(720b) Phase Behavior of PMMA/CO2/Tetraalkoxysilane Ternary 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 tetraalkoxysilane. As the foaming pressures depend on the phase separation, phase behavior of the systems is very important.

In this work, phase diagrams of CO₂/Tetramethoxysilane (TMOS), CO₂/Tetraethoxysilane (TEOS) binary systems and PMMA/CO₂/tetramethoxysilane (TMOS) ternary system were measured. PMMA/TMOS system is mutual solubility system at atmospheric pressure, while PMMA/TEOS system is immiscible system. Phase equilibria measurements were performed by visual observation of the Vapor-Liquid (VL) separation, Liquid-Liquid (LL) separation and Vapor-Liquid-Liquid (VLL) separation with synthetic method at wide range of temperatures and Pressures. Experimental conditions for binary systems were performed at CO₂ molar fractions from 0.15 to 0.85. For the ternary systems, PMMA weight fraction was from 5 wt % to 25 wt %, and PMMA molecular weight was from 15000 to 120000.

Phase behavior of two binary systems was almost the same from each other. Experimental results of these binary systems were correlated with using Peng-Robinson equation of state with van der Waals one fluid mixing rule, and the molecular interaction parameter k_ij and l_ij for CO₂/TMOS and CO₂/TEOS were determined. Both k_ij and l_ij were almost zero, which means these binary systems were almost the ideal mixture system. The mutual solubility of PMMA/CO₂/TMOS ternary systems increased with the increase in pressure and in polymer molecular weight, and decreased with the increase in temperature. Ternary phase diagrams of PMMA/CO₂/TMOS systems were constructed from the binary and ternary experimental results.