Thermal Conductivity Of Polymer Composites Research Articles

Microstructure and properties of polymeric composite materials based on polyethylene and thermally extended graphite for transport systems

The effect of thermoexpanded graphite (TEG) on the microstructure and functional properties of polymer composites based on high-density polyethylene (HDPE) has been studied by optical microscopy, differential scanning calorimetry and mechanical analysis. There has been proven the efficiency of the method of mixing polymer composites using a piston extruder, which provides a more uniform distribution of the filler in the polymer matrix. It is shown that the introduction of TEG leads to a decrease in the degree of crystallinity and melting point of systems based on high-density polyethylene, which is a consequence of the destruction or increase in the defect of the crystal structure of the polymer matrix under the influence of TEG. With the introduction of 1 % of TEG, the melting point decreased from 415.0 to 408.5 K. With the introduction of 3 % of TEG, the thermal conductivity increased from 0.18 W/(m·K) (for HDPE) to 0.76 W/(m·K). The extreme change in the thermal conductivity of polymer composites is a consequence of the formation of TEG in the polymer matrix of the percolation cluster, the mesh of the filler, which penetrates the entire volume of the material. As a result of the conductivity studies, the percolation threshold of thermal conductivity has been determined for these HDPE-TEG systems, which is 0.6 %. Microscopic studies confirmed the formation of the percolation cluster obtained by thermal conductivity. It is shown that at the content of 0.6 % of TEG, there is formed a continuous cluster. The formation of this cluster is confirmed by mechanical studies. An increase in mechanical strength has been recorded, which increases from 30.5 MPa (for HDPE) to 42.8 MPa at 5 % filler content, and this is promising for the use of these materials in transport systems.

Fabrication of silver nanoparticles/copper nanoparticles jointly decorated nitride flakes to improve the thermal conductivity of polymer composites

In this research project, the hexagonal boron nitride@(silver/copper) (h-BN@(Ag/Cu)) hybrids are successfully synthesized through a jointly decorated two-step process in this work. First, the copper nanoparticles (CuNPs) are decorated on h-BN flakes by reducing copper ions (Cu2+). Subsequently, h-BN@(Ag/Cu) hybrids are fabricated via silver nanoparticles (AgNPs) deposition on the surface of hexagonal boron nitride@copper (h-BN@Cu) flakes. The obtained h-BN@(Ag/Cu) hybrids serve as loading fillers to substantially boost the thermal conductivity of poly(dimethylsiloxane) (PDMS). The thermal conductivity of as-prepared h-BN@(Ag/Cu)/PDMS composite reaches 1.5645 W m−1 K−1 at 25 vol% filler loading. Furthermore, the electrical properties of these composites are comprehensively investigated. Additionally, the mechanism of h-BN@(Ag/Cu) hybrids for thermal conductivity improvement are demonstrated utilizing Fogg’s model. This work may provide valuable insight and information for the design and construction of high-performance thermally conductive materials in the future.

A review on high thermally conductive polymeric composites

AbstractPolymers are known as thermally insulated materials with reported effective thermal conductivity (Keff) in the range of 0.1 to 0.5 Wm−1 K−1. However, increasing demand for smaller and more powerful electronics has created the need for thermally conductive polymers for use in heat exchangers and electronic packaging applications. Given this background, much research has been done over the past two decades to increase the Keff of polymers. Based on the strategy involved, those works can be divided into two main categories: (i) increasing the Keff of the neat polymer by aligning its chains orientation; and (ii) increasing polymer Keff by fabrication of polymeric composites with thermally conductive filler networks. Among these two strategies, the former is limited to nanoscale laboratory research and is difficult to scale up for mass production. Therefore, this work is mainly focused on the latter category, thermally conductive polymeric composites, which has a higher potential for large‐scale production. This work aims to summarize, evaluate, and highlight the successful strategies of the recent efforts in enhancing the thermal conductivity of polymer composites. The major achievements, future challenges, and the outlooks of high thermally conductive polymeric composites are presented by analyzing the results of about 300 works.

Enhanced thermal conductivity of epoxy composites by constructing thermal conduction networks via adding hybrid alumina filler

AbstractHigh thermal conductivity of polymer composites could be achieved through constructing 3D continuous thermally conductive networks into polymer composites. Herein, we demonstrate a simple, effective method to optimize the segregated alumina networks by using ternary mixture of alumina particles with different diameter ratios (5.8 μm + 2.6 μm + 0.5 μm) at the fixed total content of 60 wt% via conventional melt blending method. The thermal properties of epoxy composites were investigated as a function of the weight fraction and particle size of alumina particles. The thermal conductivity (TC) values of composites with coarse fillers (13.2 μm) are in agreement with Agari model at high filler loading (57 ~ 67 wt%). And the value of C2 was ~0.949 (close to 1), indicating that the formation of heat conduction paths in the composites. The addition of 60 wt% smaller fillers (2.6 μm) facilitates a higher interaction degree between the polymer/fillers, consequently, leads to a higher Tg of 147.8°C. A high TC of 1.109 W m−1 K−1 is achieved as the ratio of alumina filler with different particle sizes is 7/2/1, corresponding to a TC enhancement of 23%–32% compared to the composites with a single particle size filler. A suitable proportion of hybrid fillers is crucial for constructing three‐dimension continuous network, in which nano‐particles filled between the micro‐particles could increase the particle‐to‐particle connectivity.

Significantly enhanced thermal conductivity of polymer composites via establishing double-percolated expanded graphite/multi-layer graphene hybrid filler network

Utilization of hybrid fillers with high thermal conductivity enhancement (TCE) efficiency is an effective method for the large-scale fabrication of polymeric thermal interface materials (TIMs) with exceptional thermal conductivity. Herein, we report the thermally conductive properties of thermoplastic urethane (TPU) composites incorporated with expanded graphite (EG) and multi-layer graphene (MLG). The effect of percolation behavior of EG/MLG hybrid fillers on the thermal conductivity is systematically revealed. It is found that the high-loading TPU composite with 20 wt% EG and 10 wt% MLG reveals an exceptional thermal conductivity of 8.52 Wm−1K−1, which corresponds to a TCE of 3450% compared to that (0.24 Wm−1K−1) of pure TPU matrix. Notably, the TCE per 1 wt% filler reaches a substantial value of 115%. The thermally conductive mechanism is proposed based on morphology and thermal contact resistance analyses. Moreover, the application of such TPU composites in thermal management of light-emitting diode lamps is exhibited, and the effectiveness is further verified through finite element simulation. Our results shed light on the significant thermal synergy between EG and MLG and demonstrate their application potential in high-performance TIMs.

Polyurethane-templated 3D BN network for enhanced thermally conductive property of epoxy composites

Utilizing three-dimensional filler has been deem as a promising approach to improve the thermal conductivity of polymer composites. In this research, we developed a polyurethane sacrificial template technique to fabricate a novel three-dimensional porous carbon bonded BN foam (3D-CBNF), aiming to improve the thermal performance of polymers (epoxy). The as-prepared 3D-CBNF/epoxy composite exhibits a high thermal conductivity (TC) of 2.11 Wm−1K−1 at a relatively low BN loading of 24.7 wt%, corresponding to a TC enhancement (TCE) of 1072% compared with the pure epoxy resin. The analysis of the thermal conductivity mechanism based on EMT and Foygel models and finite element simulation indicated that the high thermal conductivity of composites was due to the efficient heat transfer pathways provided by the 3D interconnected BN network and lower interface thermal resistance in internal of it. In addition, the as-obtained composite possessed a relatively low dielectric constant (below 4.5 at 1 MHz) and a high volume electrical resistivity (beyond 1015 Ω·cm). Overall, a novel and promising method of preparation for 3D construction with thermally conductive filler, which is designed to attain composites with high thermal conductivity, has been proposed in this work.

Effect of carbon fiber inclusions on polymeric transfer film formation on steel

High performance polymers (HPPs) with good tribological properties are commonly used in dry contacts, where their tribological performance often depends on properties of polymeric transfer materials (transfer layers) on counterfaces. Most HPPs suffer from high temperature degradation due to frictional heating, leading to excessive deformation and wear. Incorporating thermally conducting fillers increases their thermal conductivity and mechanical strength. The impact of these fillers on formation and properties of transfer layers, however, is unclear. In this work the effect of short carbon fiber fillers (CFs) on the nature of the transfer layers and tribological performance of polyetheretherketone (PEEK) and polyetheretherketone-polybenzimidizole (PBP) against steel were investigated at temperature up to 300 °C. Transfer layers of CF reinforced PEEK and PBP contain CF-related materials, resulting in a reduction of friction as compared to neat PEEK and PBP, especially around the glass transition temperature of PEEK (Tg−PEEK) when the transfer layer is relatively thick. While the inclusion of CFs increases the bulk thermal conductivity of polymer composites, the average contact temperature is not affected. Rather, local hot spots are generated. As a result, their transfer layers may have formed more readily and have undergone more severe degradation than those from neat polymer. At 300 °C, the PBP + CF transfer layer is thin possibly due to abrasion by CFs dislodged from the matrix. The improvement in the wear resistance due to CF inclusion is observed with PBP up to 300 °C due to its improved mechanical strength. PEEK + CF however suffers higher wear than PEEK below Tg−PEEK. Above Tg−PEEK, a thick transfer layer is formed and the wear of PEEK + CF reduces.

Improved through-plane thermal conductivity of 3D structured composites via BN alignment and AlN surface modification

Efficient heat-flow pathways must be built in order to improve the thermal management performance of materials. In this respect, an effective approach is the fabrication of three-dimensional (3D) network structures to generate thermally conductive polymer composites. Herein, aluminum nitride/boron nitride/epoxy (AlN/BN/EP) composites with a 3D foam structure (3D-AlN/BN/EP) are fabricated to take advantage of the thermal behavior of ammonium bicarbonate and the curing properties of the epoxy resin. The 3D foam-structured composite with a filler loading of 50 wt.% is shown to provide a 657% enhancement in thermal conductivity compared to that of the pure epoxy resin. It is also superior to randomly distributed composite materials. In addition, silane-treated AlN is shown to provide composites with increased thermal conductivity and mechanical strength. Therefore, the process described herein provides an easy way to significantly reinforce the thermal conductivity of polymer composites.

Improved Thermal Conductivity of Polymer Composites by Noncovalent Modification of Boron Nitride via Tannic Acid Chemistry

Improved Thermal Conductivity of Polymer Composites by Noncovalent Modification of Boron Nitride via Tannic Acid Chemistry

Bidirectional Modulation of Contact Thermal Resistance between Boron Nitride Nanotubes from a Polymer Interlayer.

Enhancing the thermal conductivity of polymer composites could improve their performance in applications requiring fast heat dissipation. While significant progress has been made, a long-standing issue is the contact thermal resistance between the nanofillers, which could play a critical role in the composite thermal properties. Through systematic studies of contact thermal resistance between individual boron nitride nanotubes (BNNTs) of different diameters, with and without a poly(vinylpyrrolidone) (PVP) interlayer, we show that the contact thermal resistance between bare BNNTs is largely determined by reflection of ballistic phonons. Interestingly, it is found that a PVP interlayer can either enhance or reduce the contact thermal resistance, as a result of converting the ballistic phonon dominated transport into diffusion through the PVP layer. These results disclose a previously unrecognized physical picture of thermal transport at the contact between BNNTs, which provides insights into the design of high thermal conductivity BNNT-polymer composites.

Synergistic effect of carbon fiber and alumina in improving the thermal conductivity of polydimethylsiloxane composite

The combination of various fillers can improve the thermal conductivity of polymer composites, because an efficient heat conduction network synergistically formed in matrix. The synergistic effect of two fillers, carbon fiber and alumina particle, in polydimethylsiloxane (PDMS) is investigated in this work. A filler combination results in higher thermally conductive composite than any of the single filler. The volume ratio of 4:1 shows the greatest thermal conductivity. The thermal conductivity of PDMS composite filled with 24 vol% carbon fiber and 6 vol% alumina reaches 7.91 W m−1K−1, which was 34% higher than that of 30 vol% CF/PDMS. The combined filler composite also shown better process performance due to the lower viscosity. The synergy is attributed to the optimized heat transfer network and reduced interfacial thermal resistance. Therefore, a combined filler achieved better thermally conductive performance and better process performance with cost-effective source materials.

Carbon nanofillers repair strategy for high-efficiency thermal conductivity enhancement of PBX composites at ultralow mass fraction

Owing to the existence of structural defects of nanofillers and interfacial thermal resistance, realizing high efficiency thermal conductivity (k) enhancement of polymer composites by high k fillers at low mass fraction has proven challenging. Here, aroused by the repair of natural spider web, we reported a novel strategy to mend the structural defects of carbon nanofillers (CNFs) via selective deposited of Ag nanoparticles. The morphology and microstructure of obtained CNFs@Ag were detailed characterized. With a filler loading of 0.5 wt%, a high-efficiency k enhancement had been achieved. The k of PBX composites could reach to 0.722 W/mK, enhanced by 70% compared with pure PBX. Importantly, the temperature gradient and thermal stress distribution in PBX cylinder when facing complicated thermal changes were evaluated by finite element analysis. The study here sheds new light on enhancement of thermal conductivity of polymer composites which severely limits the content of fillers using.

Silver Nanoparticle-Enhanced Three-Dimensional Boron Nitride/Reduced Graphene Oxide Skeletons for Improving Thermal Conductivity of Polymer Composites

Silver Nanoparticle-Enhanced Three-Dimensional Boron Nitride/Reduced Graphene Oxide Skeletons for Improving Thermal Conductivity of Polymer Composites

Thermal synergistic effect in hybrid filler epoxy composites consisting of graphene nanoplatelets and SiC particles

The use of hybrid filler is a promising strategy for development of thermally conductive polymer composites. This paper reported the measurement of thermal conductivity of the epoxy composite filled with a hybrid filler of graphene nanoplatelet (GNP) and silicon carbide (SiC) microparticles. For this hybrid filler, the effect of the average size of SiC on composite thermal conductivity was examined. The results showed that the thermal synergistic effect was highly affected by the average size of the SiC. By using a hybrid filler of 11% vol. GNP and 9% vol. 1 µm-size SiC micro-particles thermal conductivity has reached 3.44 W m−1 K−1. This value is 42% higher than the thermal conductivity of pure GNP composite at the same total filler loading. Moreover, additional experimental and theoretical analyses were performed to more explicitly understand the mechanism of thermal synergistic effect. It was shown that the synergistic effect between GNP and SiC is attributed to the more effective formation of thermally conductive pathways through the composite. Our results elucidate the mechanism of the thermal synergistic effect and providing information on hybrid filler design to achieve further improvement in the thermal conductivity of polymer composites.

Concurrently improving dielectric properties and thermal conductivity of Ni/PVDF composites by constructing NiO shell as an interlayer

Polymer dielectrics with super dielectric constant (e'), low loss as well as high thermal conductivity (TC) are gaining tremendous momentum owing to the ever-increasing demands on microelectronic devices. Introduction core–shell fillers into polymers has been demonstrated as a promising strategy for high-e' but low loss. Herein, nickel (Ni) particles were encapsulated by an insulating layer of NiO with various thicknesses via controlling calcination times at 550 °C under air, and the as-prepared core–shell Ni@NiO was incorporated into poly(vinyli-dene fluoride) (PVDF). The results verify the formation of a NiO shell outside of the Ni, and manifest that the PVDF with Ni@NiO particles exhibit a high e', a signally suppressive loss and conductivity, as well as a high-TC compared with raw Ni. The reason can be ascribed to multiple effects of NiO interlayer including the enhancement of interface compatibility and interface polarizations and the blocking of leakage current. Furthermore, the thickness of NiO shell exerts different influences on long-range and short-range charge migration, and it should be rationally tuned to optimize the dielectric properties and TC. This study provides an effective idea to regulate and control the dielectric properties and TC of polymer composites.

Research progress in manufacturing multifunctional polymer composite materials based on fused deposition modeling technology

3D printing technology, also known as additive manufacturing technology, is based on materials, mechanical control, computer-assisted design and other multi-cross disciplines. 3D printing enables fabrication of complex structure materials which cannot be fabricated by traditional methods. Fused deposition modeling (FDM) is one of the most well-known 3D printing technologies due to its merits like cost-effectiveness, simple in equipment and ease of operation, which has been widely used in aerospace, medical and auto industry. This review introduced the overall layout, development and planning of 3D printing technologies. This review also systematically summarized the characteristics and classifications of common 3D printing technologies, and mainly focused on the principles, advantages and requirements for the FDM technology. Especially, we aim to outline the basic requirements of polymer that suitable for FDM printing and introduce the applications of carbon-based polymer composite materials in the FDM manufacturing process. In addition, recent advances of FDM printing in fabrication of functional polymer composite materials and parts, including biomedical, electrical and thermal conductive polymer composites are reviewed in detail. The prospects for the research and applications of FDM towards manufacturing of high-performance and multifunctional polymer composite materials are proposed. At last, the challenges and key problems that need to be solved in FDM processing are considered and prospected.

Facile fabrication of three-dimensional thermal conductive composites with synergistic effect of multidimensional fillers

Thermal conductive polymer composites are promising in the application of rapidly developing modern technology. Here, a facile method to fabricate three-dimensional thermal conductive composites with multidimensional fillers was reported. One-dimensional AgNW were used to bridge the randomly dispersing two-dimensional BNNS together in poly(dimethylsiloxane) (PDMS) to form thermal conductive networks. The through-plane thermal conductivity (0.64 W m−1 K−1) of composite 2wt%AgNW/20wt%BNNS/PDMS was 237% higher than that of matrix PDMS (0.19 W m−1 K−1), while the composites still maintained good electrically insulating. A series of theoretical models were used to describe the thermal conductivity as a function of BNNS contents with or without the presence of AgNW. The synergistic effect between BNNS and AgNW was verified from the calculation of interfacial thermal resistance, which decreases from 1.06 × 10–6 m2 K W−1 for system without AgNW to 6.14 × 10–9 m2 K W−1 for system with 2 wt% AgNW. This synergistic strategy via multidimensional fillers supported the methodological possibility of returning to simplicity from various template approaches which were limited in shape and size. It was expected to extend the understanding of available theory and predict the potential formation of 3D thermal conductive networks in other systems with multidimensional fillers.

Interface thermal resistance and thermal conductivity of polymer composites at different types, shapes, and sizes of fillers: A review

AbstractThe growing demand toward miniaturization and power device packaging required new die‐attach materials with high thermal conductivity (TC). Multitudinous attention is being paid to enhance the TC of thermally conductive polymer composites as it is easy to fabricate and environmentally friendly and has low‐cost processability. However, after years of extensive research, it can be concluded that reinforcing different morphologies of fillers (types, sizes, and shapes) into polymer composite creates interfacial thermal resistance (ITR) that greatly constrains the TC value. Thus, this article presents an exhaustive review in minimizing the ITR effect by optimizing the types, sizes, and shapes of the fillers used. This literature also seeks to review the use of different morphologies of fillers in single and hybrid polymer composites. It was found that hybridizing two different fillers shows remarkable TC enhancement due to its synergistic effect and formation of three‐dimensional network/conduction path. The size and shape of fillers used play a vital role in improving the TC of the polymer composite compared with the type of filler used due to more contact area created, which significantly reduces the ITR. The results presented here may facilitate improvement in the development of future work for new die attach of the thermally conductive polymer composite.

Isotropic enhancement of the thermal conductivity of polymer composites by dispersion of equiaxed polyhedral boron nitride fillers

Recently, hexagonal boron nitride (h-BN) has attracted attention as a high-thermal-conductivity filler for insulating polymers used in electronic devices. However, since the crystal structure of h-BN is analogous to that of graphite, h-BN exhibits a platelet crystalline shape with the anisotropy of high thermal conductivity for the in-planar direction and an extremely low thermal conductivity for the trans-planar direction. Consequently, the composites dispersed by conventional h-BN platelets indicated considerably low thermal conductivity in the trans-planar direction owing to the orientation of h-BN platelets. In this study, the anisotropic thermal conductivity was improved by dispersion of equiaxed h-BN fillers. Equiaxed h-BN fillers with spherical polyhedron shape were successfully synthesized through liquid-phase crystal growth by heating an h-BN powder with a rare-earth oxide. The common low thermal conductivity observed for the trans-planar direction was improved in the epoxy composites including equiaxed h-BN fillers, which attained 21.4 Wm−1K−1 corresponding to a six-times-higher thermal conductivity than platelet h-BN filler.

A co-training style semi-supervised artificial neural network modeling and its application in thermal conductivity prediction of polymeric composites filled with BN sheets

Predicting the thermal conductivity of polymeric composites filled with BN sheets is helpful for fabricating thermal management material. In this study, a co-training style semi-supervised artificial neural network model (Co-ANN) was proposed to take advantage of unlabeled data to refine the prediction. The thermal conductivity of polymer matrix, the diameter, aspect ratio, and volume fraction of the BN sheets are considered as the input variables of the thermal conduction model. Two artificial neural network (ANN) learners with different architecture will label the unlabeled examples. Through estimating the labeling confidence from the mathematical influence and thermal conductive behavior, the most confidently labeled example will be used to augment the training dataset. The lower limit of the labeling confidence is introduced to reduce the data noise. After learning the augmented training information, a combination of two ANN regressors will construct the final Co-ANN thermal conduction model. Compared to other models, the newly developed Co-ANN thermal conduction model remarkably improves the thermal conductivity prediction and exhibits the best accuracy and generalization performance. The proposed method shows a vast potential in thermal conductive material design.