M. Naraghi
Texas A&M University,
United States
Keywords: vitrimer, self-healing, composite, interface
Summary:
Polymers are often studied under the two mutually exclusive categories of thermoplastics and thermosets. The thermoplastics feature reversible inter-chain interactions enabling properties such as self-healing, whereas thermosets possess permanent covalent crosslinks, making them well-suited for load-bearing applications in demanding environments like aerospace. Thermosets are in particular used to make advanced composites owing to the low viscosity of the uncured materials which allow for infiltration of resin in between the fibers. However, the permanent nature of the thermoset bonds, once cured, is a roadblock for maintenance of the composite in light of the defects accumulated during performance. This presentation will explore the processing–microstructure–mechanics relationships in vitrimers and their composites—an emerging class of thermosets characterized by a covalent adaptive network (CAN). Vitrimers uniquely combine the robustness of covalent bonding with the versatility of reversible crosslinking, offering promising capabilities in repair and self-healing. Through multiscale experimental investigations, the research examines phenomena ranging from microcrack reformation and interfacial mechanics in composites to recovery from both micro- and macroscale defects. We will discuss how bond reformation and healing in vitrimers depend on polymer morphology, as reflected by factors such as backbone rigidity and crosslink density and will contrast the self-healing performance in bulk versus composite samples, emphasizing the crucial role of polymer chain mobility in damage recovery. The potential for intrinsic self-healing after multiple cycles of damage will be explored and the root cause of self-healing gradual degradation will be presented. Lastly, the self-healing at the microscale, the scale of the fiber-matrix interface will be presented, and the mechanisms for the fiber-matrix bonding will be assessed by comparing the load bearing capacity of fiber-matrix interface among fibers with modified surface chemistry.