Bio-based UV-curable vitrimeric coatings incorporating DNA for enhanced flame retardancy and circularity

The development of multifunctional UV-cured coating formulations combining sustainability, flame retardancy, and circularity remains a major challenge for advanced polymeric materials. In this work, a fully bio-based UV-curable vitrimeric formulation was developed by combining a vanillin-derived Schiff-base resin with DNA from herring sperm as a sustainable intumescent flame-retardant additive. DNA was incorporated at 10 and 20% w/w, and the resulting UV-cured coating formulations were investigated in terms of morphology, thermomechanical properties, flame-retardant performance, thermally activated scratch closure, and chemical recyclability. SEM observations revealed a heterogeneous morphology arising from the limited compatibility between DNA and the hydrophobic vitrimeric matrix, while DSC and DMTA demonstrated that DNA slightly increased the glass transition temperature and storage modulus without preventing network formation. TGA showed a marked increase in char residue. Cone calorimetry revealed progressive reductions of 38% in peak heat release rate, 46% in total heat release, and 73% in total smoke release for the formulation containing 20% w/w DNA relative to the unfilled formulation. PCFC results showed a similar trend. However, all formulations remained not classified in UL-94 vertical flame-spread tests. SEM-EDS analyses of combustion residues revealed a more compact, phosphorus-rich char, consistent with a predominantly char-forming contribution of DNA in the condensed phase. DNA incorporation did not prevent repeated thermally activated scratch closure or chemical recycling through transimination. Although scratch closure at 120 °C may be the synergic effect of dynamic bond exchange and thermally activated polymer mobility, these findings demonstrate the potential of DNA-containing imine vitrimers as sustainable UV-cured coating formulations with improved fire performance and circularity.