Preparation And Properties Of Waterborne Polyurethanes For Synthetic Leather

Polyurethane has out-standing performances on elasticity, wear-resisting and peal strength. Waterborne polyurethane(WPU), on the other side, has more advance for its low VOC content, transport safety and environmental friendly. Nowadays, WPU is substituting solvent-based polyurethane for adhesives and coating agents. In the artificial leather industry, WPU has a wide range of applications, such as the middle layer, laminating resin and the surface finishing agent. In this paper, WPU dispersions containing carboxylic and sulfonic groups were synthesized using polyester polyol containing sulfonate (S-44) and 2,2 dimethylol propionic acid (DMPA) as hydrophilic functionalal group, toluene diisocyanate(TDI),4,4-diphenyl methane diisocyanate (MDI) and polyethyleneglycol adipate (PEA-2000) as the main raw materials,1,4-butanediol (BDO) as small molecule chain extender, and TMP as cross-linking agent. The conditions influencing the quality of WPU emulsion and film were studied, such as the different ratio of PEA/S44, the molar ratio of MDI/TDI,-NCO/-OH and the amount of BDO and TMP. The successfully-made WPU adhesives were used on PU/PVC artificial production line to test the practicability, and the application results are discussed and analyzed. The results are as follows:(1) The paticle size distribution of WPU synthesized by S-44 and DMPA as hydrophilic functionalal group was bimodal distribution.The addition of S-44 could reduce viscosity of WPU system and increase the solid content without affecting the water resistance. And peel strength increased first and then decreased with increased amount of S-44. The results indicated that when n(S-44)/n(PEA) was 7/3, the solid content was 53.1%, peel strength was 37 N/25mm and the water absorptivity of films was 22%, which was the optimal comprehensive performance.(2) Along with increased amount of MDI, the mechanical properties of WPU films were improved and the water absorptivity was decreased obviously. Because of the high chemical activity, the more amount of MDI, the more difficulty to control the reaction. When n(MDI)/n(TDI) was 4/6, the tensile strength was 38.56MPa, the elongation at break was 530% and the water absorptivity of films was 15%, which were the best performance.(3) With n(NCO)/n(OH) increasing, the tensile strength of WPU film was increased, elongation at break was decreased, peel strength increased first and then reduced slowly, and the water absorptivity of films first falled rapidly and then flattened out.(4) When the amout of TMP inceased, the tensile strength of WPU films increased first and then decreased while the elongation at break falled all the time. The optimal amout of TMP was 0.3%.(5) The compounding formula research indicated that the amount of thickener, antifoaming agent and flatting agent should be 0.5wt%,0.2wt% and 0.15wt% respectively. Using 4wt% of gaseous silica as filler could increase the bonding effect, and the peel strength could rise from 32N/25mm to 35N/25mm.(6) The application results showed that the resultant WPU binders could be used in the production line of PU/PVC leather.When the dosage of WPU was 70-80g/m2, the peel strength between PVC and polyester fabric could be above 35N/25mm, and it still kept more than 20N/25mm after testing in constant temperature and humidity for 7 days.