The low temperature thermal conductivity of isotropic and oriented polymers

Abstract

The thermal conductivity, kappa , has been measured as a function of temperature between 2K and 100K of polycarbonate (PC), polyvinyl chloride (PVC) isotactic polypropylene (PP), polyoxymethylene (POM), and polyethylene terephthalate (PET). For the latter three systems the variation of kappa on extrusion has also been investigated. The polymers studied include specimens of widely ranging morphologies, and an attempt is made to show how all the results fit into a coherent pattern. Some of the specific results of this and related work are: (i) For isotropic polymers the values of kappa at 2K are highest in completely amorphous polymers whereas at 100K the greatest conductivity is observed in crystalline specimens. (ii) The temperature dependences of kappa in the most highly conducting isotropic crystalline polymers exhibit maxima near 100K. (iii) For extruded crystalline polymers there is a marked anisotropy in kappa that is much greater above approximately 25K, and which increases with the degree of extrusion.