Synergistic effect of expandable graphite, diethyl ethylphosphonate and organically-modified layered double hydroxide on flame retardancy and fire behavior of polyisocyanurate-polyurethane foam nanocomposite

Halogen-free flame-retarded rosin-based rigid PIR foam nanocomposites have been successfully prepared by in-situ polymerization, which were based on renewable rosin polyester polyol, halogen-free flame retardants (such as expandable graphite and diethyl ethylphosphonate) and organically-modified nanoclay (such as organically-modified montmorillonite or organically-modified layered double hydroxide). The morphology, thermal conductivity, mechanical property, thermal stability, flame retardancy and fire behavior of PIR foam nanocomposites were comprehensively investigated. Furthermore, potential synergistic effect between organically-modified nanoclay and flame retardants on improving the flame retardancy and fire behavior of rosin-based rigid PIR foam has been investigated in detail. X-ray diffraction and transmission electron microscopy studies confirmed that exfoliated structure of OMMT or OLDH in PIR-FR45-OMMT2.0 or PIR-FR45-OLDH3.0 nanocomposite. The flammability and compressive strength tests showed that PIR-FR45-OMMT2.0 and PIR-FR45-OLDH3.0 nanocomposites possessed significantly improved flame retardancy and slightly enhanced mechanical property compared with neat PIR foam. At the same time, PIR-FR45-OMMT2.0 and PIR-FR45-OLDH3.0 nanocomposites possessed relatively low thermal conductivity, which can meet requirement of engineering applications as insulating material. Furthermore, commonly OMMT showed no synergistic effect with flame retardants when dealing with fire behavior. However, OLDH showed synergistic effect with flame retardants on improving the flame retardancy and fire behavior of rosin-based rigid PIR foam. The reason is that OLDH can promote the formation of reinforced char layer, provide an effective barrier against heat and oxygen, release noncombustible gases, and simultaneously effectively suppress smoke and gases during the combustion process.