Combination effect of ADP-intercalated kaolinite and ammonium polyphosphate on simultaneously enhancing the flame retardancy and smoke suppression of epoxy resins

In this article, ammonium dihydrogen phosphate (ADP) was successfully intercalated into kaolinite (Kaol) to prepare a novel synergist named ADP-intercalated kaolinite (K-ADP). The chemical structure of K-ADP was thoroughly characterized using various analytical methods, and then K-ADP was combined with ammonium polyphosphate (APP) to enhance the fire safety of epoxy resins (EPs). The flammability results indicate that the combination of K-ADP and APP exerts super positive effects on reducing the heat release and smoke emission of EPs than the mixture of Kaol and APP. Especially, the EP/8 wt% APP/2 wt% K-ADP has a super LOI value of 33.2% and reaches a UL94 V-0 rating accompanying with a 29.1% reduction in total heat release (THR) and a 72.7% reduction in total smoke production (TSP) compared to pure EP. The morphology and component analyses show that the combination of K-ADP and APP facilitates the formation of more phosphorus-rich crosslinking and aromatic structures in the condensed phase to enhance the compactness and intumescence of char layer, which effectively segregates heat, combustible compounds and smoke particles. Thermogravimetric analysis shows that the combination of K-ADP and APP exerts super char-forming ability in EPs, and the residual weight of EP/8 wt% APP/2 wt% K-ADP at 800°C increases from 7.8% of pure EP to 19.7%. Mechanical test shows that the addition of K-ADP displays the less adverse effect on the mechanical properties of EP composites compared to Kaol due to the better compatibility of K-ADP and epoxy matrix with DSC analysis support.

Highlights

• A novel ammonium dihydrogen phosphate-intercalated kaolinite (K-ADP) was synthesized.
• APP/K-ADP system exerts super positive effect on reducing fire hazards of EPs.
• APP/K-ADP system takes effect in both gas phase and condensed phase.
• APP/K-ADP has a satisfying balance between fire safety and mechanical properties in EPs.