Comparative Effects of Al2O3 and SiO2 Nanofillers on the Thermal, Mechanical, and Electrical Properties of XLPE Cable Insulation

Al2O3 and SiO2 nanofillers have been widely used to improve the insulation performance of cross-linked polyethylene (XLPE) for high-voltage power cables. In this work, XLPE nanocomposites containing 3 wt.% Al2O3 or SiO2 were prepared to compare the effects of the two nanofillers on the thermal, mechanical, and electrical properties of XLPE. Hydrophobic surface treatment was applied to improve nanofiller compatibility with the polymer matrix. Differential scanning calorimetry and thermogravimetric analysis were used to evaluate crystallinity and thermal stability. Tensile and creep tests were performed to assess mechanical behaviour, while volume resistivity, dielectric constant, and breakdown strength under AC, DC, and DC polarity-reversal fields were measured at 30 °C and 90 °C. The results showed that Al2O3-filled XLPE had higher crystallinity and a higher initial decomposition temperature than SiO2-filled XLPE, together with lower creep elongation, indicating better thermal and dimensional stability. In contrast, SiO2-filled XLPE exhibited higher elongation at break, a lower power-frequency dielectric constant, and improved breakdown strength. Hydrophobic surface treatment increased volume resistivity and breakdown strength and reduced data dispersion for both nanocomposites, suggesting that improved interfacial compatibility and more homogeneous microstructures contributed to performance enhancement. Overall, Al2O3 mainly improved thermal endurance and creep resistance, whereas SiO2 was more effective in enhancing dielectric and mechanical properties. These findings provide guidance for selecting nanofillers for XLPE nanocomposite insulation in high-voltage cable applications.