SMA/PUA based double-layer thermo-expandable microcapsules and their performances

In this study, the double-layered thermo-expandable microcapsules with n-hexane as the core and styrene maleic anhydride copolymer (SMA) / polyurea (PUA) as the shell materials are prepared by combination of interfacial polymerization and co-precipitation method. The successful encapsulation of n-hexane in the PUA microcapsules is confirmed by simultaneous thermal analyzer (TG-IR). The properties of the thermo-expandable microcapsules (TEMs) are investigated by thermo-gravimetric analyzer (TGA), laser particle size analyzer, optical microscope and thermo-mechanical analyzer (TMA), respectively. The results show that polyurea shows a good encapsulation effect on n-hexane. When the dosage of n-hexane is 60 wt%, the microcapsules with polyurea as the shell have the encapsulation efficiency as high as 96.7%. However, the thermo-expandable performance of PUA-TEMs is poor. Double-layered thermo-expandable microcapsules with SMA/PUA as the shell (SMA/PUA-TEMs) are then obtained by introducing SMA copolymer as a second layer to enhance the thermo-expandable performance of the microcapsules. The introduction of styrene-maleic anhydride copolymer onto the PUA-TEMs reduces the encapsulation amount of n-hexane in the microcapsules, but the thermo-expandable performance is significantly improved. When the mass ratio of SMA to PUA-TEMs is 2:1, the SMA/PUA-TEMs with the encapsulation efficiency of n-hexane of 41.1% and the particle size of about 2.5 μm are obtained. SMA/PUA-TEMs show onset and peak expansion temperatures of 195 and 216 °C, respectively, and the expansion ratio of 2.4 time. The tentative investigation of the foaming performance of the SMA/PUA thermo-expandable microcapsules in polyvinyl butyral matrix shows that the thermo-expandable microcapsules can be well dispersed in the polymer matrix and have good expandable performance. This study provides a novel kind of thermo-expandable microcapsules with high onset and peak expansion temperatures which are beneficial to produce plastic foam with high T_g or T_m.