GB988289A - Improved process for making foamable thermoplastic polymers - Google Patents

Abstract

A process for the production of foamable, spherical or substantially spherical polymer particles, such as beads, by the incorporation of a blowing agent into a particulate thermoplastic polymer by impregnation at a temperature above the softening point of the polymer but below its decomposition temperature and at elevated pressure while agitating in the presence of water and of a dispersing agent is characterized in that the dispersing agent is an organic high molecular weight polymeric water-soluble or water-dispersible sulphonated polymer or a mixed substituted derivative of cellulose. The sulphonated polymers have a molecular weight of one million or more. The mixed substituted derivatives of cellulose have a 2% aqueous solution viscosity of above 300 centipoises and are thermally stable or decompose only slowly at the treating temperatures used in the process. Carboxymethyl methyl celluloses and sulphonated vinyl aromatic polymers are suitable dispersing agents. Water-miscible organic compounds can be added to the impregnating medium. The polymers and blowing agents may be the same as those used in the process of Specification 988,290. The polymer particles may have the shape described in that Specification or may be spheres, beads or ground, crushed or broken particles. Bromine-containing organic compounds may be added during or after the impregnation step. The resulting flame-proofing effect is increased by also adding an organic peroxide to the impregnating mixture. In examples (1) pentane is fed into a pressure vessel containing a stirred mixture, at 135 DEG C., of polystyrene particles suspended in water containing carboxymethyl methyl cellulose, ammonium salt of sulphonated polyvinyltoluene, ammonium sulphate, sodium lauryl sulphate and petroleum ether. The product is foamed in an open chamber with steam at 99 DEG to 102 DEG C.; (2) a butadiene-styrene copolymer is similarly impregnated, carboxymethyl methyl cellulose being the dispersing agent; (3) extruded rods of polystyrene are similarly impregnated with normal pentane, 1,2-dibromo-1,1,2,2-tetrachloroethane and dicumyl peroxide, the product having the form of beads (which, when foamed, are self-extinguishing if ignited); (4) saturated hydrocarbons (b. pt. 30 DEG to 60 DEG C.) are used in a similar process to that of Example 1.