Effect of heat and saline water on the hydrophobic behavior of EPDM insulator.

摘要

This is a study of the aging characteristics and the mechanisms responsible for the loss and recovery of hydrophobicity in EPDM insulator, under stress conditions of heat, water salinity and the time length of aging.; Aging characteristics of EPDM insulator were determined under combined stresses of thermal, and immersion in saline solution as a function of time, by measuring the static contact angle of water droplets on the surface of insulator specimens and variations in the weight of specimens. EPDM specimens were aged by placing in stationary air and in water with different salinity levels, 5x10-3, 1, 10 and 100 mS/cm, at 0, 25, 50, 75 and 98°C, for up to 6000 h.; The effect of two cleaning methods on the contact angle of water on the surface of EPDM specimens was also studied. In the first cleaning method the surface of the specimens was cleaned with a constant spray of distilled water for about 2 minutes. In the other method, the specimens were washed and cleaned in distilled water with an ultra soft toothbrush.; The surface of EPDM was studied to investigate the effect of heat and water salinity during the aging process. ATR-FTIR spectroscopy, SEM and EDS were employed to study the physical and chemical changes on the surface.; The surface free energy and its relation to hydrophobicity was investigated. The surface energies of EPDM were determined by measuring the contact angles of water and methylene iodide during the aging process.; The recovery of hydrophobicity of EPDM specimens was investigated after removing them from the stress conditions and keeping them in stationary air at room temperature for up to 4000 h. The contact angle of water and the variations of the weight of the specimens were measured intermittently during the recovery process.; LMW fluid content of EPDM specimens was extracted by immersing them in analytical hexane. The composition of the extracted LMW fluid was investigated by the application of several identification techniques, including GC-MS, IR spectroscopy and NMR spectroscopy. It was shown that the extracted LMW fluid contained dioctyl adipate, an ester of octanol and adipic acid. Effect of heat in regeneration of the LMW fluid was also investigated.; It is suggested that in EPDM, generation of the LMW fluid in the bulk and its migration to the surface and to the top of the contamination layer maintains the hydrophobicity of the insulator in wet and contaminated conditions.