Dual‐Role Maleic Anhydride‐Grafted Ethylene‐Propylene Diene Monomer Compatibilizer for Enhanced Thermal, Mechanical, and Ablative Performance of EPDM ‐Based Nanocomposite Insulators

ABSTRACT

Ethylene‐propylene diene monomer (EPDM)‐based charring ablative nanocomposites containing clay, fumed silica, and ceramic fiber were investigated. To improve the dispersion of polar fillers in the nonpolar EPDM matrix, maleic anhydride‐grafted EPDM (EPDM‐g‐MA) was introduced as a compatibilizer at 0, 3, and 6 phr. EPDM‐g‐MA exhibited a concentration‐dependent dual role: acting as a compatibilizer at low loading (3 phr) and as a plasticizer at high loading (6 phr). The optimal concentration improved filler dispersion while mitigating plasticization. EPDM‐g‐MA enhanced polarity, as confirmed by contact angle measurements (130° → 114° → 97°) and SEM‐EDS elemental mapping, which showed more homogeneous Si, O, and S distributions. FTIR revealed changes in the Si–O–Si and O–H bands, indicating interfacial interaction. Mechanical characterization confirmed the dual role: tensile strength increased progressively (3.00 → 3.83 → 4.49 MPa) due to improved interfacial adhesion, while Young's modulus decreased at 3 phr (6.58 MPa) and partially recovered at 6 phr (7.32 MPa). The composite with 3 phr EPDM‐g‐MA exhibited the best ablative performance: lowest back‐face temperature (52°C ± 5°C), highest residual mass (85.6%), and a linear ablation rate (0.016 ± 0.01 mm/s) comparable to the uncompatibilized control and significantly lower than 6 phr (0.068 ± 0.009 mm/s). BET analysis of the charred surface showed that EM‐03 had the highest specific surface area (11.701 m ² /g) and pore volume (0.1093 cm ³ /g), while EM‐06 showed densification. Char compressive strength was highest for EM‐03, consistent with a dense, continuous char layer. At 6 phr, excessive plasticization reduced matrix cohesion, leading to a fragmented char and deteriorated ablative performance. These results demonstrate that EPDM‐g‐MA enhances elastomeric insulator performance through optimal filler dispersion and char structure reinforcement, with 3 phr being the optimal concentration.