The Effect of Cross-Linking Type on EPDM Elastomer Dynamics and Mechanical Properties: A Molecular Dynamics Simulation Study
Abstract
:1. Introduction
2. Cross-Linking Types of EPDM
2.1. Cross-Linking during Manufacturing
2.2. Cross-Linking during Thermo-Oxidation
2.3. Construction of EPDM Cross-Linked Molecules
3. Molecular Dynamic Simulation Method
3.1. MD Simulations
3.2. Potentials
3.3. Periodic Boundary Conditions
3.4. Radius of Gyration
3.5. Mean-Squared Displacement
3.6. Uniaxial Stress–Strain Behavior
3.7. Free Volume
4. Results and Discussion
4.1. Relaxation
4.2. Density
4.3. Radical Radius
4.4. Free Volume
4.5. Diffusion
4.6. Uniaxial Tensile Properties
5. Conclusions
- (1)
- The Rg shaped by cross-linked bonds with C9 participation is greater than C2*, the Rg shaped with C3 participation is smaller, and the free volume associated with the Rg follows this pattern as well. In comparison to the origin cross-linking, the Rg shaped by oxidized cross-linking of C2*-O-C2* and C9-O-C9 grows greater, whereas that of C3-O-C3 becomes smaller.
- (2)
- According to the models developed in this paper, cross-linking of C2*-C2*, C3-O-C3, and C9-O-C9 has a significant constraining effect on molecular diffusion motion, C2*-C3, and C3-C3 have a minor inhibiting effect on diffusion, while C2*-C9 and C9-C9 boost molecular self-diffusion motion.
- (3)
- The topological restrictions are weaker in C2*-C9 and C9-C9, and the FFV of M4 and M9 is more than double that of M1, offering greater free space for chain movement, which is why M4 and M6 have superior self-diffusion ability while being more cross-linked than M1.
- (4)
- Cross-links between the main chains significantly provide a positive contribution to the modulus, and the conformational entropy of the cross-linking between the C9 atoms of the side chains is higher than that between the C3 atoms. The effect of cross-links made up of the side chains and the main chain have an entropy in between that of C9-C9 and C3-C3.
- (5)
- The ether cross-linking formed by the oxidation of the side chain cross-linking enhances the inhibition effect on diffusion properties while the main chain cross-linking has the inverse result.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Molecular Types | M1 | M2 | M3 | M4 | M5 | M6 | M7 | M8 | M9 | |
---|---|---|---|---|---|---|---|---|---|---|
E1 | Free chain | 40 | 20 | 20 | 20 | 20 | 20 | 20 | 20 | 20 |
E2 | C2*-C2* | 10 | ||||||||
E3 | C2*-C3 | 10 | ||||||||
E4 | C2*-C9 | 10 | ||||||||
E5 | C3-C3 | 10 | ||||||||
E6 | C9-C9 | 10 | ||||||||
E7 | C2*-O-C2* | 10 | ||||||||
E8 | C3-O-C3 | 10 | ||||||||
E9 | C9-O-C9 | 10 |
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Wang, Y.; Liu, H.; Li, P.; Wang, L. The Effect of Cross-Linking Type on EPDM Elastomer Dynamics and Mechanical Properties: A Molecular Dynamics Simulation Study. Polymers 2022, 14, 1308. https://doi.org/10.3390/polym14071308
Wang Y, Liu H, Li P, Wang L. The Effect of Cross-Linking Type on EPDM Elastomer Dynamics and Mechanical Properties: A Molecular Dynamics Simulation Study. Polymers. 2022; 14(7):1308. https://doi.org/10.3390/polym14071308
Chicago/Turabian StyleWang, Yajian, Huifang Liu, Pengpeng Li, and Linbing Wang. 2022. "The Effect of Cross-Linking Type on EPDM Elastomer Dynamics and Mechanical Properties: A Molecular Dynamics Simulation Study" Polymers 14, no. 7: 1308. https://doi.org/10.3390/polym14071308