Effect of organic grafting expandable graphite on combustion behaviors and thermal stability of low‐density polyethylene composites

Abstract An efficient approach has been proposed for improving the flame retardancy of low‐density polyethylene (LDPE) by organic‐inorganic intumescent interfacial flame retardants, avoiding the damage to intrinsic performances of LDPE caused by high loading of flame‐retardant additives. The expandable graphite (EG) particles are successfully functionalized by a grafting process containing phosphorous, exhibiting the excellent thermal stability and high flame‐retardant efficiency. Then a battery of flame‐retardant LDPE composites with different content of grafted EG (GEG) are fabricated and investigated. The results indicate that the Underwriters Laboratories‐94 V‐0 is achieved, and the limiting oxygen index is as high as 25.1% when 12 wt% GEG particles are filled into LDPE matrix. The residues of the flame‐retardant LDPE composites observably increase with the addition of GEG. The results of cone calorimeter test also verify that GEG is an efficient flame retardant for LDPE due to the interfacial effect between graphite and inorganic flame retardant. Besides, the microtopography of residual char shows that the LDPE/GEG composites are more compact and integrated after burning. This interfacial grafting flame retardant exhibits excellent flame‐retardant efficiency and will be promising for the development of organic‐inorganic intumescent flame retardants for polymer materials.