Influence of ammonium polyphosphate-modified polypropylene on flammability characteristics of polypropylene keratin and chitosan sustainable composites

The combination of keratin fibers (KF), obtained from poultry feathers, with chitosan (Ch) are employed in polypropylene (PP) composites to enhance the flame-retardant (FR) properties. The combined effect of each additive and the use of functionalized PP with ammonium polyphosphate (PP-gAPP) as a compatibilizer, compared with PP-gMA, on composite FR properties was analyzed. This compatibilizer was prepared by melt reaction of maleic anhydride grafted PP (PP-gMA) with ammonium polyphosphate (APP). The grafting of APP was characterized by FTIR, XRD, and NMR. PP/KF/Ch composites using PP-gAPP as compatibilizer were characterized by TGA, mechanical properties, and fire-retardant tests such as UL-94 (HB), limiting oxygen index (LOI), and cone calorimeter evaluations. These tests demonstrated the enhancement in fire-retardant characteristics obtained by using PP-gAPP as a compatibilizer agent compared with PP-gMA. The combination of the additives (KF and Ch) with PP-gAPP as compatibilizer in PP, increases the modulus and tensile strength and significantly improves the LOI and reduces the peak heat release rate during cone calorimetry tests with better thermal stability and a noticeable reduction in horizontal burning rate. Most important, the results indicated that the combination of these additives produce similar flame retardancy than a reference sample with high magnesium hydroxide loading. These composites are a promising way to meet the growing demand for high-performance materials with FR characteristics using bio-fire retardant additives such as KF and Ch, in sustainable and environmentally friendly composites.