Improving the Flame Retardancy and Smoke Suppression Properties of Polyurethane Foams with SiO2 Microcapsule and its Flame-Retardant Mechanism

An efficient silicon dioxide (SiO2) microcapsule was synthesized and used for flame-retardant polyurethane foams. The polyurethane/25 wt% SiO2 microcapsule composites achieved a limiting oxygen index value of 34.8% and UL-94 V-0 rating, and SDR was significantly reduced. TG, Py-gas chromatography–mass spectrometry, energy dispersive X-ray, and Fourier Transform infrared spectroscopy (FTIP) results indicated that SiO2 microcapsule could serve as an outstanding flame retardant that operates by both chemical (condensation) and physical (cooling and blocking) mechanisms. The compact and stable char layer formed at the inner layer of the residue during thermal decomposition, and this situation results in the excellent flame retardancy of polyurethane.