Bio-Based Epoxy Adhesives with Lignin-Based Aromatic Monophenols Replacing Bisphenol A

Lignin beyond the status quo: recent and emerging composite applications

The demand for biodegradable materials across various industries has recently surged due to environmental concerns and the need for the adoption of renewable materials. In this context, lignin has emerged as a promising alternative, garnering significant attention as a biogenic resource that endows functional properties. This is primarily ascribed to its remarkable origin and structure that explains lignin's capacity to bind other molecules, reinforce composites, act as an antioxidant, and endow antimicrobial effects. This review summarizes recent advances in lignin-based composites, with particular emphasis on innovative methods for modifying lignin into micro and nanostructures and evaluating their functional contribution. Indeed, lignin-based composites can be tailored to have superior physicomechanical characteristics, biodegradability, and surface properties, thereby making them suitable for applications beyond the typical, for instance, in ecofriendly adhesives and advanced barrier technologies. Herein, we provide a comprehensive overview of the latest progress in the field of lignin utilization in emerging composite materials.

Biobased epoxy reactive diluents prepared from monophenol derivatives: effect on viscosity and glass transition temperature of epoxy resins

The use of reactive diluents is undeniably of paramount importance to develop epoxy resins which would meet more demanding and restrictive processes and applications in terms of viscosity and glass transition temperature. In the context of developing resins with low carbon impacts, 3 natural phenols namely carvacrol, guaiacol and thymol were selected and converted into monofunctional epoxies using a general glycidylation procedure. Without advanced purification, the developed liquid-state epoxies showed very low viscosities of 16 cPs to 55 cPs at 20 °C, which could be further reduced to 12 cPs at 20 °C when purification by distillation is applied. The dilution effect of each reactive diluent on DGEBA's viscosity was also assessed for concentrations ranging from 5 to 20 wt% and compared to commercial and formulated DGEBA-based resin analogues. Interestingly, the use of these diluents reduced the initial viscosity of DGEBA by a factor of ten while maintaining glass transition temperatures above 90 °C. This article provides compelling evidence of the possibility of developing new sustainable epoxy resins with characteristics and properties that can be fine-tuned by only adjusting the reactive diluent concentration.