Use of gelatin/nanocellulose compacted polyelectrolyte complexes to upcycle collagen-rich fibers into lightweight, strong, insulating and fire-safe fiber networks

The upcycling of collagen-rich waste fibers into lightweight materials represents a potential opportunity to fulfill current societal demands for a circular bioeconomy. With this objective, this paper reports a novel strategy that relies on the use of polyelectrolyte complexes beyond their conventional application fields. To this aim, compacted polyelectrolyte complexes (CoPECs) encompassing gelatin and nanocellulose are here used, for the first time, as a structural matrix to upcycle collagen-rich fibers into mechanically robust, insulating and fire safe fiber networks. The effects of pH complexing conditions on the strength of the dry CoPECs were investigated highlighting optimal mechanical properties at pH 6. This enabled the use of CoPECs for the preparation of fiber networks characterized by a wide range of compositions (fiber content up to 75%) and densities (50 and 90 kg/m3). The CoPECs matrix stabilizes and improves the formation of strong fiber-fiber joints conferring structural integrity to the networks with compressive strengths at 10% deformation up to 0.102 MPa. The thermal conductivity can be as low as 0.043 W/(m⋅K). The intrinsic flame retardant characteristics of collagen-rich fibers allow to easily stop flame propagation during flammability tests. When exposed to the heat flux of a developing fire (50 kW/m2) these materials can achieve low heat and smoke release if compared with high performing state-of-the-art solutions. This paper discloses a novel use of CoPECs for the production of advanced materials capable of balancing sustainability and functional properties while also providing a greener and safer alternative to conventional foams for transportation or building applications.