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Accelerated thermal ageing test on nanocomposites of polyvinyl chloride (PVC/SiO 2) is conducted at constant temperatures of 110 °C and 140 °C. Accordingly, different PVC/SiO 2 nanocomposite samples with different silicon dioxide (SiO 2) filler loading are prepared. The preparation of the samples was carried out based on the solution casting technique. The loading concentrations of SiO 2 in the investigating samples are 0, 1, 2.5, 5 and 7.5 wt%. The breakdown strength of the prepared PVC/ SiO 2 nanocomposite samples is evaluated before and after the thermal ageing test. The evaluation of breakdown strength is carried out based on American Society for Testing and Materials (ASTM) standard. Also, dielectric spectroscopy, which includes dielectric constant (έ) and tangent loss (tan δ) of nanocomposite, is performed before and after the thermal ageing test. Also, the mass losses during thermal ageing of all samples are evaluated. The results show that the breakdown strength, tan δ, and the dielectric constant (έ) of pure PVC and PVC/SiO 2 nanocomposites are significantly affected by the thermal ageing test. Adding a small amount of SiO 2 nanoparticles to PVC leads to improvement in its dielectric properties before and after the thermal ageing process as compared to the pure PVC. The mass loss of PVC/SiO 2 nanocomposite during thermal ageing is less than that of pure PVC and confirms the obtained result from breakdown strength.

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Iron oxide (α‐Fe2O3) nanocrystals powder was successfully synthesized via the sol‐gel method. The microstructural examination of the synthesized nanocrystals confirmed the formation of α‐Fe2O3 (hematite) structure using X‐ray diffraction and Fourier transform infrared. The synthesized nano‐hematite powder with different weight percentage up to 5 wt% was introduced to polyvinyl chloride (PVC) to fabricate PVC/Fe2O3 nanocomposites using the solution‐cast technique. The dielectric spectroscopic analysis for the investigated samples has been studied at room temperature and at different temperatures up to 120°C. The real part of the permittivity (ε′) exhibited a significant dependence on filler concentrations throughout whole temperature range. However, the dependency of both of the loss tangent (tanδ) and AC conductivity (σac) on filler concentrations is more pronounced at temperatures higher than room temperature. The obtained values of tan δ for the investigated nancomposites referred to the α‐relaxation around 70°C, which is close to glass transition temperature of the investigated PVC. The dependency of the dielectric strength on Fe2O3 nanofiller concentration was observed with enhancement in the dielectric strength reach to 20.5% for PVC/0.7 wt% Fe2O3 nanocomposite higher than the recorded value for the pristine PVC.

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