Magnesium hydroxide coated hollow glass microspheres/chitosan composite aerogels with excellent thermal insulation and flame retardancy

The development of an environmental-friendly thermal insulation and flame retardant material has attracted widespread attention in modern architecture. In this work, a kind of novel aerogel composites were prepared by incorporation of Mg(OH)2 coated hollow glass microspheres (HGM) into chitosan (CSA) matrix and then cross-linking by glutaraldehyde (abbreviated as CSA-HGM-Mg(OH)2). The as-prepared composite aerogel exhibits vertical directional channel with high porosity and excellent thermal insulation with a low thermal conductivity of 0.035 W m-1 k-1. Besides, it shows excellent flame retardancy with a high limit oxygen index (LOI) value up to 50.8, which is one of the highest values among the most of flame retardants reported previously. Also, a very low peak heat release rate (pHRR) of 24.12 kW m-2 was obtained which makes the aerogel composite reaching UL-94 V-0 rating. Such results may be attributed to a synergy effect by combination of its abundantly porous structure derived from HGM to give a better thermal insulation and excellent nonflammability of CSA and Mg(OH)2 to offer a superior flame retardancy. Taking advantages of its high mechanical strength, low cost materials, simple and scalable preparation method, CSA-HGM-Mg(OH)2 aerogel composites may hold great potential for future thermal insulation and flame retardant applications.