Síntese e avaliação de aluminossilicatos amorfos como agentes de sinergia em materiais poliméricos retardantes de chama

Abstract

One of the ways to reduce the high flammability of polymeric materials is the use of flame retardant additives, such as intumescent formulations (IF). However, the performance of intumescent formulations is still insufficient for their commercial application and, therefore, several studies seek synergy agents that can be included in the formulation to increase their efficiency. Previous work by our research group with zeolites such as fajausite and H-ZSM-5 demonstrate that the concentration and strength of the acidic sites of these crystalline aluminosilicates have an influence on the synergistic action between zeolites and the intumescent formulation. However, amorphous aluminosilicates, with controlled levels of alumina, have not yet been evaluated as synergistic agents in these formulations. Thus, this work aims to study the influence of the concentration of amorphous aluminosilicate acid sites on that synergistic action with an intumescent formulation composed of ammonium polyphosphate (APP) and pentaerythritol (PER) in a polypropylene (PP) matrix. Thus, amorphous aluminosilicates with different concentrations of alumina (0, 5, 10, 15 and 30% m/m) and of acidic sites were synthesized by two different methods: deposition of alumina on silica and synthesis using tetraethylorthosilicate (TEOS) and aluminum nitrate. The polymeric composites were processed in an internal mixer and the flame retardant properties were evaluated using the oxygen limit index (LOI) and UL-94. Thermal stability was analyzed by simultaneous TGA/DSC and heating microscopy. The amorphous aluminosilicates had their specific area and porosity evaluated by nitrogen physisorption, chemical composition by X-ray fluorescence (XRF) and acidity by temperature progammed desorption with ammonia (TPDNH3). The results show that the increase in the concentration of the acidic sites favors the synergistic action with the intumescent formulation, enhancing the flame retardant properties and the thermal stability of the composites, regardless of the method of synthesis of amorphous aluminosilicates. However, the increase in acidity of these aluminosilicates influences the synergistic action up to a limit level, where after this value, no further increases in flame retardant properties are observed.