Polystyrene thermal conductivity

Fig. 3. Aging effect on thermal conductivity of cellular plastics A, extmded polystyrene B, unfaced polyurethane C, unfaced phenolic and D, polyurethane...

Polyurethane. Polyurethanes (pu) are predominantly thermosets. The preparation processes for polyurethane foams have several steps (see Urethane polymers) and many variations that lead to products of widely differing properties. Polyurethane foams can have quite low thermal conductivity values, among the lowest of all types of thermal insulation, and have replaced polystyrene and glass fiber as insulation in refrigeration. The sprayed-on foam can be appHed to walls, roofs, tanks, and pipes, and between walls or surfacing materials directly. The slabs can be used as insulation in the usual ways. 

For materials of equivalent density water-blown polyurethanes and the hydrocarbon-blown polystyrene foams have similar thermal conductivities. This is because the controlling factor determining the conductivity is the nature of the gas present in the cavities. In both of the above cases air, to all intents and purposes, normally replaces any residual blowing gas either during manufacture or soon after. Polyurethane foams produced using fluorocarbons have a lower thermal conductivity (0.12-0.15 Btu in fr h °F ) (0.017-0.022 W/mK) because of the lower conductivity of the gas. The comparative thermal conductivities for air, carbon dioxide and monofluorotrichloromethane are given in Table 27.3. 

Except where the foam is surrounded by a skin of relatively impermeable material, it would be expected that the blowing gas would diffuse out and be replaced by air and that the thermal conductivities of the foams would increase until they approached that of expanded polystyrene of similar density. Whilst this... 

Figure 4.35 Thermal conductivity of expanded polystyrene beads as a function of density. Reprinted, by permission, from The Dow Chemical Company. Copyright 1966.

Fig. 4. Thermal conductivity of cellular plastics A, extruded polystyrene, 32 kg/m3 B, polyurethane, 32 kg/m3 and C, PVC foam, 32 kg/m3.

Colloid characterization is not the classical application of Th-FFF. Nevertheless, Th-FFF was first applied to silica particles suspended in toluene testing a correlation between thermal diffusion and thermal conductivity [397]. Although a weak retention was achieved, no further studies were carried out until the work of Liu and Giddings [398] who fractionated polystyrene latex beads ranging from 90 to 430 nm in acetonitrile applying a low AT of only 17 K. More recently, polystyrene and polybutadiene latexes with particle sizes between 50 pm and 10 pm were also fractionated in aqueous suspensions despite the weak thermal diffusion [215] (see Fig. 30). Th-FFF is also sensitive to the surface composition of colloids (see the work on block copolymer micelles), recent effort in this area has been devoted to analyzing surfaces of colloidal particles [399,400]. 

Values of the thermal conductivity, k, have been determined in the present work with a thermal conductivity probe (24). It has long been known that sulfur has a low thermal conductivity although the values are even lower in such materials as PVC and expanded polystyrene. Sulfur-bonded composites made with inexpensive fillers such as soil and sand have thermal conductivities which are below those of typical portland cement concrete but with values higher than those of sulfur itself. The values for the composites are, however, still low as may be seen by comparison with the values for conductors such as steel and copper (Table II). 

Figure 10.3 Effect of density on thermal conductivity of rigid cellular polymers. A, polystyrene [25] B, polystyrene [37] C, polyurethane-air [37] D, polyurethane-CFC 11 (CCI3F) [70] E, polyurethane [37] F, phenol-formaldehyde [37] G, ebonite [37]. To convert kg/m3 to Ib/ft3, multiply by 0.0624. Reproduced from F. O. Guenther, SPE Transactions, 2, 243 (1962), with permission from the society of Plastics Engineers, Brookfield, Connecticut, USA...

Cellular polymers, especially polystyrene and polyurethane, are also widely used for pipe and vessel insulation. The use of cellular rubber and cellular poly(vinyl chloride) in insulation for small pipes is attributed to their ease of application, combustion properties, and low thermal conductivity. 

Dow and BASF have independently developed polystyrene foam formulations that do not contain HCFCs or HFC blowing agents [88,113-118], Since these foams do not contain captive gases that have desirable insulating properties, the use of infrared attenuators has been employed to improve the thermal conductivity of the foam products. 

Introduction. It has been recognized that CFC-ll-blown rigid urethane foams are the insulation materials with the lowest thermal conductivities, in comparison with other insulation materials, such as water-blown rigid urethane foams, glass-fiber materials, or polystyrene foams. 

This type of foam is available in two forms, extruded-polystyrene foam and expanded polystyrene for molded foams. Polystyrene foams are light, closed-cell foams with low thermal conductivities and excellent water resistance. They meet the requirements for low-temperature insulation and buoyancy media (6). 

Urea-formaldehyde foams are usually brittle structures with low compressive strength (under 50 psi or 0.34 MPa). The term "frangible" may be applied to them. They are open-cell, sponge-like foams that can absorb large quantities of water. Hiese foams also exhibit thermal and acoustical insulating properties common to low-density foams. For example, their thermal conductivities range within the values quoted for polystyrene foam (0.24 - 0.33). This is the result of their low density and snail cell size (5). 

AH 103 EPS 303 Guidelines for Reporting Thermal Transmission Properties of Polystyrene Foam Insulating Materials, Thermal Conductance, and Transmittance of Built-Up Construction Systems. 

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