Conductive Polymer Matrix Composites Research Articles

Reinforcement effects of graphite fluoride on breakdown voltage rating and Pyro-Resistive properties of carbon Black/Poly (vinylidene fluoride) composites

The utilization of conductive polymer-matrix composites (CPCs) with a high concentration of filler as an overcurrent protection device can reduce operational load and improves circuit stability. However, limitations such as reduced positive temperature coefficient (PTC) intensity and inferior voltage breakdown strength hinder its development. To overcome this, the study investigates the integration of graphite fluoride into carbon black (CB)/Poly (vinylidene fluoride) (PVDF) composites. The graphite fluoride-doped CPCs demonstrate outstanding voltage resistance, PTC intensity, and electrical properties, which can be ascribed to the heightened compatibility and adhesion between CB and PVDF, resulting in diminished migration and agglomeration of conductive fillers during current shock and thermal conditions. Graphite fluoride also acts as a shield, counteracting the negative effects of electrical, chemical, and thermal breakdown failures, thus inhibiting PVDF degradation during current impact. Overall, this approach significantly enhances the voltage withstand capability of overcurrent protection devices under current saturation conditions.

Influence of filler type and content on thermal conductivity and mechanical properties of thermoplastic compounds

AbstractCombining thermal conductivity with electrical isolation is a very interesting topic for electronic applications in order to transfer the generated heat. Typical approaches combine thermally conductive fillers with a thermoplastic matrix. The aim of this work was to investigate the influence of different fillers and matrices on the thermal conductivity of the polymer matrix composites. In this study, various inorganic fillers, including aluminum oxide (Al2O3), zinc oxide (ZnO), and boron nitride (BN) with different shapes and sizes, were used in matrix polymers, such as polyamide 6 (PA6), polypropylene (PP), polycarbonate (PC), thermoplastic polyurethane (TPU), and polysulfone (PSU), to produce thermally conductive polymer matrix composites by compounding and injection molding. Using simple mathematical models (e.g., Agari model, Lewis–Nielson model), a first attempt was made to predict thermal conductivity from constituent properties. The materials were characterized by tensile testing, density measurement, and thermal conductivity measurement. Contact angle measurements and the calculated surface energy can be used to evaluate the wetting behavior, which correlates directly with the elastic modulus. Based on the aforementioned evaluations, we found that besides the volume fraction, the particle shape in combination with the intrinsic thermal conductivity of the filler has the greatest influence on the thermal conductivity of the composite.

Progress of Polymer-Based Thermally Conductive Materials by Fused Filament Fabrication: A Comprehensive Review.

With the miniaturization and integration of electronic products, the heat dissipation efficiency of electronic equipment needs to be further improved. Notably, polymer materials are a choice for electronic equipment matrices because of their advantages of low cost and wide application availability. However, the thermal conductivity of polymers is insufficient to meet heat dissipation requirements, and their improvements remain challenging. For decades, as an efficient manufacturing technology, additive manufacturing has gradually attracted public attention, and researchers have also used this technology to produce new thermally conductive polymer materials. Here, we review the recent research progress of different 3D printing technologies in heat conduction and the thermal conduction mechanism of polymer matrix composites. Based on the classification of fillers, the research progress of thermally conductive materials prepared by fused filament fabrication (FFF) is discussed. It analyzes the internal relationship between FFF process parameters and the thermal conductivity of polymer matrix composites. Finally, this study summarizes the application and future development direction of thermally conductive composites by FFF.

Wearable Conductive Polymer Matrix Composites for Breath Monitoring with Ammonia Detection

Conductive polymers, such as polyaniline (PANI), Polythiophene (PTh), polypyrrole (PPy), etc., are widely used for gas sensors due to their excellent electrical conductivity and low cost to manufacture [1]. In particular, PANI has attracted more attention due to its ease of synthesis, high environmental stability, and high reactivity with ammonia gas. In addition, the selection of acid-base dopant during the preparation process of polyaniline can adjust carrier concentrations for the change in electrical conduction or resistance to improve sensing properties. There have been many reports on the fabrication of flexible gas sensors using PANI [2-4]. Bandgar et al. [5] synthesized a low-temperature flexible polyaniline gas sensor by in-situ chemical oxidation polymerization of aniline on a polyethylene terephthalate (PET) substrate, showing 99% reproducibility, rapid response and recovery. Still, the response value was only 26% in 100 ppm ammonia atmosphere. Qi et al. [6] prepared a gas sensor by in-situ polymerization of aniline on non-woven fabric. The high air permeability of the fabric effectively improved the performance of the polyaniline-based gas sensor. Due to the outbreak of the COVID-19 pandemic, the use of face masks in public has become essential to reduce the spread of the virus. Some reports claim that the increased carbon dioxide in the mask over time may cause medical issues related to the respiratory system. Therefore, monitoring breathing air quality can help detect the wearer's vital conditions.In this study, we used a disposable mask as a flexible substrate to prepare polypropylene/carbon nanotube/polyaniline composite film through a layer-by-layer method. The polypropylene/carbon nanotube composite films were prepared by applying the carbon nanotube aqueous solution with surfactants evenly on the surface of a mask filter layer by a drop-coating method. Then, the in-situ polyaniline polymerization was performed on the surface of the polypropylene/carbon nanotube composite film through ammonium sulfate. The polypropylene/carbon nanotube /polyaniline composite film exhibits high sensitivity, fast sensing response/recovery time, room temperature operation, reliable flexibility, and cycle stability. The synthesized and wearable masks have demonstrated real-time detection respiratory rate and other breathing conditions such as CO2 and humidity. The ammonia gas sensing can also be used as a potential biomarker for health screening. The design and integration of multiple gas sensing materials in masks will help wearers better understand their own body conditions.

Research Progress in Thermal Conductivity of Polymer Matrix Composites

The heat dissipation of electronic components is of great importance to the development of microelectronics industry. Polymer matrix composites have become a research hotspot due to their advantages in molding, insulation and cost. In this paper, the mechanism and influencing factors of thermal conductivity of polymer matrix composites are introduced, the research status of thermal network formation is reviewed, and the development trend of thermal conductivity composites is forecasted.

Improving the thermal conductivity of epoxy composites using a combustion-synthesized aggregated \u03b2-Si3N4 filler with randomly oriented grains

Electrically insulating and thermally conductive polymer matrix composites are desirable for industry applications as they improve the reliability of high-performance electronic devices, particularly via heat dissipation in devices loaded with several electronic components. In this study, an aggregated β-Si3N4 filler with randomly oriented grains was produced via combustion synthesis to improve the thermal conductivity of epoxy composites. The thermal conductivities of the prepared composites were investigated as a function of the filler content, and the values were compared to those of composites loaded with commercial β-Si3N4 (non-aggregated). Negligible difference was observed in the thermal conductivities of both types of composites when the Si3N4 content was below 40 vol%; however, above 40 vol%, the aggregated β-Si3N4 filler-loaded composites showed higher thermal conductivities than the commercial β-Si3N4-loaded composites. The aggregated β-Si3N4 filler-loaded composites exhibited isotropic thermal conductivities with a maximum value of 4.7 W m−1 K−1 at 53 vol% filler content, which is approximately 2.4 times higher than that of the commercial β-Si3N4-loaded composites, thereby suggesting that the morphology of the aggregated filler would be more efficient than that of the commonly used non-aggregated filler in enhancing the thermal conductivity of a polymer matrix composite.

Synergistic Effects of Hybrid Carbonaceous Fillers of Carbon Fibers and Reduced Graphene Oxides on Enhanced Heat-Dissipation Capability of Polymer Composites.

In this study, we investigated the synergistic effects of thermally conductive hybrid carbonaceous fillers of mesophase pitch-based carbon fibers (MPCFs) and reduced graphene oxides (rGOs) on the thermal conductivity of polymer matrix composites. Micro-sized MPCFs with different lengths (50 μm, 200 μm, and 6 mm) and nano-sized rGOs were used as the thermally conductive fillers used for the preparation of the heat-dissipation polymer composites. For all MPCF fillers with a different length, the thermal conductivity values of the MPCF/epoxy composites were proportional to the MPCF length and loading amount (0–50 wt%) of MPCFs. For an MPCF:rGO weight ratio of 49:1 (total loading amount of 50 wt%), the thermal conductivity values of MPCF-rGO/epoxy composites loaded with MPCFs of 50 μm, 200 μm, and 6 mm increased from 5.56 to 7.98 W/mK (approximately 44% increase), from 7.36 to 9.80 W/mK (approximately 33% increase), and from 11.53 to 12.58 W/mK (approximately 9% increase) compared to the MPCF/epoxy composites, respectively, indicating the synergistic effect on the thermal conductivity enhancement. The rGOs in the MPCF-rGO/epoxy composites acted as thermal bridges between neighboring MPCFs, resulting in the formation of effective heat transfer pathways. In contrast, the MPCF-rGO/epoxy composites with MPCF:rGO weight ratios of 48:2 and 47:3 decreased the synergistic effect more significantly compared to rGO content of 1 wt%, which is associated with the agglomeration of rGO nanoparticles. The synergistic effect was inversely proportional to the MPCF length. A theoretical approach, the modified Mori-Tanaka model, was used to estimate the thermal conductivity values of the MPCF-rGO/epoxy composites, which were in agreement with the experimentally measured values for MPCF-rGO/epoxy composites loaded with short MPCF lengths of 50 and 200 μm.

Nanoscale thermal transport in epoxy matrix composite materials reinforced with carbon nanotubes and graphene nanoplatelets

The technology related to hybrid filler-reinforced polymer matrix composite materials is growing at a high rate with increasing interest and usage. This study presents a way of increasing the thermal conductivity of polymer matrix composites by the use of a hybrid filler consisting of carbon nanotubes and graphene nanoplatelets and preliminarily clarifies the mechanisms that lead to the synergistic reinforcement of composite thermal conductivity at the nanoscale. The focus of this study was upon the fundamental relationships between nanometer-scale reinforcement structures and macroscopic composite thermal properties. The benefits and limitations associated with the incorporation of the hybrid filler into an epoxy matrix were evaluated. The results indicated that there exists an evident synergistic reinforcing effect between carbon nanotubes and graphene nanoplatelets on composite thermal conductivity. A significant increase has been gained in composite thermal conductivity, but low loading is required in order to exploit the benefits derived from the unique structure of the hybrid filler. Filler loading must be controlled very accurately in order to ensure that a critical threshold is not reached, beyond which there is a decrease in thermal conductivity, compared to that of graphene nanoplatelet-reinforced composites. The synergistic reinforcing benefits to composite thermal conductivity and is derived from effective conducting pathways formed between carbon nanotubes and graphene nanoplatelets within polymer matrices. The results can offer practical guidance on how to improve thermal transport properties for polymer matrix composite materials.

Effect of various carbon nanofillers and different filler aspect ratios on the thermal conductivity of epoxy matrix nanocomposites

The effectiveness of carbon nanofillers in improving the thermal conductivity of polymer matrix composites has been extensively studied. However, the mechanisms that lead to the effective reinforcement of composite thermal conductivity at the nanoscale remain unclear, and the significant role of filler aspect ratio in determining composite thermal properties needs to be further clarified for various carbon nanofillers. The primary focus of this study was on understanding how important this factor is in determining the thermal properties of polymer matrix composites. The effect of various carbon nanofillers on the thermal conductivity of epoxy matrix composites was studied with special emphasis on the relationship between filler aspect ratio and composite thermal properties. The effect of filler loading on composite thermal conductivity was investigated, and the role of temperature in thermal conductivity improvement was also evaluated. The results indicated that the aspect ratio of carbon nanofillers is of great significance for improving their reinforcing effect on the thermal performance of polymer matrix composite materials. Graphene in any form can improve composite thermal conductivity more effectively than carbon nanotubes and conventional carbon-based nanofillers. A seven-fold increase in composite thermal conductivity has been achieved by incorporating 6% graphene oxide by weight into the polymer matrix. The resultant polymer nanocomposites may be more attractive at elevated temperatures for applications in thermal management, if their thermal stability problems can be effectively addressed.

Development of additively manufacturable and electrically conductive graphite–polymer composites

The selectivity between electrically conductive and insulating regions within one additively manufactured part can open new domains for customized, smart, and active products. In this article, new electrically conductive polymer matrix composites (ePMC) were developed for additive manufacturing (AM) by loading an aqueous matrix of carboxymethyl cellulose with micro-sized graphite particles. Electrically conductive AM can be achieved using the developed ePMC with the direct ink writing (DIW) technique. The effects of graphite loading on the properties of ePMCs and their suitability for AM were investigated using various characterization techniques. The non-Newtonian shear-thinning behavior of the ePMC inks indicates the suitability of these inks for DIW. Tunable electrical conductivity in the range of 87–128 S m−1 can be achieved with a 15% margin of error. DIW of scaffolds with rectilinear and honeycomb infill patterns demonstrate the additive manufacturability of the developed ePMCs. Furthermore, an application of additively manufactured and electrically conductive part as a heating element was demonstrated. The developed ePMCs can be employed in diverse applications such as AM of conductive tracks, resistors, and electrodes for capacitors and energy storage devices.

Three-dimensional carbon fiber-graphene network for improved thermal conductive properties of polyamide-imide composites

Thermal conductive polymer matrix composites are becoming more widely used in modern electronic devices. However, the dispersion of the filler in the composite material limits the improvement of its heat dissipation performance. In order to solve the problem, we prepared polyamide-imide composites with three-dimensional (3D) carbon fiber-graphene network. The network is built by braided frame of carbon fiber felt and the hydrogen bonding between carbon fiber and graphene oxide. When the amount of filler is 4.25 wt%, the vertical thermal conductivity (TC) of composites reaches 0.53 W m−1 K−1, which is 165% higher than that of pure PAI. The improvement of TC is mainly attributed to the following factors, for example, 1) the 3D carbon fiber-graphene network structure was established to construct the heat conduction path in the composite material; 2) the interaction between fillers reduced contact thermal resistance; 3) the introduction of oxygen-containing functional groups adversely affected the TC of the composite. Meanwhile, the tensile strength of the composites reaches 34.1 MPa and the Young's modulus is 1.2 GPa. The composites can be used as a heat sink for next-generation electronic devices.

Thermally conductive polybutylene terephthalate/hexagonal boron nitride composites with bimodal filler size distribution

Thermally conductive polymer matrix composites (PMC) are promising alternatives to traditional electronic packaging materials to enhance the heat dissipation of integrated circuits, due to polymer's superior electrical insulating property, low cost, and light weight. This work aims to investigate the potentials of using synergy effects of hexagonal boron nitride (hBN) platelets and spherical hBN particulates or those of hBN platlets with bimodal size distribution to promote PMC's effective thermal conductivity (keff). PMC consists of polybutylene terephthalate (PBT) and hBNs with different geometries and size distributions were used as case examples. Experimental results reveal that PMC filled with solely hBN spherical agglomerates of fine diameters possess the highest keff, owing to its isotropic thermal conductivity and compact filler-filler interaction. Moreover, two-dimensional hBN platelets, which have anisotropic thermal conductivity, of bimodal size distribution show synergistic effect on PMC's keff. To maximize PMC's keff with a minimum filler loading, an optimal mixture of hBN platelets with bimodal size distribution would help to overcome the trade-off between enhanced filler networking and increased thermal contact resistance at the filler-filler interfaces. The findings in this study provide some insights to design and fabricate thermally conductive PMC with reduced filler loading for thermal management applications.

Anisotropy of thermal conductivity in 3D printed polymer matrix composites for space based cube satellites

Polymer extrusion three dimensional (3D) printing, such as fused deposition modeling (FDM), has recently garnered attention due to its inherent process flexibility and rapid prototyping capability. Specifically, the addition of electrical components and interconnects into a 3D printing build sequence has received heavy interest for space applications. However, the addition of these components, along with the thermal load associated with space-based applications, may prove problematic for typical thermally insulating 3D printed polymer structures. The work presented here addresses thermally conductive polymer matrix composites (specifically, graphite, carbon fiber, and silver in an acrylonitrile butadiene styrene polymer matrix) to identify the effect of composite geometry and print direction on thermal anisotropic properties. The work also examines the effect of these composites on print quality, mechanical tensile properties, fracture plane analysis, micrograph imaging, and cube satellite thermal analysis. The thermal conductivity of 3D printed material systems in this work may enable the production of thermally stable 3D printed structures, supports, and devices. Key results of this work include anisotropic thermal conductivity for 3D printed structures related to print direction and filler morphology meaning that thermal conductivity can be controlled through a combination of print raster direction and material design. When the materials analyzed in this work are incorporated with other active cooling systems, space-based 3D printed applications can then be designed to incorporate increasing thermal loads, opening a new door to producing space-ready 3D printed structures.

Development of thermally conductive polymer matrix composites by foaming‐assisted networking of micron‐ and submicron‐scale hexagonal boron nitride

ABSTRACTThermally conductive polymer matrix composite (PMC) foams with effective thermal conductivities (keff) higher than their solid counterparts have been developed for the first time. Using a material system consists of low density polyethylene and micron‐scale or submicron‐scale hexagon boron nitride platelets as a case example, this article demonstrates that foaming‐assisted filler networking is a feasible processing strategy to enhance PMC's keff, especially at a low hBN loading. Parametric studies were conducted to identify the structure‐to‐property relationships between foam morphology (e.g., cell population density, cell size, and foam expansion) and the PMC foam's keff. In particular, there exists an optimal cell size to maximize the PMC foam's keff for foams with up to 50% volume expansion. However, an optimal cell size is absent for PMC foams with higher volume expansion. X‐ray diffraction (XRD) analyses reveal that both the presence of hBN platelets and foam expansion promoted the crystallization of LDPE phase. Moreover, the XRD spectra also provide evidence for the effect of foam expansion on the orientation of hBN platelets. Overall, the findings provide new directions to design and fabricate thermally conductive PMC foams with low filler contents for heat management applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42910.

A Comprehensive Study of Transistors Based on Conductive Polymer Matrix Composites

A comprehensive study is conducted on the electron transport in conductive polymer matrix composites (CPMCs), employing the nonequilibrium Green's function formalism. This paper provides a microscopic insight into the electron tunneling through the potential barriers existing between conducting sites. It is shown that Wentzel-Kramers-Brillouin approximation as well as other models with simple barrier shapes, which are widely used in literature, can lead to inaccurate results in comparison with the quantum mechanical approach using a hyperbolic barrier. In this paper, unlike most previous ones, percolation-related effects are disregarded for further focus on electron transport through the polymer potential barriers. It is assumed that a tunneling-conductive channel exists between the electrodes. This can be created either by applying electric field alignment or using a filler volume fraction higher than the percolation threshold. A two electrode resistive device is studied and the results indicate that a conductor-insulator transition occurs at a barrier thickness of ~1.7 nm and the barrier thickness should be larger than several angstroms. Next, a novel tunneling field-effect structure based on CPMCs is introduced and its characteristics are comprehensively investigated. This device features a remarkably simple structure, an extremely high channel to gate coupling, a large transconductance, and a high current level. Besides, it has the advantage of being based on polymers. This ensures favorable physical properties, ease of fabrication, and low-cost processing techniques.

Prediction and experimental validation of electrical percolation by applying a modified micromechanics model considering multiple heterogeneous inclusions

Classical micromechanics modeling cannot capture the effect of percolation threshold at a low volume fraction of conductive fillers, even though multiple heterogeneities are considered in the modeling to investigate the effect of reinforcement dispersion, electrical tunneling behavior, and conductive networks. In this study, an analytical homogenization approach for composites containing multiple heterogeneities with conductive coated layers was developed in order to predict the percolation threshold effect, the tunneling effect using hard/soft core concept, and the effective electrical conductivity of polymer matrix composites (PMCs) containing randomly oriented ellipsoidal inclusions coated by conductive layers. The electrical conductivities of polymerized cyclic butylene terephthalate (pCBT)-based composites containing nanofillers such as carbon blacks (CBs), graphene nanoplatelets (GNPs), and carbon nanotubes (CNTs) were prepared by the recently developed composite manufacturing processing using solvent-free powder mixing and in-situ polymerization for inducing uniform dispersion of nanofillers of various shapes and dimensions within a polymer matrix. When comparing the experimentally measured electrical conductivities of those composites with the predicted values obtained from the developed micromechanics models, it is confirmed that the developed approach successfully captures the percolation threshold and the tunneling effect of reinforcements on the effective electrical conductivities of composites containing various shapes of reinforcements.

A three-dimensional Monte Carlo model for electrically conductive polymer matrix composites filled with curved fibers

A three-dimensional (3-D) Monte Carlo model is developed for predicting electrical conductivity of polymer matrix composites filled with conductive curved fibers. The conductive fillers are modeled as a 3-D network of finite sites that are randomly positioned. The percolation behavior of the network is studied using the Monte Carlo method, which leads to the determination of the critical fiber volume fraction (or the percolation threshold). The effect of fiber curliness on the percolation behavior is incorporated in the current model by using 3-D arm-shaped fibers, each of which needs five independent geometrical parameters (i.e., three coordinates for its vertex and two orientation angles) for its identification. There are three controlling parameters for such fibers, namely the fiber arm length, the fiber aspect ratio, and the fiber arm angle. The new model also considers the sample size and scaling effects. The simulation results reveal an exponential relationship between the fiber aspect ratio and the percolation threshold: the higher the aspect ratio, the lower the threshold. It is also found that the curliness largely influences the percolation threshold: the more curved the fiber, the higher the threshold. However, the effect of curliness diminishes with the increase of the fiber aspect ratio. With the percolation threshold obtained from the Monte Carlo model, the effective electrical conductivity of the composite is then determined by applying the theory of percolation. The numerical results indicate that the composite conductivity decreases as the fibers become more curved and as the fiber aspect ratio decreases. These predicted trends of the percolation threshold and composite conductivity are in good agreement with existing experimental and simulation results.