New hybrid alginate-silica aerogel developments as sustainable replacements for film-type plastic packaging

Abstract

The increasing demand for disposable food packaging made from expanded polystyrene (EPS), for example, is having costly consequences. Improper disposal at consumption sites causes dramatic environmental pollution. Wind and water transport vast amounts to oceans, resulting in huge garbage patches. With ultra-low degradation rates, future generations will have to address the impact on nature caused by this "high civilization standard." Research is therefore focused on replacing plastic products with hybrid aerogels made from biodegradable marine resources such as polysaccharide and silica. The hybrid alginate-silica aerogels are obtained by combining ductile polysaccharide aerogel as a matrix material with silica granules. In a first step commercially available brittle silica aerogel granulate was mechanically treated in a water phase leading to submillimeter particle sizes without any dust evolution. Afterwards alginate powder was added to thicken the resulting suspensions. In a second step this suspension was shaped using a film applicator to produce thin films of hybrid gel. After solvent exchange to ethanol, the films were supercritically dried using CO2. The hybrid aerogel films obtained showed a thickness of less than 700 µm and an aerogel-typical mesoporous morphology with specific surface areas of about 700 m2/g. Scanning electron microscope investigations indicated a fibrillar network of alginate containing fine embedded silica particles, see fig. 1. Thermogravimetric analysis confirmed successful encapsulation of the silica phase of up to 70 wt.%. The hybrid aerogel films exhibited a low thermal conductivity of below 0.03 W/(m*K). By thermoforming, the hybrid aerogel films could be formed into desired structures. The films had a low weight, high thermal insulation and were biodegradable. Within the presentation lab scale preparation will be explained as well as its potential for upscaling receiving an economically promising and ecologically sustainable and sensible alternative to EPS.