Studies On The Dechroming Mechanism Of Organic Acid With Series Structure

The effects of carboxyl group, hydroxide radical and the molecule size of organic acid on the performance of dechroming were studied according to the changes of pH values and the amounts of chrome complexes and hydrolyzed collagen proteins in the dechroming solutions while using oxalic acid, malonic acid, succinic acid, malic acid, tartaric acid, lactic acid, and citric acid. The results showed that the amount of dechroming, that of hydrolyzed collagen proteins and the dechroming ability of dicarboxylic acid group decreased with the more carboxyl groups. The performance of dechroming of four-carbon dicarboxylic acid enhanced with the more hydroxide radicals, and the dechroming ability of tartaric acid group with two hydroxyl groups was bigger than that of succinic acid group. The dechroming ability of citric acid group with three carboxyl groups was bigger than that of lactic acid group with one carboxyl group. The effect of steric hindrance on the performance of dechroming was obvious and increasing temperature and associative hydrochloric acid could alleviate the effect degree. The dechroming ability and destructiveness on the stability of collagen of acid groups were bigger than H+. The primary and secondary dechroming sequence between H+ and acid group in acids was affected by the concentration and temperature. The hydrolyzed collagen of dechroming solutions could constitute buffer system, and increasing the amount of the hydrolyzed collagen would benefit the buffer effect. The binding points between chromium complex and collagen which acid groups attacked were of principle interest to the amounts of hydrolyzed collagen proteins. When the multipoint binding chromium complexes dechromed, the amount of the hydrolyzed collagen was higher. As to the single-point binding chromium complexes dechromed, the amount of the hydrolyzed collagen was lower.The influence factors of the coordinate reaction which different kinds of organic acid group substituted gelatine and coordinated with chromium comples. The results showed that oxalic acid, malonic acid and lactic acid might replace the coordinated hydroxide radical of the chromium comples and the pH value increased. While succinic acid, malic acid and citric acid mainly substituted the other coordination groups and the pH value decreased. The rate of coordinate reaction between organic acid group and chromium could be evaluated by the rate of hypsochromic shift belonged to the long wave peak position of the mixed solution. The effects of reaction time, reaction temperature, the molecular size of chromium complex, the molar ratio of tartaric acid/chromium oxide and coordination groups on the coordination reaction between acid and chromium complex were studied according to the changes of pH value and peak position. The results showed that the successive order of the rate of coordinate reaction between organic acid group and chromium was tartaric acid, oxalic acid, citric acid, malonic acid, lactic acid and succinic acid.Increasing the molar ratio of acid/chromium oxide and temperature had significant effect on accelerating the reaction rate.The changes of pH value and conductivity demonstrated the kinds of interaction such as substitution and deolation between oxalic acid and chromium complex according to the static process including the species, quantity and size of ions and the dynamic process migration rate of ions for example. The coordinate reaction of oxalic acid and chromium complex was investigated with acidometer and conductivity meter. The results showed that the pH value decreased and conductivity of the solution descended earlily as a result of the substitution of H2O and acid ligands. The pH value increased and the conductivity decreased late when deolation. The substitution was much easier compared with deolation. The degree of coordination reaction varied with the molar ratio of oxalic acid/chromium oxide and the molecular size of chromium complex. Increasing the molar ratio of oxalic acid/chromium oxide and decreasing the pH value of the chromium complex solution make for the coordination reaction. 1 mol Cr(â…¢) could coordinate with 1 mol oxalic acid group. The coordination reaction between tartaric acid and chromium complex was investigated combined with the changes of peak position, absorption maximum and half-band width during the reaction. The results showed that the molar ratio of tartaric acid and the molecular size of chromium complex rated to the reaction. Increasing temperature could alleviate the effect steric hindrance. Increasing the dissociation degree of the carboxyl group of the tartaric acid and the size of the chromium complex enhanced the degree of substitution, and the influence degree of the former was bigger than that of the later.The temperature dependence of storage modulus, crosslink densities and loss modulus of dechromed wet-blue compared with pickled hide and wet-blue has been studied by dynamic mechanical analysis for the first time. The differences of dynamic mechanical properties were investigated according to the thermal deformation temperature and crosslink densities. The changes of storage modulus of pickled hide and wet-blue before transition point were mainly caused by the increasing of conformational entropy and by the decreasing of crosslink densities after transition point. The storage modulus of dechromed wet-blue decreased with the reduction of crosslink densities. The higher the crosslink densities were, the stronger the thermal endurance and the lower the sensitivity to heat were. The successive order of crosslink densities was wet-blue, pickled hide and dechromed wet-blue.