Layer by Layer coatings assembled through dipping, vertical or horizontal spray for cotton flame retardancy

Silica-based assemblies have been deposited on cotton fibres through Layer by Layer technique in order to enhance their flame retardant properties. To this aim, three different deposition procedures (namely, dipping, vertical and horizontal sprays) have been considered and compared. The resulting morphologies of the deposited assemblies have been thoroughly investigated by scanning electron microscopy (SEM) and elemental analysis. SEM observations have demonstrated that only the horizontal spray allows obtaining the deposition of a very homogeneous silica coating when compared to vertical spray or dipping. As a consequence, horizontal spray has proved to ensure the best flame resistance, promoting a substantial increase of the total burning time and final residue, as assessed by flammability tests. Furthermore, cone calorimetry measurements have shown a remarkable increase of the time to ignition, and a significant decrease of heat release rate and total heat release for the fabrics treated by horizontal spray.