GB893048A - Process for making expansible polymers - Google Patents

Abstract

In producing expandable beads of a thermoplastic polymer which may be heated to form a cellular product, an aqueous suspension containing granules of the polymer, a substantially water-insoluble inorganic carrier agent and an organic liquid expanding agent having a boiling point at normal pressure below the polymer softening point, is heated, e.g. for 1 to 10 hours, under a pressure greater than atmospheric and at a temperature higher, e.g. by 25 DEG to 50 DEG C., than the softening point of the polymer and is then cooled to below the polymer softening point, e.g. to room temperature, before releasing the pressure. The polymer, which may contain a small amount of monomer, may be polystyrene, methyl polymethacrylate or copolymers such as vinylacetate-vinyl chloride, styrene-acrylonitrile, styrolene-a methyl styrolene, whilst as carrier agent Group II or III metal carbonates or phosphates, e.g. hydroxyapatite, may be used, e.g. in amount within 0,1 to 1%, by weight, of the treated polymer. As expanding agents hydrocarbons compatible with, but non-solvent for, the polymer and having a critical temperature lower than the maximum temperature attained during the process may be used, e.g. saturated or unsaturated aliphatic and cyclic hydrocarbons and halogen or nitrogen derivatives thereof. If desired the expanding agent may be added to an aqueous polymer granule/carrier agent suspension which has already been heated above the softening point of the polymer and the temperature then progressively increased to the desired degree above this point.ALSO:In producing expandable beads of a thermoplastic polymer which may be heated to form cellular structures, an aqueous suspension containing granules of the polymer, a substantially water-insoluble inorganic carrier agent and an organic liquid expanding agent having a boiling point at normal pressure below the polymer softening point, is heated, e.g. for 1 to 10 hours, under a pressure greater than atmospheric and at a temperature higher, e.g. by 25 to 50 DEG C, than the softening point of the polymer and then cooled to below the polymer. Softening point, e.g. the room temperature, before releasing the pressure. The polymer, which may contain a small amount of monomer, may be polystyrene, methyl polymethacrylate or copolymers such as vinyl acetate-vinyl chloride, styrene-acrylonitrile, styrolene-a methyl styrolene, whilst as carrier agent Group II or III metal carbonates or phosphates, e.g. hydroxyapotite, may be used, e.g. in amount within 0,1 to 1% by weight of the treated polymer. As expanding agents hydrocarbons compatible with the polymer but non-solvent therefor and having a critical temperature lower than the maximum temperature attained during the process may be used, e.g. saturated or unsaturated aliphatic and cyclic hydrocarbons and their halo-and introgen derivatives and if desired, the expanding agent may be added to the suspension of polymer and carrier agent which has already been heated to a temperature higher than the polymer softening point and the temperature then progressively increased to the desired degree above this point.