Enhanced fire behavior of rigid polyurethane foam by intumescent flame retardants

Abstract

Using expandable graphite (EG) and ammonium polyphosphate (APP) as flame retardants, we prepared two series of polyisocyanurate-polyurethane (PIR-PUR) foams (i.e., EG foams filled with different amounts of EG alone and APEG foams containing different amounts of expanded EG and APP) and evaluated the effect of the additives on the physical-mechanical property, fire behavior and thermal stability of the foams based on compressive strength test, limiting oxygen index (LOI), cone calorimeter test, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The addition of EG alone or both EG and APP into the foam greatly influences the physical-mechanical property. The compressive strength of APEG foams is closely related to the apparent density. The LOI value showed good improvement in both EG and APEG foams. The addition of APP in APEG foams gave better fire behavior than the EG foams with an obvious decrease in PHRR and increase in residue. In addition, the TGA curves illustrated that APP might be an effective charring agent to promote char formation. The SEM results showed that the incorporation of APP and EG allowed the formation of a cohesive and dense char layer, which inhibited the transfer of heat and combustible gas and increased the thermal stability of PIR-PUR.

Expandable graphite in polyurethane foams: The effect of expansion volume and intercalants on flame retardancy

“…As it was already well known, the presence of fairly high content of EG led to a decrease of the compression strength of the foams with respect to unfilled one. Since the amount and size of the different EGs used were the same for all the foams tested, the decrease of compression strength is very similar, that is the worsening of mechanical properties is related to EG size only.…”

Preparation of Boric Acid Modified Expandable Graphite and Its Influence on Polyethylene Combustion Characteristics

“…Furthermore, to improve the LOI value, vertical combustion UL-94 level and suppress the existed "popcorn effect" simultaneously, APP was added together in view of the reported synergistic effect between the two retardants. 35,36 LOI and UL-94 rating tests, thermal gravimetric and differential thermal gravimetric (TG/DTG) analyses were performed to investigate the flame retarded performance and the thermal stability. Electron microscope was applied to observe the residual char morphology.…”

Effects of inorganic fillers on the flame‐retardant and mechanical properties of rigid polyurethane foams

“…Besides, the influence of the EG content affected on flame retardant has been surveyed by Bian et al, and it revealed higher foam density and larger EG proportion were in favor of better flame retardancy. Hu et al and Meng et al also have systematically discussed the effect of EG on the flame retardancy and mechanical properties of RPUF, and they concluded that with the increasing of EG content, the flame retardancy would be improved, while the mechanical properties would be affected compared with original RPUF (Ref. RPUF).…”