Nanocellular foaming of poly (methyl methacrylate) with chlorodifluoromethane (HCFC-22)/CO2 binary mixtures as a model blowing agent

A foaming process for polymethylmethacrylate (PMMA) using a chlorodifluoromethane (HCFC-22) and carbon dioxide (CO2) binary mixture as a blowing agent at 40 MPa and 353.2 K was studied for the production of foams with high porosity and uniformity. HCFC-22 was employed as a model blowing agent because of (1) much larger solubility to polymers than CO2 and (2) well known phase diagram and physicochemical property. HCFC-22/CO2 binary mixtures improved the homogeneity of the cellular structure. The micrometer-sized cell structures seen in the foams with pure CO2 used as blowing agent were decreased in HCFC-22/CO2 binary mixtures. Homogeneous structure with cells from 0.07 µm to 0.35 µm were obtained in the binary mixtures. The binary mixtures were also effective in increasing the cell nucleation density of nanometer-sized cell structures. We were able to determine the optimal composition of HCFC-22/CO2 to coexist the high expansion ratio and homogeneous structure for PMMA foams.