Thermolatent Heterogeneous Epoxy–Acid Formulation for the Manufacture of Preimpregnated Sheets and Composites with Vitrimer Properties

Abstract

The goal of this work is to develop carbon fiber-reinforced polymer (CFRP) composites showing vitrimer properties and manufacturable by the prepreg technique. Since their invention in 2011, epoxy vitrimer matrices have shown an appealing potential to produce CFRPs with healing, adhesion, and recycling abilities. While techniques such as resin infusion or resin transfer molding have been successfully applied, production of composites by handling of preimpregnated sheets requires a specific set of properties which is still lacking. Starting from commercially available monomers, we hereby investigate the design and preparation of a thermolatent reactive composition compliant with the prepreg technique. The designed composition is heterogeneous, comprising a crystalline hardener dispersed in novolac-based epoxy resin. It thus offers (i) latency and the required viscosity profile for impregnation of carbon fibers around 100 °C, (ii) chemical inertness and tackiness for storage and handling at room temperature, and (iii) awakened reactivity for curing at higher temperatures (>130 °C). The whole CFRP composite manufacture (from resin mixing, impregnation, and composite curing) was transferred from the laboratory to an industrial environment. The resulting CFRP vitrimer composites are investigated with regard to their mechanical properties, interfacial welding, damage healing, and reprocessing through chemical depolymerization, allowing the recovery of carbon fiber sheets with limited damage.

Comparing Surface and Bulk Curing Processes of an Epoxy Vitrimer

“…In both Leibler et al. and following studies with the epoxy-acid vitrimer systems, ,,− as discussed in the previous paragraph, FTIR is generally used to track the formation of ester groups, but due to the limited resolution, only a broad and single peak from 1675 to 1775 cm –1 , centered at 1732 cm –1 , was observed and assigned to the absorption of ester groups from esterification reactions (Figure S1c). In fact, this peak is the result of an overlap between the absorption of the carbonyl group in acids and formed ester groups.…”

Epoxy Vitrimer Formulation for Resin Transfer Molding: Reactivity, Process, and Material Characterization

“…Among the array of chemistries available, two of them gather considerable attention for composite applications: − transesterification and disulfide exchanges. These chemistries have been particularly studied , with some composite processes already tested such as pultrusion, impregnation, − and resin transfer molding (RTM), − to name a few. For instance, Chabert et al prepared vitrimer-based glass-fiber composite plates via resin transfer molding .…”