Three commercial fiber optic sheathing compounds (a thermoplastic, a filled organic elastomer, and a silicone rubber) and three model systems (a polyethylene, an ethylene-propylene rubber, and an aluminum-hydroxide-filled elastomer) were investigated. The thermal properties of the materials were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). From the thermal studies (DSC, TGA, and laser ablation) it is concluded that the resistance of the linear low-density polyethylene to surface discharge activity should be considerably worse than that of the other two materials considered, a result that is consistent with service experience. At low temperatures this stems from the absence of cross-links which, in the other two materials, serve to restrict flow. Where temperatures reach much higher levels, the presence of inorganic fillers becomes an important factor in resisting thermal erosion. Thus, on the basis of the results obtained, the performance of the silicone material should be superior to that of the ethylene-based elastomer. Laser irradiation constitutes a useful means of inducing localized heating.
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