Elijah Mark Garcia, Paula Nousiainen, Uula Hyväkkö, Monika Österberg
Abstract: Chemical modification of lignin is needed to enhance its use in materials applications. However, traditional solvothermal methods for lignin modification often compromise the sustainability and scalability of the process. In this study, we developed a solventless approach for producing esterified lignin derivatives through reactive extrusion (REx). For the first time, we report the functionalization of lignin with octenyl succinic anhydride (OSA) via REx. We systematically explored the effects of temperature, residence time, OSA loading, and catalyst loading on lignin esterification efficiency using FTIR, 2D HSQC NMR, and 31P NMR spectroscopy. Our results show preferential esterification of aliphatic hydroxyls (>80%) within minutes. Esterification of lignin with OSA yielded thermoplastic lignin esters suitable for use in polymer blends and further for producing lignin-based elastomers due to the reactivity of the added carboxylic acid functionalities. Additionally, we compared the green chemistry metrics of the REx process with the solution-state approach, highlighting the clear advantages of avoiding the use of solvent. Furthermore, we successfully esterified different biorefinery lignins through REx, demonstrating the versatility of this method. The advantageous features of REx position it as the green standard technology that could boost the integration of lignin-based materials into the market.
