Synthesis of phosphonitrile derivative-modified halloysite flame retardants and their simultaneous enhancement of epoxy resins flame retardancy and mechanical properties

Design of flame retardant epoxy resins (EP) with good flame retardant and mechanical properties has been an important topic of research. In this paper, an amino-functionalized phosphonitrile intermediate (HCCP-APTES) was synthesized by nucleophilic substitution reaction between hexachlorocyclotriphosphonitrile (HCCP) and 3-aminopropyltriethoxysilane (APTES). Hal-based flame retardants (HCCP-APTES@Hal) with different ratios were prepared by chemically cross-linking them on the outer surface of halloysite (Hal). Hal and HCCP-APTES@Hal were added to EP to study their effects on the flame retardant and mechanical properties of EP. The flame retardant (3HCCP-APTES@Hal) when the mass ratio of HCCP-APTES: Hal was 3:1 was added to EP at 6 wt% and the LOI value was 27.20 %. And the cone calorimetry test (CCT) results showed that the peak heat release rate (PHRR) and peak smoke production rate (PSPR) decreased by 36.84 % and 52.08 %, respectively, compared with pure EP. HCCP-APTES-modified Hal well-improved the interfacial compatibility with EP, which led to the enhancement of mechanical properties. This study proposes new ideas and strategies for the modification of Hal and the preparation of multifunctional Hal-based flame retardants in the future.