Fire performance, mechanical strength and dimensional stability of wood flour- polyethylene composites under the influence of different fire retardants

Flammability is one of the most important parameters that often limit the application range of wood plastic composites. Therefore, the improvements of retardancy performance of these products have a considerable impact. The aim of this work was to evaluate the influence of expandable graphite (EG) and its combination with aluminum tirhydroxide (ATH), inorganic phosphate (IP) and melamine borate (MB) on the flammability of wood flour–polyethylene composites. Composites were prepared by the melt compounding method and cone calorimetry as well as limited oxygen index (LOI) tests was employed to study their flammability properties. Also, the effect of different fire retardants on the mechanical strength and water uptake of samples were investigated. Cone calorimetry characterization indicated that with incorporation of fire retardans heat release rate and burning rate decrease and char residual as well as the time to ignition increase. These findings ascribed to formation of char layer by fire retardants. The combination of EG and other fire retardants yielded better improvements in flame retardancy in comparison to the sample that has just EG as flame retardant. The LOI test was used to determine the lowest concentration of oxygen at which a material will maintain combustion in a flowing mixture of oxygen and nitrogen. The results showed that inclusion of fire retardants improve the LOI of sample. Furthermore, the presence of fire retardants decreased the tensile and flexural resistance (strength and modules) and impact strength of samples, and increased the water absorption as well as thickness swelling. Generally, among the different treatments examined, the EG–ATH retardancy system showed highest potential in flame retardancy of composites.