Method of manufacturing polystyrene foam with polymer processing additives
Disclosed is a method for making polystyrene foam which utilizes one or more atmospheric gases, particularly CO 2 , as the blowing agent in combination with a polymer processing aid (PPA), typically an ester that is relatively non-volatile at the extrusion temperature range. The blowing agent 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 foam will be substantially free of residual blowing agent and dimensionally stable at ambient temperatures.
1. A method of manufacturing polymeric foam, the method comprising:
preparing a polymeric melt from a major amount of a polymer composition having a melt flow index of at least about 10 g/10 min and at least one additive comprising bis(n-decanyl) adipate;
injecting a blowing agent composition comprising carbon dioxide as a primary blowing agent and a hydrofluorocarbon (HFC) as a secondary blowing agent into the polymeric melt to form a foamable mixture, wherein the carbon dioxide comprises less than about 4% by weight of the foamable mixture; and
extruding the foamable mixture through a die into a region of reduced pressure.
2. The method of manufacturing polymeric foam according to claim 1 , wherein the HFC comprises 1,1,1,2-tetrafluoroethane (HFC-134a).
3. The method of manufacturing polymeric foam according to claim 1 , wherein the carbon dioxide comprises between about 0.5% by weight and about 1.5% by weight of the foamable mixture.
4. The method of manufacturing polymeric foam according to claim 1 , wherein the at least one additive comprises less than about 1% by weight of the foamable mixture.
5. The method of manufacturing polymeric foam according to claim 1 , wherein the at least one additive comprises from about 0.5% by weight to about 1.5% by weight of the foamable mixture.
6. A foam board manufactured by the method of claim 1 .
7. The method of manufacturing polymeric foam according to claim 1 , wherein the at least one additive provides a density of about 2.25 pcf in the polymeric foam.
8. The method of manufacturing polymeric foam according to claim 1 , wherein the polymer composition and the at least one additive are precompounded prior to the injection of the blowing agent composition.