹、杉木单根纤维力学性能(1)不同竹龄毛竹中部靠近竹青的竹肉部分微纤丝角相差不大,2、4、6年生分别为9.91°、9.61°、9.76°,不同竹龄毛竹微纤丝角相差不大,只是2年生微纤丝角比4、6年生略大。30年生杉木幼龄材与成熟材微纤丝角分别为34.88°、15.21°,相差很大。(2)2、4、6年生毛竹中部靠近竹青的竹肉部分的单根纤维拉伸强度、弹性模量、伸长率分别为1590MPa、1710MPa、1755MPa;23.6GPa、27.1GPa、26.4GPa;7.2%、7.0%、7.0%。纤维的力学性能随竹龄略有增加,但到第4年后,纤维基本达到成熟, 4年生与6年生纤维无论是在拉伸强度、弹性模量,还是在伸长率上都已非常接近。(3)30年生杉木幼龄材与成熟材晚材管胞力学性能差异显著,拉伸强度分别为558MPa、1258MPa,弹性模量分别为8.5GPa、19.9GPa,均相差在两倍以上;断裂伸长率分别为9.9%、6.6%,也相差了50%。且成熟材管胞表现出了较强的线弹性特性,而幼龄材管胞在拉伸过程中则表现了明显的塑性屈服阶段。这与微纤丝角及纹孔有关。(4)毛竹纤维在拉伸强度、弹性模量等方面的性能明显优于杉木纤维,更适合于作为增强相用在复合材料中。2、几种植物单根纤维力学性能比较研究(1)毛竹单根纤维(为4年生中部靠近竹青的竹肉部分的纤维)断裂强度最大,平均值达1710MPa,最大达2708MPa,杉木(为30年生第25年轮晚材管胞)与其他三种纤维拉伸强度差异显著;苎麻纤维断裂伸长率最大,为8.9%,柔韧性最好;而洋麻纤维断裂伸长率明显小于其他三种纤维,只有3.2%,但其弹性模量值却明显高于其他三种纤维,平均达30.8GPa,最大达42.3GPa,刚性最大,是一种脆性纤维。(2)毛竹、杉木、苎麻、洋麻纤维断裂形式存在一定差异,其中苎麻纤维,毛竹纤维、杉木纤维的断口形状大多呈斜齿形,断口粗糙,表现明显的韧性断裂特性。因此这三种纤维的断裂伸长率较大。杉木纤维一般断在纹孔比较密集或者有其他结构缺陷的地方。洋麻纤维的断口相对上述三种纤维则平滑的多,表现出较强的脆性断裂特性。这与洋麻纤维较低的平均断裂伸长率的测试结果是一致的。(3)毛竹、杉木、洋麻、苎麻这四种纤维在纤维形貌、拉伸强度、伸长率、弹性模量、断裂形式等方面均呈现出其各自的特点,了解这些差异有利于我们更合理有效地利用好这些宝贵的资源。3、单根纤维力学性能对水分依赖特性(1)杉木(为30年生第25年轮晚材管胞)、毛竹(为4年生中部靠近竹青的竹肉部分的纤维)、苎麻、芳纶纤维力学性能对湿度变化的敏感程度不同,苎麻纤维对湿度变化最为敏感,而芳纶纤维几乎不感应外界湿度的变化。(2)与40%环境湿度下比,70%环境湿度下,毛竹、杉木、苎麻这几种天然纤维弹性模量均有所增大,90%环境湿度下却均有所下降。而芳纶纤维作为人造化学纤维,结构均匀、性能稳定,对外界湿度变化不敏感。4、不同处理洋麻单根纤维力学性能(1)离析温度对洋麻纤维力学性能影响较大,110℃下离析所得洋麻纤维力学性能优于160℃下离析所得洋麻纤维。它们的纤维平均断裂强度分别为1051MPa、810MPa;平均弹性模量分别为23.6GPa、13.5GPa,平均伸长率分别为4.5%、5.6%,均差异显著;在纤维形态上也存在一定差异,纤维的横截面面积分别为187μm2、141μm2。(2)100℃及160℃下纳米改性的洋麻纤维力学性能几乎不存在差异,只是在纤维形态上略有变化。它们的平均断裂强度分别为1001MPa、1032MPa,平均弹性模量分别为14.7GPa、14.6GPa,平均伸长率分别为6.6%、6.9%;纤维的横截面面积分别为150μm2、124μm2。更多还原

【Abstract】 The measurement of the tensile properties of single plant fibers at the cellular level is one of front technology of wood science at the present. This technology is considered to be an international problem as the small size of single fiber. The investigation of mechanical properties of the single wood and bamboo fibers is a method to make the study of mechanical properties of biomass materials into deepening and enhance the study to the cell level from the macro level which making the study of macro-mechanical properties and its impact factors of materials at micro level come true. It is important to master the essence origin of mechanical properties of wood and bamboo. Meeting the urgent need of the mechanical properties data of the wood and bamboo fibers who as a reinforcement in the fiber-based polymer composite; Providing a scientific basis for the selective use of the fiber;guiding the design and improvement of manufacturing process of product and promoting the optimization of the product performance; Providing the quantifiable targets and indicators for the genetic improvement of the wood properties. So, the study is very important in practical and theoretical.The investigation of the mechanical properties of the single fibers is an inaugurated research in china. This paper presented a detailed technique to tensile the single fiber. And then, the fracture load、cross area、tensile strength、MOE and the elongation at break of the single bamboo fiber in different age (2,4,6 years old)、the juvenile wood (the 5th rings) and the mature wood (the 25th rings) of the latewood of the Chinese fir fibers are investigated in this paper. The mechanical properties of different plant (Bamboo、Chinese fir、Ramie、Kenaf) single fibers and the sensitivity to humidity of the different fibers (Bamboo, Chinese fir, Ramie, Kevlar)at different environment humidity (40%, 70%, 90%) are also investigated in this paper. Finally, the mechanical properties of different treatment kenaf single fibers are investigated in this paper as well.Results were summarized as follows:1、The tensile properties of the single bamboo and Chinese fir fibers (1) The microfibril angle(MFA) of the 2、4、6 years bamboo are less the same with 9.91°、9.61°、9.76°,respectively. The MFA of 2years is slightly larger than the 4、6 years and the 4、6 years are almost the same. The MFA of the juvenile wood and mature wood of the Chinese fir is significantly different with 15.21°、34.88°,respectively.(2) The average value of tensile strength、tensile modulus and elongation for the 2、4、6 years bamboo fiber was 1590MPa、1710MPa、1755MPa;23.6GPa、27.1GPa、26.4GPa;7.2%、7.0%、7.0%,respectively. The mechanical properties of single fibers was increased with age, but reach a stable after 4 years later, the 4 years and 6 years fiber are very similar in the tensile strength, or in the elastic modulus and elongation.(3) The mechanical properties of the single juvenile wood and mature wood of the Chinese fir fibers were vary greatly , they were more than twice difference in tensile strength and MOE with 558MPa、1258MPa,8.5GPa、19.9GPa, respectively, the elongation at break also had a difference of 50% with9.9%, 6.6%, respectively. The single mature wood fiber showed a linear behavior presented to failure, but the load-deflection curve of juvenile wood fiber testing showed a clear plastic yielding stage. It was related to the MFA and the pits.(4) The bamboo fiber is more suitable than Chinese fir fiber for using as reinforcement in composite materials as its better performance than Chinese fir fiber in tensile strength、MOE and some other aspects.2、A comparison of tensile properties of different single cellulosic fibers(1) The average and largest tensile strength of the bamboo fiber were 1710MPa、2708MPa respectively. It was the maximum among the Chinese fir、ramie and kenaf fiber which about the same in tensile strength. The ramie fiber had the largest elongation of 8.9% and the best flexibility, while the kenaf had the lowest elongation of 3.2% that lower than the other three fibers significantly, but the kenaf had the largest MOE with the average of 30.8GPa and the largest of 42.3GPa which higher than the other three fibers significantly and the best rigidity.(2) The fracture mode of bamboo、Chinese fir、ramie and kenaf fiber was different. The fracture shape of most bamboo、Chinese fir、ramie fiber presented oblique tooth profile and the fracture surface was rough. It showed obvious ductile fracture performance which lead to the large tensile elongation. The Chinese fir fiber generally broken in the pits concentrated regions or where there was some defect. The fracture shape of kenaf fiber was smoother than the other three fibers and showed strong brittle fracture characteristics. It was in agreement with the lower elongation of the fiber.(3) The bamboo、Chinese fir、ramie and kenaf fiber showed their own characteristics in the fiber morphology、tensile strength、elongation、MOE and fracture mode which will help us to utilize these valuable resources more rationally and effectively.3、Effect of moisture on the tensile properties of single fibers(1) The sensitivity of mechanical properties to humidity was various with different kind of fibers. Among the fibers(Including Chinese fir、bamboo、ramie and Kevlar fiber) investigated, ramie fiber shows the most sensitive to the humidity, while Kevlar fiber was almost no induction to the humidity.(2) The MOE of bamboo、Chinese fir、ramie was increased in the ambient humidity of 70% but declined in the ambient humidity of 90% as compared with the fiber in the ambient humidity of 40%. While, as one of the man-made fiber, Kevlar fiber has homogeneous structure and steady performance which lead to the fiber no induction to humidity.4、The mechanical properties of the different treatment kenaf single fibers(1) The isolation temperature has a great effect on mechanical properties of the kenaf fiber. The mechanical properties of the kenaf fiber isolated at 110℃are better than the isolated at 160℃. Their average tensile strength、MOE、elongation、cross area were 1051MPa、810MPa, 23.6GPa、13.5GPa, 4.5%、5.6%, 187μm2、141μm2, respectively.(2) There is almost no difference in mechanical properties and a slight change in fiber morphology between the nano-modified at 100℃and 160℃kenaf fibers. Their average tensile strength、MOE、elongation、cross area were 1001MPa、1032MPa, 14.7GPa、14.6GPa, 6.6%、6.9%; 150μm2、124μm2, respectively.更多还原