Graphite Nanoplatelets Content Research Articles

Mechanical and Viscoelastic Properties of Carbon Fibre Epoxy Composites with Interleaved Graphite Nanoplatelet Layer

The use of interleaving material with viscoelastic properties is one of the most effective solutions to improve the damping capacity of carbon fibre-reinforced polymer (CFRP) laminates. Improving composite damping without threatening mechanical performance is challenging and the use of nanomaterials should lead to the target. In this paper, the effect of a nanostructured interlayer based on graphite nanoplatelets (GNPs) on the damping capacity and fracture toughness of CFRP laminates has been investigated. High-content GNP/epoxy (70 wt/30 wt) coating was sprayed on the surface of CF/epoxy prepregs at two different contents (10 and 40 g/m2) and incorporated at the middle plane of a CFRP laminate. The effect of the GNP areal weights on the viscoelastic and mechanical behaviour of the laminates is investigated. Coupons with low GNP content showed a 25% increase in damping capacity with a trivial reduction in the storage modulus. Moreover, a reduction in interlaminar shear strength (ILSS) and fracture toughness (both mode I and mode II) was observed. The GNP alignment and degree of compaction reached during the process were found to be key parameters on material performances. By increasing the GNP content and compaction, a mitigation on the fracture drop was achieved (−15%).

Tribological behavior of carbon-fiber-reinforced polymer with highly oriented graphite nanoplatelets

The tribological performance of carbon-fiber-reinforced polymer (CFRP) incorporated by different content of graphite nanoplatelets (GNPs) was investigated. By high pressure compression molding, the orientation of GNPs in the in-plane direction increases with the increase of GNPs content, which is beneficial to the formation of GNPs tribofilm during the friction. The results of the friction experiment show that reductions were achieved for the friction coefficient (44.7 %) and wear rate (77.8 %) of the CFRP with 15 wt% GNPs. Further, under different friction conditions including different sliding speeds, loads, time, and temperatures, the mechanism of the formation and destruction of the GNPs tribofilm was found to have a significant effect on the friction properties of CFRP.

PVB Nanocomposites as Energy Directors in Ultrasonic Welding of Epoxy Composites

Ultrasonic welding (UW) is a well-established technique for joining thermoplastic composites and has recently been utilized in the aerospace and automotive industries. In the case of thermoset composites (TSCs), a polymer-based material placed at the welding interface called an energy director (ED) is required. The choice of the coupling layer material is linked to several requirements, such as processing temperature, high adhesion to the thermoset composites (TSCs) adherend and mechanical strength of the resulting welded joints. In this work, the authors investigated the possibility of using Poly-vinyl-butyral (PVB) reinforced with graphite nanoplatelets (GNPs) as a coupling layer in the UW of TSC adherents. The effect of GNPs aspect ratio and content on the weldability of carbon fiber-reinforced plastics (CFRP) has been investigated. PVB/GNPs nanocomposites with different filler contents (from 0.5 wt% to 2 wt%) and different aspect ratios (100 and 2100) have been fabricated. The influence of the viscoelastic properties of the flat EDs on weldability has been assessed. Finally, an improvement of lap shear strength (LSS) of 80% was found for nanocomposites with 0.5 wt% of high-aspect-ratio GNPs with respect to neat PVB. The use of high damping nanocomposites as coupling materials for TSCs paves the way for a new generation of EDs in UW.

Experimental and Theoretical Analysis of Mechanical Properties of Graphite/Polyethylene Terephthalate Nanocomposites.

In this work, graphite nanoplatelets (GNP) were incorporated into poly (ethylene terephthalate) (PET) matrix to prepare PET-GNP nanocomposites using a melt compounding followed by compression moulding and then quenching process. Both static and dynamic mechanical properties of these quenched materials were characterized as a function of GNP contents using dynamic mechanical thermal analysis (DMTA) and tensile machine, respectively. The results demonstrated that the addition of GNP improved the stiffness of PET significantly. Additionally, the maximum increase in the storage modulus of 72% at 6 wt.% GNP. The incorporation of GNP beyond 6 wt.% into PET decreases the storage moduli, but they remain higher than pure PET. The observed reduction could be due to agglomeration, resulting in poorer dispersion and distribution of higher levels of GNP into the PET matrix. In contrast to the results for moduli, tensile strength and elongations at break reduce with increasing the GNP content. For example, tensile strength reduced from ∼46 MPa (neat PET) to ∼39 MPa (−15%) for the nanocomposites containing 2 wt.% GNP. This reduction is accompanied by a decline in elongation at break from ∼6.3 (neat PET) to ∼3.4 (−46%) for the same nanocomposites. Such reductions are followed by a gradual decrease in upon further addition of GNP. These reductions indicate that increasing GNP loadings, results in brittleness in nanocomposites. In addition, it was found that quenched PET and composite samples were not fully crystallized after processing and therefore (cold) crystallized during the first heating cycle DMTA, as indicated by a rise in storage moduli above the glass transition temperature during the DMTA first heat. Furthermore, mathematical models based on non-linear theories are developed to capture the experimental data. For this, a set of mechanical stress-strain data is used for model parameters’ identification. Another set of data is used for the model validation that demonstrates good agreements with the experimental study.

Development and characterization of graphite nanoplatelets filled copolymer of benzoxazine and epoxy

AbstractIn this study, graphite nanoplatelets (GNPs) were dispersed in a copolymer matrix consisting of bisphenol‐A based benzoxazine (BZ) and bi‐functional cycloaliphatic epoxy (CER), using two solvent‐free techniques: ultrasonication and three‐roll mill (3RM). The effects of GNP addition on the tensile performance, storage modulus, glass‐transition temperature (Tg), and electrical conductivity were evaluated. A maximum increase of nearly 46% and 20% in tensile modulus and strength, respectively, was found at 1.8 wt% of GNP content dispersed using the ultrasonication technique. In comparison, a superior enhancement with 55% and 37% increase in the tensile modulus and strength could be obtained at a lower GNP content, 0.9 wt%, dispersed via 3RM calendering, respectively. In the electrical conductivity measurement, a percolation threshold was achieved in the range between 0.6 wt% and 0.9 wt% of GNP content using the 3RM technique, which was in agreement with the predicted values. The theoretical stiffness obtained from the simplified Halpin‐Tsai model corresponded with the experimental data at low fractions. The incorporation of GNPs into the BZ/CER copolymer resulted in the full recovery of all the performance losses from the addition of CER to BZ. Choosing a proper dispersing technique, the 3RM calendering in this case, could lead to a minimum required GNP content for achieving superior nanocomposite performances.

Electrodynamic properties of epoxy composites with mixed filler graphite nanoplatelets + TiO2

Electrodynamic properties of L285 polymers, filled with graphite nanoplatelets (GNP) and TiO2 have been investigated in frequency ranges 1 kHz–2 MHz and 26 GHz–60 GHz. The TiO2 particles are expected to improve the dispersion of GNPs and have been shown to increase complex permittivity, with values of the real part reaching 22 in 40–60 GHz range. The values are generally higher than permittivity of composites, filled with pure GNP or mix of GNP and BaTiO3, however the dielectric losses increase sharply on reaching 4% GNP content. These properties could be used in microwave absorbers, where having higher dielectric loss is important, as well as real part of permittivity.

Thermal, electrical, and mechanical properties of highly filled HDPE/graphite nanoplatelets composites

Composites of highly filled high-density polyethylene (HDPE) graphite nanoplatelets (GNPs) are fabricated using melt extrusion and influence of GNP on thermal, mechanical and electrical properties are analysed. We observed increase in Young’s modulus and enhancement in thermal stability with filler addition. On the other hand, the degree of crystallinity and melting temperature decreased with GNPs content. The incorporation of GNPs greatly decreased the electrical resistivity by 10 orders of magnitude and 400% increase in thermal conductivity for filled HDPE was also observed. Therefore, highly-filled, functional (thermally and electrically conductive) HDPE composites with excellent mechanical and thermal stability have been prepared.

High-performance polyketone nanocomposites achieved via plasma-assisted mechanochemistry

Polyketone (PK) is an engineering plastic with excellent impact strength, chemical resistance, barrier properties, and flame retardancy. However, the development of PK nanocomposites with further improved properties obtained via compounding is challenging due to the poor compatibility between PK and nanofillers. Also, since PK is not soluble in common organic solvents, it is difficult to enhance the affinity between components by applying wet chemistry processes widely used to make other composites. Herein, we report an effective solution to improve the compatibility of PK and nanofillers via a completely dry process. The plasma-assisted mechanochemistry (PMC) process can form chemical bonds between polymers and nanofillers, thereby promoting the dispersion of the nanofillers in polymer composites. PK was compounded with graphite nanoplatelets (GNPs) using the PMC process, and the structure and properties of the composites were investigated. The composites displayed greatly improved mechanical and gas barrier properties, and thermal conductivity; compared with conventionally prepared composites having the same GNP content (10 wt%), the composites prepared via the PMC process had 9.7 times higher elongation at break (112.1%), 2.2 times higher impact strength (89.2 J/m), 2.2 times better barrier performance (0.9 g/m2·day), and 2.5 times higher thermal conductivity (1.6 and 13.9 W/mK in the through-plane and in-plane directions). This approach is an innovative route to high-performance polymer nanocomposites, even those constructed from insoluble and incompatible polymers such as PK.

Characterisation and electrical conductivity of polytetrafluoroethylene/graphite nanoplatelets composite films

Graphite nanoplatelets (GNPs), with a thickness of 3–10 graphene layers and lateral linear dimensions varying from 2 to 10 μm, were used to enhance the conductivity of polytetrafluoroethylene (PTFE) films. Ten composite films with the (GNPs) content of 0, 2, 3, 4, 5, 6, 8, 10, 15 and 20 wt% were obtained. These films were characterised using X-ray diffraction, infrared and Raman spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy (XPS). The conductivity the conductivity of the composite film increases with an increase in GNP content from 0.00095 S cm−1 at 2% wt% of GNPs to 20.4 S cm−1 at 20% wt% of GNPs. Further, a chemical bond is formed between the graphite nanoplates and polymer chains according to the XPS spectra.

Dielectric properties of epoxy composites with mixed fillers including graphite nanoplatelets/BaTiO3

The electrical properties of L285 epoxy composite materials (CMs) with a mixed filler including graphite nanoplatelets (GNP)/barium titanate(BT) at various GNP concentrations and at 35 wt.% of BT are measured using the AC impedance spectroscopy with frequencies ranging from 1 kHz to 2 MHz. The complex permittivity and its frequency dependence increase with the GNP content. The addition of a BT filler in GNP/L285 CM increases the percolation threshold in addition to a slight increase in the permittivity, allowing a higher GNP content in the composite without the formation of a conductive network. The AC conductivity increases and its dependence on the frequency decreases, as the GNP content increases.

Complex effect of graphite nanoplatelets on performance of HDPE/PA66 microfibrillar composites

Abstract The effect of nanofillers (NF) on parameters of polymer blends in microfibrillar composites (MFC) is complex due the effect of NF on melt drawing. This work concerns HDPE/PA66 modified with graphite nanoplatelets (GNP) prepared by different mixing protocols. GNP influence the dispersed phase size in the original blend negligibly and mostly lead to finer high-aspect ratio fibrils, i.e. GNP rather support elongation of inclusions than coalescence in the course of drawing. Favourable mechanical behaviour, exceeding predicted one, was found with low GNP content using the PA66 masterbatch. MFC with similar structure and GNP localization in PA66 show marked differences in properties depending on mixing protocol. Antagonistic effects found for the HDPE masterbatch indicate high effect of GNP migration between the components which affects the interphase by variation of crystallinity. The results confirm complex effect of GNP and dominancy of other GNP-induced effects over dual reinforcement with GNP and PA66 microfibrils.

Electrical, Thermal, and Morphological Properties of Poly(ethylene terephthalate)-Graphite Nanoplatelets Nanocomposites

Graphite nanoplatelets (GNP) were incorporated with poly(ethylene terephthalate) (PET) matrix by melt-compounding technique using minilab compounder to produce PET-GNP nanocomposites, and then the extruded nanocomposites were compressed using compression molding to obtain films of 1 mm thickness. Percolation threshold value was determined using percolation theory. The electrical conductivity, morphology, and thermal behaviors of these nanocomposites were investigated at different contents of GNP, that is, below, around, and above its percolation threshold value. The results demonstrated that the addition of GNP at loading >5 wt.% made electrically conductive nanocomposites. An excellent electrical conductivity of ~1 S/m was obtained at 15 wt.% of GNP loading. The nanocomposites showed a typical insulator-conductor transition with a percolation threshold value of 5.7 wt.% of GNP. In addition, increasing screw speed enhanced the conductivity of the nanocomposites above its threshold value by ~2.5 orders of magnitude; this behavior is attributed to improved dispersion of these nanoparticles into the PET matrix. Microscopies results exhibited no indication of aggregations at 2 wt.% of GNP; however, some rolling up at 6 wt.% of GNP contents was observed, indicating that a conductive network has been formed, whereas more agglomeration and rolling up could be seen as the GNP content is increased in the PET matrix. These agglomerations reduced their aspect ratio and then reduced their reinforcement efficiency. NP loading (>2 wt.%) increased degree of crystallinity and improved thermal stability of matrix slightly, suggesting that 2 wt.% of GNP is more than enough to nucleate the matrix.

Thermal Conductivity of Carbon Nanoreinforced Epoxy Composites

The present study attempts to investigate the influence of multiwalled carbon nanotubes (MWCNTs) and graphite nanoplatelets (GNPs) on thermal conductivity (TC) of nanoreinforced polymers and nanomodified carbon fiber epoxy composites (CFRPs). Loading levels from 1 to 3% wt. of MWCNTs and from 1 to 15% wt. of GNPs were used. The results indicate that TC of nanofilled epoxy composites increased with the increase of GNP content. Quantitatively, 176% and 48% increase of TC were achieved in nanoreinforced polymers and nanomodified CFRPs, respectively, with the addition of 15% wt. GNPs into the epoxy matrix. Finally, micromechanical models were applied in order to predict analytically the TC of polymers and CFRPs. Lewis-Nielsen model with optimized parameters provides results very close to the experimental ones in the case of polymers. As far as the composites are concerned, the Hashin and Clayton models proved to be sufficiently accurate for the prediction at lower filler contents.

Understanding the effect of silica nanoparticles and exfoliated graphite nanoplatelets on the crystallization behavior of isotactic polypropylene

This study explores how the presence of nanofillers with different structural and chemical characteristics, specifically silica nanoparticles and exfoliated graphite nanoplatelets (GNP), alters the crystallization behavior and polymorphism of a semicrystalline polymer, such as polypropylene (PP). The main focus of this research is to investigate how silica and GNP affect the nucleation and growth of PP crystals during isothermal crystallization. The nonisothermal crystallization behavior, including crystal structures, crystallization temperature, and rate, is also determined. PP composites with nanomaterial content up to 7 wt% were produced by melt mixing and injection molding. Both silica and graphite were found to be effective nucleating agents, significantly increasing the crystallization rate during isothermal crystallization, with greater changes observed in case of GNP composites. The effect of filler type and amount on the PP polymorphism and lamella thickness was studied by X-ray diffraction and modulated differential scanning calorimetry. Both silica and graphite were found to be effective nucleating agents for the less common b-phase of PP crystals even at low nanomaterial concentration. a-2crystal perfection and the recrystallization of the b-form in the a-form and/ or at the transcrystalline regime were found to be responsible for the recrystallization occurring upon melting in nanocomposites at high silica or medium GNP content. POLYM. ENG. SCI., 55:672–680, 2015. V C 2014 Society of Plastics Engineers

Gas transport through nanocomposite membrane composed by polyethylene with dispersed graphite nanoplatelets

The gas separation and gas barrier properties of nanocomposite membrane made of low-density polyethylene (LDPE) with dispersed graphite nanoplatelets (GNPs) were studied by gas phase permeation technique. Structural and morphological analyses indicate that in nanocomposites prepared by film blowing technology: (i) the GNPs are iso-oriented with the platelet surface parallel to the membrane surface and (ii) the GNPs inclusion does not change the crystalline fraction of the polymeric matrix nor the size of the LDPE crystallites. The H2, N2, and CO2 transport through the nanocomposite membrane was investigated in samples with nominal GNPs content of 5wt%. The GNPs inclusion reduces the permeability by approximately a factor two compared to that of the pure LDPE membrane for all the examined gases without relevant changes in the gas selectivity properties. Gas transport through the nanocomposite membrane obeys to the solution–diffusion mechanism and shows, for the examined gases, the same value of activation energy for permeation as in the pure LDPE sample. The gas barrier properties of the nanocomposite were compared with those predicted by phenomenological models. The reduced permeability cannot be explained assuming that gas molecules have to cross a tortuous migration path in the polymeric matrix but was instead attributed to the formation of rigidified polymer layers around the GNPs filler particles.

Graphite nanoplatelets/polymer nanocomposites: thermomechanical, dielectric, and functional behavior

Exfoliated graphite nanoplatelets (GNP)/epoxy resin nanocomposites were prepared and tested, varying the amount of the filler content. Systems’ morphology was investigated by means of scanning electron microscopy, while their thermal response was examined via differential scanning calorimetry (DSC). Broadband dielectric spectroscopy and dynamic mechanical thermal analysis were employed in order to characterize the produced systems. Static mechanical tests were also conducted at ambient. Reinforced systems exhibit improved performance under mechanical and electrical excitation. In particular, storage modulus increases systematically with GNP content. DSC results imply that glass transition temperature is not affected by the presence of GNP. Flexural modulus and storage modulus, as determined by static and dynamic mechanical tests, respectively, increased with filler content. Dielectric permittivity increases also systematically with GNP content. Recorded relaxation processes arise from the glass to rubber transition of the polymer matrix (α-mode), re-orientation of polar side groups of the polymer chains (β-mode), and interfacial polarization because of the accumulation of charges at the systems’ interface. Finally, the energy storing efficiency of the nanocomposites enhances with reinforcing phase in the examined frequency and temperature range. Optimum performance corresponds to the nanocomposite with maximum GNP loading.

Effect of processing method on the properties of multifunctional exfoliated graphite nanoplatelets/polyamide 12 composites

The focus of this study is to determine the effect of the processing method on the mechanical, thermo-mechanical and electrical properties of graphite nanoplatelets (GNP) reinforced polyamide 12 (PA12) composites. The two processing methods studied are injection molding (IM) and selective laser sintering (SLS). The composites made by SLS exhibited higher tensile modulus, comparable or better flexural properties and lower impact strength than those made by IM. This enhancement is supported by the higher degree of crystallinity and more effective interfacial interactions observed in the SLS composites compared to those made by IM. At higher GNP content the property enhancement is compromised due to the presence of GNP agglomerates. Furthermore, it was found that the SLS composites filled with 5wt% of GNP exhibited four orders of magnitude higher electrical conductivity compared to their counterpart made by IM which exhibited electrical properties similar to the neat PA12. The understanding of the processing-structure-property relationship investigated here can lead to composites engineered for targeted applications.

A graphite nanoplatelet/epoxy composite with high dielectric constant and high thermal conductivity

A simple strategy for the preparation of composites with high dielectric constant and thermal conductivity was developed through a typical interface design. Graphite nanoplatelets (GNPs) with a thickness of 20–50nm are fabricated and homogeneously dispersed in the epoxy matrix. A high dielectric constant of more than 230 and a high thermal conductivity of 0.54W/mK (a 157% increase over that of pure epoxy) could be obtained for the composites with a lower filler content of 1.892vol.%. The dielectric constant still remains at more than 100 even in the frequency range of 105–106Hz. When loaded at 2.703vol.%, GNP/epoxy composites have a dielectric constant higher than 140 in the frequency range of 102–104Hz and a high thermal conductivity of 0.72W/mK, which is a 240% increase over that of pure epoxy. The high dielectric constant and low loss tangent are observed in the composite with the GNPs content of 0.949vol.% around 104Hz. It is believed that high aspect ratio of GNPs and oxygen functional groups on their basal planes are critical issues of the constitution of a special interface region between the GNPs and epoxy matrix and the high performance of the composites.

Electrical and mechanical properties of graphite/maleic anhydride grafted polypropylene nanocomposites

The aim of this study was to investigate the effects of adding maleic anhydride grafted polypropylene (MA-PP) and graphite nanoplatelets (GNPs) into polypropylene. The tensile strength and flexural properties of the GNP/PP composite were enhanced with an increase in the MA-PP content and the GNP content. The maximum increase of mechanical properties was shown at 10wt.% of MA-PP having a constant GNP content of 8wt.% and at 20wt.% of GNP having a constant MA-PP content of 5wt.%, whereas a decrease in tensile strength and flexural properties was observed at 20wt.% of MA-PP. The impact strength was decreased by increasing the MA-PP content and the GNP content. The electrical resistivity of the GNP/PP composite exhibited an anisotropic characteristic due to the direction of the injection molding flow. Electrical resistivity of less than 106Ωcm regardless of the direction of the resin flow could be obtained by adding more than 20wt.% of GNP when the MA-PP content was 5wt.%. The differential scanning calorimetry results suggest that an increase of the GNP content makes it act as a nucleating agent and thus causes an increase in the crystallinity of the PP.

Facile preparation and thermal degradation studies of graphite nanoplatelets (GNPs) filled thermoplastic polyurethane (TPU) nanocomposites

A facile method with the advantage of using only one single solvent throughout the whole processing was introduced to prepare graphite nanoplatelet (GNP) filled thermoplastic polyurethane (TPU) nanocomposites. Morphological studies showed that the employed method could provide the uniform dispersion of GNPs in the TPU matrix. Storage modulus of the nanocomposites was increased with increasing GNP content, and the improvement was more obvious at temperatures below the glass transition temperature ( T g) of TPU. For the nanocomposite that contains 3.9 vol% (the maximum loading employed in this study) of GNP, it still showed a long elongation at break of over 600%. Thermogravimetric analysis (TGA) showed that the incorporation of GNPs could improve the thermal stability of the nanocomposites. In addition, cone calorimetry results showed that the GNPs could act as intumescent flame retardant and significantly reduced the heat release rate (HRR), thus improved the flame retardancy of the TPU matrix.