【作者】 陈红；

【导师】 费本华；

【作者基本信息】 中国林业科学研究院 ， 木材科学与技术， 2014， 博士

【摘要】 竹纤维细胞壁具有特有的壁层结构——初生壁和薄厚交替的多层次生壁复合而成的微纳米结构，这种结构赋予了纤维细胞刚性强、形态平直、性能稳定的特性，也是竹材优良宏观力学性质的基础。深入研究竹纤维细胞壁结构特征，不仅有助于认识竹子生长机制，而且对于发展竹类资源利用、生物能源转化以及仿生材料设计与制造等都具有重大的理论和现实意义。本研究以竹纤维细胞壁为研究对象，以其结构特征为主线，利用多种技术手段和方法以及先进的实验仪器，从竹纤维细胞壁多壁层结构的表征、竹纤维细胞壁微纤丝的排列与尺寸、竹纤维细胞壁半纤维素与纳米结构及竹纤维细胞壁力学性能的关系三个方面开展研究。在竹纤维细胞壁壁层结构的表征研究过程中，分别采用了场发射环境扫描电镜（FE-SEM）、透射扫描电镜（TEM）、原子力显微镜（AFM）对竹纤维细胞壁壁层结构进行表征，并利用AFM对竹纤维细胞壁横截面各壁层内纤维素微纤丝分布情况和壁层厚度进行测量。在竹纤维细胞壁微纤丝的研究中，主要利用AFM对不同处理的竹纤维细胞壁初生壁的纤维素微纤丝排列及大小变化进行表征；在研究半纤维素与竹纤维细胞壁纳米结构及拉伸性能的关系的研究中，主要采用傅立叶变换红外光谱（FT-IR）和X-射线衍射技术（XRD）对竹纤维细胞壁纳米结构进行分析，同时，采用单根纤维拉伸技术在细胞壁水平上研究竹纤维细胞壁拉伸性能的变化。论文的主要结论如下：（1）在FE-SEM下能够观察冷热交替处理干燥竹材中竹纤维细胞壁的多层结构。在冷热交替处理过程中，竹黄的细胞壁层比竹青的细胞壁层更容易分层；在一个维管束内，各方纤维帽的外围细胞壁在受到冷热处理时更容易分层，便于观察细胞壁的多层结构；但FE-SEM观察冷热往复交替处理干燥的竹材这种方法只能作为一个定性的观察，不能准确地表征出竹纤维细胞壁的多壁层结构。AFM具有很高的分辨率，对尺寸比较小的竹纤维细胞壁各壁层模量表征很有效。竹纤维细胞壁各壁层的模量不同。相比TEM，采用AFM表征细胞壁多壁层结构，不仅制样便捷、能定位观察而且还能够获得样品与针尖的相互作用信息。此外，AFM还是一种研究竹纤维细胞壁的微纤丝结构特征、分布情况以及纤维素微纤丝聚集体尺寸的有效手段。（2）竹纤维细胞壁多壁层结构以及各壁层的厚度随着竹纤维所处的位置改变而变化；在竹纤维细胞壁和竹薄壁细胞的横截面，纤维素微纤丝聚集体排列形式都呈随机的无规律排列；一个细胞壁各壁层内的纤维素微纤丝聚集体的密度不同，并且在壁层与壁层相邻的位置纤维素微纤丝聚集体的密度明显大于壁层内纤维素微纤丝聚集体的密度。同时，这一现象在竹薄壁细胞横截面上表象的更明显；纤维素微纤丝聚集体的尺寸在一个竹纤维细胞壁中大小变化不大，而在薄壁细胞中变化较大。（3）在AFM下能够清晰观察到竹纤维细胞壁初生壁的微纤丝聚集体的排列以及测量微纤丝聚集体大小，竹纤维细胞壁初生壁的微纤丝呈随机无须的交织状排列。超声处理和不同干燥方式都影响微纤丝的排列，微纤丝聚集体之间的距离，纤维素微纤丝聚集体的大小，以及纤维表面粗糙度。采用冷冻干燥的细胞壁，其微纤丝的结构更接近原来的结构；超声处理增加了表面粗糙度并使得微纤丝暴露的更明显，这提供了一个增加纤维表面润湿性和使竹纤维初生壁微纤丝更易被观察到的方法。（4）逐步增加氢氧化钠溶液浓度抽提脱除半纤维素处理过程中，6%、8%氢氧化钠溶液处理时，木聚糖和葡甘露聚糖逐步降解，当氢氧化钠溶液增加到10%时，木聚糖和葡甘露聚糖被去除。当氢氧化钠溶液浓度进一步增加到15%和25%时，细胞壁中有纤维素Ⅱ生成。6%和8%氢氧化钠溶液处理对竹纤维表面纤维素微纤丝的排列及纤维素微纤丝聚集体的形态影响不大，纤维素微纤丝仍旧呈随机的无序的网状排列。当氢氧化钠溶液浓度增加到10%，竹纤维表面纤维素微纤丝排列和纤维素微纤丝聚集体的形态开始由松散的无序网状排列转变成较为紧密的排列。当氢氧化钠溶液的浓度增加到15%和25%时，竹纤维表面纤维素微纤丝排列和纤维素微纤丝聚集体形态完全转变，已无网状排列形态。6%、8%和10%氢氧化钠溶液脱半纤维处理不会影响纤维结晶类型，仍旧属于典型的纤维素Ⅰ晶型，纤维素的相对结晶度先提高后降低，纤维素晶体的平均厚度有小幅度减小。15%和25%氢氧化钠溶液处理使得纤维素晶体发生降解，然后重结晶，纤维素晶型发生了从Ⅰ到Ⅱ的转变，同时，纤维素的相对结晶度有很大的提高，但纤维素晶体的平均厚度减小。（5）纤维细胞壁内部结构因为半纤维素逐步脱除出现变化，在当氢氧化钠浓度增加到10%以后，纤维细胞壁表面纤维素微纤丝之间出现细小的孔洞，细胞壁内部壁层之间出现分层。分级抽提半纤维素后，竹纤维细胞壁的纵向拉伸强度和纵向拉伸模量都降低，但脱除半纤维的程度对拉伸强度影响不大，而且当氢氧化钠溶液浓度增加到15%和25%以后，拉伸模量急剧降低；6%和8%氢氧化钠溶液处理的纤维断裂伸长率几乎没有变化，当浓度增加到10%时，纤维的断裂伸长率增加明显，当浓度增加到15%和25%，纤维断裂伸长率急剧增加，是未经碱处理的3倍以上。逐步增加碱溶液浓度分级抽提半纤维处理过程中，竹纤维细胞壁断裂的形式存在明显差异，未经过碱处理和经过6%及8%氢氧化钠溶液处理的竹纤维，断口形状呈撕裂的刷子型，表现出较多的韧性断裂特性，10%氢氧化钠溶液处理的竹纤维，其断口呈斜齿状，断口粗糙，表现出韧性断裂减少，脆性断裂增加；15%和25%氢氧化钠溶液处理的竹纤维，其断口整齐，表面粗糙，表现出明显的脆性断裂特性。更多还原

【Abstract】 Bamboo fiber has a special cell wall with a multilayer structure consist of primary andsecondary wall. Such a structure leads to strong rigidity, straight and stable mechanicalproperties of cell wall which is also the reason why the mechanical properties are so good.Further studying on the structure and properties of bamboo cell wall is not only important forknowing the growth mechanics of bamboo, but good to the utilization of bamboo resources,transformation of bioenergy and designing and making bionic.This research is studying on the structure of bamboo fiber cell wall with kinds of technicsand methods, and advanced instruments. The main contents includes three parts: studying themultilayer structure of bamboo cell wall with FE-SEM, TEM, Nanoindentation and AFM;studying the arrangement of cellulose microfibrils aggregates with AFM; and studying therelationship between hemicellulose of bamboo cell wall and nanostructure and mechanicalproperties with FT-IR, XRD and the technics for tensile testing of single fiber.The conclusions are as follows:（1）The multilayer structure of bamboo cell in treated by freezing and heating can beobserved in FE-SEM. The cell wall in the inner of bamboo splits more easily than that in theouter of bamboo after the freezing and heating treatment. The cell wall in the outside ofvascular bundle splits more easily. However, the FE-SEM method is only a qualitativeobservation. Comparing with the Nanoindentation, AFM has higher resolution, is effective formeasuring the modulus of cross section of bamboo cell wall. In comparison of TEM, observingbamboo cell wall structure with AFM is much simple which can not only observe the target cellwall,but can obtain more data. In addition, AFM is a effective method to study the cellulosemicrofibril and the distribution and diameter of microfibril aggregates in cross-section ofbamboo cell wall. While it need to notice the preparation of samples when using the AFMobserve the nanostructure of cell wall. （2）The multilayer structure and the thickness of each layer in different bamboo cell wallare different. The cellulose microfibril aggregates arrange randomly in the cross section of bothbamboo fiber cell wall and bamboo parenchyma cell wall.The distribution of microfibrilaggregates is different in different layers within on cell wall. There are more microfibrilaggregates in the place of the layer next to each other. Such a phenomenon is more obvious inparenchyma cell wall. The average diameter of microfibril aggregates in fiber cell wall is thesame, while that in parenchyma cell wall are different.（3）It is accessible to observe the nanoscale characteristics in bamboo fiber cell wall,especially the microfibrils, using AFM.The microfibril aggregates in primary cell wall ofbamboo fiber overlap, forming a randomly interwoven structure observed with AFM. And boththe ultrasonic treatment and the drying methods affected the arrangement and dimension ofmicrofibril aggregates. The structure of cell wall freeze-dried is near to the native structure.Ultrasonic treatment can increase roughness of bamboo fiber and exposure of microfibrilaggregates, which provides insight on enhancing wettability of bamboo fiber and observingmicrofibril aggregates.（4）Xylan and glucomannan degraded when bamboo fiber was treated by6%and8%NaOH solution. While the concentration increased to10%, xylan and glucomannan wereremoved. The pattern of cellulose microfibril aggregates treated by6%and8%NaOH solutiondid not change observing with AFM which changed sharply when the concentration of NaOHincrease to15%and25%. CelluloseⅠdid not change, while the CrI first increased, and thendecrease with the alkali treatments with6%,8%and10%concentration. However, when theconcentration increase to15%and25%, there some celluloseⅠtransform into celluloseⅡ.Meanwhile, the CrI increased sharply, but the average thickness of cellulose crystal increased.（5）The structure of bamboo cell wall change with the reduction of hemicellulose. Whenthe concentration of NaOH solution increased to10%, tinny pores began to appear betweencellulose microfibrils aggregates and the layer of cell wall split. With the extraction ofhemicellulose, both the tensile strength and tensile modulus of single fiber decreased. While when the concentration of NaOH increased to15%and25%, tensile modulus decreasedsharply, but tensile strength did not decrease. The elongation at break were similar when thefiber treated by6%and8%NaOH solution. When the concentration increased to10%, theelongation began to increase obviously which increased sharply when the concentration wentup to15%and25%. Besides, the form of fracture were different with different alkali treatment.The fracture form of fibers treated by6%and8%alkali solution liked the brush whichrepresented tenacity. When the concentration increased to10%, the fracture form were liketeeth, while the form were orderly when the concentration increased to15%and25%whichindicated the frangibility of fibers.更多还原