Role of Silicoaluminophosphate as a Corrosion Inhibiting Nanocontainer and Filler in Environmentally Benign Bio-Based Hybrid Coatings

Abstract

Zeolites, renowned for their versatile properties, have emerged as highly promising materials across a spectrum of applications. Coupled with their remarkable thermal and chemical stabilities, these properties broaden the horizons of zeolite applications across various industrial sectors. Their multifaceted functionality positioned them as optimal materials for filler incorporation in paints and coatings technology, offering both ecological soundness and economic viability. Moreover, in pursuit of sustainability, the selection of a bio-based polymer matrix for embedding the filler is essential. This strategic choice not only mitigates volatile organic compounds (VOCs) and toxicity but also underscores a concerted effort toward eco-conscious practices. Herein, we report the development of the bio-based hybrid coatings containing a microporous zeolite material with a one dimensional channels system (i.e., SAPO-5) as the filler and nanocontainer for an anticorrosive agent (Mo). The material (Mo-SAPO-5) was prepared through hydrothermal synthesis and ex situ modification with molybdenum. Before incorporation into the coating formulations, it was characterized via a combination of various spectroscopic and analytic techniques including powder XRD, FT-IR, and N2 sorption. Subsequently, the Mo-SAPO-5 nanocontainer system was incorporated into a castor-oil-based polyurethane matrix as a filler with variable weight ratios (up to 2 wt %). The physicochemical, mechanical, and thermal properties of the free-standing PU films were thoroughly examined through a standard protocol involving FT-IR-ATR, XRD, TGA, DSC, DMTA, and UTM. Finally, the hybrid PU films were cast on a mild steel substrate and were subjected to a corrosion inhibition study by potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) techniques, and a salt spray fog test. The studies revealed that out of all the compositions prepared, the MoS5-COPU-0.5 films (with 0.5 wt % filler) exhibited a promising anticorrosive property with the highest corrosion inhibition (C R ≈ 5.77 × 10–6 mm/year), charge transfer resistance (R ct ≈ 1.33 × 107 Ω), and phase angle (θ > 80°).