Influence of experimental conditions on the incorporation of water droplets in polystyrene (original) (raw)

concentration was high near the surface of the particles and decreased near their center resulting in a non-uniform expanded structure. Crevecoeur et al. (1999a) [2] proposed a process using only water as blowing agent, totally avoiding the use of volatile hydrocarbons. The process was divided in two stages: the first one was a water dispersion stage in which water was added in the reactor with the monomer, the initiator and a suitable surfactant under strong stirring at the polymerization temperature. The second one was a suspension stage, when the continuous suspension medium (water and a suspension stabilizer) was added and the system was allowed to react for more 4 hours. Up to 11 wt% of water was homogeneously incorporated in the particles by this method. In another work [3] , the authors demonstrated that the internal structure of the water expanded polystyrene was very similar to that of the pentane expanded one. One can observe in the works described above that the water incorporation step is of mayor importance because it determines the final morphology of the incorporated water droplets. In turn, the water droplets morphology determines the expansion behavior of the material as well the cell formation since each cell is originated from one single droplet. Furthermore, water must be homogeneously incorporated along the polystyrene particle to assure that a homogeneous expanded structure will be obtained. It can also be noted that a reduced number of works reported the production of expandable polystyrene using only water as blowing agent. However, the influence of several