Synthesis and foaming of water expandable polystyrene–clay nanocomposites

The typical process used to synthesize water expandable polystyrene (WEPS) was modified and applied to prepare water expandable polystyrene (PS)–clay nanocomposites (WEPSCN). The natural clay can be uniformly dispersed in water due to its hydrophilicity. It can be further carried into the styrene monomer by the formation of water-in-oil inverse emulsion. Via suspension polymerization, spherical PS beads with myriads of water/clay droplets inside were obtained. Upon heating via the hot medium, the PS matrix was expanded to form a cellular structure. Transmission electron microscopy results indicated that nanoclay forms a layer around the cell wall. The presence of nanoclay led to higher water content in the beads and reduced the water loss during storage. CO2 as the co-blowing agent, foams with a bi-model structure and lower densities were obtained. Furthermore, CO2 foaming offers an alternative method to utilize dried WEPS/WEPSCN beads. The presence of water cavities significantly enlarges the cell size and leads to a foam product with ultra-low density (∼0.03 g/cc) and low thermal conductivity.