【作者】 潘颖；

【导师】 毛志平；

【作者基本信息】 东华大学 ， 纺织化学与染整工程， 2011， 博士

【摘要】 天然纤维素纤维的开发利用一直是纺织行业的重要课题。近年来,随着棉粮争地、生态环境恶化和能源短缺等问题日益凸显,人们在不断地对常规植物纤维资源(如棉、麻等)加以利用之外,对新型纤维资源的开发也随之加强。采用可再生、可循环的植物纤维资源,尤其是农业废弃资源生产纤维素纤维,不仅可以缓解能源、环境问题,还丰富了纺织原料种类,对于产业的可持续发展有着重要意义。据目前国内外的研究现状而言,人们对莲纤维的认识和研究尚不深入,莲纤维的开发利用程度还非常低,对莲纤维的基础研究更是极少见诸报道。莲纤维在生物结构上与韧皮纤维存在本质的区别,因而评估莲纤维作为纺织材料的应用价值、研究莲纤维的提取制备和加工工艺均不能参照现有的植物纤维的分析和研究模式。因此,针对上述存在的问题,首先从植物解剖学的角度出发,详细研究了莲叶柄的结构组成特征、莲纤维在叶柄中的分布方式和来源组织,同时明确了莲纤维的定义及其形态结构特点,为研究莲纤维提取技术和解释莲纤维及其制品区别于其它植物纤维的结构与性能奠定基础。对于不同来源的植物纤维材料,其化学组成和纤维性能差异很大。论文在前人初步研究的基础上,深入分析了手工提取莲纤维的组成、结构及其与性能之间的关系。论文的主要工作及结论如下：(1)研究了莲叶柄的生物结构特征,明确了莲纤维的来源组织。利用石蜡切片技术研究了莲叶柄的解剖结构特征,发现莲叶柄主要是由致密的表皮组织、大量的薄壁细胞、发达的气道以及众多散生的维管束构成。其中气道约占叶柄横截面积的30%,基本薄壁组织占组织总量的60%左右。在一个发育成熟的莲叶柄横截面上可观察到100多个明显的维管束,一个维管束中通常含有1-4个不等的木质部管状分子。将成熟的新鲜莲叶柄进行组织离析,结果发现莲叶柄中主要含有5种植物细胞类型,即纤维细胞、表皮细胞、筛管、薄壁细胞和木质部管状分子细胞。除了木质部管状分子外,其它细胞均不适合用作纺织纤维材料,是被视为杂细胞而需要除去的组织。在扫描电子显微镜下观察发现,不同类型的维管束中,其木质部管状分子均可见螺旋状次生壁加厚。采用Jeffrey方法离析出单个木质部管状分子细胞,借助电子显微镜研究了其次生壁加厚类型及端壁微观结构。莲叶柄的木质部管状分子主要有环纹和螺纹两种加厚方式,但只有呈紧密带状螺旋式加厚的次生壁才能从叶柄中抽取出来成为莲纤维。管状分子的端壁微观结构特征显示,莲叶柄木质部中除了含有管胞外,还有处于发育早期的原始导管。由莲叶柄的生物结构研究可知莲纤维是存在于莲叶柄维管束中木质部管胞和原始导管的带状螺旋式次生壁加厚物。手工抽取的莲纤维呈黄白色,手感柔软,具有荷叶的天然清香,长度可达30 cm以上。每根莲纤维由数根细丝组成,细丝直径3μm左右,属于超细纤维范畴。(2)运用现代测试技术和植物纤维化学成分分析方法研究了莲纤维的主体成分及其在纤维中的分布、莲纤维的单糖组成及其功能成分的含量等。红外光谱分析表明莲纤维主要由纤维素、半纤维素和木质素组成,属于典型的木质纤维素纤维。化学成分分析表明,莲纤维中纤维素含量仅为41%左右,半纤维素、木质素和果胶质的含量达50%以上。透射电镜、激光扫描共聚焦显微镜等研究结果显示,大量的木质素成分主要分布在纤维的外围部分,而半纤维素嵌合在纤维素微纤丝之间,在整个纤维横截面上都有分布。采用高效液相色谱法分析了莲纤维的单糖组成,结果显示莲纤维多糖主要由葡萄糖、木糖、甘露糖和半乳糖组成,其中半纤维主要由木糖组成。高效液相色谱、电感耦合等离子体发射光谱和比色分析研究结果表明,总蛋白、总黄酮和生物碱含量分别为2.08%、0.34%和0.13%。微量矿质元素如Fe、Zn、Ca、Si的含量分别是棉纤维的33、4、7和12倍。(3)利用凝胶渗透色谱、广角X-射线衍射、原子力显微镜和透射电镜等详细研究了莲纤维纤维素的分子量和微细结构特征。莲纤维纤维素的平均聚合度为5696。成熟莲纤维的结晶度和取向度分别为48%和84%,微晶尺寸仅为2.5 nm,远小于棉纤维的。莲纤维表面形貌粗糙,呈现出颗粒状、纤维状和块状的形貌特征,并伴有大小不一的沟槽和孔隙。莲纤维经碱溶胀后制作超薄切片,置于透射电镜下观察,结果发现莲纤维主要是由非常薄的S1层和作为纤维主体的S2层组成,没有棉和竹纤维的次生壁多层次构造。纤维素微原纤在整个S2内以几乎平行于纤维轴的方向取向。微原纤的横向尺寸为5 nm左右。(4)研究了莲纤维的物理机械性能和抑菌性能,并分析了纤维性能与纤维组成和结构的关系。利用FAVIMAT AIROBOT全自动测试仪研究了莲纤维的线密度和一次拉伸断裂性能。莲纤维的平均细度、断裂强度、断裂伸长率和杨氏模量分别为0.91dtex、2.29 cN/dtex、2.58%和78.5 cN/dtex。统计分析结果表明,上述各指标测试值的分布离散程度大,但通过频数分析清楚地描述了各指标的取值分布状态。莲纤维的吸、放湿平衡回潮率分别为9.37%和12.30%,而在同样条件下测得棉纤维的吸、放湿平衡回潮率分别为6.22%和7.16%。莲纤维的吸、放湿速率亦高于棉纤维。莲纤维热降解过程中出现了两个明显的热失重峰,纤维素的热裂解起始温度约为361℃。抑菌性能研究发现,莲纤维对大肠杆菌只有在较短的接触时间内才表现出抑制作用,而对金黄色葡萄球菌则具有持续较强的抑菌效果,接触18h后测得抑菌率达99%以上。莲纤维的抑菌性能与它自身较多的黄酮和生物碱类化合物密切相关。更多还原

【Abstract】 Considering the increasing competition for land between food grains and non-food crops, deterioration in ecological condition and energy crisis, it is always in need to investigate natural cellulose fibers other than commonly used cotton, flax, hemp, or ramie. Natural cellulose fibers production from renewable plant resources, especially from agricultural crop residues can help to not only mitigate energy and environmental issue but also diversify the fiber into textile products and promote sustainable development of textile industry. Lotus(Nlumbo nucifera Gaertn), an aquatic perennial native to subtropical and temperate zones, has been popular since ancient times due to its esthetic, religious, medicinal, nutritional and cultural value. Additionally, lotus is very adaptive and easy to grow, provided they get an ample supply of water and sunshine. Now, there are abundant lotus resources in China. However, the lotus petioles are not being fully used. Considerable amount of lotus petioles produced after blossom season or harvest of lotus root every year are left in the pond to decompose and wasted. As expected with lotus root, these residues could generate cellulosic fibers which can be used in textiles. An example of lotus fibers for textile use is Buddhist robes which are made in Myanmar. The lightweight lotus-fiber fabric can give coolness in hot weather and warmth in cold weather. It also features an everlasting pleasant lotus fragrance. But most importantly lotus fiber products have both cultural and Buddhist significance. Lotus robes are regarded as sacred in Buddhism. But the exploration and utilization of lotus fibers is currently very limited. Now, lotus fibers are mainly produced by hand-extraction method. No parameters are available on the structure, performance and processing technology of lotus fibers. Moreover, the traditional theories used in bast fibers research do not apply to the study of lotus fibers because lotus fibers are quite different from other plant fibers in origin, morphologies and so on. Therefore, the present study firstly investigated the anatomical characteristics of lotus petioles, the distribution features of lotus fibers in the petioles and microstructure of tracheary elements end walls from a botanical point of view, then established the definition, morphology and source tissue of lotus fibers. This lays a foundation for further study on fiber extraction technology and differences between lotus fibers and other plant fibers in principal fiber structure and performances. The properties of a material are crucial in determining the value of its products. And the performance of this material is to a large extent decided already by its own chemical composition as well as external and internal structure. For plant fibers of different resources, there is great difference in their composition and quality. On the basis of the previous studies, the present work is mainly to investigate the composition and structure of hand-extracted lotus fibers as well as their relation to fiber properties. The main work and result of this thesis are as follows:(1) The anatomical structure of lotus petiole was studied to reveal what is lotus fiber and from which tissue lotus fibers originate.The anatomy of lotus petiole was studied by the aid of the paraffin section technique. The results show that lotus petiole mainly comprises of a strong and dense epidermis, thin walled ground parenchyma cells, large aerenchyma and numerous vascular bundles. Aerenchyma occupies more than 30 percent of the total cross-sectional area of the petiole and the ground tissue occupies about 65 percent. Vascular bundles scatter throughout the whole petiole. There are about 100 distinct vascular bundles and the number of tracheary elements in each vascular bundle usually ranges from 1 to 4.Mature and fresh lotus petiole was macerated and observed under light microscope. It was found that lotus petiole comprises five types of cell, namely fiber cell, epidermic cell, sieve tube, parenchyma cell and tracheary element. The quantitative and morphological characteristics of these cells indicate that all the cells except tracheary elements can not be used as textile fibers. The tracheary element is more than ten times longer than fiber cell in the same petiole and its secondary cell wall can be extended up to several dozens of centimeters.The macerated tracheary elements from mature and fresh lotus petioles were examined under SEM to observe the patterns of secondary wall thickenings and microstructure of end walls. There are several patterns of secondary wall thickening present. However, only secondary thickening in a ribbon-like helical pattern can be drawn out from the petiole to form lotus fibers for subsequent utilization. Study of the microstructure of the tracheary elements reveals that there are two pit structures present in the end walls in addition to pits with intact pit membranes: those with porose or web-like remnants pit membrane and those that lack pit membranes. This is an indication of the transitional stage between tracheids and vessel elements. This study provides supportive evidence that lotus fibers are found in both helically thickened tracheids and helically thickened primitive vessels. On the basis of the anatomy of lotus petiole, it is demonstrated that lotus fibers are the band-like, helical secondary cell wall thickenings of both xylem tracheids and primitive vessel elements in lotus petioles. The hand-extracted lotus fibers have a white-yellow color, a soft handle, and an everlasting pleasant lotus fragrance. They are more than 30 cm long and each fiber is composed of several less thin filaments. The diameter of single filament is about 3μm, similar to that of microfiber. Lotus fiber has a solid construction without lumen, which is somewhat different from other natural fibers.(2) The chemical composition, distribution of main components, and composition of monosaccharide were investigated by modern testing and measurement technology, as well as analytical method for the composition analysis of plant fibers.The infrared spectroscopy analysis shows that lotus fibers belong to typical lignocellulose fiber, which is mainly composed of cellulose, lignin and hemicellulose. The chemical analysis results show that lotus fiber contains about 41 percent of cellulose, but the content of lignin, hemi-cellulose, and pectin is more than 50 percent. The TEM and CLSM examination reveals that lignin is highly concentrated on the periphery part of the fiber, whereas, hemi-cellulose dispersedly located between cellulose microfibrils throughout the whole cross section of the fiber.The HPLC, ICP, and colorimetry study reveals that lotus fiber contains various amino acid, mineral elements, and bioactive compounds in addition to polysaccharide and lignin. The content of total protein, flavonoids, and alkaloids is 2.08%,0.34%, and 0.13%, respectively. The amount of Fe, Zn, Ca, and Si is about 33,4,7, and 12 times higher than that of cotton fiber.(3) The characteristics of molecular weight, aggregate structure, and ultra-structure of lotus fiber were detailedly studied by the aid of GPC, wide-angle X-ray diffraction, AFM, and TEM technique.Lotus fiber has a weight average molecular weight similar to that of ramie and flax fiber and an average DP of more than 5000. The crystallinity of mature lotus fiber and preferred orientation of its cellulose microfibrils are 48% and 84%, respectively. Lotus fiber has a crystal size of about 2.5 nm, much lower than that of cotton fiber. The raw lotus fibers display a rough surface topography, with granular, fibrous, or block microstructure and grooves of varying depth.The TEM study reveals that lotus fiber do not has a distinct polylamellate structure seen in other plant fibers. The fiber is composed of only two layers, namely the very thin S1 layer and the broader S2 layer. Microfibrils are oriented almost parallel to longitudinal axis of the fiber and are arranged close to each other. The cellulose microfibril diameter was estimated as 12 nm, similar to that of cotton.(4) The physical and mechanical properties of lotus fiber, as well as their relationship to the fiber composition and structure characteristics were investigated in the end.The fiber linear density and tensile performance were determined using an FAVIMAT AIROBOT automatic single fiber tester. Lotus fiber has a fineness of 0.91 dtex, much smaller than that of cotton and bast fiber. Its average tensile strength, breaking elongation, and Young’s modulus are 2.29%,2.58%, and 78.5cN/dtex, respectively. The statistical analysis indicates that the test values of the above items have a high degree of dispersion, but distribution of these values can be clearly determined by the results of frequency analysis.In comparison with cotton fiber, lotus fiber has higher moisture regain and quicker moisture absorption/desorption rate. The thermal behaviour of lotus fiber is slightly different from that of cotton fiber due to the fact that lotus fiber contains a relatively high amount of hemi-cellulose and lignin components.The antibacterial tests demonstrated bacteriostatic action of lotus fiber against both the Escherichia coli and the Staphylococcus aureus. The bacteriostatic activity against Escherichia coli was observed after only a short contact time, however, the activity against Staphylococcus aureus was significant and durative. The bacteriostatic rate on the latter strain was above 99% after an incubation time of 18 h. The bacteriostatic performance is closely linked with its relatively high amount of flavonoids and alkaloids.更多还原