Synthesis And Properties Of Amphoteric Polymers/Layered Double Hydroxide Nanocomposites

For the chromium pollution in the tanning process,a class of montmorillonite/amphotericpolymernanocompositeadditives?MMT/P?DM-AA??was developed in our group,which could achieve less chrome tanning process.In order to enhance the absorption of anionic chemicals such as dyes and fatliquors in wet finishing process,an anionic layered double hydroxides?LDH?was introduced into the leather tanning used amphoteric polymer for the first time.In contrast to MMT,LDH is a class of layered compounds composed of negatively charged anions and positively charged metal hydroxide laminates.The anion in the amphoteric polymer matrix can be ion exchanged with the anion between the LDH layers to obtain a nanocomposite.The positive charged LDH laminates and the cationic groups in the amphoteric polymer enhance the overall positive charge of the nanocomposite.Thus,the crust leather tanned by the nanocomposite has a good absorption property to anionic material in wet finishing process,which can make the crust leather deepen colored and soft.Firstly,an amphoteric polymer poly diallyldimethyl ammonium chloride-acrylic acid-sodium allyl sulfonate?P?DM-AA-SAS??was designed and synthesized.P?DM-AA-SAS?was used in low-salt pickling and less chrome tanning process,its application properties was investigated.Polymer/LDH nanocomposite P?DM-AA-SAS?/LDH with different structures were prepared by physical blending method?P?DM-AA-SAS?/LDH-B?,exfoliation/adsorption method?P?DM-AA-SAS?/LDH-E?and in-situ method?P?DM-AA-SAS?/LDH-I?.The structures of P?DM-AA-SAS?/LDH were characterized by X-ray diffraction?XRD?,transmission electron microscope?TEM?,fourier-transform infrared microspectroscopy?FT-IR?,etc.P?DM-AA-SAS?/LDH with different LDH dosage were used in leather making process,and the application properties were evaluated.Then,P?DM-AA-SAS?/LDH with different structures were applied in the leather tanning processes to evaluate the structure-activity relationship of P?DM-AA-SAS?/LDH structures and there leather application properties.At last,the mechanism of the interaction between P?DM-AA-SAS?/LDH and collagen was discussed.The results are listed below:?1?An amphoteric polymer was prepared by free radical polymerization.The optimal P?DM-AA-SAS?synthesis process was as follows:the SAS was added dropwise into the reaction mixture,the dosage of initiator?ammonium persulfate?was 8%,and the molar fraction of SAS was 0.143.The isoelectric point of P?DM-AA-SAS?could be reduced from 5.6 to 4.1 compared with P?DM-AA?,and the acid resistance of P?DM-AA-SAS?is significantly enhanced.The characterization of FT-IR,XRD and gel permeation chromatography?GPC?confirmed P?DM-AA-SAS?was prepared successfully.The number average molecular weight of P?DM-AA-SAS?was 348 and 28035,which played a good selective filling effect to the crust leather.TEM results showed that P?DM-AA-SAS?forms a random assembly of 40 nm-100 nm in aqueous solution.The application results showed that the Cr₂O₃ content can be reduced by 53.5%,Cl^-content can be reduced by 78.3%,and total dissolved solids,chemical oxygen demand,biological oxygen demand,total organic carbon in wastewater could be reduced significantly by using P?DM-AA-SAS?with chrome than that of control chrome tanning.The content of Cr₂O₃ in the wet-blue was significantly improved,the chromium in leather was evenly dispersed from the flesh side to the grain side,and the leather collagen fibers were also well dispersed.-SO₃H and-COOH on P?DM-AA-SAS?could inhibit the acid swelling of the naked hides,and the effect of-SO₃H was better than that of-COOH.?2?P?DM-AA-SAS?/LDH-B was prepared by physical blending method,and the optimal synthesis process was as follows:blending time was 2 h,ultrasonic time was 30 min,and the pH of the system was 5.0.The XRD,TEM and FT-IR characterization results showed that P?DM-AA-SAS?/LDH-B showed partial intercalated and partial exfoliated structure.The application results showed that,compared with crust leather tanned by P?DM-AA-SAS?,the absorption properties of negatively charged retanning agent,dye and fatliquor in the wet finishing process for crust leather tanned by P?DM-AA-SAS?/LDH-B were improved.Thus,the dyeing performance of treated by P?DM-AA-SAS?/LDH-B was increased by 15.6%compared with P?DM-AA-SAS?,the softness was increased by 30.2%,thickening rate was increased by 18.3%.?3?P?DM-AA-SAS?/LDH-E was prepared by exfoliation/adsorption method.LDH was exfoliated by the following process:the concentration of P?DM-AA-SAS?aqueous solution was 7.5%,and the ultrasonic time was 30×4min.P?DM-AA-SAS?/LDH-E was obtained by the assembling of exfoliated LDH with P?DM-AA-SAS?.XRD,TEM and scanning electron microscope?SEM?characterization results showed that,LDH was successfully exfoliated by P?DM-AA-SAS?,and the exfoliating process did not affect the LDH layer size.The application results showed that,with the increase of LDH dosage in P?DM-AA-SAS?/LDH-E,the performance of crust leather is gradually increasing.When the LDH dosage amount in P?DM-AA-SAS?/LDH-E was 3%,the application performances of the nanocomposite were gradually increased.The dyeing performance was increased by 18.3%,softness was increased by28.4%,the thickening rate was increased by 19.2%compared with P?DM-AA-SAS?.?4?P?DM-AA-SAS?/LDH-I was prepared by in-situ polymerization.The optimal synthesis process was as follows:the reaction temperature was 80°C,the initiator dosage was 12%,the reaction time was 6 h,and the system pH was5.0.The XRD and TEM characterization results showed that,P?DM-AA-SAS?/LDH-I was an intercalated structured nanocomposite prepared by this method.The application results show that,as the LDH dosage amount in P?DM-AA-SAS?/LDH-E was 3%,the application performance of the nanocomposite was the best.The dyeing performance was increased by 21.5%,softness was increased by 28.6%,thickening rate was increased by 20.2%compared with P?DM-AA-SAS?.?5?P?DM-AA-SAS?,P?DM-AA-SAS?/LDH-E?exfoliated structure?,P?DM-AA?-SAS/LDH-B?partial exfoliated and partial intercalated structure?,PDM-AA-SAS/LDH-I?intercalated structure?was applied in the leather processes.The results showed that thickening rate,dyeing performance,softness and physical and mechanical properties of crust leather treated by P?DM-AA-SAS?/LDH were better than those of P?DM-AA-SAS?treated.Moreover,P?DM-AA-SAS?/LDH with exfoliated structure showed the best intensification ability to most of the leather performances,and the sequence of intensification ability of P?DM-AA-SAS?/LDH was:P?DM-AA-SAS?/LDH-E>P?DM-AA-SAS?/LDH-B>P?DM-AA-SAS?/LDH-I.Dynamic light scattering?DLS?of different structural P?DM-AA-SAS?/LDH nanocomposites and inductively coupled plasma spectroscopy?ICP?and elemental energy spectroscopy?EDS?of Mg in crust leather indicate that,the exfoliated LDH nanosheets in P?DM-AA-SAS?/LDH-E were assembled with amphoteric polymers to form aggregates with smaller particle sizes?220 nm?,while P?DM-AA-SAS?/LDH-I with intercalated structure had the largest assembly size?4100 nm?,and the size of P?DM-AA-SAS?/LDH-B was 531 nm.So,the smaller the particle size of P?DM-AA-SAS?/LDH-E was easy to penetrate into the leather fibers,thus the crust leather performance could be improved the more by P?DM-AA-SAS?/LDH-E due to the highest nanocomposite amount among the leather fibers.?6?Collagen model,collagen and leather collagen fibers?leather sample?were interacted with P?DM-AA-SAS?,LDH and P?DM-AA-SAS?/LDH,respectively.The effects of P?DM-AA-SAS?/LDH on the multi-level structure of collagen fibers and interaction type with collagen was investigate.FT-IR,XRD,X-ray photoelectron spectroscopy?XPS?results showed that,the carboxyl group and sulfonic acid group on P?DM-AA-SAS?could form hydrogen and electrovalent bond with amino and amide groups on the collagen,and also could form hydrogen bond with hydroxyl group on the collagen.The hydroxyl group on LDH mainly combined with collagen by hydrogen bonding.P?DM-AA-SAS?/LDH were combined with collagen by electrovalent and hydrogen bonding with reactive groups on collagen.Atomic force microscopy?AFM?,SEM,EDS results showed that,P?DM-AA-SAS?,LDH and P?DM-AA-SAS?/LDH interacted with collagen without destroying the triple helix structure of collagen,and all of them were adhered to collagen fibers and fibrils,played a good dispersion and filling effect to the collagen fibers.Thermogravimetric analysis?TGA?and differential scanning calorimetry?DSC?results show that,the stereostructure of P?DM-AA-SAS?/LDH facilitated the formation of multi-point cross-linking between the collagen fibers,thereby improving the thermal stability of the collagen fibers.