Development of nonisocyanate polyurethane–MWCNT nanocomposites: coatings with enhanced antifouling, corrosion resistance and UV protection properties

Abstract

Nonisocyanate polyurethanes (NIPUs) and NIPU nanocomposites (NIPU-NCs) were developed from renewable sources. NIPUs were synthesized from a sustainable precursor, castor oil cyclic carbonate (CO-CC), via polyaddition with linalool diamine (LDA) at 110 °C. NIPU properties improved upon the incorporation of 0.5 wt% multiwalled carbon nanotubes (MWCNTs) via covalent (amine-functionalised MWCNTs) and non-covalent (pristine and oxidized MWCNTs) methods. These formulations resulted in the NIPU nanocomposites NIPU-MWCNT-NH₂, NIPU-MWCNTs and NIPU-MWCNT-COOH. The physicochemical, thermal and morphological properties of NIPU and NIPU-NCs were studied via multiple techniques such as FTIR, NMR, XRD, TGA, DSC, SEM, water contact angle analysis, XPS and optical microscopy. These samples were applied for coating applications on a mild steel substrate (MST) and glass slides to study antifouling, anticorrosion and UV shielding. Thermal analyses of NIPUs and NIPU-NCs revealed good thermal stability with an appropriate glass transition (T_g) and onset degradation (T_d) temperature. Indeed, water contact angle values showed hydrophilic properties, which prompt applications in marine coatings. Biodegradation studies implied that the structural network retained its stability even after immersion for 45 days in a PBS medium. Additionally, NIPUs and NIPU-MWCNT-NH₂ demonstrated enhanced UV shielding capability. Finally, NIPU-MWCNT-NH₂ exhibited anticorrosion with an impedance modulus |Z| of 7.43 × 10² (Ω cm²) and essential antifouling properties as well as significantly reduced algae adhesion to 3.143 million per mL.