Natural halloysite nanotube based functionalized nanohybrid assembled via phosphorus-containing slow release method: A highly efficient way to impart flame retardancy to polylactide

Aiming to endow polylactide (PLA) with enhanced fire retardancy with maintenance of thermal stability, halloysite nanotubes (HNT) were sequentially grafted with maleic anhydride (MAH) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to prepare nanohybrid HNT@MAH@DOPO. Slow release behavior of DOPO and its derivations was observed due to their different locations on HNT. PLA composite with 5 wt% HNT@MAH@DOPO revealed maintained initial thermal stability. In parallel, PLA/SHNT@MAH@DOPO possessed limiting oxygen index (LOI) of 38.0% and passed UL-94 vertical burning rating V-0, a notable enhancement compared to neat PLA (LOI = 24.7% and UL-94 V-2). Peak heat release rate (pHRR) and time to ignition (TT1) were respectively reduced by 20.2% and delayed by 10 s. DSC analysis illuminated that crystallization degree (chi(c)) and glass transition temperature (T-g) were both improved. The probable mechanism for improved fire retardancy was predominantly involved in slow release of DOPO derivations and subsequent flame inhibition, together with secondary barrier effect.