The use of agro-industrial waste as raw material for obtaining biobased products, such as lignin, has been widely explored to replace petrochemical-derived compounds in various technological sectors. Among the most common chemical modifications, partial acetylation of lignin stands out for improving its solubility in organic solvents and enhancing the compatibility between polymers and lignin. Although lignin is attractive due to its phenolic structure, the complexity of this structure remains an obstacle to its valorization. The objective of this work was to promote partial and selective acetylation of lignin under eco-friendly conditions, using acetic acid both as a solvent and as an acylating agent. The reaction was conducted under heating on a hot plate in the presence of 1.0% v/v H2SO4 for a period of two hours. The partially acetylated lignin (PAL) was characterized by FTIR, TGA, and solubility analysis. The results demonstrated preferential acetylation of aliphatic hydroxyls, evidenced by the appearance of bands at 1733 cm^-1 attributed to C=O stretching in ester groups, as well as the band at 1369 cm^-1 associated with C-H stretching of the methyl acetate group. The absence of bands above 1760 cm^-1 (aromatic C=O) confirms that the phenolic hydroxyls remained unaltered, reinforcing the reaction's selectivity for aliphatic groups. An increase in thermal stability was also observed, with the degradation onset temperature rising from 274 ^oC to 317 ^oC, along with a significant improvement in solubility in chlorinated organic solvents, such as chloroform and dichloromethane, with increases of 97% and 177%, respectively. On the other hand, in ethyl acetate, solubility showed only a moderate increase after partial acetylation. It can be concluded that these characteristics highlight the potential of partially and selectively acetylated lignin as a green alternative for applications in polymeric materials.

Sara Marciano

Appearances