Synergistic effects of polyoxometalate‐based ionic liquid‐doped sepiolite in intumescent flame‐retardant high‐density polyethylene

Abstract A polyoxometalate‐based ionic liquid‐doped sepiolite (SEP‐PIL) was prepared by electrostatically immobilizing phosphomolybdic acid (PMA) on natural sepiolite embedded with imidazolium cations (SEP‐IL), and its structural properties were fully characterized by various methods. Furthermore, a new intumescent flame‐retardant system (IFR) for high‐density polyethylene (HDPE) was constructed by adding SEP‐PIL into conventional HDPE/IFR composites. The retardant properties and thermal decomposition behaviors were comprehensively investigated. The results showed that the HDPE composite containing 24 wt% IFR and 1 wt% SEP‐PIL passed UL‐94V‐0 rating, and the limiting oxygen index increased from 17.8% (pure HDPE) to 27.6%. In addition, the HDPE/IFR/SEP‐PIL composite had lower peak heat release rate (PHRR) and total heat release (THR) compared to the HDPE/IFR composite. The thermogravimetric analysis demonstrated that the combination of SEP‐PIL with IFR could greatly promote the formation of residual chars. Dynamic rheological measurement further confirmed that the synergistic effect of SEP‐PIL and IFR could greatly improve the flame retardancy of HDPE/IFR/SEP‐PIL composites.