Image Number 14 for United States Patent #8119701.
Disclosed is a method for making polystyrene foam which utilizes one or more atmospheric gases, particularly combinations of HFCs and CO.sub.2, as the blowing system in combination with a polymer processing aid (PPA), typically an ester that is relatively non-volatile at the extrusion temperature range. The blowing system and the PPA may both be introduced into the molten thermoplastic polystyrene resin or the PPA may be incorporated in the solid source polystyrene resins. The resulting foams will typically exhibit improved dimensional stability at ambient temperatures.
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