Ion-induced gelation of charged nanocellulose particles in suspension is a key processing step to control the structure when creating new cellulose-based high-performance materials, such as nanoporous membranes for water purification. Additionally, by using multivalent ions as cross-linkers in the nanofibrillar network, the hydrogel itself can also be used as an absorbent to remove toxic heavy metal ions. In this study, we developed a flow-focusing mixing experiment to study the time-resolved gelation process of cellulose nanofibers and nanocrystals (CNF and CNC), both with negatively charged surface, by means of small angle X-ray scattering (SAXS). The creation of a plug flow (without shear) of dispersed CNC and CNF allows us to convert directly spatial coordinates to time instances of the hydrogel formation. Focusing the incident X-ray at a certain position in the flow, we have studied the structural parameters, including the size and density of segmental aggregates at different time-stages of the dispersion-gel transition. With monovalent ions, we examined the changes in inter-particle distances as the electrostatic charges are screened by the ions. By mixing multi-valent ions (crosslinking agents) with different concentrations of CNF and CNC, important time scales, such as the time required to develop a stable gel with a pronounced interface, were further determined. This experimental technique allowed us to greatly enhance our understanding of the cellulose-cation interactions, which can lead to optimization of cellulose material processing for varying applications in the future.<br/>

Time resolved characterization of metal ion-induced nanocellulose gelation by small angle X-ray scattering

2019 Fall National Meeting

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