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

Highly ordered mesoporous silica (SiO2) modified with phosphotungstic acid (PWA), was successfully prepared by vacuum impregnation. The chemical structure of as-designed PWA-mesoporous silica (PWA-SiO2) was characterized by transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectra and small-angle X-ray scattering. PWA-SiO2, 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-SiO2 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-SiO2 could also slightly improve the mechanical properties of PLA composites. It is proposed that PWA-SiO2, 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. (C) 2018 Elsevier Ltd. All rights reserved.