Dielectric and Chemical Properties of Polypropylene-Based Nanocomposites

Cross-linked polyethylene (XLPE) is widely used in high-voltage cables but presents recycling challenges due to its permanent chemical bonds. Polypropylene (PP) is a recyclable alternative, though its dielectric properties require enhancement. Nanofillers such as metal oxides can improve PP's performance, but their tendency to absorb moisture limits effectiveness. Zinc iron oxide (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{ZnFe}_{2} \mathrm{O}_{4}$</tex>), with low moisture absorption and good thermal stability, offers potential advantages, although its dielectric effects in PP remain underexplored. This study investigates the effect of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{Z n F e}_{\mathbf{2}} \mathbf{O}_{\mathbf{4}}$</tex> nanofillers on the dielectric properties of PP nanocomposites. Nanocomposites were prepared with filler loadings of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.5 \text{wt}. \%$</tex>, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1 \text{wt}. \%, 2 \text{wt}. \%$</tex>, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5 \text{wt}. \%$</tex> to evaluate their structural and electrical behavior. Structural interactions were characterized using FTIR spectroscopy. Dielectric properties were measured using dielectric spectroscopy over a range of frequencies. Dielectric breakdown strengths under AC and DC were tested according to ASTM D149 and D3755 standards. FTIR spectroscopy confirmed interactions between <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{ZnFe}_{2} \mathrm{O}_{4}$</tex> and the PP matrix, indicating potential structural modifications, while dielectric spectroscopy revealed an increase in real permittivity (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\varepsilon^{\prime}$</tex>) with nanofiller content, particularly at lower frequencies, due to interfacial polarization. Pure PP exhibited the highest breakdown strength (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$158 \pm 8 \text{kVmm}{ }^{-1}$</tex> for AC and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$327 \pm 10 \text{kVmm}^{-1}$</tex> for DC), and PP with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.5 \text{wt}. \% \text{ZnFe}_{2} \mathrm{O}_{4}$</tex> had comparable values. However, at 5 wt.% nanofiller concentration, breakdown strength decreased significantly to (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$144 \pm 10 \text{kVmm}^{-1}$</tex> for AC and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$203 \pm 23 \text{kVmm}^{-1}$</tex> for DC), suggesting that while <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{ZnFe}_{2} \mathrm{O}_{4}$</tex> enhances permittivity, excessive filler content leads to charge accumulation and structural inhomogeneities, ultimately reducing dielectric strength, particularly under DC conditions.