3D-PRINTABLE COMPOSITE MATERIALS AS SUSTAINABLE ALTERNATIVES TO LEATHER FOR THE UPCYCLING OF LEATHER WASTE

Leather industry has a notable environmental impact due to the tanning process. Additionally, around 30% of finished leather is wasted in manufacturing. Bio-based alternatives to leather employing diverse materials, including the ones derived from bacterial fermentation, mitigate the ecological footprint of genuine and synthetic upholstery material. Besides, the evolution of 3D printing has fostered consumer expectations for personalized products. This research aims to valorize leather waste by developing a circular, 3D printable and composite material alternative to leather. Bacterial cellulose was produced through fermentation of Kombucha tea. The composite material matrix included gelatin, hydrolyzed bacterial cellulose with H2SO4 30%(v/v), and glycerol as a plasticizer. Grinded leather waste (granulometry<0.5 mm) served as filler and was added from 10 to 20% with respect to the matrix dry weight. Various compositions of the matrix components were examined. Mechanical properties of dried composite materials were analyzed through uniaxial tensile tests. Rheological characterization of the circular materials in the wet state was conducted through oscillatory and flow tests. The Direct Ink Writing 3D printing technique was employed for shape fidelity assessments. Tensile tests showed values of ultimate strength, elongation at break and elastic modulus of the same magnitude of original state leather. Rheological analysis demonstrated a shear-thinning behavior. Moreover, thixotropy tests demonstrated a recovery after high-amplitude deformations. The 3D printed grids and coils exhibited filament uniformity with an extremely low spreading, and the shape fidelity indexes were in accordance with the desired ones. Tensile tests showed that gelatin content enhanced the mechanical strength, while the increasing of leather powder content in the composite material did not notably effect mechanical properties. Rheological flow tests showed materials suitability for extrusion-based printing, owing to their pseudo-plastic behavior. Thixotropy tests demonstrated the materials ability to recover after the extrusion process through the nozzle. This result was validated by printability tests, which revealed the high shape fidelity of printed structures. In conclusion, the development of a 3D-printable composite material, derived from waste and biobased sources, represents a significant step towards sustainable strategies within a circular economy framework.