Silication of Dimensionally Stable Cellulose Aerogels for Improving Their Mechanical Properties

Abstract

Dimensionally stable aerogels that retain their shapes and geometric sizes in solutions have been formed from cellulose subjected to an intense mechanical treatment in combination with freeze-thawing. This treatment has resulted in partial separation of numerous micro/nanosized fibrils that surround residual fibers. Their entanglement promotes an increase in the mechanical strength and stability of the aerogels in solutions. Silication (mineralization) of the cellulose aerogels has been performed by the sol–gel method in dilute solutions of a precursor, tetraethoxysilane, at its maximum concentration of 1 wt %. According to FTIR spectroscopy and scanning electron microscopy data, the modification has resulted in the formation of thin silica coatings on the micro/nanofibrils. The study of the mechanical properties in the compression mode has shown a substantial increase in the mechanical strength and a decrease in the elasticity of the aerogels as a result of their mineralization. For example, after the treatment in a 1% precursor solution, the Young’s modulus has increased by an order of magnitude, while the linear portion of the stress–strain curve has become shorter. At the same time, the existence of the thin silica coating on the micro/nanofibrils has no effect on the mechanical properties of the aerogels placed into aqueous solutions. This may be explained by the plasticizing effect of water adsorbed by hydrophilic cellulose.