Comparison of highly transparent all-cellulose nanopaper prepared using sulfuric acid and TEMPO-mediated oxidation methods

Transparent cellulose films from 2,2,6,6-tetramethylpiperidine-1-oxyl radical oxidized cellulose nanocrystals (TOCNs) and 64 wt% sulfuric acid treated cellulose nanocrystals (SACNs) were prepared from bleached wood pulp. Film morphology, optical, mechanical, thermal, and surface wettability properties were characterized and compared. The results showed that TOCNs and SACNs had different average length (200.7 vs. 163.0 nm), diameter (5.8 vs. 15.6 nm), and aspect ratio (34.4 vs. 10.4). Compared with the SACN film, TOCN films exhibited higher optical transmittance (98.4 % at 900 nm) and larger tensile strength (236.5 MPa). SACN films exhibited better thermal stability (Tₒₙₛₑₜ = 239 °C), higher crystallinity (73.4 %) and lower coefficient of thermal expansion (CTE = 8.38 ppm/k). Additionally, both films demonstrated good surface wettability. The results indicate that the TOCN and SACN films could be considered as a substrate material to replace traditional glass and plastic substrates for the next generation “Green” electronics.