Thermo-expandable microcapsules with polyurethane as the shell

Thermo-expandable microcapsules (TEMs) with polyurethane as the shell and n-hexane as the blowing agent were synthesized by interfacial reaction between isocyanate-terminated polyurethane prepolymer aqueous dispersion and polyamine chain extender. The synthetic process for the thermo-expandable PU-shelled microcapsules was established. The factors which affected the efficiency for blowing agent encapsulation were investigated by fourier transform infrared spectroscopy (FT-IR), laser particle size analyzer and thermo-gravimetric analysis (TGA). The foaming performances of the microcapsules were characterized by polarizing optical microscope with hot platform (POM) and thermo-mechanical analyzer (TMA). The results showed that PU-shelled thermo-expandable microcapsules were successfully synthesized and had good foaming performance. The NCO/OH ratio was found to have a significant effect on the encapsulation of n-hexane and the appropriate ratio was found to be 3:1. Diethylenetriamine (DETA), which is a polyamine chain extender, was found to be a more suitable chain-extender than other polyamine chain extenders in encapsulation the hexane. PU-shelled thermo-expandable microcapsules containing 25.8% blowing agent was fabricated. The onset expand temperature of TEMs was found to be 206 °C, and the maximum foaming temperature was at 235 °C, according to thermo-mechanical analysis. The volume expansion ratio of TEMs reached 27 times according to the measurement by polarizing optical microscope. The PU shelled TEMs showed good foaming performance in vinyl acetate-ethylene copolymer matrix.