| 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. |
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