Synergistic Effects of Multiple Aging Stressors on HDPE and HDPP

Abstract

The service life for power cables in our nation’s nuclear power plants have been extended beyond 40 years, however no reliable test has been found for determining the remaining lifetime of a cable in service. With experimental data and simulated models, a test and material lifetime prediction are being developed based on changes in electrical, mechanical, and chemical properties as a function of service conditions, temperature, aqueous exposure, material, and time. While it may be next to impossible to test every condition or environment for a material lifetime study, analytical models based on accelerated aging can attempt to predict both tested and untested conditions. By using models obtained from experimental data produced during accelerated aging studies, changes in mechanical properties, chemical properties, and even visual properties can be combined to better understand and more accurately predict aging.The first step to understanding insulation degradation is to understand how environmental conditions like water, temperature, and mineral or an aqueous environment affects polymer aging and how that might accelerate or decelerate aging. The aim of this thesis is to cover what effects combining these conditions might have on polyethylene and polypropylene tensile samples at a moderately elevated temperature. Additionally, how might cycling of conditions age or degrade these samples differently from samples continuously submerged. Tensile properties, hardness measurements, and surface chemical characterization of carbonyl formation through the attenuated total reflection were measured and calculated to determine the synergistic effects of aging polyethylene and polypropylene in distilled water, a copper sulfate solution, and Harrison’s solution at 90ºC through common mechanical properties and aging indicators. Additional studies were started aging both materials at elevated temperatures and oxygen partial pressures, and submersion in water. Results suggest that at 90ºC these mixed conditions did not accelerate aging over dry aged samples within a 16-week period and more time or a greater temperature would be required to create a greater difference between conditions.