Absorption kinetics of nanocellulose foams: Effect of ionic strength and surface charge.

Hypothesis: The absorption capacity and kinetics of nanocellulose foams are controlled by the surface charge of the fibers, which affects swelling and determine the porosity and structure of the network.

Experiments: Absorption kinetics were quantified at time scales ranging from fractions of a second to minutes. The mass absorption rate as well as the area profile for the liquid stains were simultaneously measured.

Findings: The absorption profile followed a three-stage mechanism: wicking, transition and fiber swelling. Absorption of fluids differing in ionic strength revealed the critical role played by electrostatic forces. Nanocellulose foam absorption capacity is 25% higher for water than for 0.9 wt% NaCl solution. The absorption kinetics of nanocellulose foam are also tuneable by modulating the surface charge. High surface charge nanocellulose foams have slower absorption in water than their low surface charged analogues. This behaviour is driven by the lower pore sizes developed in high surface charge foams, as determined by X-ray CT. Small Angle X-ray Scattering revealed structural homogeneity of high surface charge foams upon absorption of water due to high fibrillation and fiber swelling.