High-density polyethylene thermal conductivity

The thermal conductivity of a section of a commercially produced high density polyethylene foam channel was measured. The walls consisted of a 6.4 mm foam core with a skin of 1.6 mm thickness on either side. Sqnares were machined from the outer surface of the channel, so that heat flow throngh the entire thickness the core pins one skin layer and the complete section conld be... 

For amorphous polymers, the increase in thermal conductivity in the direction of the draw is usually not higher than two. Figure 2.4 [24] presents the thermal conductivity in the directions parallel and perpendicular to the draw for high density polyethylene, polypropylene, and polymethyl methacrylate. A simple relation exists between the anisotropic and the isotropic thermal conductivity [39], This relation is written as... 

Various methods have been described for the determination of thermal conductivity. Capillarity has been used to measure the thermal conductivity of low-density polyethylene, high-density polyethylene, and polypropylene at various temperatures and pressure [50]. A transient plane source technique has been applied in a study of the dependence of the effective thermal conductivity and thermal diffusivity of polymer composites [51]. 

A laser flash technique has been used to determine the diffusivity of pyroelectric polymers such as polyvinylidene fluoride [83], whereas hot-wire techniques have been used to determine the thermal diffusivity of high-density polyethylene, low-density polyethylene propylene, and polystyrene [83], Dos Santos and coworkers [84] utilized the laser flash technique to study the effect of recycling on the thermal properties of selected polymers. Thermal diffusivity expresses how fast heat propagates across a bulk material, and thermal conductivity determines the woiking temperature levels of a material. Hence, it is possible to assert that those properties are important if a polymer is used as an insulator, and also if it is used in applications in which heat transfer is desirable. Five sets of virgin and recycled commercial polymers widely used in many applications (including food wrapping) were selected for this study. 

Dao-Long et al. [9] reported that the mechanical properties of these composites are improved significantly over these of nnreinforced high-density polyethylene. Also, increasing the alumina content improves the thermal conductivity of the polymer. 

Krupa Igor, Cecen Volkan, Boudenne Abderrahim, Prokes Jan, and Novak Igor. The mechanical and adhesive properties of electrically and thermally conductive polymeric composites based on high density polyethylene filled with nickel powder. Mater. Design. 51 (2013) 620-628. 

Polyethylenes (PE) have been used for cables and pipes for cold water services for many years. They are comparatively easy to extrude with good thermal stability at about 150-180 °C for low-density polyethylene (LDPE) and LLDPE and about 175-200 °C for high-density polyethylene (HOPE). They are also competitively priced. However their applications are limited by a comparatively low upper service temperature limit. This applies to both continuous use under pressure at up to 100 °C for hot water pipes and occasional excursions to significantly higher temperatures supported by the conducting wire due to temporary electrical overload of a cable. 

Polyethylene, in eommon with other nonpolar materials, has no free electrons that can readily eonduet thermal energy. Therefore it conducts heat only by the transmission of vibrational or rotational energy from one chain segment to another, either inter- or intramolecularly. The transmission of thermal energy is more efficient in crystallites, where chain sequences are in closer proximity, than in disordered regions. Thus high density polyethylene is a better conductor of heat than low density polyethylene. Table 9 lists the heat conductivity of various polyethylene samples, selected polyolefins and engineering plastics, and some eommon nonpolymerie materials. 

Banford et al. studied the radiation effects on electrical properties of low-density polyethylene (LDPE) at 5 K with the use of a 60Co gamma source and a thermal nuclear reactor [86]. They reported that both the electrical conductivity and the dielectric breakdown strength of LDPE at 5 K were not significantly affected by radiation absorbed doses up to 10s Gy, but an erratic pulse activity under high applied fields was observed in the sample irradiated at 106 Gy. 

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