Effects of ammonium polyphosphate to pentaerythritol ratio on composition and properties of carbonaceous foam deriving from intumescent flame-retardant polypropylene

In our work, a classical system was used for intumescent flame retardant (IFR), consisting of ammonium polyphosphate (APP) and pentaerythritol (PER). Effects of weight ratio of APP to PER (APP-PER ratio) on various aspects of carbonaceous foam deriving from polypropylene (PP)/IFR composites were investigated. Tested parameters included the flame retardancy and composition, as well as the structural and thermophysical properties of the carbonaceous foam. The carbonaceous foam resulting from PP/IFR composites was a physical mixture of phosphorous degradation products (PDPs) and insoluble chars. The structural and thermophysical properties of the carbonaceous foam affected by the APP-PER ratio include its expansion ratio, air tightness, thermal conductivity and thermal diffusivity. These properties in turn affected the efficiency of both mass (O2 and combustibles) and heat transfer between the gas and the condensed phases. The content of PDPs in the mixed melt during the foaming stage and in the solidified carbonaceous foam was considered as the main regulator of these important properties of the carbonaceous foam. Concise heat and mass transfer theories were applied to qualitatively explain the results of flame retardant tests.