AC breakdown of melt-crystallized isotactic polypropylene

• Published in: Journal of applied polymer science 1988-05, Vol.35 (6), p.1459-1472
• Main Authors: Krishnakumar, B., Gupta, R. K., Forster, E. O., Laghari, J. R.
• Format: Article
• Language: English
• Subjects: Applied sciences; Electrical, magnetic and optical properties; Exact sciences and technology; Physical properties; Polymer industry, paints, wood; Properties and testing; Technology of polymers
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.1988.070350605

The effect of polymer morphology on the dielectric breakdown of isotactic polypropylene was investigated under the influence of a ramped ac voltage. Samples were prepared by melt‐pressing polypropylene beads into plaques and subsequently quenching or isothermally cyrstallizing these plaques. Some of the quenched samples were annealed at different temperatures to induce further crystallinity. The plaques were then characterized by wide‐angle X‐ray diffraction, density measurements, and differential scanning calorimetry. The 60 Hz, ac breakdown voltages of the samples were determined at 7°C, 23°C, and 45°C in a specially designed test cell. There was a lack of any significant effect on the ac breakdown strength of isotactic polypropylene of either the overall crystallinity or the crystallite thickness. This result can be understood in light of previous studies relating the electrical breakdown of polymers to morphology. It is postulated that the degree of crystallinity would influence the breakdown characteristics only when the amorphous regions constitute a small fraction of the total volume, that is, at very high crystallinity values—values beyond the range of the present study.