Epoxy vitrimer materials based on disulfide exchange chemistry : experimental study and modeling of the stress relaxation – application to composites reinforced by nanofibrillated cellulose

Beginning: December 2018
Defense: Septembre 13th, 2021

Abstract:

Epoxy thermoset resins have drawn the attention of many industries due to their versatility, from adhesives to polymer composites. Yet, the re-processability, sustainability, and durability of resins limit their use. The covalent adaptable networks (CANs) like vitrimers can afford a solution to overcome these issues. The epoxy resin, DGEBA-APDS, based on the disulfide exchange chemistry, has shown re-processability properties, but its vitrimer properties have not been fully verified. In the present work, all the vitrimer properties are reviewed to classify it as a vitrimer material. Interestingly, the vitrimer exchange operating temperature (Tv) is close to its glass transition (Tg). So, its relaxation behavior, slightly above Tg, is influenced by the bond exchange reactions and the segmental relaxations of the network. Thus, an adapted stress relaxation model that considers both relaxation phenomena is proposed. This developed rheological model leads to evaluate the epoxy vitrimer matrix reinforced by nano fibrillated cellulose (NFC). The vitrimer composite made with NFC performs a sustainable lightweight material and exhibits mechanical properties similar to non-covalent adaptable networks. A preliminary study to increase material durability has consisted in the NFC surface modification by glycidoxy silane coupling agent. A simple NFC grafting method is proposed, and the surface characterization of the silane network surrounding the NFC is well-explored

Keywords

vitrimer-epoxy, relaxation behavior, bond exchange reaction, nano fibrillated cellulose, surface modification