Synthesis And Performance Of Fatliquoring Tanning Agent Based On Poly(Amino Acid)s

Chrome tanning is the most widely used tanning method in modern leather industry.Chrome tanned leather have good softness,light resistance,high shrinkage temperature of 120 °C,whose product performance is currently unattainable by all tanning methods at present.Therefore,chrome tanning has been the most widely used tanning method in the world.However,the absorption rate of chromium in the leather processing is low,while the chromium from the waste water is quite harmful to human body and the environment,in addition,the chromium is non-renewable.Based on this,leather processing centered on chrome tanning is bound to face great challenges and pressure.Therefore,chromium-less or chromium-free tanning agents and their tanning methods are now on the focus of researchers in all leather tanning fields.In this thesis,natural(amino acid)s and edible animal and vegetable oils are used as raw materials,and triethylamine is used as the initiator to initiate the ring-opening polymerization of three(amino acids),L-oleoyllysine,L-threonine,and L-DOPA,to prepare a series of amphiphilic poly(amino acid)POLTD as a tanning agent.POLTD was used in the tanning of sheep skins,and the shrinkage temperature as the main indicator to optimize the block ratios,molecular weights and application processes.The results showed that the synthetic polymer POLTD has good tanning and filling properties,whose best application process is: 20% of tanning agent usage,8 h of penetration time with p H of 7 ? 8,6 h of binding time with p H 5 ? 6,and 0.1% of hydrogen peroxide dosage.The shrinkage temperature of leather tanned under the best application process can reach up to 74 °C.POLTD has good degradability and can be used in leather tanning which is pollution-free and neutral tanning.Combine POLTD with three metal tanning agents of chromium,aluminum and zirconium for the tanning of sheep skin,and explore the best application process.Experimental results show that POLTD and chrome have a favourable synergistic tanning effect.The best application process is: first pre-tanning with 20% POLTD,then retanning with 4% chrome for 5 hours,and the binding time is 4 hours;the use of POLTD can enhance the absorption of chrome tanning agent by leather,reduce the usage amount of chrome tanning agent,and the chromium content in the tanning wastewater is significantly reduced.POLTD and aluminum have a good synergistic tanning effect.The best application process is: first pre-tanning with 20% POLTD,retanning with 6%aluminum for 4 hours,and bonding for 4 hours;the introduction of POLTD strengthens the stability between aluminum and leather collagen fibers,improves the defect that aluminum tanning leather are not washable.However,when POLTD is tanned with zirconium tanning agent,there is a situation of competing for reaction sites.After the combined tanning,the shrinkage temperature of the crust leather is not high,and the synergistic tanning effect is bad.The pyrolysis activation energy of pure POLTD tanning,POLTD-zirconium combined tanning,POLTD-aluminum combined tanning,POLTDchrome combined tanning,chrome tanning,and zirconium tanning are calculated by the Coats-Redfern method and the Satava-Sesták method: 163.663 ? 172.084 k J/mol;182.560 ? 191.955 k J/mol;215.544 ? 239.432 k J/mol;215.1831 ? 226.256 k J/mol;189.969 ? 201.22 k J/mol;196.942 ? 207.068 k J/mol.It shows that POLTD,chromium and aluminum have excellent synergistic tanning effects,and the cross-linking strength between the leather collagen fibers is higher.Use POLTD as a retanning fatliquor for the retanning process of leather and optimize its application process,the experimental results show that the best POLTD block ratio for the retanning process is n(L-OLys): n(L-Thr): n(L-DOPA)= 13: 5: 5,the best molecular weight is about 10 KDa;the best application process is 15% tanning agent,5 h of retanning time,4 h of binding time,and the amount of hydrogen peroxide is 0.3%.After retanning,it is found that the thermal shrinkage temperature of the crust leather has increased to a certain extent.POLTD has a good fatliquoring and filling effect on the leather,which can significantly improve the physical and mechanical properties of the crust leather.