Fully bio-based thermoplastic polyurethane composites with enhanced flame retardancy via phytic acid integration

Thermoplastic polyurethane (TPU) has restricted applications owing to flammability concerns, whereas conventional intumescent flame retardants predominantly utilize non-renewable feedstocks. In this work, bio-based TPU was synthesized through prepolymer methodology employing bio-based poly (trimethylene ether) glycol, pentamethylene diisocyanate, and 1,4-butanediol. Flame-retardant bio-TPU/PA composites were subsequently fabricated by incorporating bio-based phytic acid (bio-PA) as a modifying agent. Structural characterization and performance evaluation demonstrated that at 20 phr bio-PA loading, bio-TPU/PA composites exhibited decreased tensile strength (from 20.4 MPa to 9.5 MPa) and reduced elongation at break (from 502 % to 324 %). X-ray diffraction analysis revealed that the crystalline structure of bio-TPU remained unaffected by bio-PA incorporation. Notably, the flame-retardant performance of the composites showed progressive enhancement as bio-PA content increased. Specifically, the peak heat release rate declined by 56.2 % (from 1216 kW/m 2 to 533 kW/m 2 ), and the average effective combustion heat exhibited a 24.4 % reduction (from 41 MJ/kg to 31 MJ/kg). This work establishes a sustainable strategy for developing flame-retardant bio-TPU composites, simultaneously addressing fire safety concerns and expanding the application potential of renewable polyurethane materials through environmentally benign modification approaches.