Cellulose

CELLULOSE, fiber, the main component of plant cell walls, a polysaccharide (C₆H₁₀O₅)_n. In its purest form, it is found in cotton fibers up to 85-90%; in the wood of various trees, the content of C. is 40-60%; in coniferous species, it is more abundant than in deciduous species. Cellulose is a very chemically resistant substance; it does not dissolve in water or neutral liquids; it dissolves in some alkaline and acidic liquids, in Schweizer's reagent (ammoniacal solution of copper oxide: 10-15% NH₃ and 2-2.5% CuO), in concentrated solutions of ZnCl₂, in hydrochloric solutions of SnCl₂ and SbCl₃, forming colloidal solutions, from which C. is very easily precipitated by adding substances that remove water: alcohol, sugar, salts of alkali metals, etc. When cellulose dissolves, a whole series of physical and chemical changes apparently occurs. The product of the action of alkalis on C. is hydratecellulose and mercerized C. When mineral acids act on C., the so-called hydrocellulose is obtained, a substance of complex composition, representing a mixture of unchanged C., depolymerized C., and products of its hydrolysis. Hydrocellulose still has a fibrous structure but is very brittle, restores Fehling's solution, does not stain with iodine, and partially dissolves in alkalis. When water is added to a solution of C. in concentrated sulfuric acid, amyloid (parchment paper) is obtained. When various oxidizing agents act on C., oxycellulose is obtained, a mixture of substances of different composition and with different properties depending on the oxidizing agent. In the hydrolysis of C. by acids, the final product is glucose; the intermediate products are a series of cellobiose and cello-dextrins. The action of digestive enzymes completely does not affect C., and it is broken down only by enzymes (cellulase) of various microorganisms. Cellulase breaks down C. only to the stage of cellobiose. Some bacteria (Bact. xylinum) synthesize C. from various monosaccharides. Many works have been devoted to elucidating the structure of C. Chemical research does not confirm the hypothesis of the construction of C. from associated anhydrides of glucose or cellobiose and leads to the conclusion that C. is built from long chains of cellobiose residues (β-linkage of glucopyranose) (Wilstatter, Haworth, Freudenberg, M. Bergmann, etc.). Hess, Karrer and others accept a small molecular weight for C., considering it an associated anhydride of glucose, with Hess believing that in formula II, n = 1, and Karrer and Pringsheim believing n = 2, i.e., the elementary molecule of C. is the anhydride of biose. K. Meyer and Mark, based on data from X-ray studies, also believe that the residues of glucose are connected in the cellulose molecule by a glycoside-like bond, forming long chains: 6CH₂OH I HOCH HOCH 6CH₂OH. The latter are connected between themselves through additional valences, forming crystallites (micelles). The molecular weight usually accepted for C., according to K. Meyer and Mark, is the weight of such a micelle. Its molecular weight is about 1,000,000. The thread-like structure of C. is accepted by the school of Staudinger, but unlike K. Meyer and Mark, he believes that an individual thread represents a giant molecule, in which there can be up to 1,000 glucose residues, i.e., in the formula for C., n = 1,000; each molecule is a primary colloidal particle. The chemical and physical properties of C. allow the theory of K. Meyer and Mark to be considered the most probable. C. is widely used in technology, is the starting product for paper production. Especially important are the esters of C.; for example, nitrates of C. are used for preparing fast-drying and durable varnishes, its trinitrate, pyroxylin, is a brisant explosive and is used after gelatinization and grinding as a propellant explosive (smokeless powder); celluloid, a colorless, transparent, elastic mass, is prepared from colloidal cotton (less nitrated C. than trinitrate), is used for the production of photographic film and other products. Collodion (see) has applications in medicine. Acetates of C. are used for the production of aerolacquers, films, and plastics. C. has enormous importance as the starting product for the production of artificial silk (from viscose xanthate, from nitrate, acetate, and copper-ammonia silk). Finally, in recent times, C. has been widely used for obtaining grape sugar. Esters of C. with higher fatty acids apparently are part of the cork layer. The physiological significance of C. for plants apparently is limited to its role as supporting tissue. As a nutrient for animals, C. has significance only insofar as in the thin intestine there is its breakdown by microorganisms (see Nutrition).

Hemicellulose, a plant polysaccharide, is very close to C. in its properties, but unlike C., when it is hydrolyzed, various pentoses are obtained in addition to glucose. It is still unknown whether hemicellulose is a chemically homogeneous substance or a mixture of substances. Hemicellulose is hydrolyzed more easily than C., which may be connected with the fact that in addition to its supporting function, it partly performs the role of a reserve carbohydrate. In rare cases, cellulose is also found in animal organisms. For example, its presence has been detected in ascidians (Tunicata); the C. found in them was named tunicin.

M. Karyagina.