Flame-retarded polyethylene terephthalate with carbon microspheres/magnesium hydroxide compound flame retardant

A novel compound flame retardant (carbon microspheres/magnesium hydroxide, abbreviated as CMSs/MH) was used to improve the fire performance of polyethylene terephthalate (PET). LOI, UL94, and Cone test results showed that CMSs/MH/PET composites obtained the best fire performance at the mass ratio of CMSs to MH, which was 5:5, where the CMSs/MH content was 1.0 wt. % of PET. The Py-CS-MS, TGA-DSC results, and morphology of char residue revealed the flame-retardant mechanism. CMSs/MH increased the thermal stability of PET by increasing the activation energy at the initial combustion stage. At the second stage of combustion, CMSs/MH increased the chance of recombination of free radicals and slowed the combustion. Additionally, CMSs/MH promoted the cross-linking of pyrolysis products and further improved the continuity of the char layer. Thus, a dense and continuous char layer of CMSs/MH/PET composites was produced; this char layer reduced the heat release rate and increased the amount of char residue.