Study On Preparation And Properties Of Waterborne Polyurethane Modified By Nano SiO₂

Waterborne polyurethane（WPU）,as a new eco-friendly material,not only inherits the excellent properties of polyurethane（such as adhesion,hardness,flexibility,etc.）,but reduces the use of organic solvents（even zero solvents）.This has drawn people’s a bit of attention in the kinds of fields in the world.In recent years,waterborne polyurethane has been used in textile and leather finishing,inks,adhesives,and architectural coatings,etc.And there will have an extensive prospect in the future.However,due to the introduction of hydrophilic groups in the system,the water resistance,thermal stability,and mechanical properties of waterborne polyurethane still have certain gaps compared to polyurethane,which need to be further improved.In this paper,isophorone diisocyanate（IPDI）and polytetramethylene ether glycol（PTMG）were selected as the main reaction monomers,and 2,2-dimethylolpropionic acid（DMPA）was used as a hydrophilic chain extender to prepare waterborne polyurethane.A series of waterborne polyurethane dispersions（WPUHP）with different acrylate ratios were synthesized by the introduction of acrylate grafting agent hydroxyethyl methacrylate（HEMA）and pentaerythritol triacrylate（PETA）.The effects of different acrylate grafting agent ratios on the properties of waterborne polyurethanes were studied,and the water resistance,mechanical properties and thermal stability of their films were discussed.It was found that as the proportion of hydroxyethyl methacrylate（HEMA）in the system gradually decreased,and the proportion of pentaerythritol triacrylate（PETA）gradually increased,the effective particle size of the dispersion gradually increased,and the viscosity gradually decreased.The water resistance of WPUHP films have been improved to a certain extent,the maximum contact angle is 96.4°,the tensile strength has been increased to 19.50 MPa,and the thermal stability has been enhanced to a certain extent.In addition,in order to considerable improve the performance of waterborne polyurethane,a series of waterborne polyurethane dispersions（WPUS）with different nano-SiO₂ content were synthesized based on acrylate grafting agent modified waterborne polyurethane,and the effect of different nano-SiO₂ content on the properties of the adhesive films were studied.It was found that when the nano-SiO₂ content is less than 2.5%,the performance of all WPUS dispersions were stable,and with the increase of nano-SiO₂ content,the effective particle size of the WPUS dispersions increase and the viscosity decreases;The XPS test results show that due to the lower surface energy of Si,it migrates and enriches to the outer surface of the WPUS films,which enhances the surface properties of the WPUS films;the water resistance of the modified WPUS films were improved,and the maximum contact angle is 103.0°,and the water absorption rate is reduced to 10.80%.SEM test observed that the WPUS films have a uniformly distributed rough fracture surface,and with the increase of nano-SiO₂ content,the roughness increases and contains more small bands and bumps which means that need a larger external force to break the WPUS films,and the tensile strength of the WPUS films were significantly increased to 24.10 MPa,and the thermal stability was also significantly improved.