(133c) Increasing the Reactivity of Lignin through Phenolation for Value-Added Applications: Effect of Phenolation Conditions

Lignin, the second most abundant biopolymer after cellulose, is a major contributor to plant cell walls' rigidity, strength, and water impermeability. Derived primarily from the pulp and paper industry, with an annual production capacity of approximately 50 million tons, lignin remains largely underutilized. Only 2% of lignin finds its way into value-added products such as thermosets, additives, binders, and dispersants, while the rest is predominantly used for heating purposes. Given its complex structural heterogeneity and inherent recalcitrance, lignin has been subjected to various chemical modifications to improve its reactivity, and one of the effective approaches is to increase the phenolic OH content of lignin by phenolation, which typically involves condensing phenol with lignin in an acid or alkali medium. This is because the phenolic OH groups remain the most reactive functional groups and control the chemical reactivity of lignin. In this study, we prepared several samples of phenolic lignin (in an acid/alkali medium) using conventional oil baths and microwave heating methods. The phenolic OH contents of the phenolized lignin are quantified using UV-Vis, pH-conductometric titrations, and ³¹P NMR. The molecular weights of the lignin samples are measured using GPC. Our preliminary data show that the phenolation reaction under alkaline conditions gives the highest increase of 72.8% in the phenolic OH content (3.29 mmol/g of lignin). We will conduct further analysis of the samples using 2D HSQC NMR to detect the inter-unit linkages of the lignin samples and evaluate the potential applications of the phenolized lignin in preparation of lignin-based vitrimers and lignin-enhanced asphalt.