Biobased Tannic Acid Cross-Linked Epoxy Thermosets with Hierarchical Molecular Structure and Tunable Properties: Damping, Shape Memory, and Recyclability

Biomass derivative and recyclability are two major factors in developing sustainable epoxy thermosets that cope with the global oil crisis and climate change. However, the major bottleneck persists in comparatively low strength of biobased epoxy thermosets and a complex synthesis route of recyclable epoxy thermosets. Here, we broke through the bottleneck by simply applying the biomass-based tannic acid as a multifunctional curing agent to a rigid epoxy monomer. Due to the diverse bonding abilities and particular topological structure of the tannic acid, the as-prepared epoxy thermosets exhibited a hierarchical molecular structure with high mechanical strength and tunable functionalities such as damping, shape memory, and recyclability. Specifically, two types of tannic acid cross-linked epoxy thermosets with raw hydroxyl/epoxide ratios of 0.5 and 1.0, respectively, were prepared to investigate the influence of feedstock ratios. When less tannic acid was used, a more complex topological thermoset network and better damping capability were achieved, and the effective damping temperature range was extended to 38.4 °C. On the other hand, the equal-stoichiometric epoxy thermoset possessed a higher tensile strength (∼98.4 MPa), better shape memory ability, and good recyclability. This dual sustainability concept (biomass feedstock and recyclability) may provide a promising opportunity for developing high-performance multifunctional thermoset polymers.