A Schiff base-derived macromolecular flame retardant: Imparting excellent flame retardancy, UV shielding, and mechanical properties to epoxy resins

Designing and preparing highly transparent epoxy (EP) coatings with excellent flame retardant properties and mechanical toughness has been a difficult challenge. In this work, a Schiff base-derived flame retardant (PDSASi) was designed and synthesized via a simple two-step process. Multifunctional EP composites were then prepared using this flame retardant, exhibiting excellent flame retardancy owed to the synergistic effect of phosphorus, nitrogen, and silicon elements presented in PDSASi. With the addition of only 4 wt% PDSASi, EP composites achieved a V-0 rating in UL-94 testing and exhibited an LOI value of 29.2 %. In addition, compared to pure EP, the total heat release (THR), peak heat release rate (PHRR), and CO production rate (PCOPR) were reduced by 29.7 %, 25.6 %, and 14.0 %, respectively, with the incorporation of 8 wt% PDSASi. The flame-retardant mechanism was analyzed. It was demonstrated that PDSASi exhibited excellent the condensed-phase flame retardant as well as notable gas-phase flame retardant. In addition, excellent UV resistance and high transparency were exhibited by EP/PDSASi composites. In terms of mechanical properties, the cured EP/PDSASi composites exhibited notable improvements in tensile strength and impact toughness, which were enhanced by 40.6 % and 123.8 %, respectively, compared to pure EP, owing to the incorporation of flexible silane chain segments into the molecular structure of PDSASi. In this work, the effects of PDSASi on the thermal stability, flame retardancy, UV resistance, and mechanical properties of EP were viewed as a feasible strategy for designing and preparing multifunctional, high-performance EP composites.