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Abstract

Method and apparatus are provided for treating (e.g., recycling) polystyrene foam scrap particulate in a manner which increases the density of the polystyrene while minimizing an amount of heat required to convert the polystyrene into densified solid polystyrene plastic (e.g., polystyrene flakes), thereby avoiding noticeable polymer degradation. The invention involves first heating polystyrene particulates to a semi-molten state in a heating zone so that polystyrene particulates coalesce. Pressure is then applied in a pressure zone to the polystyrene while the polystyrene is coalescing. The pressure is applied by a pressure mechanism which crushes the heated and softened polystyrene, and which preferably maintains the pressure on the polystyrene until the polystyrene cools below the softening temperature of the polystyrene. The pressure mechanism squeezes essentially all gases (entrained air and expansion gases) from the polystyrene, and thus precludes, e.g., the rebounding of the polystyrene to a pre-crushed density. The retention of sustained pressure by the pressure mechanism obviates utilization of a degree of heat which would melt the polystyrene to its completely liquid (molten) state. The sustained crushing and cooling of the polystyrene by the pressure mechanism enhances the bulk density of the polystyrene, producing polystyrene chips or flakes having an average thickness in a range of about 0.010 inch to about 0.035 inch. The heater and the pressure mechanism which comprise the apparatus of disclosed techniques and apparatus facilitate treating the polystyrene to obtain an enhanced bulk density throughput index .rho. in excess of 500, advantageously enhancing density even when polystyrene of a low input density is utilized.

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