Flame retarded rigid polyurethane foam composites based on gel-silica microencapsulated ammonium polyphosphate

Microencapsulated ammonium polyphosphate (SiAPP) was prepared by sol-gel method with gel-silica as the shell material. And also, SiAPP was characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), which confirmed the successfully fabrication of SiAPP. Furthermore, 30 php (parts per hundreds of polyol) SiAPP was introduced to prepare rigid polyurethane foam/microcapsulated ammonium polyphosphate composites (RPUF/SiAPP30). Flame retardancy, water resistance, physical properties and thermal stability of RPUF/SiAPP composites were compared with virgin RPUF and RPUF/APP composites. The results showed that RPUF/SiAPP30 which possessed excellent flame retardancy. Even after being immersed in water for 15 days, the underwriters laboratories vertical burning test (UL-94) of RPUF/SiAPP30 could pass V-1 rating with the limiting oxygen index (LOI) of 21.8 vol%, which was better that of RPUF/APP30. Compressive strength of RPUF/SiAPP30 was 0.292 MPa, which was 12.3% higher that of RPUF/APP30. SEM and Raman spectra confirmed that RPUF/SiAPP30 possessed more compact char residue with higher thermal resistance, which could inhibit mass and heat transmission in combustion. Consequently, a possible gas-solid flame-retardant mechanism of RPUF/SiAPP composite was proposed.