Engineering a Reinforced Ceramic‐Like Char Barrier for Simultaneous Heat and Smoke Suppression in Polyethylene Composites

A ceramicizable flame‐retardant system based on magnesium hydroxide (MH), methyl silicone resin (MQ), and calcium borate hydrate (CaBO) was developed for polyethylene (PE) composites to simultaneously suppress heat release and smoke production. The flame retardancy, phase evolution of heat‐treated residues, char‐layer structure, and gas‐ and condensed‐phase flame‐retardant mechanisms were systematically investigated. Compared with PE/MH composite, the incorporation of MQ@CaBO significantly reduced the heat release and smoke generation of the PE composites and improved char‐layer integrity. Notably, the PE/MH/MQ@CaBO composite exhibited suppressed heat and smoke release together with enhanced intermediate mass retention. Heat treatment and structural analyses indicated that MQ and CaBO promoted the formation of a dense and self‐supporting ceramic‐like char layer containing magnesium silicate‐ and magnesium borate‐related ceramic phases as well as boron‐containing glassy species. TG‐IR analysis showed lower evolution intensities of combustible volatile products, while Py‐GC/MS provided complementary qualitative information on the types of pyrolysis products. The improved fire safety of the PE composites was therefore attributed to the combined effect of a reinforced ceramic‐like condensed‐phase barrier and gas‐phase fuel dilution.