Additional Rigid-Foam Types

Discussions on cross-linked vinyl foams, which are rigid, can be found below under Vinyl Foams, and rigid cellular cellulose acetate (CCA) foams and polysulfone foams are discussed in the section under Miscellaneous Foams. 

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Flame-retardant rigid foams can be classified by the testing methods employed, but the results do not reflect actual fire situation. Fire-retardant rigid urethane foams can be prepared by using flame retardants of the additive type, reactive type, or a combination thereof. A review of flame retardants for polyurethane foams has been prepared by Hilado (154). 

Neither of the first two foam types can be considered to be thermodynamically stable. The third class, the solid foams, could be so considered since they possess a mechanically rigid structure formed as a result of a (presumably) irreversible chemical process during or just after foam formation. Although formulations for the production of solid foams contain additives such as surfactants and blowing agents to produce the foam matrix, their action in sustaining the foam stracture is negligible. Such foams therefore are not discussed fiuther here. 

The physical properties of rigid polyurethane foam are usually a function of the foam density. A change in strength properties requires a change in thermal insulation. In addition to density, the strength is influenced by the catalyst, surfactant, polyol, isocyanate and type of mixing used. 

Surfactants are used to control cell development. Both cell size and shape are affected to the extent that, without surfactant additives, large irregular cells may develop or the foam may collapse altogether. The most widely used type of surfactant for rigid-closed cell PU foams is based on silicone copolymers, although organic types, such as sulfonated castor oil and amine esters of fatty acids, are also used. 

In addition to the already mentioned effects in terms of attaining both flexible and rigid PU foams with improved mechanical performance, enhanced electrical conductivity, or even improved fire retardancy or sound damping, depending on the type of... 

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