Enhanced permittivity in flexible carbon-fiber and acrylic-polyurethane composites

doi:10.1016/j.matlet.2017.05.094

Materials Letters

Volume 205, 15 October 2017, Pages 44-47

https://doi.org/10.1016/j.matlet.2017.05.094 Get rights and content

Highlights

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Acrylic-polyurethane/carbon fibers composites with highly flexible were prepared.
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Colossal permittivity about 700 was observed in APu-14.7% CFs composites.
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The high permittivity behavior can be well fitted by percolation theories.
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The conductive mechanism of CFs/APu composites is hopping conduction behaviors.

Abstract

Acrylic-polyurethane (APu) as one of self-adhesive materials has been widely used in various coating industries, however it has seldom caused the researchers concern on its dielectric property. In this paper, acrylic polyurethane and carbon fibers (CFs) composites with good dispersibility have been successfully prepared. The dielectric properties and ac conductivity of the CFs/APu composites as a function of frequency and volume fraction of CFs were studied. High dielectric constant about 700 (10 kHz) was observed in APu-14.7% CFs composites. The outstanding dielectric properties make CFs/APu composites as promising candidates for thin-film capacitors, electromagnetic shielding and attenuation coatings.

Introduction

It is well known that the dielectric constants of traditional polymeric materials are relatively low (<10) in comparison with ceramic materials. However, flexible and high breakdown field strength still make it possible for applications in high charge-storage capacitors and electronics [1], [2], [3]. In order to realize these applications, it is highly desirable to substantially improve the permittivity of such polymers. One approach is randomly dispersing some ceramic powders with high dielectric constant into the polymer to increase the dielectric constant. High permittivity (ε_r′) metal oxide such as BaTiO₃ incorporated into a polymer matrix is of significant current interest. However, the permittivity was still low (<50) even when the volume fraction of BaTiO₃ was over 50 vol% [4], [5]. In addition, the composites lose their flexibility at high ceramic particulate loading [6]. An alternative strategy is to develop high permittivity percolative composites filled with conductive fillers. As the volume fraction of conductive fillers is near but does not exceed the percolation threshold, the permittivity of composites can be dramatically enhanced which is described by interfacial polarization effect [7]. However, the permittivity decrease sharply when the volume fraction of conductive fillers beyond the percolation threshold (probably due to a lot of pores induced in the composites [8]). Additionally, negative permittivity behavior is also observed when the conductive filler far above threshold [9]. In recent years, a series of high permittivity were achieved in percolative composites. Such as polymer matrix filled with Ag particles [8], [10], carbon nanotubes (CNTs) [11], carbon fibers (CFs) [12], graphite nanoplates [3]. Particularly, CFs and their composites have been found to be fascinating candidates owing to their excellent mechanical and electrical properties on the basis of large aspect ratios and high conductivity [12], [13]. What’s more, CFs are unbent fibers while carbon nanofibers are frizzy, so CFs would generate more interfacial polarization [12]. Therefore, we suppose the composites exhibit high permittivity at low volume fraction of CFs. In addition, it would be still flexible for the low percolation threshold.

Acrylic-polyurethane (APu) as one of self-adhesive materials is widely used in various coating industries because of its favorable properties, such as environmentally friendly, chemical resistance, exterior durability, high flexibility and excellent adhesion to most substrates [14], [15], [16]. But even much attention has been focused on waterborne coatings, little work has been performed to report its dielectric property.

In this work, we demonstrate significantly enhanced dielectric permittivity of CFs/APu composites with low volume fraction of CFs. The mechanical properties, dielectric permittivity and ac conductivity of CFs/APu composites were studied.

Section snippets

Experimental

Materials and synthesis: The APu (Marine Chemical Research Institute Co., Ltd., China) with different volume fraction of CFs (Toray Industries (china) Co., Ltd.) were mixed by mechanical rabbling for 30 min, then the dispersion with CFs was treated with ultrasonic for 30 min. Further, the mixture was sprayed onto polytetrafluoroethylene plate using the high-viscosity spray gun. Finally, the CFs/APu composites were obtained after fully cured at room temperature for 48 h with the average thickness

Results and discussion

Fig. 1a shows the morphologies of carbon fibers. The fibers are randomly overlaid and the diameters is about 10–12 μm with the length of 100 μm. Cured pure APu coating is showed in Fig. 1b which indicates that there are no holes in the APu surfaces. Fig. 1c and d present the fractured cross sections of CFs/APu composites including the 8.4 vol% and 14.7 vol% loading of CFs respectively. The CFs are uniformly dispersed in the APu matrix and no aggregation phenomenon is observed. It is also clearly

Conclusions

In summary, CFs/APu hybrid films with good dispersibility have been successfully prepared. The dielectric properties of the CFs/APu composite as a function of frequency and volume fraction of CFs are studied. The dielectric permittivity of composites achieves highest 700 at 10 kHz. In addition, the dielectric and conductivity properties of the films are explained by percolation theory. Frequency dispersion behavior of the ac conductivity accord with power law which confirms the conductive

Acknowledgments

This study was financially supported by the National Natural Science Foundation of China [grant No. 51402170, grant No. 51601105] and the Natural Science Foundation of Shandong Province (ZR2016EMM09).

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Enhanced permittivity in flexible carbon-fiber and acrylic-polyurethane composites

Highlights

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgments

Compos. Part A

Mater. Lett.

Mater. Lett.

Mater. Sci. Eng. R

Appl. Surf. Sci.

Mater. Lett.

Prog. Mater. Sci.

Phys. Rep.

Appl. Phys. Lett.

Adv. Funct. Mater.