Structure, Dynamics, and Mechanical-Viscoelastic Properties of NR/EUG Blends: A Molecular Dynamics Study

United-atom molecular dynamics simulations were performed to investigate the structure, dynamics, and mechanical-viscoelastic properties of natural rubber (NR)/Eucommia ulmoides gum (EUG) blends. The systems were modeled as fully amorphous matrices to isolate the intrinsic behavior of the disordered phase. Results reveal that incorporating rigid EUG chains into flexible NR induces a counterintuitive acceleration of segmental dynamics─manifested as a decreased glass transition temperature and enhanced chain diffusion─driven by local segmental ordering that facilitates chain sliding. Under uniaxial deformation, tensile strength exhibits a nonmonotonic composition dependence, with optimal reinforcement at 20% EUG content, arising from a balance between the orientational reinforcement of rigid segments and the delayed onset of cavitation. Linear viscoelastic analysis shows that enhanced dynamics shift the α-relaxation peak to higher frequencies and slightly increase energy dissipation. This contrasts with the reduced hysteresis reported for real materials, a discrepancy that stems from the absence of crystalline constraints and chemical cross-links in our amorphous models. By delineating the intrinsic role of amorphous-phase dynamics, this work provides molecular-level insights into the structure-property relationships of biobased elastomers.