Effect of stoichiometry on the thermal stability and flame retardation of polyisocyanurate foams modified with epoxy resin

Abstract Epoxy resin modified polyisocyanurate (EP-PIR) foams were successfully prepared by the reaction of polymethylene polyphenylene isocyanate (PAPI) and diglycidyl ether of bisphenol-A (DGEBA). Thermogravimetric analysis coupled with infrared spectrometry (TGA-IR) was performed to investigate the thermostability and the gaseous pyrolysis products of EP-PIR foams. The results indicated that the excellent thermostability of EP-PIR foams was due to the abundant highly thermostable isocyanurate ring and oxazolidone ring. The flame retardation of EP-PIR foams was also investigated. UL94 results revealed that the foams with [PAPI]/[DGEBA] ratio above 2.5 could reach V-0 classification. With increasing the stoichiometry of [PAPI]/[DGEBA], the limiting oxygen index values increased linearly from 24.5 to 30.0 vol %. Scanning electron microscopy images of burned foams illustrated the flame-retardant mechanism was due to the excellent charring ability. Cone calorimeter tests showed that the peaks of heat release rate were always as low as 266.5 kW/m2. Moreover, highly thermostable isocyanurate ring played an important role in the suppression of smoke emission.