Bio-derived phosphorous-nitrogen-silicon decorated halloysite nanotube towards enhancing flame retardant, UV-blocking and mechanical properties of poly(lactic acid)

Developing flame retardant and UV-blocking polylactide (PLA) with reinforced mechanical properties is important but challenging. Herein, bio-derived phytic acid was decorated on halloysite nanotube though silane grafting, ring-opening reaction with melamine and then electrostatic interactions with phytic acid. The obtained phopsphorous-nitrogen-silicon decorated halloysite nanotube (PNSiHNT) was incorporated into PLA to prepare PLA composites. The surface modification significantly improved the compatibility between PNSiHNT and PLA, and the flame retardant, UV-shielding and mechanical properties of the composites were enhanced. At 5% mass loading, the peak heat release and total heat release were reduced by 18% and 12% compared to pure PLA, respectively, superior to most phytic acid-based flame retardants. The relevant mechanism analysis showed that PNSiHNT can restrain the emission of combustible volatiles and promote the formation of protective char layer. Moreover, the flame-retardant PLA showed excellent UV-shielding ability with an ultraviolet protection factor (UPF) value of around 120. Due to the reinforcing effect of PNSiHNT and the strong interfacial interactions between PNSiHNT and PLA matrix, the PLA/PNSiHNT showed 77% and 116% increase in tensile strength and elongation at break compared to the bulk PLA. This study provides a strategy for designing bio-derived organic/inorganic systems for enhancing flame retardant, UV-blocking and reinforced PLA.