Chemical composition analysis and structural features of banana rachis lignin extracted by two organosolv methods

Abstract Two organosolv methods involving Formic acid/Acetic (FA) acid and Sulphuric acid/Ethanol (SE) solvent mixtures were investigated for lignin extraction from banana rachis biomass residues. Different heating methods were also applied during each extraction process, respectively direct conduction heating and microwave heating. The chemical composition and structural features of the extracted lignin fractions were further analyzed by ATR-FTIR, TGA, elemental analysis and 13C NMR methods. SE extraction method showed a higher extraction yield (58.7%) and allowed also to obtain a lignin fraction with higher purity (76.5% Vs 71.0% for FA lignin). In addition, SE extraction method allowed a higher pulp yield which meant a better selectivity for lignin extraction thanks to the microwave heating method. SE lignin also showed a higher thermal stability due to its higher purity and higher density. The higher molecular weight found for FA lignin residues (7622.7g/mol Vs 5957.7g/mol for SEL) was suspected to be due to co-extracted carbohydrate residues bounded to extracted lignin macromolecules. These results allowed us to establish the SE extraction method (Sulphuric acid/Ethanol/water solvent with microwave heating) as effective for lignin extraction from banana rachis straw.