Preparation And Property Of Thermally Expandable Microspheres

With magnesium hydroxide (Mg(OH)2) as dispersant, acrylonitrile (AN) andmethyl methacrylate (MMA) as main polymerization monomer,azobisisobutyronitrile (AIBN) as initiator, bayerite trimethylolpropane triacrylate(TMPTA) as crosslinking agent, we successfully prepared the microspheres havinggood foaming properties by suspension polymerization. Through a series of analyticaltests, including electron microscope, LS13320particle size analyzer and hot stagemicroscopy, the study discussed the effections on particle size, distribution andfoaming properties of the preparation technology (dispersant, stirring speed, blowingagents, wall material, all conditions, reaction temperature and adding additives).Experimental results showed that the addition of nearly saturated sodium chloridecould eliminate caking and floc. Concentration of particle size distribution was morefavorable using polyvinyl polyvinylpyrrolidone (PVP) as dispersant than polyvinylalcohol (PVA).To some extent, increasing stirring speed could obtain more finemicrospheres, but initial particle could be damaged when stirring speed was too large.The size distribution was more concentrated using continuous shear mixing emulsifier5min in7000rpm. In the case of the same amount, particle size distribution was morenorrow using azobisisobutyronitrile as initiator than benzoyl peroxide. Furthermore,the reaction temperature and sodium dodecyl sulfate affected the particle size anddistribution of the microspheres. The smaller microspheres particle was, the biggerinner pressure was. The higher boiling point of foaming agent was, the higherconcentration foaming temperature was. The more the amount of the foaming agentwas, the lower the concentration foaming temperature was. Using33.3%foamingagent could obtain the microspheres having medium-temperature foaming, betterfoaming stability and larger expansion ratio.Adding third monomer with different Tgand chemical properties had a greater impact on the foaming properties of themicrospheres. Using butyl acrylate as the third monomer had better foaming stability.Eventually using1%AIBN as initiator,0.6%TMPTA as crosslinking agent,27.8%isooctane as foaming agent at60℃prepared microspheres having betterfoamingstability and larger expansion ratio.In oil phase system, the microspheres were successfully prepared with centralizeparticle size distribution and higher foaming temperature by adding monomers like methacrylic acid(MAA) having higher glass transition temperature and usingmagnesium hydroxide as dispersant. The foaming temperature was above190℃andmicrospheres had wider stabilizing bubble temperature range. By adjusting andformulating the preparation technology, we found that in the process of preparing hightemperature foaming microspheres, the microspheres were prepared with higherfoaming temperature and larger ratio of microspheres using10%MAA and28%isooctane. In addition, the test of solvent risistance and storage time in roomtemperature were done to demonstrate the foaming performance. The results indicatedthat the high temperature foaming microspheres had good solvent resistance andexcellent air tightness.