Fiber-reinforced polymer composites (FRPs) with thermoset matrices are valued for their high specific stiffness, strength, and lightweight properties. However, their vulnerability to fire, along with the release of heat, smoke, and toxicity, limits their broader application. Thermoset FRPs soften, decompose, and collapse under combustion, making it critical to develop flame-retardant versions with lower fire hazards, improved fire insulation, and delayed mechanical integrity loss.

Despite progress in flame-retardant materials, efforts to boost heat/fire insulation and maintain mechanical integrity during fire are still limited. Besides, current testing methods for fireproofing FRPs are time-consuming and require significant materials.

To tackle these challenges, this thesis aims to: (a) develop flame-retardant FRPs with lower fire hazards like heat and smoke; (b) create composites with better insulation; (c) design a bench-scale device for easier validation of these materials.

1. In Chapter 3, bilayer epoxy resin-based coating layers were designed, formulated, and blade-coated onto the substrate of fiberglass thermoset composites. The peak heat release rate (PHRR) and total smoke release (TSP) were lowered by 50% and 65% respectively when adding bilayer coating layers. The heat/fire insulation properties for the bilayer-coated sample were enhanced, with backside temperatures kept at less than 300℃ with no fire burn-through.

2. In Chapter 4, a cobalt-based nanohybrid was ingeniously designed, synthesized, and employed as a highly efficient synergist for commercial ammonium polyphosphate-filled bio-epoxy resin and its fiberglass composites. The filled resin showed a 74% reduction of PHRR due to its enhanced intumescent effect. Nevertheless, the intumescent effect was significantly retarded in fiberglass composite, showing only a 36% reduction of PHRR. Besides, the heat/fire insulation properties were only slightly improved after adding the synergist.

3. In Chapter 5, a bench-scale mechanical testing machine was designed, manufactured, and mounted on a widely used cone calorimeter aiming to validate the fire protective effects of the composites designed in Chapters 3 and 4 in a facile, material-saving manner. The machine was produced and calibrated. The fire protective coating showed higher efficacy in delaying in-plane axial mechanical loss under static force and fire damage compared to flame retardants added into the polymer matrix. Besides, protective effects were also found in postponing the loss of off-axial mechanical properties. The usage of the derived heat release information was also discussed.

4. In Chapter 6, a facile, chitosan/phytic acid-based polyelectrolyte coating was synthesized and dip-coated on the surface of flax fabrics. The treated flax fabric showed self-extinguishing properties with low burnt length. The modified plant fiber/epoxy composite showed a reduction of PHRR by 36% and slowed mass decomposition. Heat/fire insulation tests also showed more than a 200% increase in resist-to-burn-through time.

In conclusion, the above research findings highlight the benefits and limitations of different flame-retardant strategies, providing insights for advancing FRP designs from coupon to component levels.