Flame retardant rigid polyurethane foam composites based on microencapsulated ammonium polyphosphate and microencapsulated expanded graphite

Microencapsulated ammonium polyphosphate (GMAAPP) and microencapsulated expanded graphite (PUEG) were prepared by in situ polymerization with glycidyl methacrylate (GMA) and polyurethane as the shell material respectively. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and thermogravimetry (TG) were used to characterize GMAAPP and PUEG. The results confirmed the successful fabrication of GMAAPP and PUEG. On this basis, a series of flame-retardant rigid polyurethane foam composites were prepared with GMAAPP and PUEG loading by the one-step water-blown method. The flame retardancy, mechanical properties, thermal insulation, and thermal stability of RPUF/GMAAPP30, RPUF/PUEG30, and RPUF/GMAAPP20/PUEG10 composites were investigated by limiting oxygen index (LOI), Underwriters Laboratories vertical burning test (UL-94), TG, thermal conduction and density test. The results showed that the thermal stability at the high temperature of RPUF composites can be improved by the addition of GMAAPP and PUEG. SEM test confirmed significantly enhanced compatibility between the microencapsulated flame retardant particles and RPUF matrix, which obviously improved the integrity of the cell structure. RPUF/GMAAPP30, RPUF/PUEG30 and RPUF/GMAAPP20/PUEG10 exhibited LOI of 22.3 vol%, 25.3 vol%, 24.6 vol% with all composites passed V-0 rating in UL-94 test. The physical performance test indicated that RPUF/GMAAPP20/PUEG10 exhibited thermal conductivity of 0.0395 W/m·K and compressive strength of 0.292 MPa, which possessed the best comprehensive physical performance. Char residue analysis suggested the combination of GMAAPP and PUEG increased graphitization degree and compactness of char residues for RPUF composites, thus effectively improving the fire safety of the composite.