Abstract :
The electric strength of polythene in the absence of surface discharges decreases sharply above room temperature, and there is evidence that this is an electromechanical effect. An optical-lever system, suitable for measuring electromechanical strains in recessed polythene specimens at 80° C, showed that true compressive strains were masked by a much larger movement of the whole recess caused by lateral expansion in the compressed polythene. When the movement was suppressed, no electromechanical compressions were detected, and there were indications of a significantly higher electric strength. The existence of an electromechanical effect was confirmed by comparing electric strengths of three grades of polythene over a range of temperatures and detecting differences caused by impulse and slowly applied d.c. electric stresses.
