Microcellular natural rubber using supercritical CO₂ technology

Microcellular natural rubber (NR) prepared using a supercritical CO₂ technology is a promising alternative to replace traditional foaming agent due to environmental concern. Crucial parameters for the foaming process including CO₂ saturation time (30, 60, 90, 120, 180) min, pressure (0, 8.5, 10.5, 12.5) MPa, temperature (45, 55, 65, 85) °C, and crosslinking characteristics of NR (pre-vulcanized time at 15 min and 30 min) were orderly conducted. The results obtained showed a decrement of average cell size (less than 10 μm), cell size distribution, and expansion ratio depending on an enhancement of saturation time and pressure. However, the increment of saturation temperature affected the increase in average cell size, cell size distribution, and expansion ratio. In case of the crosslinking behavior, an escalation of the pre-vulcanized time of rubber influenced the decrement in average cell size, cell size distribution and expansion ratio resulting from an elevation of matrix crosslinking.