Local time-dependent microstructure of aging TEMPO nanofibrillated cellulose gel

Abstract

The aging behavior of TEMPO-CNF suspensions is investigated using rheological measurements and experiments involving the free-falling solid sphere. The properties of CNF suspensions, which are formed of water and cellulose fibers with a large aspect ratio, are fundamentally different from those commonly known as model low-density gels. We characterize their aging utilizing SAOS rheometry following a period of shear rejuvenation, measuring the effect of aging time on the observed stress overshoot, and additionally measure the rheological hysteresis under continuous shear. In addition to such tests, which probe the sample at the bulk level, we study their local aging behavior via the Stokes’ experiment. During SAOS, the aging of the material results in a logarithmic growth of the elastic modulus over the first 50 minutes. In the Stokes’ experiment, depending on the sphere size, we find a systematic decrease in the sphere velocity with aging times up to 16 days and identify a range of intermittent particle motion. Based on our experimental evidence, we propose that the aging effect within the TEMPO-CNFs occurs due to the restructuring of fibrous elements by Brownian diffusion and that the aging of the system does not develop homogeneously across the whole sample as a consequence of the wide size distribution of CNFs. Finally, we note that this may be one of the primary reasons why the rheological data on even the same batch of CNFs show a large scatter. Graphical abstract

The Application of Cellulose Nanofibrils in Energy Systems

“…This modification facilitates easier fibrillation and improves the overall efficiency of the CNF production process [30]. This weakens the cellulose structure, making it easier to mechanically disintegrate the fibers [31]. Furthermore, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation, discovered by Akira Isogai et al, is a prominent example of pretreatment for the production of CNFs [32].…”

Stabilization of Beeswax-In-Water Dispersions Using Anionic Cellulose Nanofibers and Their Application in Paper Coating

“…Their carboxyl group content mainly depends on the amount of hypochlorite used, reaching a maximum of roughly 1.5 mmol/g [ 9 , 10 ]. Regarding the aforementioned application as a thickener, aqueous suspensions of TOCNFs may attain gel behavior, along with yield stress values above 20 Pa, at concentrations as low as ~0.3 wt% [ 3 , 11 ]. This, in turn, is also useful for the Pickering stabilization of oil-in-water systems, since one of the mechanisms postulated for this task is the rheological hindrance of the motion of the droplets [ 1 ].…”