Thermal conductivity of oriented polymer films

The effect of stretching on the thermal cond. of polyethylene (PE) films is presented and compared to results obtained previously for oriented polyacetylene films and PE fibers. As expected, the longitudinal thermal cond. increases with the stretching level and thermal cond. values comparable to those obsd. on metallic alloys are obtained on ultra-drawn PE films. Above a certain stretching level which depends on the polymer, the thermal cond. does not increase any more and becomes either independent on an increase in the drawing level or decreases with it. In the transverse direction, the thermal cond. is slightly lower than that of the isotropic polymer at high temp. The temp. dependence of the transverse thermal cond. of drawn films varies much like that of the isotropic polymer, while the longitudinal cond. decreases more rapidly with decreasing temp. (T2 variation). On the drawn PE films, a dip is obsd. in the temp. dependence between 8 and 17 K, both in the longitudinal and in the transverse direction. This anomaly is much pronounced in the transverse direction.