Cellulose chain polymerisation

The cellulase complex diffuses through the pore system to the microfibrils, attacks the cellulose chains and hydrolyses each chain to the end. The diflerences in the efficacy of cellulases on various fibres are dependent on number of factors such as the amounts of non-cellulosic wood pulp-derived matter, the degree ol polymerisation, the type and degree of crystallinity, and the type and number of chemical substitutions to the cellulose [27-30]. Key features for the cellulose substrate are crystallinity, accessible surface area and pore dimensions [31 ]. Variation of any of these factors, e.g., structural changes of cellulose substrate by pre-treatments, will influence the course of the entire degradation process [32, 33]. 

The course of biotransformation and the final product properties depend both on the type and composition of the enzyme complex and on the cellulose structure such as the average polymerisation degree and its distribution, crystallinity, capillary system and swelling behaviour as well as the physical-chemical parameters of processes such as ratio enzyme activity to cellulose content, time and temperature reactions. The increased susceptibility of cellulose chains is a result of the modified stmcture and developed intrinsic surface of cellulose obtained by using suitable pre-treatment methods, particularly mechanical processing. ... 

Cellulose can be replaced by starch or even proteins (Bhattacharya et al, 1997). Of course, it is possible to carry out other graft-polymerisation reactions on cellulose or starch, for instance with acrylic monomers. The obtained material is useful, but it lacks biodegradability due to the synthetic side chains. 

Many graft copolymers can be obtained by creating active radical centres capable of initiating polymerisation of vinylic or acrylic monomers on the cellulose backbone. The properties of cellulose are completely modified by the presence of these grafted chains. 

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. 

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