Effect of Polyborosiloxane on the Flame Retardancy and Thermal Degradation of Intumescent Flame Retardant Polypropylene

A novel synergistic flame retardant agent containing boron and silicon, namely polyborosiloxane (PBSil), was prepared via the condensation reaction of boric acid (BA), tetraethoxysilane (TEOS), and octamethyl cyclotetrasiloxane (OMCTS). The obtained PBSil was then combined with an intumescent flame retardant (IFR) to flame retard polypropylene (PP), and the effects of PBSil on the flame retardancy and thermal degradation of the PP/IFR composite were investigated. It was found that PBSil could improve the compatibility between the IFR and the PP matrix, thereby improving the mechanical properties of the composite. Compared with zinc borate, zeolite, and nano-silica, PBSil showed much better flame retardancy and smoke suppression in the PP/IFR composite. When the content of PBSil was 3.0 wt%, the limiting oxygen index (LOI) value of the flame retardant PP was increased from 29.0% to 35.0%, and the UL-94 rating was improved from V-1 to V-0 rating. Simultaneously, the heat release rate (HRR) and smoke production rate (SPR) of the composite were decreased dramatically. The thermogravimetric (TG) analysis, Fourier transform infrared (FTIR), and thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR) results showed that, PBSil could enhance the thermostability of the IFR, and promote the char formation. Furthermore, the compactness and thermostability of the intumescent char were significantly improved, contributing to the improvement of the flame retardancy of the composite.