In this study, we found a simple and effective method to fabricate lightweight poly(vinylidene fluoride) (PVDF)/10 wt% graphene nanoplatelet (GnP) nanocomposite foams with excellent electromagnetic ...interference (EMI) shielding effectiveness. To this end, solvent blending, film casting, and hot compression procedures were used. The PVDF/10 wt%-GnP nanocomposite foams, which had different microcellular structures, were obtained by adjusting the foaming parameter. Notably, the electrical conductivity and the EMI shielding properties decreased linearly with elevated foaming degree ( i.e. , the void fraction). Furthermore, they quickly decreased, having a large slope with an increasing void fraction, when the void fraction was below the critical foaming degree of 55% void fraction. When the void fraction was above this critical foaming degree, the electrical conductivity and EMI shielding values decreased slowly with a smaller slope. The EMI shielding properties were critically determined by the foam thickness. The EMI shielding properties of the PVDF/10 wt%-GnP foam with a void fraction of 48.7% increased from 12.4 to 32.2 dB at 26.5 GHz and from 15.2 to 37.4 dB at 40 GHz when the sample thickness increased from 1.5 to 3.0 mm. We concluded that the PVDF/GnP composite foams with tunable electrical conductivity and light weight offered much promise for use as excellent EMI shielding materials. Moreover, this study adopted a novel approach toward the design of conductive lightweight polymer/carbon composite foams for use in a wide range of electronic applications.
In this study, flexible polyurethane foam (PUF) composites were prepared using three types of Flash Graphene (FG) produced from different feedstock material. The acoustic, thermal, and mechanical ...properties of foam composites containing 0.025 wt% FG were characterized. It was shown that PUF-1 and PUF-3 had higher sound absorption in the frequency range of 500–2000 Hz compared to neat PUF (baseline). PUF-3 experienced a 47% reduction in thermal expansion coefficient relative to the baseline. The tensile strength and compressive modulus of all composites increased by 16–26% and 33–37% respectively. Compression force deflection and tear strength did not change relative to the baseline. This may be explained by the relatively low flake diameter and aspect ratio of each FG which led to agglomeration and impacted load transfer between the filler and matrix. Overall, the addition of 0.025 wt% FG1 and FG3 improved acoustic, thermal, and tensile properties of PUF without diminishing compression force deflection and tear resistance. PUF reinforced with FG had similar or enhanced properties compared to PUF containing commercially available, exfoliated graphene nanoplatelets (GNP). This supports the use of FG as a relatively sustainable, low-cost alternative to exfoliated GNP or chemical vapor deposition (CVD)-grown graphene in porous polymer composites.
•Flexible polyurethane foam composites prepared with 0.025 wt% Flash Graphene.•Flash Graphene improves low frequency sound absorption of flexible polyurethane foam.•Thermal expansion coefficient of Flash Graphene composites decreased by 47%.•Flash Joule Heating is an alternative mass-production method to graphite exfoliation.
A class of microcellular polymer nanocomposites of multi-walled carbon nanotubes (MWCNT) is reported that exhibits a stable and significantly high dielectric permittivity coupled with a stable and ...low dielectric loss in a wide range of frequency. Polypropylene (PP)-MWCNT nanocomposites with a cellular structure were prepared by melt mixing followed by physical foaming in an injection molding process. The generation of a cellular structure inside the nanocomposites provides a unique planar-like arrangement of the MWCNTs around the cells. This enhances the dielectric permittivity of nanocomposites up to an order of magnitude. Therefore, microcellular PP-1.25vol% MWCNT presents a dielectric permittivity of ε′=57.2 and a dielectric loss of tan δ=0.05 at 0.1MHz, highly superior to the best values of the solid nanocomposites prepared by regular compression molding (ε′=14.1 and tan δ=0.39) and by injection molding (ε′=17.8 and tan δ=0.04). Also, microcellular PP-1.66vol% MWCNT exhibits ε′=95.6 and tan δ=0.14, which surpasses the dielectric performances reported in the literature. Hence, these nanocomposites with a cellular structure provide a novel and general approach to develop microscopically tailored structures for dielectric applications using facile methods. Such dielectrics can be used for energy storage in modern electronics and electrical power systems.
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•High performance dielectrics of MWCNT-polymer are reported.•A 10-fold increase in the dielectric permittivity is achieved via the unique MWCNT arrangement within the cellular structure.•The dielectric performance surpasses most of the previously reported values.•A facile and upscalable method is used to fabricate such dielectrics.
This study reports on the effects of the matrix's crystal type (α or γ crystal) and chain mobility on the electrical properties of polypropylene (PP)/carbon nanotube (CNT) composites. Isothermal ...crystallization of the composites was performed at various temperatures and under atmospheric and elevated pressures with supercritical carbon dioxide (scCO2). Remarkably, experimental results indicated that the composites' isothermal annealing at 150 °C under a supercritical carbon dioxide (scCO2) pressure of 31 MPa reduced their percolation threshold by nearly 50%, via the formation of a significant amount of γ crystals. On the other hand, isothermal annealing of PP/CNT at 135 °C under the scCO2 conditions destructed the conductive network via promoting heterogeneous nucleation of α crystals on the CNT surface. Consequently, this led to a desirable combination of a high dielectric permittivity of ε' = 58.0 and a low dielectric loss of tan δ = 0.2 of PP/1.0 wt% CNT composites at a frequency of 100 Hz.
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•Crystallization can either promote or destruct the conductive networks in CPCs.•High temperature annealing under scCO2 promoted the formation of γ crystals.•The formation of γ crystals led to 50% reduction in percolation threshold.•Annealing at 135 °C and high scCO2 pressure resulted in low electrical conductivity.
Carbon fiber reinforced polyethylene composites have garnered recent interest in many industrial fields owing to their inherent benefits of excellent chemical and corrosion resistance, and processing ...ease. The interfacial strength between polyethylene and carbon fiber has been understudied to this point but it is critical to the performance of these new composite parts. In this study the apparent interfacial shear strength between three differently sized carbon fibers and high-density polyethylene containing various levels of maleic anhydride grafted polyethylene coupling agent has been evaluated. Overall, the compatibilizer content plays a more significant role than the fiber sizing but it was found that there are competing and complementary effects between them. Additionally, based on examination of the post debonding frictional forces, the mechanics of the pullout test are changed even with a small content of maleic anhydride even where the magnitude of the interfacial shear strength is unchanged.
•Interfacial shear strength measured for high-density polyethylene and carbon fiber by the single fiber pullout method.•Commercially sized and unsized carbon fibers are compared in HDPE with up to 12.5 wt% maleic anhydride coupling agent.•Carbon fiber sizing chemistry is correlated to adhesion properties.•Complimentary and competing effects observed between fiber sizings and matrix compatibilization.
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•Biodegradable composites were produced by in situ nanofibrillation of PCL/PLA blends.•Unprecedented PCL/PLA compatibility was achieved due to epitaxial ...crystallization.•Nanofibrillation increased PCL/PLA compounds’ stiffness and strength several folds.•Nanofibrillation improved PCL’s elastic behaviour and gas barrier properties.
Improvement of compatibility in blends of PCL and PLA has attracted the attention of the scientific community due to their complimentary mechanical properties. In this work, in situ nanofibrillation has been proposed as an ideal approach towards the green and economical production of PCL/PLA blends with an unparalleled level of compatibility of the blend components. Scanning electron microscopy showed that the transformation of the dispersed PLA phase into stretched nanofibrils drastically improved PCL/PLA interfacial adhesion. Investigations on the blends' crystallization behaviors using polarized optical microscopy, differential scanning calorimetry, and wide angle X-ray scattering suggested that the improvements in the nanofibrillar composites' (NFCs) compatibility could be associated with the increase in their compatibility due to PCL's heterogeneous crystal nucleation on the nanofibrillated PLA domains. This behavior was ascribed to a promotion of the epitaxial crystallization of the PCL on the nanofibrillated PLA’s crystals following a change in the orientation of the PLA’s crystal lamellae. The PCL’s tensile properties were significantly improved after the inclusion of even small quantities (as low as 5 wt%) of the PLA nanofibrils. The tensile strength of the NFC with 15 wt% of the PLA was over 100% higher than that of the neat PCL. Dynamic mechanical analyses and shear rheology measurements showed substantial improvements in the PCL’s elastic behavior after nanofibrillation. This effect was shown to improve the PCL’s tensile strength via delaying the yield point during tension. The NFCs also showed dramatically improved oxygen barrier properties due to the improvements in the PCL-PLA compatibility.
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•In situ microfibrillation of PLA/PA blends was used to produce fully bio-based films.•Flexible PA microfibrils were successfully produced and dispersed in PLA matrix.•Physical ...gelation even at low contents of microfibrils improved PLA’s melt strength.•The microfibrils greatly improved the PLA’s crystallization behavior.•Oxygen and water vapor transmission rates of the PLA film were reduced significantly.
Despite its many advantages, poly(lactic acid)’s (PLA’s) vast commercialization as a packaging material has been hindered by its numerous drawbacks such as low melt elasticity, slow crystallization, and low gas barrier properties. In this pioneering research, we introduce the concept of in situ microfibrillation process as an efficient, cost-effective, and environmentally friendly technique for the enhancement of PLA films’ properties. In situ microfibrillar composites (MFCs) with PLA matrix and different (petroleum and bio-based) polyamide (PA) microfibrils were produced via a fast and simple melt extrusion and hot stretching process. Morphological observations demonstrated the successful transformation of the dispersed PA phase into very long and flexible microfibrillar shapes with diameters of nearly 200nm. Shear rheological investigations proved that the MFCs had dramatically improved melt elasticities compared with the pure PLA. The crystallization kinetics of the PLA was also significantly improved after the microfibrillation process which was attributed to the heterogeneous crystal nucleation effects of the microfibrils. Gas permeability measurements confirmed substantial reductions in the oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) of the PLA film after the microfibrillation process followed by isothermal annealing. The MFCs also showed significantly improved tensile properties in comparison with the PLA.
There is an urgent need for dielectric-based capacitors to manage the increase in storage systems related to renewable energy production. Such capacitors must have superior qualities that include ...light weight, a high dielectric constant, and ultra-low dielectric loss. Poly(vinylidene fluoride) (PVDF)/carbon (carbon nanotube (CNT) or graphene nanoplatelet (GnP)) nanocomposite foams are considered promising alternatives to solid PVDF/carbon nanocomposites. This is because they have excellent dielectric properties, which are due to the preferred orientation of their carbon materials occurring in the foaming process. In the PVDF/carbon foams, their microcellular structure significantly influenced their electrical conductivity and dielectric properties. In the PVDF/CNT composite foams, the electrical conductivity was increased by an increased degree of foaming that was below a critical foaming degree. The CNTs even formed conductive networks and this caused current leakage. Thus, in the PVDF/CNT foam sample with an expansion ratio of 4.0 where a high dielectric constant of 80.6 was obtained, a relatively high dielectric loss of 3.51 was observed at the same time. In the PVDF/GnP composite foams, the presence of a microcellular structure forcefully increased the distance between GnPs. This induced and produced the insulating quality of the PVDF/GnP foams. In addition, the parallel graphene nanoplatelets that accompanied this process were close together, and they isolated the polymer layer, or air, as a medium between themselves. An unprecedentedly high dielectric constant of 112.1 and an ultra-low dielectric loss of 0.032 at 100 Hz were obtained from the PVDF/GnP composite foam with a high expansion ratio of 4.4 due to charge accumulation at the aligned conductive filler/insulating polymer (or air bubble) interface.
We prepared poly(vinylidene fluoride) (PVDF)/carbon/Ni-chain composites by dispersing Ni chains, and either carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs) into a PVDF solution. The ...electrical conductivity and the electromagnetic interference (EMI) shielding properties of the PVDF/CNT/Ni-chain and the PVDF/GNP/Ni-chain composites were increased by increasing the Ni-chain filler content. The electrical conductivity of the PVDF/CNT/10 wt%Ni-chain composite was lower than the PVDF/CNT/6 wt%Ni-chain composite. We attributed this abnormality to the Ni chains having blocked the CNT connections, when there was a high Ni-chain content. Furthermore, the PVDF-based composites' EMI shielding properties were effectively tuned by controlling the films' thicknesses. The total shielding of the PVDF/CNT/6 wt%Ni-chain and the PVDF/GNP/8 wt%Ni-chain composite films increased from 23.6 to 57.3 dB and from 22.7 to 55.8 dB, as their thicknesses were increased from 0.3 mm to 0.6 mm, respectively. The synergetic relationship between the Ni chains and the carbon materials (CNT or GNP), meant that the main EMI shielding mechanisms of the PVDF/carbon/Ni-chain composites had resulted from the absorption process. Moreover, these composites possessed high thermal conductivity, which can convert microwave energy into Joule heating systems. Thus, these PVDF-based composite films can be used to make high-efficiency EMI shielding devices that can rapidly dissipate heat.
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Melt blending is one of the most promising techniques for eliminating poly(lactic acid)’s (PLA) numerous drawbacks. However, success in a typical melt blending process is usually achieved through ...the inclusion of high concentrations of a second polymeric phase which can compromise PLA’s green nature. In a pioneering study, we introduce the production of in situ microfibrillar PLA/polyamide-6 (PA6) blends as a cost-effective and efficient technique for improving PLA’s properties while minimizing the required PA6 content. Predominantly biobased products, with only 3 wt % of in situ generated PA6 microfibrils (diameter ≈200 nm), were shown to have dramatically improved crystallization kinetics, mechanical properties, melt elasticity and strength, and foaming-ability compared with PLA. Crucially, the microfibrillar blends were produced using an environmentally friendly and cost-effective process. Both of these qualities are essential in guarantying the viability of the proposed technique for overcoming the obstacles associated with the vast commercialization of PLA.
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