A novel paradigm approach to design structural natural fiber composites from fully sustainable CO2-derived thermosets with outstanding interfacial strength and circular features

We herein propose capitalizing on strong hydrogen bonding from novel bio-CO2-derived dynamic thermosets to achieve high-performance natural fiber composites (NFC) with circular features. CO2- and biomass-derived polyhydroxyurethane (PHU) thermosets were selected, for the first time of our knowledge, as matrices for their ability to make strong H-bond, resulting in outstanding mechanical properties for NFC. Exploiting this H-bond key feature, exceptional interface bonding between flax and PHU was confirmed by atomic force microscopy and rationalized by atomistic simulation. Without any treatment, an increase of 30% of stiffness and strength was unveiled compared to an epoxy benchmark, reaching 35 GPa and 440 MPa respectively. Related to the thermoreversible nature of hydroxyurethane moieties, cured flax-PHU were successfully self-welded and displayed promising properties, together with recyclability features. This opens advanced opportunities that cannot be reached with epoxy-based composites. Implementing CO2-derived thermosets in NFC could lead to more circular materials, critical for achieving sustainability goals.