Effect of filler on thermal aging of composites for next-generation power lines

The thermal aging of pultruded composite rods was investigated to determine the effects of filler on oxidation kinetics and degradation mechanisms. The unidirectional hybrid composite rods were comprised of a carbon-fiber core, a glass-fiber shell, and an epoxy matrix filled with clay particles. A reaction-diffusion model was implemented for each of the two hybrid sections to calculate the oxygen-concentration profile and the thickness of the oxidized layer (TOL) within the composite rods, and results were compared with measured oxidation kinetics. The TOL was measured for samples exposed isothermally in air and in vacuum at 200 °C for up to 13,104 h (1.5 year), and the measured values were similar to modeling predictions (within 10%). The domain validity for the reaction-diffusion model was determined from gravimetric experiments (weight-loss measurement), which showed that after prolonged thermal exposure, the degradation mechanism changed from thermal oxidation to thermal degradation. Thermogravimetric analysis (TGA) was performed to determine the thermal degradation and stability of the aged composite. In addition, the effect of thermal aging on glass transition temperature (Tg) and short beam shear (SBS) strength was determined for isothermal exposures at 180 °C and 200 °C.