Wet-State Densification of Ionically Cross-Linked Nanocellulose Gels for Producing Stiff Porous Structures

Area of Science:

• Materials Science
• Nanotechnology
• Polymer Science

Background:

• Cellulose nanofiber (CNF) aerogels offer transparency and thermal insulation.
• A key limitation of CNF aerogels is their inherent mechanical weakness.

Purpose of the Study:

• To develop a novel wet-state densification strategy for CNF aerogels.
• To enhance the mechanical properties of CNF aerogels without compromising optical and thermal performance.

Main Methods:

• CNF dispersions were cross-linked with zirconium ions to form hydrogels.
• Uniaxial compression and supercritical drying were employed to create densified aerogels.
• Characterization included density, mechanical stiffness, light transmittance, and thermal conductivity measurements.

Main Results:

• Densified aerogels exhibited bulk densities ranging from 25-95 mg cm^-3.
• Anisotropic layered structures were formed, maintaining mesopores (10-60 nm) and high surface area (380-440 m² g^-1).
• Aerogels with 95 mg cm^-3 density achieved high tensile stiffness (~122 MPa) with ~75% light transmittance and 21 mW m^-1 K^-1 thermal conductivity.

Conclusions:

• Wet-state densification effectively improves the mechanical robustness of CNF aerogels.
• The developed aerogels successfully combine mechanical strength, optical transparency, and thermal superinsulation.
• This strategy offers a pathway to advanced functional materials for diverse applications.