Rigid polyurethane foam thermal insulation

Rigid polyurethane foams are mostly based on polyether alcohol and are highly cross-linked. Rigid foams are many times blown by halogenated alkanes like trichlorofluoromethane. These foams have closed cell structures and are used for thermal insulation. Semi-rigid foams are used in car crashpads and packaging. 

Rigid polyurethane foam is used primarily as thermal insulation for buildings, trucks, rail cars, shipping containers, tanks, pipelines, cold-storage warehouses, and frozen food display cases. 

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. 

AX-113 An Assessment of the Thermal Performance of Rigid Polyurethane Foam Insulation for Use in Building Construction (U-108). 

It is estimated that 615 million pounds of rigid polyurethane foam were made during 1979.(1). The market for these foamed plastics has been growing at an annual 15 percent rate for the last few years. It is projected that similar growth may resume in future years. The construction market is the key to future growth, as the greatest share of rigid polyurethane foam is used in thermal insulation applications. 

This condition is expected to improve gradually. The consumption of rigid polyurethane foams as thermal insulation can be expected to increase with the renewed building activity. 

In other installations, there might be a gap between the foam and the required thermal barrier, thus permitting air intrusion. The phenomenon of decreasing R-value has presented the industry with a dilemma. What is the proper statement to make about the thermal resistance of one s rigid polyurethane foam insulation The lower the R-value statement you make, the less competitive your product will be. In the past, it has been difficult to advertise the aged R-values when your competition advertises only the initial R-values. 

The main field of polyurethane application is the furniture industry, around 30% of the total polyurethanes produced worldwide is used for the production of mattresses from flexible slabstock foams. Automotive manufacture is the second important application for flexible and semiflexible polyurethanes (seat cushioning, bumpers, sound insulation, and so forth). Rigid polyurethane foams are used in thermal insulation of buildings and refrigerators, cold stores, pipe insulation, refrigerated transport, thermal insulation in chemical and food industries. The polyurethane elastomers are used for shoe soles,... 

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. 

Rigid polyurethane foam, injected as a liquid, forms a good adhesive bond to most surface layers, and it has a relatively high Young s modulus. Consequently, the sandwich structure performs efficiently in terms of bending stiffness per unit panel mass (Chapter 4). Lightweight sandwich panels are used in roofs and walls. If thermal insulation is of paramount importance, as in cold stores, the foam thickness can be increased to 125 mm. 

Rigid polyurethane foam is mainly useful for thermal insulation. 

Nieuwenhuyse, E. (2006) Thermal Insulation Materials Made of Rigid Polyurethane Foam, Report No. 1, Brussels, Belgium Foundation of European Rigid Polyurethane Foam Associations. 

Plastics — rigid polyurethane foam, expanded polyst3u-ene, honeycomb, crosslinked PVC foam (one of the most important core materials), poljnnethacrylimides, other plastics foams (excellent thermal insulation, weaker and more expensive than paper). 

Isocyanate/Isocyanurate. Isocyanates react with polyols to form rigid polyurethane foams, a major type of thermoset plastics. While these are very useful in thermal insulation, they are limited by failure at high temperature and by flammability. One way to solve these problems is to convert part of the isocyanate to isocyanurate by cyclotrimeriza-tion (Fig. 3.64). Whereas the isocyanate-polyol reaction forms polyurethane rapidly at room temperature, the cyclotrimeiization of isocyanate to isocyanurate requires strong alkaline catalysis and heat to compete successfully. The resulting isocyanurate rings build considerable heat resistance (150 to 250°C, short-term <800°C) and flame-retardance into the polyurethane foam. They are useful for insulating pipelines and boilers. 

EN 13165, Thermal Insulation Products for Buildings - Factory Made Rigid Polyurethane Foam (PU) Products - Specification, 2012. 

Replacement of CFCs in rigid polyurethane foams has been a much more serious problem, since the main use of these foams is as heat insulators and the main property required is therefore low thermal conductivity. Blowing gases of high... 

Rigid polyurethane foam is often poured into cavities, providing both thermal insulation and physical strength. Aircraft carrier hulls and refrigerators and freezers are insulated by in-place applied rigid polyurethane foam. 

Prociak [49] studied the effect of the method of sample preparation, the temperature gradient, and the average temperatnre of measnrement on the thermal conductivity of rigid polyurethane foams blown with hydrocarbons and hydrofluorocarbons. The thermal insulation properties of different cellular plastics, such as rigid and flexible polyurethane foams, as well as expanded polystyrene, were compared. The thermal conductivity and thermal diffusivity of foams were correlated with the polyurethane matrix structure to demonstrate the effect of cell anisotropy on the thermal insulation properties of the rigid foams blown with cyclopentane and HFC-365/227 (93 wt% pentafluorobutane/7 wt% heptafluoropropane). 

Rigid polyurethane foams are closed-cell structures which are usually produced with a density of about 2 Ib/ft. Since the major interest in rigid foams has been for thermal insulation, the thermal conductivity of the foams is a physical property of some importance. About 97% of the volume of a typical foam is occupied by gas, the nature of which therefore has an appreciable effect on the thermal conductivity. This point is illustrated by Table 14.4 which shows the conductivities of various gases and foams. Newly made carbon dioxide-blown foam has low conductivity but the carbon dioxide rapidly diffuses through the polymer and is replaced by air the conductivity therefore increases until it reaches the value for air-filled foam. Trichlorofluoromethane diffuses very slowly and an equilibrium appears to be reached when the air to fluorocarbon in... 

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