A feasibility study on the deposition and in-situ modification of soda lignin by suspension plasma spraying

In this study, low-energy suspension plasma spraying (LE-SPS) was introduced as a novel approach for the deposition and simultaneous plasma-induced chemical modification of soda lignin. A colloidal lignin particle suspension was deposited onto glass substrates using a modified plasma spraying system with radial suspension injection. Scanning electron microscopy revealed continuous and dense coatings with an average thickness of approximately 4 µm. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and 1H/13C nuclear magnetic resonance (NMR) spectroscopy analyses indicated substantial plasma-induced chemical restructuring. The coatings exhibited increased oxygen-containing functionalities, including carbonyl and carboxyl/ester-type contributions, together with changes in aromatic signals. These spectroscopic changes are consistent with oxidative modification of lignin and increased contributions from ether- and ester-like environments. Overall, the results demonstrated that LE-SPS enabled lignin deposition accompanied by chemical transformation into a chemically reorganized lignin-based coating without additional crosslinkers, catalysts, or organic solvents.