Optimization of flame retardant content with respect to mechanical properties of natural fiber polymer composites: Case study of polypropylene/flax/aluminum trihydroxide

Flammability behavior of natural fiber polymer composites (NFPC) is an essential factor to define their scope of application. It was of great importance to quantitatively optimize the quantities of the flame retardants (FR) with respect to the corresponding mechanical properties as well as the flame retardance behavior. Flax/polypropylene (PP) system was selected in this study due to its diverse applications. Aluminum trihydroxide (ATH) which was an inorganic hydrate was used as a FR and smoke suppresser because of its environmentally–friendly nature. Flax and PP in the presence of a coupling agent were extruded together. Flax loading with respect to the host polymer was studied at 30% and 50%. Afterward, the compounds were mixed with three grades of ATH namely Apyral 32, 40CD, and 60CD which were loaded at different amounts ranging from 30 to 60 wt%. The synergetic effect of zinc borate (ZB) and ammonium polyphosphate Exolit AP‐422 was also investigated. Both mechanical and flammability behavior were assessed with respect to ATH and its synergists. It was found that 40 wt% of Apyral 60CD was enough to reach V‐0 level with a marginal loss of tensile strength namely 12.5% and 7% for samples of 30% and 50% flax, respectively. Higher loading of ATH at 60% results in strength reduction by 37%–40%. Cone calorimetry results proved the reduction of both heat release rate (HRR) and smoke release. Synergism with both additives improved the UL94 rating and decreased the HRR as well. POLYM. COMPOS., 37:3310–3325, 2016. © 2015 Society of Plastics Engineers