Initial Stage of Foaming of PMMA/TMOS/CO2 Systems

In recent years, for the effective energy usage, development of high performance heat insulator is the subject of research for engineers. A poly(methyl methacrylate) (PMMA) foam that inside of the foam filled with silica aerogel is regarded as one of the promising candidate for high performance heat insulator. This composite material will be commercially produced with a supercritical carbon dioxide (CO₂) assisted extruding of the mixture of the PMMA and tetramethoxysilane (TMOS). In this work, for the basic understanding of the foaming of the PMMA/TMOS/CO₂ mixtures, in situ observation of the initial stage of the foaming was observed with new type of view cell that was developed in our laboratory.

It was found that with the addition of the TMOS in the PMMA/CO₂ system, the pressure drop which is necessary for the foam formation became monotonously larger with the increase in the amount of TMOS. On the other hand, the mean bubble diameter once decreased with the addition of the TMOS, and increased with the further increase in the amount of TMOS. The dependence of foam density of the amount of TMOS was vice versa. These facts were presumably due to the change of interfacial tension of PMMA/TMOS/CO₂ mixture and CO₂, and of the viscosity of the mixtures. Further experiments should be conducted for the full understandings of the foaming mechanism of this system.