Recovery of hydrophobicity of ethylene propylene diene monomer aged by heat and saline water

The recovery of hydrophobicity of ethylene propylene diene monomer (EPDM) insulator after aging by long exposure to a stress of saline water at different temperatures is investigated. The hydrophobicity is determined by measuring the contact angle of a droplet of distilled water on EPDM rubber. The aging of EPDM rubber was done by immersing it for up to 576 h in saline water solutions in the range 5.0-10/sup 5/ /spl mu/S/cm. The aging temperatures were 0, 25, 50, 75 and 98/spl deg/C. After aging, the specimens were kept in air at room temperature for up to 2,500 h during which the recovery of hydrophobicity and weight changes were measured. From these results, surface free energy and diffusion coefficients of EPDM rubber were evaluated.