Correlation between indenter modulus and elongation-at-break observed for four electrical insulating polymers

The correlation between degradation-induced changes in two important indicators of mechanical properties, namely elongation at break (EAB) and indenter modulus (IM), is examined for flame-retardant ethylene propylene rubber (FR-EPR), silicone rubber (SiR), flame-retardant crosslinked polyethylene (FR-XLPE), and XLPE. The samples were degraded by heat or concurrently by heat and radiation. In the case that the polymers become hard after they were degraded, the two indicators show a good correlation. However, if they become brittle, their correlation is not good. Regarding this, their correlation is good in SiR, while it is not good in FR-XLPE and XLPE. In FR-EPR, the correlativity changes, depending on the aging condition and presumably its additives.