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

Abstract

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/Cu0.0625 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/Cu0.0625 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/Cu0.125 sample reduce to 227.8 m2/m2, 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.