Production of EPS Raw Material

Spherical beads that can be expanded into foam under the influence of heat or steam are produced directly by suspension polymerization in the presence of blowing agent. The term suspension polymerization describes a process in which water-insoluble monomers are dispersed as liquid droplets with suspension stabilizer and vigorous stirring to produce polymer particles as a dispersed solid phase. Initiators used in suspension polymerization are oil-soluble. The polymerization takes place within the monomer droplets. The kinetic mechanism of the suspension process is considered to be a free radical, water-cooled microbulk polymerization [1]. 

Suspension stabilizing agents are present in the suspension to obtain and stabilize a desired droplet distribution of the dispersed phase. The suspension stabilizer has to be soluble or wetted in/by water. The particle size can cover 

The suspension polymerization for the production of EPS is carried out in a jacket batch reactor with a stirrer and usually two or more baffles. The volume of the vessels is normally between 20 and 100 m3. 

Usually the polymerization process is carried out in two or more stages. During the first stage, the final particles are formed, and in the second stage blowing agent is added and this penetrates into the beads. The duration of the second step is preferably determined by the residual monomer concentration that needs to be achieved (normally 1000 ppm). For both stages of the process, initiators with different decomposition characteristics have to be applied to initiate the polymerization. 

To decrease the viscosity at this stage of polymerization requires a continuous or stepped increase in the polymerization temperature [10-15]. The simultaneous addition of small amounts of bifunctional monomers and chain transfer agents ( tr 2) also results in a more desirable molecular weight distribution with a flat, low A/w side and a sharply decreasing high Mw flank. The procedure of later addition of the chain transfer agent before the gel effect takes off is preferred. 

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