Zein-based thermo-reversible films for flexible electronics

In recent years, the need for more circular and sustainable electronics has promoted the research into printed solutions. The increasing interest in flexible electronics pushed through solutions that adapt to human testing, such as wearable electronics, health trackers, motion sensors, etc. The most commonly used materials, such as polyimide, polytetrafluoroethylene, polydimethylsiloxane (PDMS), fluoropolymers, polyolefin and silicone rubber, have a crucial role in achieving the flexibility of electronic devices thanks to their remarkable mechanical characteristics. These oil-based solutions show notable critical issues, such as access to raw materials, complexity of the synthesis phases, environmental impact during production, degradation into toxic products, disposal of end-of-life devices. Hence, the use of environmentally friendly, recyclable, and sustainable materials, from printed circuit boards to electrical circuit elements, has enormous low-impact and “green” potential, offering the possibility of minimizing the future environmental impact of electronics. [1] Biobased materials are considered the most promising candidates for next-generation flexible electronics because of their high sustainability. Proteins are intriguing biobased polymers to be considered for the development of flexible electronic devices, for several reasons: they can be taken from waste, in large amount, they offer a variety of chemical structure, they can be depolymerized and recycled to monomers. In this work, zein was selected as the staring protein, and flexible films were developed. The proteome of zein was first determined through LTQ XL mass spectrometer. After this evaluation, the chemical modifications were designed as a function of the final application. Two routes were explored: (i) the tuning of the sulphur based crosslink network, (ii) the derivatization with new functionalities (Figure 1). The breaking and restoring of sulfur bridges allows the macromolecule to have the same primary chemical sequence but a different secondary structure. This strategy, named the RES method, offers the possibility of achieving improved mechanical properties while maintaining the chemical structure. The chemical modification was instead performed on the native protein by reacting oxygen- and nitrogen-based functional groups with properly prepared dienes able to react through the Diels-Alder reaction. The so-obtained diene-enriched zein derivatives were able to be reversibly crosslinked with dienophiles by simply heating the mixture. The cross-linked films are the basis of superior mechanical properties such as high modulus, high fracture robustness, and resistance to solvents. The reversibility was checked through the retro-diels alder reaction. [2,3] The samples were characterized by DSC, FT-IR, and NMR analysis. In addition to the mechanical properties, molecular dynamics studies were performed. They made it possible to understand the reorganization of the protein as a function of the chemical modifications. References 1. B. Kılıçarslan, I. Bozyel, D. Gökcen, C. Bayram, Macromol. Mater. Eng. 2022, 307, 2100978 2. J. Ax, G. Wenz, Macromol. Chem. Phys. 2012, 213, 182−186 3. P. Mineo, V. Barbera, G. Romeo, F. Ghezzo, E. Scamporrino, F. Spitaleri, U. Chiacchio, J. APPL. POLYM. SCI. 2015, 42314