Improvement of mechanical properties and flame retardancy of epoxy resin by phosphorylated cyclotriphosphazene hyperbranched polymeric flame retardants

A new phosphorylated cyclotriphosphazene hyperbranched polymer (HBPDP) was prepared by a nucleophilic substitution reaction of diphenyl chlorophosphate (DPCP) with a cyclotriphosphazene hyperbranched polyester (HBP) and introduced into epoxy resin (EP) materials. The introduction of HBPDP can improve the tensile strength and toughness of EP materials. Among them, the strength and toughness of 1% HBPDP/EP composites reached the best with 82.74 MPa and 408.50 J/m(3), respectively. As the loading of HBPDP increased, the strength and toughness of HBPDP/EP composites decreased. Furthermore, the inclusion of HBPDP accelerated EP material degradation and increased the residue. More crucially, introducing HBPDP to EP materials can lower the amount of heat, smoke, and harmful gases released during burning, as well as enhance the flame retardancy and smoke suppression properties of the materials. The results showed that when 5 wt% HBPDP was added, the LOI value of EP composites reached 29.7%, which passed the UL-94 V-0 rating test. Meanwhile, compared with pure EP, the THR, TSP and smoke CO content of 5% HBPDP/EP composites were reduced by 27.3%, 20.3% and 60.7%, respectively, generating more and denser residual carbon layers.