Ladder-like cross-linked network of epoxy resin through multi-site interaction: Flame retardancy and mechanical properties

Most epoxy resins (EP) suffer from sacrificial mechanical properties in flame retardancy applications. Through a facile reaction between N-aminoethylpiperazine (N-AEP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), a novel multi-site interaction flame retardant, DOPO-based aminoethylpiperazine (abbreviate as AEPO), was successfully synthesized, which could form a ladder-like cross-linked network with EP. EP modified by AEPO (EP-AEPO) was tested for flame retardancy using the limiting oxygen index (LOI), the vertical burning test (UL-94), and the cone calorimeter test (CCT). According to the results, EP-10 (EP with 10 phr of AEPO) could pass UL-94 V-0 rating and get a LOI value of 35.5%, the peak heat release rate (PHRR) and total heat release (THR) of EP-10 were also decreased by 25.2% and 29.8%, respectively, which caused by the synergistic charring effect of phosphorus and nitrogen elements contained in the structure of AEPO. Due to the ladder-like cross-linked network formed through multi-site interaction, the mechanical properties demonstrated a significant improved. This work opened up a new strategy for achieving a comprehensive improvement on multifunctional EP through the design of a novel ladder-like cross-linked network with multi-site interaction.