5 - Miscellaneous and specialty foams: Epoxy Foams, Polyester Foams, Silicone Foams, Urea-Formaldehyde Foams, Polybenzimidazole, Foams, Polyimide Foams, Polyphosphazene Foams, and Syntactic Foams

Abstract

This chapter discusses thermosetting foams and presents additional material of interest on syntactic foams. Syntactic foams are made using a resin matrix to which hollow spheres of various materials have been added. The resultant product is foam like material made without the use of a blowing agent. The most common matrix resins are epoxies and polyesters, although urethanes, PVC plastisols, and phenolic resins have also been used. Indeed, any polymer that can be made liquid, either before final polymerization or by heat, can be used as the binding resin. In syntactic foams, the resin matrix is the continuous phase and the hollow spheres the discontinuous phase. The foam elements in syntactic foams may be glass microspheres, with diameters ranging from 20 to 200 microns, or other spheres with diameters ranging from 0.05 mm to 2 em, which are classed as macrospheres. The materials used to form the spherical particles are glass, phenolic resins, silica, and naturally occurring materials such as perlite and coal dust. The most commonly used materials are glass and phenolic spheres. The syntactic foams are made by simply mixing the microspheres or macrospheres into the catalyzed resin until the desired consistency is obtained. In most cases the materials are mixed to a patty-like state or, if a casting material is desired, to a state in which the material can just be cast.