Synthesis And Application Performance Of Less-Salt Pickling Chrome Tanning Auxiliary

The traditional chrome tanning can produce large amounts of chrome tanning wastewater which contains with high concentration of salt,not only pollute the environment,but also cause chromium waste of resources,and increase the difficulty and the cost of wastewater treatment,which is not conducive to the sustainable development of tanning industry.Based on the charge repulsion expansion theory of acidic collagen,in order to realize the chrome tanning process less salt pickling chrome tannage,a series of functional chrome tanning agents rich in much sulfonic acid were synthesized,and applied in chrome tanning process,which could effectively reduce the neutral salt and Cr?III?in the wastewater.Acrylic acid?AA?and Styrene sulfonate?SSS?were treated as raw material,low molecular weight AA-SSS copolymer?AS oligomer?has been synthesized,in the reaction system of the?NH₄?₂S₂O₈-NaHSO₃.Orthogonal experiment is used to determine AS polymer synthesis condition of the best inhibiting acidity skin swelling,the result showed that: n?AA?: n?SSS?= 1.5:1,the dosage of?NH₄?₂S₂O₈ and NaHSO₃ are total mass respectively 5% and 3% of the monomer.Polymerization reaction has been proved by FT-IR,gel permeation chromatography spectrum showed that the polymer of Mn was 2069,and distribution coefficient is 1.05;With 3%?based on the weight of limed skin,similarly hereinafter?best AS oligomer for assisting pickling,swelling degree of acidic pelt was 11.51%,with 3.2% salt could completely inhibit acid skin swelling,and achieve the goal of less salt pickling.A significant change of the Cl-content in waste liquid was to reduce from 345.06mmol/L to 145.26 mmol/L.Compared with traditional pickling chrome tanning wet-blue leather,SEM showed that: less salt pickling chrome tanning wet-blue fiber had cleaner grain,clear pores.DSC showed that the thermal decomposition areas of less salt pickling tanning is smaller.XRD analysis showed that the XRD crystallinity of acidic skin,traditional wet-blue leather,less salt pickling wet-blue leather were 68.21%,13.49% and 3.23% respectively.AS less salt pickling tanning process have more influence on the crystalline of internal structure of acid skin.5-sulfosalicylic acid,methyl benzene sulfonic acid,taurine,dodecyl sulfonic acid,amino sulfonic acid,2-amino-1,4-benzene disulfonic acid were used in assisting pickling.3% AS oligomer and 2.1% the 2-amino-1,4-benzene disulfonic acid were used in assisting pickling together,it could achieve salt-free pickling.This less-salt approach can cut down the content of Cr₂O₃ in wastewater from 3.945g/L to 3.522g/L,and had nothing Cl-;the physical mechanical properties of leather was a bit poor.DSC curves showed the integral area and peak width of conventional wet-blue are greater than less salt pickling chrome tanning leather,better thermal stability,and poorer uniformity of the inner structure.A kind of Schiff bases?GA?which contained sulfonic group and carboxyl was synthsized by the reaction between 2-amino-1,4-benzene disulfonic acid and glyoxylic acid,that reaction was proved by FTIR and 1HNMR.If 2% GA compound with 1% salt were used in pickling process,acidic pelt swelling could be achieved restraining.4.5% chrome powder was used in tanning,shrink temperature of wet-blue leather could reach 105.5 ?.Compared with the conventional process,less salt pickling and less chrome tanning system could significantly reduce Cr₂O₃ from 3.305g/L to 1.546g/L and reduce Cl-from 374.2mmol/L to 59.6mmol/L in waste liquid.SEM images showed that the longitudinal section fiber dispersion degree was similar,grain more neat,more smooth and finer.EDS showed that chromium element distribution in longitudinal section was uniform,physical and mechanical performance is better.Phenol,concentrated sulfuric acid,formaldehyde,urea,bisphenol S are treated as raw materials,a kind of synthetic tanning agent containing sulfonic acid and phenol hydroxyl has been synthesized.The relative molecular weight determined by GPC was 1961,distribution coefficient was 1.01.When 3.0% AS oligomer,2.0% synthetic tanning agent,1.6% salt common were used in pickling,swelling could be suppressed.By application testing,less salt pickling Cr₂O₃ content in chrome tanning waste liquid was dropped from 3.945 g/L to 2.654 g/L,Cl-was reduced from 345.06 mmol/L to tendency for 50.43 mmol/L.The DSC curve showed: conventional pickling chrome tanning wet-blue integral area was greater than the less salt process,higher thermal stability of the conventional acid chrome tanned.XRD analysis showed that the traditional pickling chrome leather and less salt pickling leather crystallinity were 13.49%,5.64% respectively.Less salt pickling tanning crystallinity is lower,which had more affects on the internal structure of acid skin.