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.

中文翻译：

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尺寸稳定的纤维素气凝胶的硅化，以改善其机械性能

摘要

由纤维素经过严格的机械处理并结合冻融形成的尺寸稳定的气凝胶已在溶液中保持其形状和几何尺寸。该处理导致围绕残留纤维的许多微米/纳米原纤维的部分分离。它们的缠结促进了溶液中气凝胶的机械强度和稳定性的增加。纤维素气凝胶的硅化（矿化）已通过溶胶-凝胶法在前驱体四乙氧基硅烷的稀溶液中进行，最大浓度为1 wt％。根据FTIR光谱学和扫描电子显微镜数据，该修饰导致在微/纳非昔布上形成二氧化硅薄涂层。对压缩模式下的机械性能的研究表明，由于气凝胶的矿化作用，其机械强度大大提高，而气凝胶的弹性却降低了。例如，在1％前体溶液中处理后，杨氏模量增加了一个数量级，而应力-应变曲线的线性部分变得更短。同时，在微米/纳米纤维上存在二氧化硅薄涂层对放置在水溶液中的气凝胶的机械性能没有影响。这可以通过亲水性纤维素吸附的水的增塑作用来解释。在1％前体溶液中处理后，杨氏模量增加了一个数量级，而应力-应变曲线的线性部分变得更短。同时，在微米/纳米纤维上存在二氧化硅薄涂层对放置在水溶液中的气凝胶的机械性能没有影响。这可以通过亲水性纤维素吸附的水的增塑作用来解释。在1％前体溶液中处理后，杨氏模量增加了一个数量级，而应力-应变曲线的线性部分变得更短。同时，在微米/纳米纤维上存在二氧化硅薄涂层对放置在水溶液中的气凝胶的机械性能没有影响。这可以通过亲水性纤维素吸附的水的增塑作用来解释。