Characterization of oat husk soda lignin from a Finnish biorefinery process

This study provided a detailed structural analysis of oat husk lignin (OHLN) obtained from a Finnish biorefinery process using the BIOFORSENSE®-technology. A combination of quantitative13C NMR with DEPT-135 and DEPTQ enabled accurate quantification of S/G/H units, interunit linkages, and condensation degree without chemical derivatization (e.g., acetylation). The results were directly comparable to those obtained by 31P NMR. Furthermore, diffusion NMR (1D and 2D DOSY) was used to detect incorporated fatty-acid and extractive residues and to separate low-molecular-weight contaminants from the polymeric backbone, offering new insights into lignin–carbohydrate/extractive associations. Analysis of inter-unit linkages indicated a relatively low β-O-4 content (8.6 per 100 aromatic units). Phenolic hydroxyl content was 4.83 mmol/g. FT-IR, Py-GC/MS, GPC, and SDT/TGA, established additional structural features and properties. The syringyl to guaiacyl ratio was 0.7 and the average molar mass was 5.4 kDa. Thermal analyses showed a Tg at approximately 180 °C, and a char residue of 39 %. OHLN is a renewable, sustainable raw material with favorable structural properties, making it suitable for diverse applications such as adhesives, resins, coatings, and bio-based chemicals. Unlike many other lignins, OHLN's origin from food material and the use of chemical free extraction technologies make it especially promising for food grade applications.