Water expandable polystyrene (WEPS) Part 1. Strategy and procedures

Conventional expandable polystyrene (PS) is prepared via the suspension polymerisation of styrene containing pentane isomers as a blowing agent. The polystyrene beads are expanded by heating above the glass transition temperature, T_g. During the expansion process, pentane, which contributes to the formation of ozone in the lower atmosphere, is released into the environment. The objective of this study was to replace pentane isomers with a harmless blowing agent, namely water. The procedure adopted to use water as a blowing agent was as follows. Water was emulsified by means of a suitable emulsifier in a prepolymerised styrene/polystyrene mixture possessing a high viscosity in order to fixate the emulsified water droplets. Subsequently, this inverse emulsion was suspended in water containing a suitable suspending agent and polymerisation was completed. This procedure resulted in spherical PS beads containing small water droplets which were capable of expanding the PS matrix upon heating above T_g.