# PpyNT/NR/NBR Composites with Excellent Microwave Absorbing Performance in X-Band
## 4 Conclusions  
In this study, PPyNTs with several micrometers in length, 104.2 \(\pm\) 18.4 nm in diameter, 31.4 \(\pm\) 3.4 nm in wall thickness, and 0.35 S/cm in conductivity are prepared from a reactive self-degraded template method. Microwave absorbing rubber based on PPyNT as absorbing filler and immiscible NR/NBR blend as matrix is fabricated via a simple mixing technique in the rubber industry. To optimize the material system achieving excellent MA performance in the frequency of 8.2-12.4 GHz, the PPyNT content and the ratio of NR/NBR are investigated in detail. Results show that the selective distribution of PPyNT in the NR phase is regardless of PPyNT content and NR/NBR ratio. In contrast, the impedance matching and attenuation capability of the composites are regulated by composite composition. The 6 phr PPyNT filled NR/NBR (90/10) has the best comprehensive MA performance, which shows a strong reflection loss value of \(-\)56.67 dB and a broad effective bandwidth of 3.7 GHz at 2.9 mm, surpassing most rubber-based microwave absorbers reported in the literature over the same frequency range. Based on the electromagnetic loss mechanism analysis, its excellent absorption performance can be attributed to superior impedance matching, conduction loss, dipolar polarization, interface polarization, and multiple scattering. This novel microwave-absorbing rubber composite is a promising candidate for high-performance microwave absorption material in radar stealth and flexible electronics.  
Figure 6: Schematic illustration of microwave absorbing mechanism for 6 phr PPyNT filled NR/NBR (90/10) composite.  
**Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/polym15081866/s1](https://www.mdpi.com/article/10.3390/polym15081866/s1)]([https://www.mdpi.com/article/10.3390/polym15081866/s1](https://www.mdpi.com/article/10.3390/polym15081866/s1)), Figure S1: (a) Diameter and (b) Wall thickness distribution of PPyNTs (\(n=150\)); Figure S2: TEM images of PPyNT/NR/NBR (50/50) with different PPyNT contents (a) 3 phr; (b) 6 phr; (c) 9 phr; (d) 12 phr; Figure S3: The real \(\epsilon^{\prime}\) (a) and imaginary \(\epsilon^{\prime\prime}\) (b) parts of the complex permittivity of PPyNT/NR/NBR (50/50) with different PPyNT contents; Figure S4: TEM images of 6 phr PPyNT filled NR/NBR composites with different ratios of NR/NBR: (a) 10/90; (b) 30/70; (c) 50/50; (d) 70/30; (e) 90/10; Figure S5: Attenuation constant of 6 phr PPyNT filled NR/NBR composites with different ratios of NR/NBR; Figure S6: 2D contour maps of \(\left|Z_{\text{in}}/Z_{\text{0}}\right|\) values of 6 phr PPyNT filled NR/NBR composites with different ratios of NR/NBR: (a) 10/90; (b) 30/70; (c) 50/50; (d) 70/30; (e) 90/10.  
**Author Contributions:** Writing-original draft, Data curation, Formal analysis, H.Y.; Investigation, A.W., X.F., H.D., T.Z. and S.Z.; Writing-review & editing, Methodology, Formal analysis, Supervision, J.S. and C.S. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work is supported by the Shandong Provincial Natural Science Foundation (No. ZR2020 ME069) and (No. ZR2020 ME060), National Natural Science Foundation of China (No. 51503114) and Sino-German Academy of Young Scientists (No. 20-12-3-1-hz-2).  
**Institutional Review Board Statement:** Not applicable.  
**Data Availability Statement:** Data presented in this study are available on request from the corresponding author.  
**Conflicts of Interest:** The authors declare no conflict of interest.