Enhanced Morphology-Dependent Tensile Property and Breakdown Strength of Impact Polypropylene Copolymer for Cable Insulation
Abstract
:1. Introduction
2. Materials and Methods
2.1. Sample Preparation
2.2. Characterization
3. Results
3.1. Enhanced AC Breakdown Strength and Elongation at Break of IPC
3.2. Differences of Crystalline Structure Between IPC and iPP
3.3. Morphology of PP and IPCs
3.4. Trap distribution of iPP and IPC
4. Discussion
4.1. Schematic Diagram of the Spherulite Structure Evolution Affected by the Rubber Phase
4.2. Role of the Rubber Phase on the Mechanical Properties
4.3. Relation Between the Microstructure and Trap Distribution of IPC
4.4. Mechanism of the Enhanced Breakdown Strength of IPC
5. Conclusions
- (1)
- Impact copolymerization is an effective way to optimize the electrical and mechanical properties of iPP simultaneously. Compared with iPP, the breakdown strength and elongation at break of IPC15 increase about 8.0 and 64.9%, respectively. However, a sharp decrease in the breakdown strength and elongation at break can be found with an excessive rubber phase content.
- (2)
- The enhanced breakdown strength of IPC15 is attributed to the impact of lamella thickness and crystalline structure defects. The lamella thickness of IPC15 is larger than iPP and IPCs, which leads to an elevated breakdown strength. It is also suggested that the crystalline structure defects caused by ethylene segments in the PP crystal are responsible for the increase in the deep trap density and level of IPC15, which can further lead to an increased breakdown strength. The high elongation at break of IPC15 is influenced by the rubber microspheres among the lamellas. The elongation at break can be increased by rubber microspheres through enhancing the relative sliding among lamellas under external force and reducing the stress concentration.
- (3)
- The sharply decreased breakdown strength of IPC30 is considered to be caused by the expansion of amorphous regions. An increased rubber phase content leads to a significant decrease in crystallinity, which further results in the decrease in the deep trap level and density. It was found that the lamella thickness of IPC30 is the thinnest. The breakdown strength sharply declined due to the decreased lamella thickness and deep trap.
Author Contributions
Funding
Conflicts of Interest
References
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Sample Code | Weibull Parameters | |
---|---|---|
α | β | |
XLPE | 108.6 ± 8.4 | 13.5 |
iPP | 143.4 ± 7.8 | 27.5 |
IPC15 | 154.9 ± 9.4 | 22.2 |
IPC30 | 117.8 ± 8.3 | 15.8 |
Sample Code | Tm(°C) | Tc(°C) | ΔHm(J/g) | Xc(%) | L(nm) |
---|---|---|---|---|---|
XLPE | 112.1 | 93.3 | 79.87 | 27.8 | / |
iPP | 169.0 | 116.0 | 65.13 | 31.2 | 31.99 |
IPC15 | 171.1 | 118.1 | 63.47 | 30.4 | 36.04 |
IPC30 | 168.0 | 110.6 | 43.57 | 20.9 | 30.37 |
Sample Code | ET (eV) | Ntrap (m−3) | ||
---|---|---|---|---|
Shallow | Deep | Shallow | Deep | |
iPP | 0.949 | 1.055 | 7.43 × 1020 | 1.79 × 1021 |
IPC15 | 0.942 | 1.063 | 9.36 × 1020 | 2.04 × 1021 |
IPC30 | 0.928 | 1.048 | 1.55 × 1021 | 1.49 × 1021 |
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Yang, K.; Liu, Y.; Yan, Z.; Tian, Y.; Liu, Y.; Jing, Z.; Li, J.; Li, S. Enhanced Morphology-Dependent Tensile Property and Breakdown Strength of Impact Polypropylene Copolymer for Cable Insulation. Materials 2020, 13, 3935. https://doi.org/10.3390/ma13183935
Yang K, Liu Y, Yan Z, Tian Y, Liu Y, Jing Z, Li J, Li S. Enhanced Morphology-Dependent Tensile Property and Breakdown Strength of Impact Polypropylene Copolymer for Cable Insulation. Materials. 2020; 13(18):3935. https://doi.org/10.3390/ma13183935
Chicago/Turabian StyleYang, Kai, Yun Liu, Zhimin Yan, Ye Tian, Yitao Liu, Zhenghong Jing, Jianying Li, and Shengtao Li. 2020. "Enhanced Morphology-Dependent Tensile Property and Breakdown Strength of Impact Polypropylene Copolymer for Cable Insulation" Materials 13, no. 18: 3935. https://doi.org/10.3390/ma13183935