The effect of embedding highly insulating granular aerogel in cellulosic aerogel

• Novel particulate aerogel–aerogel composites were synthesized.
• Granular silica aerogel were embedded in a cellulosic aerogel matrix.
• Non-fragile composites with thermal conductivity below 0.05 W/mK were produced.
• High-density silica aerogel grains reinforces the cellulose aerogel largely.
• Low-density silica aerogels have only a small reinforcing effect.

We investigate aerogel–aerogel composites to develop new materials for thermal insulation applications with reduced fragility and without release of dust. Two different kinds of highly insulating silica aerogels (SiO2) were embedded into a cellulosic aerogel: a high-density (0.25 g/cm3) tetramethylorthosilicate (TMOS) based and a low-density (0.15 g/cm3) waterglass based hydrophilic granular silica aerogel which are added to the salt hydrate melt of 59 wt.% calcium thiocyanate and 2 or 3 wt.% of cellulose during the synthesis of a cellulosic aerogel. The silica aerogel species show a different behavior regarding the interaction with the cellulose network in the composite examined by scanning electron microscopy. With the synthesis method we were able to produce non-fragile aerogel–aerogel composites and a strong stiffening effect regarding Young’s modulus was achieved compared to pure aerogels. Density obtained is 0.04–0.15 g/cm3 and thermal conductivity reached is between 0.04–0.05 W/mK.

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