In the past, it has been considered that the main purpose of cotton fiber scouring process is to remove cotton wax and oil to improve permeability. The commonly used enzymes include pectinase, cellulase, protease, lipase and so on.
Pectinase
Pectin is produced by D-galacturonic acid α－ The 1,4-glycoside bonded polysaccharide is the main chain. Some of its carboxylic esters are methyl esters. The different content of methyl esters in pectin leads to different hydrophobic properties of pectin. In the main chain, there are branches of rhamnose, arabinose, galactose, xylose and other sugars. It is a polymer with complex molecules. Although pectin contains a large number of hydrophilic hydroxyl and carboxyl groups, some of them exist in the form of calcium and magnesium pectinate, which affects the wettability of cotton fiber. Therefore, when treating with pectinase, chelating agent must be added to capture the calcium and magnesium ions in calcium pectinate or magnesium salt to form water-soluble chromium complex and remove it, and wetting agent must be added to improve the full wetting and penetration of Pectinase in water.
PROTOPECTINASE is the general name of enzymes that catalyze insoluble protopectin to decompose water-soluble pectin; Pectinase is the general name of various enzymes that catalyze soluble pectin. Pectinase generally includes pectinesterase, hemiuronidase and pectin lyase. Pectin esterase decomposes the ester bond in pectin molecule to form polygalacturic acid, while hemiuronidase hydrolyzes and interrupts the galacturonic acid-1,4-glycoside bond generated by the above decomposition, while pectin lyase passes the 1,4-glycoside bond of polygalacturic acid β－ Remove soluble substances that are cleaved into molecules by elimination reaction.
In 1998, novozyme company in Denmark isolated alkaline pectinase with the trade name bioprep 3000 L. in 2003, it launched group modified alkaline pectinase scourzyme L, which can be used in weak alkalinity. The combination with surfactant can improve the effect of removing oil and wax and obtain better gross effect.
During Alkaline Pectinase Scouring, due to the high molecular weight of the enzyme, it is not easy to penetrate into the fiber. Therefore, the enzyme solution enters the pectin layer through the cracks or micro gaps of the pectin layer. When the pectinase contacts with the pectin, it catalyzes and decomposes the pectin to form a soluble low molecular weight material, which is dissolved in water, and then removed by hot water washing, so as to improve the wettability of the fabric.
The wettability of pectinase and cellulase is improved most obviously, because the two enzymes can produce synergistic effect. Pectinase hydrolyzes epidermal pectin to produce more action sites for cellulase, and cellulase will also expose more pectin in epidermal layer to pectinase. The synergistic effect of pectinase and cellulase has been confirmed by many research results.
Cellulase
Cellulase is a multicomponent enzyme, including endo – β－ 1,4-gluconase, exo – β－ 1,4-glucosidase and glucosidase play a synergistic role. If classified according to pH, they can be divided into acidic and medium cellulase and alkaline.
As early as 1998, neutral or acidic cellulase has been used to wash indigo dyed denim instead of stone blue, which can achieve the same effect. Traditional denim is interwoven with indigo warp and natural weft. Due to the change of people’s aesthetic outlook, special requirements are put forward for denim. At first, using the characteristics of low water washing fastness and lower wet rubbing fastness of indigo dye, the stone grinding process is widely used, resulting in the return of the old. However, the pumice used becomes sand particles after treatment and enters the wastewater, resulting in the bad consequences of broken yarn and hem of jeans. In 1988, cellulase was tried to replace stone mill and achieved good results.
In the scouring process, cellulase and pectinase are used at the same time. Because most of the symbiotic impurities on cotton fiber are distributed on the surface and primary cell wall, if cellulase is used for catalytic degradation, the symbionts can be removed at the same time, which is particularly effective and beneficial to the removal of cottonseed shell. However, the strength of cotton fiber also decreases, so only a small amount of cellulase can be used in an appropriate range to help alkaline pectinase improve the scouring effect. Usually, manufacturers have mixed a small amount of cellulase in commercial pectinase, and users do not need to add it additionally.
Protease and lipase
Protein impurities are the most abundant in cotton fiber symbiosis. Therefore, protease was used to remove the protein in cotton fiber during cooking, which can improve the wettability of cotton, indicating that protein also affects the wool effect of cotton, but it is not a decisive factor. Because protein is easily hydrolyzed in alkaline water, protein can be removed in alkaline medium without protease.
In the past, it was considered that cotton wax was an important factor affecting the wettability of cotton. After pectinase removed pectin, a small amount of cotton wax could be removed under the action of emulsifier, and the distribution state of cotton wax could be changed, which made the cotton wax distributed in dots and destroyed the water repellent property of cotton wax. Some people use lipase treatment, and it is found that the effect is very poor, and the cotton wax is rarely removed. This is because lipase can not decompose the oil wax with high carbon chain, but can only play a role in low-carbon fat (such as triglyceride), so it can not completely remove the cotton wax. In fact, even without removal, it has little effect on the dyeing performance. Therefore, it is generally unnecessary to add protease and lipase when cotton fiber is cooked with biological enzymes. The actual production shows that the alkaline pectinase containing a small amount of cellulase is 1 g / L and the emulsifier is 1 g / L, and the pH is 9 3. When the temperature is 67 ℃, soak for 1 hour, and then conduct oxygen bleaching. Compared with the oxygen bleaching after high-temperature boiling of concentrated alkali liquor, the same wettability and approximate whiteness can be obtained. The K / s value of dyed cloth after dyeing is basically the same, COD decreases and BOD increases, which is conducive to the biochemical treatment of wastewater. Compared with traditional cooking, it meets the requirements of green production. If we strengthen the research of biological enzymes and achieve the same quality as novozyme in Denmark, the price of biological enzymes will certainly decrease.
The development of enzyme and its application in industry can be traced back to the 19th century and has developed rapidly in recent 50 years [49-51]. Although China is a large textile country, the research and development of modern textile enzyme preparations is slow. Except for amylase desizing and protease degumming of silk, most textile enzyme processing processes and enzyme preparations come from abroad.
