How Cellulose Nanofibrils Affect Bulk, Surface, and Foam Properties of Anionic Surfactant Solutions

Abstract

We study the generation and decay of aqueous foams stabilized by sodium dodecyl sulfate (SDS) in the presence of unmodified cellulose nanofibrils (CNF). Together with the rheology of aqueous suspensions containing CNF and SDS, the interfacial/colloidal interactions are determined by quartz crystal microgravimetry with dissipation monitoring, surface plasmon resonance, and isothermal titration calorimetry. The results are used to explain the properties of the air/water interface (interfacial activity and dilatational moduli determined from oscillating air bubbles) and of the bulk (steady-state flow, oscillatory shear, and capillary thinning). These properties are finally correlated to the foamability and to the foam stability. The latter was studied as a function of time by monitoring the foam volume, the liquid fraction, and the bubble size distribution. The shear-thinning effect of CNF is found to facilitate foam formation at SDS concentrations above the critical micelle concentration (c SDS ≥ cmc). Compared with foams stabilized by pure SDS, the presence of CNF enhances the viscosity and elasticity of the continuous phase as well as of the air/water interface. The CNF-containing foams have higher liquid fractions, larger initial bubble sizes, and better stability. Due to charge screening effects caused by sodium counter ions and depletion attraction caused by SDS micelles, especially at high SDS concentrations, CNF forms aggregates in the Plateau borders and nodes of the foam, thus slowing down liquid drainage and bubble growth and improving foam stability. Overall, our findings advance the understanding of the role of CNF in foam generation and stabilization.

Nanocellulose: From Fundamentals to Advanced Applications

“…Many pioneering applications already employ nanocellulose-stabilized colloids, for instance, preparation of 3D-printing inks (Huan et al, 2018(Huan et al, , 2019, novel bio-nanocomposites (Reid et al, 2019;Bielejewska and Hertmanowski, 2020), and in gastric stable delivery systems (Bai et al, 2019;Liu and Kong, 2019), pertaining to NCs' outstanding stability and biocompatible nature. Xiang et al discovered that cellulose nanofibrils form more stable foams compared to cellulose nanocrystals, attributed to cellulose nanofibrils ability to spread into the bulk, ensuing enhanced interfacial and bulk elasticity (Xiang et al, 2019). Bai et al investigated the stabilization of concentrated edible oil-in-water Pickering emulsions by modifying the surface of naturally derived cellulose nanocrystals with a food-grade cationic surfactant (ethyl lauroyl arginate) (Bai et al, 2018).…”

Film formation and foamability of cellulose derivatives: Influence of co-binders and substrate properties on coating holdout

“…This result could be explained by an increasing amount of MFC located between the bubbles and thus a greater water holding capacity and reduced drainage (Xiang et al 2019), which was also indicated by the gravimetric water retention data. The foam collapsed more with increasing MFC solids content in the MFC-SDS foams, which may indicate an inadequate amount of SDS, as foam stability decreases with decreasing addition of SDS (Lappalainen et al 2014;Xiang et al 2019). Although the 3 wt% EHEC-MFC foam could be considered a wet foam, it did not break during the measured time period.…”

Foam forming of fiber products: a review

“…Also in Ref. [56] foams containing cellulose nanofibers (CNF) were found to have improved stability due to CNF forming aggregates in the Plateau borders and nodes of the foam, which slowed down liquid drainage and bubble growth and thus improved foam stability.…”