Understanding Process‐Induced Structural Changes in Rice Straw Technical Lignins to Determine Their Valorization Potential

Abstract

A detailed understanding of the composition and chemical structures of technical lignins is essential for designing effective valorization strategies. This study examined four lignins from rice straw: soda lignin (SL), ethanol organosolv lignin (EOL), and two dioxane organosolv lignins (DOL‐a and DOL‐b), to compare their chemical composition and structure. Supported by semi‐quantitative NMR analysis, these lignins exhibited distinct structural differences primarily driven by the choice of extraction method. SL underwent extensive β–O–4 cleavage (∼3% remaining), whereas dioxane‐extracted lignins retained relatively higher levels of β–O–4 ether linkages (6.7–7.5 per 100 aromatic units). On the other hand, EOL showed distinctive preservation of native p ‐coumarate and ferulate units, indicating reduced side‐chain degradation, thereby providing a structural basis for the downstream differences in ash content and functional groups observed across the lignin fractions. Molecular weight (Mw) analysis further reiterated the impact of extraction method, with lignin molar masses ranging from ∼1790 to ∼5200 g mol −1 , accompanied by corresponding variations in polydispersity (PDI ∼2.1–5.9). Based on insights from this study, we developed a predictive framework to assign applications to these lignins, extracted via different routes. This approach highlights how extraction selection directly controls lignin quality, enabling rational matching of lignin fractions for targeted downstream applications.