Controlling the melt dripping of polyester fabrics by tuning the ionic strength of polyhedral oligomeric silsesquioxane and sodium montmorillonite coatings assembled through Layer by Layer

This work deals with the Layer by Layer (LbL) assembly of hybrid organic/inorganic flame retardant coatings made of Octa-ammonium POSS (polyhedral oligomeric silsesquioxane) and sodium montmorillonite clay on polyester (PET) fabrics. The effects of ionic strength on the achieved flame retardancy properties were investigated. The coating growth as a function of different ionic strengths was evaluated by infrared spectroscopy. 0.10 M NaCl was found able to promote the highest adsorption of each coating species at each deposition step strongly affecting clay stacking as evaluated by X-ray diffraction measurements. The coatings on PET assembled at high ionic strength turned out to be more homogeneous and thicker than the reference one. Thanks to the increased thickness and better surface coverage, the same coatings efficiently suppressed the melt dripping phenomenon and significantly slowed down flame spread rate in horizontal flammability tests with only 2 wt% of coating mass added. Furthermore, the same performances were maintained after 1 h washing at 70°C. By cone calorimetry, coated fabrics showed a strong reduction in the combustion kinetics by nearly halving the peak of heat release rate. This paper provides an important insight on the viability of tuning deposition of LbL coatings on fabrics employing industrial-like processes by simple modification of ionic strength.