Flexible Electronic Substrate Film Fabricated Using Natural Clay and Wood Components with Cross‐Linking Polymer

Abstract

Requirements for flexible electronic substrate are successfully accomplished by green nanocomposite film fabricated with two natural components: glycol-modified biomass lignin and Li montmorillonite clay. In addition to these major components, a cross-linking polymer between the lignin is incorporated into montmorillonite. Multilayer-assembled structure is formed due to stacking nature of high aspect montmorillonite, resulting in thermal durability up to 573 K, low thermal expansion, and oxygen barrier property below measurable limit. Preannealing for montmorillonite and the cross-linking formation enhance moisture barrier property superior to that of industrial engineering plastics, polyimide. As a result, the film has advantages for electronic film substrate. Furthermore, these properties can be achieved at the drying temperature up to 503 K, while the polyimide films are difficult to fabricate by this temperature. In order to examine its applicability for substrate film, flexible electrodes are finely printed on it and touch sensor device can be constructed with rigid elements on the electrode. In consequence, this nanocomposite film is expected to contribute to production of functional materials, progresses in expansion of biomass usage with low energy consumption, and construction of environmental friendly flexible electronic devices.

Development of Clay‐Based Films

“…However, high hydrophobicity is not achieved by fixation of Li ions alone. Experimental results show that even with partial fixation of Li, it is possible to fabricate films with high water vapor barrier properties ,,. The water vapor permeability of a polyimide‐Li‐exchanged dioctahedral smectite self‐supporting film with a thickness of ∼20 μm was as low as 1.2×10 −5 g m −2 day −1 atm −1 at 40 °C and 90 % relative humidity …”

“…The CBF microstructure is often analyzed by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Dense, highly ordered arrays of clay platelet crystals have been observed by TEM,,,,, which can facilitate flexibility in the film. In addition, oriented and ordered crystal packing was deduced from XRD results ,,,,.…”

“…The increased decomposition temperature of GL in the composite was attributed to intercalation of GL between the silicate layers . The thermal expansion coefficient of a self‐standing CBF containing Li‐exchanged natural smectite, GL, and a cross‐linking polymer in a weight ratio of 7 : 2 : 1, respectively, was 6–8 ppm/K over a wide temperature range …”

“…The third way to prepare water‐resistant films is to use reduced‐charge smectites (RCS), which has resulted in the successful development of films with high water vapor barrier properties ,,,,. Water‐resistant smectite is prepared by exchanging interlayer Na ions with Li ions followed by heat treatment.…”

A Robust, Air‐Stable and Recyclable Hydrogel Toward Stretchable Electronic Device Applications

“…It is foreseeable that the commercialization of integrated stretchable circuits in diverse applications such as smart sensors, artificial skin, and prosthetics would be the main focus in the following decade. Meanwhile, how to relieve environmental pollutants and energy consumption from modern consumer electronics has also been brought to the forefront of public attention . In general, the majority of a typical chip array is made up of their mechanical supporting substrate that facilitates electrical interconnections for the mounted components.…”