Fibre and Lignin

Van Soest, P.J. (1973) Collaborative study of acid-detergent fibre and lignin. Journal of the Association of Official Analytical Chemists 56, 781-784. 

Figure 2.43 The combination of cellulose fibres and lignin makes the cell walls hard, thick and very strong. These properties reinforce the cells against collapse.

Van Soest PJ (1963) Use of detergents in the analysis of fibrous feeds. II. A rapid method for the determination of fibre and lignin. J Assoc Off Agric Chem 46 829-835... 

Fig. 26.3. The molecular structure of a cell wall. It is a fibre-reinforced composite (cellulose fibres in o matrix of hemicellulose and lignin).

Dietary Fibre. An area of some contention is what should be included as dietary fibre. There are several different methods of measuring dietary fibre and all of them will give different results on the same sample. The EU favours the Association of Analytical Chemists (AOAC) method, which includes lignin and resistant starch, while the UK has preferred the Englyst method and has defined fibre as nonstarch polysaccharides from cell walls as the only substances that count as fibre. 

Dietary fibre was defined by Hugh TroweU as the plant polysaccharides and lignin which are resistant to hydrolysis by the digestive enzymes of humans . This definition lacks chemical precision, because non-flbrous pectins and gums are also present. The term nonstarch polysaccharide (NSP) is often preferred, although the term dietary fibre still persists. Unfortunately, NSP is also not satisfactory since some starch, known as resistant or par-... 

Cellophane is, after chemical modification, obtained from the cellulose in wood, just as paper (from cellulose and lignin), cellulose fibres ( rayon ), and cellulose plastics. Leather is made from animal hides in a tanning process. 

Cellulose is one of the most widely distributed natural polymers, since it is one of the principal components of vegetable tissue. It always occurs in nature in the form of fibres varying from the knap-like fibres covering cotton seeds, to the woody substance of trees. The name cellulose is used both for cellulose isolated from the plant, and thus a chemical compound, and for cellulose in situ in the form normally occurring in the plant. In the second case cellulose together with hemicelluloses and lignin form the main constituents of the plant. 

The first high-strength carbon fibres were produced in the 1950s (see Donnet and Bansal, 1984). The early carbonized products were rayon-based, but it was soon found that the mechanical properties and the carbon yield could be improved by the use of polyacrylonitrile (PAN) as the precursor. Also, less expensive fibres of somewhat lower strength and modulus could be made from various other precursors including petroleum pitch and lignin. However, cotton and other forms of natural cellulose fibres possess discontinuous filaments and the resulting mechanical properties were consequently found to be inferior to those of the rayon-based fibres. 

To determine if any component of the dietary fibre in the cereals investigated here was correlated with zinc bioavailability, hemicellulose, cellulose and lignin were determined by the method of Mongeau and Brassard (16). The results are summarized in Table 5. 

Figure 2.11. Cross-section of delignified swollen lamellae in a spmce fibre after removal of lignin by sulphite pulping, solvent exchange (to swell the fibre) and pol)mier impregnation (to replace the solvent hy a hard pol)Tner) prior to sectioning (Young, 1986).

Wood only shrinks when water is lost from the cell walls and it shrinks by an amount that is proportional to the moisture lost below fibre saturation point. To a first approximation the volumetric shrinkage is proportional to the number of water molecules that are adsorbed within the cell wall, and that in turn is related to the number of accessible hydroxyls on the cellulose, hemicelluloses and lignin, and to the amount of cell wall material, i.e. the basic density of the wood (Figure 4.2). 

Tomizuka, I. Johnson, D.J. Microvoids in pitch-based and lignin-based carbon fibres as observed by x-ray small angle scattering. Yogyo-Kyokai-Shi 1978, 86 (4), 186. 

The cellulosic materials are finely entangled with the wool fibre and require chemical treatments for their removal. As well as the cellulose the wool burrs also contain hemi-cellulose and lignin. 

Cellulose is the main constituents of flax fibre (Fig. 1-14). The unretted flax contains about 16.7% hemicellulose, 1.8% pectins, 2% lignin and 1.5% fats and waxes. The polymer of flax consists with a degree of polymerisation of about 18000 cellobiose units. Flax is an assembly of ultimates cemented together within the fibres and an assembly of these fibres into bundles. These assemblies are prone... 

A06A C Bulk Producers Within this group there are fibres, which consist of plant polysaccharides and lignins. Fibres can be divided into non-soluble and gelforming. The non-soluble fibres are resistant against any effect of the intestinal bacteria, while the... 

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