Properties of Rigid Urethane Foams

Properties of Rigid Urethane Foams. General. Almost all physical properties of rigid urethane foams depend on their foam densities, as shown in the following equation  

Mean Mnipartlura, 7S f. Alummyni tiaa smmI AttO two yaar at 70-IWF. and Sa96% RN OanMy. 

DISTANCE FROM EDGE OF PANEL, inches (Relationship disenssed and illustrated in Foam Bulletin 60-5-23) 

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Du Pont de Nemours Co.(Inc.)., Properties of Rigid Urethane Foams, June 21, (1963), Revised Sept. 1966, In a booklet "New Information About Urethane Foam made with Du Pont Hylene". 

Flexible polyurethane foams are blown with water, methylene chloride, and chlorofluorocarbons (CFCs). Carbon dioxide from the water/isocyanate reaction functions as the blowing agent. The methylene chloride and CFCs assist in the blowing and contribute properties such as added softness and resilience. The CFCs also contribute to the insulation properties of rigid urethane foams. 

Frisch, K.C., "Relationship of Chemical Structure and Properties of Rigid Urethane Foams," Journal of Cellular Plastics, 1(2) 325-330 (April 1965). 

SOME PHYSICAL PROPERTIES OF RIGID URETHANE FOAMS. 

Piechota, H. 5ome correlations between raw materials, formulation, and flame retardant properties of rigid urethane foams. Journal of Cellular Plastics, 1(1), 186-199 (1965). 

Properties superior to those of rigid urethane foams are as follows ... 

Urethane foams can be classified into two principle types, i.e., flexible and rigid foams. In some cases, flexible foams can be further subdivided into flexible and semi-flexible (or semi-rigid) foams. The differences in physical properties of the two foams are mainly due to the differences in molecular weight per cross-link, the equivalent weight and functionality of the polyols, and the type and ctionality of the isocyanate. 

C linkages and are hydrolytically unstable others do not contain a silicone-carbon bond and are stable. In general, higher-viscosity silicone copolymers are more efficient and wiU provide foams with finer cell structures. Surfactants are used at the 0.5% to 1% level in rigid urethane foams. With too little silicone foam, cell structure is large. Too much silicone does not affect the foam properties, but is wasteful. There is no known health hazard with the use of silicones (20). 

The physical properties for Reaction-Injection-Molded urethane foam cannot readily be determined because they are, as all sandwich structures, highly dependent on the particular shape of the article and the ratio of skin to foam or, in other words, the density distribution through the part. Typical densities for these new structural foams are 30 — 45 lbs./ft.3 with average moduli of elasticity of 120,000 — 250,000 p.s.i. The compression strengths are higher than those shown in Table VI for rigid foams without skins. 

Due to the low cost, the excellent physico-mechanical properties of the resulting urethane - isocyanuric foams, thermal and fire resistance and low level of smoke generation, the most important applications of aromatic polyester polyols are for rigid PU/PIR foams in the boardstock market (continuous rigid foam lamination) and for building insulation. 

Isocyanates react with polyether polyols to produce polyurethane foams. The amount of polyether polyol required varies widely depending on the desired properties of the finished urethane however, a typical flexible urethane contains about 55% propylene oxide and a typical rigid urethane contains about 30% [9]. 

Though closed-cell rigid polyurethane foams are excellent thermal insulators, they suffer form the drawback of unsatisfactory fire resistance even in the presence of phosphorus- and halogen-based fire retardants. In this context, polyisocyanurates, which are also based on isocyanates, have shown considerable promise. Isocyanurate has greater flame resistance then urethane. Although rigid polyurethane is specified for the temperatures up to 200°F (93°C), rigid polyisocyanurate foams, often called trimer foams, withstand use temperatures to 300°F (149°C). Physical properties and insulation efficiency are similar for both types. 

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