Degradation Behaviors and Mechanism of Nitrile Butadiene Rubber Caused by Insulating Medium C5F10O
2. Experiment Method
2.1. Thermal Accelerated Ageing Method
2.2. Preparation for the NBR Samples
3. Deterioration Behaviors of NBR Aged in C5F10O/N2 Mixture
3.1. Compressive Modulus
3.2. Surface Morphology and Element Content of NBR
- Preliminary reaction. In the long-term contact with C5F10O, copolymer of butadiene and acrylonitrile starts to react with C5F10O, resulting in a decrease in the elasticity and strength on the partial surface. However, the effect is not significant in the initial stage, so the rubber surface remains smooth.
- Additive migration. As the surface of NBR continues deteriorating, it is easier for the reinforcing agent inside the rubber to come out of the less-strength surface during its immigration urged by heat. This is also why bulges wrapping ZnO or CaCO3 crystals were found on the NBR surface.
- Additive precipitation. As the elasticity and hardness of the rubber surface continue to decrease, more and more additives migrate to the surface of the rubber and then pierce the weakened surface, forming observable dot-like crystals. After that, the additives begin to extend on the damaged surface and finally form dendritic crystals on the protrusions, whose volume is also greatly enlarged. This process further promotes the deterioration of the rubber’s mechanical performance.
4. Deterioration Mechanism Analysis of NBR Aged in C5F10O/N2 Mixture
4.1. Reaction Mechanism of NBR and C5F10O
4.1.1. Primary Decomposition of C5F10O
4.1.2. C=C Double Bonds in NBR
4.2. Simulation of Rubber Mechanical Properties Based on Molecular Dynamics
4.2.1. Model Building
4.2.2. Deterioration Mechanism of NBR
- The compressive modulus of NBR aged in C5F10O/N2 mixture is significantly smaller than that of NBR aged in N2, indicating that C5F10O is incompatible with NBR rubber. Therefore, when in long-term contact with C5F10O in the electrical equipment, the sealing performance and the service life of NBR will be weakened.
- NBR aged in C5F10O undergoes a three-stage deterioration process based on changes in its surface morphology and atomic composition: (I) a preliminary reaction between NBR and C5F10O results in the reduction of surface strength; (II) reinforcing agents such as ZnO and CaCO3 inside the NBR migrate to the surface, forming bumps that encase crystals on the rubber surface; (III) with further weakening of the surface strength, the reinforcing agents penetrate the rubber surface and exhibit branch-like extensions at the bumps. Each stage is accompanied by a decrease in the mechanical strength of NBR.
- DFT and MD simulations suggest that the C=C double bonds in the molecular chain of NBR can react with CF3 radicals generated by the primary decomposition of C5F10O. Then the addition of C=C double bonds and introduction of CF3 groups on the molecular chain will cause a decrease in the elastic, shear and bulk modulus of NBR. This results in the internal reinforcing agents precipitating onto the surface of NBR, thereby further intensifying the irreversible deterioration of its mechanical properties.
Institutional Review Board Statement
Data Availability Statement
Conflicts of Interest
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She, C.; Zeng, F.; Dai, L.; Li, L.; Yao, Q.; Tang, J. Degradation Behaviors and Mechanism of Nitrile Butadiene Rubber Caused by Insulating Medium C5F10O. Polymers 2023, 15, 2282. https://doi.org/10.3390/polym15102282
She C, Zeng F, Dai L, Li L, Yao Q, Tang J. Degradation Behaviors and Mechanism of Nitrile Butadiene Rubber Caused by Insulating Medium C5F10O. Polymers. 2023; 15(10):2282. https://doi.org/10.3390/polym15102282Chicago/Turabian Style
She, Congdong, Fuping Zeng, Liangjun Dai, Long Li, Qiang Yao, and Ju Tang. 2023. "Degradation Behaviors and Mechanism of Nitrile Butadiene Rubber Caused by Insulating Medium C5F10O" Polymers 15, no. 10: 2282. https://doi.org/10.3390/polym15102282