Читать книгу Biomolecules from Natural Sources - Группа авторов - Страница 65

Cellulose is a polysaccharide that is the main constituent of all plant tissues and fibers. The name cellulose, from Latin cellula, was coined in 1838 by French chemist Anselme Payen. Special forms of cellulose fiber are found in most plants in the leaves and stalks, with cotton fiber (95% cellulose) [149]; wood (about 50%) being the principle industrial sources of cellulose [150]. Because of its ubiquity in the plant kingdom, cellulose is arguably the most abundant polymer on earth, with billions of tons produced annually through photosynthesis. The strong glucosidic bonds ensure the stability of the cellulose in various media. Cellulose is mostly insoluble and highly crystalline. Chemical reactions such as esterification are conducted on the free hydroxyl groups to improve its thermoplastic behavior. The main uses of cellulose are for paper, membranes, dietary fibers, explosives and textiles [151]. Cellophane^TMis a blend of cellulose and diaphane [152]. A transparent paper-like product that is impervious to moisture and used to wrap candy, cigarettes, etc. The name was coined in 1912 by Swiss chemist Jacques Edwin Brandenberger, the invention of the material dates from 1908. Cellophane films are obtained by dissolution of cellulose in a sodium hydroxide and carbon disulphide solution (Xanthation) and then by recasting in a sulphuric acid bath. Degradation takes place after six weeks of composting. Cellophane films are mainly used in food packaging where they are valuable for their barrier properties against microorganisms, gases and smells. Cellulose acetate is mainly used in the synthesis of membranes for reverse osmosis.

Cellulose is the principle part of most plant cell walls, and is currently of interest because of processes for paper making, and as a major structural component of textile fibers such as (Gossypium spp.), ramie (Boehmeria nivea), jute (Corcorus capsularis), flax (Linum usitatissiumum) and sisal (Agare sisalana). Surgical cotton is actually made from wood. Cellulose used as biopolymer, biomaterial, drug delivery, bacterial microparticles [153, 154].

Bacterial cellulose is synthesized in a process whereby the polymer material is extruded from the bacterial cells. Most cellulose-producing bacteria (i.e., Acefobacter) extrude cellulose as a ribbon-like product from one fixed site on the cell surface. This results in a network of interlocking fibers forming. Bacterial cellulose is produced under conditions of agitated fermentation. Bacterial cellulose is a water-insoluble material that has a large surface area because of its large network of fibers; bacterial fibers have roughly 200 times the surface area of fibers from wood pulp. This, coupled with their ability to form hydrogen bonds, makes them unique when used as suspensions, they have pseudoplastic thickening properties. The bacterial cellulose is used for dressing chronic wounds [155], nanocomposites [156], cancer treatment [157], natural rubber latex formation [158], antimicrobial food packaging applications [77], biocomposite [159], gravity-driven oil/water separation [160] and many others.