Superior Mechanical Performance of Cellulose Acetate via Enhanced Chain Segment Mobility by Tuning Isophorone Diisocyanate Content

The brittleness of cellulose acetate (CA) severely restricts its use in demanding applications. This study presents a strategy to overcome this limitation through chemical crosslinking with isophorone diisocyanate (IPDI). By precisely tuning the IPDI dosage, we achieved an optimal, moderately crosslinked film, denoted as CA17.5. Remarkably, this film broke the strength–ductility trade‐off typical of plasticization, exhibiting exceptional mechanical properties at 25°C: a tensile strength of 63.69 ± 2.09 MPa (79.4% increase), an elongation at break of 19.48% ± 2.03% (432.2% increase), and an impact energy per unit thickness of 14.54 ± 1.05 J·mm −1 (396.2% increase). Superior performance was retained at −40°C. Contrary to the conventional view that crosslinking invariably restricts chain mobility, we demonstrate that a moderate network can enhance it. This enhancement is attributed to the introduction of flexible segments and the disruption of the rigid hydrogen‐bond network by IPDI. Molecular dynamics simulations quantitatively confirmed this mechanism, showing a significant increase in the mean square displacement (MSD) for CA17.5. Our work provides a simple yet powerful method to fabricate high‐toughness CA materials, significantly broadening their application potential.