THERMAL-CONDUCTIVITY IN ULTRAORIENTED POLYETHYLENE

On a set of strips of ultraoriented polyethylene of ultrahigh molecular weight the thermal diffusivity has been measured at room temperature. The draw ratio lambda was between 12 and 250. The diffusivity increases with draw ratio and begins to level off at about lambda = 50. The maximum diffusivity alpha approximately 1.9 X 10(-5) M2/s corresponding to a thermal conductivity of k = 37.5 W/mK obtained in the stretching direction is 4 times that of steel. In the perpendicular direction the diffusivity decreased to alpha = 10(-7) M2/s (i.e., half its initial value). The plot of conductivity versus modulus enables an extrapolation to the ultimate modulus (300 GPa), yielding k" less-than-or-equal-to 80 W/mK. This value being higher than that of many metals corresponds to a crystal in the impurity-governed range i.e., the lower limit of crystal thermal conductivity.