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

Area of Science:

• Materials Science
• Polymer Science
• Computational Chemistry

Background:

• Natural rubber (NR) and Eucommia ulmoides gum (EUG) are biobased elastomers with potential applications.
• Understanding the structure-property relationships in NR/EUG blends is crucial for material design.

Purpose of the Study:

• To investigate the structure, dynamics, and mechanical-viscoelastic properties of natural rubber (NR)/Eucommia ulmoides gum (EUG) blends using molecular dynamics simulations.
• To elucidate the molecular-level mechanisms governing the behavior of these biobased elastomers in their amorphous phase.

Main Methods:

• United-atom molecular dynamics simulations were employed to model fully amorphous NR/EUG blends.
• Simulations analyzed segmental dynamics, glass transition temperature, chain diffusion, tensile strength under uniaxial deformation, and linear viscoelastic properties.

Main Results:

• Incorporating rigid EUG into flexible NR accelerated segmental dynamics, lowering the glass transition temperature and enhancing chain diffusion.
• Optimal reinforcement in tensile strength was observed at 20% EUG content due to a balance of orientational reinforcement and delayed cavitation.
• Enhanced dynamics shifted the alpha-relaxation peak and slightly increased energy dissipation, differing from experimental results due to the absence of crystallinity and cross-links.

Conclusions:

• The study provides molecular-level insights into the structure-property relationships of amorphous NR/EUG blends.
• Local segmental ordering in EUG-containing NR facilitates chain sliding, leading to counterintuitive dynamic enhancement.
• The findings highlight the intrinsic role of amorphous-phase dynamics in biobased elastomer behavior, distinct from effects in real materials with crystalline constraints and cross-links.