Rheology of Cationic Polyurethane/crylate Dispersions and Mechanical Properties of Films

A series of cationic polyurethane-polyacrylate(PUA)dispersions was obtained through seed emulsion polymerization,using trimethylolpropane(TMP)as cross-linker and hydroxyethyl acrylate(HEA)as coupling agent to connect polyurethane(PU)and polyacrylate(PA).Effects of TMP content and HEA content on the particle size and rheological behavior of the PUA dispersions were systematically investigated,and the mechanical properties influenced by TMA and HEA of the PUA films were also studied.When TMP is solely introduced into PUA system,the particle size and storage modulus of dispersion increase and loss modulus decreases with increasing TMP content.Compatibility and breaking stress of the film also increase,but breaking elongation decreases.However,excessive TMP causes great increase in loss modulus and elasticity;phase separation behavior thereby takes place in PUA dispersions,leading to a decrease in stability.When HEA is introduced into the PUA system independently,the particle size decrease with increasing HEA content,the dispersion transforms from viscous to viscoelastic state,and simultaneously changes from Newtonian fluid to pseudoplastic fluid.Interactions between PUA colloidal particles are also enhanced and dispersions are demonstrated to be anti-thixotropic liquid.When TMP and HEA are both introduced into PUA system by fixing TMP content at 0.4%,the dispersion transforms from positive thixotropic liquid to complex thixotropic liquid with increasing HEA content.Viscosity and interaction between colloidal particles alsoincreased with increasing HEA content,as well as the pseudoplasticity and thixotropy of dispersions.Meanwhile the mechanical properties of the films are significantly improved.