Preparation and properties of thermo-expandable microcapsules with anionic/nonionic waterborne polyurethane as the shell

In this study, we developed a new type of thermo-expandable microcapsules (TEMs) with the anionic/nonionic waterborne polyurethane as the shell and low boiling point agent, n-hexane, as the blowing agent. Thermo-gravimetric analyzer (TGA), laser particle size analyzer, thermo-mechanical analyzer (TMA) and scanning electron microscope (SEM) were used to investigate the blowing agent encapsulation, particle sizes and expansion performances of the TEMs, respectively. Results showed that the nonionic hydrophilic monomer, polyethylene glycol monomethyl ether (MPEG), improved the amount of encapsulation and encapsulation efficiency of n-hexane in TEMs and affected the expansion performance of the TEMs. When the amount of MPEG was 13.4 wt%, the amount of encapsulation and encapsulation efficiency of n-hexane in TEMs could reach 13.2 wt% and 66%, respectively, with the particle size of about 80 nm. 1,4-Butanediol (BDO) enhanced the encapsulation of n-hexane in TEMs. When the amount of BDO was 33.2 mol %, DMPA was 6.7 wt % and MPEG was 13.4 wt %, respectively, the TEMs showed good thermo-expansion performance. The TEMs showed the onset expansion temperature of 206 degrees C, the peak expansion temperature of 220 degrees C, and the expansion ratio of 4.1 times, respectively. The successful foaming of the TEMs in epoxy resin indicates that the prepared TEMs have great potentials in foam material applications.