Mechanism of action of different d-spacings clays on the intumescent fire retardance of polymers

A series of sodic and organophilic clays with different d-spacings was added to a polymeric matrix of poly (ethylene-co-butyl acrylate) EBA-30, containing an intumescent formulation of ammonium polyphosphate (APP) and pentaerythritol (PER), in order to investigate the influence of the d-spacings of the clays on their synergistic effects with the intumescent formulation. A series of samples was evaluated through cone calorimetry, SEM, TG-FTIR, FTIR, and XRD of burned residues. The results revealed that the addition of clays with smaller d-spacings led to a synergistic interaction with the intumescent formulation, and consequently to an improvement in the flame retardance of the materials. This effect was not observed with the addition of clays with d-spacings larger than 30 A. For these materials, the formation of a less homogeneous and structured intumescent layer, and a delay in the formation of the phosphocarbonaceous species which act as char precursors was observed. This delay could be responsible for the loss of synergy and also for the type of char morphology formed when larger d-spacings clays were used. XRD analyses results indicated that the presence of clays in the materials promoted changes in the crystalline phase of the char when the samples were submitted to higher temperatures. Those changes probably allowed for the maintenance of the structures at high temperatures. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1759–1771, 2013