Study of polyamide 6-based nanocomposites

The miscibility and crystallinity of polyamide 6 (PA6) and poly(vinyl pyrrollidone) (PVP) were studied, and one Tg was observed for all blends of PA6 with PVP. PVP molecules were adsorbed on silicate layers in the melt PA6 during the high temperature mixing. Three kinds of conventional flame-retarding additives (ammonium sulfamate, melamine cyanurate and pentabromobenzyl acrylate), combining with organically modified layered montmorillonite (OMMT) or sodium montmorillonite (Na+MMT) were added to PA6 by melt mixing at high temperature. The flammability behaviors of the three different synergistic systems were studied using UL-94, oxygen index and cone calorimeter. A similar flame retardancy (FR) effect of clay on treated PA6 is observed for all three systems. In general, the high FR degree of UL-94 rating is maintained upon adding a relatively low amount of MMT. Increased mass % of OMMT is antagonistic to the FR effect of conventional flame-retarding additives in the UL-94 rating. The rate of dripping decreases while the size and mass of drops in the UL-94 tests increases with increasing wt% OMMT, indicating an increase in viscosity of the melt. Addition of PVP to the synergistic systems decreases the viscosity and partially restores the FR rating. Na+MMT does not significantly increase the viscosity. The FR ratings are fully preserved for the sulfamate system and partially preserved for the other two systems upon addition of Na+MMT. The PHRR (peak heat release rate) in the cone calorimeter decreases with an increase in the loading of OMMT. The time of ignition decreases upon the adding of OMMT. This is explained by the low thermal conductivity of the clay containing surface layer of samples during pyrolysis and combustion. The chars collected in the cone combustion are predominantly alumino silicates. The addition of OMMT gradually decreases the tensile strength and elongation, and slightly increases the modulus, in all three systems. Mechanistic considerations are presented.