Natural fibres hemicellulose

Hemicelluloses are constituted of different hexoses and pentoses glucose, mannose, xylose, etc. Since these heteropolysaccharides are often branched polymers, they cannot constitute crystalline structures. However, their function in the constitution of natural fibres is crucial. Together with lignin, they constitute the bonding matrix of the cellulose microfibres. 

The chemical composition as well as the morphological microstmcture of vegetable fibres is extremely complex due to the hierarchical organisation of the different compounds present at various compositions. Depending on the type of fibre, the chemical composition of natural fibres varies. Primarily, fibres contain cellulose, hemicellulose and lignin. The property of each constituent contributes to the overall properties of the fibre. 

Hemicellulose is the other major constituent of plant-based namral fibres and it is made up of a combination of 5- and 6-ring carbon polysaccharides [22], It is a branched polymer and has much shorter polymer chains (degree of polymerisation of between 50 and 300) compared to native cellulose. In addition to this, hemicellulose is very hydrophilic in nature [35], easily hydrolysed by acids and soluble in alkali. The role of hemicellulose in natural fibres is to form the supporting matrix for cellulose microfibrils. 

Natural fibres are classified into three main groups, namely, bast (or stem), leaf and seed (or fruit). Bast fibres such as jute, hemp, kenaf and flax are fibrous bundles found in the inner bark of the plant stem. The fibre bundles consist of filaments of fibre cells made up of mainly cellulose and hemicelluloses. The cementing material between the fibre bundles is lignin while the filaments are held together by pectins. These fibres are separated from the woody matter through a process of natural... 

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. 

From ATR-FTIR, solid-state NMR, XRD and SEM, it was concluded that the sugar cane fibre consists of cellulose and non-cellulose (fatty acid, wax and hemicellulose). A schematic of a natural cellulose fibre from a sugar cane leaf is shown in Figure 13.11. 

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. 

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