Preparation Of Graphene Oxide Nano Tanning Agent And Study On Its Tanning Properties

Chrome tanning agent has the advantages of simple tanning process and good properties of tanned leather.Therefore,chrome tanning agent is still the most widely used as leather tanning agent at present.However,the absence of chromium resources in China,the low absorption of chrome tanning agent during tanning,difficulty treatment of chromium-containing wastewater and harmful to the environment of the chromium-containing wastewater and waste residue,developing of chrome-free tanning or less chrome tanning and green tanning agents have become the hot sports of research in recent years.Nowadays nano-tanning agent has been placed on the high hopes by researchers,people have researched the tanning properties of some nanomaterials,such as montmorillonite,SiO₂,TiO₂,ZnO and carbon nanotubes.People hope can find a nano green tanning agent and use it to replace chrome tanning agent.The research results show that the tanning effects of these nanomaterials were poor,they could not be used as tanning agents for leather tanning alone at present.The main reason is that the nanomaterials are lack of chemical groups in its structure,which can interact with collagen fibers.Through analysis,we believe that the nanomaterials used as leather tanning agent not only should produce nano tanning effect because of nano effect,but also should form chemical bonding tanning effect through chemically reacting between reactive chemical groups in structure and collage fibers.The synergistic effect of nano tanning effect and chemical bonding combination could generate excellent tannage effect,which was also our idea to develop new nano-tanning agent.The emergence of graphene oxide?GO?brings hope for the development of new nano-tanning agent.GO nano-layer and its chemical groups can produce nano tanning effect and chemical bonding tanning effect with leather collagen fibers.Therefore,GO has the advantage of structure as nano-tanning agent.In this paper,the tanning properties of GO with different structure and size were studied,on the basis of which GO-Cr???coordination complex and Poly?methacrylic acid-sodium allyl sulfonate?covalent grafting modified GO(GO-g-P?MMA-SAS?were prepared.The tanning properties of GO were further improved,and the corresponding tanning mechanism was put forward.The details were as follows:?1?The relationship between the structure and tanning properties of GO was studied,the tanning process of GO was explored,the tanning mechanism of GO was analysed.GO with different oxidation degree and size was prepared by Hummers method and ultrasonic dispersion,and used in leather tanning process.The effects of oxidation degree and dosage of GO on tanning properties were studied systematically.The results showed that GO with high oxidation degree and small size had the best tanning effect.When the dosage of GO was 0.4%based on the acid skin mass and the time of ultrasonic dispersion was 60 min,the T_s of tanned leather was 73.9?.The chemical bonding effect produced by carboxyl group,hydroxyl group of GO in structure and active groups on collagen fibers such as ammonia group,hydroxyl group,as the same time the nano-effect produced by collagen fibers and GO with nanometer size made GO have tanning effect.?2?The tanning properties of combination tanning with GO and chrome tanning agent,GO-Cr???coordination complex was studied.In the experiment of combination tanning with GO and chrome tanning agent,the adding order of tanning agent had an effect on the tanning effect.The tanning properties of GO and chromium tanning agent added at the same time was the best.The tanning properties of combination tanning could be further improved by increasing the dosage of GO and prolonging the ultrasonic time properly.GO dispersion solution with 32.7%oxygen content was obtained by ultrasounding graphite oxide for 60 minutes.Combination tanning with 3%chrome tanning agent and0.4%GO dispersion liquid,the T_s of tanned leather reached at 93?,tensile strength was 20.3 N/mm²,tearing strength was 37 N/mm,thickening rate was33.7%and permeability was 2550 mL/cm²·h,the chromium content in waste liquid reduced from 1162 mg/L to 792 mg/L.All indexes were better than the tanned leather with chromium tanning agent or GO alone.In addition,GO-Cr???coordination complex was prepared for tanning.Equivalent to 2.5%chromium tanning agent and 0.4%GO dispersion liquid,the T_s of tanned leather was95.5?,tensile strength was 22.6 N/mm²,tearing strength was 39 N/mm,thickening rate was 35.7%and permeability was 2590 mL/cm²·h,the chromium content in waste liquid reduced from 748 mg/L to 428 mg/L.The result of tanning experiments indicated that the tannig properties of GO-Cr???complex was better than combination tanning with GO and chrome tanning agent.Cr³⁺produced coordination reaction with carboxyl and hydroxyl group of GO.The thickness and diameter of GO in GO-Cr???coordination complex were smaller than GO dispersion solution,which made GO better infiltrate into the interior of leather collagen fiber.GO had strong tanning effect because of the nano-effect,chemical bonding effect of GO and synergistic effect with chromium tanning agent.?3?Through free radical copolymerization GO-g-P?MAA-SAS?copolymer was prepared,in which methacrylic acid?MAA?and sodium allylsulfonate?SAS?were grafted to GO surface.The tanning properties of GO-g-P?MAA-SAS?tanned alone,combination tanning with chromium tanning agent and GO-g-P?MAA-SAS?,GO-g-P?MAA-SAS?retanning were studied.In GO-g-P?MAA-SAS?tanning alone,the dosage of GO-g-P?MAA-SAS?was 10%based on the acid skin mass,GO dosage was 0.4%,the T_s of tanned leather was 89.6?,tensile strength was 22.7 N/mm²,tear strength was 46.3 N/mm,elongation at break was 73.5%,water vapor permeability was 1.88 mL/cm²·h.The tanning properties of GO-g-P?MAA-SAS?was better than P?MAA-SAS?/GO blend and P?MAA-SAS?.In combination tanning with 10%GO-g-P?MAA-SAS?and 2%chrome tanning agent,the T_s of tanned leather was 92.5?,tensile strength was24.8 N/mm²,tear strength was 58.3 N/mm,elongation at break was 73.5%,and water vapor permeability of leather was 1.93 mL/cm²·h.Each performance of lether tanned with 10%GO-g-P?MAA-SAS?and 2%chrome tanning agent was close to the chrome tanned leather tanned with 5%chrome tanning agent,which showed that GO-g-P?MAA-SAS?could reduce the amount of chromium tanning agent.As a retanning agent,the change of leather properties was related to the GO content in GO-g-P?MAA-SAS?.The properties of leather was better with increasing the content of GO in GO-g-P?MAA-SAS?.The dosage of GO in GO-g-P?MAA-SAS?was 0.4%based on the weight of blue-wet leather,leather T_s was 109?,tensile strength was 32.8 N/mm²,tear strength was 63.7 N/mm,the thickening rate was 22.3%,the permeability was 3470 mL/cm²·h.Through the research of properties of GO-g-P?MAA-SAS?tanned alone,combination tanning and retanning,the size of GO became smaller and the permeability of GO increased after the formation of grafting polymer GO-g-P?MAA-SAS?,which increasedthe interaction between GO and collagen fiber,strengthened the nano-effect and chemical bonding effect of GO,and improved the tanning effect.