Copper metal-organic framework toward flame-retardant enhancement of thermoplastic polyurethane elastomer composites based on ammonium polyphosphate

In this article, copper metal-organic framework (MOF-Cu) was synthesized and used as synergism with ammonium polyphosphate (APP) to prepare flame-retardant thermoplastic polyurethane (TPU) composites. The synergistic flame-retardant effects between MOF-Cu and APP in TPU composites were studied by cone calorimeter (CCT), limiting oxygen index tests (LOI), vertical burning tests (UL-94), smoke density test, etc. The results showed that MOF-Cu had some flame-retardant effects on TPU, and APP had good flame retardancy in TPU/APP composites. And, the flame retardancy of TPU/APP was further enhanced when MOF-Cu was used as synergism with APP. It has been found that the peak heat release rate (pHRR) and total heat release (THR) values of TPU/Cu 0.0625 sample were reduced by 26.0% and 1.3% compared with pure TPU, respectively. And the pHRR and THR values of TPU/APP sample were reduced by 70.3% and 15.8% compared with pure TPU. In the case of TPU/APP/Cu 0.0625 sample, the pHRR and THR values were furtherly reduced by 19.2% and 63.4% compared with TPU/APP, because of the minor amount of MOF-Cu. It has been found MOF-Cu cannot suppress the smoke release and reduce the total smoke release (TSR) value. However, 0.125 wt% MOF-Cu can make the TSR value of TPU/APP/Cu 0.125 sample reduce to 227.8 m 2 /m 2 , which was 23.4% lower than that of TPU/APP. The good synergistic flame-retardant effect between MOF-Cu and APP was obtained by the catalyzing carbonization process to form the char residue layer with high graphitization and expansion degree.