Simultaneous enhancements in the mechanical, thermal stability, and flame retardant properties of poly(1,4-butylene terephthalate) nanocomposites with a novel phosphorus-nitrogen-containing polyhedral oligomeric silsesquioxane

Highly efficient flame retardants for engineering plastics are needed to reduce the deterioration of the mechanical and other properties of the host polymer. Herein, a novel functionalized polyhedral oligomeric silsesquioxane (F-POSS) containing phosphorus and nitrogen has been synthesized by the reaction between N-phenylaminopropyl-POSS and diphenylphosphinic chloride. Untreated POSS and F-POSS have been respectively mixed with poly(1,4-butylene terephthalate) (PBT) to prepare the nanocomposites via the melt blending method. PBT/F-POSS shows improved mechanical properties, thermal stability and thermo-oxidative resistance in comparison with PBT/POSS. F-POSS exhibits a more significant inhibiting effect on the smoke production of PBT in the early heating stage of smoke density testing without a flame. In cone calorimeter tests, the peak heat release rate (PHRR), peak smoke production rate (PSPR), peak carbon dioxide production (PCO₂P) and peak carbon monoxide production (PCOP) of PBT/F-POSS are reduced by 50%, 46%, 45% and 35%, respectively, compared to those of neat PBT. Residue analysis indicates that more C and O elements are left during the expansion and carbonization process in which phosphinic groups of F-POSS can capture the free radicals or decomposed products produced from PBT to form a stable SiO_xC_yP_z network. The multiple protective char layers act as a thermal barrier at the surface of the substrate to reduce the fire, smoke and toxicity hazards. This work provides a facile and simple way to achieve high-performance PBT nanocomposites. © 2017 The Royal Society of Chemistry.