The role of pre-hydrolysis on multi step sol–gel processes for enhancing the flame retardancy of cotton

The flame retardancy properties of cotton have been enhanced by exploiting an optimized multistep sol–gel process, consisting of a pre-hydrolysis step, followed by consecutive depositions of hybrid phosphorus-doped silica layers, using DPTS as precursor of the oxidic phases. Upon optimization, it has been demonstrated that just one phosphorus-doped silica layer is able to strongly reduce the heat release rate (−52 %), and the total smoke release (−56 %) and its rate (−62 %) with respect to the untreated fabric. In addition, the deposition of three layers allows achieving a higher flammability resistance if compared to a single layer, as indicated by the final residue after the flammability tests. As far as flammability resistance is concerned, the new coatings have shown a good durability when subjected up to five washing cycles according to ISO 6330 standard.