Studying the Structure of Colloidal Polymer-grafted Nanocellulose Fibril Dispersions by SAXS

Introduction

Cellulose nanomaterials are attracting increasing attention as a sustainable building block in materials science. These cellulose-based materials – which have one or more of their external dimensions at the nano-scale – can be divided into three classes: cellulose nanofibrils (CNF), cellulose nanocrystals (CNC) and bacterial cellulose (BC).
Cellulose nanomaterials have several unique properties, such as their strength, rheological properties, reactivity and tendency to form films. A big advantage over other materials is that cellulose is abundant, i.e. can be obtained from natural, renewable resources. (1,2)

The surface of nanocellulose can be chemically modified by polymer grafting in order to tune, e.g. the viscoelastic properties of nanocellulose for application in rheology modifiers or to adjust the reinforcement effect in composite materials. As an example, the introduction of ionic functional groups on the CNF surface increases repulsion between the fibrils and therefore improves the colloidal stability. (3)

However, the actual structure of such polymer-grafted nanocellulose has not been clarified in detail yet, in particular the confirmation of the grafted polymer as well as the twist of the core nanocellulose.

In this report, the structure of polymer-grafted cellulose nanofibers in a colloidal dispersion system is investigated by using a combination of small-angle X-ray scattering (SAXS) studies with all-atom molecular dynamics simulation.

The small-angle X-ray scattering method measures the size and shape of nanosized particles and assemblies. It is particularly suitable for studying samples in solution, e.g. particle dispersions, which can otherwise only be analyzed by microscopy techniques that might involve alteration/destruction of the nanostructure during sample preparation. (4) All-atom molecular dynamics (MD) simulation helps to visualize the detailed structure (conformation of the CNF and grafted polymer chain as well as the chemical bonding between them).

References

1. Kontturi, E., Nonappa, Ikkala, O. et al., Adv. Mater. 2021, 33, 2004349.
2. Kangas, H., Research report “Guide to cellulose nanomaterials” VTT-R-05013-14, 2014.
3. Fujisawa, S., Takasaki, Y., Saito, T., Nano Lett. 2023, 23, 880-886.
4. Schnablegger, H., Singh, Y., The SAXS Guide – Getting acquainted with the principles. 5th Ed. (2023), Anton Paar GmbH: Graz, Austria