Electromagnetic wave absorption and structural properties of wide-band absorber made of graphene-printed glass-fibre composite

Lightweight composites combining electromagnetic wave absorption and excellent mechanical properties are required in spacecraft and aircraft. A one- dimensional metamaterial absorber consisting of a stack of glass fibre/epoxy layers and graphene nanoplatelets/epoxy films was proposed and fabricated through a facile air-spraying based printing technology and a liquid resin infusion method. The production process allows an optimum dispersion of graphene nanoplatelets, promoting adhesion and mechanical integration of the glass fibre/epoxy layers with the graphene nanoplatelets/epoxy films. According to experimental results, the proposed wide-band absorber provides a reflection coefficient lower than −10 dB in the range 8.5–16.7 GHz and an improvement of flexural modulus of more than 15%, with a total thickness of ∼1 mm. Outstanding electromagnetic wave absorption and mechanical performance make the proposed absorber more competitive in aeronautical and aerospace applications

A review on nano fibre technology in polymer composites

The enormous attention and interest by both academics and industrial field for greener, biodegradable and renewable materials implicate a persuasive trends towards the encroachment of nano-materials science and technology in the polymer composite field. Nanocomposites creates high impacts on the development of nano materials with advanced features to solve potential risks with their wider industrial applications. Nano fibres are highly engineered fibres with diameters less than 100 nm that offer several advantages over conventional fibres. One dimensional (1D) nanostructure fillers such as carbon nanofibre and cellulose nanofibre are the most common, promising and unique for developing multifunctional nanocomposites with better properties and extensive applications compared to micro size fibres. Nano fibre technology brings revolution by providing products that are completely safe, truly greener, reliable and environmentally friendly for industries, researchers and users. This review article is intended to present valuable literature data on research and trend in the fields of carbon and cellulose nano fiber, nanocomposites with specific focus on various applications for a sustainable and greener environment

Effects of carbon nanotubes/graphene nanoplatelets hybrid systems on the structure and properties of polyetherimide-based foams

Foams based on polyetherimide (PEI) with carbon nanotubes (CNT) and PEI with graphene nanoplatelets (GnP) combined with CNT were prepared by water vapor induced phase separation. Prior to foaming, variable amounts of only CNT(0.1–2.0wt%) or a combination of GnP(0.0–2.0 wt %) and CNT (0.0–2.0 wt %) for a total amount of CNT-GnP of 2.0 wt %, were dispersed in a solvent using high power sonication, added to the PEI solution, and intensively mixed. While the addition of increasingly higher amounts of only CNT led to foams with more heterogeneous cellular structures, the incorporation of GnP resulted in foams with ¿ner and more homogeneous cellular structures. GnP in combination with CNT effectively enhanced the thermal stability of foams by delaying thermal decomposition and mechanically-reinforced PEI. The addition of 1.0 wt % GnP in combination with 1.0 wt % CNT resulted in foams with extremely high electrical conductivity, which was related to the formation of an optimum conductive network by physical contact between GnP layers and CNT, enabling their use in electrostatic discharge (ESD) and electromagnetic interference (EMI) shielding applications. The experimental electrical conductivity values of foams containing only CNT ¿tted well to a percolative conduction model, with a percolation threshold of 0.06 vol % (0.1 wt %) CNTPostprint (published version

Mechanical and multifunctional properties of polymer composites based on nano-structures

Mención Internacional en el título de doctorThe continuous development of industries, such as aerospace, automobile or energy, requires a new generation of polymer composites with novel functionalities, i.e. desired values of thermal and electrical conductivities, while maintaining their mechanical properties to be used in structural applications. One example of this new generation of composites could be hybrid fibre-reinforced polymers, consisting in fibre-reinforced polymers in which the matrix is appropriately modified with fillers. As a first step in the above mentioned approach, in this thesis the modification of polymers with different carbon-based fillers is analysed. Graphite nanoplatelets and carbon nanotubes were used to prepare polypropylene composites. Both fillers provided modest improvements on mechanical properties, while the electrical conductivity of the CNT composites was comparable to similar materials previously reported. The third filler was a novel micron-scaled carbon material which exhibited potential to perform as reinforcing agent in polymeric matrices. It was found that the filler significantly enhanced the thermal stability of the composites, while having modest effect on their thermal conductivity and mechanical behaviour. In order to produce polymer composites with specific combination of properties, hybrid carbon-based fillers, using spherical micro- and nano-particles as substrates, were obtained by the chemical vapour deposition technique (CVD). The first developed hybrid filler consisted in alumina nanoparticles and carbon nanotubes and it was used as filler for epoxy matrix composites. The obtained composites showed enhanced thermal and electrical conductivity compared with the neat matrix, although having similar mechanical behaviour. Finally, hollow glass microspheres with carbon nanofibres grown on its surface were obtained and then dispersed within a urethane acrylate resin. The main characteristic of the resulting composites is their low density and thermal conductivity while having higher electrical conductivity, compared to the neat resinEl continuo desarrollo de industrias como la aeroespacial, del automóvil o de la energía, requiere una nueva generación de materiales compuestos poliméricos con nuevas características, como niveles deseados de conductividades térmicas y eléctricas, y que al mismo tiempo mantengan unos niveles de propiedades mecánicas adecuados para ser usados en aplicaciones estructurales. Un ejemplo de materiales compuestos poliméricos mejorados podrían ser los materiales compuestos híbridos de matriz polimérica reforzados con fibras, en los cuales la matriz polimérica está modificada con los refuerzos apropiados. Como primera etapa en el desarrollo de los materiales anteriormente mencionados, en ésta tesis se han analizado varios polímeros modificados con diferentes refuerzos basados en carbono. Se han empleado nanoplaquetas de grafito y nanotubos de carbono para la preparación de materiales compuestos de matriz polipropileno. Ambos refuerzos proporcionaron ligeros aumentos de las propiedades mecánicas, mientras que la conductividad eléctrica de los materiales con nanotubos de carbono es comparable a la de materiales similares reportados en la literatura disponible. El tercer material es un novedoso refuerzo micrométrico basado en carbono, que ha sido empleado para el procesado de materiales compuestos de polipropileno. Éste refuerzo mejoró significativamente la estabilidad térmica del polipropileno al mismo tiempo que produjo mejoras más modestas en conductividad térmica y propiedades mecánicas. Con el objetivo de obtener materiales compuestos con las combinaciones deseadas de propiedades, se han obtenido materiales híbridos en estructuras de carbono por medio de un proceso de deposición química en fase vapor. Para ello se han empleado partículas cerámicas micro y nanométricas. En primer lugar se ha desarrollado un material híbrido compuesto por nanopartículas de alúmina y nanotubos de carbono, usado como refuerzo para una resina epoxi. Los materiales compuestos obtenidos presentaron mayores niveles de conductividad térmica y eléctrica mayores comparados con la matriz sin modificar, sin embargo su comportamiento mecánico era similar al de la resina. En segundo lugar se han obtenido microesferas de vidrio huecas con nanofibras de carbono sintetizadas en su superficie. Éste material se ha usado como refuerzo de materiales compuestos con una resina uretano acrilato. Las principales características de los materiales desarrollados son su baja densidad y conductividad térmica y alta conductividad eléctrica, comparada con la resina pura.Chapter 3: This work was supported by the European Commission under the 7th Framework Program, NFRP project (PICIG12-GA-2012-33924). R.G.V. gratefully acknowledges the Spanish Ministry of Science and Innovation for financial funding through the Ramon y Cajal Fellowship. J.P.F-B is grateful for support from the “Marie Curie” Amarout Programme. -- Chapter 4: This work was supported by the European Commission under the 7th Framework Program, NFRP project (PICIG12-GA-2012- 33924), ROBOHEALTH-A project (DPI2013-47944-C4-1-R) funded by Spanish Ministry of Economy and Competitiveness and from the RoboCity2030-II-CM project (S2009/DPI-1559), funded by Programas de Actividades I+D en la Comunidad de Madrid and cofunded by Structural Funds of the EU. R.G.V. gratefully acknowledges the Spanish Ministry of Science and Innovation for funding through the Ramon y Cajal Fellowship. L.C.H-R acknowledges the support from the Spanish Ministry of Education through the FPU programme (FPU14/06843). The authors would also thank to the Ministerio de Economía y Competitividad for the Torres Quevedo Grant of Pere Castell (PTQ12-05223). -- Chapter 5: This work was supported by the European Commission under the 7th Framework Program, NFRP project (PICIG12-GA-2012-33924). R. G. V. gratefully acknowledges the Spanish Ministry of Science and Innovation for financial funding through the Ramon y Cajal Fellowship. L. C. H-R acknowledges the support from the Spanish Ministry of Education through the FPU programme (FPU14/06843).-- Chapter 6: This work was supported by the European Commission under the 7th Framework Program, NFRP project (PICIG12-GA-2012-33924). R. G. V. gratefully acknowledges the Spanish Ministry of Science and Innovation for financial funding through the Ramon y Cajal Fellowship. L. C. H-R acknowledges the support from the Spanish Ministry of Education through the FPU programme (FPU14/06843).-- Chapter 7: This work was supported by the European Commission under the 7th Framework Program, NFRP project (PICIG12-GA-2012-33924), ROBOHEALTH-A project (DPI2013-47944-C4-1-R) funded by Spanish Ministry of Economy and Competitiveness and from the RoboCity2030-II-CM project (S2009/DPI-1559), funded by “Programas de Actividades I+D en la Comunidad de Madrid” and co-funded by Structural Funds of the EU. R. G. V. gratefully acknowledges the Spanish Ministry of Science and Innovation for financial funding through the Ramon y Cajal Fellowship. L. C. H-R acknowledges the support from the Spanish Ministry of Education through the FPU programme (FPU14/06843).Programa Oficial de Doctorado en Ciencia e Ingeniería de MaterialesPresidente: Miguel Ángel López Manchado.- Secretario: Silvia González Prolongo.- Vocal: Cristina Vallés Calliz

Mechanical and Electrical Characterization of Hybrid Carbon Nanotube Sheet-Graphene Nanocomposites for Sensing Applications

The unique mechanical and electrical properties of carbon nanotubes and graphitic structures have drawn extensive attention from researchers over the past two decades. The electro-mechanical behavior of these structures and their composites, in which electrical resistance changes when mechanical deformation is applied facilitates their use in sensing applications. In this work, carbon nanotube sheet- epoxy nanocomposites with the matrix modified with various contents of coarse and fine graphene nanoplatelets are fabricated. The addition of a secondary filler results in improvements of both electrical and mechanical properties. In addition, with the inclusion of the second filler, change in resistivity with mechanical deformation (manifested by gauge factor) is significantly enhanced. Nanocomposite with 5 wt. % coarse graphene platelets achieved is the most effective resistivity-strain behavior and largest gauge factor. Similar trend in variation of gauge factor variation was observed for fine graphene nanoplatelet - nanotube sheet nanocomposites. An analytical model for explaining these observations, incorporating strain and the effect of second filler, is developed. Sensors fabricated using these hybrid nanocomposites can be potentially used in damage sensing of aerospace carbon-fiber composites

Innovative composite materials with high graphene content

Nanocomposites based on the biomimetic brick and mortar architecture are gathering great attention recently due to the outstanding properties of the natural analogues. Thanks to the very high in-plane orientation of nanoplatelets and the low matrix content, these materials exhibit good mechanical performance combined with excellent functional properties based on the nanoplatelets characteristics. Key feature of these materials is the presence of a regular nanostructure that consists of alternated nanoplatelet and matrix layers. This thesis addresses the study of mechanical and functional properties of nacre-like composite materials based on graphite nanoplatelets (GNPs). Particular attention is devoted to providing an insight into stress transfer mechanism in high filler content composites and describing the parameters that influence the efficiency of stress transfer. GNPs have been chosen as filler thanks to the good combination of mechanical, thermal and electrical properties, and the very low cost. This would allow the mass production of graphene-based material with remarkable properties that could give a breakthrough in the materials field and industrial applications. In particular, nacre-like GNPs/Epoxy thin films at different filler content have been prepared by a top-down manufacturing technology and their mechanical properties in tension have been experimentally evaluated. The elastic modulus has been found to exhibit a maximum of ~15 GPa between 53-67 vol% filler content and then it starts dropping at higher loadings. This is attributed to a discontinuous polymeric matrix layer, and thus to an incomplete GNP surface coverage at high filler content. As a result, the effective area for stress-transfer is considerably reduced at the expense of the reinforcement efficiency. To better understand the quality of stress transfer between the two phases, a microscopic investigation has been carried out by micro Raman spectroscopy, highlighting the poor stress transfer between the two phases at high filler content. In the light of this, a model is proposed for predicting the stress transfer characteristics in brick-and-mortar systems by paying attention to possible non-uniform matrix distribution over the nanoplatelets. It has been observed that at relatively high filler content, the elastic modulus of these systems drops after a critical concentration deviating from the expected behaviour, which dictates that the higher the filler content the higher the macroscopic elastic modulus. Thus, understanding the mechanism at the base of stress transfer in composite with brick and mortar architecture is of great importance and allows the definition of design strategies for the optimization of the mechanical properties of this class of material. The proposed analysis captures well the observed effects and paves the way for the development and further improvement of this new class of engineering materials. The material architecture of GNPs based films also contribute to the excellent thermal end electrical conductivity of the material. Also, the high anisotropy between in plane and cross-plane conductivities of GNPs is reproduced at the macroscale by the thin films. In fact, at 70 vol%, GNPs/Epoxy films exhibit in plane and cross plane thermal conductivities of 216 W/mK and 8 W/mK respectively and sheet resistance of 0.33 Ω/sq. This makes the material an excellent shield for high radiative heat flux and electromagnetic waves. Therefore, these exceptional multifunctional properties and the good structural performances of GNP/Epoxy films, can be exploited to improve those of FRP. They can be easily integrated into fibre reinforced polymers (FRP), without adding any additional steps in the fabrication process, and without compromising the weight and mechanical performances of the material. In this thesis, it has been investigated the possibility of improving fire resistance of composites by integrating on their surface protective coatings. Graphene rich films have been bonded on the heat-exposed surface of Carbon Fibres Reinforced Plastic (CFRP) laminates observing a significant reduction of the temperatures on the heated surface and of the damaged area when exposed to high power radiative heat fluxes. The behaviour of CFRP composite has also been assessed through cone calorimeter test and the effect of graphene films protection has been investigated. In addition, the reaction of CFRP composite to high power radiative heat flux have been further investigated by laser spot heating. The effect of the protective layer thickness has been tested with different laser power (25, 50, 75, 100, 150 kW/m2), simulating standard testing conditions (AC 20-135 and ISO 5660-1 Standards). Finally, damage level and residual mechanical of exposed samples have been assessed as a function of the level of protection. A significant improvement of the post-heat flexural moduli and a significant reduction of the damaged areas have been obtained in graphene films protected laminates

A review of electrical and thermal conductivities of epoxy resin systems reinforced with carbon nanotubes and graphene-based nanoparticles

Epoxy (EP) resins exhibit desirable mechanical and thermal properties, low shrinkage during cuing, and high chemical resistance. Therefore, they are useful for various applications, such as coatings, adhesives, paints, etc. On the other hand, carbon nanotubes (CNT), graphene (Gr), and their derivatives have become reinforcements of choice for EP-based nanocomposites because of their extraordinary mechanical, thermal, and electrical properties. Herein, we provide an overview of the last decade's advances in research on improving the thermal and electrical conductivities of EP resin systems modified with CNT, Gr, their derivatives, and hybrids. We further report on the surface modification of these reinforcements as a means to improve the nanofiller dispersion in the EP resins, thereby enhancing the thermal and electrical conductivities of the resulting nanocomposites

Multifunctional Biocomposites Based on Polyhydroxyalkanoate and Graphene/Carbon Nanofiber Hybrids for Electrical and Thermal Applications

Most polymers are long-lasting and produced from monomers derived from fossil fuel sources. Bio-based and/or biodegradable plastics have been proposed as a sustainable alternative. Amongst those available, polyhydroxyalkanoate (PHA) shows great potential across a large variety of applications but is currently limited to packaging, cosmetics and tissue engineering due to its relatively poor physical properties. An expansion of its uses can be accomplished by developing nanocomposites where PHAs are used as the polymer matrix. Herein, a PHA biopolyester was melt blended with graphene nanoplatelets (GNPs) or with a 1:1 hybrid mixture of GNPs and carbon nanofibers (CNFs). The resulting nanocomposites exhibited enhanced thermal stability while their Young's modulus roughly doubled compared to pure PHA. The hybrid nanocomposites percolated electrically at lower nanofiller loadings compared to the GNP-PHA system. The electrical conductivity at 15 wt.% loading was ~ 6 times higher than the GNP-based sample. As a result, the electromagnetic interference shielding performance of the hybrid material was around 50% better than the pure GNPs nanocomposites, exhibiting shielding effectiveness above 20 dB, which is the threshold for common commercial applications. The thermal conductivity increased significantly for both types of bio-nanocomposites and reached values around 5 W K-1 m-1 with the hybrid-based material displaying the best performance. Considering the solvent-free and industrially compatible production method, the proposed multifunctional materials are promising to expand the range of application of PHAs and increase the environmental sustainability of the plastic and plastic electronics industry.Comment: 26 page