Flame retardancy of polystyrene/nylon-6 blends with dispersion of clay at the interface

Ammonium polyphosphate (APP) and clay were utilized to flame-retard polystyrene/nylon-6 (PS/PA6) blends. The results of FTIR spectra and transmission electron microscopy (TEM) indicated that APP and clay were exclusively dispersed in the PA6 phase. Selective localization of clay at the interface of polymer blends was achieved by the method that poly(styrene-co-maleic anhydride) (SMA) was first reacted with clay, and then blended with PA6/PS. The influences of the distribution of clay and the morphology of PS/ PA6 blends on flame retardancy were investigated. The flame retardancy was evaluated by limiting oxygen index (LOI), vertical flammability test, and cone calorimeter tests. For blends with a dispersed PA6 phase, the dispersion of clay in blends has an insignificant effect on the flame retardancy. However, in blends with a continuous PA6 phase, the flame retardancy of blends with clay dispersed at the interface was better than that of blends with clay dispersed in PA6 phase. An investigation of thermogravimetric (TG) analysis revealed that the thermal stability of blends with clay dispersed at the interface showed obvious change with blends in which clay dispersed in PA6 phase. Scanning electron microscopy (SEM) characterization showed that the dispersion of clay at the interface had the benefit of forming a compact residue char, which augmented the flame retardancy. A completely loose residue char observed in the blends with continuous PA6 phase in which contained clay platelets should be responsible for the deterioration of flame retardant properties. Energy dispersive spectrometry (EDS) analysis revealed that the reassembling of the clay platelets on the surface of intumescent char caused the formation of loose residue char. On the contrary, the dispersion of clay platelets on whole intumescent char was more favourable to the improvement of flame retardancy. (C) 2014 Elsevier Ltd. All rights reserved.