Exploring the Effects of Nano-CaCO3 on the Core-Shell Structure and Properties of HDPE/POE/Nano-CaCO3 Ternary Nanocomposites

To address the dilemma of the stiffness and toughness properties of high-density polyethylene (HDPE) composites, titanate coupling agent-treated CaCO3 nanoparticles (nano-CaCO3) and ethylene-octene copolymer (POE) were utilized to blend with HDPE to prepare ternary nanocomposites via a two-sequence-step process. Meanwhile, a one-step process was also studied as a control. The obtained ternary nanocomposites were characterized by scanning electron microscopy (SEM), Advanced Rheometrics Expansion System (ARES), Dynamic Mechanical Analysis (DMA), wide-angle X-ray diffraction analysis (WXRD), and mechanical test. The SEM results showed one or two CaCO3 nanoparticles were well-encapsulated by POE and were uniformly dispersed into the HDPE matrix to form a core-shell structure of 100-200 nm in size by the two-step process, while CaCO3 nanoparticles were aggregated in the HDPE matrix by the one-step method. The result of the XRD showed that the nano-CaCO3 particle played a role in promoting crystallization in HDPE nanocomposites. Mechanical tests showed that the synergistic effect of both the POE elastomer and CaCO3 nanoparticles should account for the balanced performance of the ternary composites. In comparison with neat HDPE, the notched impact toughness of the ternary nanocomposites of HDPE/POE/nano-CaCO3 was significantly increased. In addition, the core-shell structure absorbed the fracture impact energy and prevent further propagation of micro-cracks, thus obtaining a higher notched Izod impact strength.

In Situ Filler Addition for Homogeneous Dispersion of Carbon Nanotubes in Multi Jet Fusion-Printed Elastomer Composites

The dispersibility of fillers determines their effect on the mechanical properties and anisotropy of the 3D-printed polymeric composites. Nanoscale fillers have the tendency to aggregate, resulting in the deterioration of part performance. An in situ filler addition method using the newly developed dual-functional toughness agents (TAs) is proposed in this work for the homogeneous dispersion of carbon nanotubes (CNTs) in elastomer composites printed via multi jet fusion. The CNTs added in the TAs serve as an infrared absorbing colorant for selective powder fusion, as well as the strengthening and toughening fillers. The printability of the TA is theoretically deduced based on the measured physical properties, which are subsequently verified experimentally. The printing parameters and agent formulation are optimized to maximize the mechanical performance of the printed parts. The printed elastomer parts show significant improvement in strength and toughness for all printing orientations and alleviation of the mechanical anisotropy originating from the layer-wise fabrication manner. This in situ filler addition method using tailorable TAs is applicable for fabricating parts with site-specific mechanical properties and is promising in assisting the scalable manufacturing of 3D-printed elastomers.

Enhanced Electrical and Thermal Conductivities of Polymer Composites with a Segregated Network of Graphene Nanoplatelets

Introducing a segregated network constructed through the selective localization of small amounts of fillers can be a solution to overcome the limitations of the practical use of graphene-based conductive composites due to the high cost of fillers. In this study, polypropylene composites filled with randomly dispersed GNPs and a segregated GNP network were prepared, and their conductive properties were investigated according to the formation of the segregated structure. Due to the GNP clusters induced by the segregated structure, the electrical percolation threshold was 2.9 wt% lower than that of the composite incorporating randomly dispersed GNPs. The fully interconnected GNP cluster network inside the composite contributed to achieving the thermal conductivity of 4.05 W/m∙K at 10 wt% filler content. Therefore, the introduction of a segregated filler network was suitable to simultaneously achieve excellent electrical and thermal conductivities at a low content of GNPs.

Enhanced Mechanical Property of Polyamide-6/Graphite Sheet Composites with Segregated 3D Network Binary Structure for High Thermal Conductivity

Segregated conductive polymer composites exhibit excellent electrical properties with a low percolation threshold. However, the mechanical properties of the segregated conductive polymer composites were always poor because the conductive fillers at the interfaces hinder polymer chain diffusion and thus lead to weak interfacial interaction between the conductive fillers and the polymer matrix. In this paper, polyamide-6 and polyamide-612 microspheres were synthesized via the in situ anionic ring opening of caprolactam and laurolactam. Segregated graphite sheets/polyamide-6(GS/PA6) and polyamide-612(PA612) composites with good mechanical properties were realized via high-pressure solid-phase compression molding. The microstructures of the composite samples were observed by scanning electron microscopy, which showed that the formation of a GS-conductive network at the PA6 granule interfaces in the segregated conductive structures and the adopting of PA612 considerably improved the interfacial adhesion of the composites. A superior impact strength of 5.1 kJ/m² was achieved with 50 wt% PA612 loading owing to improvements in the interface compatibility between PA6 and GS. The composites possessed an ultralow percolation threshold, which was ascribed to the segregated network structure being successfully constructed inside the material. As for GS/PA6 composites, the combination of segregated GS-conductive networks achieved an ultralow percolation of 2.8 vol%. The percolation of 80PA6/20PA612-GS composites was slightly higher, measuring up to 3.2 vol%. Moreover, the thermal conductivity of the 80PA6/20PA612-GS composites increased from 0.26 to around 0.5 W/(m·K), which was 1.9 times larger than the pure polyamide.

High-Temperature Response Polylactic Acid Composites by Tuning Double-Percolated Structures

Due to the properties of a positive temperature coefficient (PTC) effect and a negative temperature coefficient (NTC) effect, electrically conductive polymer composites (CPCs) have been widely used in polymer thermistors. A dual percolated conductive microstructure was prepared by introducing the polybutylene adipate terephthalate phase (PBAT) into graphene nanoplatelets (GNPs)-filled polylactic acid (PLA) composites, intending to develop a favorable and stable PTC material. To achieve this strategy, GNPs were selectively distributed in the PBAT phase by injection molding. In this study, we investigated the crystallization behavior, electrical conductivity, and temperature response of GNP-filled PLA/PBAT composites. The introduction of GNPs into PLA significantly increased PLA crystallization capacity, where the crystallization onset temperature (T_o) is raised from 116.7 °C to 134.7 °C, and the crystallization half-time (t_1/2) decreases from 35.8 min to 27.3 min. The addition of 5 wt% PBAT increases the electrical conductivity of PLA/PBAT/GNPs composites by almost two orders of magnitude when compared to PLA/GNPs counterparts. The temperature of the heat treatment is also found to play a role in affecting the electrical conductivity of PLA-based composites. Increasing crystallinity is favorable for increasing electrical conductivity. PLA/PBAT/GNPs composites also show a significant positive temperature coefficient, which is reflected in the temperature-electrical resistance cycling tests.

Flexible Perfluoropolyethers-Functionalized CNTs-Based UHMWPE Composites: A Study on Hydrogen Evolution, Conductivity and Thermal Stability

Flexible conductive composites based on ultra-high molecular weight polyethylene (UHMWPE) filled with multi-walled carbon nanotubes (CNTs) modified by perfluoropolyethers (PFPEs) were produced. The bonding of PFPE chains, added in 1:1 and 2:1 weight ratios, on CNTs influences the dispersion of nanotubes in the UHMWPE matrix due to the non-polar nature of the polymer, facilitating the formation of nanofillers-rich conductive pathways and improving composites' electrical conductivity (two to five orders of magnitude more) in comparison to UHMWPE-based nanocomposites obtained with pristine CNTs. Electrochemical atomic force microscopy (EC-AFM) was used to evaluate the morphological changes during cyclic voltammetry (CV). The decrease of the overpotential for hydrogen oxidation peaks in samples containing PFPE-functionalized CNTs and hydrogen production (approximately -1.0 V vs. SHE) suggests that these samples could find application in fuel cell technology as well as in hydrogen storage devices. Carbon black-containing composites were prepared for comparative study with CNTs containing nanocomposites.

Endowing Acceptable Mechanical Properties of Segregated Conductive Polymer Composites with Enhanced Filler-Matrix Interfacial Interactions by Incorporating High Specific Surface Area Nanosized Carbon Black

Tuning the high properties of segregated conductive polymer materials (CPCs) by incorporating nanoscale carbon fillers has drawn increasing attention in the industry and academy fields, although weak interfacial interaction of matrix-filler is a daunting challenge for high-loading CPCs. Herein, we present a facile and efficient strategy for preparing the segregated conducting ultra-high molecular weight polyethylene (UHMWPE)-based composites with acceptable mechanical properties. The interfacial interactions, mechanical properties, electrical properties and electromagnetic interference (EMI) shielding effectiveness (SE) of the UHMWPE/conducting carbon black (CCB) composites were investigated. The morphological and Raman mapping results showed that UHMWPE/high specific surface area CCB (h-CCB) composites demonstrate an obviously interfacial transition layer and strongly interfacial adhesion, as compared to UHMWPE/low specific surface area CCB (l-CCB) composites. Consequently, the high-loading UHMWPE/h-CCB composite (beyond 10 wt% CCB dosage) exhibits higher strength and elongation at break than the UHMWPE/l-CCB composite. Moreover, due to the formation of a densely stacked h-CCB network under the enhanced filler-matrix interfacial interactions, UHMWPE/h-CCB composite possesses a higher EMI SE than those of UHMWPE/l-CCB composites. The electrical conductivity and EMI SE value of the UHMWPE/h-CCB composite increase sharply with the increasing content of h-CCB. The EMI SE of UHMWPE/h-CCB composite with 10 wt% h-CCB is 22.3 dB at X-band, as four times that of the UHMWPE/l-CCB composite with same l-CCB dosage (5.6 dB). This work will help to manufacture a low-cost and high-performance EMI shielding material for modern electronic systems.

Waste to Value-Added Product: Developing Electrically Conductive Nanocomposites Using a Non-Recyclable Plastic Waste Containing Vulcanized Rubber

This study intends to show the potential application of a non-recyclable plastic waste towards the development of electrically conductive nanocomposites. Herein, the conductive nanofiller and binding matrix are carbon nanotubes (CNT) and polystyrene (PS), respectively, and the waste material is a plastic foam consisting of mainly vulcanized nitrile butadiene rubber and polyvinyl chloride (PVC). Two nanocomposite systems, i.e., PS/Waste/CNT and PS/CNT, with different compositions were melt-blended in a mixer and characterized for electrical properties. Higher electrical conduction and improved electromagnetic interference shielding performance in PS/Waste/CNT system indicated better conductive network of CNTs. For instance, at 1.0 wt.% CNT loading, the PS/Waste/CNT nanocomposites with the plastic waste content of 30 and 50 wt.% conducted electricity 3 and 4 orders of magnitude higher than the PS/CNT nanocomposite, respectively. More importantly, incorporation of the plastic waste (50 wt.%) reduced the electrical percolation threshold by 30% in comparison with the PS/CNT nanocomposite. The enhanced network of CNTs in PS/Waste/CNT samples was attributed to double percolation morphology, evidenced by optical images and rheological tests, caused by the excluded volume effect of the plastic waste. Indeed, due to its high content of vulcanized rubber, the plastic waste did not melt during the blending process. As a result, CNTs concentrated in the PS phase, forming a denser interconnected network in PS/Waste/CNT samples.

Engineering Segregated Structures in a Cross-Linked Elastomeric Network Enabled by Dynamic Cross-Link Reshuffling

Construction of segregated structures in polymer composites is an efficient way to improve the electrical conductivity and reduce the percolation threshold by confining conductive fillers into the interstitial areas between polymer domains. Yet, it remains a great challenge to engineer segregated structures into thermosets as the cross-linked structure prohibits the "sintering" of polymer domains into a coherent material. Thus far, the state of art approaches to create segregated network in cross-linked polymers involve tedious procedures and are limited to latex mixing technology. Here, inspired by solid state plasticity of vitrimers, we present a simple method to create segregated structures in covalently cross-linked networks by compression molding of conductive filler-coated vitrimer granules. Specifically, dynamic boronic ester-cross-linked styrene-butadiene rubber vitrimers was ground into granules and then mechanically mixed with carbon nanotubes (CNTs) to coat CNTs onto vitrimer granules, followed by hot-press molding. During the molding process, the transesterifications of boronic esters enable cross-linked granules to adhere together through molecular bonding, and the high viscosity of granules forces CNTs to selectively localize at their boundary region. As a result, coherently segregated composites with an ultralow percolation threshold, good flexibility, and healing capability are obtained. With this example, we envisage that this work provides a conceptual method to create segregated structures in cross-linked polymers.

Construction of low melting point alloy/graphene three-dimensional continuous thermal conductive pathway for improving in-plane and through-plane thermal conductivity of poly(vinylidene fluoride) composites

As the temperature of hot spots increases in electronic devices, thermal management is a key issue for maintaining a device's reliability and performance. The usual approaches of quickly extracting the heat from the hot spots have focused on aligning two-dimensional filler along the in-plane orientation in the polymer matrix. Meanwhile, improving the through-plane thermal conductivity of polymer-based composites is as important as in-plane thermal conductivity. In this study, poly(vinylidene fluoride) composites with three-dimensional continuous thermal conductive pathways of a low melting point alloy (LMPA)/graphene were prepared through a two-step method. Poly(vinylidene fluoride)@graphene (PVDF@Gr) microspheres were firstly prepared by an in-situ water-vapor induced phase separation method. Subsequently, PVDF@Gr/LMPA composites were obtained by hot-pressing after mixing the LMPA with the PVDF@Gr microspheres. Attributed to the unique solid-liquid phase transition advantage of the LMPA and the good matching of the phonon power spectrum between the LMPA and the graphene, the PVDF@4.8Gr/10LMPA composites with 4.8 vol% graphene and 10.0 vol% LMPA exhibited an outstanding in-plane thermal conductivity of 9.41 W m^-1 K^-1 and through-plane thermal conductivity of 0.35 W m^-1 K^-1, which was nearly increased by 245% and 130% compared to that of the PVDF@4.8Gr composites, respectively. The enhanced elasticity modulus and reduced thermal expansion coefficient were attributed to the LMPA constructing a three-dimensional continuous thermal conductive pathway along with the graphene and reducing interface thermal resistance. This study offeres a straightforward and repeatable method for fabricating highly thermally conductive polymer composites and widens the application of LMPAs in the fields of thermal management.

An Effective Design Strategy for the Sandwich Structure of PVDF/GNP-Ni-CNT Composites with Remarkable Electromagnetic Interference Shielding Effectiveness

It is well-known that attractive electromagnetic interference (EMI) shielding performance depends on functional (e.g., electrical and magnetic) fillers and structural designs. This paper presents a novel three-layered sandwich structure of poly(vinylidene fluoride) (PVDF)-based nanocomposites, consisting of graphene nanoplatelets (GNP), nickel (Ni), and carbon nanotubes (CNT). The unique three-layered sandwich structure of GNP-Ni-CNT exhibited excellent EMI shielding ability due to the several interfaces of the multilayered structure with electric loss by the conductive fillers and magnetic loss by the magnetic filler. The overall shielding performance could be further improved by increasing the overall thickness and the number of layers. With a fixed thickness of 0.6 mm, the shielding effectiveness of the PVDF/GNP-Ni-CNT three-layered and six-layered structure composite at 15 GHz was 41.8 and 46.4 dB, respectively. These results provide a useful strategy to prepare various EMI shielding materials with a sandwich structure, presenting tremendous opportunities to design and manufacture advanced EMI shielding materials and equipment.

Factors that Affect Network Formation in Carbon Nanotube Composites and their Resultant Electrical Properties

This review paper explores the formation of carbon nanotube (CNT) polymer composites as a function of material and processing parameters. The effect of different polymer systems, increasing multiwall CNT content, modification of CNTs, processing conditions, and aspect ratio are discussed in detail for multi-walled carbon nanotubes (MWCNT) composites along with some examples for SWCNT composites. All of these factors influence the microstructure and how the network of CNTs forms within it. Often, researchers choose to modify the CNTs to aid in their distribution; however, this may result in a reduction or increase in conductivity depending on many factors. The electrical properties are directly affected by changes in the CNT network and how the material has been processed. As soon as the network forms, percolation occurs and the conductivity increases. In order to understand how to control the properties of CNT composites, all material characteristics and processing conditions must be taken into account.

Improved mechanical and electromagnetic interference shielding performance of segregated UHMWPE/CNTs via microwave-assisted sintering

Constructing the segregated networks is an efficient strategy to simultaneously achieve the high electrical conductivity and electromagnetic interference (EMI) shielding performance in conductive polymer composites (CPCs). Herein, an advanced molding technique based on microwave (MW)-assisted sintering was proposed to prepare the segregated ultrahigh molecular weight polyethylene/carbon nanotube (UHMWPE/CNT) composites. Scanning electron microscopy and optical microscopy images indicated that CNTs enriched on the surfaces of UHMWPE granules through ball milling, and the clear and complete conductive networks were observed in UHMWPE/CNT composites in the following MW sintering process, revealing that a perfect segregated structure was successfully constructed. The segregated UHMWPE/CNT composites exhibited an excellent electrical conductivity and EMI shielding performance of 49.3 S/m and 50 dB, respectively, along with a low percolation threshold of 0.10 vol%. Meanwhile, benefiting from the volumetric heating, an ideal mechanical property was also obtained in prepared composite by MW sintering. Compared with the conventional molding method, MW-assisted sintering shows its unique advantages, including better structural construction, shorter processing time, and lower energy consumption, which provides an efficient and environment-friendly method to fabricate CPCs with superior conductive and EMI shielding performance.

Segregated poly(arylene sulfide sulfone)/graphene nanoplatelet composites for electromagnetic interference shielding prepared by the partial dissolution method

Segregated conductive polymer composites have been proved to be outstanding electromagnetic interference shielding (EMI) materials at low filler loadings. However, due to the poor interfacial adhesion between the pure conductive filler layers and segregated polymer granules, the mechanical properties of the segregated composites are usually poor, which limit their application. Herein, a simple and effective approach, the partial dissolution method, has been proposed to fabricate segregated poly(arylene sulfide sulfone) (PASS)/graphene nanoplatelet (GNP) composites with superior EMI shielding effectiveness (SE) and high tensile strength. Morphology examinations revealed that the GNPs were restricted in the dissolved outer layer by the undissolved cores, and there was a strong interaction between the PASS/GNP layer and the pure PASS core. The resultant PASS/GNP composites showed excellent electrical conductivity (60.3 S m^-1) and high EMI SE (41 dB) with only 5 wt% GNPs. More notably, the tensile strength of the PASS/GNPs prepared by partial dissolution reached 36.4 MPa, presenting 136% improvement compared to that of the conventional segregated composites prepared by mechanical mixing. The composites also exhibited high resistance to elevated temperatures and chemicals owing to the use of the special engineering polymer PASS as a matrix.

Stretchable elastomer composites with segregated filler networks: effect of carbon nanofiller dimensionality

Electrically conductive elastomer composites (CECs) have great potential in wearable and stretchable electronic applications. However, it is often challenging to trade off electrical conductivity and mechanical flexibility in melt-processed CECs for wearable electronic applications. Here, we develop CECs with high electrical conductivity and mechanical elasticity by controlling the segregated networks of carbon nanofillers formed at the elastomer interface. The carbon nanofiller dimensionality has a significant influence on the electrical and mechanical properties of thermoplastic polyurethane (TPU) composites. For instance, 3D branched carbon nanotubes (carbon nanostructures, CNSs) have a very low percolation threshold (Φ _C = 0.01 wt%), which is about 8-10 times lower than that of 1D carbon nanotubes (CNTs) and 2D graphene nanosheets (GNSs). Besides, the TPU/CNS system has a higher electrical conductivity than other fillers at all filler contents (0.05-2 wt%). On the other hand, TPU/CNT systems can retain high elongation at break, whereas for the TPU/GNS systems elongation at break is severely deteriorated, especially at a high filler content. Different electrical and mechanical properties in the TPU-based CECs enable potential applications in flexible conductors/resistors and stretchable strain sensors, respectively.

Effect of phase coarsening under melt annealing on the electrical performance of polymer composites with a double percolation structure

The effect of phase coarsening on the evolution of the carbon black (CB) nanoparticle network under quiescent melt annealing and the electrical performance of polypropylene/polystyrene/carbon black (PP/PS/CB) composites with a double percolation structure was investigated. The results showed that when the CB content is low, the coarsening process of PP/PS/CB blends can be divided into two stages. In the first stage, the coarsening rate is fast before the formation of the CB nanoparticle network, and after annealing for a certain time, the evolution of the co-continuous morphology can drive the CB nanoparticles to self-assemble into a complete nanoparticle network. In the second stage, the coarsening rate is slow after the formation of the CB nanoparticle network. When the CB content is high, the CB nanoparticle network can be maintained throughout the whole annealing process, so that the conductivity and morphology of the PP/PS/CB composites are stable. Moreover, the electrical conductivity of the PP/PS/CB composites greatly increases after annealing for a certain time, and a percolation threshold as low as 0.07 vol% can be obtained. These results reveal the relationship between the evolution of the morphology and the conductivity in the conductive polymer composites with a double percolation structure, and provide a more in-depth and comprehensive understanding of the double percolation structure.

Constructing 3D Graphene Networks in Polymer Composites for Significantly Improved Electrical and Mechanical Properties

Graphene-based polymer composites with superior electrical and mechanical performance are highly desirable because of their wide range of applications. However, due to the mismatch between charge jumping and the load transfer of adjacent graphene sheets, it remains difficult to achieve significant, simultaneous improvements in electrical and mechanical properties of graphene-polymer composites. To overcome this issue, we here propose an effective strategy to constructed unique 3D conductive networks in which the compatibility of graphene and polymer can be improved by controlled decoration of few-defect graphene sheets, while segregated graphene networks retain good charge-jumping capability. The final composites exhibit an ultra-low electrical conductive percolation threshold of 0.032 vol % and an ultra-high electrical conductivity of 60 S/m at only 2.45 vol %, superior to most of the reported results. They also reveal significantly improved thermodynamic properties, tensile strength, and toughness. We believe that such a simple, industrially feasible method contributes to boost the development of high-performance, functional graphene-polymer composites.

Facile, green and affordable strategy for structuring natural graphite/polymer composite with efficient electromagnetic interference shielding

The mechanical mixing and hot compaction method was firstly used to fabricate graphite/polymer segregated composite for efficient electromagnetic interference shielding.

A simple strategy to enhance electrical conductivity of nanotube-conjugate polymer composites via iodine-doping

Only the conductivities of iodine-doped CNT–polymer composites containing heteroatoms show a sharp increase.

Formation of conductive networks with both segregated and double-percolated characteristic in conductive polymer composites with balanced properties

Morphological control of conductive networks involves the construction of segregated or double-percolated conductive networks is often reported to reduce the electrical percolation threshold of conductive polymer composites (CPCs) for better balance among electrical conductivity, mechanical properties, and filler content. Herein, the construction of conductive networks with both segregated and double-percolated characteristics is achieved based on polypropylene (PP)/polyethylene (PE) and multi-wall carbon nanotubes (CNTs). CNTs were firstly dispersed in PE; then PE/CNTs were compounded with PP particles well below the melting temperature of PP. It is observed that the percolation threshold (pc) decreases with increasing PP particle size (size 3.6 mm, pc=0.08 wt %), which agrees with previous theoretical prediction and experiment in much smaller particle size range. To further study this, the amount of CNTs in PE is varied. It is shown that the degree of PE/CNTs coating on PP particles varies with CNTs as well as PE content in these composites, and have significant influence on the final electrical property. Furthermore, a model combines classical percolation theory and model for segregated network has been proposed to analyze the effect of particle size, degree of coating and thickness of coating on the percolation behavior of these CPCs. In such a model the percolation of CNTs in PE phase as well as PENT phase in the segregated structure can be described. Overall, through such method, a much better balance among mechanical property, conductivity, and filler content is achieved in these CPCs comparing with the results in literature.