Modification of mesoporous silica with phosphotungstic acid and its effects on the combustion and thermal behavior of polylactic acid composites

Abstract Highly ordered mesoporous silica (SiO 2 ) modified with phosphotungstic acid (PWA), was successfully prepared by vacuum impregnation. The chemical structure of as-designed PWA-mesoporous silica (PWA-SiO 2 ) was characterized by transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectra and small-angle X-ray scattering. PWA-SiO 2 , in association with intumescent flame retardant (IFR), was introduced into polylactic acid (PLA) by melt blending to obtain flame resistant composites. The flammability evaluation indicated that the presence of 19.0 wt% IFR and 1.0 wt% PWA-SiO 2 in PLA achieved the maximal LOI value of 47.2%, passed the UL-94 V-0 rating, and significantly decreased the peak heat release rate from 622.4 kW m −2 of neat PLA to 182.3 kW m −2 . The introduction of PWA-SiO 2 could also slightly improve the mechanical properties of PLA composites. It is proposed that PWA-SiO 2 , which exhibits excellent catalytic effect, can play roles together with IFR in both condensed phase through promoting the formation of continuous dense char layer and gas phase through releasing non-flammable gas.