Synthesis and Application of H-ZSM-5 Zeolites with Different Levels of Acidity as Synergistic Agents in Flame Retardant Polymeric Materials

Abstract

Several studies show a synergistic effect between intumescent formulations and aluminosilicates, such as zeolites and clays, but little is known about the effect of acidity of these additives on the synergistic action. In this work, H-ZSM-5 zeolite was submitted to desilication treatments for 30 min and for 2 h, and silicalite-1 was synthesized. The objective was to obtain samples of equivalent crystalline structure, but with different amounts of acid sites, in order to evaluate the effect of acid concentration of H-ZSM-5 zeolites on the synergistic action with an intumescent formulation composed by ammonium polyphosphate and pentaerythritol in polypropylene. H-ZSM-5 zeolites and silicalite were characterized by X-ray diffraction, nitrogen adsorption analysis and temperature-programmed desorption of ammonia. The desilication produced H-ZSM-5 zeolites with similar volumes of mesopores in both treatments, but the zeolite resulting from 2 h of desilication presented a higher concentration of acid sites than the zeolite from 30 min. The flame-retardant properties were evaluated by UL-94 classification, limiting oxygen index, glow-wire, thermogravimetric analysis and heating microscopy. The results showed that increasing the concentration and accessibility of the acid sites of H-ZSM-5 zeolites the flame-retardant properties of the studied composites improved. It is suggested that the increase of acid site concentration positively influences the catalysis of the reaction between ammonium polyphosphate and pentaerythritol, favoring the production of the precursors of the intumescent layer.

Synergistic Action of Montmorillonite with an Intumescent Formulation: The Impact of the Nature and the Strength of Acidic Sites on the Flame-Retardant Properties of Polypropylene Composites

“…Recently, our group published two pioneer studies about the effect of the acidity of zeolites on the synergistic action with a polypropylene (PP) composite containing APP and PER as the intumescent formulation. Bernardes et al [25] showed that increasing the concentration and accessibility of the acidic sites of H-ZSM-5 zeolites improves the Montmorillonite (Mt) has been widely investigated as a mineral filler in intumescent flame retardants due to its power in reducing polymer flammability, even when added in small amounts to the polymeric composite [16][17][18]. Among Mt's advantages should be highlighted not only its ability to retard heat transfer between the environment and the polymeric material, but also its ability to lower the supply of volatile products released to the gas phase [19].…”

“…Recently, our group published two pioneer studies about the effect of the acidity of zeolites on the synergistic action with a polypropylene (PP) composite containing APP and PER as the intumescent formulation. Bernardes et al [25] showed that increasing the concentration and accessibility of the acidic sites of H-ZSM-5 zeolites improves the flame-retardant properties of the composites. Ribeiro et al [26] showed that, for faujasite Y zeolites, moderate strength acidic sites are responsible for a better performance in the flammability tests, while stronger ones impair the flame-retarding properties.…”

Synergistic effects of polyoxometalate‐based ionic liquid‐doped sepiolite in intumescent flame‐retardant high‐density polyethylene

“…However, the intumescent formulation alone cannot provide the desired flame‐retardant properties for commercial use. Due to the low thermal stability, the intumescent layer began to crack at temperatures above 400°C and the underlying materials were exposed to the flame again 6 …”

Fire-Safe Polymer Composites: Flame-Retardant Effect of Nanofillers

“…A particularly useful laboratory test for evaluating the fire performance of samples is the LOI (ASTM D-2863) ( Figure 11 ) [ 137 ]. LOI represents the minimum oxygen concentration in an oxygen/nitrogen mixture that can maintain the flame combustion of a material for 3 min or consumes 5 cm of sample length (ASTM D-2863 and ISO 4589) [ 83 , 138 , 139 , 140 ]. In accordance with ISO 4589, LOI is measured for a sample (80 × 10 × 4 mm 3 ) placed vertically in the center of a glass chimney.…”