Ambient-dried cellulose fibers-silica composite aerogels: impact of fibers characteristics
Résumé
Ambient dried silica aerogels, formerly so-called silica xerogels, possess morphology and properties really close to silica aerogels except one important point: during ambient pressure drying silica gel breaks into small pieces because of high capillary pressure developed in the system. However, when silica gel is “reinforced” by a non-woven fiber matrix, the materials, so-called “blankets”, can be obtained via ambient pressure drying. As well as silica aerogels obtained via drying in supercritical conditions, “blankets” have thermal superinsulating properties with thermal conductivity in room conditions considerably below that of air, 0.013 – 0.017 W/m.K vs 0.025 W/m.K, respectively. One of the main drawbacks of “blankets” is the high level of release of silica powder. In this work, we used man-made short cellulose fibers, Tencel®, to synthesize silica-based composite ambient-dried aerogels which are monolithic, with thermal conductivity around 0.016 – 0.018 W/m.K in room conditions and almost dust-free. The influence of fiber length and concentration on composite overall shrinkage, bulk density and mechanical as well as thermal properties will be presented. The properties of composite aerogels prepared from the same silica precursor and dried with supercritical CO2 and ambient dried will be compared. Using short cellulose fibers finally appears an alternative way of the synthesis of thermal superinsulating materials involving biomass and avoiding supercritical drying.