Lignin-Based Covalent Adaptable Network Polymers─When Bio-Based Thermosets Meet Recyclable by Design

Covalent adaptable networks (CANs) play an important role in polymer chemistry, as they provide an innovative link between thermoplastics and thermosets. The breakthrough idea behind CANs is to at least partially replace irreversible crosslinks in classic thermoset polymers with dynamic covalent bonds that allow for reversible polymer character and recyclability. Besides, CANs also offer other popular features such as self-healing, weldability, configurability, and shape memory. Most CANs are still petroleum-based, yet shifting toward more sustainable approaches is of the utmost interest. Considering this and the high abundance of lignocellulosic biomass, this perspective focuses on all the research found on lignin-based CANs, including both those starting from fractionated lignin and from lignin-based monomers. This is clearly a new branch within bio-based CANs that holds great potential in various industries. Additionally, some examples of thermoset polymers derived from the same lignin building blocks are given to showcase important chemical transformations that can be used for CANs design in the future. Although CAN design has been extended to many different types of bonds, imines and disulfides largely prevail in the current literature. Lastly, a SWOT (strengths, weaknesses, opportunities, and threats) analysis is presented, considering the performance, competition, opportunities, and drawbacks of lignin-derived CANs.