Title : Zein-based reversible and irreversible substrates for flexible electronics
Abstract:
Introduction:
Commonly used materials such as polyamide, polytetrafluoroethylene, polydimethylsiloxane (PDMS), fluoropolymers, and polyolefins play a critical role in achieving the flexibility and stability of electronic devices due to their mechanical and chemical/physical properties. Access to raw materials, complexity of synthesis, environmental impact, degradation into toxic products and disposal at end-of-life are the main critical issues with such petroleum-based materials. Therefore, the use of bio-based, recyclable and sustainable materials has enormous potential because of their low impact on ecosystems, offering the
possibility to minimise the environmental impact of electronics. [1] The focus of this work is the exploitation of zein, a protein considered waste due to its amino acid composition, which determines poor nutritional properties; zein has also been used for its chemical-physical properties. The main challenges in using zein as a substrate for flexible electronics were its poor mechanical properties and low water resistance. Therefore, both reversible and irreversible chemical modifications were evaluated and applied to improve the mechanical properties of zein; recyclability was also incorporated thanks to the reversibility of the transformations and the hydrolysable nature of zein itself. In particular, the reversible new materials were prepared by the reversible Diels-Alder (DA) reaction between zein (diene) and a dienophile crosslinker (maleimide) [2,3]; while the irreversible new materials were prepared by acrylation of zein and copolymerization with an acrylic polymer [4].
Results and discussion:
The properties of zein were characterised by SDS-PAGE analysis, DSC, FT-IR and solubility tests. Zein was chemically modified: for thermoreversible crosslinking by functionalisation with a diene, for irreversible crosslinking by functionalisation with acrylic groups. Cross-linked films exhibit superior mechanical properties (high modulus, increased fracture toughness, flexibility and elasticity) and solvent resistance compared to unmodified zein films. Reversibility has been demonstrated using the retro-Diels Alder reaction.
SAMPLE ABSTRACT TEMPLATE
Schematic representation of flexible substrates: from chemical modification to film addition. In addition, dienophile crosslinkers with different aliphatic bridge lengths were evaluated to study their effect on films properties; in particular, a bis-maleimide with poly(ethylene) glycol (PEG600) was designed and synthesised to act as a soft segment between the protein chains. Also the effect of modified soybean
oil as secondary crosslinker was evaluated for irreversible thermosets. The samples were characterised by DSC, FT-IR and NMR analysis. The mechanical properties of the films were studied and molecular dynamics studies were perormed to understand the reorganisation of the protein as a function of the chemical modifications and the dienophiles used.
Conclusions:
Zein was chemically modified and dienophiles were synthesised for the preparation of irreversible and thermoreversible substrates for flexible electronics. The new zein-based recyclable materials showed good
mechanical properties. In addition, the new substrates displayed good properties for printing conductive inks.
