The Study On Leather Finishing Of Waterborne Polyurethane With High Physical Properties

As the last process of tanning,finishing is necessary to give the leather a good sense of observability but also has good adhesion between the coating and the crust.Duing to its good formability,covering,chemical stability and good resistance to weather,Polyurethane resin is widely used in leather finishing as a film-forming agent.Waterborne polyurethane(WPU) can overcome the shortcomings of the solvent polyurethane to be an environmentally friendly and functional products.WPU synthesized by 4,4’-diphenylmethane diisocyanate(MDI)can easily yellowing,limiting its application in white and lightcolored leather.Polycarbonate diol and isocyanate mixed by MDI and isophorone diisoeyanate(IPDI)were used to synthesis prepolymer.then nano-Ti02 dispersions were added in two ways namely blend or synthetic.The influence of the ratio of different diisocyanate and the dosage of nano TiO2 on the film yellowing factor were also discussed.By tracking the changes of NCO content in the pre-polymer,the appropriate prepolymer reaction time is about 2h and infrared spectroscopy shows that the target product was obeserved;Through detecting the film resistance to yellowing under ultraviolet light,the experiment determined the ratio of MDI and IPDI was 8:2 and the adding amount of nanometer TiO2 was 2%to 4%,and the results of TEM also showed that the aromatic waterbased polyurethane from powder synthesis method had good storage stability and anti-yellowing properties;TG analysis and XRD results showed that the thermal decomposition temperature could increase by 70℃ then greatly improved the thermal stability of the film,while reduced the crystallinity and therefore improved the applicability of WPU,but the mechanical properties of the film had a certain degree of reduction.Increasingly scarce oil resources,the development of renewable and recycling of resources is a general trend.As the only vegetable oil containing hydroxy Castor oil have applied to the synthesis of polyurethane,available to polyurethane products with good performance.Different castor oil based waterborne polyurethane emulsions were observed using poly adipic acid castor oil ester diol and a series of isocyanate(MDI,IPDI,toluene diisocynate TDI,Hexamethylene diisocyanate-HDI)with different conditions.By tracking the remaining content of-NCO groups in the pre-polymer,the appropriate prepolymer reaction time is about 2h;Comparing the appearance of the emulsion the initial R value was obtained 3 to 3.5 and emulsions synthesized from aliphatic isocyanate(IPDI and HMDI)have better stability;FT-IR analysis showed that the target product was obtained;With the content of hard segment increasing,the tensile strength increases while elongation at break decreases;In the same hard segment content,the CO-WPU has a higher tensile strength than polyester polyurethane,while elongation at break decreases slightly;TG analysis showed that the CO-WPU can be maintained lower weight loss rate at a higher temperature,and the thermal decomposition temperature is increased by 30 ℃;The XRD results showed that the CO-WPU has a lower crystallinity.Leather finishing applications experiments showed that the modified PCU finishing leather samples had high resistance to yellowing grade and good moisture rub,abrasion fastness;In addition to better resistance to yellowing grade,PCU synthesized by powder synthesis method and blend have no basic differences in other performance aspects;CO-WPU finishing leather also have kind of folding fastness,moisture wiping performance and abrasion resistance.