Initial Stage of Foaming of Poly(methyl methacrylate)/ Carbon Dioxide / Tetraethoxysilane Ternary System

Polymer foams are well known to have high shock absorbing ability, good handling ability and many other good characteristics. Further, with carbon dioxide (CO₂) as a foaming agent, microcelluler foams that have high foam density and mechanical strength could be obtained. However, CO₂ have also the weak point that the adiabaticity is comparatively low. In this study, to overcome the weak point of the CO₂ as the foaming agent, addition of third component which will fill inside of the foam was examined. In this study, tetraethoxysilane (TEOS), was chosen as an additive for the Poly(methyl methacrylate) (PMMA)/CO₂ system due to the possibility of the formation of silica aerogel in the foam bubble to form composite material. In this study, foaming behavior, or the leading time of foaming after pressure release and bubble diameters growth rate as well as number density increase of bubbles, was examined with PMMA/CO₂ and PMMA/TEOS/CO₂ systems. With increasing the quantity of TEOS, the bubble diameters of foamed PMMA became smaller and the bubble density became larger. On the other hand, the leading time for foaming after the pressure release on PMMA/TEOS/CO₂ mixtures became longer. It is well known that the foaming of the polymers could be explained by the uniform nucleation theory. Based on the theory, from results suggests that the addition of TEOS lowers the interfacial tension however, latter fact implies that the increase in surface tension. From an experimental evidence of the PMMA/TEOS/CO₂ phase behavior, it became clear that the foaming behavior of the ternary systems could be explained from the phase separation pressure of TEOS/CO₂ binary system.