Preparation Of Epoxidized Starch-based Chromium-free Tanning Agent And Its Tanning Behavior

Leather making is transforming discarded raw animal hides via a variety of physi-cal,chemical,and biological processes into multipurpose and high-value leather,which can increase the usefulness of raw hides and benefit society economically.Because of its superior tanning qualities and simple operating manner,chrome tanning is widely employed in the leather industry.However,the chrome tanning chemical has seriously harmed the environment despite generating high-quality leather.Particularly,the production of chromium-containing wastewater,sludge,and solid waste during the chrome tanning process has steadily developed into a technological bottleneck that is preventing the leather industry from developing sustainably.Therefore,the development of green ecological chrome-free tanning chemicals to enable sustainable processing and production of ecological leather and minimize pollution has become one of the primary areas for the future growth of the tanning industry.Based on the characteristics of environmental friendliness,plentiful resources,cheap cost and simple availability,and biodegradability,natural starch has become a type of biomass chemical materials with tremendous potential for application in the tanning industry.In this thesis,soluble corn starch(St)was modified with an environmentally friendly epoxy monomer(triglycidyl-isocyanurate,TGIC)as the main raw material to create a new starch-based biomass tanning agent(SCT)rich in epoxy groups.The primary research effort of this thesis is as follows.(1)SCT was successfully synthesized using St and TGIC as raw materials,with tetramethylethylenediamine(TMEDA)as a catalyst.Using the epoxy value as the evaluation index,the ideal conditions for SCT synthesis were found to be 0.75 molar of TGIC to St monomer,60℃,and a 6 hour reaction period.Under these conditions,the epoxy value content of the produced SCT molecules may reach 0.284 mol/The structure of the SCT tanning agent was identified using nuclear magnetic resonance(NMR)and Fourier transform infrared spectroscopy(FT-IR).The SCT tanning agent’s tanning process was initially established as follows:neutral bath at the start of tanning,pH 8.0-8.5 at the end of tanning,and the shrinkage temperature(Ts)of SCT-tanned leather produced under these conditions could reach more than 80℃.The SCT tanned leather performs better overall when compared to TWS tanned leather that is commercially available.(2)The SCT tanning agent’s tanning procedure has been optimized.The Ts,physical,and mechanical characteristics of the acid-impregnated sheep skins after tanning were used in this thesis as the major research indices.The amount of tanning agent,tanning temperature,and tanning duration were investigated using single-factor testing to see how each of these factors affected the tanning effect of the SCT tanning agent.The tanning procedure for the SCT tanning agent was then optimized.According to the experimental findings,the SCT tanning agent tans best at a rate of 12%,with a bath pH between 6.5 and 7.0 at the start of tanning,3 hours of room temperature tanning,an 8.0 pH at the conclusion of alkali extraction,35 degrees Celsius,and 3 hours of continuous mechanical action.In these circumstances,the tanned leather produced by SCT tanning had a Ts of 84℃,a tensile strength of about 10.02 MPa,a tear strength of about 24.17 N/mm,and an elongation at break of around 54%.(3)This thesis further explored the impact of SCT-aluminum tanning agent(SCT-Al)combination tanning on the performance of billets in light of the drawbacks of SCT tanning,such as lack of softness and poor coloring effect of billets.In this investigation,sheep skins that had been de-acidified and softened were pre-tanned using SCT,and then combination tanning with aluminum tanning agents was added.The univariate approach was used to optimize the amount of aluminum tanning agent,and the best amount was chosen based on changes in the billet leather’s completed leather look,mechanical strength,and other comprehensive features.The findings demonstrated that the Ts of the tanned leather could still reach 79.8℃ when the amount of SCT tanning agent was 8%of the mass of sheep sour leather,the amount of aluminum salt was 6%,and the combined tanning pH was 4.0.In addition,SCT-Al tanned leather has superior mechanical properties compared to SCT and TWS tanned leather alone(tensile strength of 6.27 MPa,tear strength of 37.52 N/mm,and elongation at break of 70.07%).This makes SCT-A1 tanned leather ideal for the processing and production of white wet leather.In conclusion,the SCT tanning agents created for this investigation had positive tanning results.After tanning with SCT and SCT-A1 tanning agents,the finished leather displayed good mechanical properties,wet and thermal stability,yellowing resistance,and organoleptic properties compared to conventional commercially available organic chromium-free tanning agents.It also had a high isoelectric point,which aided in improving the billet leather’s absorption of subsequent wet finishing materials(anionic fatliquors and dyes).Additionally,SCT can be utilized as a pre-tanning ingredient in salt-free acid immersion tanning systems due to its capacity to seal the amino groups on collagen and prevent swelling of bare hides during acid immersion.As can be seen,this thesis builds a novel organic,biomass-based,chromium-free tanning agent using starch and a green epoxy crosslinker in order to give a theoretical foundation and real-world experience for biomass materials in the ethical processing and production of eco-leather.