Foam, Plastic

Name:
Foam, Plastic
Detailed information:
A cellular plastic that may be either flexible or rigid. Flexible foams may be polyurethane, rubber latex, polyethylene, or vinyl polymers; rigid foams are chiefly polystyrene, polyurethane, epoxy, and polyvinyl chloride. The blowing agents used are sodium bicarbonate, halocarbons such as CCl₃F, and hydrazine. Flexible polystyrene foam is available in extruded sheets and also in the form of beads made by treating a polystyrene suspension with pentane; these expand from 30 to 50 times on heating and are used as automobile radiator sealants. Rigid foams are widely used for boat construction, filtration, fillers in packing cases, absorption of oil spills, and building insulation. The latter application involves a fire risk described below.

Hazard:

The most widely used types of organic foam plastics (polystyrene, polyurethane, polyisocyanurate) are combustible; even when fire-retardant agents are incorporated, such foams will burn. The extent of burning or fire severity will vary with surface treatment, end-use location, recipe, and degree of protection. Thin coatings of fire-retardant paint, metal, or automatic sprinkler systems may not adequately protect against rapid fire spread. Organic foamed plastic surfaces should not be left exposed. Multiple adjacent surfaces such as walls and ceiling create a most severe hazard because of the chemical kinetics associated with radiative, conductive, and convective currents developed during a building fire. New methods of making such plastic foams as polyurethane that are reported to reduce their combustibility have been developed, for example, use of trichlorobutylene oxide instead of propylene oxide. Use of urea-formaldehyde foams for building insulation has been restricted in some areas due to potential toxic effect of the formaldehyde.