Silicone rubber/graphite nanosheet electrically conducting nanocomposite with a low percolation threshold

A novel electrically conductive nanocomposite was successfully fabricated by dispersing homogeneously conductive graphite nanosheets (GN) in an insulating silicone rubber (SR) matrix. GN were prepared by powdering expanded graphite with sonication in aqueous alcoholic solution. The particular geometry of GN 30–80 nm in thickness with high aspect ratio contributes to the advantage of forming the conducting network, so that the percolation threshold of SR/GN nanocomposite is about 0.009, much lower than that of composites with conventional graphite. The SR/GN nanocomposite presents a remarkable piezoresistive behavior under much low pressure, related to the low elastic modulus of the composite. The elastic modulus of the nanocomposite with various GN content and at the different speed of compression was discussed. POLYM. COMPOS., 28:493–498, 2007. © 2007 Society of Plastics Engineers     

Synthesis and properties of poly(4,4′-oxybis(benzene)disulfide)/graphite nanocomposites via in situ ring-opening polymerization of macrocyclic oligomers

An effective method for the preparation of poly(4,4′-oxybis(benzene)disulfide)/graphite nanosheet composites via in situ ring-opening polymerization of macrocyclic oligomers were reported. Completely exfoliated graphite nanosheets were prepared under the microwave irradiation followed by sonication in solution. The nanocomposites were fabricated via in situ melt ring-opening polymerization of macrocyclic oligomers in the presence of graphite nanosheets. The graphite nanosheets and resulted poly(arylene disulfide)/graphite nanocomposites were characterized with field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), tensile tester and electrical conductivity measurements. Compared with pure polymer, the electrical conductivity of the poly(arylene disulfide)/graphite nanocomposites were dramatically increased and had a value of about 10⁻³ S/cm for the nanocomposite containing 5 wt% graphite. The nanocomposites exhibit as both high performance polymeric material and electrically conductive material. Therefore, they show potential applications as high temperature conducting materials.     

Thermophysical properties of foliated graphite/nickel reinforced polyvinyl chloride nanocomposites

A novel, polymer‐based foliated graphite/nickel nanocomposites with high thermal conductivity, mechanical properties, and low dielectric constant was developed. The network structure of polyvinyl chloride (PVC) reinforced foliate graphite and nickel nanoparticles (GN) were tested in terms of X‐ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive x‐ray analysis (EDX), and thermal‐gravimetric analyses (TGA). Thermogravimetric analysis revealed a large improvement in the thermal stability of PVC/GN nanocomposites. Thermal conductivity and diffusivity of the composites increased with increasing GN content and temperature. The obtained experimental thermal conductivity result are compared with the existing theoretical models. The measured values of thermal conductivity were in excellent agreement with those calculated from the Agari model. In addition, specific heat, coefficient of thermal expansion (TEC), micro porosity, and crosslinking density (CLD) of composites were investigated. The mechanical properties such as tensile strength, tensile modulus, hardness, and elongation at break of the nanocomposites were improved with inclusion GN which is proportional to GN content. Finally, the dielectric properties of PVC/GN nanocomposites as a function of frequency have been investigated in details. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electromagnetic wave absorbing performance of multiphase (SiC/HfC/C)/SiO2 nanocomposites with an unique microstructure

Dielectric properties and electromagnetic (EM) wave absorbing performance of monolithic (SiC/HfC/C)/SiO₂ nanocomposites (denoted as SHCOs) have been investigated in the X-band (8.2–12.4 GHz). The multiphase SHCOs are composed of insulating SiO₂ and SiC/HfC/C nanocomposite fillers (SHC), which fillers composed of semiconducting β-SiC, conductive HfC-Carbon core-shell nanoparticles, and interconnected carbon nanoribbons. Dielectric response indicates that the increased SHC content results in an enhanced imaginary part of the permittivity and dielectric loss, leading to an improved EM absorbing performance. The unique microstructure with an EM wave-transparent SiO₂ matrix is favorable for impedance matching and effective EM wave propagation. The enhanced interface polarization and conduction loss are considered as the key mechanisms for EM wave attenuation. The minimum reflection loss of the SHCOs achieves – 60.7 dB containing 20 vol% of SHC (at 9.98 GHz) with the sample thickness of 3.33 mm, and the effective absorbing bandwidth (EAB) covers ca. 72 % of the X-band. The monolithic (SiC/HfC/C)/SiO₂ nanocomposites with outstanding EM wave absorbing performance are promising candidates for EM application at high temperatures.     

Preparation of erythritol–graphite foam phase change composite with enhanced thermal conductivity for thermal energy storage applications

Three-dimensional interconnected graphite composite foam as a heat conductive matrix was fabricated by using low cost polymeric precursors and polyurethane (PU) foam as carbon source and sacrificial macroporous template, respectively. Erythritol–graphite foam as a stable composite phase change material (PCM) was obtained by incipient wetness impregnation method. The thermophysical properties such as thermal diffusivity, specific heat, thermal conductivity and latent heat of the erythritol–graphite composite foam were measured. From the results, it was found that the thermal conductivity of the erythritol–graphite composite foam (3.77 W/mK) was enhanced 5 times as compared with that of pristine erythritol (0.72 W/mK). This enhancement can significantly reduce the charging and discharging times of the PCM storage system. There is no chemical reaction between erythritol and graphite as confirmed by X-ray diffractometer (XRD). The PCM/foam composite has a melting point of 118 °C and latent heat of 251 J/g which corresponds to the mass percentage (75 wt.%) of the erythritol within the composite foam. The obtained results confirmed the feasibility of using erythritol–graphite foam as a new phase change composite for thermal energy storage (TES) applications, thus it can contribute to the efficient utilization and recovery of solar heat or industrial waste heat.     

Electrical conductivity transformation mechanism of GNPs/CB/SR nanocomposite foams

Highly flexible and electrically conductive graphene nanoparticles/carbon black/silicon rubber (GNPs/CB/SR) based nanocomposite foams were formed by using azodicarbonamide (AC) physical foaming technology. The foaming parameters (foaming agent and foaming time) were analyzed to investigate the influence on the electrical properties and microcellular structure. The electrical percolation threshold of GNPs/CB/SR nanocomposite foams approximately decreases from 25% to 30%, as the volume expansion increases through foaming. Nanocomposite foams with conductive fillers of 3–12 wt %, foaming agent of 12–18 wt %, foaming time of about 150–500 s, relative densities of 1.0–0.4 g/cm³ were achieved, providing a scheme to evaluate the transformation of electrical properties with different foaming degree. It is worth noting that the product of AC agent concentration and foaming time reaches a certain value, and the highest electrical conductivity of foamed nanocomposites could be achieved. The nonmonotonicity changing of the electrical conductivity was demonstrated. Combined with the microtopography characterization, the cell growth effect was introduced to illustrate the transformation mechanism of the electrical conductivity. The relationship between the microcellular structure and the electrical conductivity of the foamed nanocomposites was established, which is essential for further optimizations of the foaming materials for the targeted application. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45996.     

Soy Oil-Based Rigid Polyurethane Biofoams Obtained by a Facile One-Pot Process and Reinforced with Hydroxyl-Functionalized Multiwalled Carbon Nanotube

Highly conductive, thermally insulating, and three-dimensional (3D) macromolecular network-structured nanocomposite biofoams with very low density were designed from soy oil-based polyurethane (PU) and hydroxyl-functionalized multiwalled carbon nanotubes (MWCNT-OH) using a facile one-pot process with water as the sole blowing agent. Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and Fourier Transform Infrared spectroscopy (FTIR) analyses revealed homogeneous dispersion as well as interaction or reaction of MWCNT-OH with the PU biofoam matrix or a polymeric methylene diphenyl diisocyanate (MDI) to form a 3D macromolecular network structure. Mechanical properties and electrical conductivity were remarkably enhanced with the increase of MWCNT-OH. Dynamic mechanical analysis and thermogravimetric analysis results showed that all the nanocomposite PU biofoam products had good thermal stability properties. Hence, the prepared nanocomposites hold promise as rigid biopolyurethane (BioPU) foams, serving the needs of the conductive composite material fields.     

Broadband dielectric properties of multiwalled carbon nanotube/polystyrene composites

This study investigates the dielectric properties of multiwalled carbon nanotube (MWCNT)/polystyrene (PS) composites over the broadband frequency range, i.e., 10^?1 to 10⁶ Hz. The results showed that the real permittivity and imaginary permittivity increased remarkably with increased MWCNT concentration. For instance, at 100 Hz, the real permittivity and imaginary permittivity of the pristine PS was 2.71 and 0.01, respectively, which increased to 5.22 × 10⁴ and 3.28 × 10⁷ at 3.50 wt%, respectively. The increase in the real permittivity was related to the formation of a large number of nanocapacitor structures, i.e., MWCNTs as nanoelectrodes and polymer matrix as dielectric material, i.e., interfacial polarization. The increase in the imaginary permittivity with MWCNT loading was attributed greater number of dissipating charges, enhanced conductive network formation, and boosted polarization loss arising from interfacial polarization. It was also observed that the real and imaginary permittivities were frequency independent in the insulative region, whereas they decreased drastically with frequency in the conductive region. The descending trend of real permittivity with frequency in the conductive region was related to charge polarization relaxation, whereas the reduction in imaginary permittivity with frequency was attributed to lower Ohmic loss and polarization loss. POLYM. ENG. SCI., 55:173–179, 2015. © 2014 Society of Plastics Engineers     

热塑性聚氨酯／纳米铜复合材料的制备与表征

选择热塑性聚氨酯（PU）为基体材料,用自制纳米铜颗粒代替铜丝或铜管等块体铜,采用机械共混的方法制备了一种全新的宫内节育器（IUD）材料——聚氨酯／纳米铜复合材料,并采用红外光谱（FFIR）分析、X射线衍射（XRD）分析、扫描电镜分析（SEM）、力学性能测试、热重分析等表征方法对自制纳米铜粉和复合材料的结构及性能进行了表征。结果表明,利用液相还原法成功制备了纳米级铜粉,聚氨酯／纳米铜复合材料的拉伸强度、撕裂强度随着纳米铜含量的增加略有增加,热稳定性随着纳米铜含量的增加稍有降低,为下一步复合材料铜离子的可控释放研究工作提供了很好的基础。     

Electrical properties of polycarbonate/expanded graphite nanocomposites

In present study, polymer matrix nanocomposites based on polycarbonate as matrix and expanded graphite (EG) as reinforcement were fabricated using a simple solution method followed by hot pressing. Scanning electron microscopy revealed almost uniform dispersion and three dimensional networks of EG particles in the matrix. The dc and ac electrical conductivities of the nanocomposites increased with increasing EG content in the matrix. The electrical percolation threshold was observed between 1 and 2 wt % EG. The improvement in the conductivity of 10 wt % nanocomposite was found more than 13 orders of magnitude higher than that of pure matrix. The dielectric constant (at 1 MHz) of the nanocomposite containing 10 wt % EG was increased to about 137. The significant increase in electrical conductivity, dielectric constant, and dissipation factor for the nanocomposites might be good for the applications in antistatic/electromagnetic interference shielding applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47274.     

Synthesis and characterization of polyurethane/Mg‐Al layered double hydroxide nanocomposites

Layered double hydroxide (LDH) is a new type of nanofiller, which improves the physicochemical properties of the polymer matrix. In this study, 1, 3, 5, and 8 wt % of dodecyl sulfate‐intercalated LDH (DS‐LDH) has been used as nanofiller to prepare a series of thermoplastic polyurethane (PU) nanocomposites by solution intercalation method. PU/DS‐LDH composites so formed have been characterized by X‐ray diffraction and transmission electron microscopy analysis which show that the DS‐LDH layers are exfoliated at lower filler (1 and 3 wt %) loading followed by intercalation at higher filler (8 wt %) loading. Mechanical properties of the nanocomposite with 3 wt % of DS‐LDH content shows 67% improvement in tensile strength compared to pristine PU, which has been correlated in terms of fracture behavior of the nanocomposites using scanning electron microscope analysis. Thermogravimetric analysis shows that the thermal stability of the nanocomposite with 3 wt % DS‐LDH content is ≈ 29°C higher than neat PU. Limiting oxygen index of the nanocomposites is also improved from 19 to 23% in neat PU and PU/8 wt% DS‐LDH nanocomposites, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Reaction kinetics and characteristics of polyurethane/clay nanocomposites

The reaction behavior and physical properties of polyurethane (PU)/clay nanocomposite systems were investigated. Organically modified clay was used as nanofillers to formulate the nanocomposites. Differential scanning calorimetry was used to study the reaction behavior of the PU/clay nanocomposite systems. The reaction rate of the nanocomposite systems increased with increasing clay content. The reaction kinetic parameters of proposed kinetic equations were determined by numerical methods. The glass transition temperatures of the PU/clay nanocomposite systems increased with increasing clay content. The thermal decomposition behavior of the PU/clay nanocomposites was measured by using thermogravimetric analysis. X‐ray diffractometer and transmission electronic microscope data showed the intercalation of PU resin between the silicate layers of the clay in the PU/clay nanocomposites. A universal testing machine was used to investigate the tensile properties of the PU/clay nanocomposites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1641–1647, 2005     

Comparative study of electromagnetic interference shielding properties of injection molded versus compression molded multi-walled carbon nanotube/polystyrene composites

This study compares electromagnetic interference (EMI) shielding properties of injection molded versus compression molded multi-walled carbon nanotube/polystyrene (MWCNT/PS) composites, i.e., properties such as EMI shielding effectiveness (EMI SE), electrical conductivity, real permittivity and imaginary permittivity. The injection molded (MWCNT-aligned) samples showed lower EMI shielding properties than compression molded (randomly distributed MWCNT) samples that was attributed to lower probability of MWCNTs contacting each other due to MWCNT alignment. The compression molded samples showed higher electrical conductivity and lower electrical percolation threshold than the injection molded samples. The compression molded samples at MWCNT concentrations of 5.00 and 20.0 wt.% showed real permittivity two times and imaginary permittivity five times greater than the injection molded samples. The EMI SE for the compression molded samples at MWCNT concentrations of 5.00 and 20.0 wt.% was 15.0 and 30.0 dB, respectively, significantly greater than EMI SE for the injection molded samples. Lower EMI SE for the injection molded samples was ascribed to lower electrical conductivity, real permittivity (polarization loss) and imaginary permittivity (Ohmic loss). Comparison of the EMI shielding properties of the compression molded versus injection molded samples confirmed that EMI shielding does not require filler connectivity; however it increases with filler connectivity.     

Subsurface mechanical properties of polyurethane/organoclay nanocomposite thin films studied by nanoindentation

A series of the exfoliated or intercalated PU/organoclay nanocomposite thin films were prepared by in situ polymerization of polyol/organoclay mixture, chain extender and diisocyanate. The surface mechanical properties of the PU/organoclay nanocomposite films were investigated by means of nanoindentation. The results show that the hardness, elastic modulus and scratch resistant of the nanocomposites dramatically improved with the incorporation of organoclay. This improvement was dependent on the clay content as well as the formation structure of clay in the PU matrix. At 3% clay content, the hardness and elastic modulus of intercalated nanocomposites increased by approximately 16% and 44%, respectively, compare to pure PU. For exfoliated nanocomposite, the improvements in these properties were about 3.5 and 1.6 times higher than the intercalated ones. The exfoliated PU nanocomposites also had greater hardness and showed better scratch resistance compared to the intercalated ones.     

Electrical properties of FeII‐terpyridine‐Modified cellulose nanocrystals and polycaprolactone/FeII‐CTP nanocomposites

Supramolecular crosslinked Fe^II‐terpyridine cellulose nanocrystals (Fe‐CTP) were prepared by surface modification of cellulose nanocrystals with 4′‐chloro‐2,2′:6′,2″‐terpyridine and subsequent reaction with Fe(II)SO₄. The prepared complex was characterized using transmission electron microscopy (TEM), ultraviolet spectroscopy (UV), thermogravimetric analysis (TGA), and measuring its electrical properties at temperatures from 25 to 70°C. Use of Fe‐CTP at loadings from 1% to 10% (wt. ratio) in nanocomposites with polycaprolactone polymer was investigated; the nanocomposites were characterized regarding their electrical properties, which studied using broadband AC‐relaxation spectroscopy in the frequency range between 0.1 Hz and 1 MHz. The results were compared to that of PCL nanocomposites containing multiwalled carbon nanotubes (CNT). Variation in real and imaginary parts of permittivity has been explained on the basis of interfacial polarization of fillers in the polymer medium. The percolation limit of the conductive CNT and Fe‐CTP as studied by ac conductivity measurements has also been reported. Fe‐CTP showed conductivity values in the range of semiconductors. PCL/Fe‐CTP nanocomposites showed conductivity values from 1.98 × 10⁻¹¹ to 3.76 × 10⁻⁶ while PCL/CNT nanocomposites showed conductivity values from 1.4 × 10⁻¹⁰ to 3.67 × 10⁻⁴ S/m for 1–10 wt% CNT content. POLYM. COMPOS., 37:2734–2743, 2016. © 2015 Society of Plastics Engineers     

Synthesis of graphite nanosheets/polyaniline nanorods composites with ultrasonic and conductivity

The graphite nanosheets/polyaniline (GN/PANI) nanorods composites were fabricated via ultrasonic polymerization of aniline monomer in the presence of GN, which was used as electric filling. The kind of doped acids, the concentration, and the contents of the GN were used as impact factors to the conductivity of the materials that were investigated. The structure of nanocomposites were characterized by FTIR and SEM. The results show that ultrasonic can effectively restrain the agglomerate of the aniline and come to uniformity nanorods composites. The conductivity reached to 4.8 S/cm and 22 S/cm, respectively. The thermal stability of GN/PANI nanorods composites is superior to pure PANI as shown by TG analysis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermally conducting polymer/nanocarbon and polymer/inorganic nanoparticle nanocomposite: a review

ABSTRACT

This review addresses fundamentals and progress in field of thermally conducting polymer/nanocarbon nanocomposite. Upsurge in thermal conductivity of materials may lead to rapid heat diffusion, which in turn may prevent degradation. Thermally conductive nanofillers (carbon nanotube, graphene, nanodiamond, inorganics) have been effectively employed to form desired nanocomposite. In polymer/nanocarbon nanocomposites, thermal conductivity depends on nanofiller type, dispersion, loading level, polymer nature, morphology, and crystallinity. Thermal conductivity parameter has been significantly considered in aerospace, automotive, electronics, and energy-related industries, where thermal dissipation has become a challenging problem. In future, it is desired to design high performance nanocomposites with manageable thermal conduction.     

Synthesis and characterization of elastomeric polyurethane and PU/clay nanocomposites based on an aliphatic diisocyanate

This investigation reports preparation of polyurethane and polyurethane/clay nanocomposites based on polyethylene glycol, isophorone diisocyanate (IPDI), an aliphatic diisocyanate and 1,4‐ Butanediol as chain extender by solution polymerization. In this case PU/clay nanocomposites were prepared via ex‐situ method using 1, 3, and 5 wt % of Cloisite 30B. Thermogravimetric analysis showed that the maximum decomposition temperature (T_max) of the PU/clay nanocomposite is much higher than the pristine PU. The tensile properties improved upon increasing the organoclay (Cloisite 30B) content upto 3 wt %, and then decreased to some extent upon further increasing the nanoparticle loading to 5 wt %. Optical properties of the nanocomposites were studied by UV‐vis spectrophotometer. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) were used to study the morphology of the nanocomposites. It was observed that with the incorporation of 3 wt % nanoclay the crystallinity in PU nanocomposite increases, then diminishes with further loading. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3328–3334, 2013     

A novel carbon nanotube nanopaper polyurethane coating for fiber reinforced composite substrates

High performance carbon nanotube (CNT) nanopaper (NP) reinforced polyurethane (PU) nanocomposite coating with high potential for aerospace and automotive applications was successfully fabricated and evaluated in this work. Different PU formulations were used to fabricate nanocomposites to study the effect of hard segment content on resin infiltration and nanocomposite mechanical properties. The process window of PU infiltration into the CNT NP was established by rheology measurements and thermal gravimetric analysis (TGA). The micro-structure morphology of the nanocomposite was characterized by scanning electron microscope (SEM). Uniform CNT distribution in PU matrix was observed in the high-resolution SEM images, which indicated good resin impregnation quality. Based on mechanical properties and process window, a PU formulation was selected as matrix to fabricate NP/PU nanocomposite coating for carbon fiber/epoxy composites (CFPC) substrate. The flexural strength and impact resistance of the CFPC were significantly improved by 9% and 14.7% after applying the NP/PU nanocomposite coating. Aimed at industrial applications, a continuous nanopaper fabrication process was successfully demonstrated in this work. Through the process window study, a continuous process to fabricate nanocomposite is proposed for future scale-up.     

Thermal and dielectric properties of low-density polyethylene/NaA zeolite composites

The effect of the weight fraction of NaA zeolite on thermal properties (specific heat capacity, thermal diffusivity, thermal conductivity) and dielectric properties (electrical conductivity, real and imaginary electric permittivity) of composites based on low-density polyethylene (LDPE) and NaA zeolite is examined. Composite samples containing from 5 to 30 wt% zeolite are prepared using the compression molding technique. The degree of dispersion and the weight fraction of filler in the LDPE/NaA zeolite composites are determined using X-ray diffraction. A linear decrease in the values of the specific heat capacity with an increase in the weight fraction of zeolite is observed using differential scanning calorimetry. The laser flash method is used to determine the thermal diffusivity of the composites. An increase in effective thermal diffusivity and abrupt increase in the range from 15 to 20 wt% of zeolite are established. It is demonstrated that effective thermal conductivity increases with an increase in the weight fraction of zeolite, and an abrupt increase in the range from 15 to 20 wt% is observed. Dielectric spectroscopy measurements are performed to determine the real and imaginary parts of permittivity. An increase of real and imaginary parts of permittivity of LDPE/NaA zeolite composites, with increasing weight fraction of zeolite, is established. Two relaxation peaks of the imaginary parts of permittivity of LDPE/NaA zeolite composites are detected. An increase of electrical conductivity with increasing weight fraction of zeolite and abrupt increase in the range 15 to 20 wt% are noticed. © 2021 Society of Industrial Chemistry.