Vitrimer Composites: Understanding the Role of Filler in Vitrimer Applicability

Vitrimers, a subset of covalent adaptable networks (CANs), are a class of polymer material capable of self-healing and shape reprocessing at temperatures above their topology freezing temperature (Tv), where dynamic covalent bond exchange reactions dominate. In particular, epoxy vitrimers have the strength of a traditional epoxy at low temperatures (T < Tg) coupled with the processing capabilities of a thermoplastic at high temperatures (T > Tv). In addition, epoxy vitrimer composites are attractive as a potential industrial material due to their enhanced thermomechanical performance. While this class of epoxy materials is of significant interest, research on these composites is still premature, and the influence of filler is poorly understood. Herein, we demonstrate the impact of filler addition upon the thermomechanical properties, self-healing, and shape processing capabilities of the resulting vitrimer composites when incorporated with either graphene or clay. We report that filler concentration and dispersion both play a key role in creep suppression, increases in the Tv, and improved mechanical properties (e.g., modulus and strength) irrespective of filler composition. Meanwhile, filler addition does not considerably impact composite shape memory or shape reconfigurability but increases the self-healing capabilities. However, increases in composite modulus require additional heat and stress to allow for comparable shape change compared with their neat counterparts. Vitrimer composites facilitate a unique tunability previously impossible via chemical variations alone. By varying filler composition, concentration, and dispersion quality, composite design with tailorable Tv, strength, and processability is possible, making it suitable for various applications (e.g., actuators, strain sensors, coatings).