Fabrication of polyphosphazene covalent triazine polymer with excellent flame retardancy and smoke suppression for epoxy resin

Abstract A kind of polyphosphazene covalent triazine polymer (PCTP) was fabricated through a facile trimerization reaction of 4-hydroxybenzonitrile substituted hexachlorocyclotriphosphazene (HCCP). The as-prepared PCTP containing phosphorus and nitrogen elements was added into epoxy resins (EP) to improve their fire resistance and smoke suppression property. As obtained from cone calorimeter test, compared with the neat EP, the values of peak heat release rate (P-HRR), total heat release (THR) and total smoke production (TSP) of EP@PCTP composites were reduced by 73%, 69% and 42%, respectively, when 8.7 phr PCTP was loaded into the EP matrix. Meanwhile, the limiting oxygen index (LOI) value was also increased greatly from 22.3% to 28.0%, and the EP composites successfully passed UL-94 V-0 rating with 6.4 phr PCTP incorporated. The results may be resulted from the more compact and higher coherence char layer of EP@PCTP composites, and PCTP could function both in condensed and gaseous phases due to the barrier effect and dilution effect during the combustion. The water resistance of the EP matrix was also enhanced effectively due to the presence of PCTP. In addition, the nearly unchanged glass transition temperature (Tg) and mechanical properties of the resultant EP@PCTP composites confirmed the excellent compatibility between PCTP and EP matrix, which endows its promising application potential in polymer materials.