Extraction of New Vegetable Tanning Agent from Coriaria nepalensis Bark and Its Application in Tanning

Content: Traditional chromium tanning agents cannot conform to the requirement of sustainable and cleaner development under current leather producing. Compared with chromium tanning agents, vegetable tanning agents have been widely used in tanning process by the virtue of its non-toxicity, low pollution, biodegradability and regenerability. In this study, a novel vegetable tanning agent was extracted from the Coriaria nepalensis bark (CNB) by alkali solution. In order to optimize extraction conditions, the response surface Box-Behnken design was used in this experiment. The key factors including alkali concentration, extraction time, extraction temperature, liquid to solid ratio and extraction times. The experimental results showed that under the conditions of 0.22% sodium hydroxide concentration, 63 min extraction time, 83℃ extraction temperature and 24 liquid to solid ratio, the yield of tannins in CNB is 15%, tannins in extractives up to 50%. Afterwards, the composition and molecular mass were evaluated, we discovered that the extractives belong to hydrolyzable tannins and its molecular mass ranged from 599 to 1457 Da. Furthermore, the extractives were used in sheep garment tanning process. The results showed that the shrinking temperature of tanned leather can reach to 75 ℃. Applying the extractives to the retanning process, the shrinking temperature of retanned leather can reach to 130 ℃. Surprisingly, the color of tanned or retanned leather coincide with the requirement of light leather. Take-Away: 1 New vegetable tanning agent from Coriaria nepalensis bark. 2 The vegetable tanning agent belongs to hydrolyzable tannins and its molecular mass ranged from 599 to 1457 Da. 3 The shrinking temperature of tanned leather and retanned leather can reach to 75 ℃ and 130 ℃ respectively