Cobalt ions loaded polydopamine nanospheres to construct ammonium polyphosphate for the improvement of flame retardancy of thermoplastic polyurethane elastomer

Fire safety and environmental friendliness are the two key factors for the industrial application of polymer-based composites; hence, highly efficient and halogen-free flame-retarding polymer composites have been developed to achieve the above attributes. In the present work, halogen-free flame retardant Co-PDA-APP was prepared by modifying the surface of ammonium polyphosphate (APP) with dopamine (DA) and cobalt ions (Co) to enhance the fire safety of thermoplastic polyurethane elastomer (TPU). When only 3 wt% of Co-PDA-APP was added, the limiting oxygen index (LOI) reached to 25% and passed the V-0 rating in UL-94 test. The peak of heat release rate (PHRR) and peak of smoke production rate (PSPR) decreased by 66.0% and 76.4% comparing to the relative values of neat TPU. Moreover, thermogravimetry Fourier-transform infrared and Raman spectroscopy were carried out to investigate the flame-retardant mechanism of Co-PDA-APP in the TPU composite. The intumescent flame-retardant mechanism was found to be dominant, and APP, PDA, and Co promoted the formation of a physical barrier and enhanced the fire safety of the TPU composite. Furthermore, the tensile strength was 24.4 MPa, which was preserved at a high level comparing to that of TPU/APP3 composites.