Recent Strategies for Lignin-Based Thermosets

Lignin has gained interest in academia as a raw material for advanced materials such as thermosets. Attractive features include its natural and technical abundances, its structural compositions, distribution of functionalities and most importantly its origin from renewable sources, i.e. lignocellulosic biomass. In this chapter, we will focus on lignin-based thermosets, specifically reviewing the recent strategies for such applications in polyurethanes, phenol-formaldehyde resins and epoxy thermosets. In these contexts, the advantages and competitiveness of lignin over conventional petrol-based will be discussed based on comparisons with benchmark properties. The chapter emphasizes the unique polymer chemistries adopted by different researchers, the effects of the chemical and physical properties of lignin on both reactivities during synthesis and thermomechanical properties of materials. Furthermore, the direct use of lignin in the unmodified state is contrasted with the use of selectively modified lignins in these polymer systems. The use of multifunctional lignin oligomers as raw material is also contrasted with the use of lignin platform monomers obtained through de-polymerization approaches. Finally, the challenges of lignin or monomers thereof, as a raw material in these applications are discussed to direct the future outlook of this research area.