EXPANDABLE POLYSTYRENE COMPOSITION

A polystyrene (PS) composition (I) in the form of expandable beads based on (1) 100 parts by weight (pts. wt.) styrene polymer and (2) 2.2-4.0 pts. wt. blowing agent(s) also contains (3) 0.01-0.4 pt. wt. plasticiser(s). Independent claims are also included for (1) a method (M1) for the production of (I) in one or more stages, one of which involves the (co)polymerisation of styrene in aqueous suspension (2) a method (M2) for the production of medium-density expanded PS objects from (I), by thermal pre-expansion to give beads with an apparent density of 40-190 g/l, followed by stabilisation in air for 6-48 hours at 0-40[deg]C and 50-160 kPa (abs.) and then processing in a heated mould (3) pre-expanded beads with an apparent density of 40-190g/l, containing 100 pts. wt. styrene polymer, 0.5-3.0 pts. wt. blowing agent and 0-0.4 pt. wt. plasticiser (4) a method (M3) for the production of pre-expanded beads with an apparent density of 40-190 (preferably 50-125) g/l by thermal pre-expansion of (I) (5) medium-density expanded PS objects made from (I) or from the above pre-expanded beads by the above methods, with a density of 40-190 (preferably 50-125) g/l .