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 a polymeric foam product, the method comprising:
preparing a polymeric melt from a major amount of a polystyrene polymer and a minor amount of at least one additive according the formula:
wherein X is nitrogen or oxygen, and wherein R 5 is selected from the group consisting of C 1 -C 20 alkyl, aryl, alkaryl, and alkoxylate;
injecting carbon dioxide into the polymeric melt to form a foamable mixture; and
extruding the foamable mixture through a die into a region of reduced pressure.
2. A method of manufacturing a polymeric foam product according to claim 1 , wherein the at least one additive is selected from the group consisting of:
3. A method of manufacturing a polymeric foam product according to claim 1 , wherein the at least one additive provides a density of about 2.25 pcf in the polymeric foam product.
4. A method of manufacturing a polymeric foam product according to claim 1 , wherein the amount of the at least one additive is adjusted to provide a desired open cell content in the polymeric foam product.
5. A method of manufacturing a polymeric foam product according to claim 1 , wherein the polystyrene polymer and the at least one additive are precompounded prior to the injection of carbon dioxide.
6. A method of manufacturing a polymeric foam product according to claim 1 , further comprising injecting one or more blowing agents in addition to said carbon dioxide into the polymeric melt to form the foamable mixture.
7. A method of manufacturing polymeric foam according to claim 6 , wherein the one or more additional blowing agents comprises a hydrofluorocarbon (HFC).
8. A method of manufacturing polymeric foam according to claim 7 ,
wherein the one or more additional blowing agents comprise 1,1,1,2-tetrafluoroethane (HFC-134a).
9. A method of manufacturing polymeric foam according to claim 6 , wherein the carbon dioxide comprises less than about 4% by weight of the foamable mixture.
10. A method of manufacturing polymeric foam according to claim 9 ,
wherein the carbon dioxide comprises between about 0.5% by weight and about 1.5% by weight of the foamable mixture.
11. A method of manufacturing polymeric foam according to claim 6 , wherein the at least one additive comprises less than about 1% by weight of the foamable mixture.
12. A method of manufacturing polymeric foam according to claim 6 , wherein the at least one additive comprises from about 0.5% by weight to about 1.5% by weight of the foamable mixture.
13. A foam board manufactured by the method of claim 6 .