Expandable polystyrene thermal conductivity

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.

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). 

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). 

A 1 kg product that must be kept at a temperature of 0°C is packaged with 2 kg of ice in a 1.5 cm thick expanded polystyrene container, with inside dimensions measuring 0.4 m x 0.4 m x 0.6 m. How long will the product be protected The thermal conductivity of the polystyrene foam is 0.030 w/m K. The outside temperature is constant at 25°C. 

Expanded polystyrene products have widely increased the market for polystyrene resin (see the section on polystyrene foams in Chapter 2). With as light a weight as 2 Ib/ft (0.032 g/cm ), the thermal conductivity of expanded polystyrene is very low, and its cushioning value is high. It is an ideal insulation and packaging material. Common applications include ice buckets, water coolers, wall panels, and general thermal insulation applications. 

Expanded polystyrene foam (EPS) has different applications, because of its physical form (beads) and properties (higher permeability to water and less effective adhesion to facing materials than polyurethane). The expansion gases, pentane and steam, escape fairly rapidly from the foam, so the thermal conductivity of the foam filled with air is about twice that of the best polyurethane foam—a 50 mm thick slab of foam has a U-value of 0.5-0.6 Wm K . EPS mouldings can be used as shutters (formwork) for pouring concrete in a composite wall. The two EPS layers are connected at intervals to fix the thickness of the concrete. Extruded polystyrene foam (XPS) is used in plank form for insulation imder the concrete floor of houses, and in roofing panels. 

THERMAL CONDUCTIVITY, SPECIFIC HEAT, HYGROSCOPICITY, AND WATER ABSORPTION IN EXPANDED POLYSTYRENE. REHANEKJ TRUXAK PLASTICKE HMOTY KAUCUK... 

Styrofoam (Dow Chemical Co.) is the tradename for expanded polystyrene foam. It is made by a process similar to the one described for foamed polyethylene. The materials have a closed-cell structure with very low thermal conductivity and low moisture absorption. One of the serious limitations of polystyrene foam is its rather low maximum operating temperature of approximately SO C. It is used mainly as thermal insulation in buildings, flotation apparatus, decorations, and packaging. 

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). 

By such methods, it is possible to prepare polystyrene foam with density as low as 1 Ib/ft. This material has extremely low thermal conductivity, being comparable to expanded cork and glass wool in this respect. 

Polystyrene (PS) is prepared by the polymerization of styrene (CeHs—CH=CH2), also known as vinylbenzene. Commercial PS is mostly of the atactic variety and is therefore amorphous. The polymer, on decomposition, unzips and forms the monomer with some benzene and toluene. Its major defects are poor stability to weather exposure, turning yellow and crazing in sunlight. In spite of these drawbacks and its brittleness it has found wide use as molded containers, Uds, bottles, electronic cabinets. As a foamed plastic it is used in packaging and insulation. The thermal conductivity of the expanded PS foam is about 0.03 Wm K The foam can absorb aromatic hydrocarbons usually found in the exhaust of automobiles and buses, causing the foam to disintegrate after long periods of normal exposure to a polluted environment. 

Applications of expanded polystyrene Insulation Polystyrene foam at densities below llOkg/m exhibits a thermal conductivity X (u) of 0.037 W/m.K (k = 0.26 Btu.in/ft h°F). As a general rule, therefore, polystyrene foam insulation must be 70% thicker than a urethane foam to provide equivalent heat loss characteristics, but since material costs are substantially lower for polystyrene both foams are used depending upon requirements. 

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