Natural fibers lignin

Fibers for commercial and domestic use are broadly classified as natural or synthetic. The natural fibers are vegetable, animal, or mineral ia origin. Vegetable fibers, as the name implies, are derived from plants. The principal chemical component ia plants is cellulose, and therefore they are also referred to as ceUulosic fibers. The fibers are usually bound by a natural phenoHc polymer, lignin, which also is frequentiy present ia the cell wall of the fiber thus vegetable fibers are also often referred to as lignocellulosic fibers, except for cotton which does not contain lignin. 

Climatic conditions, age, and the digestion process influence not only the structure of fibers but also the chemical composition. Mean values of components of plant fibers are shown in Table 4. With the exception of cotton, the components of natural fibers are cellulose, hemi-cellu-lose, lignin, pectin, waxes, and water-soluble substances. 

The filaments of all plant fibers consist of several cells. These cells form crystalline microfibrils (cellulose), which are connected together into a complete layer by amorphous lignin and hemi-cellulose. Multiple layers stick together to form multiple layer composites, filaments. A single cell is subdivided into several concentric layers, one primary and three secondary layers. Figure 5 shows a jute cell. The cell walls differ in their composition and in the orientation of the cellulose microfibrils whereby the characteristic values change from one natural fiber to another. 

Among the natural fibers are cellulose, the primary structural component of plants and bacterial cell walls animal fibers such as wool and silk and biochemical fibers. Plant fibers are composed of cellulose (see Figure 1), lignin (see Figure 2), or similar compounds animal fibers are composed of protein (see Figure 3). 

Lignocellulosics are three-dimensional, polymeric composites made up primarily of cellulose, hemicelluloses, and lignin. Table 1 shows the chemical composition of several different types of natural fibers. It is interesting to... 

Current research indicates that there is a growing interest in natural fibers. Natural fibers Ifom jute were tested in thermosetting and thermoplastic resins. Lignin fillers were used in phenol-formaldehyde, SBR, SBS, and S1S ° and with good results. The opportunities for applications of natural fibers in industrial products have been the subject of recent reviews. Cellulose whiskers with a high reinforcing value were obtained from wheat straw. " Wood fibers were found applicable to such diverse materials as polypropylene... 

Cellulosic fiber reinforced polymeric composites find applications in many fields ranging from the construction industry to the automotive industry. The reinforcing efficiency of natural fiber is related to the namre of cellulose and its crystallinity. The main components of natural fibers are cellulose (a-cellulose), hemicelluloses, lignin, pectins, and waxes. For example, biopolymers or synthetic polymers reinforced with natural or biofibers (termed biocomposites) are a viable alternative to glass fiber composites. The term biocomposite is now being applied to a staggering range of materials derived wholly or in part from renewable biomass resources [23]. 

This is one of the most important natural fibers. It is produced in India, Bangladesh, Thailand, Vietnam, and other countries. It contains 56-64 wt% cellulose, 29-25% hemicellulose, 11-14% lignin, and a small proportion of fats, pectin, ash, and waxes. Application of jute fiber in RPs with matrices of TS resins such as unsaturated polyester or vinyl ester resins has been widely studied. To date the poor adhesion to hydrophobic TPs, such as polyethylene and polypropylene, has to date limited application in TPs. 

Jute fiber (JF) has been popular since the start of this century, principally as a filler and as a reinforcement with TP matrices. These low-cost natural fibers consist mainly of cellulose and hemicellulose chains running parallel to the fiber direction and lignin. High performance, average unidirectional-oriented tensile strength (T ) is 500 MPa, elastic modulus (E) is 40 GPa, and elongation is 1.7%. Other fiber properties are density 1.45 and weight 0.21 g/m. 

Recent basic research has turned up new approaches for innovative materials combining elements of, and integrating the advantages of, wood and synthetic plastics. Lignin is one of the main components of this new class of plastic-like, wood-like biocomposites. The resulting mixture of lignin, natural fibers, and additives is a compound processable as a thermoplastic. The processed materials are short fiber composites. Arboform is a trade name for this class of compounds. 

Nagele, H., Pfitzer, J., Nagele, E. et al. (2002) ARBOFORM - A thermoplastic, processable material from lignin and natural fibers, in Chemical Modification, Properties, and Usages of Lignin (ed. Th.Q. Hu), Kluwer Academic / Plenum Publisher, New York, pp. 101-120. 

Thielemans, W. and Wool, R.P. (2004) Butyrated kraft lignin as compatibilizing agent for natural fiber reinforced thermoset composites. Composites Part A Applied Science and Manufacturing, 35,327-338. Satheesh Kumar, M.N., Mohanty, A.K., Erickson, L. and Misra, M. (2009) Lignin and its applications with polymers. Journal of Biobased Materials and Bioenergy, 3, 1-24. 

Natural fiber types Cellulose Lignin Pectin... 

Natural fiber Type of fiber Density Composition (%) Cellulose Hemicellulose Lignin Degradation peak temperature (°C) (First derivative) (Ref.) Tensile strength (MPa) Young s modulus (GPa)... 

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