Structure Regulation Of Vinyl Polymer-LDHs Supramolecular Intercalated Materials For Modifying Collagen Fibers

Chrome tanning plays a leading role in the global leather industry because of the excellent comprehensive properties for the resulting leather.However,a large amount of waste containing chromium produced by the traditional chrome tanning process has caused a pressure on the environment.In addition,the limit of Cr(VI)content in chrome-tanned leather products is becoming more stringent,and there is a growing market demand for chrome-free leather products.Therefore,the development of eco-friendly chrome-free tanning agents and tanning methods has become an effective way to solve the problem of environmental pollution of traditional chrome tanning from the source and meet the market demand of consumers for ecological leather products.Layered double hydroxides(LDHs)are a kind of typical two-dimensional lamellar nanosheets consisting of positively charged metallic layers and an interlayer region containing anions and solvated molecules.It can give the polymer matrix with excellent mechanical properties,thermal stability and adsorption properties due to its non-toxic,highly tunable structure and composition.Notably,LDHs can form organic/inorganic nanohybrid materials with collagen molecules via hydrogen bonding and electrostatic interactions,providing a potential application of LDHs as tanning agent in leather tanning process.In this dissertation,based on the structural adjustability of LDHs,the metal element Zr was introduced into the LDHs lamellar structure,and the MgAlZr-LDHs with suitable size and good reactivity was obtained.Then,the vinyl polymer-LDHs supramolecular intercalated materials with good dispersibility and reactivity were constructed by ion exchange method.The vinyl polymer-LDHs supramolecular intercalated materials were used in tanning processing,the structure-activity relationship between the structure and tanning properties of vinyl polymer-LDHs supramolecular intercalated materials were established.Further,the supramolecules combined 3%Zr(SO4)2 was used for tanning,the combination tanning method of vinyl supramolecular intercalated materials-zirconium sulfate was optimized.Finally,the interactions among the vinyl polymer-LDHs supramolecular intercalated materials,zirconium sulfate and collagen and its effects on the hierarchical structures of collagen fibers were revealed.These results can provide theoretical guidance and important reference for application of vinyl polymer-LDHs supramolecular intercalated materials in leather tanning process.The main contents are as follows:(1)Preparation of MgAlZr-LDHs for modifying collagen fibers.The MgAlZr-LDHs was prepared by coprecipitation method.The X-ray diffraction(XRD)and scanning electron microscopy(SEM)results showed that the lamellar MgAlZr-LDHs with an average diameter of 42 nm and a high crystallinity and regular crystal shape,when the precipitation pH value was 12 and the molar ratio of Mg/Al/Zr was 2.0/0.7/0.3.TEM,Zeta potential and X-ray photoelectron spectroscopy(XPS)indicated that by decreasing pH value of MgAlZr-LDHs suspension,resulting in partial dissolution of MgAlZr-LDHs and formation of the surface defects.With the pH value increasing again,the metal ion leached from MgAlZr-LDHs was nucleated again,and its size gradually increased.The MgAlZr-LDHs was used to the tanning process of pickled goat skin,and the optimum tanning conditions of MgAlZr-LDHs were obtained,conferring the leather with a highest Ts of 68.4℃ when the dosage of MgAlZr-LDHs was 5%,initial pH value was 3.0 and final pH value was 5.0.The energy dispersive X-ray spectroscopy(EDS)results demonstrated an uneven distribution of MgAlZr-LDHs from flesh layer to grain layer in the leather.Moreover,the influences of metal molar ratio on the physical properties of leather were investigated.The results showed the leather with a highest Ts,enzymatic resistance,and physical,mechanical properties and lowest swelling ratio when the molar ratio of Mg/Al/Zr was 2.0/0.7/0.3.With the increase of Zr content in MgAlZr-LDHs,the dyeing property and softness of the leather also increased.(2)Preparation of vinyl polymer-LDHs supramolecular intercalated materials for modifying collagen fibers.In order to improve the dispersibility of MgAlZr-LDHs in leather and the reactivity with collagen,the P(MAA-IA)-LDHs and GEP(MAA-IA)-LDHs supramolecular intercalated materials were obtained using anionic vinyl polymer P(MAA-IA)and amphoteric vinyl polymer GEP(MAA-IA)to intercalate MgAlZr-LDHs via ion exchange method.XRD,fourier transform infrared(FT-IR)and transmission electron microscope(TEM)showed that with increase of the amount of P(MAA-IA)and GEP(MAA-IA),P(MAA-IA)-LDHs and GEP(MAA-IA)-LDHs exhibited gradually obvious intercalation structure.When the mass ratio of P(MAA-IA)and GEP(MAA-IA)to LDHs was 2.5:1,the layer spacing of P(MAA-IA)-LDHs and GEP(MAA-IA)-LDHs increased from 0.783 nm to 1.252 nm and 1.170 nm,respectively,the average diameter of P(MAA-IA)-LDHs and GEP(MAA-IA)-LDHs was 40 nm and 45 nm,respectively.The results of TEM,Zeta potential and XPS indicated that by decreasing pH value of the P(MAA-IA)-LDHs and GEP(MAA-IA)-LDHs suspension,resulting in the partially dissolution of the supramolecular intercalated materials and formation of the surface defects.P(MAA-IA)-LDHs and GEP(MAA-IA)-LDHs were used to the tanning process of pickled goat skin,respectively.The optimum tanning conditions of P(MAA-IA)-LDHs and GEP(MAA-IA)-LDHs were obtained,conferring the P(MAA-IA)-LDHs and GEP(MAA-IA)-LDHs tanned leather with a highest Ts of 70.6℃ and 72.3℃,respectively,when the dosage of tanning agents was 5%,the initial pH value was 3.0 and the final pH value was 5.0.The EDS results demonstrated a uniform distribution of P(MAA-IA)-LDHs and GEP(MAA-IA)-LDHs in leather.Moreover,the influences of LDHs,P(MAA-IA)-LDHs,and GEP(MAA-IA)-LDHs on the physical properties of leather were investigated.Compared to LDHs,the Ts,enzymatic resistance,and physical and mechanical properties of P(MAA-IA)-LDHs and GEP(MAA-IA)-LDHs tanned leather improved,the swelling ratio decreased,the dyeing property and softness of P(MAA-IA)-LDHs tanned leather-decreased and the dyeing property and softness of GEP(MAA-IA)-LDHs tanned leather were similar to that of LDHs.(3)A chrome-free combined tanning method based on supramolecular intercalated materials-Zr(SO4)2 had been developed.The tanning process was mostly optimized as adding the supramolecular intercalated materials firstly and followed by Zr(SO4)2,3%supramolecular intercalated materials,initial pH value of 2.0 and final pH value of 4.0,conferring leather with a highest Ts of 83.7℃.EDS results demonstrated that the incorporation of the supramolecular intercalated materials make Zr(SO4)2 more evenly distributed in the resulting leather compared to Zr(SO4)2 tanned leather.Inductively coupled plasma-atomic emission spectrometry(ICP-AES)showed that the absorption rate of Zr(SO4)2 increased from 76.2%to 91.5%with the introduction of GEP(MAA-IA)-LDHs.Compared with 3%Zr(SO4)2 tanned leather,the Ts,enzymatic resistance,dyeing property,softness,physical and mechanical properties,and porosity of the leather tanned by supramolecular intercalated materials-Zr(SO4)2 all improved,and the swelling ratio decreased.In addition,the BOD/COD values of the wastewater increased with the introduction of positively charged supramolecular intercalated materials,resulting in the wastewater with a good biodegradability.(4)Interaction mechanism of vinyl polymer-LDHS supramolecular intercalation material and Zr(SO4)2 with collagen.Collagen solution,skin powder and pelt were interacted with vinyl polymer-LDHs supramolecular intercalated materials and Zr(SO4)2,respectively.The interaction of the vinyl polymer-LDHs supramolecular intercalated materials,Zr(SO4)2 with collagen and their effects on the hierarchical structure of collagen fibers were investigated.XRD and SEM results indicated that the supramolecular intercalated materials and Zr(SO4)2 can permeate and bind onto the collagen fibers and collagen fibrils,without destroying the natural D-periodic banding of the collagen fibrils.The results of FT-IR,XPS,and Zeta potential showed that the triple-helical structure of collagen molecules was not destroyed by the introduction of the supramolecular intercalated materials and Zr(SO4)2.Moreover,the Al3+and Zr4+exposed in the supramolecular intercalated materials laminates can bind with the carboxyl and amino groups in the collagen molecules via coordination bonds,the hydroxyl group in the supramolecular intercalated materials laminates can form hydrogen bonds with the collagen molecules.The positively charged supramolecular intercalated materials can form ionic bonds with the negatively charged carboxyl groups in the collagen molecules.Zr(SO4)2 were mainly bound with the carboxyl group in the collagen molecules through coordination bonds.