Lignocellulosic waste pretreatment and esterification using green solvents

•Biomass pretreated by an Organosolv process was dissolved and acetylated in AMIM Cl.•The cellulose and lignin present were acetylated by a homogenous reaction.•Films precipitated by evaporation from dioxane were obtained from the acetylated biomass.•Biomass dissolution and modification was attained with a fully synthesized ionic liquid. Five selected oak sawdust (Quercus sp) pulps (biomass-pt) provided by an ethanosolv pretreatment were dissolved and esterified using the ionic liquid (IL) 1-allyl-3-methyl-imidazolium chloride (AMIM Cl). The AMIM Cl was fully synthesized, purified and used for biomass esterification. The IL synthesis started with a quaternization reaction of 1-methylimidazol with allyl chloride. No reacted materials were removed by vacuum evaporation at 80 °C. AMIM Cl was characterized using 1H and 13C NMR. Afterward, biomass-pt was dissolved in AMIM Cl and acetic anhydride was added for lignocellulose acetylation. The acetylated material was recovered from the IL using water as anti-solvent. Further purification was made with chloroform. Additionally, for comparison, heterogeneous acetylation of biomass-pt was performed. All the acetylated products were dissolved in dioxane to form films by evaporation-precipitation. The films obtained were characterized microscopically, calorimetrically and by FTIR. From the FTIR and the calorimetric analysis it was concluded that in the heterogeneous acetylation, lignin did not react, and also prevented cellulose from having a high degree of acetylation, greater than commercial cellulose triacetate (TAC). Meanwhile, Lignin was esterified when the pulps were acetylated in AMIM Cl. The analysis by SEM and AFM showed there was a good interaction between acetylated cellulose and acetylated lignin, due to the thickness of the films and the low roughness factor. The AMIM Cl was then the optimal media for biomass acetylation. It could be used as obtained from the synthesis and purification methods proposed.