Surface decoration of Halloysite nanotubes with POSS for fire-safe thermoplastic polyurethane nanocomposites

Abstract

• POSS modified HNTs were synthesized successfully by using a silane agent as a chemical bridge. • The POSS in combination with HNTs endows TPU with excellent flame retardancy without scarifying the mechanical property. • The incorporation of 2 wt% HNTs-POSS into TPU could effectively reduce the peak of the peak of CO production rate and total smoke release during combustion. Halloysite nanotubes (HNTs) have been considered as a promising flame retardant fillers for polymers. In this work, the polyhedral oligomericsilsesquioxane (POSS) containing amino group was covalently grafted on the surface of HNTs with 3-(2,3-epoxypropoxy)propytrimethoxysilane as a chemical bridge. The POSS modified HNTs (HNTs-POSS) dispersed uniformly in the thermoplastic polyurethane (TPU) matrix and endowed TPU nanocomposites with enhanced tensile properties and fire safety. Cone calorimeter tests revealed that the introduction of 2 wt% HNTs-POSS to TPU matrix remarkably reduced the peak of heat release rate (PHRR) and total heat release (THR) by 60.0% and 18.3%, respectively. In addition, the peak CO production rate and total smoke release (TSR) could be significantly suppressed by the addition of HNTs-POSS. The well dispersed HNTs in combination with the ceramified silicon network from the thermal decomposition of POSS contributed to the formation of a continuous and compact char layer, exhibiting a tortuous effect by inhibiting heat diffusion and evaporation of volatile gaseous. In addition, the released crystal water from HNTs could dilute the combustible volatiles and then decline the combustion intensity. The tensile tests demonstrated that introduction of 2 wt% HNTs-POSS would enhance the maximum stress of TPU nanocomposite with a slight decrease of elongation at break. The combination of HNTs and POSS through the construction of effective interfacial interactions provides a feasible way to effectively enhance the fire safety of TPU nanocomposites without scarifying ductility.