Preparation And Foaming Properties Of Thermoplastic Expandable Core/Shell Microspheres

Thermoplastic expandable core/shell microspheres with a thermoplastic polymer shell and a hydrocarbon core had been prepared by suspension polymerization. The microspheres were powder,20-40μm in diameter, with narrow particle distribution and excellent foaming properties. This study screened suitable dispersants or complex dispersant system, discussed the effect of some preparation parameters on particle size distribution and foaming properties, and investigated the preparation of microspheres pre-capsulated with gelatin modified by amino resins.Dispersants and additives were important parameters for the particle size or particle distribution. The results showed that the particle size was small and size distribution was narrow with magnesium hydroxide as solid dispersant and PVP(K30) as dispersants. Magnesium hydroxide could be removed from the surface of the microspheres under acidic conditions. Surfactant could reduce the size of the particle effectively and sodium chloride could change the morphology of the microspheres and increase the yield. The mass ratio of dispersed phase and oil phase was determined by the quality requirements of the microspheres and the equipment. The microspheres had narrow size distribution when the ratio was 5:1.Homogenizing speed, homogenizing time, stirring speed and heating speed were also important parameters for the particle size and distribution. The results showed that the particle size was small and size distribution was narrow when homogenizing speed was at 8000rpm and homogenizing time was 7min. Increasing stirring speed made the size become narrower, but the initial particle was damaged when stirring speed was too higher. With rapid heating speed the particle size became larger, size distribution became wider and shell polymer became non-uniform. The stirring speed was at 400rpm and the heating speed was not too rapid.Monomers and foaming agent were important parameters for the foaming properties. The concentration expandable temperature raised with increasing molecular weight and decreased with increasing content of foaming agent. The results showed that the microspheres had excellent foaming properties and large foaming ratio when the ratio of MAN and AN was 1:4, the ratio of MMA and BA was 4.25:1 and the content of VAc was 1.17% using 1% AIBN as initiator,0.4% HDDMA as crosslinking agent and 30% 10 as foaming agent. The microspheres pre-capsuled with gelatin modified by amino resins had excellent foaming properties.