Preparation,Characterization And Application Of Reactive Amphoteric Leather Retanning Agent

At present,chrome tanning is facing a series of environmental risks,which restricts the sustainable development of leather industry.Therefore,chromium-free ecological leather manufacturing technology has become an important development direction of leather industry.Therefore,it's an important development direction to chromium-free ecological leather manufacturing technology of leather industry.Compared with chrome tanned leather,the surface of the leather tanned by non-metallic tanning and the interior of the fiber are short of positive charge of metal ions and have strong negative and electric properties.The surface of the leather and the interior of the fibers are short of metal ions of positive charged and have strong negative electric properties.As a result,the reactivity between the leather and the traditional anionic dyeing materials is poor,which leads to the decrease of the dyeing effect of the leather.Thus,it is very important to study the key dyeing and finishing materials such as high performance retanning agents matching the non-metallic tanning system.For that reason,the reactive amphoteric polyurethane retanning agents and reactive amphoteric polymer retanning agents which contained multi-aldehyde groups,anions and cations were synthesized by polyaddition reaction and free radical polymerization,respectively.Then they are used in retanning process in non-metal tanning system in order to produce a firm bond between reactive aldehydes and alkaline amino groups in collagen fibers.At the same time,the cationic groups in the molecule were used to control the surface charge of the green leather in order to improve the reactivity of non-metallic tanned leather and traditional anionic dyeing materials.The research content of this paper includes two parts:(1)New amphoteric polyurethane emulsions(AAPU)containing aldehyde groups were prepared by addition reaction using isophorone diisocyanate(IPDI),polytetrahydrofuran glycol(PTMG),2,4-dihydroxybenzaldehyde(DDBA),2,2-bis(hydroxymethyl)propionic acid(DMPA)and N-methyldiethanolamine(N-MDEA)as raw materials.The effects of r value(ratio of-NCO in IPDI to the amount of total hydroxyl in other materials),R value(ratio of-NCO in IPDI to the—OH in PTMG)and dosage of hydrophilic chain extender(DMPA)on the particle size and stability of emulsions were investigated.The structure of main components of AAPU retanning agent was characterized by UV,FT-IR and~1H-NMR.The size,morphology and electrification of emulsion particles were measured by DLS,TEM and Zeta potential analyzer,the thermal stability and molecular crystallinity of AAPU retanning agent were studied by thermogravimetric analysis(TGA)and X-ray diffraction(XRD).Then AAPU retanning agent was applied to the retanning process of non-metal tanning system(less-vegetable tanning leather system and F-90 system).The effects of retanning on the binding ability and properties of crust leather with anionic wet finishing materials were investigated by means of absorption of anionic dyes and fatliquors,scanning electron microscopy(SEM),XRD,TGA and differential scanning calorimetry(DSC).The results showed that the emulsion particles exhibited relatively regular spherical structures with an average particle size of42.6 nm and isoelectric point of 5.16 when the r value was controlled at 1.2,R=1.40 and the dosage of DMPA was 5%(based on the total mass of raw materials,the same below).The application results show that the Ts of crust leather retanned by AAPU retanning agent can increase by 9.6?,and the dye absorptivity of vegetable-tanned light leather and white-wet leather treated with AAPU retanning agent can reach 99.89%and 99.49%,the dyeing bath is transparent and bright,and the absorptivity of fatliquor is 98.56%and 97.11%,respectively.The value of K/S,thickening rate,tensile strength,tearing strength,softness and water vapor permeability of crust leather are also improved.It is higher than the crust leather treated with traditional acrylic resin retanning agent.What's more,the crystallinity of collagen fibers treated by AAPU retanning agent was small and the fibers were loose.The results showed that AAPU retanning agent had good retanning performance in non-metal tanning system.(2)The amphoteric polymer retanning agent containing aldehyde groups(PADU)was synthesized by free radical polymerization using acrylic acid(AA),dimethyldiallyl ammonium chloride(DADMAC)and undecenal(UDAL)as monomers and azodiisobutyronitrile(AIBN)as initiator.The effects of reaction time,reaction temperature,amount of initiator and the ratio of monomers on the preparation process were investigated.The structure and property of PADU retanning agent was characterized by FT-IR,~1H-NMR,TGA and XRD.The effect of binding ability with anionic wet finishing materials and the properties of crust leather retanned by PADU were investigated the retanning experiment in non-metal tanning system.The results showed that the PADU with the expected structureandisoelectricpointof4.25whenT=79°C,AA:DADMAC:UADL=1:4:5(the ratio of the amount of each monomer)and the dosage of initiator was 3%(based on the total mass of the monomer).The molecular chain of PADU was regular with good thermal stability.The results of retanning application in non-metallic tanning system showed that the Ts of less-vegetable tanned leather and white wet leather increased by 11°C and7.6°C respectively after retanning with PADU retanning agent.The absorption of anionic wet finishing materials were promoted by using the PADU retanning agent and the absorption rate of dyes can reach 99.58%and 99.2%respectively.The waste liquid after dyeing was clear and transparent;the surface of crust leather was uniform and full in color.The physical and mechanical properties of crust leather were better than those of traditional acrylic retanning agent.The above results show that the prepared PADU retanning agent has certain retanning properties in non-metallic tanning system.