Silicophosphate Fire Retardant Coatings for Expanded Polystyrene

Abstract

Silicophosphate coatings are one of the current vectors in the field of increasing the fire resistance of extruded polystyrene foam (XPS), which is widely used in construction as a thermal insulation material. The article presents a study of the effectiveness of fire-retardant coatings based on silicic acid sols modified with orthophosphoric acid and phosphate buffer solutions. The effect of phosphorus-containing additives on the rheological properties of the compositions was determined spectrophotometrically. The highest survival rates (~2 h) were observed in sols containing phosphate buffer solutions. Using differential thermal analysis, the influence of phosphate additives on the nature of polycondensation of polysilicic acid formed during the creation of a fire-retardant composition based on aqueous solutions of liquid glass and acetic acid was established and confirmed by infrared spectroscopy. The addition of orthophosphoric acid contributes to the formation of network silicate structures that slowly decompose under the influence of temperature with a minimal increase in mass loss, which is a guarantee of preserving the integrity of the coating. However, the results of fire studies of coatings with orthophosphoric acid additives did not give a stable positive result, so in further studies, phosphate salts of alkali metals were used in the form of phosphate buffer pairs. Phosphate ions are able to be incorporated into the structure of the siloxane framework of polysilicic acid, increasing its fire resistance, which was confirmed by IR spectroscopy. The use of phosphate buffer solutions is more promising, because, firstly, it provides increased survivability of the composition and, secondly, it promotes melting of the coating under the influence of fire, therefore, during shrinkage of polystyrene foam, the coating changes its shape without the formation of cracks and reliably protects the finishing material from fire. Conducting fire tests made it possible to establish that all the studied compositions are able to eliminate the main disadvantage of polystyrene foam combustion - the formation of burning drops. It was established that the use of potassium phosphate salts provided the best fire protection for extruded polystyrene foam, which was confirmed by fire tests and microscopic examination of the material of different grades.