GNP Loading Research Articles

Epoxy/Graphene Nanoplatelet (GNP) Nanocomposites: An Experimental Study on Tensile, Compressive, and Thermal Properties.

This paper presents an experimental investigation of nanocomposites composed of three ratios of epoxy/graphene nanoplatelets (GNPs) by weight. The 0.1, 0.2, and 0.3 wt.% specimens were carefully manufactured, and their mechanical and thermal conductivity properties were examined. The tensile strength and modulus of epoxy/GNPs were enhanced by the large surface area of graphene nanoplatelets, causing crack deflection that created new fracture fronts and friction because of the rough fracture surface. However, the compressive strength was gradually reduced as GNP loading percentages increased. This was probably due to severe plastic yielding on the epoxy, leading to catastrophic axial splitting caused by premature fractures. Furthermore, the highest thermal conductivity was 0.1283 W/m-K, representing a 20.92% improvement over neat epoxy (0.1061 W/m-K) when 0.3 wt.% GNPs were added to the epoxy. This was because of efficient heat propagation in the GNPs due to electron movement through percolative paths. The tensile failure mode in epoxy/GNP nanocomposites showed a few deflected and bifurcated rough cracks and brittle, dimple-like fractures. Contrarily, compressive failure mode in GNP-added epoxy showed plastic flexural buckling and brittle large-axial splitting. The epoxy/GNP nanocomposites were considered a damage-tolerant material.

A Feasible Compatibilization Processing Technique for Improving the Mechanical and Thermal Performance of Rubbery Biopolymer/Graphene Nanocomposites.

Over the last few decades, processing and compatibility have become challenging and interesting investigation areas of polymer matrix nanocomposites. This study investigated the addition of maleic anhydride (MAH) at different ratios with graphene nanoplatelets (GnPs) in poly(lactic acid)/modified natural rubber/polyaniline/GnP (PLA/m-NR/PANI/GnP) nanocomposites via two processing methods: a two-step technique and a one-pot technique. The former technique involved first preparing a master batch of PLA grafted with MAH, followed by a second step involving the melt blending of the nanocomposite (T1) using MAH-g-PLA. On the other hand, the one-pot technique involved the direct mixing of MAH during the melt-blending process (T2). The mechanical, morphological and thermal properties of the prepared nanocomposites were investigated. The findings showed that adding MAH significantly improved the tensile strength and elongation at break by about 25% for PLA/m-NR/PANi/GnP nanocomposites, with an optimal ratio of 1:1 of MAH-g-PLA to GnP loading using the T1 technique. FTIR analysis confirmed the chemical interaction between MAH and PLA for T1 nanocomposites, which exhibited improved phase morphology with smoother surfaces. MAH-compatibilized nanocomposites had enhanced thermal stabilities when compared to the sample without a compatibilizer. The findings show that the compatibilized PLA nanocomposite is potentially suitable for bio-inspired materials.

Stretching induced alignment of graphene nanoplatelets in polyurethane films for superior in-plane thermal conductivity and electromagnetic interference shielding

The rapid innovation of flexible smart electronics has increased the demand for flexible thermally conductive films with the high performance of electromagnetic interference shielding (EMI). This study focuses on graphene nanoplatelets/polyurethane (GnP/PU) films that were fabricated utilizing the solution casting approach. The stretching-induced alignment method was then used to align the GnP sheets horizontally in the PU matrix by uniaxially stretching to a particular degree. The resultant stretched GnP/PU films with 10 wt% GnP loading at a stretching degree of 130% show an excellent in-plane thermal conductivity (λ∥) and EMI shielding effectiveness values of 10.68 W m−1 K−1 and 41 dB in the frequency range of 8–12 GHz which are 679% and 60%, respectively, higher than that of corresponding unstretched ones. The outstanding λ∥ and EMI shielding effectiveness can be ascribed to the horizontal alignment of GnP sheets in the PU matrix. That, in turn, may decrease the interfacial thermal resistance, and facilitate the establishment of effective phonon and electron transfer in the stretched GnP/PU films. The obtained films demonstrated superior heat dissipation and mechanical properties compared to neat PU film. Therefore, the prepared GnP/PU films have great potential as heat spreaders and EMI shielding material in flexible smart electronics.

Organic–Inorganic Hybrid Conductive Network to Enhance the Electrical Conductivity of Graphene-Hybridized Polymeric Fibers

With the rapid development of wearable electronic textiles, flexible and knittable polymer conductive fibers have received unprecedented attention from researchers. Practical applications of these devices are, however, impeded by their low electrical conductivity and suboptimal mechanical properties. In this study, we demonstrate an organic–inorganic hybrid strategy to build a conductive network in polymeric fibers (CPFs) at low GnP loading using an industrial wet-spinning method. Both the conductivity and spinnability of wet-spun graphene-hybridized poly(vinyl alcohol) (PVA/GnP) fibers are systematically investigated. A secondary additive, poly(3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) is also incorporated for the fabrication of newly hybridized PVA/GnP/PEDOT:PSS (denoted as PVA/GnP/S) fibers. In addition, a hybrid synergistic effect that features a synergistic enhancement of their conductivity (33.6 S/m) has also been well demonstrated. Meanwhile, this type of hybrid fiber maintains its excellent mechanical performance (4.82 cN/dtex with a 16.2% strain) even after subsequent twisting and weaving into conductive fabrics. As an electron transport carrier, this fiber can widely be applied in wearable electronics.

Performance of Graphene/Polydimethylsiloxane Surfaces against S. aureus and P. aeruginosa Single- and Dual-Species Biofilms.

The increasing incidence of implant-associated infections has prompted the development of effective strategies to prevent biofilm formation on these devices. In this work, pristine graphene nanoplatelet/polydimethylsiloxane (GNP/PDMS) surfaces containing different GNP loadings (1, 2, 3, 4, and 5 wt%) were produced and evaluated on their ability to mitigate biofilm development. After GNP loading optimization, the most promising surface was tested against single- and dual-species biofilms of Staphylococcus aureus and Pseudomonas aeruginosa. The antibiofilm activity of GNP/PDMS surfaces was determined by the quantification of total, viable, culturable, and viable but nonculturable (VBNC) cells, as well as by confocal laser scanning microscopy (CLSM). Results showed that 5 wt% GNP loading reduced the number of total (57%), viable (69%), culturable (55%), and VBNC cells (85%) of S. aureus biofilms compared to PDMS. A decrease of 25% in total cells and about 52% in viable, culturable, and VBNC cells was observed for P. aeruginosa biofilms. Dual-species biofilms demonstrated higher resistance to the antimicrobial activity of GNP surfaces, with lower biofilm cell reductions (of up to 29% when compared to single-species biofilms). Still, the effectiveness of these surfaces in suppressing single- and dual-species biofilm formation was confirmed by CLSM analysis, where a decrease in biofilm biovolume (83% for S. aureus biofilms and 42% for P. aeruginosa and dual-species biofilms) and thickness (on average 72%) was obtained. Overall, these results showed that pristine GNPs dispersed into the PDMS matrix were able to inhibit biofilm growth, being a starting point for the fabrication of novel surface coatings based on functionalized GNP/PDMS composites.

Comparative investigation of the properties of graphene nanoplatelet reinforced titanium diboride and niobium diboride ceramics

In this study, the effect of GNP concentration on the mechanical properties of spark plasma sintered TiB2 and NbB2 ceramics was investigated. GNP reinforced TiB2 and NbB2 specimens were aimed to produce with nearly full densification. Herein, SEM investigations, Raman analysis, and oxidation behavior of the samples were reported. GNP addition into the TiB2 and NbB2 matrices showed a different effect on various properties of the composites. GNP loading tends to enhance densification by removing native oxides of both TiB2 and NbB2 matrices. GNPs were more effective in the oxygen removal mechanism for TiB2 composites than NbB2. The highest relative density was obtained for TiB2-GNP and NbB2-GNP composites as 98.6% with 7 vol% and 5 vol% GNP additions, respectively. The Vickers microhardness decreased with increasing GNPs loading for both matrices. NbB2-GNP composites possessed higher fracture toughness and better oxidation resistance than TiB2-GNP composites.

Influence of Graphene Nanoplatelet Lateral Size on the Electrical Conductivity and Electromagnetic Interference Shielding Performance of Polyester Nanocomposites.

Polyester nanocomposites reinforced with graphene nanoplatelets (GnPs) with two different lateral sizes are prepared by high shear mixing, followed by compression molding. The effects of the size and concentration of GnP, as well as of the processing method, on the electrical conductivity and electromagnetic interference (EMI) shielding behavior of these nanocomposites are experimentally investigated. The in-plane electrical conductivity of the nanocomposites with larger-size GnPs is approximately one order of magnitude higher than the cross-plane volume conductivity. According to the SEM images, the compression-induced alignments of GnPs is found to be responsible for this anisotropic behavior. The orientation of the small size GnPs in the composite is not influenced by the compression process as strongly, and consequently, the electrical conductivity of these nanocomposites exhibits only a slight anisotropy. The maximum EMI shielding effectiveness (SE) of 27 dB (reduction of 99.8% of the incident radiation) is achieved at 25 wt.% of the smaller-size GnP loading. Experimental results show that the EMI shielding mechanism of these composites has a strong dependency on the lateral dimension of GnPs. The non-aligned smaller-size GnPs are leveraged to obtain a relatively high absorption coefficient (≈40%). This absorption coefficient is superior to the existing single-filler bulk polymer composite with a similar thickness.

Printability and performance of 3D conductive graphite structures

Direct ink writing (DIW) of graphite-epoxy composites has gained significant importance in a number of applications in fabricating highly conductive free-standing 3D structures. Processing of the composite inks, which consist of highly loaded graphene nanoplatelets, first involves a detailed understanding of the underlying rheological properties. However, little is known about the effect of processing/print parameters, e.g., print speed has on the orientation of such 2D particles during the printing process and how this subsequently influences the macroscopic properties of the final cured composite. In this work, inks with solid loadings of 7−18 wt% were dispersed into a low viscosity epoxy resin (EPON 862) to form a shear thinning, viscoelastic material. The optimal GNP loading for printing is determined through rheological measurements, and the electrical properties are measured as a function of particle concentration and print speed. The results show a sharp increase in conductivity by a factor of ten as the print speed is increased from 5 to 40 mm/s, and all printed samples had conductivities higher than 10−3 S/cm. We attribute this change in conductivity to the shear stresses generated during the deposition of the ink, resulting in a shift in the orientation of the 2D platelet-like fillers. Such results showcase the ability to tune the electrical properties of a printed structure with a constant loading of filler. The present work helps develop design rules for processing of graphene-based 3D structures with enhanced properties (electrical) using additive manufacturing. We envision the use of such structures in a number of applications such as thermal interface materials, shielding materials for electronic devices, and light-emitting devices, to name a few.

Mechanical, toughness and thermal properties of 2D material- reinforced epoxy composites

Developing epoxy composites with high thermal conductivity and excellent mechanical properties becomes imperative in electronic and aerospace industries. This study investigates and compares the effect of adding boron nitride (BN) sheets and graphene platelets (GnPs) on the mechanical properties and thermal conductivity of epoxy resin. The study shows that incorporation of BN or GnPs into epoxy matrix significantly enhanced both mechanical properties and thermal conductivity of epoxy composites. At fractions ranging 1–4 wt%, GnPs/epoxy composites provide higher Young's modulus, fracture toughness (K1c) and critical stress energy release rate (G1c) compared to BN/epoxy composites. The thermal conductivity of the epoxy composites is up to the maximum of 0.33 Wm−1K−1 at 4 wt% of GnP loading, which is much higher than that of the composites filled with the same loading of BN (0.23 Wm−1K−1). The study emphasizes the importance of adding thin nanosheets (thickness 3–5 nm) at low loadings in developing epoxy composites to achieve desired mechanical and thermal properties.

Electrical and Chemical Properties of Graphene over Composite Materials: A Technical Review

Graphene is a material that has superior mechanical, electrical, and thermal properties. It has drawn the attention of many scientific researchers for this purpose. In this paper, three different types of fillers, GNPs, MWCNTs and EG reinforced epoxy nanocomposites were mainly studied. Different shear mixing speeds and shear mixing times were considered during the study of the nanocomposites with 0.1 wt% loading of the fillers. The effects of various types of fillers and different shear mixing speeds and durations on mechanical and electrical properties of the final composites were examined. The GNPs-reinforced epoxy nanocomposite was the only one that showed a 13% improvement in elastic modulus as compared to pure epoxy when the shear mixing conditions were 3000 rpm for 2 hours. The research also studied the effects of different loadings of GNPs and the addition of acetone as a solvent on the final mechanical, electrical and thermal properties of the composites (with the fixed shear mixing speed and time). The tensile strength of the composites reduced drastically when the loading of GNPs increased while the elastic modulus shows some increase with the growth in GNP loading. The study found that GNPs reinforced composites did not show the percolation threshold even with 5 wt% (with the ratio to the weight of epoxy) loading of the GNPs. The GNPs-reinforced epoxy composites showed an 116% improvement in the thermal conductivity as compared to the pure epoxy samples when the GNPs loading was 5 wt%. The results from the studied literatures also showed that the samples prepared with the addition of acetone had higher thermal diffusivity than the samples prepared without acetone.

Mechanically robust, electrically and thermally conductive graphene-based epoxy adhesives

This study develops a facile approach to fabricate adhesives consists of epoxy and cost-effective graphene platelets (GnPs). Morphology, mechanical properties, electrical and thermal conductivity, and adhesive toughness of epoxy/GnP nanocomposite were investigated. Significant improvements in mechanical properties of epoxy/GnP nanocomposites were achieved at low GnP loading of merely 0.5 vol%; for example, Young’s modulus, fracture toughness (K1C) and energy release rate (G1C) increased by 71%, 133% and 190%, respectively compared to neat epoxy. Percolation threshold of electrical conductivity is recorded at 0.58 vol% and thermal conductivity of 2.13 W m−1 K−1 at 6 vol% showing 4 folds enhancements. The lap shear strength of epoxy/GnP nanocomposite adhesive improved from 10.7 MPa for neat epoxy to 13.57 MPa at 0.375 vol% GnPs. The concluded results are superior to other composites or adhesives at similar fractions of fillers such as single-walled carbon nanotubes, multi-walled carbon nanotubes or graphene oxide. The study promises that GnPs are ideal candidate to achieve multifunctional epoxy adhesives.

High Thermal Conductivity Silicone Elastomer Doped with Graphene Nanoplatelets and Eutectic GaIn Liquid Metal Alloy

This paper reports the thermal conductivity and mechanical properties of Sylgard 184 polydimethylsiloxane (PDMS) elastomer loaded with graphene nano-platelets (GnPs) and eutectic Ga-In (EGaIn) liquid metal droplets. We fabricated samples with different GnP and EGaIn concentrations and measured their thermal conductivity using the steady-state absolute technique. The results show that the thermal conductivity of the elastomer can be enhanced up to 5.6X when both GNP and EGaIn are included in the elastomer. Without EGaIn, the enhancement is limited to 4.4X. The results suggest that EGaIn inclusion did not change the viscosity of the uncured material significantly at any GnP loading level. We also observed that addition of just EGaIn to PDMS did not have a significant impact on the material’s stiffness while lowering its ultimate tensile strength by a factor of 2X and the maximum elongation at the break point by a factor of 1.6X. On the other hand, it was demonstrated that GnP addition to pure PDMS or EGaIn doped PDMS made the elastomer stiffer and less tear resistant with lower elongation at the break point.

Thermoelectric Nanocomposite Foams Using Non-Conducting Polymers with Hybrid 1D and 2D Nanofillers.

A facile processing strategy to fabricate thermoelectric (TE) polymer nanocomposite foams with non-conducting polymers is reported in this study. Multilayered networks of graphene nanoplatelets (GnPs) and multi-walled carbon nanotubes (MWCNTs) are deposited on macroporous polyvinylidene fluoride (PVDF) foam templates using a layer-by-layer (LBL) assembly technique. The open cellular structures of foam templates provide a platform to form segregated 3D networks consisting of one-dimensional (1D) and/or two-dimensional (2D) carbon nanoparticles. Hybrid nanostructures of GnP and MWCNT networks synergistically enhance the material system’s electrical conductivity. Furthermore, the polymer foam substrates possess high porosity to provide ultra-low thermal conductivity without compromising the electrical conductivity of the TE nanocomposites. With an extremely low GnP loading (i.e., ~1.5 vol.%), the macroporous PVDF nanocomposites exhibit a thermoelectric figure-of-merit of ~10−3. To the best of our knowledge, this ZT value is the highest value reported for organic TE materials using non-conducting polymers and MWCNT/GnP nanofillers. The proposed technique represents an industrially viable approach to fabricate organic TE materials with enhanced energy conversion efficiencies. The current study demonstrates the potential to develop light-weight, low-cost, and flexible TE materials for green energy generation.

Polypropylene nanocomposites reinforced with low weight percent graphene nanoplatelets

Abstract Polypropylene (PP) based graphene nanocomposites (NCs) find diverse applications in material science such as a material for making lightweight storage tanks. Herein, NCs with graphene nanoparticles (GnPs) and PP were prepared, using solution mixing method. GnPs have a slight effect on the crystalline structure of PP, as shown by X ray diffraction (XRD) results; thereby rendering the functionality of PP intact. There were little changes in the rheological behavior of the composite and the frictional losses incurred due to mobility of polymer chains were reduced with an increase in the GnP loading from 0.5% to 5%—a range not yet explored.

The thermo-mechanical response of PP nanocomposites at high graphene loading

Authors have successfully fabricated polypropylene/graphene nanoplatelets (PP/GNPs), nanocomposites that are thermally conductive, processable, and flame resistant. Thermal conductivity measurements indicated that the thermal coefficient scaled linearly with GNP loading, where a value of 2.0 W m− 1 K− 1 was achieved at 40 wt-% loading. Tensile measurements indicated that the modulus increased linearly with GNP loading, while the Izod impact, after an initial decrease, remained constant for loadings up to 50 wt-%. Small angle X-ray scattering (SAXS) showed a large decrease in the amount of lamellar structure relative to the neat PP, while wide angle X-ray scattering (WAXS) showed a high degree of crystallinity. These results are consistent with formation of a new type of layered nanocomposite, composed of crystalline PP chains oriented onto layered GNPs.

Strength improvements in toughened epoxy composites using surface treated GnPs

ABSTRACTNanographitic materials are gaining enormous interest as a new class of reinforcement for nanocomposites, promising revolutionary electrical, thermal, and mechanical properties. However, the progress has been quite limited especially in terms of mechanical properties. Here we report a significant leap, >2× increases in tensile strength and modulus of an epoxy composite using surface treated graphite nanoplatelets (GnPs). This corroborated by increases in Tgs as well as the presence of oxygen‐functionalized groups verified by XPS, suggest improved distribution and chemical interaction at the filler‐to‐matrix interface. Toughness values also showed increases with concentration, without compromising the strength or failure strain. However, if solvent levels during degassing were not reduced sufficiently, negligible contributions to strength and stiffness were observed with GnP loading. Subsequent elevated temperature treatments increased the strength of the composite due to cure enhancement of the matrix material, yet did not provide mechanical enhancements due to the incorporation of the filler. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40802.

황산처리된 녹조류 보강 폴리프로필렌 바이오복합재료에 대한 그래핀 첨가영향

폴리프로필렌(PP)을 매트릭스로, 황산처리된 녹조류(SGA)를 보강재로 사용한 바이오복합재료(biocomposites)의 기계적 특성을 향상시키기 위해 그래핀(GNP)의 평균입자크기와 첨가량에 따른 SGA/GNP/PP 복합재료를 제조하고 그 특성을 분석하였다. GNP의 첨가량에 의해 굴곡강도 및 충격강도는 점차 감소하는 경향을 나타내었다. 반면에, SGA와 GNP의 영향으로 인해 굴곡탄성률 및 저장탄성률은 크게 증가하였다. 평균입자크기가 <TEX>$5{\mu}m$</TEX>(GNP5)인 크기가 작은 GNP를 보강재로 사용하였을 경우 평균입자크기가 <TEX>$15{\mu}m$</TEX>(GNP15)인 GNP를 보강재로 사용한 복합재료와 비교하여 상대적으로 우수한 기계적 특성을 보였다. 이는 상대적으로 GNP5의 효과적인 분산에 기인한 것이다. 반면에, GNP5를 보강재로 사용한 복합재료의 열팽창에 대한 저항 특성은 GNP15와 비교하여 상대적으로 감소한 결과를 나타내었으며, 이는 열전도 특성이 우수한 GNP5가 상대적으로 넓고 고르게 분포되어있기 때문에 복합재료 전체에 열이 쉽게 전달되었기 때문으로 해석할 수 있었다. 결과적으로 SGA/GNP/PP 복합소재는 굴곡저항, 저장탄성률, 댐핑특성 등은 충분히 향상되어 범용 바이오컴포지트로 적용가능하였다. To improve the mechanical properties of polypropylene (PP) biocomposites reinforced with sulfuric acidtreated green algae (SGA), SGA/graphite nanoplatelets (GNP)/PP biocomposites were prepared and their properties were evaluated depending on the particle size and content of GNP. The flexural and impact strength of SGA/GNP/PP biocomposites decreased with the addition of GNP, whereas the flexrual and storage moduli were greatly improved with increasing GNP loading. SGA/GNP/PP biocomposites reinforced with GNP5 showed generally better mechanical properties compared to that reinforced with GNP15 mainly due to the improved dispersion of the smaller GNP. SGA/GNP/PP biocomposites reinforced with GNP5 showed a lower resistance to the thermal expansion because the relatively uniform dispersion of smaller GNP was responsible for the effective heat transfer to the polymer matrix. As a result, SGA/GNP/PP biocomposite was acceptable for the general purpose application due to the improved flexural resistance, storage moduli, and damping characteristics.

Pt and TCO free hybrid bilayer silver nanowire–graphene counter electrode for dye-sensitized solar cells

Here we report a novel transparent conductive oxide (TCO) and Pt free silver nanowire and graphene nanoplatelet (AgNW–GNP) based hybrid counter electrode (CE) for dye-sensitized solar cells (DSSCs) having appreciable photovoltaic performances compared to reference Pt–FTO based DSSCs. Simple solution processed bilayer AgNW–GNP hybrid CEs were prepared to investigate its applicability in DSSCs based on their electrocatalytic and charge transport properties. DSSCs prepared with AgNW–GNP hybrid CEs containing the GNP loading of 0.88μg/cm2 showed the photoconversion efficiency of 1.61±0.13% which is comparable with that of 1.87±0.15% made of standard Pt–FTO CEs.

Simultaneous enhancements in damping and static dissipation capability of polyetherimide composites with organosilane surface modified graphene nanoplatelets

Polyetherimide (PEI) possesses excellent thermal resistance and advanced mechanical properties, for which it has been used as interior materials in various transportation structures. Multifunctional PEI nanocomposites, in particular, with high damping properties and satisfactory static dissipation capability, will be more significant for those applications. In this study, PEI/graphene nanoplatelet (GNP) nanocomposites were fabricated via solution processing. Effects of GNP loading and surface silanization of GNPs on damping capacity and static dissipation properties were studied. The addition of the GNPs effectively increased the storage modulus of PEI, especially storage modulus at higher temperature (200 °C). The silanization of GNPs, on one hand, improved the dispersion quality; on the other hand, provided strong interfacial bonding with PEI matrix, which benefited the stress transfer within the composites. The superior damping capacity enhancements for the resulting nanocomposites are: with the loading of 3.0 wt% silanized GNP, the storage modulus of PEI increased approximately 4 times and 200 times at 30 °C and 200 °C, respectively, and the damping factor is 3 times higher than PEI. In addition, with the addition of 3.0 wt% GNPs, both low electrical resistivity (∼10 6 Ω∗cm) and low dielectric constant (∼7) were realized, corresponding to excellent volume static dissipation capability, however, silanization resulting in good interfacial bonding did not cause invisible impact on the electrical and dielectric properties of the nanocomposites. The superior damping capacity and static dissipation property make them suitable for intra-structure materials for airplane and transportation.

Poly(propylene)/Graphene Nanoplatelet Nanocomposites: Melt Rheological Behavior and Thermal, Electrical, and Electronic Properties

Poly(propylene) polymer nanocomposites containing graphene nanoplatelets (GnPs) with different loadings are fabricated via a facile ex-situ solution approach. Improved thermal stability and higher crystallinity are observed in the PNCs. Both electrical conductivity and real permittivity increase with increasing GnP loading. Electrical conductivity percolation is observed at 12.0 wt% GnP. The rheological behavior of the PNC melts are also investigated. It is found that the modulus and viscosity are reduced at small GnP loadings and increased above a critical loading.