Lignin extraction from empty fruit bunch fibre using different types of alpha-hydroxy acid-based deep eutectic solvents via microwave-assisted heating
DOI:
https://doi.org/10.15282/cst.v6i1.11231Keywords:
Lignin, Deep Eutectic Solvent, Microwave-Assisted HeatingAbstract
This study investigates the efficiency of deep eutectic solvent (DESs) synthesized using choline chloride (ChCl) as a hydrogen bond acceptor (HBA) and alpha-hydroxy acids (AHAs) as hydrogen bond donors (HBDs) for lignin extraction from oil palm empty fruit bunches (EFB) via microwave-assisted reaction. DESs with varying molar ratios of ChCl to AHAs, specifically oxalic acid (OA) dihydrate, known as dicarboxylic acid, and lactic acid (LA), a monocarboxylic acid, were prepared at 1:1 and 1:10 ratios, respectively. The presence of hydroxyl (OH) groups in AHAs facilitated DES formation at both ratios. ChCl: LA demonstrated a significantly higher lignin extraction yield, 76.61%, compared to ChCl: OA dihydrate, 29.36%. This is due to the lower viscosity and higher mobility of the DESs, which enhance solvent-solute interactions. The Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed strong intermolecular bonding in the extracted lignin, with characteristic peaks corresponding to phenolic, aliphatic hydroxyl, and benzene ring vibrations, indicating the preservation of the lignin's aromatic structure. Thermogravimetric Analysis (TGA) showed that lignin extracted with ChCl: OA dihydrate and ChCl: LA exhibited higher thermal stability and char yield than raw EFB, with distinct degradation stages. Differential Scanning Calorimetry (DSC) determined the lignin samples' glass transition temperatures (Tg), with ChCl: LA showing the highest Tg at 90 °C, attributed to its higher purity and reduced carbohydrate content. Overall, the study highlights the critical role of HBD functional groups and DES composition in optimizing lignin extraction efficiency and thermal properties, with potential implications for biomass pretreatment processes via microwave-assisted reaction.
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