Influence of Amorphous Silica‐Aluminas Acidic Sites Concentration on the Flame‐Retarding Properties and on the Thermal Stability of Intumescent Polypropylene Composites

ABSTRACT This work evaluates the influence of the acidic sites concentration in amorphous silica‐aluminas (ASAs) on the flame‐retardant properties and the thermal stability of intumescent polypropylene (PP) composites. ASAs with different concentrations of alumina and acidic sites were synthesized by surface alumina deposition and coprecipitation methods. The polymeric composites had their flame‐retardant properties evaluated by limiting oxygen index (LOI) and UL‐94. The thermal stability was analyzed by thermogravimetric analysis (TGA). The ASAs had their textural properties evaluated by nitrogen physisorption, their chemical composition by X‐ray fluorescence (XRF) and their acidity by temperature‐programmed ammonia desorption (TPD‐NH 3 ). The results show that the presence of ASA, regardless of the synthesis method, increased the thermal stability of the composites. Besides, the presence of acidic sites favors the flame‐retardant properties of the intumescent composites, leading to LOI values of 29% and 30%, as well as a V‐0 classification in UL‐94 test. Moreover, after reaching this LOI value threshold, the increase in the acidity of these silica‐aluminas did not promote further increase in the flame‐retardant properties.