Rigid and Semirigid Foams

Many tests commonly applied to plastics in the form of solids, elastomers, coatings, and sealants may of course also be applied to cellular plastics. For example, notched impact strength tests can be applied to high-density structural foams, and it is very common to quote Shore hardness values for skin hardnesses of rigid and semirigid foam moldings. It is the intention here, however, to restrict the discussion to tests derived exclusively for plastics containing a cellular structure. 

Available forms. Blanket (felt and batt), block, cements, loose fiU, foil and sheet, formed or foamed in place, flexible, rigid, and semirigid. 

Carwinate []. TM for isocyanates used to make urethane elastomers, coatings, foam adhesives, rigid plastics, sealants, and one-shot flexible, semiflexible, and semirigid foams. 

Rigid foam PS, PU, and phenolic resin, and the semirigid foam of PE were examined with regard to their mechanical properties. The effects of preloading the foams on their mechanical properties are discussed. 

Semirigid foam is usually tested using methods normally applied to rigid or flexible foams. In some instances they are tested for ultimate elongation (as a percentage to BS903. Part A2 [74]). The surface hardne.ss is also important in. some molded part applications, and that property can be measured using standard Shore A hardness procedures. 

A rigid foam is defined as one in which the polymer matrix exists in the crystalline state or, if amorphous, is below its Tg. Following from this, a flexible cellular polymer is a system in which the matrix polymer is above its Tg. According to this classification, most polyolefins, polystyrene, phenolic, polyycarbonate, polyphenylene oxide, and some polyurethane foams are rigid, whereas rubber foams, elastomeric polyurethanes, certain polyolefins, and plasticized PVC are flexible. Intermediate between these two extremes is a class of polymer foams known as semirigid. Their stress-strain behavior is, however, closer to that of flexible systems than to that exhibited by rigid cellular polymers. 

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