The effect of ozone on polymer degradation in Polymer Core Composite Conductors

The matrix material of high voltage Polymer Core Composite Conductors used in the next generation power transmission is generally a moderately high temperature epoxy, which has the potential of experiencing extreme aging effects in-service, including severe ozone degradation. It is well known that polymers are susceptible to oxidation by ozone, due to chain scission and the breaking of crosslinks. It is also known that ozone is present around high voltage transmission systems and its concentration rapidly increases close to energized transmission lines. Therefore, the primary goals of this study were to investigate (1) the effects of aging in ozone at room temperature of a high temperature epoxy, which could be used in the polymer composite conductors and (2) the effect of ozone exposure on a hybrid polymer matrix composite rod, presently used in-service. It was found using nanoindentation that the ozone oxidation depth on the surface of neat resin specimens was limited to about 120 μm. It was also observed that exposure to 1% ozone for up to three months at room temperature did not negatively affect the flexural performance of either the neat resin epoxy, or the composite. Comparatively small variations in the bending strength and deformations of the specimens were associated with an initial increase in crosslinking of the epoxy followed by a small increase in chain scission and bond breaking. These effects also demonstrated themselves in the type of the viscoelastic behavior of the polymer after aging. The scission of the polymer chains in the neat resin and rod specimens was further evidenced by FTIR spectroscopy, where the aged neat resin specimens showed an increase in absorption around the 3500 cm^-1 wavenumber associated with the formation of carbonyl groups and carboxylic acids.