Hybrid aerogel bead production

Abstract

The ever-growing demand on single use food packaging materials made from expanded polystyrene (EPS) comes at a high price. Careless disposal at the place of consumption leads to environmental pollution. Driven by wind and collected by rivers, an incredible amount of EPS reaches the oceans. Large garbage patches are the result of the ‘high civilization standard’ and future generations have to deal with the impact on nature due to ultralow degradation rates. Aiming at the replacement of EPS products we are developing biodegradable hybrid aerogel beads from marine polysaccharides and silica. The combination of a ductile polysaccharide aerogel network that covers the brittle silica phase is a promising strategy to overcome the biggest drawback of silica aerogel when handled – dustiness. Commercial hydrophobic silica aerogel granulate (P300 from Cabot Corp.) in water phase was treated with a rotor-stator machine. The efficient breakdown of particles from 3 mm to sizes below 100 µm was dust free and scalable. Resulting suspensions were thickened with chitosan. With our focus on scalability, we employed the JetCutter® method to produce gel beads. Flow rates up to 38 kg/h together with bead generation frequencies around 1500 Hz led to uniform millimeter sized beads. After solvent exchange to ethanol the beads were supercritically dried with CO2. Following physisorption measurement practice hybrid aerogel beads showed specific surface areas around 300 m2/g and mesoporosity. Scanning electron microscope investigations revealed a fibrillar network of chitosan in which fine silica particles were embedded. Energy-dispersive X-ray spectroscopy as well as thermogravimetric analysis proofed successful encapsulation of the silica phase up to 12 wt.%. Thermal conductivity of hybrid aerogel beads was measured below 0,03 W/(m*K) according to the heat flow method. Compacted hybrid aerogel beads to monolithic structures combine lightweight, thermal insulation and biodegradability. Chitosan/silica aerogel beads are a sustainable alternative to EPS.