Study On Synthesis And Application Performance Of Acrylic Copolymer Retanning Agents With Series Of Molecular Weight

Retanning process is one of the most important processes in leatherproduction, which plays a vital role in the modern leather industry.Acrylic copolymer retanning agents is among the most importantretanning agents, which owns wide application, endows leather withfallibility, fullness, smooth and close grain. It also enables the wastewaterafter retanning to be non-toxic and treated easily, and possesses positivemeaning in lessening the chrome pollution in leather production.Consequently, acrylic copolymer retanning agent has been the focus ofleather industry. Molecular weight is one of the most important factorswhich affect performance of acrylic retanning agent. Filling properties,physical and mechanical of leather are relative closely to molecularweight of copolymer. In general, filling properties, softness, and fullnessas well foaming of leather are improved along with the increase ofmolecular weight of retanning copolymer within the allowable range.However, the molecular weight is not as larger as better. If molecularweight of copolymer is too large, copolymer retanning agent can notinfiltrate easily into the leather, which leads to coarse surface of leather,and the "lost color" phenomenon; smaller molecular weight of copolymercan improve the permeability of the polymer, being beneficial to smooth,firm surface of leather, and increase the strength except for the filling.Acrylic copolymer retanning agent prepared by our group before thisstudy possessed good stability, low cost, good elasticity, smooth surface,good mechanical properties and less chrome in the retanning wastewater.However, it was found fill capability and softness was slight insufficientin retanning process especifically in sofa leather and clothing leather.This study was designed to further improve application performanceon the basis of previous research, and prepared a series of products tomeet demands of market. Molecular weight of acrylic copolymerretanning agent controlled by synthesis conditions was investigated. The effect of temperature, monomer concentration, ratio of monomers, anddosage of initiator on rotational viscosity, molecular weight andapplication performance was discussed and the synthesis process to adjustthe molecular weight was optimized; application performance ofcopolymer was adjusted by controlling of the molecular weight of theacrylic. Then, acrylic copolymer retanning agents with a series ofmolecular weight were prepared and characterized by X-ray diffraction,gel permeation chromatography to investigate the reactive group of theacrylic polymers of different molecular weight, crystallinity andmolecular weight and its distribution change; retanning agents with aseries of molecular weight were applied in retanning to detect theinfluence of molecular weight of retanning copolymer on applicationperformance. Retanning agents with a series of molecular weight,different types of surfactants and retanning filling material werecompounded to examine its application performance with centrifugalstability and application performance as index；retanning agents with aseries of molecular weight were applied in the laboratory and in theleather factory to examine its performance uniformity.The experimental results show that: with the increase of temperature,the decomposition efficiency of initiator was higher and the molecularweight was smaller, but higher temperature would lead to the implosion,the appropriate temperature should be controlled at70°C; withincreasing of initiator, the copolymer molecular weight decreased after apeak molecular weight with initiator dosage1%; the molecular weight ofcopolymer decreases with increasing of neutralization; when dosage ofchain transfer agent respectively were5%to160%of the total monomermass conditions, molecular weight of the polymer decreased withincreasing of the chain transfer agent, and the trend is so obvious that weconfirm the method of controlling the dosage of chain transfer to adjustedmolecular weight of the copolymer in synthesis process.Results of FTIR, X-ray, and GPC of acrylic retanning agent with aseries of molecular weight showed that with increasing of dosage of chaintransfer agent, molecular weight of polymer decreases, and degree ofcrystallinity reduced, but the chain groups of molecular did not change significantly.The retanning application results showed that with increasing ofmolecular weight of the acrylic copolymer retanning agent, crust filling,choose fill, dyeing uniformity, tensile strength, tear strength were allincreased, but softness, elongation at break were decreased. The effect ofmolecular weight on the shrinkage temperature of crust is not obvious.Optimal compounding surfactant was poly (ethoxylated fatty alcohol),which improved crust properties of acrylic retanning agent complex withits non-ionic surface, not only in promoting the penetration of the tanningagent molecules in complex, but also in easing the macromolecularcomplex tanning agent molecular mass of the leather surface, the surfaceis more delicate; the application result of tanning filler in polymers andother compound was ineffective.Factory application results showed that the macromolecular acrylicretanning agent made leather soft, clear in plump foam sense, strong andsensual, and clear lines of grain, pore relaxation and suitable for sofaleather retanning fill; foam sense of crust after tanning by smallmolecules acrylic retanning agent was not obvious while sensuality wasnot strong, but it owned good convergence, tight leather body, suitable forfilling in the complex upper leather tanning. Factory application andlaboratory application results showed that the property testing index ofcrust leather after retanning agents with a series of molecular weightreached the industry standards.