Preparation Of High Performance Waterborne Polyurethane Adhesive For Synthetic Leather

Waterborne polyurethane synthetic leather is one of the main directions of environmental protection and green development of synthetic leather,and the comprehensive performance of the leather depends on the performance of waterborne polyurethane.The present waterborne polyurethane adhesive has low solid content,poor bond strength and water resistance,which seriously restricts its industrial application in synthetic leather industry.In view of the above problems,the bond strength and water resistance of waterborne polyurethane adhesives had been studied in this thesis,and the main contents are as follows:Firstly,the hydrazine capped epoxy resin modified polyurethane emulsions had been prepared,and the preparation conditions,polyurethane structures and properties were analyzed.The results showed that the pre-polymerization reaction time and chain expansion time should not exceed 60 min,the best performance of the emulsion was obtained when the amount of chain expander DMPA was 8%,the content of epoxy resin E51 should not exceed8%,the viscosity of the pre-polymer before emulsification should be controlled within 6600Pa·s^-1,the stirring speed should not be less than 1500 r/min during emulsification,and a stable emulsion could be obtained with continued emulsification of 30 min when the system has completed the phase change from water-in-oil to oil-in-water.Epoxy resin and hydrazine group can graft with WPU,and epoxy resin can increase the melting temperature of polyurethane,in which HMDI type polyurethane increases more than IPDI type polyurethane,and the intensity of crystalline diffraction peak of E51 modified polyurethane is obviously smaller than that of unmodified polyurethane,meanwhile,the 2θangle of polyurethane became smaller and the distance between grains increased.Secondly,ketone-carbonyl hydrophobic polyacrylate emulsions were prepared by using octadecyl acrylate（SA）and butyl acrylate（BA）as soft monomers,and methyl methacrylate（MMA）and styrene（St）as hard monomers.And the effects of the preparation conditions and diacetone acrylamide（DAAM）on the structure of polyacrylates were investigated.The results showed that the optimum synthesis conditions were as follows:n _SA:n _BAratio is 6:4,n_soft:n_hardratio is 1:1,dosage of acrylic acid（AA）is 7%,and solid content is no more than25%.DAAM can copolymerize monomers,which can improve the hydrophobicity and thermal stability of polyacrylates,but decrease the glass transition temperature,crystallization temperature and enthalpy of crystallization.Finally,carbonyl hydrazine self-crosslinked polyacrylate/epoxy resin modified polyurethane adhesive emulsions were prepared by inverse phase emulsification method,and the structure and application properties of the adhesives was analyzed.The results showed that hydrazine-capped WPU and ketocarbonyl PA coexisted in the composite emulsion by physical mixing when hydrazine-capped epoxy resin modified polyurethane was emulsified with ketocarbonyl polyacrylate emulsion;the composite emulsion prepared with PA solid content is 15%and an n _N-N:n _C=Oratio is 1:0.7 had the best performance;the ketocarbonyl and hydrazine groups could undergo self-cross-linking reaction during drying;PA could improve the peel strength of the adhesive,the maximum value of peel strength arrived at 4.42 k N·m^-1when the drying temperature was 70℃,and the drying time was 12 h.The peel strength was further improved to 4.97 k N·m^-1after 7 days at room temperature,while the peel strength only decreased by 0.65 k N·m^-1after soaking in water.