Extruded polystyrene foams with bimodal cell morphology

Extrusion foaming using supercritical carbon dioxide (CO2) as the blowing agent is an economically and environmentally benign process. However, it is difficult to control the foam morphology and maintain its high thermal insulation comparing to the conventional foams based on fluorocarbon blowing agents. In this study, we demonstrated that polystyrene (PS) foams with the bimodal cell morphology can be produced in the extrusion foaming process using CO2 and water as co-blowing agents and two particulate additives as nucleation agents. One particulate is able to decrease the water foaming time so both CO2 and water can induce foaming simultaneously, while the other increases the CO2 nucleation rate with little effect on the CO2 foaming time. Our experimental results showed that a dual particulate combination of nanoclay and activated carbon provided the best bimodal structure. The bimodal foams exhibited much better compressive properties and slightly better thermal insulation for PS foams.