Effects of nanoparticles on the flame retardancy of the ammonium sulphamate‐dipentaerythritol flame‐retardant system in polyamide 6

This paper extends the work of Lewin et al., which showed that high levels of flame retardancy could be conferred on polyamide 6 (PA6) in the presence of small concentrations of ammonium sulphamate (AS) and dipentaerythritol (DP). PA6 samples were compounded with similarly low concentrations (2.5%w/w AS and 1%w/w DP) with or without nanoclays and fumed silica present at 1 and 2%w/w levels. Compounded samples were characterized by X‐ray diffraction, thermal analysis (differential thermal analysis/thermogravimetric analysis) and Fourier transform infrared. Flammability properties were measured by UL‐94, limiting oxygen index (LOI) and cone calorimetry test methods. All PA6 blended samples with or without nanoparticles were found to be V‐2 rated which differed from the results reported by Lewin et al. for similar samples where V‐0 ratings were obtained for clay‐free samples. LOI increases promoted by the inclusion of AS and DP alone were slightly reduced following the addition of all nanoparticles with the functionalized clays showing the largest effect. Introduction of silica, however, had the smallest effect in reducing LOI. Cone calorimetric results showed that while the presence of AS and DP raise peak heat release rate values with respect to PA6, addition of nanoparticles reduced values to below that for pure PA6. These reductions are dependent on nanoparticle concentration although differences between them, within experimental error, are very similar. While smoke generation is little affected by addition of AS and DP, the presence of nanoparticles promotes a slight increase. Results were interpreted in terms of previously published mechanisms for PA6‐AS‐DP thermal degradation and nanoparticle‐polymer interactions. Copyright © 2012 John Wiley & Sons, Ltd.