Effect of a bio-based copolymer containing lysine, dopamine and triazine on flame retardancy and mechanical properties of thermoplastic polyurethane/ammonium polyphosphate

A bio-based copolymer (TDDL) containing lysine, dopamine, triazine was synthesized using cyanuric chloride, dopamine and lysine, respectively. The TDDL was used as a charring agent and ammonium polyphosphate (APP) was used as an acid source to improve the flame retardancy of thermoplastic polyurethane (TPU). The flame retardancy and thermal degradation behaviors of TPU blends were investigated using UL-94 vertical burning, limiting oxygen index (LOI), cone calorimetry tests and thermal gravimetric analysis (TGA). TPU blend containing 8 wt% APP displays a UL-94 V0 rating and a LOI value 30.0 vol%. While TPU blend containing 6 wt% APP/TDDL displays a UL-94 V0 and a LOI 29.6 vol% suggesting good synergistic effect between TDDL and APP. In addition, TDDL reduces the heat release rate of TPU/APP blend, and promotes the formation of a perfect char layer during the combustion process, and suppresses the release of combustible gas and smoke. Moreover, TPU blends have better modulus and elongation at break than those of TPU.