Development of DOPO-resveratrol epoxy materials and glass/carbon fiber composites with improved flame retardancy and structural properties

This work reported the synthesis and characterization of a bio-based epoxy resin derived from resveratrol (RESEP) and its modification with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to enhance flame retardancy. The resin was cured with 4,4’-diaminodiphenyl sulfone (DDS) and reinforced with glass and carbon fibers to produce structural composites. The influence of DOPO content (2.5–10 wt. %) on curing behavior, thermal stability, mechanical properties, and fire performance was systematically evaluated. Infrared and differential scanning calorimeter analyses confirmed the partial reaction of DOPO with epoxy groups, reducing curing enthalpy and affecting crosslink density. Dynamic mechanical analysis revealed exceptionally high glass transition temperatures (up to 305°C) for neat resin, with moderate decreases at higher DOPO loadings. Mechanical tests showed improved stiffness and toughness at 5 wt. % of DOPO, while thermal analysis indicated char yields above 50%. The optimal DOPO content was identified as 5 wt. %, achieving V-0 classification in the UL-94 test and enhanced LOI (34.2%) due to synergistic interaction with the RESEP matrix, providing a combination of increased flame retardancy, mechanical strength, and thermal robustness. Incorporation of glass and carbon fibers further improved fire performance and mechanical properties, with glass fibers providing the highest LOI (58.0%) and carbon fibers the greatest stiffness. Interlaminar shear strength (ILSS) was also evaluated as function of fiber and DOPO content. Differences in thermal conductivity and heat transfer between the fibers influenced polymer degradation and flame propagation, highlighting the potential of RESEP-DOPO fiber-reinforced composites as sustainable, high-performance materials for applications requiring stringent fire safety. These findings highlight the potential of RESEP-DOPO systems for high-performance, flame-retardant applications in structural sectors.