Abstract
During the past decade, cellulose nanofibrils (CNFs) have shown tremendous potential as a building block to fabricate new advanced materials that are both biocompatible and biodegradable. The excellent mechanical properties of the individual CNF can be transferred to macroscale fibers through careful control in hydrodynamic alignment and assembly processes. The optimization of such processes relies on the understanding of nanofibril dynamics during the process, which in turn requires in situ characterization. Here, we use a shear-free mixing experiment combined with scanning small-angle X-ray scattering (scanning-SAXS) to provide time-resolved nanoscale kinetics during the in situ assembly of dispersed cellulose nanofibrils (CNFs) upon mixing with a sodium chloride solution. The addition of monovalent ions led to the transition to a volume-spanning arrested (gel) state. The transition of CNFs is associated with segmental aggregation of the particles, leading to a connected network and reduced Brownian motion, whereby an aligned structure can be preserved. Furthermore, we find that the extensional flow seems to enhance the formation of these segmental aggregates, which in turn provides a comprehensible explanation for the superior material properties obtained in shear-free processes used for spinning filaments from CNFs. This observation clearly highlights the need for different assembly strategies depending on morphology and interactions of the dispersed nanoparticles, where this work can be used as a guide for improved nanomaterial processes.
Highlights
With the grand challenge of dealing with global warming and unsustainable usage of synthetic polymers, there is a growing demand for advanced materials extracted from natural resources that are both biobased and biodegradable, which could provide the backbone for a circular bioeconomy
Nanocellulose extracted from lignocellulose biomass using the top-down de brillation process can be divided into two types: cellulose nanocrystals (CNCs) and cellulose nano brils (CNFs).[1]
In order to quantify the segmental aggregates, we developed a model using simpli ed small-angle X-ray scattering (SAXS)-simulations where each segmental aggregate can be assumed to consist of N 1⁄4 10, 20.100 parallel nano bril elements that are randomly sampled within a circle of radius R 1⁄4 10, 20.100 nm
Summary
With the grand challenge of dealing with global warming and unsustainable usage of synthetic polymers, there is a growing demand for advanced materials extracted from natural resources that are both biobased and biodegradable, which could provide the backbone for a circular bioeconomy. The main advantage of CNFs, are their inherent ability to form volume-spanning networks at very low concentrations,[17,18,19,20,21,22] making them highly desirable as building blocks in membranes, barriers, aerogels, 4940 | Nanoscale Adv., 2021, 3, 4940–4951
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