Improvement of heat release methodologies using mass loss calorimeter and oxygen consumption hood to assess flammability of wood plastic composites

The mass loss calorimeter provides a robust method for evaluating flammability of very sooty materials such as wood plastic composites as a lower cost and rugged alternative to the reliable and effective cone calorimeter. The high amounts of smoke and carbon monoxide associated with these materials resulted in a much-reduced heat release rate, resulting in incomplete combustion of the diffusion flame, which required modifications to the standards in measuring heat release rate via oxygen consumption or carbon dioxide production or thermopiles. In addition to liquid fuels of ethylene glycol and methanol, the solids polystyrene and polymethyl methacrylate were used as calibration materials for the mass loss calorimeter and the instrumented heat release rate hood. Because of concerns about the flue gas thermopile methodology for heat release rate measurements, a second thermopile was attached to the exterior of the metal pipe chimney typically used for heat release rate calculations in the mass loss calorimeter. A heat balance analysis indicated that this is an effective design compared with alternative designs. Estimates of flaming heat release rate are reported using both signals from the thermopiles for calculation of heat release rates and confirmed with the updated oxygen consumption analysis under an instrumented hood. This special fire test arrangement was used to assess the flammability of four different wood plastic composites, some with fire-retardant treatments, such as ammonium polyphosphate and brominated, all of which tended to have high smoke production leading to high-radiant energy losses. The reduction of heat release rate with 10% by content of fire-retardant treatment was confirmed by both heat release rate measures. The average heat release rate decreased 19% to 39% when fire retardants were added, relative to this wood flour–polyethylene composite.