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Simultaneous/direct chemomechanical densification and downsizing of weak paulownia wood to produce a strong, unidirectional, all-wooden nanocomposite


Microstructure-free, strong, binderless, all-wooden nanocomposites (AWNCs) with unidirectional nanofibrils were directly fabricated from lightweight paulownia raw wood (RW) through simultaneous chemomechanical densification and downsizing processes with three main steps: (1) partial delignification, (2) partial dissolution with ionic liquid (IL) or oxidation with the free radical 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and ammonium persulfate (APS) and (3) hot pressing with cyclic pressurizing-depressurizing conditions. The density of RW was 0.310 g/cm3, while the density of the AWNCs drastically increased to 1.24 g/cm3. Field emission scanning electron microscopy (FE-SEM) demonstrated that the microstructure of RW fibers was directly dismantled into wood nanofibrils during AWNC production. Two-dimensional wide angle X-ray diffraction (2D-WAXS) patterns confirmed the unidirectional structure of the AWNCs. Fourier transform infrared spectroscopy (FTIR) successfully confirmed the effect of all chemical treatments on the specimens. Thermogravimetric analysis (TGA) demonstrated that AWNC-TEMPO and AWNC-APS had the lowest thermal stability. AWNC-TEMPO had the highest flexural (246 ± 15 MPa) and tensile (265 ± 17 MPa) strengths, while RW showed the minimum corresponding values of 38 ± 7 MPa and 18 ± 2.5 MPa, respectively.

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EK would like to acknowledge the financial support of the Iranian Ministry of Sciences, Research, and Technology. The authors are also grateful for Nano Novin Polymer Co. (Iran) for its kind cooperation within the primary experiments of this study.

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Correspondence to Hossein Yousefi.

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Kaffashsaei, E., Yousefi, H., Nishino, T. et al. Simultaneous/direct chemomechanical densification and downsizing of weak paulownia wood to produce a strong, unidirectional, all-wooden nanocomposite. Polym J 55, 691–702 (2023).

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