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 quantitative 13 C 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 31 P 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 T g 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. (531 x 1328 pixels (h x w) or proportionally more and is readable at a size of 5 × 13 cm using a regular screen resolution of 96 dpi. TIFF, EPS, PDF or MS Office files). • Oat husk lignin was characterized by various NMR techiques • DOSY indicated an incorporation of fatty acid into the lignin structure. • Oat-husk lignin showed a moderate β–O–4 content (8.6 %) and molar mass (5.5 kDa). • Hydroxyl group content was 4.83 mmol/g and Tg approximately 180 °C.