Microwave assisted extraction and Mannich type modification of date palm trunk lignin: Structural, surface, and thermal characterizations

This study involves the extraction of the lignin from the date palm trunk biomass using natural deep eutectic solvent (NADES) followed by microwave assisted method. The extracted lignin is first alkalized and modified using anhydrous ethylenediamine and formaldehyde at different mass ratios (alkalized lignin: EDA: formaldehyde), i.e., 1:1:1.08 (M1), 1:1:3.5 (M2), and 1:1:9 (M3). Different characterization techniques such as, FTIR, XRD, TGA, DTG, DSC, XPS, SEM, SEM-EDAX, and UV-DRS are used to evaluate the influence of progressive modification. FTIR analysis exhibited that modification results in changes in the functional groups, i.e., hydroxyl, ether, and amine. SEM analysis shows morphological transformation from the rough/fractured surface of control lignin to the progressively dense and agglomerated structures of modified lignin. SEM-EDAX observed the presence of nitrogen after modification. XPS analysis showed that after modification an increased surface nitrogen is observed consistent with amination. The XRD analysis showed that all samples are amorphous in nature and controlled by broad diffuse halos. The UV-DRS study exhibited that all samples possess the broad UV absorption of lignin. The progressive changes observed in the 280–300 nm and 300–400 nm. Hence, date palm trunk lignin can be potentially valorized using EDA: formaldehyde modification to get nitrogen functionalized lignin. The potential applications of the modified lignin may be suggested in adsorbents, bio-based resin, coatings, and lignin based advanced composites are considered as possible directions assuring steadfast performance testing.