Effects of carbon fibers on the flammability and smoke emission characteristics of halogen-free thermoplastic polyurethane/ammonium polyphosphate

In the present study, the effects of carbon fibers (CFs) on flame retardancy, smoke emission, thermal and mechanical properties of thermoplastic polyurethane (TPU)/ammonium polyphosphate (APP) are investigated. The cone calorimeter results show that the combination of 15.00 wt% APP + 5.00 wt% CF greatly lowered peak heat release rate, total heat release, and total smoke release, as well as increased char residue, which is due to a compact char layer formed on the ablating surface of TPU-4 composites, as shown by the SEM results. Smoke suppression properties investigated by smoke density test demonstrate that CF combined with APP greatly reduced the smoke emission. The TPU composite containing 5.00 wt% CF has the highest LOI value of all the intumescing composites studied. Meanwhile, the addition of CF also caused enhanced mechanical properties of TPU composites to a certain degree. Thermogravimetric (TG) analysis indicates that CF combined with APP enhanced the high-temperature thermal stability of TPU composites compared with the pristine TPU, due to the increase of the char residue. Thermogravimetric analysis/infrared spectrometry (TG-IR) results demonstrate that CF could catalyze the further decomposition of TPU composites and remarkably reduce the production of aromatic compounds as a smoke precursor, which are the major parts of smoke.