Dielectric Properties of Polyether Sulfone/Bismaleimide Resin Composite Based on Nanolumina Modified by Super-Critical Ethanol

Abstract

Nano-alumina was chemically modified with super-critical ethanol enabling a surface active coating. Modified nano-alumina was incorporated in polymer blends based on thermoplastic polyether sulfone and thermosetting bismaleimide resin to produce novel nanocomposites designated as SCE-Al₂O₃/PES-MBAE. In the SCE-Al₂O₃/PES-MBAE nano-composites, the matrix was originally formed from 4,4′-diamino diphenyl methane bismaleimide (MBMI) using the diluents of 3,3′-diallyl bisphenol A (BBA) and bisphenol-A diallyl ether (BBE), while polyether sulfone (PES) was used as toughening agent along with super-critically modified nano-alumina (SCE-Al₂O₃) as filler material. The content of SCE-Al₂O₃ was varied from 0 wt.% to 6 wt.%. The nano-composites were characterized for their morphological, spectroscopic and dielectric properties. Fourier transform infrared spectroscopy (FT-IR) indicated that ethanol molecules had adhered to the surface of the nano-Al₂O₃ in super-critical state. A reaction between MBMI and allyl compound occurred and SCE-Al₂O₃ was doped into the polymer matrix. Volume resistivity of the composite initially increased and then decreased. The modification due to SCE-Al₂O₃ could overcome the undesirable impact of PES by using a bare minimum level of SCE-Al₂O₃. The dielectric constant (ε) and dielectric loss (tan δ) as in the case of volume resistivity were initially increased and then decreased with the content of SCE-Al₂O₃ in the composite. The dielectric constant, dielectric loss and dielectric strength of SCE-Al₂O₃ (4 wt.%)/PES (5 wt.%)-MBAE nano-composite were 3.53 (100 Hz), 1.52 × 10⁻³ (100 Hz) and 15.66 kV/mm, respectively, which indicated that the dielectric properties of the composite fulfilled the basic requirements of electrical and insulating material. It was evident from the morphological analysis that the SCE-Al₂O₃ was evenly dispersed at the nanoscale; for example, the size of SCE-Al₂O₃ in SCE-Al₂O₃ (4 wt.%)/PES (5 wt.%)-MBAE measured less than 50 nm.