Abstract

Aerogels are low density foam-like materials that are obtained from a sol-gel process in which the solvent used is replaced by air without collapsing the previously formed three-dimensional structure. In this work, we have studied the properties of aerogels composites that have been generated only from natural substances, using gelatin as matrix, clay and tannic acid as modifiers and water as unique solvent. The aerogels were obtained through lyophilization. While pure gelatin aerogel behaves like an elastic and low-stiffness foam, the addition of tannic acid and clay allow obtaining high resistant foams, reaching of up to a 9-fold increase in the elastic modulus, maintaining very low densities ( 0.14 g/cm3). These increases were obtained, on the one hand, due to a change in the aerogel micro-structure that evolved from a layered towards a honeycomb one. On the other hand, the alkaline conditions employed lead to the oxidation of tannic acid that was then able to establish covalent bonding with the amino groups of gelatin. The presence of well-dispersed clay in the matrix significantly reduced the rate of thermal degradation of the compounds due to its rearrangement into a stable protective layer on the surface of the material. Under conditions similar to those developed in a fire, the compound exhibited low flammability and high resistance to the spread of fire thanks to the synergistic action between clay and tannic acid. The achievement of multifunctional properties in these natural aerogels, allows broadening its applications, making that eventually, can replace traditional petroleum-derived foams, such as polyurethane, polystyrene or phenol-formaldehyde that have a notable environmental impact.