Natural fibers cellulose structure

Among the three essential components of natural fibers, cellulose is a non-branched macromolecule and contains chain of variable length of 1-4 linked / -d-anhydroglucop5rranose units (Thakur and Thakur, 2014]. It has been reported that the length of chain in cellulose fibers depends on the source of cellulose from which it is procured. Hemicellulose, on the other hand, is composed of a group of polysaccharides with the exclusion of pectin and has a branched structure. It has been reported that hemicellulose remains associated with cellulose even after the removal of 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. 

Solid cellulose forms a microcrystalline structure with regions of high order, i.e., crystalline regions, and regions of low order that are amorphous. Naturally occurring cellulose (cellulose I) crystallizes monoclinic sphenodic. The molecular chains lay in the fiber direction ... 

The mechanical and physical properties of natural fibers vary considerably, as it is with all natural products. These properties are determined by the chemical and structural composition, which depend on the fiber type and growth circumstances. With this cellulose, the main component of all natural fibers varies from fiber to fiber. 

Horns and hooves were the raw materials for the early polymer preparations. These materials were ground up and treated in various ways so that they could be fabricated into such items as combs to use for ladies hair, and other specialty things of that sort. The next development was the use of cellulose from cotton or from wood as the raw material which was studied for making films and fibers. Work on the cellulose structure had provided information that it was a hydroxylated product, and by converting the hydroxyls to esters, the natural cellulose could be turned into a soluble material, which was spun into fibers and cast into films to make the first cellulose rayon-type material and cellulose films. 

Paper products (newsprint, tissue, packaging, etc.) are made from pulps that consist of natural fibers derived from vascular plants such as trees, sugar cane, bamboo, and grass. The vascular fiber walls are composed of bundles of cellulose polymeric filaments. This long, linear glucose polymer is what paper is made from. The polymer has the structure shown in Scheme 8.18. 

Cellophane film Is prepared from regenerated cellulose and Is similar to rayon fiber In that It has a lower molecular weight than cotton and contains a small amount of hemlcellulose, as does linen. Cellophane film, therefore, although not a duplicate of any natural fiber, Is similar enough In chemical structure and morphology to make It useful as a model system. Moreover, Its transparency and the precision of Its manufacture make It quite useful for this type of study. 

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). 

Once dehydrated, the microfibrils are practically without functionality in ordinary food processing and preparation operations, because the inert microcrystallites are difficult for water to penetrate. The polymorphs, cellulose I and II (Blackwell, 1982 Coffey el al., 1995), are differentiated by their molecular orientation, hydrogen-bonding patterns, and unit-cell structure. Cellulose I is the natural orientation cellulose II results from NaOH treatment under tension of cellulose I with 18-45% alkali (mercerization). The I—II transition is irreversible. Mercerization strengthens the fibers and improves their lustre and affinity for dyes (Sisson, 1943). Sewing thread was relatively pure mercerized cotton until the advent of synthetic polymer fibers. 

Water absorption by natural fibers, such as cellulose causes the formation of mtemal forces capable of rotating fibers around their axis. This twisting motion introduces stress into the structure of composite. ... 

The more fundamental aspects of fiber constitution and behavior are dealt with in Astbury s Fundamentals of Fibre Structure 27) and Textile Fibres under the X-Rays 28), Hermans Contributions to the Physics of Cellulose Fibres 39), and Physics and Chemistry of Cellulose Fibres (40 Marsh s Textile Science (40 Preston s Fibre Science 59) and the High Polymers series of monographs, three of which are concerned with natural fibers—Volume IV, Natural and Synthetic High Polymers, by Kurt H. Meyer 53), Volume V, Cellulose and Cellulose Derivatives, edited by Emil Ott 56), and Volume VI, Mechanical Behavior of High Polymers, by Turner Alfrey, Jr. 21 ... 

The natural fibers of cotton and wood are the most important commercial sources of cellulose. Thus, knowledge of their structure is essential to any discussion of its enzymatic degradation. Several excellent reviews of cellulose structure have been published recently those on cotton by Hamby (22) and Warwicker et al. (76), and on wood in the volumes edited by Zimmerman (79) and C6t6 (7), as well as the discussions of the ultrastructure of plant Cell walls by Miihlethaler (47) and Rollins (59) make more than a general summary here unnecessary. 

Since the cellulose and other major constituents of natural fibers are insoluble molecules and are deposited within the cell walls in an intimate physical mixture of great structural complexity, formation of this requisite physical association can be achieved only by diffusion of these enzymes to susceptible sites on the gross surfaces of the fiber or the microfibrillar and molecular surfaces within the fiber wall. Thus, any structural feature... 

Size and Diffusibility of Cellulolytic Enzymes in Relation to the Capillary Structure of Cellulose. As discussed earlier, enzymatic degradation of cellulose requires that the cellulolytic and other extracellular enzymes of the organisms diffuse from the organism producing them to accessible surfaces on or in the walls of the fiber. This accessible surface is defined by the size, shape, and surface properties of the microscopic and submicroscopic capillaries within the fiber in relation to the size, shape, and diffusibility of the enzyme molecules themselves. The influence of these relationships on the susceptibility and resistance of cellulose to enzymatic hydrolysis has not been verified experimentally in natural fibers but the validity of the concepts that follow is demonstrated by the work of Stone, Scallan, Donefer, and Ahlgren (69). 

Cellulose the major structural component of woody plants and natural fibers, such as cotton a polymer of glucose. 

Further development of linear condensation polymers resulted from the recognition that natural fibers such as rubber, sugars, and cellulose were giant molecules of high molecular weight. These are natural condensation polymers, and understanding their structure paved the way for the development of the synthetic condensation polymers such as polyesters, polyamides, polyimides, and polycarbonates. The chronological order of the development of polymers is shown in Table 1.1. 

The best-known renewable primary sources for natural fibers are wood and cotton. Both of these natural materials consist of basic fibrous units known as fibrils, the diameter of which is probably equivalent to that of the cellulose crystallites. Crystalline and amorphous regions alternate along the length of the fibrils. Several elementary fibrils may also be united in fibrillary structural units [84]. 

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