Advanced Coatings Based on Nanocomposites of Epoxy with 2-D Hexagonal Boron Nitride Nanosheets

Abstract

Incorporating nanofillers into organic coatings is an effective method of improving their long-term corrosion resistance. Due to their electrical insulation, hydrophobicity, and chemical inertness, boron nitride nanosheets (hBNNS) have piqued the interest of researchers. The practical application of hBN in polymer composites is limited by surface incompatibility and the tendency to form aggregates, hindering long-term corrosion protection. Surface modification of nanoparticles promotes dispersion and improves adhesion to substrates, which are crucial for corrosion resistance. This thesis offers a comparative corrosion protection study of epoxy nanocomposite coatings incorporated with hBN, hBNNS, and functionalized hBNNS fillers. The nanosheets are functionalized with 3-aminopropyltriethoxysilane (APTES), Polyethyleneimine (PEI), and Perfluorooctyl-triethoxysilane (FTS). The impact of the filler/nanofiller type and loading on the corrosion protection of composite coatings is investigated. Ball milling treatment is used to exfoliate hBN to hBNNS, where XRD depicted peak (002) broadening and intensity reduction, corresponding to lowered particle thickness. Exfoliation introduced hydroxyl groups linked to the boron atoms on the surface of hBNNS, providing active sites for surface modification. The cross-sectional surface fracture SEM images of functionalized hBNNS/EP coatings, confirmed presence of tortuous pathway for corrosive ions to diffuse into the coating, compared to EP, hBN/EP, and hBNNS/EP coatings. The water contact angle was increased by incorporation of functionalized hBNNS, from 86° for hBNNS/EP to 91.0°, 90.5°, and 98.7° for the hBNNS-APTES/EP, hBNNS-PEI/EP, and hBNNS-FTS/EP. Electrochemical impedance spectroscopy (EIS) was employed to assess the long-term corrosion resistance of coatings submerged in a 3.5 wt.% NaCl aqueous solution. After 90 days of immersion, the impedance modulus (Zf=0.01 Hz) of epoxy nanocomposite coatings containing 0.25 wt.% hBNNS functionalized with APTES, PEI, and FTS was 8.85, iii 6.24, and 7.96 GΩ.cm2, respectively. These impedance moduli of the functionalized hBNNS/EP are 4-6 times higher than that of hBNNS/EP. Failure of the EP and hBN/EP was recorded on days 28 and 36, respectively. The hBNNS/EP (BM0.25) showed an onset of coating failure at the end of exposure time, introducing Warburg diffusion resistance. Meanwhile, functionalized hBNNS/EP coatings, at all loadings, exhibited prolonged corrosion protection.