Synthesis and manufacturing of fibre-reinforced vitrimeric composites based on epoxy and benzoxazine matrices

Abstract

Epoxy and polybenzoxazine vitrimers have been synthesised in this study and used as composites matrices to assess their self-healability. A disulphide bond- endowed reference epoxy vitrimer was formulated based on the established chemistry of diglycidyl ether of bisphenol A and 4-aminophenyl disulphide. Also, a new high-temperature benzoxazine vitrimer (coded BH-A) was synthesised through solventless one-pot method, featuring disulphide bond. The thermal, rheological, cure kinetics and relaxation behaviour of the vitrimers was studied as well as the mode I delamination response of their carbon fibre composites before and after healing. Both the epoxy and benzoxazine systems are high- temperature systems with a glass transition temperature of 163°C and 155°C, respectively and topology freezing transition temperatures of 149.5°C and 78°C, respectively. The cure kinetics of both resins are autocatalytic and were modelled with an average reaction rate error of 5.2% and 14.1% for the epoxy and benzoxazine systems, respectively. The rheological behaviour of the epoxy vitrimer allows manufacturing of composites by liquid moulding, whereas the rheological behaviour of benzoxazine vitrimer is appropriate for manufacturing of composites through resin film infusion. The epoxy system undergoes full stress relaxation in 16 seconds at 220°C and can be healed at this temperature under a pressure of 50 bar in 90 minutes, whereas the benzoxazine system relaxes fully within 5 seconds at 190°C and can be healed at this temperature with a pressure of 4 bar in 30 minutes. Fracture toughness recovery in both composites depends on the historical crack opening prior to healing and follows an exponential decay from a value of 100% at the previous crack tip to about 13 – 20 % at the position of maximum previous crack opening. The self-healing of the benzoxazine composite is superior to that of the epoxy system, as it is achieved within the practically realistic composite manufacturing conditions.