Preparation And Application Of Modified Polyurethane Retanning Agent With Function Of Reducing Formaldehyde

The content of free formaldehyde in leather is an important index to check whether the finished leather is qualified or not.With the improvement of people's quality of life,the standard of free formaldehyde content in leather products has become more and more stringent.Therefore,how to reduce the content of free formaldehyde in leather has become a hotspot of domestic and foreign researchers in recent years.It has been found that amino group in collagen have good reactivity with formaldehyde,so collagen has the function of reducing formaldehyde.Chromotropicacid,alsoknownaschromogenic(1,8-dihydroxy naphthalene-3,6-disulfonic acid),is a substance commonly used for quantitative determination of formaldehyde,so it can also be used for reducing formaldehyde.In addition,polyurethane retanning agent is a common leather retanning agent.Based on this,two new polyurethane retanning agents with function of reducing formaldehyde were prepared by modifying polyurethane with collagen extracted from leather waste and chromotropic acid,and their structure and retanning properties were studied.In order to reduce the content of free formaldehyde in leather at the same time of retanning process,it not only realizes the recycling and reuse of waste collagen,change"waste"into"treasure",but also simplify the tanning process and realize the integration of retanning and formaldehyde removal.The specific studies as follows.Firstly,isophorone diisocyanate(IPDI)and polypropylene glycol 400(PPG400)were used as raw materials,dibutyltin dilaurate(DBTDL)was used as catalyst,N-methyl diethanolamine(MDEA)and chromotropic acid(CA)were used as cationic chain extender and anionic chain extender,respectively,and the amphoteric polyurethane emulsion were synthesized.Through single factor experiments of R value and MDEA dosage,the optimum synthetic conditions were obtained:R value was 2.5.A series of amphoteric polyurethane emulsions were synthesized by controlling the amount of CA and they were numbered AWPU(1),AWPU(2),respectively.Their structure,particle size,potential and conductivity were measured by ultraviolet-visible-near infrared spectrophotometer(UV-VIS-NIR),Fourier transform infrared spectroscopy(FT-IR),nano-particle surface potential analyzer and conductivity meter.The results showed that CA has been embedded in the main chain of polyurethane and the product has the expected structure.AWPU(3)(also known as CAGAPU),namely IPDI:PPG:CA=5:2:1,has the smallest emulsion particle size and the best stability.The reaction between CAGAPU with formaldehyde standard solution confirmed that CAGAPU has potential application value in reducing formaldehyde.The structure,crystallization and thermal stability of the amphoteric polyurethane(PU)and CA grafted amphoteric polyurethane(CAGAPU)were determined by FT-IR,nuclear magnetic resonance hydrogen spectroscopy(~1H-NMR),X-ray diffraction analyzer(XRD)and thermogravimetric analyzer(TG).The results showed that the expected product structure was obtained,the crystallinity and thermal stability of CAGAPU were improved.Then,CAGAPU was used in the retanning process of aldehyde tanned leather.By comparing the shrinkage temperature,mechanical strength,sensory properties,SEM morphology,formaldehyde content of acid leather,aldehyde tanned leather,PU retanned leather,CAGAPU retanned leather and market retanned leather,it was concluded that:the optimum dosage of CAGAPU is 10%of leather weight;CAGAPU retanning system can not only effectively improve the shrinkage temperature and sensory properties of leather,but also reduce the formaldehyde content of aldehyde tanned leather from 294.38 ug/kg to56.08ug/kg,and the removal rate of free formaldehyde had reached 80.95%.Compared with market retanning system,BOD,TDS and TSS of CAGAPU retanning system decreased by 31.82%,9.90%and 30.80%.Finally,a new polyurethane emulsion(MPU)was obtained by using IPDI and PPG 400 as raw materials and using waste collagen and CA to modify polyurethane simultaneously.Through single factor experiments of R value and CA dosage,the optimum synthetic conditions were obtained:R value was 3 and CA dosage was 0.02mol.A series of polyurethane emulsions were synthesized by controlling the amount of collagen.They were numbered MPU(1),MPU(2),MPU(3),MPU(4)and MPU(5),respectively.The structure,particle size,potential and conductivity of the nanoparticles were measured by FT-IR,surface potential analyzer and conductivity analyzer.The results showed that CA and collagen have been embedded in the main chain of polyurethane,and the product has the expected structure.The reaction between MPU with formaldehyde standard solution confirmed that MPU has potential application value in reducing formaldehyde.The structure,crystallization and thermal stability of the collagen and modified polyurethane(MPU)were determined by FT-IR,~1H-NMR,XRD and TG.The results showed that the expected product structure was obtained,the crystallinity of MPU was reduced,and the thermal stability was improved.MPU was used in the retanning process of F90 tanned sheepskin.By comparing the shrinkage temperature,mechanical strength,sensory properties and formaldehyde content of leather treated with different dosages of MPU,blank group,tannin extract retanning agent,modified glutaraldehyde retanning agent and chrome retanning agent,it was concluded that:MPU retanning system can not only effectively improve the shrinkage temperature and sensory properties of leather,but also reduce the formaldehyde content of aldehyde tanned leather from 295.96ug/kg to 65.24 ug/kg,and the removal rate of free formaldehyde had reached 77.96%.Through the kinetics experiment of the reaction between MPU with formaldehyde,it was proved that the reaction between MPU and formaldehyde belongs to the first-order kinetics reaction.The research of this paper is expected to provide new ideas for cleaner production and free formaldehyde problem in leather industry.