Electronic Eco-leather—Flexible Composite from Biowaste with Laser Patterned Graphene for Sensors Application

The fabrication of flexible electronics and sensors using biobased waste is one of the trends in sustainable materials science and engineering. The optimal combination of mechanical and electrical properties of materials is the leading approach to develop advanced wearable electronics, such as e-skins and e-textiles^1-3.<br/>In this study we present a novel leather-like composite based on biowastes: almond shell powder (ASP) and chitosan, with the latter being derived from crustaceans exoskeletons. The high cellulose content (38.7%) in the ASP, measured using a modified standard for the determination of structural carbohydrates and lignin in biomass raw material, improves the mechanical properties of the composite: the material shows high tensile strength and high flexibility, with the possibility to be sewed as standard fabrics or leather. The addition of chitosan as a polymeric matrix, results in a flexible and biodegradable composite, as confirmed by the results of mechanical tests (Young's modulus = 14 - 21 MPa, depending on the ASP content in the composite) and biodegradation tests in the soil. At the same time the high lignin concentration in shells (30.6%) improves the material thermal stability, making it also an ideal precursor for laser-induced graphene (LIG). LIG is a three-dimensional porous and conductive carbon structure, obtained by the IR or UV irradiation of substrates (i.e. synthetic and natural polymers), which undergo a laser induced pyrolysis through photo-chemical or thermal reactions. LIG synthesis and patterning is a cost-effective, one-step, fast, and digital process that meets the needs for sustainable fabrication^4,5.<br/>The LIG obtained from ASP/chitosan composites by IR and UV laser scribing shows low sheet resistance and high specific surface area. Moreover, SEM and Raman spectroscopy characterizations reveal different micro/nano morphologies depending on laser settings and confirm the successful conversion of the composite precursors in LIG to create conducting elements.<br/>The obtained eco-leather shows high potential for use in flexible, wearable sensors. Proof of concept applications have been tested for environmental humidity monitoring and for various electrical circuits/electrodes, opening the way to a wide range of applications.<br/>(1) A.C. Bressi et al. ACS Appl. Mater. Interfaces, 2023, 15, 30, 35788–35814.<br/>(2) Z. Hui et al. Adv. Mater. 2023, 35, 2211202.<br/>(3) M. Cetin et al. Materials Science & Engineering B. 2023, 287, 116140.<br/>(4) A. Dallinger et al. ACS Appl. Mater. Interfaces 2020, 12, 19855.<br/>(5) N. F. Santos et al. Adv. Mater. Technol. 2021, 6, 2100007.