Research on two sides horizontal flame spread over rigid polyurethane with different flame retardants

In order to reveal the effect of flame retardant to rigid polyurethane foam (RPUF), a medium-scale experimental platform was built to study horizontal two sides flame spread with non-flame retardant rigid polyurethane and rigid polyurethane with expanded graphite (EG) (5 mass% and 10 mass%), aluminum hypophosphite (AHP) (5 mass%) and aluminum diethylhypophosphite (ADP) (5 mass%), respectively. The results show that the flame retardant will limit the flame combustion intensity, and the combustion intensity of five samples follows the order as RPUF > RPUF/EG5 > RPUF/AHP5 > RPUF/ADP5 > RPUF/EG10. Meanwhile, with the addition of flame retardant, the combustion mechanism is different. The specimen with the addition of EG has the most obvious bending deformation, and the bending deformation of RPUF/EG10 is significantly higher than others, which is mainly caused by the low strength of EG. For RPUF/ADP5, the flame spread gives the maximum value, which can be attributed to the decreased ignition time and no reduction FGI. Due to the intumescent carbon layers formation when adding AHP, hindering mass and heat transportation, extinguishment happens eventually. On the other hand, the flame retardant of ADP shows better retardancy including the decreasing flame height, flame width, heat flux and flame temperature than others.