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 mu m to 0.35 mu m 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.

Automated summary

The use of HCFC-22/CO2 binary mixtures as blowing agents can improve the homogeneity and porosity of PMMA foams, leading to a more uniform cellular structure with smaller cell sizes.