Preparation and characterization of phenolic foams with eco-friendly halogen-free flame retardant

The high solid resol phenolic resin was prepared via step polymerization of formaldehyde, paraformaldehyde, and phenol using sodium hydroxide and calcium oxide as catalysts, and employed to prepare the phenolic foams (PFs) by the introduction of retardant additives including eco-friendly halogen-free flame retardants (ammonium polyphosphate), char-forming agents (pentaerythritol), and synergists (zinc oxide, molybdenum trioxide, cuprous chloride, and stannous chloride). The effects of these additives on flame retardancy, heat resistance, and fire properties of flame-retardant composite phenolic foams (FRCPFs) were evaluated by limiting oxygen index (LOI) tests, thermogravimetric analyzer, and cone calorimeter tests. It was found that the flame retardan significantly increased the LOIs of FRCPFs. Compared with PF, heat release rate, total heat release, effective heat of combustion, production or yield of carbon monoxide (COP or COY), and Oxygen consumption (O2C) of FRCPFs all remarkably decreased. However specific extinction area and total smoke release significantly increased, which agreed with the gas-phase mechanism of the flame-retardant system. The results indicate that FRCPFs have excellent fire-retardant performance and less smoke release. APP/PER/ZnO is shown to be better flame-retardant system for PFs.