Mix and match: Industrial-waste leather fibers substitute flame retardants and reinforce mechanical properties in appropriately processed thermoplastic poly(urethane) composites

• Extrusion variables are a key to flame retardancy and mechanical properties • Industrial-waste leather fibers were used as flame retardant adjuvant • Different viscoelastic behavior is highlighted in thermoplastic polyurethane (TPU) composites • UL 94 V-0 rating was achieved for sustainable TPU flame retardant composites • 50% of the flame-retardant can be replaced by waste leather fibers The research and development of firesafe and sustainable polymer materials with appropriate mechanical properties for cable jacketing applications is addressed. Composites based on thermoplastic polyurethane (TPU) combining industrial-waste leather fibers and a commercial flame-retardant additive (ammonium polyphosphate – APP) are investigated. TPU composites were extruded under different temperature profiles and rotational speeds to obtain flame-retardant composites with appropriate mechanical properties. The detailed investigation of viscoelastic properties, morphology, tensile mechanical properties, pyrolysis, forced-flaming combustion and reaction to small flame highlights that applying optimized processing is key to producing TPU composites with the best tensile mechanical properties and flame retardancy. This finding was associated with the production of a highly elastic network, which was attributed to better dispersion and distribution of leather fibers and APP particles. TPU composites, combining 5 phr (parts per hundred resin) industrial-waste leather fibers and 5 phr APP, were compared to composites using 10 phr of APP. The same UL 94 V-0 classification, equal reduced fire risk (MARHE) with diminished smoke release, similar Young’s modulus and elongation at break, and improved tensile strength (20%) are achieved by replacing 50% APP with industrial-waste leather fibers; thus, the industrial-wastes leather fibers are simultaneously upcycled for this specific application.