Effects of surface acid-activated kaolinite on the fire performance of polypropylene composite

Highlights: •Acid-activated kaolinite (Acid-Kaol) was successfully prepared. •Acid-Kaol significantly improved the flame retardancy and thermostability of PP. •Flame retardant mechanism of PP composite containing Acid-Kaol was discussed. -- Abstract: Modified kaolinite containing Lewis acidic sites (Acid-Kaol) was prepared by calcination of kaolinite (Kaol) and successive acid treatment. Acid-Kaol was then introduced into polypropylene (PP) with intumescent flame-retardant (IFR). The flammability and thermostability of PP/IFR/Acid-Kaol were studied by limiting oxygen index (LOI), vertical buring test (UL-94), cone calorimeter test (CCT) and thermogravimetric analysis (TGA). LOI value of PP/25 wt.% IFR composite was 31.1%, it increased to 34.9% by 1.5 wt.% Acid-Kaol substitution with IFR. Moreover, the peak of heat release rate (PHRR) of PP/IFR/Acid-Kaol decreased 46.8% compared with that of PP/IFR composite. The residues after CCT were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectrometer (XPS) and FTIR. It was indicated that Acid-Kaol accelerated crosslinking during combustion and promoted char formation, which will act as insulating barrier to protect the matrix from further decomposed.