Cellulose microfibrillar structure

These polymers are distinguished from cellulose by the presence of both/ -(l— 3)- and / -(l— 4)-linked D-glucosyl residues, lower molecular weights (some noncellulosic glucans are water-soluble), and susceptibility to hydrolysis by / -D-glucanases that cannot hydrolyze cellulose. Unlike cellulose, whose microfibrillar structure and structural role in the cell wall has been clearly established, the function of these polymers as structural components of the wall is still a subject of controversy there is some evidence that they are energy-reserve materials.110-201 202... 

Microfibrillar structure of bacterial cellulose is responsible for most of its properties such as high tensile strength, higher degree of polymerization and crystallinity index. 

Microfibrillar structure of cellulose. Cr, elementary nanocrystallite A, amorphous noncrystalline domain. 

The microfibrillar structure of cellulose has been established beyond doubt through the application of electron microscopy [64-65] and great variations in dimensions, depending on origin, have been reported [47-48, 66], The application of transmission electron microscopy [67-72] has established with certainty that the microfibril is the basic crystalline element of native cellulose [1, 67, 68-70, 73], Different levels of structural organisation of cellulose are now well characterized. 

Cellulose is the primary structural component of the cell wall and, after removal of lignin and various other extractives, it is also the primary structural component of paper. Chemically, it is a semicrystalline microfibrillar linear polysaccharide of /M,4-linked d-glucopyranose (Figure 2.6). 

An unusual (1— 3)- 3-D-xylan appears to be the skeletal material for a number of seaweeds, and occurs with microfibrillar morphology, just as for cellulose. However, the birefringence of the fibrils is n ative, whereas for cellulose it is positive, and this observation suggests a helical structure, seen, by examination of molecular models, to be quite plausible. An x-ray fiber diagram for the material conditioned at 98% relative humidity is shown in Fig. 19. The principal characteristic of this diagram is that the most intense reflections are not on the equator this is a feature of molecules of the helical type, such as those of nucleotides or proteins. From an analysis of the x-ray data, Frei and Preston concluded that a double... 

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... 

The cell walls differ among themselves in their composition and orientation of the cellulose microfibrils. In most plant fibres, these microfibrils are oriented at an angle to the normal axis called the microfibrillar angle (Fig. 19.2). The characteristic value for this structural parameter varies from one plant fibre to another. 

Fibrillar fines obtained from cellulosic fibres are known for their unique structure, material characteristics, and potential applications (Hubbe et al. 2008). An amorphous lignin and hemicellulose matrix separates the elementary nanofibrils in natural vegetable fibres. Based on raw material sources, pretreatment and subsequent defibrillation procedures will produce a broad spectrum of fibril structures as well as nomenclatures used to describe them. Thus, we find various terms adopted in the field, such as nanoscale-fibrillated cellulose, cellulosic fibrillar fines, cellulose aggregate fibrils, and microfibrillar cellulose. 

Strength properties of the fibre are dependent mainly on the fibrillar structure, microfibrillar angle, and the cellulose content. There is a correlation between percentage elongation and microfibrillar angle d as follows ... 

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