Elastomeric composites based on ethylene–propylene–diene monomer rubber and conducting polymer-modified carbon black

Thermally stable elastomeric composites based on ethylene–propylene–diene monomer (EPDM) and conducting polymer-modified carbon black (CPMCB) additives were produced by casting and crosslinked by compression molding. CPMCB represent a novel thermally stable conductive compound made via “in situ” deposition of intrinsically conducting polymers (ICP) such as polyaniline or polypyrrole on carbon black particles. Thermogravimetric analysis showed that the composites are thermally stable with no appreciable degradation at ca. 300°C. Incorporating CPMCB has been found to be advantageous to the processing of composites, as the presence of ICP lead to a better distribution of the filler within the rubber matrix, as confirmed by morphological analysis. These materials have a percolation threshold range of 5–10 phr depending on the formulation and electrical dc conductivity values in the range of 1 × 10⁻³ to 1 × 10⁻² S cm⁻¹ above the percolation threshold. A less pronounced reinforcing effect was observed in composites produced with ICP-modified additives in relation to those produced only with carbon black. The results obtained in this study show the feasibility of this method for producing stable, electrically conducting composites with elastomeric characteristics. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Improvement in thermal conductivity and mechanical properties of ethylene‐propylene–diene monomer rubber by expanded graphite

Thermally conductive fillers are usually employed in the preparation of rubber composites to enhance thermal conductivity. In this work, ethylene‐propylene‐diene monomer rubber (EPDM)/expanded graphite (EG) and EPDM/graphite composites with up to 100 phr filler loading were prepared. Compared to EPDM/graphite compounds with the same filler loading, stronger filler network was demonstrated for EPDM/EG compounds. Thermal conductivity and mechanical properties of EPDM/graphite and EPDM/EG composites were compared and systematically investigated as a function of the filler loading. The thermal conductivity of both EPDM/graphite and EPDM/EG composites increased with increasing volume fraction of fillers, and could be well fitted by Geometric Mean Model. The thermal conductivity as high as 0.910 W · m⁻¹ · K⁻¹ was achieved for the EPDM/EG composite with 25.8 vol% EG, which was ∼4.5 times that of unfilled EPDM. Compared to EPDM/graphite composites, EPDM/EG composites exhibited much more significant improvement in thermal conductivity and mechanical properties, which could be well correlated with the better filler‐matrix interfacial compatibility and denser structure in EPDM/EG composites, as revealed in the SEM images of tensile fracture surfaces. POLYM. COMPOS., 38:870–876, 2017. © 2015 Society of Plastics Engineers     

Carbon nanotube composites fabricated through filament winding process for battery preheating application

Carbon nanotube (CNT) polymer composites have broad application prospects in thermal management as electrothermal heaters. Nevertheless, challenge remains in achieving high electrical conductivity for the composites due to the contradiction between CNTs and insulated polymers. To address this issue, herein, innovative use of interface strategy approach by constructing synergistic nanomaterial networks on carboxyl CNTs yarn winding composites for improving the interfacial adhesion and electrical performance. In the work, carboxyl CNTs yarn/CNTs-graphene oxide (GO) polyvinyl alcohol (PVA) composites (C-CY-HP-C) were proposed and manufactured via filament winding process. The as-constructed C-CY-HP-C demonstrated a remarkable interfacial shear strength of 2057.16 N mm⁻¹, which was 53.59% higher than that of control CNTs yarn/PVA winding composites. In addition, the C-CY-HP-C achieved an attractive electrical conductivity of 346.39 S cm⁻¹ owing to the electronic transmission channels were formed. Notably, the superior electrical conductivity facilitated a rapid-response of electrothermal performance for the C-CY-HP-C. It reached a steady-state temperature of 229.9°C within 10 s when the voltage was 1.2 V. Concurrently, it exhibited an impressive heating rate of 10.8°C min⁻¹ at an ambient temperature of −20°C as the battery surface heater. These findings shed light on the development of technique for battery preheating system based on CNTs yarn/polymer composites.     

Preparation,structure, and properties of end‐functionalized miktoarms star‐shaped polybutadiene–sn–poly(styrene–butadiene) rubber

Two miktoarm star‐shaped rubbers with large‐volume functional groups of 1,1‐diphenylhexyl at the ends of arms (DMS–PB–SBR) and one miktoarm star‐shaped rubber with n‐butyl groups at the ends of arms (BMS–PB–SBR) were prepared by 1,1‐diphenylhexyllithium (DPHLi) and n‐butyl lithium as initiators, respectively. The molecular structures and morphological properties of the three rubbers (MS–PB–SBR) were studied and compared with those acquired from the blend consisting of star‐shaped solution‐polymerized butadiene styrene rubber (S‐SSBR) and butadiene rubber (PBR) prepared by ourselves. The results showed that MS–PB–SBR exhibited a more uniform distribution of PBR phase and a smaller phase size of PBR than that of S‐SSBR/PBR blend. It is found that MS–PB–SBR composites filled with CB showed the lower Payne effect than that of S‐SSBR/PBR/CB composite, suggesting that the MS–PB–SBR/CB composite (particularly the DMS–PB–SBR/CB composites) would possess excellent mechanical properties, high wet‐skid resistance, and low rolling resistance. For the studied MS–PB–SBR systems, the contribution of large‐volume functional groups at the end of PBR molecular chains to decrease the rolling resistance was larger than that of Sn coupling effect. It is envisioned that the miktoarm star‐shaped rubbers with 1,1‐diphenylhexyl groups at the molecular ends would be useful for making treads of green tires. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40002.     

Electrical conductivity of epoxy/silicone/carbon black composites: Effect of composite microstructure

The objective of this work is to study the effect of electrical conductivity and physical‐mechanical properties of carbon black (CB) filled polymer composites. This goal is achieved by synthesizing epoxy/silicon phase separated blend structure of composites filled with CB. The percolation threshold of epoxy/silicone/CB composites decreased and the total conductivity increased compared to the pure epoxy/CB composite. A threefold increase was obtained with tensile strength of epoxy/silicone/CB composite with 25 wt% of silicone and 5 wt% of CB in comparison with epoxy/CB systems. This composite has conductivity of about 10⁻⁶ S/cm, which is six orders of magnitude higher than for epoxy/CB composites at the same concentration of CB. POLYM. COMPOS., 35:2234–2240, 2014. © 2014 Society of Plastics Engineers     

Electrical and mechanical properties of conducting carbon black filled composites based on rubber and rubber blends

The electrical and mechanical properties of new conductive rubber composites based on ethylene–propylene–diene rubber, acrylonitrile butadiene rubber (NBR), and their 50/50 (weight ratio) blend filled with conductive black were investigated. The threshold concentrations for achieving high conductivity are explained on the basis of the viscosity of the rubber. The electrical conductivity increases with the increase in temperature whereas the activation energy of conduction decreases with an increase in filler loading and NBR concentration in the composites. The electrical hysteresis and electrical set are observed during the heating–cooling cycle, which is mainly due to some kind of irreversible change occurring in the conductive networks during heating. The mechanisms of conduction in these systems are discussed in the light of different theories. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 887–895, 1999     

Electrical Conductivity of Styrene‐Butadiene Rubber/Polyester Short‐Fiber Reinforced with Different Types of Carbon Black

Abstract

Measurements of electrical conductivity for a composite of styrene‐butadiene rubber (SBR) and polyester (PE) short‐fiber reinforced with different types of carbon black [high abrasion furnace (HAF) and fast extruding furnace (FEF) black] in increasing quantities have been carried out at different temperatures (30–60°C). To find out the effect of the type of carbon black, particle size, and the quantity of carbon black, on the electrical conductivity of the SBR/PE short‐fiber composites. It was found that the electrical conductivity increases as the carbon content increases in the composites. Samples loaded with FEF carbon black showed lower conductivity values in comparison with those loaded with HAP carbon black, besides, they possess a reasonable conducting stability as the temperature rises. The results are discussed and interpreted.     

The order addition effect of carbon black/graphite on the electrical properties of rubber composites

Acrylonitrile‐butadiene rubber (NBR) filled with two types of fillers [high abrasion furnace carbon black (C), and graphite (G)] is made to find out the effect of order addition of C and G on the electrical conductivity of the composites. The temperature and frequency dependence of the (dc and ac) conductivity and dielectric constants have been measured. The values of the thermal expansion and thermal conduction coefficient of NBR rubber lead to the difference in I–V characteristics between CB‐ and G‐NBR rubber composites during the measurement. When graphite is first added to NBR, the electrical conductivity of (GC_20‐20) matrix is larger than that of the (CG_20‐20) matrix, whereas the carbon black is added first. At low temperature (T < 90°C), the higher values of the dielectric constant (ε′) for the sample GC_20‐20 compared with that of the CG_20‐20 sample is due to the conducting nature and structure of graphite, whereas the carbon shows less crystallinity and conductivity than graphite. Opposite behavior is noticed at temperature higher than 90°C. The dc conductivity of all composites increases with increasing temperature exhibiting a positive temperature coefficient of conductivity (PTCσ). The conductivity at high temperatures region is controlled by the thermal excitation transport mechanism, whereas at low temperatures region is dominated by tunneling process. The increase in the value of dielectric constant (ε′) with temperatures for the sample GC_20‐20 compared with the sample CG_20‐20 is due to the conducting nature and structure of graphite, and the carbon less crystalline than the graphite. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrical conductivity of carbon black/single-wall carbon nanotube/low-density polyethylene ternary composite foam

In order to obtain high electrical conductive low-density polyethylene (LDPE) foam, carbon black (CB), single-wall carbon nanotube (SWCNT), and LDPE (CB/SWCNT/LDPE) ternary composite foams were successfully fabricated by chemical compression molding method. The electrical conductivity, mechanical properties, microstructure, density, and crystallinity of the foam were studied in detail. It can be found that CB and SWCNT have synergistic effect. For the CB/SWCNT/LDPE composite foam which containing 19 wt % CB and 0.05 wt % SWCNT, its density is only 0.082 g cm⁻¹ and the electrical conductivity can reach at 2.88 × 10⁻⁵ S cm⁻³, which is far more than 15 orders of magnitudes of pure polyethylene and 4 orders of magnitudes times higher than sample which CB content is 19 wt %. It is noteworthy that ultralow concentration of SWCNT could drastically improve the electrical conductivity and reduce the density of LDPE foams. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48382.     

Highly electrically and thermally conductive silicon carbide-graphene composites with yttria and scandia additives

Dense silicon carbide/graphene nanoplatelets (GNPs) and silicon carbide/graphene oxide (GO) composites with 1 vol.% equimolar Y₂O₃–Sc₂O₃ sintering additives were sintered at 2000 °C in nitrogen atmosphere by rapid hot-pressing technique. The sintered composites were further annealed in gas pressure sintering (GPS) furnace at 1800 °C for 6 h in overpressure of nitrogen (3 MPa). The effects of types and amount of graphene, orientation of graphene sheets, as well as the influence of annealing on microstructure and functional properties of prepared composites were investigated. SiC-graphene composite materials exhibit anisotropic electrical as well as thermal conductivity due to the alignment of graphene platelets as a consequence of applied high uniaxial pressure (50 MPa) during sintering. The electrical conductivity of annealed sample with 10 wt.% of GNPs oriented parallel to the measuring direction increased significantly up to 118 S·cm⁻¹. Similarly, the thermal conductivity of composites was very sensitive to the orientation of GNPs. In direction perpendicular to the GNPs the thermal conductivity decreased with increasing amount of graphene from 180 W·m⁻¹ K⁻¹ to 70 W·m⁻¹ K⁻¹, mainly due to the scattering of phonons on the graphene – SiC interface. In parallel direction to GNPs the thermal conductivity varied from 130 W·m⁻¹ K⁻¹ up to 238 W·m⁻¹ K⁻¹ for composites with 1 wt.% of GO and 5 wt.% of GNPs after annealing. In this case both the microstructure and composition of SiC matrix and the good thermal conductivity of GNPs improved the thermal conductivity of composites.     

Effect of hot air aging on properties of EPDM/SmBO3/EVA and EPDM/ATO/EVA composites

Ethylene–propylene–diene rubber (EPDM)/samarium borate (SmBO₃)/ethylene‐vinyl acetate (EVA) copolymer and EPDM/antimony‐doped tin oxide (ATO)/EVA composites are aged at 150°C for different intervals. Surface modification is used to improve filler to matrix interphase. The main aim is to investigate the effect of filler type and vinyl acetate (VA) content in EVA on stability of EPDM composites. It is found that acidic ATO particles can lower pH level of EPDM composites and then promote the degradation of acetic acid during aging. Moreover, when VA content exceeds 14 wt %, the instable VA content causes more acetic acids escape during aging. With the increasing of aging time, EPDM/SmBO₃ control and EPDM/SmBO₃/EVA composites tend to become darker while EPDM/ATO and EPDM/ATO/EVA composites would become yellow. And the color change is correlated well with the variation of carbonyl index. The chemical crosslink points prevent crystals in EVA from melting at aging temperature (150°C), and the variation of crosslink density influences the crystallinity during aging. The tendency of tensile strength is well consistent with that of swelling ratios, and electric properties are correlated with increased polar groups and crystallinity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of conductive polypyrrole composites by in‐situ polymerization

Two kinds of conductive polypyrrole composites were prepared by in‐situ polymerization of pyrrole in a suspension of chlorinated polyethylene powder or in a natural rubber latex using ferric chloride as oxidizing agent. The preparation conditions were studied and the results showed that it is better to swell the chlorinated polyethylene powder with the monomer first, followed by addition of the oxidant, than to add the oxidant first, and that conversion can reach 98% for 6 h at room temperature. The conductivity percolation threshold of the composite is about 12%. The composites can be processed repeatedly, exhibiting a maximum tensile strength over 9 MPa and a maximum conductivity near 1 S cm⁻¹. The polypyrrole/natural rubber composites were prepared successfully by using a nonionic surfactant (Peregal O) as stabilizer at pH less than 3 with a molar ratio of FeCl₃/pyrrole = 2.5 below 45 °C. The latter composites show a low conductivity percolation threshold about 6%, a maximum tensile strength over 10 MPa and a maximum conductivity over 2 S cm⁻¹. The composites were characterized by FTIR and TGA. The polypyrrole/chlorinated polyethylene composites are very stable in air and almost no decrease of conductivity was observed for over 10 months examined. © 1999 Society of Chemical Industry     

Electroconductive ceramic composites with low-to-zero shrinkage during sintering

Dense low or even zero shrinkage TiN/Si₃N₄ and ZrN/Si₃N₄ composites have been obtained by reaction of transition metal silicides TiSi₂, ZrSi₂ and Ti₅Si₃ with nitrogen gas in the temperature range 700–1500 °C. After transformation to nitrides, densification of the reaction-bonded composites is achieved (95–97% TD) in a subsequent sintering step up to 1800 °C in flowing nitrogen. Since the nitridation reaction is accompanied by volume expansions, linear shrinkage of the sinter bodies in relation to the die-pressed powder compacts is very low. In the case of TiSi₂ even zero shrinkage was achieved by adjusting the green density during axial compaction by variation of the applied stress. The electrical conductivities of the obtained ceramic specimen differ strongly due to the volume amounts of the conducting phases and different microstructures. The conductivity of the composites made from pure silicides or their mixtures ranges from 10⁻¹ to 10⁵ Ω⁻¹ cm⁻¹.     

Electrically conductive composites of polyurethane derived from castor oil with polypyrrole‐coated peach palm fibers

Electrically conducting fibers were prepared through in situ oxidative polymerization of pyrrole (Py) in the presence of peach palm fibers (PPF) using iron (III) chloride hexahydrate (FeCl₃·6H₂O) as oxidant. The polypyrrole (PPy) coated PPF displayed a PPy layer on the fibers surface, which was responsible for an electrical conductivity of (2.2 ± 0.3) × 10⁻¹ S cm⁻¹, similar to the neat PPy. Electrically conductive composites were prepared by dispersing various amounts of PPy‐coated PPF in a polyurethane matrix derived from castor oil. The polyurethane/PPy‐coated PPF composites (PU/PPF–PPy) exhibited an electrical conductivity higher than PU/PPy blends with similar filler content. This behavior is attributed to the higher aspect ratio of PPF–PPy when compared with PPy particles, inducing a denser conductive network formation in the PU matrix. Electromagnetic interference shielding effectiveness (EMI SE) value in the X‐band (8.2–12.4 GHz) found for PU/PPF–PPy composites containing 25 wt% of PPF–PPy were in the range −12 dB, which corresponds to 93.2% of attenuation, indicating that these composites are promising candidates for EMI shielding applications. POLYM. COMPOS., 38:2146–2155, 2017. © 2015 Society of Plastics Engineers     

Expanded Graphite–Epoxy–Flexible Silica Composite Bipolar Plates for PEM Fuel Cells

Silica impregnated expanded graphite–epoxy composites are developed as bipolar plates for proton exchange membrane (PEM) fuel cells. These composite plates were prepared by solution impregnation, followed by compression molding and curing. Mechanical properties, electrical conductivities, corrosion resistance, and contact angles were determined as a function of impregnated content. The plates show high flexural strength with 5% methyltrimethoxysilane (MTMS) addition (20 MPa) and in‐plane conductivity of 131 S cm⁻¹ that meet the DOE target (>100 S cm⁻¹). Corrosion current values as low as 1.09 μA cm⁻² were obtained. The contact angle was found to be 80°. Power density of 1 W cm⁻² was achieved with custom made expanded graphite–polymer composite plates. High efficiency values were obtained at low current regions.     

Elastic polyaniline with EPDM and dodecylbenzenesulfonic acid as plasticizers

Elastomeric polyaniline was prepared by being mixed with ethylene–propylene–diene (EPDM) rubber in low concentrations (10, 20, or 30 wt %). The mixture was made in an internal mixer coupled to a torque rheometer. The polyaniline was doped with dodecylbenzenesulfonic acid (DBSA) via reactive processing during the mixing. When the EPDM rubber was added to the polyaniline and DBSA, the doping reaction was not interrupted, as demonstrated by an increase in the torque values. We chose the relative DBSA and EPDM concentrations to obtain the highest conductivities (10⁻¹ to 10⁻³ S cm⁻¹) and the best mechanical properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1768–1775, 2001     

Conducting Shape Memory Polyurethane‐Polypyrrole Composites for an Electroactive Actuator

Summary: Electroactive shape memory composites were prepared using polyurethane block copolymer and conducting polypyrrole by chemical oxidative polymerization. The electrical conductivity, thermal and mechanical properties, and morphology of the composites were investigated, and a voltage‐triggered shape memory effect was demonstrated. The polyurethane synthesized had a transition temperature near 46 °C. The presence of polypyrrole increased the conductivity of the composites, and a high conductivity of the order of 10^?2 S/cm was obtained at 6–20 wt.‐% polypyrrole. Such a conductivity of composites was enough to show electroactive shape recovery by heating above the transition temperature of 40–45 °C due to melting of the polycaprolactone soft segment domain. Thus a good shape recovery of 85–90% could be obtained in the shape recovery test with bending mode when an electric field of 40 V was applied.

Electroactive shape recovery behavior of PU/PPy composite.     

Hybrid composites of ABS with carbonaceous fillers for electromagnetic shielding applications

This work evaluates the influence of two types of carbonaceous fillers, carbon black (CB) and carbon nanotubes (CNTs), on the electrical, electromagnetic, and rheological properties of composites based on poly(acrylonitrile‐co‐butadiene‐co‐styrene) (ABS) prepared by the melt mixing. Electrical conductivity, electromagnetic shielding efficiency (EMI SE) in the X‐band frequency range (8–12.4 GHz), and melt flow index (MFI) results showed that ABS/CNT composites exhibit higher electrical conductivity and EMI SE, but lower MFI when compared to ABS/CB composites. The electrical conductivity of the binary composites showed an increase of around 16 orders of magnitude, when compared to neat ABS, for both fillers. Binary composites with 5 and 15 wt % of filler showed an EMI SE of, respectively, ?44 and ?83 dB for ABS/CNT, and ?9 and ?34 dB for ABS/CB. MFI for binary composites with 5 wt % were 15.45 and 0.55 g/10 min for CB and CNT, respectively. Hybrid composites ABS/CNT.CB with 3 wt % total filler and fraction 50:50 and 75:25 showed good correlation between EMI SE and MFI. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46546.     

Graphene nanoplate and multiwall carbon nanotube–embedded polycarbonate hybrid composites: High electromagnetic interference shielding with low percolation threshold

This study has reported the preparation of polycarbonate (PC)/graphene nanoplate (GNP)/multiwall carbon nanotube (MWCNT) hybrid composite by simple melt mixing method of PC with GNP and MWCNT at 330°C above the processing temperature of the PC (processing temperature is 280°C) followed by compression molding. Through optimizing the ratio of (GNP/MWCNT) in the composites, high electromagnetic interference shielding effectiveness (EMI SE) value (∼21.6 dB) was achieved at low (4 wt%) loading of (GNP/MWCNT) and electrical conductivity of ≈6.84 × 10⁻⁵ S.cm⁻¹ was achieved at 0.3 wt% (GNP/MWCNT) loading with low percolation threshold (≈0.072 wt%). The high temperature melt mixing of PC with nanofillers lowers the melt viscosity of the PC that has helped for better dispersion of the GNPs and MWCNTs in the PC matrix and plays a key factor for achieving high EMI shielding value and high electrical conductivity with low percolation threshold than ever reported in PC/MWCNT or PC/graphene composites. With this method, the formation of continuous conducting interconnected GNP‐CNT‐GNP or CNT‐GNP‐CNT network structure in the matrix polymer and strong π–π interaction between the electron rich phenyl rings and oxygen atom of PC chain, GNP, and MWCNT could be possible throughout the composites. POLYM. COMPOS., 37:2058–2069, 2016. © 2015 Society of Plastics Engineers     

Preparation of polystyrene–graphite conducting nanocomposites via intercalation polymerization

In situ polymerization of styrene was conducted in the presence of expanded graphite obtained by rapid heating of a graphite intercalation compound (GIC), to form a polystyrene–expanded graphite conducting composite. The composite showed excellent electrically conducting properties even though the graphite content was much lower than in normal composites. The transition of the composite from an electrical insulator to an electrical semiconductor occurred when the graphite content was 1.8 wt%, which is much lower than that of conventional conducting polymer composites. TEM, SEM and other studies suggest that the graphite was dispersed in the form of nanosheets in a polymer matrix with a thickness of 10–30 nm, without modification of the space between carbon layers and the structure of the graphite crystallites. The composite exhibited high electrical conductivity of 10^?2 S cm^?1 when the graphite content was 2.8–3.0 wt%. This great improvement of conductivity could be attributed to the high aspect ratio (width‐to‐thickness) of the graphite nanosheets. The rolling process strongly affected the conductivity and the mechanical properties of the composite. © 2001 Society of Chemical Industry