Study On Mannich Reaction Modified Acrylic Copolymer Retanning Agent

In leather industry,acrylic polymer is widely used as retanning agent because of its many excellent properties.However,a large number of carboxyl groups in acrylic polymers decrease positive electricity of leather via binding to the amino groups,leading to the reduction of binding sites in leather with anionic dye?commonly used in leather making?.In order to solve this problem,cationic groups were often introduced into acrylic polymers by Mannich reaction.Mannich reaction is a three component condensation reaction involving aldehydes,amines and compounds with active hydrogen.However,formaldehyde is the most commonly used in Mannich reaction systems for chemical modification of polymer molecules,which has toxicological risks on environment and human and has been listed in the restricted substances.Therefore,the effect of different aldehyde components on the application properties of Mannich reaction modified acrylic polymers were studied,and suitable low toxic aldehydes were selected to replace formaldehyde and modified acrylate polymer retanning agent via Mannich reaction.Firstly,the poly?acrylic acid-acrylamide-acrylonitrile??P?was synthesized by free radical initiation and solution polymerization.P was modified by Mannich reaction with different aldehyde components?glyoxal,glutaraldehyde,2-furaldehyde,benzaldehyde,methylglyoxal?and applied in retanning process.The basic properties,assistant-dyeing properties and retanning properties of retanning agents were investigated.The results showed that glutaraldehyde?GA?and methylglyoxal?MG?as aldehyde components had higher amination degree and better application performance,especially assistant-dyeing performance.Comparing with the free formaldehyde content of MTA,that of GAMP and MGMP significantly reduced to 4.17 mg·kg^-1 and 5.56 mg·kg^-1,respectively.And the assistant-dyeing performances of GAMP and MGMP were better than that of MTA.Therefore,GA and MG were suitable for replacing formaldehyde in Mannich reaction modified acrylic polymer retanning agent.Both of acrylic acid unit and acrylamide unit in P could be used as the acid component of Mannich reaction,but the reaction activities were different.Therefore,the activity of Mannich reaction in the presence of acrylic acid unit and acrylamide unit was discussed.The acrylamide homopolymer?PAM?and acrylic acid homopolymer?PAA?were synthesized by free radical initiation and solution polymerization.The amination degree was used as the index,and the reaction conditions of Mannich modified PAM and PAA with GA and MG were optimized by the single factor experiments.Mannich reaction of the PAM and PAA mixture?PAM/PAA?was carried out under superior conditions.The amination degree of GA-PAM/PAA prepared at pH 4 and 7 was higher than the amination degree weighted average of GA-PAM and GA-PAA under the corresponding conditions at 80°C,indicating that the Mannich reaction between PAM and PAA in the mixed system had a reciprocal promotion.Comparing with the weighted average of amination degree of MG-PAM and MG-PAA,the amination degree of MG-PAM/PAA was higher at 40°C,and lower at 60°C.This indicated that the Mannich reaction between PAM and PAA in the mixed system was promoted each other at 40°C and inhibited eath other at 60°C.