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As mentioned in Section 8.1, the main use for rigid polyurethane foam is as a source of insulation. The primary industries utilizing rigid polyurethane foams are the construction and the appliance applications [5]. Even applications under the heading "other" in Figure 8.6 serve the purpose of insulation as used for pipe and tank insulations or insulation from vibration and noise when used in automotive cavity filling. The foam differences in these different applications are minor compared with the differences with for instance, flexible foams. The differences that do exist are a result of optimization for the purpose of meeting performance or processing requirements unique to the particular application. For instance, spray foam insulations must provide a high degree of flame retardance and very rapid gelation so that the spray insulation can be applied to vertical surface with minimal dripping or sag [6]. In contrast appliance foams must also form quickly, but not so quickly that the injected formulation cannot fill a mold cavity with any structural encumbrances to flow that may exist [7]. Further, appliance rigid foam must contribute substantially to the overall appliance structural stability, but not deform the appliance exterior in any way. Finally, as a widely used consumer material with energy-saving functions, polyurethane rigid foams have been the target of governmental regulation and performance requirements that have driven demand and innovation. The manner in which foam designers cope with these demands—some of these demands conflicting with each other—is discussed in the Sections 8.2 and 8.3.

Construction Foams

Rigid polyurethane foams used for construction purposes must serve the insulation and energy conservation goals of the application and not act in any detrimental way to the overall structural integrity of the building [8]. Construction is an immensely complex market [9], and the development of polyurethane rigid foams has proliferated several methods of delivering insulation properties to the building site. Polyurethane rigid foams are produced in composite panels, in two-component spray foams, and more recently in aerosol spray cans.

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