3D-printable circular composites as sustainable leather alternative for the valorization of tanneries' solid waste

• Valorization of leather shavings as filler in composite materials • Formulation of 100% circular and bio-based leather alternative composites • Mechanical properties of composites akin to vegetable-tanned leather • Optimization of a versatile composite employable as a printing plate and ink • Customization of leather like alternative with direct ink writing The leather industry has environmental impacts due to tanning processes and produces substantial solid waste, with up to 80% of treated hides not disposed of sustainably. The fashion industry is seeking bio-based alternatives to genuine leather and exploring innovative technologies for the on-demand customization of accessories. This study aims to optimize a bio-based, circular, and 3D-printable composite material as an alternative to vegetable-tanned leather, employing glutaraldehyde-treated leather scraps. A versatile composite was optimized, including up to 30%(w/w) of glutaraldehyde-treated leather shavings and 55%(w/w) of hydrolyzed bacterial cellulose as fillers embedded in a gelatin-glycerol matrix. This material can be dried into sheets, acting both as a leather alternative and a printing plate for the same material in a water-based form, enabling the customization of the composite leather alternative sheet. The dried composite reached mechanical properties akin to vegetable-tanned leather grain (Tensile strength: 3.8MPa, Deformation at break: 20.1%, Young’s modulus: 210.2MPa). The waterborne composite showed the required rheological properties for Direct Ink Writing. The extrudable material was successfully 3D-printed, employing the composite as a printing plate, simulating the personalization of leather alternative. These findings valorized leather waste to produce customized circular leather and leather-like alternative via additive manufacturing, promoting sustainable and avant-garde practices in the fashion sector.