Low Filler Content Research Articles

A biomass derived porous carbon for broadband and lightweight microwave absorption

With the continuous progress of science and technology, the traditional magnetic material is no longer able to meet the new complex electromagnetic (EM) environment due to its high bulk density. Therefore, the novel excellent EM absorber with the feature of thin thickness, low density, broad absorption bandwidth and strong absorption intensity is highly desired. Herein, we fabricated a porous carbon with ultrahigh porosity through a facile KOH activation from biomass waste pumpkin seed shell for lightweight EM wave absorption application. By optimizing the porous structures, the strong absorption intensity of −50.55 dB is achieved at thin thickness of 1.85 mm under low filler content of only 10 wt %. More interestingly, a broad frequency bandwidth of 7.4 GHz could cover the whole Ku band. These outstanding microwave absorption performances, couple with low cost ingredients and ease of fabrication process enable the porous carbon framework as the next generation promising candidate for lightweight and remarkable EM absorber.

Bioinspired modification strategy to improve thermal conductivity of flexible poly(vinyl alcohol)/nanodiamond nanocomposite films for thermal management applications

Polymer nanocomposites with high thermal conductivity (K) have promising prospects in thermal management. However, how to achieve good dispersion and strong interfacial adhesion between nanofillers and polymers, and to obtain optimal K at low filler concentrations remains a challenging subject. Here, bioinspired dopamine chemistry was used to form thin polydopamine (PDA) coatings on the surface of nanodiamond (ND) particles (ND@PDA). A series of nanocomposite films consisting of ND@PDA and poly(vinyl alcohol) (PVA) was fabricated via a facile solution casting technique. PDA with strong adhesion and catechol groups remarkably improved interactions between the ND@PDA and the PVA matrix. DSC and XRD data show that crystallinity of nanocomposites is greatly improved with increasing ND@PDA concentrations. As a result, a significantly high K value of 5.864 W/mK was obtained with filler loadings of 10 wt%, which was about 1780% higher than that of neat PVA. The results show that dopamine chemistry-modified ND effectively suppress the phonon scattering at the matrix-filler interface and facilitate efficient transfer of phonons. Moreover, the incorporation of 10 wt% ND@PDA shows considerable enhancement in mechanical performance (35.38 MPa), volume resistivity (6.088 × 1015 Ω cm) and thermal stability. These highly thermal conductive and electrical insulating polymer nanocomposites with low filler loadings are expected to achieve a wide range of thermal management applications.

The mixture of silver nanowires and nanosilver-coated copper micronflakes for electrically conductive adhesives to achieve high electrical conductivity with low percolation threshold

For electrically conductive adhesives (ECAs), it is critical to ensure high electrical conductivity and good adhesion reliability for practical applications in electronic products. In this study, high conductivity ECAs at low filler content were achieved by fully utilizing the synergistic effect of nano- and micro-scale fillers. Nanosilver-coated copper micronflakes (Ag@Cus) prepared by an electroless plating method were selected as the main conductive fillers. Silver nanowires (AgNWs) made by a simple one-step polyol method were dispersed as auxiliary conductive fillers in Ag@Cus, providing more possibilities for establishing a large number of conductive bridges. Furthermore, the curing process of matrix resin was predicted based on curing kinetics and was verified by corresponding experiments to determine the optimal curing parameters. The results show that the combination of AgNWs and Ag@Cus in ECAs can significantly reduce the bulk resistivity and percolation threshold compared with the single component. In particular, the bulk resistivity of ECAs filled with AgNWs and Ag@Cus (mass ratio 1:9) is as low as 9.42 × 10−5 Ω cm when the filler content is only 60 wt%.

Micro‐tomographic characterization of composite recycled glass‐silicone foams for applications in civil engineering

ABSTRACTNoninvasive X‐ray micro‐computed tomography was applied for a complete quantitative and qualitative analysis of the cellular structure of composite foams constituted by a silicone matrix and a glass production waste filler. Composite foams with different glass filler weight content in the range 0–80% were synthesized and characterized. The tomographic analysis was employed in order to assess the structural heterogeneities, void fraction values, and bubble size distribution for all composite foams. The 3D micro‐CT images analysis, performed at different cross‐sections, highlighted heterogeneous cell growth or more elongated cells in the case of low and high filler content foams, respectively. Batch with 60% of glass filler was identified as a composite foam with effective void fraction values and relatively uniform spheroidal cellular structure (average sphericity 0.723 and diameter 0.107 mm). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48718.

Substantially improving mechanical property of double percolated poly(phenylene sulfide)/poly(arylenesulfide sulfone)/graphene nanoplates composites with superior electromagnetic interference shielding performance

ABSTRACTThe electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) can be conspicuously enhanced at low conductive filler contents with the formation of segregated structure in the conductive polymer composites (CPCs). Nevertheless, poor interface adhesion of segregated composites results in poor mechanical properties due to the selective distribution of conductive fillers. In this work, a flexible approach was applied to fabricate the poly(phenylene sulfide)/poly(arylene sulfide sulfone)/graphene nanoplates (GNPs) composite with a unique double percolated structure. This composite exhibits an outstanding EMI SE of 38.8 dB with only 3 wt % GNPs, which is comparable to that of the conventional segregated structure counterpart. What is more, the tensile strength and Young's modulus of double percolated composites with 3 wt % GNPs are remarkably improved by ~892 and ~274% compared to conventional segregated structure, achieving 37.7 and 1788.3 MPa, respectively. This work provides a valuable method for producing CPCs with high EMI shielding performances and outstanding mechanical properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48709.

Influence of inorganic filler content of resin luting agents and use of adhesive on the performance of bonded ceramic

Statement of problemThe inorganic filler of resin-based luting agents and the use of an adhesive layer could influence the bonding ability, mechanical performance, and interface morphology of bonded feldspathic ceramic. PurposeThe purpose of this in vitro study was to investigate the influence of resin-based luting agents loaded with different inorganic filler content, with or without an adhesive, on microtensile bond strength, biaxial flexural strength, and the adhesive interface morphology of bonded ceramic specimens. Material and methodsExperimental resin-based luting agents with low (55wt%), intermediate (65wt%), and high (75wt%) filler contents were bonded to ceramic specimens, with or without a layer of adhesive. The resin-based luting agents were characterized by measuring viscosity, elastic modulus, Poisson ratio, and degree of conversion (n=3 for each test). The response variables for the bonded ceramic specimens were ceramic-resin microtensile bond strength (n=30), biaxial flexural strength (n=30) and characteristic strength, and Weibull modulus. Scanning electron microscopy was used for fractographic and interface analyses of the specimens fractured in the microtensile test (n=3). Data were subjected to ANOVA with the post hoc Tukey test (α=.05). Weibull moduli were also calculated. ResultsIncreased inorganic filler content yielded significantly higher viscosity, stiffness, and film thickness. However, the Poisson ratio and degree of conversion were not affected. The lowest bond strength values were observed for the resin-based luting agents with high inorganic filler content when no adhesive was used and for the resin-based luting agent with low filler content when the adhesive was used. The increase in filler content of the resin-based luting agent appeared to be associated with a higher frequency of mixed failures. Increased filler content resulted in higher biaxial flexural and characteristic strength and decreased structural reliability. The adhesive helped fill irregularities on ceramic and slightly increased film thickness but had only a minor effect on mechanical strength. ConclusionsExperimental resin-based luting agent loaded with high inorganic filler content strengthened the bonded feldspathic ceramic and yielded significantly higher viscosity and film thickness. In contrast, the bond strength was lower if no adhesive was used.

Cotton Candy-Templated Fabrication of Three-Dimensional Ceramic Pathway within Polymer Composite for Enhanced Thermal Conductivity.

With the minimization and higher power of electronic devices, materials with effective heat dissipation and high electrical insulation have attracted relentless interest. Especially, highly thermally conductive, highly electrically insulating but low filler content of polymer-based composites are desirable. Herein, a facile and eco-friendly cotton candy-templated method (CTM) to construct three-dimensional heat transport pathways inside epoxy resin is reported. The fabricated Al2O3/epoxy composites with enhanced heat transport capability feature a 15-fold increase in thermal conductivity at a filler content of 36.2 vol % compared to pristine epoxy. Moreover, the remarkable thermal conductive property has excellent stability over a wide range of temperature before and after heating and cooling cycles. Meanwhile, the CTM composite still retain highly electrical insulation. The cotton candy-templated method proposed in this work is a new avenue for the preparation of three-dimensional heat transport pathways within polymer-based composites for microelectronic packaging and electrical engineering systems.

High-efficiency electromagnetic interference shielding realized in nacre-mimetic graphene/polymer composite with extremely low graphene loading

Electromagnetic interference (EMI) shielding performance of composites are usually limited by their electrical conductivity and permeability, which largely depend on the conductive filler content, aspect ratio, magnetic permeability, etc. Higher filler content usually leads to high cost, poor dispersion and easy agglomeration, making the polymer composites mechanically brittle and difficult to process. Therefore, it is highly desirable to develop composite with low conductive filler content while maintaining its high EMI shielding performance. Here, in our work a high-performance EMI shielding was realized in nacre-mimetic graphene/polymer composites with extremely low graphene loading. A nacre-mimetic 3D conductive graphene network with biaxial aligned lamellar structure was prepared by a unique bidirectional freezing technique. With such a nacre-mimetic, highly aligned network, our graphene/polymer composites exhibit anisotropic conductivities, mechanical properties and therefore remarkable EMI shielding effectiveness at an extremely low graphene content. Specifically, the biomimetic composites with 0.42 wt% graphene content shows an enhanced EMI shielding effectiveness of ∼65 dB after annealing the graphene aerogels at 2500 °C, which is comparable to the copper foil. More remarkably, as the composite is low in density, its specific shielding effectiveness is even higher than that of metal foils and solid materials with high conductive filler content.

Enhanced mechanical and thermal properties of polyurethane‐imide foams with the addition of expended vermiculite

AbstractPolyurethane‐imide (PUI) foams, in combination with the mechanical performance of polyurethane and flame retardancy of polyimide, were prepared by polyimide prepolymer method. Expended vermiculite (EV), with a wider layer spacing than vermiculite, was used as the filler to further enhance the mechanical and thermal properties of the PUI foams. The effect of filler content on the morphology of foams was also investigated. The results showed that the mean cell diameter of foams became smaller and the cell size distribution was more uniform at low filler content. The addition of EV resulted in a substantial increase in thermal stability. The compression strength increased from 0.024 to 0.065 MPa with an increase in EV content from 0% to 9.6%. The limited oxygen index values increased from 24% to 30.8% with an increase in filler content from 0% to 9.6%. Hence, PUI foams could significantly enlarge its application range with the addition of EV.

Photothermal Polymer Nanocomposites of Tungsten Bronze Nanorods with Enhanced Tensile Elongation at Low Filler Contents.

We present polymer nanocomposites of tungsten bronze nanorods (TBNRs) and ethylene propylene diene monomers (EPDM). The combination of these components allows the simultaneous enhancement in the mechanical and photothermal properties of the composites at low filler contents. The as-synthesized TBNRs had lengths and diameters of 14.0 ± 2.4 nm and 2.5 ± 0.5 nm, respectively, and were capped with oleylamine, which has a chemical structure similar to EPDM, making the TBNRs compatible with the bulk EPDM matrix. The TBNRs absorb a wide range of near-infrared light because of the sub-band transitions induced by alkali metal doping. Thus, the nanocomposites of TBNRs in EPDM showed enhanced photothermal properties owing to the light absorption and subsequent heat emission by the TBNRs. Noticeably, the nanocomposite with only 3 wt% TBNRs presented significantly enhanced tensile strain at break, in comparison with those of pristine EPDM, nanocomposites with 1 and 2 wt % TBNRs, and those with tungsten bronze nanoparticles, because of the alignment of the nanorods during tensile elongation. The photothermal and mechanical properties of these nanocomposites make them promising materials for various applications such as in fibers, foams, clothes with cold weather resistance, patches or mask-like films for efficient transdermal delivery upon heat generation, and photoresponsive surfaces for droplet transport by the thermocapillary effect in microfluidic devices and microengines.

First MnO2-based electrorheological fluids: high response at low filler concentration

Nanoparticles of MnO2 with different shapes (needle-like α-MnO2 and spherical δ-MnO2) were proposed as promising fillers for electrorheological fluids (ERFs). A thorough study of the dielectric properties of α-MnO2 and δ-MnO2 suspensions in silicone oil enabled estimation of the values of their dielectric permittivity and dielectric relaxation times. The study of MnO2-filled materials with various filler contents, and under various electric field strengths, in shear and uniaxial tensile and compressive stress regimes, revealed that needle-like α-MnO2 nanoparticles, in comparison with spherical δ-MnO2 particles, lead to better mechanical properties of the fluids. The most intriguing property of MnO2-based electrorheological fluids is their high electrorheological response at low filler content: ERF containing only 4.5 vol.% of α-MnO2 in silicone oil demonstrated a 18 kPa tensile strength in a 5 kV electric field.

Significantly enhanced thermal conductivity in polyimide composites with the matching of graphene flakes and aluminum nitride by in situ polymerization

AbstractHighly thermally conductive polymer composites are urgently required for effective heat dissipation in advanced electronic devices. Rational matching of thermal conductive fillers and proper preparation method are important for obtaining a highly thermally conductive composites at low filler content. Here we report polyimide (PI) composites filled with graphene flakes (GF) and polyhedral aluminum nitride (AlN), which simultaneously exhibit high thermal conductivity, improved thermal mechanical properties, and excellent thermal stability. PI composite films were readily prepared by in situ polymerization at the presence of fillers that are dispersed with sonication. The thermal conductivity of PI composite films reached 11.19 Wm−1 K−1 at the low content of 1 wt% GF and 10 wt% AlN, which is ascribed to the construction of synergistically enhanced heat transfer pathways by the combination of the hybrid fillers. The PI composite films with hybrid fillers also showed lower electrical conductivity than that of the PI composite films with single GF filler. This study provides an effective method for preparation of high‐performance thermal management materials.

Review on recent progress in synthesis of graphene–polyamide nanocomposites

In polymer nanocomposites, graphene is possibly the most promising nanofiller. Graphene produces impressive properties for polymers at very low filler content, which makes it highly interesting in building high-performance materials compared to other classes of polymer nanocomposites. Graphene-modified polymer nanocomposites have attracted much attention in scientific literature because of the need of superior materials with desirable properties such as electrical, mechanical, thermal, flame retardant, and gas barrier. Frequent studies have been attempted to produce graphene–polyamide (G-PA) nanocomposites with novel and improved properties. Based on this review, one can identify the synthesis technique and preparation for G-PA nanocomposites, which can further be useful in numerous applications.

The dispersion of CNT in TPU matrix with different preparation methods: solution mixing vs melt mixing

Melt mixing and solution mixing are two commonly used methods for the preparation of polymer nanocomposites. In this work, thermoplastic polyurethane (TPU) composites with unmodified MWCNTs and carboxyl MWCNTs (MWCNT-COOH) were prepared using melt mixing and solution mixing. The dispersion of filler in TPU matrix and the macro-properties of composites under different processing conditions were systematically investigated. It was found that for pristine MWCNTs, a better dispersion was obtained using solution method at relatively low content of fillers (≤2.5 wt%); but when the content of MWCNT was above 2.5 wt%, melt mixing under high shear force was more effective to achieve a homogeneous dispersion. The similar result was confirmed in TPU/MWCNT-COOH composites, with the critical concentration shifted to 5.0 wt%, indicating that the interaction between CNT and TPU also played role on the dispersion of CNT in TPU matrix via solution mixing. Our finding is important for the preparation of polymer/CNT nanocomposites with good dispersion depending on the filler content and mixing methods.

Enhanced Dielectric Performance of P(VDF-HFP) Composites with Satellite–Core-Structured Fe2O3@BaTiO3 Nanofillers

Polymer dielectric materials are extensively used in electronic devices. To enhance the dielectric constant, ceramic fillers with high dielectric constant have been widely introduced into polymer matrices. However, to obtain high permittivity, a large added amount (>50 vol%) is usually needed. With the aim of improving dielectric properties with low filler content, satellite–core-structured Fe2O3@BaTiO3 (Fe2O3@BT) nanoparticles were fabricated as fillers for a poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) matrix. The interfacial polarization effect is increased by Fe2O3 nanoparticles, and thus, composite permittivity is enhanced. Besides, the satellite–core structure prevents Fe2O3 particles from directly contacting each other, so that the dielectric loss remains relatively low. Typically, with 20 vol% Fe2O3@BT nanoparticle fillers, the permittivity of the composite is 31.7 (1 kHz), nearly 1.8 and 3.0 times that of 20 vol% BT composites and pure polymers, respectively. Nanocomposites also achieve high breakdown strength (>150 KV/mm) and low loss tangent (~0.05). Moreover, the composites exhibited excellent flexibility and maintained good dielectric properties after bending. These results demonstrate that composite films possess broad application prospects in flexible electronics.

Improvement in mechanical and thermal properties of polypropylene nanocomposites using an extremely small amount of alkyl chain-grafted hexagonal boron nitride nanosheets

In this study, hexagonal boron nitride nanosheets grafted with aliphatic groups (Alkyl-BN) were synthesized by a sonication-assisted alcoholysis reaction using hexagonal boron nitride (hBN) with 1-dodecanol, and a series of polypropylene (PP) nanocomposites were prepared by mixing PP with different amount of Alkyl-BN. The PP/Alkyl-BN nanocomposite containing a very small amount of Alkyl-BN showed much improved mechanical properties than those of neat PP and PP/hBN nanocomposites. For instance, Young's modulus value of PP/Alkyl-BN nanocomposite containing 0.5 wt% of Alkyl-BN is larger than that of neat PP by 17.5% while that of PP/hBN nanocomposite containing 0.5 wt% of hBN is larger by only 1.2%. The tensile strength value of PP/Alkyl-BN was found to be larger than that of the neat PP by 7.4% due to the enhanced interfacial interaction between Alkyl-BN and PP chains. Furthermore, the PP/Alkyl-BN nanocomposites exhibited enhanced thermal conductivity and stability than the neat PP and PP/hBN nanocomposite. This research clearly shows that the improved thermal and mechanical properties of polymer nanocomposites can be achieved with a very low filler content by the enhancement of the interfacial interaction between the filler materials and the polymer matrix.

Polyacrylonitrile/liquid crystalline graphene oxide composite fibers – Towards high performance carbon fiber precursors

We have prepared high performance, continuous carbon fiber precursors mimicking the industrial processing by wet spinning technology using polyacrylonitrile (PAN)/liquid crystalline graphene oxide (LCGO) for the first time. This work highlights the unexplored production of novel PAN composite fibers with addition of very low percentage of LCGO without using any surface modifications or coating. Following the coagulation process, as spun PAN/LCGO fibers were passed through a series of wash baths operated at various temperatures and multiple hot stretching baths prior to drying, and taken-up using a traversing winder. Current study also investigates the chemical and microstructural changes of PAN due to the addition of very low amounts of GO without the use of binders or surface treatments. The tensile strength and tensile modulus of the fibers were significantly improved with low filler content up to 1 wt% of LCGO into PAN dope that is, a 115% improvement of tensile strength and 152% increase of tensile modulus were achieved at a filler loading of 0.5 wt% whereas 138% improvement in tensile strength at 1 wt% of LCGO. This study revealed that it is possible to produce high strength precursor fibers by wet spinning with the addition of low filler content by make use of LCGO in PAN solution; this can further provide pathways for making high performance carbon fibers.

Low percolation 3D Cu and Ag shell network composites for EMI shielding and thermal conduction

Metal-coated polymer bead based composites are promising as electromagnetic interference (EMI) shielding and thermally conductive materials because they form a percolation 3D metal shell network at very low filler content. Herein, we fabricated 3D Cu/Ag shell network composites through electroless plating of metal on polymer beads and a simple hot pressing technique. Cu and Ag shells provide a continuous network for electron and heat conduction; thus, yielding excellent EMI shielding effectiveness of 110 dB at a 0.5 mm thickness and a thermal conductivity of 16.1 W m−1K−1 at only 13 vol % of metal filler. The properties of composites depend on the size of polystyrene (PS) beads and large size metal-coated PS bead composites exhibit higher electrical conductivity, EMI shielding effectiveness, and thermal conductivity than small size bead composites. These results are ascribed to the reduction in the number of contact interfaces between metal-coated beads, which minimizes the interfacial resistance. This study is set to pave the way for designing advanced EMI shielding and thermal conductive materials by a scalable and efficient synthesis approach.

Nanofibrous poly(ethylene oxide)‐based structures incorporated with multi‐walled carbon nanotube and graphene oxide as all‐solid‐state electrolytes for lithium ion batteries

AbstractNanofibrous solid polymer electrolytes were prepared using the electrospinning method. These nanofibres were constructed from poly(ethylene oxide), lithium perchlorate and ethylene carbonate, which were incorporated with multi‐walled carbon nanotube (MWCNT) and graphene oxide (GO). The morphological properties of the as‐prepared electrolytes and the interaction between the components of the composites were characterized using scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. X‐ray spectra and differential scanning calorimetry indicated an increase in amorphous regions of the nanofibrous electrolytes on addition of the fillers. However, the crystalline regions were increased on incorporation of fillers into polymeric film electrolytes. The conductivity values of the nanofibrous electrolytes reached 0.048 and 0.057 mS cm−1 when 0.35 wt% MWCNT and 0.21 wt % GO were introduced into the nanofibrous structures, respectively. The capacity and cycling stability of the nanofibrous electrolytes were improved by incorporation of MWCNT filler. Furthermore, stress and elongation modulus were improved at low MWCNT and GO filler contents. Results revealed that the nanofibrous structures could be promising candidates as solvent‐free electrolytes applicable in lithium ion batteries. © 2019 Society of Chemical Industry

Modification of mechanical and color properties of polypropylene with colored nano‐SiO2 prepared from diatomite

ABSTRACTDiatomite powder was dissolved in alkali to form sodium silicate, which was then used to prepare colored nano‐SiO2 (CNS) by the process of chemical precipitation. The CNS was analyzed by means of X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. To explore the application of colored nano‐SiO2 in polypropylene (PP), CNS was incorporated into PP T30s. The mechanical and colorimetric properties of prepared CNS/PP composites were also investigated. The results of tensile tests indicated that the nanoparticles could simultaneously provide PP with stiffening, strengthening, and toughening effects at a low filler content (typically 2% by volume). At the same time, with CNS filler, the PP composites acquired a bright red color. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48328.