FIRE-RETARDANT MECHANISTIC ASPECTS OF MELAMINE CYANURATE IN POLYAMIDECOPOLYMER

Melamine cyanurate (MC) acts as a fire retardant for a Nylon 6,6-Nylon 6 copolymer (PA) via a condensed-phase mechanism as shown by a parall el increase in oxygen index (OI) and nitrous oxide index (NOI) as a fu nction of MC loading. MC induces melt dripping in vertically burning P A, which can enhance the OI because of heat elimination via molten mat erial. However, MC also increases the OI when the PA/MC mixtures are b urned in a cup, which prevents dripping. Thus, besides the well-known dripping-cooling physical action, another fire-retardant role is playe d by MC. This was studied by investigating the mechanism of thermal de gradation of PA/MC mixtures by means of thermogravimetry (TG) and diff erential thermal analysis (DTA). It was seen that volatilisation begin s in PA/MC mixtures at a temperature lower than that expected on the b asis of the behaviour of PA and MC heated separately. Burning in the c one calorimeter showed that MC decreases the time to ignition of PA an d the heat release rate (RHR) in the first minutes of combustion, whic h could be related to the TG results. (C) 1997 Elsevier Science Limite d.