Multi-functional hydroxyapatite/polyvinyl alcohol composite aerogels with self-cleaning, superior fire resistance and low thermal conductivity

Hybrid inorganic/polymer composite aerogels combine the advantages of both components which can overcome the brittle fracture of inorganic aerogels as well as high flammability of polymeric aerogels. Herein, we reported a facile approach to prepare polyvinyl alcohol (PVA)-hydroxyapatite (HAP) composite aerogel by freeze-casting process towards multi-functional aerogel materials. The incorporation of HAPs led to significant reduction in the peak heat release rate (−79%), total heat release (−76%), specific extinction area (−65%) and CO production (−45%). Vertical burning tests also manifested that PVA-HAP composite aerogels displayed excellent fire resistance and self-extinguishing behaviours. The resultant PVA-HAP composite aerogels also showed a low thermal conductivity (33.6-38.7 mW m−1 K−1). The hydrogen bonding formed between the HAP and the PVA matrix endowed the resultant composite aerogels with a specific modulus (58.7 kN m−1 kg−1) which was comparable to or even higher than those reported by state-of-the-art foams, including polystyrene foams, polyurethane foams and silica aerogels. After a facile polydimethylsiloxane treatment, the resultant PVA-HAP composite aerogels also exhibited water-repellent and self-cleaning capacity, which is a promising candidate as building insulating materials.