Study on synthesis of polyurethane‐epoxy composite emulsion

Abstract The stable polyurethane‐epoxy composite emulsion with the epoxy‐amine oligomer (DEA‐EP) and the epoxy resin oligomer has been prepared by step‐growth polymerization and controlled crosslinking technique. The emulsion forming transparent films can be cured at room temperature with trimethylolpropane tris (1‐ethyleneimine) propionate (TMPTA‐AZ). The DEA‐EP structure and its reaction with urethane prepolymers were proved by Fourier transform infrared spectra (FTIR). The studies on particle size, the particle size distribution, viscosity, and the films' transmittance (Tr) indicated that both trimethylol propane (TMP) and DEA‐EP contributed to improving the resin blends' compatibility and reducing the viscosity. The epoxy resin content can increase up to 20.0 wt % (based on the total content of the polyurethane and epoxy resin) and the emulsion was still stable. The data from the tensile test experiments showed that with the epoxy content increasing, the tensile strength (σ b ) and Young's modulus were proportionately raised, but the elongation at break (ε b ) decreased. Tensile tests also revealed that introducing TMPTA‐AZ as an outside‐crosslinker can increase the tensile strength. By adding 0.3 wt % of TMPTA‐AZ, the ε b reduced from 429% to 371% and the σ b increased from 4.4 to 13.73 MPa; by adding 1.8 wt % of TMPTA‐AZ, ε b of the film was 67% of ε b of the film with 0.3 wt % of TMPTA‐AZ, but its σ b was 24.77 MPa and 180% of σ b of the film with 0.3 wt % of TMPTA‐AZ. The cured films possessed excellent water and toluene resistance: water uptake (48 h, 3.1%; degree of curing: 70%), toluene uptake (210 h, 8%. degree of curing: 70%). Better properties of the composite emulsion will confer it as a potential application in low volatile industrial coatings. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010