Thermal performances and fire behaviors of rosin-based rigid polyurethane foam nanocomposites

Microencapsulated intumescent flame retardants were successfully prepared by in situ polymerization technology and their structures were characterized by FTIR spectra, SEM microphotographs, and TG analyses. Microencapsulated treatments on expandable graphite (EG) and ammonium polyphosphate (APP) increased the expanded volume of EG and improved the water resistance of APP. After incorporation of microencapsulated intumescent flame retardants into RPUF, the prepared rosin-based rigid polyurethane foam possessed more uniform cell structure and higher compressive strength than incorporation of the same amount of intumescent flame retardants. It is attributable to improved interfacial adhesion and stress transfer between microencapsulated intumescent flame retardants and RPUF matrix. Simultaneously, after incorporation of microencapsulated intumescent flame retardants into RPUF, the prepared rosin-based rigid polyurethane foam possessed better flame retardancy and fire behavior than incorporation of the same amount of intumescent flame retardants. It is attributed to better synergistic effect between microencapsulated expandable graphite and ammonium polyphosphate in gas and condensed phases. Furthermore, synergistic flame retardant rosin-based rigid polyurethane foam nanocomposite was successfully fabricated by adjusting the appropriate ratio of microencapsulated intumescent flame retardants and organically modified layered double hydroxide. The LOI value and the specific compressive strength for filled MEG(10)/MAPP(10)/OLDH3.0 foam increased about 36.4 and 1.7 % compared with neat RPUF. The cone calorimetry measurement showed that the average heat release rate, total heat release, average smoke production rate, average rate of smoke release, average specific extinction area, total smoke release, and CO/CO2 mass ratio of filled MEG(10)/MAPP(10)/OLDH3.0 foam decreased about 23.2, 20.2, 50.0, 48.3, 35.4, 33.0, and 21.3 % compared with neat RPUF, respectively. Therefore, using microencapsulated intumescent flame retardants and organically modified layered double hydroxide are promising strategies for simultaneously improving the flame retardancy, mechanical property, and fire behavior of rigid polyurethane foams.