| 摘要 |
An expandable thermoplastic composition is prepared by passing polystyrene, powdered polyethylene, the quantity of polystyrene used exceeding the quantity of polyethylene used, and a blowing agent boiling below the incipient softening point of the polystyrene through a screw extruder in which the polystyrene and polyethylene become molten, extruding the molten composition at a temperature greater than the softening temperature of the polystyrene and polyethylene before they have had an opportunity to expand, and quenching the extruded mixture to a temperature less than the softening temperature of the polystyrene and polyethylene. The expandable thermoplastic composition so produced may be pelletized before moulding. Instead of adding the blowing agent separately to the composition it may be incorporated in the polystyrene prior to mixing in the extruder. Suitable blowing agents are aliphatic hydrocarbons boiling between 20 DEG C. and 100 DEG C., e.g. pentane. In addition pellets of the expandable composition may be coated with a multi-component blowing agent of citric acid monohydrate and sodium bicarbonate prior to the moulding process. The compositions are described as being moulded in the shape of bottles and boards.
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