Preparation and properties of flame retardant rigid polyurethane foam composites based on microencapsulated ammonium polyphosphate and microencapsulated expanded graphite

Microencapsulated ammonium polyphosphate (PUAPP) and microencapsulated expanded graphite (PUEG) were prepared by in situ polymerization with polyurethane as shell material. XPS, FTIR, TG and SEM were used to characterize PUAPP and PUEG. The results show that polyurethane is effectively coated on the surface of ammonium polyphosphate and expanded graphite, and PUAPP and PUEG are successfully fabricated. On this basis, a series of flame-retardant rigid polyurethane foam (RPUF) composites were prepared with PUAPP and PUEG loading by one-step water-blown method. The flame retardancy, mechanical properties, thermal insulation and thermal stability of PUAPP/RPUF, PUAPP/RPUF and PUAPP-PUEG/RPUF composites were investigated by limiting oxygen index (LOI), underwriters laboratories vertical burning test (UL-94), TG, universal testing machine, heat conduction and density test. The results show that the thermal stability at high temperature of RPUF composites can be improved by the addition of PUAPP and PUEG. The charresidues of PUAPP/RPUF, PUAPP/RPUF and PUAPP-PUEG/RPUF at 700℃ are increased from 1.2wt% to 6.9wt%, 11.2wt% and 10.7wt%, respectively. Flame retardant tests show that the microencapsulated flame retardant can effectively improve flame retardancy of RPUF composites. When 10.4wt% PUAPP is added, the LOI of the PUAPP/RPUF composite is increased to 22.3vol% with V-0 rating in UL-94 test; when 10.4 wt% PUEG is added, the LOI of the PUAPP/RPUF composite is increased to 25.3vol% with UL-94 V-0 rating; PUAPP-PUEG/RPUF composite presents LOI of 24.3vol% with UL-94 V-0 rating. SEM and Raman tests indicate that PUAPP and PUEG can increase graphitization degree of char residues for RPUF composites with enhanced compactness of the char residues.