Association of Cellulose, Hemicellulose and Lignin in Okra bast Natural Fiber

Association of Cellulose, Hemicellulose and Lignin

There is no conclusive proof with regard to the chemical union of hemicellulose with cellulose in the okra fiber. In case of ligno-cellulosic fiber the opinion is that hemicellulose except xylan can not enter cellulose crystallites due to spacing difficulty. The cellulosans (mainly xylan) associated with the true cellulose in the cellulosic structure, are relatively short chain compounds, and occupy longitudinally the same space as the glucose units in the cellulosic chains. Xylan and cellulose are laid as a mixed crystallite structure probably with an incrusting cement consisting of lignin and hemicellulose.

It was elsewhere reported that a trisaccharide “gruce-xylo-arabinose” was isolated from delignified okra holocellulose supporting some chemical bonding affinity between cellulose and hemicellulose. But physical data from x-ray study do not appear to justify any chemical union between cellulose and hemicellulose.

Regarding the possibility of cellulose-lignin combination, the view is that the lignin cannot enter the cellulose crystallite due to the same spacing difficulties, but a small amount of lignin is intimately associated at the cell wall boundaries of cellulose. Chemical union exists between lignin and hemicellulose and it is the ester type linkage between the alcoholic hydroxyl group of lignin and the carboxyl group of polyuronic acid of hemicellulose appear, and the other type linkage between phenolic hydroxyl group of lignin and hydroxyl group of hemicellulose.

Hemi-COOH+HO-lignin= Hemi-COO-lignin ester linkage
Hemi-OH+HO-lignin= Hemi-O-lignin ether linkage

Thus, the main constituents of okra and other cellulosic fibre, alpha-cellulose, hemicellulose and lignin, are in closest physical association and because of their chemical properties overlap, sharp separation is a matter of extreme difficulty. -Cellulose which is the supreme structural element of the fibre while lignin and hemicellulose are distributed throughout the entire body of the fibre. The major portion of lignin is located in the intercellulose spaces, which in combination with hemicelluloses, serves as a cementing material for the ultimate cell units.