Exploring the Limits of High-T_g Epoxy Vitrimers Produced through Resin-Transfer Molding

Abstract

Over the past few years, scientists have developed new ways to overcome the recycling issues of conventional thermosets with the introduction of associative covalent adaptable networks (i.e., vitrimers) in polymer materials. Even though various end-use vitrimers have already been reported, just a few of them have targeted high-performance industrial applications. Herein, we develop a promising high-performance epoxy vitrimer based on a commercially available resin widely used in aeronautics with the highest glass transition temperature (T g ) of 233 °C ever reported for a vitrimer. A complete study of its physicochemical properties and cure kinetics was conducted, enabling the construction of the first time−temperature−transformation (TTT) diagram reported in the literature. This diagram allows a full determination of the processing and curing parameters leading to the manufacturing of vitrimer samples by the resin-transfer molding (RTM) process. The reshapability and limits therefrom of this high-T g vitrimer were evaluated by three successful thermoforming cycles without degradation.

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

“…For instance, at a curing temperature of 160 °C, it would take around 33 min to reach a conversion of at least 0.9. This time is comparable to that of similar aromatic systems previously reported …”

“…This means that the SR1710-SD network should exhibit higher free volume than the SR1710-V analogue, with a possible impact on network density. This was already observed by our group on RTM6-based materials, although the density difference should be less notable for SR1710 systems as the volume of methyl substituents is lower than diethyl substituents present in the RTM6 part B permanent hardener. As expected, a higher density was obtained for SR1710-V with a value of 1.244 compared to 1.172 for SR1710-SD.…”

“…To achieve this objective, the chemical structures of SR1710 (epoxy resin) and SD3303 (permanent hardener) were studied to select a commercially available dynamic hardener compatible with this chemistry. Following our previous work on RTM6, a commercially available dynamic hardener, 4-AFD (4-aminophenyl disulfide), was chosen . The dynamic properties arise from the disulfide linkage incorporated within the hardener, which experiences both associative and dissociative exchanges at elevated temperatures .…”

“…Despite the lack of explicit details on the chemical composition, they reported mechanical properties comparable to materials currently found in aircraft. Recently, we developed a high-performance epoxy vitrimer formulation, based on RTM6 with one of the highest reported glass transition temperature ( T g ) for epoxy vitrimers (233 °C), although with some limitations of reprocessability . However, of all of the studies on vitrimer composites produced by RTM resin, only the latter covered cross-linking kinetics and reactivity with a time–temperature–transformation (TTT) , diagram, allowing the optimization of the process parameters and curing cycles.…”

Vanillin-based dual dynamic epoxy building block: a promising accelerator for disulfide vitrimers

“…The reduction of reprocessing time and temperature is a subject of attention as this chemistry has shown some limitations at high temperature. 16,17 In the course of developing disulfide vitrimers with faster stress relaxation, researchers have explored the possibility to combine several dynamic chemistries within the same material. For example, accelerating effects were reported by employing disulfide exchanges in combination with transesterification.…”