Smoke suppression and phosphorus-free condensed phase flame-retardant epoxy resin composites based on Salen-Ni

To avoid potential ecological and health problems caused by phosphorus-based flame retardants, a novel phosphorus-free PBA-Salen-Ni flame retardant is successfully synthesized in this work. In a nutshell, boron-containing metal complexes are prepared by nickel salts and chelating PBA-Salen molecule (PBA: p-phenylenediboronic acid). While the obtained material inherently has good compatibility and can endow polymers with good flame retardant properties at low addition levels. Besides, the char shielding layer and the "labyrinth effect" of the special porous char layer structure formed after the combustion of EP/PBA-Salen-Ni retard the transfer of volatile products, giving EP excellent smoke suppression properties. The results show that the limiting oxygen index value of the EP/PBA-Salen-Ni composites is increased from 25.6% (pure EP) to 30.5%, and it can pass the UL-94 V-0 rating when the addition amount is only 5wt%. Particularly, compared with pure EP, the total smoke production (19.9 m2) and peak heat release rate (859.6 kW m−2) of EP/PBA-Salen-Ni composites are reduced by 36% and 33%, respectively. Therefore, this work provides a new idea for the rational design of phosphorus-free flame retardants that are mainly on condensed phase flame retardancy and have a good smoke suppression effect.