The nature of cellulose
Cellulose is a macromolecular polysaccharide composed of D-1 glucose, which is composed of β-1,4 glycosidic bonds, and has a molecular weight of about 50,000 to 2,500,000, which is equivalent to 300 to 15,000 glucosyl groups. The formula can be written as (C6H10O5)n. It is the main component of vascular plants, lichens and some algae cell walls. The capsule of Acetobaeter and the sac of the cercaria are also found to have cellulose. The seed hair of cotton is high purity (98% cellulose. So-called α-cellulose) This name refers to the portion of the complete cellulosic standard sample from the original cell wall that could not be extracted with 17.5% NaOH. β-cellulose (β-cellulose), γ-cellulose (γ-cellulose) is the fiber corresponding to hemicellulose. Although α-cellulose is usually mostly crystalline cellulose, β-cellulose and γ-cellulose contain various polysaccharides in addition to cellulose. Cellulose of cell walls forms microfibers. The width is 10-30 nm, and the length is up to several micrometers. X-ray diffraction and negative staining (negative staining) are applied. According to electron microscopy, the linear part of the linear arrangement of chain molecules is 3-4. Nano-basic microfibers. It is speculated that these basic microfibers are combined to form microfibers. Cellulose is soluble in Schwitzer reagent or concentrated sulfuric acid. Although it is not easy to be hydrolyzed by acid, dilute acid or cellulase can make cellulose D-glucose, cellobiose and oligosaccharide. In acetic acid bacteria, there is an enzyme that synthesizes cellulose from UDP glucose primer (cellulose synthase (UDPforming EC22.214.171.124). It has been obtained in higher plants. A standard sample of the same active granular enzyme. This enzyme usually uses cellulose synthase (GDP forming) EC126.96.36.199, and in the case of transfer by UDP glucose, β-1,3 bond occurs. The mixing of microfibers and the mechanism of controlling cellulose alignment are not well understood. On the other hand, in terms of cellulose decomposition, it is estimated that when the primary cell wall is stretched, a part of the microfibers is due to the action of cellulase. It is broken down and becomes soluble.
Cellulose is insoluble in water and organic solvents such as ethanol and ether, and can be dissolved in copper ammonia Cu(NH3)4(OH)2 solution and copper ethylenediamine [NH2CH2CH2NH2]Cu(OH)2 solution. Water can cause limited swelling of cellulose, and certain aqueous solutions of acids, bases, and salts can penetrate into the crystalline region of the fiber, producing infinite swelling and solubilizing the cellulose. There is no significant change in the heating of the cellulose to about 150 ° C, beyond which the temperature will gradually coke due to dehydration. The cellulose is hydrolyzed with a relatively concentrated inorganic acid to form glucose, etc., and reacts with a concentrated caustic solution to form alkali cellulose, and reacts with a strong oxidizing agent to form oxidized cellulose.
Cellulose production method
The laboratory method of cellulose is to treat the plant raw materials with water and organic solvent, and then remove the lignin contained therein with chlorine, chlorite, chlorine dioxide and peracetic acid to obtain cellulose and hemicellulose, and then adopt Various methods remove hemicellulose to produce pure cellulose. The industrial process is to cook the plant material with a sulfite solution or an alkali solution, remove the lignin, and then further remove the residual lignin by bleaching, and the resulting bleached pulp can be used for papermaking.
A polymer compound having an ether structure made of cellulose.
Each glucosyl group in the cellulose macromolecule contains three hydroxyl groups, a primary hydroxyl group on the sixth carbon atom, a secondary hydroxyl group on the second and third carbon atoms, and a hydrogen in the hydroxyl group is substituted by a hydrocarbon group to form a cellulose ether derivative. Object.
According to the chemical structure classification of the substituents, they can be classified into anionic, cationic and nonionic ethers.
Depending on the etherifying agent used, there are methyl cellulose, carboxymethyl cellulose, ethyl cellulose, benzyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, cyanoethyl cellulose, Benzyl cyanoethyl cellulose, carboxymethyl hydroxyethyl cellulose, phenyl cellulose, and the like. Methylcellulose and ethylcellulose are more practical.
The solubility of cellulose after etherification changes significantly, and it can be dissolved in water, dilute acid, dilute alkali or organic solvent. The solubility depends mainly on three factors: (1) the characteristics of the groups introduced during the etherification process, introduced The larger the group, the lower the solubility, the stronger the polarity of the introduced group, the more soluble the cellulose ether is in water, and (2) the degree of substitution and the distribution of the etherified group in the macromolecule. Most cellulose ethers can only be dissolved in water under a certain degree of substitution, and the degree of substitution is between 0 and 3. (3) The degree of polymerization of cellulose ether, the higher the degree of polymerization, the more difficult to dissolve; the higher the degree of polymerization Low, the wider the range of substitutions that are soluble in water. Cellulose ethers are widely used in construction, cement, petroleum, food, textile, detergent, paint, pharmaceutical, paper and electronic components industries.