Review of sustainable, eco-friendly, and conductive polymer nanocomposites for electronic and thermal applications: current status and future prospects

Abstract

Biodegradable polymer nanocomposites (BPNCs) are advanced materials that have gained significant attention over the past 20 years due to their advantages over conventional polymers. BPNCs are eco-friendly, cost-effective, contamination-resistant, and tailorable for specific applications. Nevertheless, their usage is limited due to their unsatisfactory physical and mechanical properties. To improve these properties, nanofillers are incorporated into natural polymer matrices, to enhance mechanical durability, biodegradability, electrical conductivity, dielectric, and thermal properties. Despite the significant advances in the development of BPNCs over the last decades, our understanding of their dielectric, thermal, and electrical conductivity is still far from complete. This review paper aims to provide comprehensive insights into the fundamental principles behind these properties, the main synthesis, and characterization methods, and their functionality and performance. Moreover, the role of nanofillers in strength, permeability, thermal stability, biodegradability, heat transport, and electrical conductivity is discussed. Additionally, the paper explores the applications, challenges, and opportunities of BPNCs for electronic devices, thermal management, and food packaging. Finally, this paper highlights the benefits of BPNCs as biodegradable and biodecomposable functional materials to replace traditional plastics. Finally, the contemporary industrial advances based on an overview of the main stakeholders and recently commercialized products are addressed.

Keywords: Electrical conductivity; Functional materials; Nanocomposites; Nanofillers; Thermal stability and conductivity.

Fig. 1

A The relationship between (a) the dielectric constant and (b) dielectric loss at different frequencies is shown for the samples labeled CSNA0, CSNA1, and CSNA2. These samples contain 0%, 1%, and 3% weight of Al₂O₃ content, respectively, in CS: AgNO₃. The measurements were taken at ambient temperature [35]. Copyright: . However, the nanocomposites display frequency-independent behavior at higher frequencies (A. a). Therefore, ε′ is relatively constant with changes in the frequency; this is because of such rapid field alteration that the dipoles will no more be able to orient themselves in the field direction after effecting in the permittivity and dielectric loss [24]. The rise in dielectric constant in the lower frequency range is mostly due to polarization, which weakens the electrostatic binding strength near grain boundaries. It is worthy to note that the loss of electrostatic binding strength is predominantly affected by polarization [40] © 2019 The Authors. Published by Elsevier B.V. This is an open-access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/). B The scattering and absorption behavior of the dielectric permittivity and tangent δ (C) of the Ecoflex®:SWCN hybrid layer vary with different concentrations of SWCN [36].Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).Outstanding values of the permittivity and ε′ in the low-frequency range (< 1 kHz) are explained by the presence of the extrinsic polarization impact (space charge effect) due to blocking of charge carriers (dipoles) near the electrodes at the sample-electrode interface (named electrode polarization phenomenon) or at boundaries of nanomaterials and polymer matrix of composites [37]. Polarization is defined as the smallest displacement of these charges, which produce dipoles at the material borders. [38]. As known, the ε′ of a substance measures the storing electrical energy ability during exposing time to an electric field, associated with the amount of polarization inside the materials [28]. With frequency increasing, lower values of ε′ could be associated with the polarization relaxation process (dipolar relaxation) [37, 39]

Fig. 2

A Scanning electron microscope (SEM) images of: (a) GD nanoparticles with 6% ash content weight; magnification of 10,000. Fractured surface of (b ) uuPLA, (c) upPLA, and (d) PLA-FG; magnification of 1000 × . uuPLA refers to unfilled and unprocessed PLA, upPLA refers to unfilled and processed PLA, and PLA-FG refers to PLA with plasticizer and compatibilizer. B (a) The dielectric constant of GD6-PLA-FG nanocomposites, (b) The dielectric loss of GD6-PLA-FG nanocomposites, (c) The dielectric constant of GD03-PLA-FG nanocomposite, and (d) The dielectric loss of GD03-PLA-FG nanocomposites at a temperature of 298.15 K. uuPLA refers to unfilled and unprocessed PLA, upPLA refers to unfilled and processed PLA, PLA-FG refers to PLA with plasticizer and compatibilizer, GD6 refers to graphite/diamond mixture with 6% ash content weight, GD03 refers to graphite/diamond mixture with 0.3% ash content weight, numbers indicate the weight percentage of the filler (GD6, GD03).[46]. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/4.0/).

Fig. 3

A The composite films with varying amounts of multi-walled carbon nanotubes (MWCNT) were analyzed using a Field Emission Scanning Electron Microscope (FE-SEM) to obtain micrographs. B Additionally, the frequency dependency of the dielectric properties (a) ε′, (b) ε″, and c)tan δ were plotted, and (d) a comparison of these properties as a function of MWCNT nanoparticle loading was made in MWCNT/PLA/PEG nanocomposites. [32]. Copyright: © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)

Fig. 4

Measurement of the temperature effects on the dielectric properties including dispersion (A) and absorption (B), as well as the dielectric absorption at 10 kHz (C) and specific selected temperatures (D) for pure Ecoflex® la yer. [36].Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Biodegradable and renewable eco-friendly polymers have several advantages: light-weighted, excellent mechanical properties, flexibility, good processability, and low dielectric loss [28, 31]. Traditional ceramic materials have advantages such as a high dielectric constant and minimal dielectric loss; however, they often possess poor breakdown strength and flexibility [28]. Along with the benefits of biodegradable polymers, they display low dielectric permittivity at room temperature. Therefore, to achieve the optimum dielectric values of polymer materials, there is a demand for uniform diffusion of a suitable nanofiller in an appropriate low content, known as polymer nanodielectrics (PNDs), so that it does not interfere with PNDs’s technological performance and without agglomeration in the polymer matrix following the intended application [42]. The nanofiller concentration-dependent dielectric permittivity, and sensibly low values of the tailored dielectric BPNCs, indorsed their application as tunable next-generation polymer nanodielectrics, with multifunctional properties, including flexible-type biodegradable microelectronic components, energy-storing capacitors, and various technological and industrial applications [14]. Also, the low dielectric constant and low dielectric loss materials are appropriate for insulator purposes in microelectronic devices [27]

Fig. 5

The electrical conductivity of alginate and bionanocomposites with varying nanoparticle: in-plane (A) and through-plane (B) [66]. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Effect of Nanofiller Loading on BPNCs Electrical Conductivity. C The electrical conductivity of nanocomposites made of PP/PLA40 and MWCNTs tested at various levels of filler content. D The amount of GNPs in GNP/NFC composite paper was varied to measure its electrical conductivity. E The relationship between electrical conductivity and the percentage of filler content, examined in different systems. The inset of the study shows a schematic representation of electric percolation thresholds (EPT) and the values obtained in this research. [71]. Copyrights: © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)

Fig. 6

A Thermal conductivity of biopolymer films made from cassava starch with varying levels of borax addition [90]. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). B Effect of PC/MWCNTs masterbatch content on thermal conductivity of PCL/PBS blends and their respective nanocomposites [91]. Copyright: © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Influence of PC/MWCNTs masterbatch content on the thermal conductivities of the nanocomposites. C Thermal conductivity variations of CNT/PLA, GNP/PLA, and (CNT + GNP 1:1)/PLA composites with varying filler concentrations [71]. Copyright: © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). D TGA thermograms results [109]. Copyright: © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)

Fig. 7

A TGA thermograms of the pure PVA [108]. Copyright Reproduced with permission under the Creative Commons Attribution License. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). B Comparison of TGA thermograms for both pristine PVA film and PVA-ND nanocomposites, with an additional focus on the DTGA curve of PVA-ND/3 nanocomposite (including the original TGA curve) [108]. Copyright Reproduced with permission under the Creative Commons Attribution License. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). C TGA thermograms of the pure PLA and composites [110]. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). D DSC curves of the pure PBS [111]. Copyright: © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)

Fig. 8

A DSC curves of the pure PVA film and the PVA-ND nanocomposites [108]. Copyright Reproduced with permission under the Creative Commons Attribution License. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/4.0/). B DSC curve of A pure PLA filaments and composite filaments with MWCNT, and B composite filaments with PPG as plasticizer [110]. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). C SEM micrographs illustrating the distinctive morphologies of various BBPNCs developed: (a) Surface deposition of Zeolitic imidazolate frameworks (ZIF-8)/chitosan BPNCs as electrospun films on AZ91 magnesium alloy [117]. (b) Nanodiamond/PCL-based BPNCs, and (c): Nanobioglass/PCL-based BPNCs, both prepared via a three-dimensional printing technique, for their application as tissue engineering scaffolds

Fig. 9

Commercial applications of BPNCs in different fields