Biomimetic nacre-like aramid nanofiber-holey MXene composites for lithium-sulfur batteries

Polysulfide shuttle and lithium dendrite formation limit practical applications of lithium-sulfur (Li-S) batteries. To address these issues, we propose a nacre-inspired design of MXene/aramid nanofiber (ANF) separator with “brick-and-mortar” microstructure. The combination of shortened ion transfer distance generated by holes on MXene and enlarged interlayer spacing provided by ANFs creates a hierarchical ion path “highway” that modulates the efficiency of ion transportation while synergistically suppressing the polysulfide shuttles. Furthermore, benefitting from the introduction of ANF, the composite membrane has good mechanical properties and impact tolerance. With simultaneous mitigation of dendrite growth and polysulfide poisoning of anodes, the cells with nacre-inspired separator exhibited excellent rate capability to 5 C and had a possible long cycle life of 3,500+ cycles with capacity decay of 0.013% per cycle to 3 C. This work offers a membrane design strategy inspired by the structure of pearl layers, aiming to resolve materials performance challenges of high-performance energy storage. © 2023 The Author

Thermal conductivity, morphology and mechanical properties for thermally reduced graphite oxide-filled ethylene vinylacetate copolymers

Systematic variation of copolymers (Poly (ethylene-covinylacetate)) composition provide an opportunity to change matrix polarities and thus explore their effects on the polymer/filler interactions and composite properties. The main objective of this work is to study the effect of vinyl acetate (VA) content on the extent of exfoliation and dispersion of thermally reduced graphite oxide (TrGO), as well as its impact on the thermal conductivity and mechanical properties of the resultant composites. The use of ethylene vinyl-acetate (EVA) copolymers of different (0-40 wt%) vinyl acetate content with similar melt viscosities allowed us to keep the processing conditions constant and quantitatively compare the thermal conductivity and mechanical properties of composites with different matrix polarities. Composites with conductive graphite (GT) and multiwalled carbon nanotubes (MWCNT) were also prepared and examined for comparison. Melt dispersion of TrGO in EVA copolymers was quantified using a range of characterization techniques: transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray scattering measurements. Electron microscopy and X-ray diffraction revealed highly exfoliated morphology of TrGO throughout the entire matrix, while GT remained multi-layer even after melt processing. Nanocomposites reinforced with TrGO showed significantly improved thermal conductivities and mechanical properties combined with low rheological percolation thresholds comparable to those achieved using MWCNT and GT. We propose a formalism to assess the thermal conductivity and mechanical properties of graphene nanocomposites based upon the interfacial excess energies of EVA copolymers. (C) 2017 Elsevier Ltd. All rights reserved

Experimental characterization and morphology investigation of composites based on high-density and low-density polyethylene reinforced with non-crimp-stitched glass fabrics

In this study, the effects of matrix material on mechanical properties were investigated in glass fiber reinforced high-density and low-density polyethylene composites. Also, in order to compare the fiber configuration effect on anisotropic behavior, unidirectional and biaxial glass fabrics were used as reinforcement material. Composite laminates were manufactured via the compression molding technique. Tensile and three-point bending flexural tests were conducted up to failure on specimens cut out in different directions. Extensive fracture photomicrographs were presented for observing the failure modes (e.g. delamination) of the composites resulting from a variety of loading conditions. In addition, Scanning electron micrographs of postfractured surfaces of composites were interpreted in an attempt to explain the failure mechanisms (adhesive or cohesive failure) of the composites

Epoxy- and Polyester-Based Composites Reinforced With Glass, Carbon and Aramid Fabrics: Measurement of Heat Capacity and Thermal Conductivity of Composites by Differential Scanning Calorimetry

The primary purpose of the study is to investigate the temperature dependence of heat capacity and thermal conductivity of composites having different fiber/matrix combinations by means of heat-flux differential scanning calorimetry (DSC). The materials used as samples in this study were epoxy- and polyester-based composites. Noncrimp stitched glass, carbon, and aramid fabric were used as reinforcements for making unidirectional composites. For the heat capacity measurements the composite sample and a standard material are separately subjected to same linear temperature program. By recording the heat flow rate into the composite sample as a function of temperature, and comparing it with the heat flow rate into a standard material under the same conditions, the temperature dependence of heat capacity of the composite sample is determined. Measurements were carried out over a wide range of temperatures from about 20 to 250 degrees C. The differential scanning calorimeter was adapted to perform the thermal conductivity measurements in the direction perpendicular to the fiber axis over the temperature range of 45-235 degrees C. The method used in this study utilizes the measurement of rate of heat flow into a sensor material during its first-order phase transition to obtain the thermal resistance of a composite material placed between the sensor material and the heater in the DSC. POLYM. COMPOS., 30:1299-1311, 2009. (C) 2008 Society of Plastics Engineer

Comparison of mechanical properties of epoxy composites reinforced with stitched glass and carbon fabrics: Characterization of mechanical anisotropy in composites and investigation on the interaction between fiber and epoxy matrix

The primary purpose of the study is to evaluate and compare the mechanical properties of epoxy-based composites having different fiber reinforcements. Glass and carbon fiber composite laminates were manufactured by vacuum infusion of epoxy resin into two commonly used noncrimp stitched fabric (NCF) types: unidirectional and biaxial fabrics. The effects of geometric variables on composite structural integrity and strength were illustrated. Hence, tensile and three-point bending flexural tests were conducted up to failure on specimens strengthened with different layouts of fibrous plies in NCF. In this article, an important practical problem in fibrous composites, interlaminar shear strength as measured in short beam shear test, is discussed. The fabric composites were tested in three directions: at 0 degrees, 45 degrees, and 90 degrees. In addition to the extensive efforts in elucidating the variation in the mechanical properties of noncrimp glass and carbon fabric reinforced laminates, the work presented here focuses, also, on the type of interactions that are established between fiber and epoxy matrix. The experiments, in conjunction with scanning electron photomicrographs of fractured surfaces of composites, were interpreted in an attempt to explain the failure mechanisms in the composite laminates broken in tension

FTIR and SEM analysis of polyester- and epoxy-based composites manufactured by VARTM process

Polyester- and epoxy-based composites containing glass and carbon fibers were manufactured using a vacuum-assisted resin transfer molding (VARTM) process. Fourier transform infrared (FTIR) spectroscopy analyses were conducted to determine the interaction between fibers and matrix material. The results indicate that strong interaction was observed between carbon fiber and epoxy resin. However, weak interactions between remaining fiber-matrix occur. Scanning electron microscopy (SEM) analysis was also performed to take some information about strength of interaction between fibers and matrix material. From SEM micrographs, it is concluded that the findings in SEM analysis support to that obtained in FTIR analysis. Another aim of the present work was to investigate the influence of matrix on composite properties. Hence, the strengths of composites having same reinforcement but different matrix systems in axial tension and transverse tension were compared. Short beam shear test has been conducted to characterize the interfacial strength in the composites. (C) 2008 Wiley Periodicals, Inc

The mechanical and adhesive properties of electrically and thermally conductive polymeric composites based on high density polyethylene filled with nickel powder

Electrically and thermally conductive composites made using high density polyethylene (HDPE) matrix blended with a special grade of branch-structured nickel particles were studied. Composites with high filler content were highly electrically and thermally conductive. The electrical conductivity of composites reached a value of 8.3×103Sm−1 when filled with 30vol.% of the filler, and the thermal conductivity obtained using this filler content was found to be 1.99Wm−1K−1. The percolation concentration of the filler within the HDPE matrix, which was determined from electrical conductivity measurements, was determined to be 8vol.%.Young’s modulus of composites significantly increased from 606MPa to 1057MPa when composites were filled with 20vol.% of the filler. Further increasing the filler content caused no further increase in Young’s modulus, probably due to high aggregation of the filler. The stress at break of the composites behaved nonlinearly; the low filler content suppressed necking, resulting in a decrease in stress at break, whereas higher filler content (higher than 10vol.%) led to reinforcement of the composites and therefore increased the stress at break.The presence of nickel particles throughout the HDPE matrix increased the hydrophilicity of the composites. The contact angle of water on the neat HDPE decreased from 93° to 80° as the nickel content of the matrix was increased to 13vol.% of nickel. Further increases in the filler content did not alter the contact angle. Similarly, the strength of the adhesive joint formed by the composite and aluminum foil increased from a value of 16Nm−1 for the neat HDPE to 27Nm−1 when the HDPE matrix was filled with 13vol.% of the filler.NMT-ERANET “APGRAPHEL” and by project VEGA 2/0119/12

Effects of fiber surface treatments on mechanical properties of epoxy composites reinforced with glass fabric

In this study, effects of fiber surface treatments on mechanical behavior and fracture mechanism of glass fiber/epoxy composites were investigated experimentally. To change the composition of the glass and regenerate to the hydroxyl groups, activation pretreatment of heat cleaned woven glass fabric was performed using (v/v) HCl aqueous solution at different concentrations before silane treatment. The treatment of silanization of heat cleaned and acid activated glass fibers with gamma-glycidoxypropyltrimethoxysilane were performed. In this work, short beam shear test has been conducted to determine the performance of the acid treatment and the silane treatment in terms of the interlaminar shear strength. The silane coating on the heat cleaned glass fibers increased the interlaminar shear strength of the composite. However, the silane coating on the acid activated glass fibers did not improve the interlaminar shear strength of the composite. In addition, the strengths of the glass fabric specimens in tension and flexure were investigated. When the glass fibers are first treated with HCl solution and then with silane coupling agent, the tensile strengths of the composites decreased significantly. Scanning electron photomicrographs of fractured surfaces of composites were performed to explain the failure mechanisms in the composite laminates broken in tension

The Structure of gamma-Glycidoxypropyltrimethoxysilane on Glass Fiber Surfaces: Characterization by FTIR, SEM, and Contact Angle Measurements

The purpose of this article is to determine the structure of gamma-glycidoxypropyltrimethoxysilane (gamma-GPS) on glass fiber surfaces. The interfacial adhesion of glass fiber-polymer can be improved by the silane treatment of the glass fiber. To change the composition of the glass and regenerate to the hydroxyl groups, activation pretreatment of heat cleaned woven glass fabric was performed using a 10% (v/v) hydrochloric acid aqueous solution for different durations before silane treatment. The treatment of silanization of heat cleaned and acid activated glass fibers with (gamma-GPS) were conducted at various time intervals. These fibers would be used to quantify the relationship between contact angle of glass fiber surface and the interfacial shear strength of the fiber-polymer interface. The effect of acid activation on glass surface and the interaction between glass fibers and silane coupling agent were examined using Fourier transform infrared spectroscopy. The experiments, in conjunction with electron photomicrographs of glass surfaces treated with coupling agent, are interpreted in an attempt to explain the stability of coupling agent-glass interfaces. From SEM analysis, it was clearly observed that agglomerations of silane agent in the cavities among the heat cleaned fibers are available. However, this case was not observed for the silanization of acid activated glass fibers. In addition, contact angle measurements on glass fibers were performed to evaluate surface structure. POLYM. COMPOS., 30:550-558, 2009. (C) 2008 Society of Plastics Engineer