Avaliação do fracionamento por solventes na obtenção de ligninas com diferentes propriedades es-truturais

Abstract

Lignin is an amorphous three-dimensional polymer of complex and heterogeneous structure present in the plant cell walls. In traditional methods of lignin extraction, it is difficult to control its molar mass, which makes it difficult to use in polymer chemistry. An alternative to improve its homogeneity and reduce its complexity is the use of the solvent fractionation process. The aim of this work was to evaluate the effects caused by the use of a solvent mixture fractionation process in the lignin soluble fractions yielded. Lignin extraction was performed from the dry coconut endocarp using the organosolv method under the following conditions: ethanol concentration 65% v / v in water, dry coconut endocarp powder mass ratio / volume of solution of 1:10 (g / mL), temperature of 130 ° C, reaction time of 6 minutes and H2SO4 as catalyst at 1.0% w / w concentration. Solvent fractionation was performed using solvent mixtures with different polarities (methanol / dichloromethane, ethanol / chloroform and acetone / ethyl acetate) in different ratios (25:75, 50:50 and 75:25). Among the nine soluble fractions obtained (F1 to F9), two were chosen for structural characterization, such as F4 (methanol / dichloromethane, 50:50 ratio) and F5 (ethanol / chloroform, 50:50 ratio) based on their molar masses and yields. The molar mass distribution of the non-fractionated lignin and soluble fractions F4 and F5 was investigated by GPC and structural features by FTIR and HSQC 1H-13C NMR. The results obtained by these techniques showed that the methanol / dichloromethane mixture solubilized lignin fragments with the smallest molar masses and the ethanol / chloroform mixture the fragments with the largest molar masses, which presented different monomer compositions, with the F4 fraction having the largest amounts of S and PB units, and fraction F5, the highest amount of G units.