Robust and fire retardant borate-crosslinked poly (vinyl alcohol)/montmorillonite aerogel via melt-crosslink

Abstract A highly robust and flame retardant borate-crosslinked poly (vinyl alcohol)/montmorillonite aerogel is fabricated through a novel melt-crosslink method. In this way, the PVA/MMT hydrogel was prepared by immersing the frozen PVA/MMT sol into a borax solution, inducing crosslinking between diols of PVA and borate exactly during the ice melt. As a result, rearrangement of the polymer chains and subsequent expansion result in finer and more compact network. The corresponding aerogel is obtained by freeze-drying. The optimal crosslinking conditions, including the borax concentration and crosslinking time, are determined by rheology of the hydrogels. This method provides a new idea for the preparation of crosslinked aerogels and improvement of mechanical and flame retardant properties simultaneously. The mechanical strength of the crosslinked aerogel is relatively high among the existing fire safety polymer/nanoclay composite aerogels with 30%–60% loading of inorganic matters at a low density level. The flame retardant properties are indicated by significant improvements of limiting oxygen index (LOI) to a value of 27.6% and achievement of UL-94 V-0 rating and remarkable decrease of the fire indexes in cone calorimetry (CC) test. The combustion behaviors are further studied by the results of SEM, energy dispersive X-ray spectrometer (EDX) and X-ray photoelectron spectroscopy (XPS).