Study On The Synthesis And Application Of High Exhaustion Chrome Tanning Auxiliaries

Two kinds of polymer chrome tanning auxiliaries ECPA and OXD- I were prepared. ECPA with various functional groups such as -COOH, -CHO, -OH and -NR2 was synthesized by means of copolymerization from acrylic monomers and vinyl monomers, while OXD-1 was prepared via special chemical synthesis method. ECPA containing 38.0-44.0% carboxyl group, 2.0% hydroxyl group, 2.0 % aldehyde group, 1.5-2.0% tertiary amino group and 5.0-7.0% benzene ring exhibited high exhaustion of both chromium and dyestuff as well as oil. Because of lower glass transition temperature (Tg) and containing a great deal of activity groups of ECPA, leather tanned with ECPA and chrome can be imparted with good fullness , elasticity and flexibility. At the temperature range of -40℃ to 280℃, ECPA showed no decomposition and its solution exhibited good stability between pH value 1-8. Similarly, OXD-1 with carboxyl group, hydroxyl group and tertiary amino group possessed excellent property of improving absorption of chrome. Most of all, it can raise the shrinkage temperature of leather obviously.The optimum application conditions of the auxiliaries were achieved via a series of leather making experiments. The results showed that 3% ECPA or 2% OXD- I was combined with 5% KMC in leather tanning, final pH of the chrome tanning was adjusted to 4.0 or so by urotropin, the content of Cr2O3 in the wastewater will bedecreased to 0.2g/l and chromium uptake will reach to 96.8%. Furthermore, the treated leather was imparted with good fullness and dyeing performance. The tensile strength and tear strength of leather were better than those of industry standard. When 1.0% OXD-I and 1.5% ECPA were used together, the similar results were achieved. Comparing with traditional chrome tanning, the tensile strength of leather increased 45%, and the dosage of chromium was decreased by 40%, the content of Cr2O3 in the wastewater was decreased from 1.68 g/l to below 0.2 g/l and chromium uptake was raised from 70% or so to 97.0%. Meanwhile, a large amount of water was saved and leather making time was reduced.The high exhaustion chrome tanning mechanisms of ECPA and OXD-I were respectively studied via approaches of UV, DSC and so on. The DSC study indicated that the aldehyde group of ECPA or oxazolidine group of OXD-I can react with the amino group in the side-chain of collagen and formed covalent bond. As a result, plenty of carboxyl group, hydroxyl group and tertiary amino group of ECPA or OXD-I can be introduced onto the backbone of collagen. UV study showed that carboxyl group of ECPA or OXD-I coordinating with Cr(III) provided a possibility of high chromium uptake. The carboxyl groups in both the auxiliaries and side-chain of collagen could coordinate with chrome and thus formed cross-linking and single-point reaction, producing irreversible fixation of chrome which were suggested to be the key reason contributing to the complete absorption of chrome.