Hybrid Nanocelluloses Isolated through Electron-Beam Irradiation in the Wet State: Redispersibility in Water and Superstability for Pickering Emulsions

Abstract

A sustainable nanofabrication approach is developed for isolating hybrid nanocelluloses (Hy-NCs) comprised of both long flexible fibers (CNFs) and needle-like crystals (CNCs) from a hardwood wet pulp (WP) using electron-beam irradiation (EBI). The method was applied to prepare spray-dried powders that could be transparently redispersed. As a result, the disassociated wet pulps had increased carboxylate contents of 0.04-0.12 mmol g(-1) compared to the initial wet pulps and the corresponding dried pulps. The irradiated pulp was subsequently disintegrated by alkaline high-pressure homogenization to form stable Hy-NC dispersions which retained background transparency due to the considerable negative surface charges of -34 to -38 mV. The resulting NC-WP-E0500 and NC-WP-E1000 dispersions were prepared in two mixtures with CNF/CNC ratios of 68/32 and 33/67, based on a 700 nm length to determine CNF and CNC, with the average lengths of 927 +/- 512 and 653 +/- 382 nm, respectively. NCWP-E1000 was neutralized with CO2, spray-dried to prepare dehydrated products, and was clearly redispersible. We also studied oilin-water (O/W) Pickering emulsions formed by the Hy-NC particles, observed by merged confocal and SEM images. NC-WPE1000 promoted monodispersed oil droplets of around 2.6 mu m where bimodal distribution converged, which remained stable even when creaming force was applied for highly concentrated (dense) emulsion applications. This could be attributed both to the degree of viscoelastic thickening and depletion stabilization by the still repulsive and nonabsorptive CNFs in the continuous phase and the absorption caused by CNC layer at the O/W interfaces in the emulsions.