Chitosan/polybenzoxazine/clay mixed matrix composite aerogels: preparation, physical properties, and water absorbency

The present study reports development of chitosan/polybenzoxazine/clay mixed matrix composite aerogels (MMCAs) using freeze-drying of various sodium montmorillonite (Na-MMT) colloidal dispersions in chitosan/ benzoxazine polymers blend in aqueous solution. Thermal treatment of aerogels leads to produce crosslinked MMCAs. The microstructure characteristics of the MMCAs were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The thermal properties of the MMCAs were evaluated by thermal gravimetric analysis (TGA). The obtained MMCAs have ultra-low densities within a very small range (< 0.073 g/cm(3)) and exhibited that their porosities higher than 93%. The effect of Na-MMT on thermal properties of the chitosan/ polybenzoxazine MMCAs was investigated. The onset decomposition temperatures were significantly enhanced with clay-loading, implying the superior thermal stability of these composites. Due to the thermal ring-opening polymerization of benzoxazine, the effect of heat treatment on dimensional stability and water absorption of the chitosan/benzoxazine-based aerogels have also been investigated, which have not yet been studied elsewhere. The results demonstrated that polymerized aerogels are highly stable not only in neutral water, but also in acidic medium. The obtained MMCAs exhibit to be efficient water absorbents. The results revealed that the MMCAs are relatively high water absorption up to 2900 wt% at ambient conditions.