Synergistic flame-retardant effect and mechanisms of boron/phosphorus compounds on epoxy resins

To explore the component synergistic effect of boron/phosphorus compounds in epoxy resin (EP), 3 typical boron compounds, zinc borate (ZB), boron phosphate (BPO₄), and boron oxide (B₂O₃), blended with phosphaphenanthrene compound TAD were incorporated into EP, respectively. All 3 boron/phosphorus compound systems inhibited heat release and increased residue yields and exerted smoke suppression effect. Among 3 boron/phosphorus compound systems, B₂O₃/TAD system brought best flame-retardant effect to epoxy thermosets in improving the UL94 classification of EP composites and also reducing heat release most efficiently during combustion. B₂O₃ can interact with epoxy matrix and enhance the charring quantity and quality, resulting in obvious condensed-phase flame-retardant effect. The combination of condensed-phase flame-retardant effect from B₂O₃ and the gaseous-phase flame-retardant effect from TAD effectively optimized the action distribution between gaseous and condensed phases. Therefore, B₂O₃/TAD system generated component synergistic flame-retardant effect in epoxy thermosets.