Study On The Interaction Between Zirconium Sulfate With ?-hydroxyl Acid And Dicarboxylic Acid

The chrome tanning method has been used for more than 100 years in the tanning industry.However,the chrome tanning process and the waste products of chrome tanning leather will cause serious pollution to the environment.As the improvement of people's awareness of environmental protection and environmental protection legislation pressure,chrome tanning will face the fate of being replaced.Research and development the environment-friendly chrome-free tanning agent is making a great significance for the sustainable development of leather industry.The consumption of zirconium tanned leather is non-toxic and harmless.The leather comprehensive performance of zirconium tanned leather ranks only second to chrome tanned leather,and zirconium resources are abundant.So zirconium tanning agent is considered to be a better substitute for chrome tanning agents.In this paper,zirconium sulfate is used as the representative of zirconium tanning agent,and the mechanism of complex tanning process is simplified.Simulation study on the interaction of zirconium sulfate with skin collagen molecules containing acid?monocarboxyl,polycarboxyl?and dicarboxylic acid structure compound were characterized by FTIR,XRD,UV-Vis,¹³C NMR,EA,deprotonation calculation and so on.Under the condition of 30 temperature and pH?0.5,the interaction complexes of zirconium sulfate with the representative compounds of ?-hydroxyl acid?monocarboxyl,polycarboxyl?and dicarboxylic acid structure compounds were prepared through solution synthesis of complexes by using water as solvent.Studies have shown that the coordination of Zr⁴⁺with-OH and-COOH ona-hydroxy acid?monocarboxyl,polycarboxyl?can occur simultaneously,and coordination with the-COOH of dicarboxylic acid can also occur.When Zr⁴⁺coordinates with-COOH,Zr⁴⁺coordinates with the hydroxy oxygen rather than carbonyl oxygen.The coordination number of zirconium sulfate with-OH and-COOH on hydroxyacetic acid and lactic acid are 2,which are synthesized a couple of five membered ring structure by the double tooth coordination chelate.However,the coordination number of zirconium sulfate with-OH and-COOH on mandelic acid are 1,which are synthesized five membered ring structure by the double tooth coordination chelate.The reaction products of zirconium sulfate and ?-hydroxyl acid?monocarboxyl?are difficult to dissolve in water and laboratory organic solvents,but it is not alkali resistant.By using sodium hydroxide solution,saturated sodium bicarbonate solution and saturated sodium tetraborate solution to adjust the system pH to 7,the chelating products will dissolve and remain stable.This can explain to some extent the phenomenon of fade tanning in the process of zirconium tanning with the increase of pH.However,the reaction product of zirconium sulfate anda-hydroxy acid?polycarboxyl?is soluble in water,and the water solubility of the reaction product of citric acid and zirconium sulfate is better than that of malic acid and zirconium sulfate.So it is speculated that when zirconium sulfate interacts with a-hydroxy acid?polycarboxyl?,the greater the number of carboxyl groups,the better the water solubility of the complexes.To some extent,it can explain why zirconium tanning leather is not as good as chrome tanning.