Two heads are better than one: Aluminum trihydroxide / phosphorous flame retardant combination in natural waste fiber biocomposites

Future polymeric materials that replace fossil fuel-based engineering plastics demand the use of renewable sources as well as the implementation of key properties such as flame retardancy, processing, and mechanical properties. This study focuses on the combination of aluminum trihydroxide (ATH) and phosphorus-based flame retardants in compositable thermoplastic starch reinforced with sustainable multifunctional leather waste fibers. The flame retardants engender different flame-retardant modes of action, improving overall performance when combined. The partial substitution of ATH with phosphorous flame retardant allowed a reduction in flame retardant loading. Materials with 90 phr of ATH reached a limiting oxygen index of 31.5 vol.-% and a UL-94 rating of V-1, whereas the combination of 73 phr ATH and 7 phr of diphenyl ocytyl phosphate achieved a V-0 rating and a slightly reduced peak of heat release rate. This study demonstrates the potential of multicomponent systems implementing waste fiber–reinforced biocomposites. • Multi component systems based on bio polymers, waste fibers, flame retardant and synergist are an alternative to conventional flame retardant polymers. • Phosphorous based flame retardants synergize with aluminum trihydroxide to improve the flame retardancy in bio composites. • Best performance is achieved when the decomposition temperature range of the synergist and the polymer overlaps because all reactive species are present at the same time to improve the char formation. • Leather waste fibers as sustainable fillers improve the flame retardancy and contribute to a better waste management.