Two-step Foaming Process for Production of PMMA Nanocellular Polymer Foams via Ultra-high Pressure and Rapid Depressurization

Abstract A two-step foaming process was developed that uses different temperatures in each step and combines ultra-high saturation pressure (Ps > 50 MPa) and rapid depressurization (> 1.25 GPa/s) for production of nanocellular polymer foams. The effect of process conditions were investigated using polymethylmethacrylate (PMMA) and carbon dioxide. Foams with small cells ( 1015 nuclei cm-3) were obtained, which were of a finer structure than those made by previous one-step foaming process. N0 tended to increase even at Ps =100 MPa. A fine cell structure (30.5 nm ± 10.4 nm) was observed with scanning transmission electron microscopy (STEM), and was confirmed when two-step process conditions were used. The process and advantages of ultra-high pressure are discussed with regard to porosity, cell size and N0.