Study On The Modification Of Waterborne Polyurethane

Based on the present situation of waterborne polyurethane in coating application,a series of waterborne polyurethane with different proportions were designed and was modified by three materials in this paper.The results of the experiment were validated by molecular dynamics simulation software.The specific research contents are as follows:（1）According to the effects of different chemical components,different ratio of NCO/OH,different kinds of hydrophilic chain extender and different blocking agents on the viscosity and stability of polyurethane emulsion and the mechanical properties and thermal stability of polyurethane film.We conclude that the higher the proportion of 2,6–TDI,the better the mechanical properties,the better the stability,to sum up,choose the TDI–65/35type.The higher the R value,the better the mechanical properties,but the worse the stability,the comprehensive choice of R value is 1.1.The mechanical properties of PEG as polyether were better than PPG,and the stability was better,so the comprehensive choice of polyether is PEG-1000.（2）Based on the principle of molecular dynamics（MD）and molecular mechanics（MM）,the Material Studio 7.0 was used to study the compatibility,admixture,intermolecular interaction parameters,molecular radial distribution function and mechanical properties of three different kinds of modified polyurethane and non-modified polyurethane.Analyze and study the structural differences of the three modified polyurethane,poly（methyl acrylate）modified PU,F2641 modified PU,polyphenylmethylsiloxane modified PU and non-modified PU.The results show that the absolute values of the solubility parameters of polyurethane and PMA,F2641 and PPMS satisfy the following values:|△δ|<（1.3-2.1）(J·cm^-3)^1/2,the binding curves of the system are also very similar,indicating that the polyurethane is compatible with the three modifiers and can be well mixed.The cohesive energy density of polyurethane was decreased by the addition of PMA,while the CED increased by the addition of F2641 and PPMS.The CED of PU/F2641 system is the largest of the three,and when the addition amount is 5%,the stability is the best.From the molecular radial distribution function of the three modifiers,it can be seen that the compatibility of PMA is not very good,while the compatibility of F2641 and PPMS modified blends are good.The modulus of polyurethane modified by PMA,F2641 and PPMS are slightly improved by calculating.The theoretical basis of the selection and optimization of polyurethane modification method in traditional experiment is provided by molecular simulation.