Lignin Extracted from Rubber Seed Shell by Ultrasound-Assisted Organosolv Pretreatment

Abstract

Purpose Herein, the extraction of lignin from rubber tree residues (Hevea brasiliensis Müll. Arg), particularly from the seed shell, is reported with the aim of providing added value to this plantation. Methods The protocol employed consisted of an organosolv extraction using formic or acetic acids and p-TsOH as catalyst assisted by ultrasound, avoiding the use of high temperatures and mineral acids. Results 22% yield of lignin was obtained from the dried rubber seed shell using the formic acid/p-TsOH combination in comparison with 13% yield obtained with acetic acid/p-TsOH. The extracted lignin was oxidized isolating typical fragments derived from syringyl, guaiacyl and p-hydroxyphenyl units. The lignin was characterized by IR, UV, NMR, TGA and DSC. Moreover, total phenol content and antioxidant activity were also evaluated. Conclusion The results exhibited the presence of typical lignin aromatic composition. The lignin obtained by the seed shell could be effectively employed in numerous future applications and the method could be considered as a low-cost acid catalysed process.