In recent years, lignin specific activities, such as antioxidation and antibacterial and anti-ultraviolet performance, have drawn more and more attention. Nevertheless, the insufficient radical scavenging (antioxidation) activity has become one of the main drawbacks that limits its high-value application. In this study, lignin nanoparticles (LNPs) were prepared via a facile acid treatment strategy. Subsequently, surface amination of LNPs (a-LNPs) was carried out through the Mannich reaction. Specifically, the antioxidant behavior of LNPs and modified LNPs was evaluated by DPPH/DMPO radical scavenging and in vitro HeLa cell reactive oxygen species (ROS) scavenging tests, which demonstrated that the antioxidation activity of a-LNPs was more evident than that of both LNPs and butylated hydroxytoluene (BHT) commercial antioxidant. The mechanism of the radical scavenging ability of aminated LNPs was elucidated and proved to be related to the bond dissociation enthalpy of Ar−O•••H, determined by the electron-donating effect of the substituted groups in the ortho-position. Meanwhile, the morphologies, solubilities, and UV-absorbing and antibacterial behavior of LNPs and a-LNPs were also studied, and the results showed that a-LNP sample exhibited higher UV resistance performance than LNPs. We expected that the modified LNPs with high antioxidation activity can serve as a safe and lower-cost biobased antioxidant.

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In recent decades, the continuous depletion of fossil fuels and the increasingly serious environmental issue have aroused wide attention on the development of biopolymers based on renewable biomass. Lignin is the second most abundant organic bio‐based macromolecule second to cellulose, and it can be widely found in plants. Furthermore, various phenol derivatives can be obtained by their depolymerization processes. The development of bio‐renewable polymeric materials originating from lignin‐derivative phenol monomers, such as vanillin, syringaldehyde, eugenol, vanillyl alcohol, vanillic acid, and ferulic acid, will not only valorize the bio‐sourced materials but also effectively reduce petroleum resource consumption and mitigate the environmental pollution. Therefore, an updated overview of the synthesis processes of these bio‐based polymers developed in the past decade, which includes both thermosets and thermoplastics such as epoxy, phenolic, polyimine, polybenzoxazine, polyurethane, and polyesters, are elucidated. In addition, the applications of these bio‐based polymers and their composites in flame‐retarded materials, degradable and reprocessable materials, dielectric materials, optoelectronic materials, as well as smart responsive materials are also intensively discussed. In line with the gradual development of synthesis technologies, we believe that derivatives of lignin will turn into one of the most promising materials to be considered for the preparation of high‐performance and functional bio‐based polymer materials.

Vanillin, as a lignin-derived mono-aromatic compound, has attracted increasing attention due to its special role as an intermediate for the synthesis of different biobased polymers. Herein, intrinsically flame-retardant and thermalconductive vanillin-based epoxy/graphene aerogel (GA) composites were designed. First, a bifunctional phenol intermediate (DN-bp) was synthesized by coupling vanillin with 4, 4′-diaminodiphenylmethane and DOPO, and the epoxy monomer (MEP) was obtained by the epoxidation reaction with DN-bp and epichlorohydrin. Then, various amounts of MEP and diglycidyl ether of bisphenol A (DER) were mixed and cured. Interestingly, the flexural strength and modulus were greatly enhanced from 72.8 MPa and 1.3 GPa to 90.3 MPa and 2.8 GPa, respectively, at 30 wt % MEP, due to the rigidity of MEP and strong intermolecular N−H hydrogen bonding interactions. Meanwhile, the cured epoxy achieved a UL-94 V0 rating with a low P content of 1.06%. The flame-retardant vanillin-based epoxy was then impregnated into the thermal conductive 3D GA networks. The obtained epoxy/graphene composite showed excellent flame retardancy and thermal conductivity [λ = 0.592 W/(m•K)] with only 0.5 wt % graphene in the system. Based on these results, we believe that this work would represent a novel solution for the preparation of high-performance biobased flameretardant multipurpose epoxies.

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