Unveiling the potential of dual-extrinsic/intrinsic self-healing lignin-based coatings for anticorrosion applications

The development of self-healing ecofriendly coatings for anticorrosion applications provides stronger protection than passive coatings and mitigates the environmental pollution resulting from petroleum-derived coatings. Due to its intrinsic anticorrosion characteristics, lignin is a viable precursor for the formulation of self-healing anticorrosion coatings. However, the structural rigidity of lignin and the lack of self-healing functionalities in pristine lignin-based coatings hinder the comprehensive application of lignin in this field. Accordingly, we introduced Diels-Alder (DA)-based self-healing functions in the lignin-based coatings and meanwhile, the coatings were chemically conjugated with corrosion inhibitors to further improve the anticorrosion performance. A thin layer (16 μm) of the coating increased the E corr from −480 mV (for bare steel) to +91 mV and reduced the corrosion rate (CR) >4000 times. The dual self-healing properties of the coating are attributed to the synergistic action of the DA adduct and the conjugated corrosion inhibitor. Practically, in response to the emergence of microcracks in the coating structure, trace amounts of the corrosion inhibitor are released into the microcracks to form a protective layer on the unveiled metal surface. Simultaneously, DA adducts undergo reversible reactions at specific temperatures (50–120 °C) promoting complete restoration of the microcrack.