Abstract: An expandable polystyrene composition in the form of expandable beads, comprising by weight (1) 100 parts of a styrene polymer, (2) from 2.2 to less than 4.0 parts of at least one blowing agent, and (3) from 0.01 to 0.4 part of at least one plasticizing. The composition is particularly useful for manufacturing medium density expanded moulded polystyrene objects, particularly with a density from 40 to 190 g/l. A process for manufacturing such objects,is provided, together with pre-expanded beads with a buld density of 40 to 190 g/l, containing by weight (a) 100 parts of a styrene polymer, (b) from 0.5 to less than 3.0 parts of at least one blowing agent, and (c) from 0 to 0.4 part of at least one plasticizing agent.

Abstract: The invention relates to an expandable polystyrene composition in the form of expandable beads, comprising by weight (1) 100 parts of a styrene polymer, (2) from 2.2 to less than 4.0 parts of at least one blowing agent, and (3) from 0.01 to 0.4 part of at least one plasticizing. The composition is particularly useful for manufacturing medium density expanded moulded polystyrene objects, particularly with a density from 40 to 190 g/l. The invention also relates to a process for manufacturing such objects, employing an expandable polystyrene composition in the form of beads containing by weight (1) 100 parts of a styrene polymer, (2) from 2.2 to less than 4.0 parts of at least one blowing agent, and (3) from 0 to 0.4 part of at least one plasticizing agent. The process comprises (i) a pre-expansion stage by heating the expandable beads so as to form pre-expanded beads with a bulk density of 40 to 190 g/l, (ii) a stabilization stage by contacting the pre-expanded beads with a gaseous medium at 0 to 40° C.