Hemicelluloses value chains

Apart from dehydration of glucose or fructose in the presence of alcohols and acid catalysts, synthesis strategies via 5-(chloromethyl)furfural and subsequent heating in the desired alcohol or utilizing furfuryl alcohol as feedstock have been demonstrated [89-98], While 5-(chloromethyl)furfural may be derived in one step based on cellulose, a synthesis procedure starting from furfuryl alcohol utilizes hemicellulose as feedstock, bridging the C5 and C6 carbohydrate value chain. 

Table VII shows that the activation energies of artificially aged pulps BBC and BPC are consistently lower than for the control samples. The lower values indicate that the rate-determining reaction can proceed more readily after artificially aging. This may be a result of the introduction of carbonyl groups or of the introduction of chain ends as a result of hydrolysis of the hemicellulose and cellulose. Such modifications of the original pulp may act as weak links or sites at which further degradation is facilitated.

Cellulose purity can be determined by RIO, SIO S18, and S18. The RIO value, which is the percentage of the cellulose sample insoluble in 10% sodium hydroxide solution at 20°C, represents long-chain cellulose. The SIO value is the percentage of the cellulose sample soluble in 10% NaOH. Of course, RIO equals 100 SIO. The S18 value is the percentage of the cellulose sample soluble in 18% NaOH at 20°C. The SIO - S18 value represents short-chain cellulose. The S18 value represents mostly hemicellulose. The terms RIO, SIO - S18, and S18 are similar in value to a-, p-, and y-cellulose, respectively [4]. 

A number of sub-fractions have been isolated from the hemicellulose B fraction of the husks of Sorghum grain. Three of these sub-fractions were each found to contain residues of L-arabinose, D-xylose, D-galactose, D-glucose, and D-glucuronic acid and its 4-0-methyl ether. Structural studies confirmed that the three polysaccharides were xylans with the usual )8-l,4-linked main chain. There were considerable differences in the D.P. of these polysaccharides, the values obtained being 993, 2380, and 851. 

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