Preparation of Renewable Thiol-yne “Click” Networks Based on Fractionated Lignin for Anticorrosive Protective Films Applications

The synthesis of novel, renewable lignin-based protective films with anticorrosive properties is presented in this work. Thermosetting films are prepared by means of tandem UV-initiated thiol-yne “click” synthesis and Claisen rearrangement strategy. These films contain high lignin loading, 46–61%, originating from a birch wood reductive catalytic fractionation process using a nickel catalyst. Lignin fractions with varying monomer content are compared before resins preparation, namely a mixture of monomers and oligomers without fractionation, or after fractionation via extraction and membrane separation. This study aims to determine if separation of lignin monomers and oligomers is necessary for the application as a thermosetting polymeric resin. The resulting protective films exhibit remarkable adhesion to a metal surface and excellent solvent resistance, even after exposure to corrosive environment. Moreover, those films show superior barrier properties, studied with Odd Random Phase Electrochemical Impedance Spectroscopy. After 21 days of exposure, the examined films still show impressive high corrosion protection with the low frequency impedance around 1010 Ωcm2 and capacitive behavior. This work demonstrates an interesting proof-of-concept where laborious, costly and energy-intensive separation of the depolymerized lignin mixture of monomers and oligomers is not necessary for the successful resin synthesis with excellent properties using the applied synthetic strategy.