EFFECT OF THERMAL CYCLING ON DC CONDUCTIVITY AND MORPHOLOGY OF POLYETHYLENE

The effects of long period repeated thermal cycling in the presence of d.c. electric field on the d.c. conductivity, morphology and degree o f crystallinity of low density polyethylene (LDPE) were investigated. D.C. conductivity measurements indicate that a reasonable steady state conductivity could be achieved after a period of 10 days of thermal c ycling between 80 degrees C and 40 degrees C in the presence of a d.c. electric field across the sample followed by another LO days of condu ctivity measurements at constant temperature of 80 degrees C. Crystall inity evaluation as well as morphological investigations using scannin g electron microscopy (SEM) of etched surfaces of the material before and after thermal cycling and conductivity measurements show that the investigated material has undergone structural changes after that long period of thermal cycling and conductivity measurements. An attempt i s made to correlate between the d.c. conductivity results and the obse rved structural changes in the material.