Cellophane or Nanopaper: Which Is Better for the Substrates of Flexible Electronic Devices?

Flexible electronic devices have gained broad applications in electrical sensors, photoelectrical displays, and energy storage devices, which result in a great demand for flexible and degradable substrates. The substrates require excellent thermal aging resistance to maintain the stability of flexible electronic devices in long-term use. Cellulose films, including cellophane, cellulose nanofibril (CNF) nanopaper, and cellulose nanocrystal (CNC) nanopaper, can be used as the substrates for flexible electronic devices. However, cellulose films prepared by different building blocks could affect thermal aging stability and the life of flexible electronic devices. In this work, the effects of thermal aging (105 °C for 5 days) on surface groups, crystalline structures, surface morphology, and mechanical, optical, and thermal properties of cellulose films were studied. Through sputtering and screen printing, conductive lines and circuits were prepared on cellulose films. The effects of thermal aging on electrical stabilities of conductive lines and circuits on cellulose films were investigated. Compared with the sizes of building blocks and crystalline structures of cellulose films, surface groups of building blocks were more responsible for thermal aging stability of cellulose films. As the substrate of flexible electronic devices, cellophane with hydroxyl groups exhibited better thermal aging stability (optical and thermal stabilities and stretchability) than nanopaper with carboxyl groups and sulfate ester groups.