High-flame retarding properties of polyacrylonitrile copolymer nanocomposites with synergistic effect of elemental sulfur-doped reduced graphene oxide and bio-derived catechol units

Polyacrylonitrile (PAN)-based flame retardants have been investigated as environmentally friendly high-flame retarding materials. High-flame retarding properties can be achieved in PAN copolymers via efficient thermal oxidative stabilization (TOS). In this study, PAN copolymers of dihydroxy styrene monomers with simple catechol units were synthesized as high-flame retardants using an efficient TOS process. To further improve the flame-retarding properties, PAN copolymer composites were prepared with graphene oxide (GO) and sulfur-doped reduced GO (SrGO). Differential scanning calorimetry (DSC) analysis revealed that the activation energy of the composites for cyclization reaction during TOS decreased with SrGO content. Micro combustion calorimeter revealed enhanced flame-retarding properties of P(AN-co-DHS₃)-SrGO composites, resulting in a low heat release capacity (21 J/gK) and high limiting oxygen index (44.7%) (superior to Nomex®). The high-flame retarding properties could be attributed to the high char layer produced by efficient TOS of the copolymer with the catechol unit and radical scavenging effect of sulfur-functionalized SrGO. Therefore, the incorporation of SrGO into PAN copolymers with catechol units is a good alternative for developing environmentally friendly high-flame retardants.