Cellulose

Article

October 20, 2021

Cellulose is one of the most important polysaccharides. It is a polymer, that is, it is made up of a large number of glucose molecules joined thanks to a bond that takes the name of glycosidic. The molecule is mainly contained in plants. The polymer chain is not branched.

Structure

The chains are arranged parallel to each other and are linked to each other by means of hydrogen bonds, forming fibrils, very long chains, difficult to dissolve. These fibrils are locally very ordered to the point of reaching a crystalline structure. The crystalline part is hydrophobic, i.e. it does not absorb water, and therefore in order to obtain a hydrophilic product (such as common cotton) it is necessary to subject the cellulose to a set of treatments called mercerization, named after the English textile chemist and industrialist John Mercer who conceived the process in 1844 and patented it in 1851. About half of the cell walls of plants are made up of cellulose, but cotton, for example, is almost 100% cellulose. Cellulose is hydrolyzed, under particular conditions, into the cellobiose disaccharide which is subsequently hydrolyzed to glucose. In the human intestine this hydrolytic process does not take place because the enzymes to break the β (1 → 4) glycosidic bond are lacking. In the forestomach of ruminants and in the caecum of monogastric herbivores (equidae), on the other hand, there are numerous bacteria and symbiont protozoa that convert the β bond into an α bond, which can be severed by all animals.

Economy of cellulose

Cellulose is commercially important in that numerous derivatives are obtained from it: cellulose diacetate, used for example in the production of eyeglass frames or to make combs; rayon is obtained from cellulose in a solution of sodium hydroxide and carbon sulphide, cellophane can be obtained with the same method. Other products are paper and viscose. From cellulose it is possible to obtain another important product with a high commercial value, nanocellulose, which has many industrial applications (biomedicine, green building, Oil & Gas industry). The various constituent groups of cellulose can react with nitric acid to give cellulose nitrate (an explosive known as "fulminant cotton" or "fulminant"). The name cellulose was introduced in 1839 by Anselme Payen, a French professor of Applied Chemistry. Cellulose is one of the many polymers found in nature. Cellulose is an excellent fiber. Cotton and hemp are made up of fibrous cellulose.

Chemical extraction and obtaining of chemical pulp

The chemical processes are aimed at dissolving the lignin in the acidic or alkaline aqueous phase and separating it from the insoluble cellulose. The chemical composition depends on the composition of the wood used; the yield is influenced by various factors, including the type of wood, the processing techniques and the process of obtaining it. It can reach 90-95%. Appearance: bundles of fibers of variable length, fiber fragments and isolated fibers; energy consumption: about 12 kcal / ton of pasta; Following the processing of the woody parts of a tree, cellulose pulp is obtained. It consists mostly of cellulose and to a lesser extent of processing by-products and constituents of the original wood. It differs from wood pulp for the greater quantity of cellulose and the lower presence of other compounds originating in wood (such as lignin).

Pasta quality

A pulp with a high lignin content gives rise to paper with low resistance to aging and prone to yellowing due to the presence of double bonds. This cheaper paste is used for newspapers, cartons and other paper items of daily use. The most valuable pulp, called chemical pulp, allows to obtain higher quality papers, used for example for glossy magazines or for other u

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