Preparation And Performance Of Enzyme-containing Additives For Leather Manufacturing

Tanning industry plays an important role in livestock and leather products. However, large amount of chemical materials used in tanning process will bring environmental pollution. The key point to solve pollution is to use environmental friendly materials and to fulfill cleaner production. Because of high efficiency, specificity, degradability and no pollution, enzyme has been considered to be a potential green material to achieve cleaner tanning. The research of enzyme in leather industry is expanding and deepening. At present, the lack of study on enzyme penetration in skin for the structural characteristics of different stage lead to the development of enzyme preparation and application control in leather processing have blindness. In addition, enzyme could be influenced by external conditions during using and storage and lost activity which reduce the stability of enzyme products. Based on this, the main work in this study included the following parts:(1) The performance of different proteases for soaking was investigated and the preparation of compound soaking enzyme was optimized by single-factor experiment. The compound soaking enzyme was applied in soaking process of goatskings. A method to detect the penetration of proteases in skins was developed by FITC labled protease. The penetration and action behavior of proteases in skins was discussed. The results indicated that the compound soaking enzyme was better than commercial soaking enzyme in goatskins soaking process. FITC labeled protease soaking show that protease molecular weight had influence on the its penetration and hydrolysis of the protein in the skin. The penetratation rate of larger molecular weight proteases was slower than that of smaller molecular weight proteases. A combination of different molecular weight proteases had better synergistic effect in soaking. The action process of protease in skins was proposed as following: Epidermal keratin in raw skin has impediment to proteases penetratation into skin from epidermis, therefore, at the initial stage, protease penetrated mainly through the pores and hair follicles and then hydrolysed protein. Subsequently, proteases entered skins from hair follicles and hydrolyse protein. With the extension of soaking time, proteases gradually penetrated into skins from grain and flesh side to hydrolyse protein.(2) A compound bating enzyme was prepared via sigal-factor method and then was applied in bating of goatskins. The penetration behavior of proteases in pelt before bating was studied by FITC labeled proteases. The results indicated that the combination of 80U/g trypsin, 80U/g Lime G and 0.015% sodium laurylsulfonate had the best bating performance. Compared with commercial enzyme, this compound bating enzyme had stronger hydrolysis to protein, and the shrinkage temperature of wet-blue and mechanical properties of crust leather bated with compound bating enzyme were higher. The compound bating enzyme had benefit to the dispersion of collagen fibers without damage to grain. The average pore diameter of pelt before bating was much larger than the size of proteases. Therefore, the pore structure of pelt had little impediment to the penetration of proteases and proteases penetrated into pelt through grain and flesh side to hydrolyse protein. Compared to the proteases molecular weight, species and the relative specificity of the proteases played a more important role in bating process.(3) Single-factor method was adopted to optimize the preparation of organic acid-based non-ammonia deliming agent. On the base of non-ammonia deliming agent and compound bating enzyme, a enzyme-containing non-ammonia deliming agent was prepared. The application performance and synergy mechanism of enzyme-containing non-ammonia deliming agent in deliming-bating was studied. The synergistic effect between deliming agent and enzyme was explored. The results showed that the enzyme-containing non-ammonia deliming agent could improve the penetration of deliming agent and the biodegradability of deliming waste water. Study of FITC labeled proteases on deliming process indicated that proteases could penetrated into skins and hydrolyse protein. The synergy mechanism between non-ammonia deliming agent and bating enzyme in one bath was proposed based on the application performance and penetration of enzyme in delimed pelt. The enzyme-containing non-ammonia deliming agent could be used in deliming-bating process and bating enzyme did not affect the mechanical properties of crust leather.(4) Nano Si O2 were used to immobilize papain. Effect of reaction condition on immobilized papain were investigated. The stability of immobilized papain was tested. Then the immobilized papain was applied in soaking and bating process. Mechanism of nano Si O2 immobilized papain in bating process was discussed. The results indicated that the thermal and storage stability of Si O2 immobilized papain was improved compared with papain. When Si O2 immobilized papain was applied insoaking, it had similar hydrolysis to protein with papain. And in bating process, Si O2 immobilized papain did not affect hydrolysis to protein, shrinkage temperature of wet-blue and mechanical properties of crust leather. Nano Si O2 could enter between fibers and contributed to collagen dispersion. Study of FITC labeled nano Si O2 immobilized papain in bating process indicated that nano Si O2 immobilized papain had no effect on the penetration of papain in bating pelt. The possible process of nano Si O2 immobilized papain in bating was proposed as following: Under bating p H condition some papain were released from nano Si O2 and be free in the bating liquor, and then the released papain and part of immobilized papain penetrated into skins and hydrolyse protein to obtain bating performance.