Synthesis Of Amphoteric Vinyl Polymer/Inorganic Nanocomposite Tanning Agent And Its Modification Of Collagen Fiber

Chrome tanning is one of the most mature methods of the leather industry,which brings good performance to resultant leather. However, the low absorptionrate of chrome tanning agent leads to a large number of chromium-containingwaste discharge to soil, water and caused serious pollution. The aim of this studyis to invent green leather chemicals and reduce the pollution of traditionaltanning industry by nano-technology. Amphoteric vinyl polymer/inorganicnanocomposite tanning agents were prepared to modify collagen in order toincrease the absorption of chrome tanning agent and reduce the pollution ofchrome tanning in leather industry, meanwhile, increase collagen stability andimpart excellent performance.In this study, diallyl dimethyl ammonium chloride was chosen as cationicmonomer, amphoteric vinyl polymer poly （diallyl dimethyl ammonium chloride-acrylic acid） and poly （diallyl dimethyl ammonium chloride-acrylic acid-acrylamide-hydroxyethyl acrylate） were prepared by single factor experiment.The morphology of PDMDAAC-AA and PDMDAAC-AA-HEA-AM underdifferent pH conditions was studied by transmission electron microscopy （TEM）.The results showed that two kinds of amphoteric vinyl polymer were allpH-sensitive，with pH increases morphology of them was spherical, rod and longconifer-like. Different types of inorganic nano materials （montmorillonite, nanoZnO, nano Al₂O₃and nano TiO₂） were introduced to prepared amphotericvinyl-based nanocomposite tanning agent by uniform experiment. With tanningresults as indexes, the effects of types of inorganic nano-materials on applicationperformance were investigated. Finally, nano-ZnO and MMT were chosen toprepare nanocomposite tanning agent.Amphoteric vinyl polymer/ZnO nanocomposite tanning agents （PDM/ZnO） were prepared by blending, in situ polymerization and in situ sol-gel method andcharacterized by Fourier transform infrared spectroscopy （FT-IR）, X-raydiffraction （XRD） etc. Compared with amphoteric vinyl polymer tanned leather,nanocomposite prepared by blending method had little effect on shrinkingtemperature and thickness increment ratio of resultant leather was53.0%;shrinkage temperature of leather tanned nanocomposite prepared by in-situmethod with3%BCS was92.9℃, thickness increment ratio was as high as174.47%and chromium load in wastewater was14mg/L; shrinkage temperatureof leather tanned nanocomposite prepared by in-situ sol-gel method with3%BCS was94.5℃, thickness increment ratio was63.7%, chromium load inwastewater was21mg/L and physical and mechanical properties of resultantleather was almost the same as traditional chrome tanning process. Mechanisticschematic model of the PDM/ZnO and collagen was proposed.PDMDAAC-AA-AM-HEA/ZnO pre-modified collagen fiber and introducedmore functional group as-OH and-COOH, meanwhile nano ZnO was depositedon the collagen fibers. Then chrome tanning agent was added, multi-pointcrosslinking among collagen fibers and nano composite, increased the stabilityof the collagen. Compared with the traditional chrome tanned leather, dispersionof collagen fiber was obvious. Furthermore, the resultant leather had good UVresistance and anti-bacterial properties.Deepening dyeing amphoteric vinyl polymer/ZnO nano-composite tanningreagent （PDMDAAC-MAA-AA-HEA/ZnO） was prepared by in situ sol-gelmethod. The effect of functional monomer acrylamide （AM）, ethyl acrylate（EA）, butyl acrylate （BA）, hydroxyethyl acrylate （HEA）, methyl acrylate,dodecyl acrylate （LA） and tetradecyl methacrylate （TA） on retanning propertiesand hyperchromic effect was studied. The results showed that the introduction ofamide groups have little effect on the performance of the crust, and withincreasing of ester chain length thickness increment ratio of resultant leather wasincreased. When introducing of5%acrylate （HEA）, thickness increment ratioreached22.22%, physical and mechanical properties increased s lightly and K/Svalue improved50.8%. PDMDAAC-MAA-AA-HEA/ZnO was characterized byFT-IR and the XRD and the results showed that vinyl polymer/ZnO compositematerial was prepared successfully. Compared with PDMDAAC-MAA-AA -HEA retanned leather amphoteric vinyl polymer/ZnO nano composite retanningagent gave good ultraviolet resistance property to resultant leather, enabled thefibers uniformly dispersed. In addition, elongation at break increased by20.4%,tear strength increased by21.1%, while the dyeing effect was significantlyimproved, the K/S value increased by98.3%.Amphoteric vinyl polymer/montmorillonite nano composite （PCM） hadbeen developed. The effects of the amount of initiator and the amount ofmontmorillonite on tanning properties were studied. The results indicated thatwhen the initiator dosage was6%and amount of montmorillonite was5%, PCMhad the best performance. Molecular weight and structure of PCM werecharacterized by GPC and TEM respectively. The results indicated that themolecular weight of PCM was about3000, montmorillonite was homogeneouslydispersed in the polymer matrix with both exfoliation and intercalation structures.The cleaner approach to chrome-less tanning of goatskin, cattle skin and hidesplit suede leather by both pickling and pickling-free processing has beendeveloped. The results showed that compared with traditional chrome tanningleather shrinkage temperature of leather was lower, but reached industrystandards, fullness of resultant leather was improved significantly and physicaland mechanical properties were not decreased. PCM might form morecomplexion with collagen fiber helix chain, leading to more structural distortionof collagen molecules. Beside the discharges of chrome tanning process, thewhole continuous wet processes after tanning were reduced.Morphological characteristics and structure of collagen fiber weredetermined by SEM and XRD. The result showed that leather tanned by PCMwith BCS had clearer grain, and could effectively maintain the shape of the pores.PCM might form more complexation with collagen fiber helix chain, leading tomore structural distortion of collagen molecules, however did not disruption ofits triple helical structure. Trypsin degradation curves determine the cleanerapproach might increase the degradation of leather. EDS liner scanning showsthe dispersion of chromium in leather cross section. The results revealed thatchromium in chrome tanned leather is higher on surface but lower inside leatherwhile for cleaner tanning process chromium distribution was more even in allparts of leather. Schematic of PCM and BCS in the collagen fibers was illustrated. Firstly, PCM reacted with collagen fibers, at the same time flake-likemontmorillonite deposited both in intra-triple and inter-triple helix. MeanwhilePCM introduced more carboxyl groups into microfibrils. Then Cr clustersdeposited among collagen fibrils, while smaller Cr complexes diffuse intomicrofibrils. A large number of carboxyl resulted in more intermolecular andintramolecular cross-linking. Therefore, the excellent properties of resultantleather can also be achieved, even with small amount of chromium powder.This study provides a theoretical reference for the synthesis and applicationof nano-composite tanning agent. It plays an important role in taking full uses ofresources, reducing the pollution of heavy metal chromium pollution andimproving the quality of leather products.