Entanglement Network Suppresses Toughness Deterioration in Polycarbonate at Superhigh Strain Rates

The influence of molecular chain entanglement on the mechanical performance of polycarbonate (PC) at superhigh strain rates has been investigated, which is valuable for its safety applications like window glazing. The mechanical testing results across a wide strain rate range (0.01-100 s^-1) show that toughness increases with strain rate, but significant deterioration of stiffness and toughness occurs at 100 s^-1. This phenomenon is, for the first time, observed in real time using digital image correlation (DIC), revealing severe stress concentration and strain localization at 100 s^-1. Nevertheless, we find this deterioration is significantly suppressed by the high entanglement density. It strengthens the strain hardening regime and dynamic mechanical analysis (DMA) is showing that both loss modulus and tan δ values increase with entanglement density in the β-relaxation region, indicating enhanced energy dissipation, which may be the underlying origin of the improved ability to resist deformation. This work is providing fundamental insights into tailoring entanglement networks to suppress energy absorption deterioration under extreme deformation conditions.