Improvement of flame retardancy and thermal stability of polypropylene by P-type hydrated silica aluminate containing lanthanum

Raw kaolinite (kaol) was experimentally transformed to P-type hydrated silica aluminate (HSA-P). After treated by LaCl3·7H2O solution, the final product of La-loaded for P-type hydrated silica aluminate (HSA-P-La) was obtained. The middle and final products were characterized using fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM). Kaol, HSA-P, HSA-P-La was introduced into PP with intumescent flame retardants (IFR), respectively. And their effect on the flame retardant and thermal properties of PP composites was studied by limiting oxygen index (LOI), vertical burning test, cone calorimeter test (CCT) and thermogravimetric analysis (TGA). The LOI increases from 18.0% of neat PP to 31.2 in composite of 75 wt% PP/25 wt % IFR, further increases to 32.5, 35.1, 37.5 in 75 wt% PP/23.5 wt % IFR/1.5 wt% Kaol, HSA-P or HSA-P-La, respectively. CCT results show heat release content and rate is best controlled in PP/IFR/HSA-P-La composite. Morphology observation indicates the char layer of PP/IFR/HSA-P-La composite is most compact and thick, which guarantees excellent fire resistance. At same time the effect of HSA-P/HSA-P-La was also compared with generally used A-type hydrated silica aluminate (HSA-A)/HSA-A-La. Anyway HSA-P/HSA-P-La exhibited higher efficiency than HSA-A/HSA-A-La in both flame retardancy and thermostability.