Facile fabrication of mechanically-strong and flame retardant alginate/clay aerogels

Mechanically-strong sodium alginate/clay aerogel were fabricated by addition of p-toluenesulfonic acid using a freeze-drying method. The adjusting of pH from 8 (the control) to 6, on the one hand lead to the crosslinking of alginate, on the other hand thickened the clay sol. The compressive modulus of A5C5 aerogel significantly increased from 6.0 +/- 0.4 MPa (pH = 8) to 17 +/- 3 MPa (pH = 6). The morphological structure characterization showed that the microstructure of aerogels changed from layered to network with decreasing pH value, with cell size ranging from 4 to 8 mu m. The rheological behavior showed that the addition of p-toluenesulfonic acid would significantly improve the viscosity of the precursors at low frequency. The combustion tests indicated that all the alginate/clay aerogels possess excellent flame retardancy. The addition of p-toluenesulfonic acid further slightly increased the thermal stability and fire safety of the material. This facile preparation procedure of strengthened polymer/clay aerogel via adjusting pH is promising and can be spread.