Poly(vinylalcohol)/chitosan-based high-strength, fire-retardant and smoke-suppressant composite aerogels incorporating aluminum species via freeze drying

Abstract

In this work, new types of organic-inorganic composite aerogels were fabricated via the freeze-drying method based on the chemical interaction between bio-based chitosan and aluminum chloride, in combination with physical cross-linking among chitosan, inexpensive polyvinyl alcohol (PVA) and alumina sols derived from the acidic hydrolysis of aluminum isopropoxide (AIP). The microstructural evolution of the freeze-dried chitosan-aluminum/PVA (CAP) aerogels revealed that varied amount of aluminum salt could influence the three-dimensional architecture. Especially, the CA1.5P aerogel with herringbone-like structure had high compressive strength of 8.55 MPa, corresponding to the specific modulus of 66.3 m2 s−2. Compared to the polymeric chitosan/PVA aerogel, the CAP aerogels showed better fire retardancy, as confirmed by limited oxygen index (LOI) tests and cone calorimeter (CC) tests. Remarkably, the introduction of inorganic components from AIP (about 7.7–20.1 wt%) led to an increased LOI value (35%–41.1%) and lower total heat release and total smoke release. The proposed mechanism suggested that the enhanced flame retardancy benefitted greatly from the formation of alumina-rich hybrid chars with the assistance of thermal degradation of chitosan, which resulted in barrier effects of controlling the heat and smoke hazards. In addition, silanization modification of the composite aerogel was performed by a facile chemical vapor deposition (CVD) treatment to improve the hydrophobicity. The aluminum-incorporated organic-inorganic aerogels with high mechanical strength, good fire-resistance and smoke-suppressant performance could be seen as potential alternatives to traditional flame-retardant foams.