Design and performance study of EP/CFRP based on phosphorus-containing ionic liquids: Synergistic enhancement of high strength, high toughness, and flame retardancy

Carbon Fiber Reinforced Polymers (CFRP) are advanced materials with extensive application potential. However, their use is significantly limited by the complexity of the production process and the flammability of the matrix resin. Modification is typically achieved through the addition of flame retardants; however, the existing preparation processes for these retardants are complex, and the introduction of additive flame retardants often compromises the mechanical properties of the composite materials. This work utilizes a "soft chemistry" approach to design and synthesize a novel phosphorus-containing ionic liquid (PIL) through a straightforward one-step neutralization reaction. The effects of PIL content on the thermal performance, mechanical properties, and flame retardancy of the composites were investigated. Compared to pure epoxy (EP), the 2.0PIL sample exhibited a 68.20 % increase in flexural strength, a 433.33 % increase in flexural strain at break, a 62.98 % increase in notched impact strength, a 23.64 % increase in tensile strength, and a 103.99 % increase in tensile strain at break. The 2.0PIL sample demonstrated superior flame retardancy, achieving a UL-94 V-0 rating and an LOI of 31.8 %. The PHRR, PSPR, THR, TSP, and CO 2 P of the 2.0PIL sample were reduced by 65.76 %, 56.53 %, 41.93 %, 47.59 %, and 61.53 %, respectively, compared to the EP matrix. Additionally, the CFRP with 2.0PIL demonstrated excellent mechanical and flame-retardant properties. Specifically, the flexural strength increased by 26.44 % and the ILSS improved by 41.08 % compared to the EP/CFRP samples. Furthermore, the PHRR, PSPR, THR, and TSP were reduced by 5.39 %, 51.27 %, 17.96 %, and 24.55 %, respectively, indicating satisfactory fire safety performance. This work provides a new, simple, and fast approach for designing thermosetting epoxy resin and carbon fiber composite materials for "Flame Retardant Toughening Integration".