In this study, self-supporting flexible supercapacitor electrodes were prepared by wrapping polypyrrole (PPy) on the surface of the TEMPO-oxidized cellulose nanofiber (TOCN)/reduced graphene oxide (RGO) film using a layer-by-layer selfassembly method under an oil−water separation environment. The obtained film had a three-dimensional-layered structure and exhibited a certain porosity, which is favored for the electrochemical performance. The areal capacitance of the TOCN/RGO/PPy film electrode was as high as 915 mF cm −2 , and 96.6% capacitance was retained after 2000 cycles of charge and discharge. Also, it maintained a higher rate retention of 98.4% after undergoing bending 200 times. These capacitance values are significantly better than RGO or PPy single-component films or their mixture with similar constituents. Furthermore, a solid-state symmetric supercapacitor was assembled by combining the TOCN/RGO/PPy electrode and CNF hydrogel films as a separator, which displayed an excellent specific capacitance of 195.8 F g −1 and a volumetric capacitance of 9.8 F cm −3 at the current density of 0.1 mA cm −2 . Meanwhile, an outstanding energy density of 13.04 Wh kg −1 with a power density of 200.6 W kg −1 was also obtained. These facts fully suggest that the TOCN/RGO/PPy film with a three-dimensional-layered structure in this study is promising for highperformance flexible energy-storage electrodes.
In this work, poplar veneer (PV) rotary-cut from fast-growing polar was delignified to prepare flexible transparent poplar veneer (TPV). Lignin was gradually removed from the PV and then epoxy resin filled into the delignified PV. The study mainly concerns the effect of lignin content on microstructure, light transmittance, haze, tensile strength, and thermal stability of the PVs impregnated with epoxy resin. The results indicate that the lignin could be removed completely from the PV when the delignification time was around 8 h, which was proved by FTIR spectra and chemical component detection. Moreover, according to SEM observation and XRD testing, the porosity and crystallinity of the PVs were gradually increased with the removal of lignin. Also, the optical properties measurement indicated that the light transmittance and haze of the TPVs gradually increased, and the thermal stability also became more stable as shown by thermogravimetric analysis (TG). However, the tensile strength of the TPVs declined due to the removal of lignin. Among them, TPV8 exhibited excellent optical properties, thermal stability, and tensile strength. Consequently, it has great potential to be used as a substrate in photovoltaics, solar cells, smart windows, etc.
There has been growing interest in transparent conductive substrates due to the prevailing flexible electron devices and the need for sustainable resources. In this study, we demonstrated a transparent fast-growing poplar veneers prepared by acetylated modification, followed by the infiltration of epoxy resin. The work mainly focused on the effect of acetylation treatment using a green catalyst of 4-Dimethylpyridine on the interface of the bulk fast-growing poplar veneer, and the result indicated that the interface hydrophobicity was greatly enhanced due to the higher substitute of acetyl groups; therefore, the interface compatibility between the cell wall and epoxy resin was improved. The obtained transparent fast-growing poplar veneers, hereafter referred to as TADPV, displayed a superior optical performance and flexibility, in which the light transmittance and haze were 90% and 70% at a wavelength of 550 nm, respectively, and the bending radius and bending angle parallel to grain of TADPV were 2 mm and 130°, respectively. Moreover, the tensile strength and tensile modulus of the TADPV were around 102 MPa and 198 MPa, respectively, which is significantly better than those of the plastic substrates used in flexible electron devices. At the same time, the thermal conductivity tests indicated that TADPV has a low coefficient of thermal conductivity of 0.34 Wm−1 K−1, which can completely meet the needs of transparent conductive substrates. Therefore, the obtained TADPV can be used as a candidate for a flexible transparent substrate of electron devices.
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