A. General statements

Polymer materials (Novichenok and Shulman, 1971) are widely used as electric, thermal, and cooling insulators or as elements undergoing thermal effects. To estimate correctly the strength, operating and thermal characteristics we need to allow for their dependence on the rheological factor and, in particular, for mechanical history (orientation during production with one or another draw velocity).

The thermal conductivity of oriented polymers is a tensor quantity which is dependent on the strain direction relative to the heat flux vector. Figure 1a illustrates a noticeable increase in λ_∥ along the draw axis and a decrease in λ_⟘ in the transverse direction. In semicrystalline polymers, the orientation causes high anisotropy of the thermal conductivity which decreases with lower temperature. Thus, with relative draw ϵ = 13, λ_∥/λ_⟘ = 10 for high-density polyethylene, while at T < 10 K this ratio is 1.5.

Figure 1 Anisotropic thermal conductivity of some polymers vs. degree of uniaxial draw

B. Design relations