Thermally conductive cyanate ester nanocomposites filled with graphene nanosheets and multiwalled carbon nanotubes

In this work, dodecylamine‐modified graphene nanosheets (DA‐GNSs) and γ‐aminopropyl‐triethoxysilane‐treated multiwalled carbon nanotubes (f‐MWCNTs) are employed to prepare cyanate ester (CE) thermally conductive composites. By adding 5 wt% DA‐GNSs or f‐MWCNTs to the CE resin, the thermal conductivities of the composites became 3.2 and 2.5 times that of the CE resin, respectively. To further improve the thermal conductivity, a mixture of the two fillers was utilized. A remarkable synergetic effect between the DA‐GNSs and f‐MWCNTs on improving the thermal conductivity of CE resin composites was demonstrated. The composite containing 3 wt% hybrid filler exhibited a 185% increase in thermal conductivity compared with pure CE resin, whereas composites with individual DA‐GNSs and f‐MWCNTs exhibited increases of 158 and 108%, respectively. Moreover, the composite with hybrid filler retained high electrical resistivity. Scanning electron microscopy images of the composite morphologies showed that the modified graphene nanosheets (GNSs) and multiwalled carbon nanotubes (MWCNTs) were uniformly dispersed in the CE matrix, and a number of junction points among MWCNTs and between MWCNTs and GNSs formed in the composites with hybrid fillers. Generally, we can conclude that these composites filled with hybrid fillers may be promising materials of further improving the thermal conductivity of CE composites. Copyright © 2014 John Wiley & Sons, Ltd.     

Poly(lactic acid)-based polymer composites with high electric and thermal conductivity and their characterization

Electrically and thermally conductive polymer composites on the basis of biodegradable poly(lactic acid) (PLA) were developed and studied in this work. Pristine single-walled carbon nanotubes (CNTs) and powder of natural graphite (G) were used as fillers in polymer composites. PLA-based composites were prepared by melt-compounding method. The volume resistivity of PLA/CNT composites can be changed by more than ten orders of magnitude compared to that for neat PLA. The thermal conductivity of PLA/G composites can be changed from 0.193 W⋅m⁻¹⋅K⁻¹ (neat PLA) up to 2.73 W⋅m⁻¹⋅K⁻¹. Loading small quantity of CNTs into PLA/G composites increases the thermal conductivity not less than by 40% of magnitude. Besides, all developed PLA-based composites are suitable for processing by injection molding, extrusion or additive manufacturing technology (3D printing).     

Experimental and modeling analysis of mechanical-electrical behaviors of polypropylene composites filled with graphite and MWCNT fillers

The incorporation of carbon fillers can improve the thermal and electrical conductivities of polymer composites but will also have a significant effect on the flexural and tensile behavior. In this paper, two types of carbon fillers were added to polypropylene - carbon nanotubes and synthetic graphite. The influences of these filler materials on the tensile, flexural and fracture toughness characteristics were measured and the electrical conductivity of composites was also investigated. It was observed that the fillers lead to a remarkable increase in the flexural and tensile modulus of polypropylene composites. The maximum flexural and tensile strengths slightly increased with the addition of graphite, however, they were significantly increased in the case of carbon nanotubes because MWCNTs possess exceptional stiffness and strength and their length to diameter ratio is extremely high when compared with graphite. Electrical conductivity of polypropylene composites was evaluated. Noteworthy, composites based on synthetic graphite show a percolation process at one order of magnitude concentration higher than MWCNT filled polypropylene. Fracture toughness results open a wide range of applications for PP-MWCNT composites. Several prediction models were inspected in this research and it was concluded that inverse rule of mixtures model showed the most accurate predictions of the tensile modulus for composites made of polypropylene.     

Significant enhancement of electrical and thermal conductivities of polyethylene carbon nanotube composites by the addition of a low amount of silver nanoparticles

Electrically and thermally conductive high‐density polyethylene composites filled with hybrid fillers, multiwall carbon nanotubes (MWCNTs) and silver nanoparticles (Ag‐NPs), have been prepared in the melt state. The investigation of their electrical and thermal conductivities while comparing with high‐density polyethylene/MWCNT binary composites shows that the addition of only 3 vol% of Ag‐NPs does not reduce the electrical percolation threshold (P_c) that remains as low as 0.40 vol% of MWCNTs but leads to an increase in the maximum dc electrical conductivity of PE/MWCNT composites by two orders of magnitudes. Moreover, the association of both Ag‐NPs and carbon nanotube particles improved our composite's thermal conductivity. Copyright © 2014 John Wiley & Sons, Ltd.     

Towards efficient electromagnetic interference shielding performance for polyethylene composites by structuring segregated carbon black/graphite networks

An electromagnetic interference (EMI) shielding composite based on ultrahigh molecular weight polyethylene (UHMWPE) loaded with economical graphite-carbon black (CB) hybrid fillers was prepared via a green and facile methodology, i.e., high-speed mechanical mixing combined with hot compression thus avoiding the assistance of the intensive ultrasound dispersion in volatile organic solvents. In this composite, the graphite-CB hybrid fillers were selectively distributed in the interfacial regions of UHMWPE domains resulting a typical segregated structure. Thanks to the specific morphology of segregated conductive networks along with the synergetic effect of large-sized graphite flakes and small-sized CB nanoparticles, a low filler loading of 7.7 vol% (15 wt%) yielded the graphite-CB/UHMWPE composites with a satisfactory electrical conductivity of 33.9 S/m and a superior shielding effectiveness of 40.2 dB, manifesting the comparable value of the pricey large-aspect-ratio carbon nanofillers (e.g., carbon nanotubes and graphene nanosheets) based polymer composites. More interestingly, with the addition of 15 wt% graphite-CB (1/3, W/W) hybrid fillers, the tensile strength and elongation at break of the composite reached 25.3 MPa and 126%, respectively; with a remarkable increase of 58.1% and 2420% over the conventional segregated graphite/UHMWPE composites. The mechanical reinforcement could be attributed to the favor of the small-sized CB particles in the polymer molecular diffusion between UHMWPE domains which in turn provided a stronger interfacial adhesion. This work provides a facile, green and affordable strategy to obtain the polymer composites with high electrical conductivity, efficient EMI shielding, and balanced mechanical performance.     

Preparation of high thermal conductive aluminum nitride/cyanate ester nanocomposite using a new macromolecular coupling agent

Novel glycidyl methacrylate–butyl acrylate–maleic anhydride (GBM) terpolymers with different molecular weights were synthesized by radical polymerization and characterized using fourier transform infrared, nuclear magnetic resonance (¹H‐NMR and ¹³ C‐NMR), and gel permeation chromatography. Each GBM terpolymer was used to modify aluminum nitride (AlN), and the modified AlN, coded as AlN(GBM), was added to 2,2′‐bis(4‐cyanatophenyl)isopropylidene (CE) resin for preparing composites. Composites based on original AlN or γ‐(2,3‐epoxypropoxy)propyltrimethoxysilane‐modified AlN (AlN(K)) were also prepared for comparison. Although GBM and γ‐(2,3‐epoxypropoxy)propyltrimethoxysilane have similar reactive groups, the results indicate that GBM shows more attractive integrated advantages, reflected by the fact that CE/AlN(GBM) composites have better thermal stability, higher thermal conductivity, and higher glass transition temperature than those of CE/AlN(K). These properties result from better dispersion of fillers, improved interfacial adhesion between fillers and CE resin, and increased cross‐linking density. This study demonstrates that the nature of the coupling agents is an important factor to develop high performance composites for cutting‐edge industries. Copyright © 2011 John Wiley & Sons, Ltd.     

Low percolation conductive graphite flakes-filled poly(urethane-imide) composites with high thermal stability via imidization self-foaming structure

In the study, the conductive graphite flakes filled poly(urethane-imide) composites (PUI/GFs) with high performance were constructed by the thermal imidization self-foaming reaction. It was found that the foaming action could promote the redistribution of GFs during curing process and the formation of stable linear conductive pathways. The percolation threshold of PUI/GFs composites was lowered from 1.26 wt% (2000 mesh GFs) or 0.86 wt% (1000 mesh GFs) to 0.79 wt% (500 mesh GFs), which were relatively low percolation thresholds for polymer/GFs composites so far. When the content of 500 mesh GFs was 4.0 wt%, the electrical conductivity of the composite was as high as 3.96 × 10^?1 S/m. Also, a poly(urethane-imide) (PUI) matrix with excellent thermal stability (T_d10%: 334.97 °C) and mechanical properties (elongation at break: 324.52%, tensile strength: 15.88 MPa) was obtained by introducing the rigid aromatic heterocycle into the polyurethane (PU) hard segments. Moreover, the zero temperature coefficient of resistivity for the composites was observed at the temperature range from 30 °C to 200 °C. Consequently, PUI/GFs composites may provide the novel strategy for considerable conductive materials with high thermal stability in electrical conductivity.     

The addition of functionalized graphene oxide to polyetherimide to improve its thermal conductivity and mechanical properties

The thermal and electrical conductivity and mechanical properties of polyetherimide (PEI) containing either alkyl‐aminated (enGO) or phenyl‐aminated graphene (pnGO) oxides were studied. A solution casting method was used to prepare functionalized graphene oxide/PEI composites with different filler contents. The introduction of functionalized graphene oxide to the PEI matrix improved the thermal conductivity, electrical conductivity, and mechanical properties. The thermal conductivities of the enGO 3 wt%/PEI and pnGO 3 wt%/PEI composites were 0.324 W/mK and 0.329 W/mK, respectively, due to the high thermal conductivity of the graphene‐based materials and the strong interface adhesion due to the filler surface treatment between the fillers and the matrix. The electrical conductivities of the functionalized graphene oxide/PEI composites were larger than that of PEI, but the electrical conductivity values were generally low, which is consistent with the magnitude of the insulator. The strong interfacial adhesion between the fillers and the matrix led to improved mechanical properties. Copyright © 2014 John Wiley & Sons, Ltd.     

A new process of fabricating electrically conducting nylon 6/graphite nanocomposites via intercalation polymerization

A new process was developed to fabricate electrically conducting nylon 6/graphite nanocomposites via intercalation polymerization of ϵ‐caprolactam in the presence of expanded graphite. The transition from an electrical insulator to an electrical semiconductor for nylon 6 occurred when the graphite volume content was 0.75, which was much lower than that of conventional conducting polymer composites. The electrical conductivity reached 10⁻⁴ S/cm when the graphite content was 2.0 vol %. The TEM microphotographs suggested that the low percolation threshold and the great improvement of electrical conductivity could be attributed to the high aspect ratio (width‐to‐thickness), the high expansion ratio in c axis of the graphite sheets and the homogeneous dispersion of the nanoscale graphite particles in the nylon 6 matrix. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1626–1633, 2000     

Synergetic effect of thermal conductivity and flame retardancy of cyanate ester composites containing DOPO and BN with great dielectric properties

DOPO and boron nitride (BN) fillers with different particle sizes and several loadings were employed to improve the properties of cyanate ester (CE) resin. The effects of BN content and particle size on the thermal conductivity of the BN‐DOPO/CE ternary composites were discussed. The influence of enhancing the thermal conductivity of the ternary composites on their flame retardancy was studied. The consequences showed that increasing the thermal conductivity of BN‐DOPO/CE composites had an active impact on their flame retardancy. Approving flame retardancy of the ternary composites was certified by the high limiting oxygen index (LOI), UL‐94 rating of V‐0, and low heat release rate (HRR) and total heat release (THR). For instance, in contrast with pure CE matrix, peak of HRR (pk‐HRR), average of HRR (av‐HRR), THR, and average of effective heat of combustion (av‐EHC) of CEP/BN_{0.5 μm}/10 composite were decreased by 51.7%, 33.8%, 18.7%, and 18.9%, respectively. Thermal gravimetry analysis (TGA) showed that the addition of BN fillers improves the thermal stability of the composites. Moreover, the ternary composites possess good dielectric properties. Their dielectric constants (ε) are less than 3, and dielectric loss tangent (tgδ) values are lower than neat CE resin.     

New polymer electrolyte membrane for medium-temperature fuel cell applications based on cross-linked polyimide Matrimid and hydrophobic protic ionic liquid

New hydrophobic protic ionic liquid, 2-butylaminoimidazolinium bis(trifluoromethylsulfonyl)imide (BAIM-TFSI), has been synthesized. The ionic liquid showed good thermal stability to at least 350 °C. The conductivity of BAIM-TFSI determined by electrochemical impedance method was found to be 5.6 × 10^?2 S/cm at 140 °C. Homogeneous composite films based on commercial polyimide (PI) Matrimid and BAIM-TFSI containing 30–60 wt% of ionic liquid were prepared by casting from methylene chloride solutions. Thermogravimetric analysis data indicated an excellent thermal stability of PI/BAIM-TFSI composites and thermal degradation points in the temperature range 377 °C–397 °C. The addition of ionic liquid up to 50 wt% in PI films does not lead to any significant deterioration of the tensile strength of the polymer. The dynamic mechanical analysis results indicated both an increase of storage modulus E′ of PI/BAIM-TFSI composites at room temperature and a significant E′ decrease with temperature compared with the neat polymer. The cross-linking of the PI with polyetheramine Jeffamine D-400 allowed to prepare PI/Jeffamine/BAIM-TFSI (50%) membrane with E′ value of 300 MPa at 130 °C. The ionic conductivity of this cross-linked composite membrane reached the level of 10^?2 S/cm at 130 °C, suggesting, therefore, its potential use in medium-temperature fuel cells operating in water-free conditions.     

Electrically conducting electrospun silk membranes fabricated by adsorption of carbon nanotubes

We present a simple method of obtaining electrically conducting electrospun silk non-woven membranes consisting of nanofibers with multi-walled carbon nanotubes (MWCNTs) adsorbed on their surface. Nanofibrous membranes with fibroin diameters of 460 ± 40 nm were formed from aqueous Bombyx mori fibroin solution by electrospinning. The MWCNTs adhered well to the surface of the highly porous silk nanofibrous membranes when Triton X-100 was used as the surfactant for the dispersion of the MWCNTs in aqueous media. The electrical conductivity of the membranes was 2.4 × 10⁻⁴ S/cm due to the presence of the MWCNTs on their surface. In addition, the strong interaction between the MWCNTs and nanofibers keeps them from separating each other, even after ultrasonication. The combination of the high conductivity of the membranes and the simple process used to fabricate them could lead to significant advances in the development of new materials, such as electromagnetic interference shielding or electrostatic dissipation membranes.     

Preparation of polystyrene/MWCNT‐Valine composites: Investigation of optical,morphological, thermal,and electrical conductivity properties

The attempt of this research was to examine the effect of multiwalled carbon nanotube (MWCNT)‐Valine as efficient fillers on the thermal, optical, and electrical behaviors of polystyrene (PS). To reduce aggregation and obtain uniform spreading of fillers into the PS, at first, MWCNTs' surfaces were modified by Valine amino acid. Then, different contents of MWCNT‐Valine (0.5, 1, and 2 wt%) were added to PS by ultrasonication processes. The field emission scanning electron microscopy and transmission electron microscopy results showed a uniform distribution of modified MWCNTs into the matrix. The thermal properties of nanocomposites were improved by increasing nanofiller content. In addition, embedding of MWCNT‐Valine into the PS matrix increased the electrical conductivity of nanocomposites in comparison with pure PS.     

Enhanced toughness and strength of conductive cellulose-poly(butylene succinate) films filled with multiwalled carbon nanotubes

Cellulose (CE) composite films with high tensile strength, modulus, remarkable elongation as well as excellent electrical conductivity were successfully prepared by dispersing poly(butylene succinate) (PBS) and multiwalled carbon nanotubes (MWCNTs) in CE matrix via the help of ionic liquid 1-allyl-3-methylimidazolium chloride. Fourier transform infrared spectroscopy and differential scanning calorimetry results verified that a physical interaction junction existed between PBS and CE. Scanning electron micrograph (SEM) showed that the low content PBS was uniformly dispersed in CE matrix, leading to a tough and ductile fractured surface. The elongation at break of CE composite film with 1 wt% PBS was increased to 25.9 %, which showed an increase of 325 % compared to that of neat CE film (6.07 %). But high-content PBS acted as the structural defect in the CE matrix. MWCNTs were further added to improve the mechanical and conductive properties of the composite film. The tensile strength and Young’s modulus of MWCNT/CE-PBS composite film with 4 wt% MWCNTs were respectively increased by 33.6 and 140 % compared to CE-PBS film. The electrical conductivity of MWCNT/CE-PBS film was also improved by 8–9 orders of magnitude from 2.5 × 10^?14 to 1.3 × 10^?5 S/m.     

Influence of organo-clay on electrical and mechanical properties of PP/MWCNT/OC nanocomposites

The electrical, thermal and mechanical properties of nanocomposites, based on polypropylene (PP) filled by multi-walled carbon nanotubes (MWCNTs) and organo-clay (OC), were studied with the purpose of finding out the effect of OC on the microstructure of MWCNTs dispersion and PP/MWCNT/OC composites. It was found that addition of organo-clay nanoparticles improved nanotube dispersion and enhanced electrical properties of PP/MWCNT nanocomposites. Addition of organo-clay (MWCNT/OC ratio was 1/1) reduced the percolation threshold of PP/MWCNT nanocomposites from ?_c = 0.95 vol.% to ?_c = 0.68 vol.% of carbon nanotubes, while the level of conductivity became 2–4 orders of magnitude higher. The DSC and DMA analyses have shown that the influence of organo-clay on the thermal and mechanical properties of material was not significant in composites with both fillers as compared to PP/OC. Such an effect can be caused by stronger interaction of OC with carbon nanotubes than with polymer matrix.     

Spherical filler-promoting thermally conductive pathway in graphite-containing polymer composites for high heat radiation

Graphite is an efficient and affordable filler for polymer composites, allowing the control of thermal conductivity. In comparison to other thermally conductive fillers, graphite is lightweight and flexible but affords anisotropic thermal conductivity. Herein, the control of thermal conductivity of graphite-containing polymer composite sheet using spherical polymer particles as additional fillers is described. The thermal conductivity in the through-plane direction (λ_t) of the composite sheet is enhanced by varying the composition ratio of the two fillers (flaky graphite and spherical particles), and optimizing the forming temperature and pressure. Graphite-containing (25 wt%) polymer composite sheet formed by compression at 150 °C and 10 MPa exhibits λ _t value of 0.66 W/m K. Upon mixing of polystyrene microspheres, λ _t is successfully increased. The maximum value of thermal conductivity for a composite sheet with 35 wt% of graphite and 50 wt% of spherical particles is 7.51 W/m K, at 180 °C and 10 MPa. The graphite-containing polymer matrix forms a sequentially connected network-like structure in the composite sheet. Excess polymer microspheres lead to the formation of void structures inside the composite sheet, reducing the thermal conductivity. Thermo-camera observations proved that the composite sheets with higher λ _t value showed comparably high heat radiations. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 607–615     

玻璃纤维对聚甲醛基导电复合材料性能的影响

采用在转矩流变仪中熔融混合的方法制备了聚甲醛(POM)/多壁碳纳米管(MWCNTs)/玻璃纤维(GF)和POM/炭黑(CB)/GF复合材料,研究了GF的加入对复合材料的导电性能、结晶行为和动态力学性能的影响.采用场发射扫描电镜(FESEM)观察了复合材料中导电填料的分散状态,发现GF的加入对MWCNTs和CB的分散状态没有明显影响.虽然GF为导电惰性填料,但因其加入起到了占位作用,明显提高了导电填料的有效浓度,从而使复合材料的体积电阻率明显降低.采用示差扫描量热仪(DSC)研究了复合材料中POM的结晶行为,发现GF的加入对POM的结晶温度、熔点和结晶度均无明显影响.采用动态机械分析仪(DMA)对复合材料的动态力学性能进行了研究,表明GF的加入能够明显地提高复合材料的储能模量.     

β成核剂修饰多壁碳纳米管增强聚丙烯纳米复合材料的分散及结晶行为

利用非共价键改性方法,用芳香二羧酸酰胺类的β成核剂(β-NA)改性多壁碳纳米管(MWCNTs),采用溶液法制备了聚丙烯(PP)/β-NA-MWCNTs复合材料.通过广角X射线衍射(WAXD)分析了复合材料的结晶形态,结果表明β-NA-MWCNTs诱导聚丙烯生成大量β晶,同时提高了复合材料的结晶度.含5.0 wt％β-N...     

Polyaniline-coated coconut fibers: Structure,properties and their use as conductive additives in matrix of polyurethane derived from castor oil

Electrically conducting fibers based on coconut fibers (CF) and polyaniline (PANI) were prepared through in situ oxidative polymerization of aniline (ANI) in the presence of CF using iron (III) chloride hexahydrate (FeCl_3.6H₂O) or ammonium persulfate (APS) as an oxidant. The PANI-coated coconut fibers (CF-PANI) displayed various morphologies, electrical conductivities and percentages of PANI on the CF surface. For both systems, a PANI conductive layer was present on the CF surface, which was responsible for an electrical conductivity of around 1.5 × 10⁻¹ and 1.9 × 10⁻² S cm⁻¹ for composites prepared with FeCl₃.6H₂O and APS, respectively; values that are similar to that of pure PANI. In order to modify the structure and properties of polyurethane derived from castor oil (PU) both CF-PANI and pure PANI were used as conductive additives. The PU/CF-PANI composites exhibited higher electrical conductivity than pure PU and PU/PANI blends. Additionally, the PU/CF-PANI composites showed a variation in electrical resistivity according to the compressive stress applied, indicating that these materials could be applied for pressure-sensitive applications.     

Effect of nano/micro‐mixed ceramic fillers on the dielectric and thermal properties of epoxy polymer composites

Nano/micro ceramic‐filled epoxy composite materials have been processed with various percentage additions of SiO₂, Al₂O₃ ceramic fillers as reinforcements selected from the nano and micro origin sources. Different types of filler combinations, viz. only nano, only micro, nano/micro, and micro/micro particles, were designed to investigate their influence on the thermal expansion, thermal conductivity, and dielectric properties of epoxy polymers. Thermal expansion studies were conducted using thermomechanical analysis that revealed a two‐step expansion pattern consecutively before and after vitreous transition temperatures. The presence of micro fillers have shown vitreous transition temperature in the range 70–80°C compared with that of nano structured composites in which the same was observed as ~90°C. Similarly, the bulk thermal conductivity is found to increase with increasing percentage of micron‐size Al₂O₃. It was established that the addition of micro fillers lead to epoxy composite materials that exhibited lower thermal expansion and higher thermal conductivity compared with nano fillers. Moreover, nano fillers have a significantly decisive role in having low bulk dielectric permittivity. In this study, epoxy composites with a thermal expansion coefficient of 2.5 × 10^?5/K, thermal conductivity of 1.18 W/m · K and dielectric permittivity in the range 4–5 at 1 kHz have been obtained. The study confirms that although the micro fillers seem to exhibit good thermal conductivity and low expansion coefficient, the nano‐size ceramic fillers are candidate as cofillers for low dielectric permittivity. However, a suitable proportion of nano/micro‐mixed fillers is necessary for achieving epoxy composites with promising thermal conductivity, controlled coefficient of thermal expansion and dielectric permittivity. Copyright © 2013 John Wiley & Sons, Ltd.