Fabrication and evaluation of epoxy resin film adhesive with excellent heat resistance and potential flame retardance

To obtain a heat-resistant and flame-retardant epoxy film system that can be stored for a long time, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was used to modify an imidazole curing agent, and thus a new reactive flame retardant curing agent (DMH) was successfully synthesized. A phenolic epoxy resin matrix with an oxazolidinone (EPO) structure was synthesized through the reaction of a phenolic epoxy resin (EPN) and toluene diisocyanate (TDI), and polyethersulfone (PES) was used as a toughening agent. After characterization of the material, the curing process was also considered. The results showed that the film adhesive maintained reaction inertness around room temperature and was effectively cured at a curing temperature of 130 °C and released moderate heat. Cone calorimetry testing further confirmed the excellent flame retardance of the film adhesive. The T5% temperature obtained from thermogravimetric analysis (TGA) was as high as 366 °C, which proved its good thermal stability. On this basis, the mechanical properties of the film adhesive didn't decrease, and the addition of PES ensured its good toughness. When used as the adhesive for cured resin aluminum-honeycomb sandwich samples, the lap shear strength (LSS) of the sample reached 35.6 MPa. Due to these advancements, the film adhesive system has the potential for application in a wide range of fields.