Stiffness modeling of thermoset polymer fibers

Abstract

AbstractRecent progress in creating micro and nano‐scale thermoset polymer fibers through extensional flow reveals remarkable mechanical properties. For instance, epoxy microfibers display a notable increase in stiffness, strength, and toughness as their diameter decreases. This size‐dependent behavior, well‐explored and explained in thermoplastic polymers, is far from being understood in thermoset polymers, as their densely cross‐linked network structure seems to restrain preferential directionality. Our theoretical analysis proposes that, during the pre‐gel curing phase, when the thermoset polymer begins clustering but remains in a liquid state, substantial cluster elongation is induced by the extensional flow. This elongated formation persists to some extent after curing completion, resulting in enhanced mechanical properties along the fiber's primary axis. Concurrently, the high extension reduces fiber diameter, leading to a power‐law diameter dependence of fiber stiffness. The model agrees well with experimental data from tensile tests on epoxy microfibers, highlighting the potential to fine‐tune mechanical properties by controlling the curing process, and laying the groundwork for future improvements.