Influence of the morphology of zinc oxide nanoparticles on the properties of zinc oxide/nanocellulose composite films

Abstract

Zinc oxide (ZnO) nanoparticles with different morphologies, including spheres, rods, and needles, and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNs) were mixed in water and then cast and dried to give ZnO/TOCN (1:9 w/w) composite films to investigate the influence of ZnO nanoparticle morphology on composite film properties. TOCNs were used as the matrix of ZnO-containing composite films because TOCN films have high transparencies. The film densities varied from 1.25 to 1.63 g/cm3 and porosities ranged from 5.4 to 22 vol% depending on the ZnO nanoparticle morphology. The (100) plane of the rod- and needle-like wurtzite ZnO particles were preferentially oriented to the composite film surfaces. The Young's modulus and tensile strength of the composite films were similar regardless of nanoparticle morphology, whereas the ZnO/TOCN films with higher porosities had greater elongations at break and works of fracture. The composite films with rod- and needle-like ZnO particles had low oxygen permeability at 50% relative humidity. All the ZnO/TOCN composite films screened ultraviolet (UV) light, and the film with spherical ZnO nanoparticles had the highest visible-light transmittance. The ZnO/TOCN composite films and their components showed photoluminescence when exited by UV light with the highest intensity at 370-nm UV light. The composite films in aqueous methylene blue (MB) solution under UV irradiation restricted the UV-induced ZnO-catalyzed degradation of MB.