Polystyrene foams structural foam process

Impact polystyrene with ignition-resistant additives is used for appliance housings, such as those for television and small appliances. Structural foam impact polystyrene modified with flame-retardant additives is used for business machine housings and m furniture because of its decorability and ease of processing. Consumer electronics, such as cassettes, reels, and housings, is a fast growing area for use of polystyrenes. Medical applicatiuns include sample collectors, petri dishes, and test lubes. 

While unaffected by water, styrofoam is dissolved by many organic solvents and is unsuitable for high-temperature applications because its heat-distortion temperature is around 77°C. Molded styrofoam objects are produced commercially from expandable polystyrene beads, but this process does not appear attractive for laboratory applications because polyurethane foams are much easier to foam in place. However, extruded polystyrene foam is available in slabs and boards which may be sawed, carved, or sanded into desired shapes and may be cemented. It is generally undesirable to join expanded polystyrene parts with cements that contain solvents which will dissolve the plastic and thus cause collapse of the cellular structure. This excludes from use a large number of cements which contain volatile aromatic hydrocarbons, ketones, or esters. Some suitable cements are room-temperature-vulcanizing silicone rubber (see below) and solvent-free epoxy cements. When a strong bond is not necessary, polyvinyl-acetate emulsion (Elmer s Glue-All) will work. 

Whereas all conventional thermoplastic fabrication techniques have been successfully employed to convert pellets of HIPS into useful articles, extrusion (film, sheet, profile and multi-layer) and injection molding (solid, structural foam and gas-assist) are the predominant processing technologies. Innovative hardware technologies, in both extrusion and injection molding, have provided means to combine less expensive materials, such as polystyrene, with polymers or structures offering key performance characteristics. 

The experimentally determined cell diameters depend not only on the type of the starting polymer but also on the composition of the blowing agent and the foaming process. Thus, the critical parameters of the cellular structures of unpressed polystyrene foams of grades PSB and PSB-S are ... 

Many solid adsorbents liberate gas as a result of desorption of volatile liquids under the influence of heat. Typical adsorbents with microporous structures such as activated carbons, or precipitated silicas and renewable resources have been used as a coblowing agent in producing low-density extruded polystyrene foam boards. Incorporation of corn cobs or other renewable vegetable matter containing about 10% water together with a primary PBA into polystyrene in the extrusion process produced a low-density polystyrene foam board with bimodal cellular structures. This type of foam with bimodal cell structures has about 10-15% lower K-factor than similar foams without bimodal cellular structures. Similar results were obtained with a precipitated silica for producing a low-density extruded polystyrene foam with bimodal cellular structures. ... 

A variety of foams can be produced from various types of polyethylenes and cross-linked systems having a very wide range of physical properties, and foams can be tailor-made to a specific application. Polypropylene has a higher thermostability than polyethylene. The production volume of polyolefin foams is not as high as that of polystyrene, polyurethane, or PVC foams. This is due to the higher cost of production and some technical difficulties in the production of polyolefin foams. The structural foam injection molding process, described previously for polystyrene, is also used for polyethylene and polypropylene structural foams (see Figure 2.61). 

Modified Poiyphenyiene Ether Thermoplastic polyphenylene ether alloys with impact polystyrene. Has good impact strength, resistance to heat and fire, but poor resistance to solvents. Processed by injection and structural foam molding and extrusion. Used in auto parts, appliances, and telecommunication devices. Also called MPE, MPO, and Modified Polyphenylene Oxide. 

Polystyrene is an aromatic polymer made from styrene, an aromatic monomer which is commercially manufactured from petroleum. Polystyrene is commonly injection moulded or extruded while expanded polystyrene is either extruded or moulded in a special process. Solid polystyrene is used in disposable cutlery, plastic models, CD and DVD cases, etc. Foamed polystyrene is mainly used for packing materials, insulation, foam drink cups, etc. Polystyrene foams are good thermal insulators and therefore used as building insulation materials such as in structural insulated panel building systems. They are also used for non-weight-bearing architectural structures. The information on OPF-polystyrene composites is limited. 

Styrofoam (Dow Chemical Co.) is the tradename for expanded polystyrene foam. It is made by a process similar to the one described for foamed polyethylene. The materials have a closed-cell structure with very low thermal conductivity and low moisture absorption. One of the serious limitations of polystyrene foam is its rather low maximum operating temperature of approximately SO C. It is used mainly as thermal insulation in buildings, flotation apparatus, decorations, and packaging. 

This chapter describes the development and manufacture of the Thorn 1 IC 40 Model television-screen frame, sandwich moulded in high-impact polystyrene (HIPS) by Elco Plastics Ltd, Hemel Hempstead. The sandwich moulding (SM) process is described in some detail in PST 2 and comparisons are drawn with structural foams (SF) which share many common features with SM. 

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