ABSTRACT
Plastics fall into the category of materials of intermediate thermal conductivity (0.15-0.4 W/mK). They are an order of magnitude more conductive than foams and insulation but about five times less conductive than ceramics and glass. This puts them in an unique class by themselves. They have not been heavily characterized in the past for many reasons: the measurements have been difficult, with highly variable results, coupled with a lack of demand. In recent years, the need for thermal conductivity data has grown dramatically. This important property is essential in almost every heat transfer calculation, from such basic applications as component heat conduction and dissipation to the complex computer programs used to simulate plastics manufacturing processes. In the latter case, because thermoplastics are typically processed in the melt state, the use of roomtemperature-measured thermal conductivity data may result in serious errors, because the melt state thermal conductivity of polymers can differ significantly from solid-state values. Empirical rules have been used in the past to estimate melt state values from the typically available solid-state data. These rules are often suspect because have they been based on avail-able information in the literature, which is scarce and often inaccurate, especially at high temperatures. Additionally, some rules do not take into consideration effects such as those of crystallinity, composition, or matrix-filler interfacial contact, on which thermal conductivity is strongly dependent. Theoretical studies on the thermal conductivity of polymers have been hampered by the inconsistency and paucity of experimental data.
