Synthesis of an effective bio-based flame-retardant curing agent and its application in epoxy resin: Curing behavior, thermal stability and flame retardancy

In this work, a bio-based macromolecule ammonium phytic acid named as PA-AEP was synthesized successfully via neutralization reaction between phytic acid (PA) and N-aminoethylpiperazine (AEP) and served as a monocomponent flame-retardant curing agent to improve the flame retardancy and smoke suppression of epoxy resin (EP). Curing behavior, flame retardancy and combustion behavior of PA-AEP cured epoxy resin were investigated. By comparison with EP/AEP reference sample, EP/PA-AEP samples showed good flame retardancy and smoke suppression effect because of the addition of PA-AEP. The PA-AEP cured EP sample passed UL-94 V-0 rating and achieved to a limiting oxygen index (LOI) value of 28.0% with 20 wt% PA-AEP. Cone calorimeter test results showed that, compared with EP/20% AEP reference sample, both the peak of heat release rate (PHRR), total heat release (THR), the peak of smoke production release (SPR) and total smoke production (TSP) of EP/20 wt% PA-AEP sample were decreased by 44.4%, 55%, 49% and 80.8%, respectively. In addition, by analyzing the char residues and volatile pyrolysis products, it was concluded that PA-AEP mainly played an important role in condensed phase which was associated with the formation of phosphorus-rich intumescent char layer.