Polystyrene foamable

Property ASTM Test Phenolics Foamedin Syntactic Place Castable Polyvinyl Chloride Rigid Closed Cell Phenylene Oxide Foamable Resin Polycarbonate Polystyrene Medium-Density Foam Polystyrene Molded Extruded Polyurethane Rigid Closed Cell... 

Foamable polystyrene beads are generally produced by two basic processes ... 

Insecticides, and particnlarly termiticides, may be dissolved in monomers polymerised to form foamable polymers, snch as polystyrene. The resulting monomer and insecticide may then be polymerised in a conventional manner and either impregnated with a blowing agent or expanded using an extrasion process to produce polymeric foam having insecticidal properties. The polymer may also contain a flame retardant. Such polymers and the foam made therefrom may be used in the constraction industry, particularly where insect infestation is a concern. 

Example 5.24 Preparation of Foamable Polystyrene and of Polystyrene Foam... 

Of critical importance, analysis of poly(methyl methacrylate) (PMMA) showed that at a saturation temperature, T, of 40°C, a saturation pressure, P%, of 1,500 psig (at these conditions, carbon dioxide is considered a supercritical fluid), and a saturation time, ts, of 24 h, a 1 mm thick disk absorbed 16.4 wt% carbon dioxide. Additionally, at a foaming temperature, Tf, of 120°C and a foaming time, tf, of 1 min, PMMA had a stable volumetric expansion ratio of 20. Other polymers also absorbed significant quantities of carbon dioxide, such as polystyrene (PS) and poly(vinylidene chloride-co-acrylonitrile) (P(VDC-AN)), which absorbed 8.9 and 2 wt% carbon dioxide, respectively, yet the stable foams that were formed had expansion ratios of less than 2 at the same conditions used to form the PMMA samples. Another polymer poly(vinyl methyl ketone) (PVMK) achieved an expansion ratio of 20. However, the foams were unstable, readily collapsed, and exhibited large voids ( 5 mm diameter), which are inconsistent with microcellular foams. The fact that PVMK readily collapsed after the foaming process made it difficult to determine the concentration of carbon dioxide in the sample. These results led to the eventual incorporation of the MMA monomer into the polymer formulation from the standpoint of carbon dioxide-induced microcellular foamability. 

Two dominant processes have developed for the production of PS foam extrusion and expansion of foamable beads. For polystyrene, the polymerization process is endothermic and, therefore, requires external heat. This requirement essentially eliminates the in situ application of insulation as is possible with the exothermic PU foams. 

---