Extraction and modification of lignin to support enhanced utilisation using critical fluids

Lignin is abundant naturally occurring biopolymer currently produced as a by-product from the pulping and \npaper industry, where the process generates lignin in the form of lignosulphonates. While there are many applications for lignin there are all low value and attempts to add value to lignin are hindered by its complex physico-chemical nature and the presence of sulphur. Adopting the biorefining concept the study evaluates the impact of direct (DE) and sequential extraction (SE) of Miscanthus x giganteus using sub-critical water with associated modifiers on the physical and chemical properties of the extracted lignin. Even though higher delignification was achieved by DE (81.5%) than SE (58.0%), the lignin recovered from the SE process showed significantly higher purity (91.5%). Fourier Transform Infrared Spectroscopy (FTIR) analysis also revealed the abundance of free hydroxyl groups (OH) within the lignin derived from SE. Further it was demonstrated that lignin agglomerates, which are widely known to form post extraction, could be de-agglomerated by simply reducing the ethanol concentration from 50% to 1% and therefore intramolecular forces. Although the finding does not offer an adequate explanation regards to the driving forces of lignin aggregates at different ethanol concentration, the esterification reaction to attach C12 fatty acids to lignin derived from SE at 50% ethanol concentration (5 mg/mL) demonstrated that the amount of hydroxyl groups available increased the level of fatty acid incorporated onto the lignin macromolecule with 81.2% esterification conversion. A modified lignin \nproduced has the potential to be used as a precursor for added value bio-based materials.