Materials Today Communications
Volume 11, June 2017, Pages 112-118
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Three-dimensional printing of highly conductive polymer nanocomposites for EMI shielding applications

https://doi.org/10.1016/j.mtcomm.2017.02.006Get rights and content

Highlights

  • A conductive 3D printing ink with conductivity up to ∼5000 S m−1 was fabricated.

  • Conductive scaffolds with different structural parameters were 3D printed.

  • EMI shielding and transparency of the printed structures were investigated.

  • The specific EMI shielding effectiveness increased for ∼200% using 3D printing.

  • Scaffolds’ transparency increased from opaque to 75% by modifying their structures.

Abstract

Here we applied three-dimensional (3D) printing of conductive microstructures for the functional optimization of lightweight and semi-transparent electromagnetic interference (EMI) shields. Highly conductive 3D printable inks with electrical conductivities up to ∼5000 S m−1 were fabricated from carbon nanotubes/polylactic acid (CNT/PLA) nanocomposites. Solvent-cast 3D printing enabled us to fabricate conductive scaffold microstructures and investigate the influence of various important structural parameters (i.e., inter-filament spacing, number of layers and printing patterns) on their transparency and EMI shielding effectiveness. The results revealed a significant improvement of the specific EMI shielding effectiveness of CNT/PLA nanocomposites printed as 3D scaffolds compared to CNT/PLA hot-pressed in solid forms (∼70 vs ∼37 dB g−1 cm3). The transparency of the scaffolds could vary from ∼0% to ∼75% by modifying their printing patterns and inter-filament spacing. To the best of our knowledge the conductivity of the fabricated ink is the highest among the other reported 3D printable polymer composite inks and this is the first reported systematic study on EMI shielding using a 3D printing technique. These results are highly beneficial for the fabrication and structural optimization of EMI shields where light and/or transparent structures are advantageous, such as in aerospace systems, portable electronic devices or smart fabrics.

Introduction

Conductive polymer nanocomposites (CPNs) are composed of conductive nanofillers (e.g. carbon nanotubes, graphene and metallic nanowires) dispersed in a polymer matrix. The utilization of CPNs for electromagnetic interference (EMI) shielding [1], [2], [3], [4], [5], lightning strike protection in airplanes [6], [7], sensors [8], [9], and in the field of electronics [10], [11], [12], [13] have been reported. Among diverse applications of CPNs, EMI shielding is especially demanding due to the industrial requirements of lightweight and highly conductive materials [3]. Emitted electromagnetic (EM) waves from electronics can potentially be hazardous to people’s health and interfere with the operation of electronic devices [14]. In this regard, the proliferating market of electronics has heightened the necessity to resolve the growing EMI issues.

Metals are common materials employed as EMI shields [15]; however, metallic shields have drawbacks like corrosion, high cost, high weight, and expensive to process. Hence, during the last decade, technological breakthroughs and research focus in the field of EMI shielding materials have been intensely directed towards the development of CPNs [16], [17], [18]. CPNs benefit from the intrinsic properties of polymers (i.e., light weight, low cost, corrosion resistance, and easy processing) combined with tuneable electrical conductivity derived from the adjustable filler morphology (i.e. conductive network) within the polymer matrix [19]. Electrical conductivity is a key parameter for effective EMI shielding materials [4], [20]. Most of common polymers are inherently insulative; however, embedding sufficient amount of conductive nanofiller into polymer matrices leads to the formation of conductive networks across the nanocomposite. This transforms the whole nanocomposite into a conductive material. Conduction via physical contacts between conductive nanofillers in combination with electron tunnelling and hopping between conductive nanofillers are the main mechanisms for the electron transference in CPNs [21], [22].

Forming CPNs can be achieved by different common methods such as injection molding, compression molding or solvent casting [17], [23]. Recently, three-dimensional (3D) printing method has also attracted the attention of researchers due to its capability for fabrication of complex shapes at relatively high speed since no mold fabrication is required [24], [25]. As yet, different types of 3D printing (3DP) method, such as fused deposition modeling (FDM) [26], [27], [28], selective laser sintering (SLS) [29], stereolithography (SLA) [30], [31], UV assisted 3DP (UV3DP) [32], [33] and solvent cast 3DP (SC3DP) [34], [35] have been developed. Among the different 3D printing technologies, FDM is the most frequently used 3D printing method [36]. In this method, the polymer melt extrudes out of a heated nozzle to form a 3D shape by layer-by-layer deposition on a platform. Fabrication of conductive structures is challenging using FDM method since metals have very high melting temperatures and CPNs with a high concentration of conductive fillers have high viscosity at their melting point, obstructing the printing nozzle and hampering the printing process.

In SLS method, the initial material is in a form of powder and the 3D shape forms when the powder particles attach to each other due to the sintering of the powder particles caused by the heat of a focalized laser. The printing powder can be metal or CPN particles. The main shortcoming of SLS to the other 3D printing methods is the complexity, the high price of the printing equipment, and the lack of control on the alignment of the nanofillers dispersed in the polymer matrix.

In UV3DP method, the UV light is focalized on the tip of the printing nozzle and cures the UV-curable polymer while the polymer extrudes out of the nozzle [37]. SLA is based on the local polymerization of a thermoset polymer by a laser beam. Printing conductive materials with these two methods are highly challenging since adding nanofillers inside a thermoset polymer can hinder the polymerization and cross-linking processes. SC3DP functions based on the solidification of the polymer-solvent mix due to the rapid evaporation of the solvent during the printing process [34], [35]. The advantages of this method compared to the above-discussed 3D printing techniques are its simplicity, low price, and the possibility of adjusting the ink’s viscosity by modifying its solvent concentration, enabling us to print various types of nanocomposites with high concentration of the nanofillers. The details related to SC3DP method are previously published [34], [35].

In this paper, we report the fabrication of highly conductive CPNs used as the ink for SC3DP method. Employing the fabricated CPNs, we developed 3D printed conductive grid-like configurations and investigated the effect of their structural parameters (i.e., inter-filament spacing, number of printed layers and printing patterns) on their EMI shielding performance and transparency. The specific EMI shielding of the CPNs in different structures were also investigated to provide more insight about the structural effects on the EMI SE considering the mass of the EMI shield.

Section snippets

Nanocomposite and ink preparation

Multi-walled carbon nanotube/polylactic acid (CNT/PLA) nanocomposites were prepared by mixing a solution of PLA (PLA 4032D, Natureworks LLC) dissolved in dichloromethane (DCM) with carbon nanotubes (Nanocyl™ NC7000, Sambreville, Belgium) using ball mill mixing method (SPEX SamplePrep 8000 M Mixer/Mill) [38]. DCM dissolves well the PLA matrix and the high volatility of DCM makes it a suitable solvent for the SC3DP ink [34], [35]. First, PLA was dissolved in DCM at a concentration of 10 wt.% by

Results and discussion

Mixing CNT with a solution of PLA-DCM via ball mill mixing method enabled us to fabricate CNT/PLA nanocomposites with CNT concentrations up to 40 wt.%. Based on our experience of CNT/PLA fabrication using various mixing methods such as solution mixing or melt extrusion [40], the ball mill mixing method was more suitable for the synthesis of CNT/PLA nanocomposites with high CNT concentrations (>10 wt.%). This is mainly due to the fact that the problems associated with the high viscosity of the

Conclusions

Highly conductive 3D printable ink with an electrical conductivity up to ∼5000 S m−1 was obtained from CNT/PLA conductive nanocomposite. 3D printing was used to build conductive, light, and semi-transparent scaffold structures tested for EMI shielding application. The specific EMI SE of the printed scaffolds could reach to about two times more than the one for the solid form of the conductive CNT/PLA nanocomposite (∼70 dB g−1 cm3 vs ∼37 dB g−1 cm3). This is highly useful for EMI shields where

Acknowledgements

The authors acknowledge the financial support from Natural Sciences and Engineering Research Council of Canada (NSERC – grant number: RGPAS-446198-2013 and RGPIN/05503-2015). We would like to thank Dr. Richard Vernhes from École Polytechnique de Montréal for providing us technical assistance with the optical characterization. We also thank Dr. Shuang-Zhuang Guo for his technical assistance with the solvent-cast 3D printing method.

References (53)

  • M. Arjmand et al.

    Carbon

    (2011)
  • D. Chung

    Carbon

    (2001)
  • M. Gagné et al.

    Prog. Aerosp. Sci.

    (2014)
  • X. Kang et al.

    Anal. Biochem.

    (2007)
  • J.-M. Thomassin et al.

    Mater. Sci. Eng. R-Rep.

    (2013)
  • M. Arjmand et al.

    Carbon

    (2012)
  • A. Ameli et al.

    Carbon

    (2013)
  • M. Trojanowicz

    TrAC Trends Anal. Chem.

    (2006)
  • M. Arjmand et al.

    Carbon

    (2016)
  • M. Arjmand et al.

    Compos. Sci. Technol.

    (2015)
  • D.W. Hutmacher

    Biomaterials

    (2000)
  • D.T. Pham et al.

    Int. J. Mach. Tools Manuf.

    (1998)
  • X. Zhang et al.

    Sens. Actuators A Phys.

    (1999)
  • Z. Spitalsky et al.

    Prog. Polym. Sci.

    (2010)
  • C. Martin et al.

    Compos. Sci. Technol.

    (2004)
  • W. Bauhofer et al.

    Compos. Sci. Technol.

    (2009)
  • G. Postiglione et al.

    Compos. Part A Appl. Sci. Manuf.

    (2015)
  • J. Czyżewski et al.

    J. Mater. Process. Technol.

    (2009)
  • N. Li et al.

    Nano Lett.

    (2006)
  • F. Qin et al.

    J. Appl. Phys.

    (2012)
  • S. Celozzi et al.

    Electromagnetic Shielding

    (2008)
  • P.J. Glatkowski, D.H. Landis, J.W. Piche, J.L. Conroy, Patent Number: US6986853 B2,...
  • K. Inpil et al.

    Smart Mater. Struct.

    (2006)
  • S. Bae et al.

    Nat. Nano

    (2010)
  • G. Eda et al.

    Nano Lett.

    (2009)
  • S. Stankovich et al.

    Nature

    (2006)
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