High Filler Content Research Articles

A Malleable Composite Dough with Well-Dispersed and High-Content Boron Nitride Nanosheets.

Aggregation of two-dimensional (2D) nanosheet fillers in a polymer matrix is a prevalent problem when the filler loading is high, leading to degradation of physical and mechanical properties of the composite. To avoid aggregation, a low-weight fraction of the 2D material (<5 wt %) is usually used to fabricate the composite, limiting performance improvement. Here, we develop a mechanical interlocking strategy where well-dispersed high filling content (up to 20 wt %) of boron nitride nanosheets (BNNSs) can be incorporated into a polytetrafluoroethylene (PTFE) matrix, resulting in a malleable, easy-to-process and reusable BNNS/PTFE composite dough. Importantly, the well-dispersed BNNS fillers can be rearranged into a highly oriented direction due to the malleable nature of the dough. The resultant composite film has a high thermal conductivity (4408% increase), low dielectric constant/loss, and excellent mechanical properties (334%, 69%, 266%, and 302% increases for tensile modulus, strength, toughness, and elongation, respectively), making it suitable for thermal management applications in the high-frequency areas. The technique is useful for the large-scale production of other 2D material/polymer composites with a high filler content for different applications.

Enhanced Microwave Absorption for High Filler Content Composite Molded from Polymer Coated Flaky Carbonyl Irons Modified by Silane Coupling Agents

Enhanced Microwave Absorption for High Filler Content Composite Molded from Polymer Coated Flaky Carbonyl Irons Modified by Silane Coupling Agents

Size matters: asphaltenes with enlarged aromatic cores promote heat transfer in organic phase-change materials.

Recent experiments and atomistic computer simulations have shown that asphaltene byproducts of oil refineries can serve as thermal conductivity enhancers for organic phase-change materials such as paraffin and therefore have the potential to improve the performance of paraffin-based heat storage devices. In this work, we explore how the size of the polycyclic aromatic cores of asphaltenes affects the properties of paraffin-asphaltene systems by means of atomistic molecular dynamics simulations. We show that increasing the size of the asphaltene core from 7-8 aromatic rings to ∼20 rings drastically changes the aggregation behavior of asphaltenes. Instead of relatively small, compact aggregates formed by small-core asphaltene molecules, enlarged cores promote the formation of extended single-column structures stabilized in paraffin by asphaltene's aliphatic periphery. Chemical modification of the asphaltenes by removing the periphery leads to the formation of bundles of columns. In contrast to small-core molecules, asphaltenes with enlarged cores do not suppress paraffin crystallization even at high filler concentrations. Remarkably, asphaltenes with enlarged aromatic cores are able to increase the thermal conductivity of liquid paraffin to a greater extent compared to their small-core counterparts. This effect becomes even more pronounced for modified asphaltenes without the aliphatic side groups. Overall, our computational findings suggest that asphaltenes with enlarged aromatic cores can significantly improve the performance of heat storage devices based on organic phase change materials.

Polystyrene Waste Recycling Process as an Alternative Antistatic Packaging Raw Material

Composite synthesis from styrofoam (polystyrene-based) was carried out by solvent blending method in which the solvent used was gasoline. The carbon black (CB) was used as filler comes from coconut shells. The samples were given a variation of filler composition: 0, 1, 3, and 5% of the total weight of the composite to be formed. In this method, stirring was carried out for at least 120 minutes (200 rpm in atmospheric conditions). The stirring process is carried out until the mixture becomes homogeneous, as indicated by the slurry formation. After that, the process continues to the printing stage using glass mold and drying in a windy room that is sufficiently exposed to sunlight for 3 days. The sample obtained is a composite measuring 8 cm x 8 cm. The tests carried out were the ATR-FTIR, SEM, conductivity, and mechanical tests. From the results of the ATR-FTIR test, there was no visible difference between the styrofoam before being treated with the composites, thus proving that the solvent had evaporated. The results of the SEM test show that there are lumps in the sample with higher filler concentrations, so it is possible to need additional time or stirring speed to distributed the filler evenly. Meanwhile, the conductivity test proved that the addition of carbon-based filler could increase the conductivity of the composites.

Response-Surface-Methodology-Based Increasing of the Isotropic Thermal Conductivity of Polyethylene Composites Containing Multiple Fillers.

To optimize the thermal conductivity of high-density polyethylene, 15 hybrid filler composites containing either aluminum oxide, graphite, expanded graphite, carbon nanotubes or a combination of the former, have been studied using an extrusion-compression processing tandem. The experimental density of the cube-shaped specimens is substantially lower than the theoretical density calculated by the linear mixing rule, mainly for the composites with high filler contents. The morphology of the composites, as studied by scanning electron microscopy (SEM), highlighted a good dispersion quality and random orientation of the fillers in the test specimens but also revealed air inclusions in the composites, explaining the density results. It is shown that the addition of filler(s) increases both the melt viscosity (up to ca. 270%) and the thermal conductivity (up to ca. 1000%). Hence, a very strong increase of TC can be practically hampered by a too high viscosity to enable processing. Supported by ANOVA analysis, the application of response surface methodology (RSM), assuming a perfect compression, indicates that all fillers have a significant effect on the thermal conductivity and synergistic effects can be achieved. The regression model obtained can adequately predict the thermal conductivity of composites of various compositions, as already confirmed based on three validation experiments in the present work.

Versatile Polypropylene Composite Containing Post-Printing Waste.

The paper presents the results of the research on the possibility of using waste after the printing process as a filler for polymeric materials. Remains of the label backing were used, consisting mainly of cellulose with glue and polymer label residue. The properly prepared filler (washed, dried, pressed and cut) was added to the polypropylene in a volume ratio of 2:1; 1:1; 1:2; and 1:3 which corresponded to approximately 10, 5, 2.5 and 2 wt % filler. The selected processing properties (mass flow rate), mechanical properties (tensile strength, impact strength, dynamic mechanical analysis) and thermal properties (thermogravimetric analysis, differential scanning calorimetry) were determined. The use of even the largest amount of filler did not cause disqualifying changes in the determined properties. The characteristics of the obtained materials allow them to be used in various applications while reducing costs due to the high content of cheap filler.

Effect of Micro- and Nano-Lignin on the Thermal, Mechanical, and Antioxidant Properties of Biobased PLA-Lignin Composite Films.

Bio-based poly(lactic acid) (PLA) composite films were produced using unmodified soda micro- or nano-lignin as a green filler at four different contents, between 0.5 wt% and 5 wt%. The PLA-lignin composite polymers were synthesized by solvent casting to prepare a masterbatch, followed by melt mixing. The composites were then converted into films, to evaluate the effect of lignin content and size on their physicochemical and mechanical properties. Differential scanning calorimetry (DSC), supported by polarized light microscopy (PLM), infrared spectroscopy (FTIR-ATR), X-ray diffraction (XRD), and transmission electron microscopy (TEM) were employed to investigate the PLA crystallization and the interactions with Lignin (L) and Nanolignin (NL). The presence of both fillers (L and NL) had a negligible effect on the glass transition temperature (chain diffusion). However, it resulted in suppression of the corresponding change in heat capacity. This was indicative of a partial immobilization of the PLA chains on the lignin entities, due to interfacial interactions, which was slightly stronger in the case of NL. Lignin was also found to facilitate crystallization, in terms of nucleation; whereas, this was not clear in the crystalline fraction. The addition of L and NL led to systematically larger crystallites compared with neat PLA, which, combined with the higher melting temperature, provided indications of a denser crystal structure in the composites. The mechanical, optical, antioxidant, and surface properties of the composite films were also investigated. The tensile strength and Young's modulus were improved by the addition of L and especially NL. The UV-blocking and antioxidant properties of the composite films were also enhanced, especially at higher filler contents. Importantly, the PLA-NL composite films constantly outperformed their PLA-L counterparts, due to the finer dispersion of NL in the PLA matrix, as verified by the TEM micrographs. These results suggest that bio-based and biodegradable PLA films filled with L, and particularly NL, can be employed as competitive and green alternatives in the food packaging industry.

Multiphase approach for calculation of tunneling conductivity of graphene-polymer nanocomposites to optimize breast cancer biosensors

A multiphase approach for the estimation of the electrical conductivity of graphene-based products from the properties of graphene, tunnels, and interphase is proposed. First, a simple model estimates the conductivity of interphase around the nanosheets, and subsequently, the conductivity of pseudoparticles containing graphene, tunnels, and interphase is estimated. Finally, a progressed model estimates the conductivity of the systems containing a polymer and pseudoparticles. The predictions of the multiphase technique were evaluated through comparison with experimented values and by parametric analyses. The predictions showed good agreement with the experimental values. Furthermore, the results of parametric studies supported the correctness of the multiphase technique. Thin and large graphene nanosheets can increase the conductivity to 0.14 S/m, and a high filler concentration and the presence of large tunnels could enhance the conductivity to 50 S/m. The maximum conductivity of 0.016 S/m is gained by an interphase depth of 10 nm and a filler conduction of 2.5 × 105 S/m. The developed model can be used for optimizing breast cancer biosensors since the conductivity is the main factor for detection.

Quantifying structure and dynamics of bound and bulk polymer in tailor-made rubber-silica nanocomposites

The dynamics of long polymer chains in the presence of nanoparticles have been investigated. The nanocomposites of interest were inspired by tire industry-like rubber materials and consisted of entangled polyisoprene linear chains mixed with chemically pre-treated silica nanoparticles. Combining rheology, dielectric spectroscopy, and neutron spin echo measurements, we measured the modification of the polymer chain dynamics from bulk state to high filler concentration over a broad range of time and length scales. We show that the end-to-end relaxation does not seem to be impacted, whereas the polymer dynamics is significantly slowed down at a very local scale in the presence of nano-fillers. In addition to this length scale dependent different dynamics, additional Neutron Spin Echo spectroscopy experiments and Small Angle Scattering on labelled polymer chains, irreversibly bound to the filler surface and re-dispersed in a fully deuterated matrix, revealed a negligible dynamical behavior of this particular population of localized chains in the rubber layer. The conformational statistics of these chains is that of self-avoiding walk train within a shell that is thinner than the size of the chain. To the best of our knowledge, this work is the first of its kind which measures the single chain form factor in the bound layer of chemically multi-linked chains to the filler surface.

Influence of the filler distribution on PDMS-graphene based nanocomposites selected properties

Insufficient homogeneity is one of the pressing problems in nanocomposites’ production as it largely impairs the properties of materials with relatively high filler concentration. Within this work, it is demonstrated how selected mixing techniques (magnetic mixer stirring, calendaring and microfluidization) affect filler distribution in poly(dimethylsiloxane)-graphene based nanocomposites and, consequently, their properties. The differences were assessed via imaging and thermal techniques, i.a. Raman spectroscopy, differential scanning calorimetry and thermogravimetry. As microfluidization proved to provide the best homogenization, it was used to prepare nanocomposites of different filler concentration, whose structural and thermal properties were investigated. The results show that the concentration of graphene significantly affects polymer chain mobility, grain sizes, defect density and cross-linking level. Both factors considered in this work considerably influence thermal stability and other features which are crucial for application in electronics, EMI shielding, thermal interface materials etc.

Adaptable thermal conductive, high toughness and compliant Poly(dimethylsiloxane) elastomer composites based on interfacial coordination bonds

Compliant elastomers have been widely used in industry and daily life benefited from their large reversible deformability. But poor thermal conductivity and toughness of unfilled elastomers usually limit their use in thermal management. The most common method to increase these properties is to incorporate thermally conductive fillers to polymeric materials. However, thermally conductive network formed by the large of fillers not only decreases the elastomeric compliance, but may also damages the toughness. Herein, to study the effect of polymer/filler interfacial interaction on thermal and mechanical properties, we choose shorter poly(dimethylsiloxane) without entanglement to construct elastomer composites by non-covalent interfacial carboxyl/aluminum and carboxyl/zinc oxide coordination bonds. Time-domain thermoreflectance technique demonstrates that the strong interfacial interaction leads to reduced interfacial thermal resistance between polymeric materials and fillers, resulting in enhanced thermal conductivity of the elastomer composites. Otherwise, two independent dynamic coordination bonds have been investigated on temperature- and frequency-sweep rheometer. The results reveal that the elastomer composites can counteract the negative effect of high filler content on toughness and compliance according to energy-dissipation of dissociation and generation of dynamic coordination bonds. Thanks to the enhanced interfacial interaction, our material shows high toughness (1073 J/m2), thermally conductive (2.37 W/(m·K)), compliant (stress is 0.11 MPa and elongation break is 910%) and fully reprocess. For the application as thermal interface materials, we demonstrate effective heat dissipation on chip and LED. Our present work suggests that the design principles based on interfacial coordination interaction can be applied to the development of new classes of elastomer composites.

Designing Approach of Fiber‐Reinforced Polymer Composite by Combination of Fibrillated Olive Pomace and Marble Powder

AbstractThe development of effective methods to utilize industrial and agricultural wastes is crucial from the perspective of a circular economy. Marble powder and olive pomace (OP), byproducts of olive oil production and marble processing, are considered one of the major sources causing severe environmental pollution, especially in Mediterranean countries. Herein, marble powder and OP are aimed to use as fillers in polypropylene (PP)‐based polymer composite. In addition, fractionated OP is further fibrillated by a combination of mechanical grinding and ionic liquid treatment to enhance its performance as a reinforcement. After treatment for 24 h, the particle size decreases from about 2.1 to 1.1 µm, and the lignocellulosic composition also varies due to the partial removal of hemicellulose. Finally, the compounding ratio of polymer composites consisting of PP, marble powder, fibrillated OP, and compatibilizer is optimized using response surface methodology (RSM) to achieve both high mechanical properties and high filler contents. Mechanical properties of polymer composite fabricated with optimum ratio are in excellent agreement with those predicted by RSM. Furthermore, the yield strength and Young's modulus of polymer composite are 33.9 MPa and 1.89 GPa, accordingly, which are higher than those of PP.

High content of spherical nanosilica filled epoxy resin master batch with low viscosity and superior thermomechanical performance

Spherical nanosilica is reckoned as an indispensable filler in electronic encapsulation to improve the thermomechanical performance of epoxy resin matrix. How to achieve higher content and better dispersion of spherical nanosilica in epoxy resin remains a big challenge. Here, Surface-modified spherical nanosilica was prepared on the basis of Stöber method in the presence of binary silane coupling agents as surface modifier. High content of as-modified spherical nanosilica was introduced into bisphenol F epoxy resin (denoted as EP) matrix by one-step liquid-phase method to afford SiO2/EP master batch. The viscosity, thermal stability and dynamic thermo-mechanical properties of SiO2/EP composites with different filler contents derived from SiO2/EP master batch were systematically investigated. Findings indicate that organosilanes grafted onto the surface of silica nanoparticles contribute to improving their compatibility and dispersibility within EP matrix, leading to a relatively low level of viscosity of EP-matrix composites especially under a high nanofiller dosage and improving their dynamic thermomechanical properties and thermal expansion stability as well. Moreover, SiO2/EP master batch made from liquid-phase method exhibits better performance compared with that prepared by physical blending way. It is a facile way to prepare EP master batch with high filler content, low viscosity and superior performance, meanwhile brings processing convenience for application in electronic encapsulation.

Influence of iron tailing filler on rheological behavior of asphalt mastic

• Limestone filler (LF) was substituted by iron tailing filler (ITF) in mastics under different f/b ratios. • The interaction between ITF and asphalt matrix was primarily physical. • ITF possessed a superior stiffening effect on mastics than LF. • A new index Δ T d was proposed to quantify the low-temperature performance of ITF mastics. • The substitution of ITF should be controlled within 1.0 f/b ratio. Iron tailings, one kind of widespread solid waste, were preliminarily regarded as a potential substitute for mineral filler in asphalt mixtures. However, the overall rheological properties of asphalt mastics incorporating iron tailing filler (ITF) and the effect mechanism of ITF remain unclear, which is detrimental to the generalized utilization of ITF in asphalt pavement. To fill this gap, the present study selected ITF and limestone filler (LF) to fabricate mastics with four filler/asphalt weight (f/b) ratios (0.6, 0.8, 1.0, 1.2). The blending mechanism and surface morphology of mastics were revealed by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The rotational viscosity test, dynamic shear rheometer test as well as bending beam rheometer test, were conducted to comprehensively study the rheological behavior of mastics. A new index Δ T d was proposed to quantify the influence of ITF on low-temperature cracking performance. Results show that the interaction between ITF and asphalt matrix is predominantly physical, and ITF possesses a smaller particle size which is beneficial to stiffening the mastics. However, the worse infiltration and distribution uniformity of ITF in mastics than that of LF may result in poorer adhesion. Regarding the rheological behavior, the substitution of ITF can highly improve the viscosity, complex modulus, and creep stiffness while slightly decrease the phase angle, viscosity-temperature susceptibility, and m -value of mastics, indicating a higher stiffness and elasticity of ITF mastics. Notably, the plateau region of phase angle may appear in ITF mastics with high filler concentration at low frequencies, representing a more significant elastic response. Besides that, Δ T d remains between −3.5 and −1.1 ℃. These results prove that the substitution of ITF is advantageous for the anti-rutting performance of asphalt pavement but may jeopardize its workability and low-temperature cracking resistance in particular with the excessive incorporation (f/b ratio > 1.0) of ITF.

Introduction of an adhesion factor to cube in cube models and its effect on calculated moduli of particulate composites

The cube in cube approach was used by Paul and Ishai-Cohen to model and derive formulas for filler content dependent Young’s moduli of particle filled composites assuming perfect filler matrix adhesion. Their formulas were chosen because of their simplicity, and recalculated using an elementary volume approach which transforms spherical inclusions to cubic inclusions. The EV approach led to expression of the composites moduli that allows introducing an adhesion factor kadh ranging from 0 and 1 to take into account reduced filler matrix adhesion. This adhesion factor scales the edge length of the cubic inclusions, thus reducing the stress transfer area between matrix and filler. Fitting the experimental data with the modified Paul model provides reasonable kadh for PA66, PBT, PP, PE-LD and BR which are in line with their surface energies. Further analysis showed that stiffening only occurs if kadh exceeds sqrt{{E}_{mathrm{M}}/{E}_{mathrm{F}}} and depends on the ratio of matrix modulus and filler modulus. The modified model allows for a quick calculation of any particle filled composites for known matrix modulus EM, filler modulus EF, filler volume content vF and adhesion factor kadh. Thus, finite element analysis (FEA) simulations of any particle filled polymer parts as well as materials selection are significantly eased. FEA of cubic and hexagonal EV arrangements show that stress distributions within the EV exhibit more shear stresses if one deviates from the cubic arrangement. At high filler contents the assumption that the property of the EV is representative for the whole composite, holds only for filler volume contents up to 15 or 20% (corresponding to 30 to 40 weight %). Thus, for vast majority of commercially available particulate composites, the modified model can be applied. Furthermore, this indicates that the cube in cube approach reaches two limits: (i) the occurrence of increasing shear stresses at filler contents above 20% due to deviations of EV arrangements or spatial filler distribution from cubic arrangements (singular), and (ii) increasing interaction between particles with the formation of particle network within the matrix violating the EV assumption of their homogeneous dispersion.

TOCN/copper calcium titanate composite aerogel films as high-performance triboelectric materials for energy harvesting

The development of high-performance cellulose-based triboelectric nanogenerators (TENG) has been a subject widely concerned by researchers. Here, we prepared a composite aerogel film based on TEMPO-oxidized cellulose nanofiber (TOCN) and copper calcium titanate (CaCu3Ti4O12, CCTO) nanoparticles. Under their comprehensive effects of the enhanced dielectric performance, the TOCN/CCTO-20 composite film with 20 % CCTO content based TENG device showed the best output performance of an open circuit voltage of 152 V, a short circuit current of 33.8 μA and a power density of 483 mW/m2, which were 3.37, 4.07 and 3.71 times higher than that of the pure TOCN based TENG device, respectively. In addition, effects of external force conditions, aerogel film size parameters and the agglomeration state of high filler content on the output performance were also studied. These results indicated that the TOCN/CCTO composite aerogel films can be used as efficient and low-cost cellulose-based triboelectric positive materials for energy harvesting.

Thermal conductivity of several geopolymer composites and discussion of their formulation

AbstractWe fabricated 50.8‐mm cube‐shaped samples of metakaolin geopolymer (GP) composites with various additives chosen to increase or decrease the thermal conductivity of the composite. Sodium‐based GP (NaGP) and GP composites were more conductive than potassium‐based GP (KGP) composites for a given phase fraction of filler, but the maximum amount of filler phase was higher with KGP due to the lower viscosity of the KGP mixture. The highest thermal conductivity achieved was about 8 W/m K by KGP + 44‐vol% graphite flakes, whereas NaGP + 27 vol% graphite flakes reached 4.7 W/m K. The thermal conductivity was strongly affected by the moisture remaining in the composite, which appeared to have a greater effect at higher filler content. On the other hand, the size of alumina particles (6, 40, or 120 μm) did not have any apparent effect on thermal conductivity for the same filler content. Larger particles caused less change in mixture viscosity, though, thus permitting incorporation of higher filler phase fractions and therefore higher thermal conductivity.

Investigating the weathering performance of epoxy silicone nanocomposite coatings containing various loadings of Glycidoxypropyltrimethoxysilane-modified Zinc oxide nanoparticles

This research presents the modification of ZnO nanoparticles by Glycidoxypropyltrimethoxysilane (GPTMS) to produce hybrid nanostructured additives to improve the weathering resistance of epoxy silicone coatings. The modified ZnO nanoparticles were incorporated into epoxy silicone coatings at different loading dosages. The coatings were then weathered in an accelerated weathering chamber and removed after specific intervals (0, 500, and 1000 h) for further characterization. The effect of different loadings of modified ZnO nanoparticles (0.1, 0.5, and 1 wt%) on the weathering resistance of epoxy silicone coatings was studied using SEM, AFM, FTIR, and contact angle measurement, UV–visible spectroscopy, optical microscope, gloss, Vickers hardness, and gonio-spectrophotometer. All results showed that the addition of modified nanoparticles effectively promoted (6 times improvement based on carbonyl index) the weathering resistance of the epoxy silicone coating. It was also concluded that the coatings filled at a low level (0.1 wt%) of GPTMS-modified ZnO provided much more superior weathering performance than those loaded with higher filler content (0.5 and 1 wt%). It was explained by the more crosslinked network formed and the fine distribution of modified filler within the matrix at low filler content.

Magnetically assisted drop-on-demand 3D printing of microstructured multimaterial composites

Microstructured composites with hierarchically arranged fillers fabricated by three-dimensional (3D) printing show enhanced properties along the fillers’ alignment direction. However, it is still challenging to achieve good control of the filler arrangement and high filler concentration simultaneously, which limits the printed material’s properties. In this study, we develop a magnetically assisted drop-on-demand 3D printing technique (MDOD) to print aligned microplatelet reinforced composites. By performing drop-on-demand printing using aqueous slurry inks while applying an external magnetic field, MDOD can print composites with microplatelet fillers aligned at set angles with high filler concentrations up to 50 vol%. Moreover, MDOD allows multimaterial printing with voxelated control. We showcase the capabilities of MDOD by printing multimaterial piezoresistive sensors with tunable performances based on the local microstructure and composition. MDOD thus creates a large design space to enhance the mechanical and functional properties of 3D printed electronic or sensing devices using a wide range of materials.

Polynomial chaos expansion for uncertainty propagation analysis in numerical homogenization of 2D/3D periodic composite microstructures

This paper proposes the use of adaptive polynomial chaos expansion (PCE) for uncertainty propagation analysis of the numerical homogenization of polymer composites doped with random dispersions of spherical inclusions. The developed PCE acts as a surrogate model bypassing the computationally intense numerical homogenization of the elastic properties of 2D/3D representative volume elements (RVEs) loaded with moderate to high filler contents. Numerical results and discussion are presented to assess the accuracy and computational efficiency of 2D and 3D homogenization meta-models. The ability of the developed approaches to perform uncertainty propagation analyses with minimum computational effort represents the main contribution of this work, which holds vast potential for the stochastic design of macroscopic composite structural elements.