Studies On The New Simplified Technology Of Tanning

Tanning is the traditional industry which has comprehensive advantages in our country. In the past 10 years, our country's leather industry developed rapidly with the adjustment of the world's industrial structure. The leather production of our country has accounted for about 30% of the world and become the center of the world's tanning industry. However, in China, the tanning industry has the third major pollution in the light industry. With the increase of people's environmental consciousness and the issue of new discharge standards., the sustainable development of the leather industry is facing with severe challenges.The conventional tanning process has a wide pH range. It involves so many steps such as soaking, liming, reliming, deliming/bating, pickling, chrome tannage, basification, chrome retanning, basify, nueturazation, washing, retanning, dyeing, fatliquoring and acid fixing. It has many acid-base operations such as liming—deliming, pickling—basifycation, nueturazation--acidification, such pH changes demands the usage of acids and alkalis, which leads to the generation of salts and wastewater, at the same time it will damage the leather. Especially, a lot of NaCl are needed to add to control acid swelling in the pickling step. So many salts would cause dehydration of pelt and make leather flat, and the addition of NaCl will cause the salt pollution in the environment.In order to reduce the environment pollution of leather industry, in recent years, people have done a lot of works, such as pickling without salts, high pH chrome tanning and so on. But all these works have not fundamentally changed the tanning process.In this paper, we studied a new simplified technology of tanning. The new technology used the pH condition of the delimed/bated pelt, which was 7.0-8.0, and this pH value outclassed the isoelectric point of collagen protein. So the collagen carboxyl was electronegativity. When the anionic retanning agent, acid dyestuff and anionic fatliquor were added in this high pH, the retanning materials could easily penetrate into leather because of the higher pH. After the materials penetrated uniformly, pH value was lowered slightly to 4.5~5.5 to fix these filling materials, and simultaneously the conditions were provided for chrome tanning. Here, the penetration and fixing of chrome molecular would be taken place simultaneously. Without basification, the solution pH value would fit for chromium penetration because of its acidity and hydrolyzation. And the final pH value was 4.0±. With the new technology, the acid-base damages to leather were avoided, the physical-mechanical properties were enhanced in a certain extent and a large number of neutral salt were avoided, the pollution was reduced. There are only six steps in the whole wet operation in the new technology: soaking, liming, reliming, deliming and bating, filling/dyeing /fatliquoring, chromium tanning, etc.. The new technology could greatly simplify the process, reduce the use of chemical materials and save time and energy.In this paper, we did the experiments by using cow limed hides and sheep limed hides respectively. The various filling materials'influence to the properties of crust leather was studied, the experiments of match of filling materials and the contrast with conventional process were did. At the same time, the analysis of lightening pollutions in the tanning procedures were did. According to the testing results of chromium absorption rate, tensile strength, tear strength, shrinkage temperature, softness and sensory evaluation, the new technology could simplify the process compared to the conventional process. And it also could greatly reduce the quantity of neutral salt and wastewater. The new technology was a major breakthrough to the conventional process, and it had a great significance for achieving the clean production and sustainable development of leather industry.