Trinity effect of potassium sulfonate-benzimidozale towards self-intumescent flame-retarded polyester with low fire hazards

Additive-type Intumescent flame retardants (IFRs) are widely used in many polymeric materials to reduce fire hazards. However, the migration behavior of IFRs in the long-term use process leads to poor flame retardance durability and undesirable health issue. To address these problems, a novel reactive monomer (MS-K) containing potassium sulfonate and benzimidozale groups was synthesized and chemically linked into the backbones of model polymer (Polyethylene terephthalate, PET). When the PET-copolymer burnt, the sulfonate group worked as acid and gas sources, and the benzimidozale group acted as carbon source. The trinity effect (acid, gas and carbon sources) of benzimidozale-potassium sulfonate structure gave rise to the self-intumescent carbonization behavior of PET matrix. As a result, the formed intumescent char-layer exerted a significant condensed-phase flame retardant effect that can hinder the oxygen exchange, isolate from the heat source and suppress the volatilization of combustible small molecules. Thus, the corresponding PET-copolymer exhibited extremely low fire hazards with UL-94 V-0 rating, a high limiting oxygen index of 32.5 vol%, greatly decreased peak heat release rate (decreased by 58%) and total smoke production (decreased by 39%). The strategy of reactive trinity-macromolecule not only exhibits excellent intumescent flame-retardant effect, but also completely eliminates the migration issue, which represents a promising way to replace the traditional additive-type IFRs.