Electrically conducting systems based on polymers—II. Investigations of the structure of conductive compositions based on hardened resins

Abstract

In the previous work the basic principles of the formation of conductive systems from uncured resins were dealt with [1]. The present work is concerned with the examination of the hardening process whereby the materials under examination pass gradually from the viscous-flow to the solid state during the period of observation. The authors followed the structural changes occurring during the hardening of compositions based on a phenol-formaldehyde resole resin and the epoxide resin E-40 containing various proportions of acetylene black, and compared the results with the results of the measurement of electrical properties. In experiments on the hardening of the resins the specimens were held for a suitable time at a high temperature—the phenol-formaldehyde compositions at +150° and the epoxide compositions at +80°. In order to study the structural changes occurring during the curing process an apparatus was designed, which in conjunction with a Polyani dynamometr and a PMT-3 micro hardness gauge enabled the variation in viscosity of the polymeric systems during hardening to be followed. The apparatus was a modification of the Volarovich and Tolstoi dynamometer [2] in conjunction with a Polyani dynamometer. By measuring the limiting load P required to stretch rods of the hardened compositions it is possible to determine the absolute shear stress.