Preparation and characterization of zinc oxide/TEMPO-oxidized cellulose nanofibril composite films

Abstract

ZnO particle/water and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibril (TOCN)/water dispersions were mixed at various ratios under stirring. The aqueous ZnO/TOCN mixtures were sonicated, cast, and dried to prepare ZnO/TOCN composite films with various ZnO/TOCN weight ratios. The ZnO contents of the films were controlled to 0–50% (w/w). When the ZnO content was increased to 5–50%, the porosity of the composite films increased to 14–23%. This is probably because the positively charged ZnO particles and negatively charged TOCN elements formed aggregates in both aqueous mixtures and dried films. The ZnO/TOCN composite film of thickness 10 µm containing 10% ZnO had more than 80% light transmittance at 600 nm, and high UV-screening properties. The composite films containing 25 and 50% ZnO had almost perfect UV-screening properties, but their light transmittances at 600 nm were only 60–80%. All the composite films had low coefficients of thermal expansion (<10 ppm/K). Because the composite films consisted of stiff TOCNs and ZnO, but had porous structures, the tensile strength and strain-to-failure decreased slightly with increasing ZnO content from 0 to 10%. The composite film containing 50% ZnO had explicitly ductile properties because of its high porosity.