Flammability of polyamide 6 using the sulfamate system and organo-layered silicatet

A high degree of flame retardancy (FR) of polyamide 6 (PA6) is obtained by adding low weight per cent NH2SO3NH4 (ammonium sulfamate, AS) and dipentaerythritol (Di). This result is preserved when I wt% of organo-layered montmorillonite (OMMT) is dispersed in the AS + Di formulation. Increasing OMMT decreases these FR ratings. The surfaces of the gallery or exfoliated layers of OMMT adsorb and immobilize a part of AS + Di preventing its contribution to the FR reactions. The addition of the hydrophilic poly(vinylpyrrolidone) (PVP) partly restores the original FR ratings so a greater amount of AS + Di remains effective. The decrease in the high heat release rate (HRR) of the AS + Di containing PA6 by OMMT imparts to the PA6 lowered peak HRR (PHRR) and slower burning. Addition of pristine montmorillonite (MMT) up to 5 wt% does not decrease the UL-94 V-0 rating. The smaller surface area of the relatively large particles of the non-colloidal pristine MMT adsorbs less AS + Di than OMMT. A straight line relationship was found between oxygen index (00 values and ignition times in the cone calorimeter. The char resulting from combustion is composed mainly of MMT and some graphitic carbon. XRD found that the d(100) spacing for the clay in the final chars from burning was found to be 1.27nm, corresponding to a 20 peak of 7.0. No correlation between the size of the floccular structures on the char surface and the decrease in PHRR is found. Mechanistic considerations are presented. Copyright (c) 2007 John Wiley & Sons, Ltd.