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.