Halogen-free phosphorus-containing flameretardant epoxy composites

Epoxy resins are widely applied in transportation, aerospace, electrical and electronic (EE) industrial sectors due to their excellent properties, such as mechanical strength, chemical and heat resistance, adhesiveness and electrical insulation. Nevertheless, flammability is one paramount disadvantage of epoxy-based materials in most applications. As a result of the current concern for the environment and the human health, halogen-free phosphorous-containing flame retardants (P-FRs) are considered to be the most promising additives to enhance the fire resistance of epoxy materials for industrial applications. Within this context, the main objectives of this doctoral thesis were four. The first one was to synthesize and characterize P-FRs with varied phosphorous’ (P’) chemical environments in the molecular structures. The second one was that investigate the impact of P’ chemical environment in P-FRs on flame retardancy of epoxy and epoxy/carbon fiber composites with P-FRs. The third one was that understand the impact of P’ chemical environment on the flame-retardant mechanism of P-FRs in the gas and the condensed phases of the epoxy, respectively. Finally, the thermal stability and mechanical properties of flame-retardant epoxy and epoxy/carbon fiber composites were studied. Following these objectives, the synthesis and characterization of two series of PFRs with varied P’ chemical environments based on phenylphosphonate (PO-Ph) and phenylphosphoric (PO-OPh) structures are presented in Chapter 3. A comprehensive comparison of both series of P-FRs on flame retardancy of epoxy was carried out via different tests (limiting oxygen index, UL 94 and cone calorimeter) and presented in Chapter 4. The thermal stability and mechanical properties of epoxy containing P-FRs were studied as well. Chapter 5 summarizes the flame-retardant mechanisms of the two series of P-FRs in epoxy that were assessed from both gas and condensed phases via investigating the thermal decomposition behaviors of P-FRs and epoxy with P-FRs, respectively. The thermal phenomena in epoxy with P-FRs during the combustion were investigated via recording surface and near-to-surface temperatures in the UL 94 test. Flame-retardant mechanisms were proposed for the two series P-FRs in epoxy based on the results. Finally, flame-retardant RTM 6/carbon fiber reinforced composites (CFR) were developed based on the results in the previous chapters and the overall results are presented in Chapter 6. Flame-retardant CFR were prepared by resin transfer moulding. The rheological, mechanical properties and flame retardancy of flame-retardant CFR were studied with different tests. In particular, the combustion of the CFR and of the RTM6 epoxy matrix were compared and analyzed as well as the interlaminar shear strength and in-plane shear strength of CFR with and without flame retardants