Multiscale Composites Research Articles

Reprint of Graphene foam/carbon nanotube/poly(dimethyl siloxane) composites for exceptional microwave shielding

Highly porous poly(dimethyl siloxane) (PDMS) composites containing cellular-structured microscale graphene foams (GFs) and conductive nanoscale carbon nanotubes (CNTs) are fabricated. The unique three-dimensional, multi-scale hybrid composites with inherent percolation and a high porosity of 90.8% present a remarkable electromagnetic interference shielding effectiveness (EMI SE) of ∼75dB, a 200% enhancement against 25dB of the composites made from GFs alone with the same graphene content and porosity. The corresponding specific EMI SE measured against the composite density is 833dBcm3/g. These values are among the highest for all carbon filler/polymer composites reported thus far. Significant synergy arises from the hybrid reinforcement structure of the composites: the GFs drive the incident microwaves to be attenuated by dissipation of the currents induced by electromagnetic fields, while the CNTs greatly enhance the dissipation of surface currents by expanding the conductive networks and introducing numerous interfaces with the matrix.

Novel solvent-thermal preparation of a SnO2 nanoparticles/expanded graphite multiscale composite with extremely enhanced electrical performances for Li-ion batteries

A novel SnO2 nanoparticles (NPs)/expanded graphite (EG) multiscale hybrid composite was prepared via an elaborately designed solvent-thermal reaction and the following anneal treatment. A mixed solvent system of acetone-H2O with volume proportion of 3:1 was employed for the solvent-thermal reaction in order to realize moderate hydrolysis rate of Sn4+ and favorable wettability between solvent molecules and EG surface. Acetone played a very positive role for the uniform nucleation and crystal growth of SnO2-NPs, which could be proved by the ultrafine sizes of 3–6nm and well-crystallized texture of SnO2-NPs, as well as their homogeneous anchor on the surface of EG. As an anode material for Li-ion batteries, the SnO2-NPs/EG composite exhibited excellent long-term cycling stability, e.g. decay-free reversible capacity of 976mAhg−1 after 100 cycles, and good rate capability (>400mAhg−1 at 2000mAg−1). The extraordinary electrochemical performances arise from the structural advantages of the composite: the ultrafine SnO2-NPs with high dispersity on conductive EG matrix supply not only large quantity of accessible active sites for lithium-ion insertion but also good conductivity and short diffusion length for lithium ions. These results suggest the SnO2-NPs/EG composite would be a promising candidate as anode material for next-generation LIBs.

Multiscale modeling of stress transfer in continuous microscale fiber reinforced composites with nano-engineered interphase

This study is focused on the mechanical properties and stress transfer behavior of multiscale composites containing nano- and micro-scale reinforcements. The distinctive feature of construction of this composite is such that the carbon nanostructures (CNS) are dispersed in the matrix around the continuous microscale fiber to modify microfiber-matrix interfacial adhesion. Such CNS are considered to be made of aligned CNTs (A-CNTs). Accordingly, multiscale models are developed for such hybrid composites. First, molecular dynamics simulations in conjunction with the Mori-Tanaka method are used to determine the effective elastic properties of nano-engineered interphase layer composed of CNS and epoxy. Subsequently, a micromechanical pull-out model for a continuous fiber multi-scale composite is developed, and stress transfer behavior is studied for different orientations of CNS considering their perfect and imperfect interfacial bonding conditions with the surrounding epoxy. Such interface condition was modeled using the linear spring layer model with a continuous traction but a displacement jump. The current pull-out model accounts for the radial as well as the axial deformations of different orthotropic constituent phases of the multiscale composite. The results from the developed pull-out model are compared with those of the finite element analyses and are found to be in good agreement. Our results reveal that the stress transfer characteristics of the multiscale composite are significantly improved by controlling the CNT morphology around the fiber, particularly, when they are aligned along the axial direction of the microscale fiber. The results also show that the CNS-epoxy interface weakening significantly influences the radial stress along the length of the microscale fiber.

Unlocking the potential of graphenes for the development of multi-scale composites – Functionalization via plasma

The potential of graphene is well known amongst material and composites manufacturers, as discussed by Dr Martin Kemp.

Synergistic effect of MWCNTs functionalization on interfacial and mechanical properties of multi-scale UHMWPE fibre reinforced epoxy composites

Multi-walled carbon nanotubes (MWCNTs) as a secondary reinforcement were incorporated to an epoxy matrix reinforced with ultra-high molecular weight polyethylene (UHMWPE) fibre. To achieve a high level of compatibility with epoxy matrix, both the UHMWPE fibre and MWCNTs were chemically treated with glycidyl methacrylate (GMA) and amino-thiol end radicals via free radical polymerization and click chemistry, respectively. The effects of these treatments on properties of the multi-scale composites, i.e. epoxy consisting of micro (UHMWPE) and nano (MWCNT) size reinforcements, were studied through investigation of micromechanical and macromechanical properties of the composites. Results showed both fibre surface treatment and matrix modification improved fibre-matrix wettability, work of adhesion, interfacial shear strength (IFSS), and tensile properties. Compared with untreated composites e.g., UHMWPE fibre/epoxy, the combination of a low loading of aminated MWCNTs (a-MWCNTs) and GMA-treated UHMWPE fibre in an epoxy resin enhanced work of adhesion, IFSS, tensile strength, and tensile modulus by ∼26.0%, ∼336.1%, ∼67.3%, and ∼35.5%, respectively. Analysis of surface morphology of micro and macro composites were performed by SEM observations, demonstrating that the mechanical interlocking effect along with the covalent bonding at interface are synergistically playing a major role in such significant improvements in composite properties.

Viscoelastic response and interlaminar delamination resistance of epoxy/glass fiber/functionalized graphene oxide multi-scale composites

Graphene oxide (GO) was functionalized using three different diamines, namely ethylenediamine (EDA), 4,4′-diaminodiphenyl sulfone (DDS) and p-phenylenediamine (PPD) to reinforce an epoxy/glass fiber (EP/GF) composite laminate, with the aim of improving the overall composite mechanical performance. Different mechanical characterization techniques were used to determine the mechanical performance, including: tensile stress strain, double cantilever beam (DCB) mode-I fracture toughness and dynamic mechanical thermal analysis (DMTA). Scanning electron microscopy (SEM) was used to support the results and conclusions. The results demonstrated remarkable enhancements in the mechanical performance of EP/GF composite laminates by incorporation of functionalized graphene oxide (FGO) nanofiller, whilst the mechanical performance of the GO reinforced composite only improved marginally. Finally, the mechanical performance of the EP/GF/FGO multi-scale composites was found to be dependent on the type of FGO functional groups; of which EDA exhibited the highest performance. These investigations confirmed that the EDA-FGO-reinforced EP/GF composites possess excellent potential to be used as multifunctional engineering materials in industrial applications.

On the nature of interface of carbon nanotube coated carbon fibers with different polymers

Experimental investigations are carried out to analyse the wetting behaviour of carbon nanotube (CNT) coated carbon fiber to determine their suitability to process carbon nanotube coated carbon fiber/polymer multiscale composites for structural applications. To overcome the problem of agglomeration, CNTs are grown directly on the surface of carbon fibers as well as fabric using thermal chemical vapour deposition (CVD) technique. The term multiscale is used because different reinforcement mechanisms operate at the scale of long fibers and CNTs which are of few micrometers in length. The load carrying capacity of these multiscale composites critically depends on the efficiency and extent of load transfer from low strength matrix to high strength fiber which in turn depends on the interfacial strength between CNT coated carbon fiber and polymer matrix. A systematic analysis of wetting behaviour of CNT coated carbon fiber with epoxy and polyester matrix is carried out in this study. It is shown that CNT coated carbon fibers as well as fabric show better wettability with epoxy matrix as compared to polyester matrix. This results in stronger interface of CNT coated carbon fiber with epoxy as compared to polyester in multiscale composite system. A similar observation is made in nanoindentation testing of single fiber multiscale composites processed with epoxy and polyester matrix. In addition, it is observed that wettability, interfacial strength and average properties of CNT coated carbon fiber/polymer composites are a function of CNT density on the surface of carbon fibers.

Electrically conductive functionalized-GNP/epoxy based composites: From nanocomposite to multiscale glass fibre composite material

Abstract The electrical behaviour and mechanical properties of functionalized graphene nanoplatelets (GNPs) reinforced epoxy-based composites were evaluated. These properties were analysed scaling up from the nanocomposite to the multiscale composite material. The electrical conductivity of 12 wt % GNPs reinforced nanocomposites was in the order of 10 −4 S/m, in contrast to the in-plane conductivity of multiscale composite materials with the same GNPs content, which was found to be ∼10 −3 S/m. This was attributed to microstructural features that also provoke the electrical conductivity through the thickness diminish down to ∼10 −4 S/m in multiscale composites. Additionally, mechanical properties were enhanced by the dispersion of GNP in nanocomposites but experienced a reduction in glass fibre composites because of the formation of a weak interface between the GNPs filled matrix and fibres.

Modeling and Simulation of Nano and Multiscale Composites

Modeling and Simulation of Nano and Multiscale Composites

Effect of filtration in functionalized and non-functionalized CNTs and surface modification of fibers as an effective alternative approach

Abstract Fabrication of multiscale composites by the addition of CNT in epoxy matrices as previous step to the impregnation process leads to several manufacturing difficulties associated to filtration effects and viscosity increments. These effects have been analyzed finding a relation between the type of CNT and the dispersion degree with the change in the rheological behavior and the heterogeneity of the mechanical properties. This heterogeneity is associated to filtration effects of the nanoreinforcement. Modification of the carbon fibers by a nanoreinforced sizing has been presented as an alternative, obtaining homogeneous composites and avoiding the filtration effects. These multiscale composites have higher electrical and interlaminar mechanical properties.

Graphene foam/carbon nanotube/poly(dimethyl siloxane) composites for exceptional microwave shielding

Highly porous poly(dimethyl siloxane) (PDMS) composites containing cellular-structured microscale graphene foams (GFs) and conductive nanoscale carbon nanotubes (CNTs) are fabricated. The unique three-dimensional, multi-scale hybrid composites with inherent percolation and a high porosity of 90.8% present a remarkable electromagnetic interference shielding effectiveness (EMI SE) of ∼75dB, a 200% enhancement against 25dB of the composites made from GFs alone with the same graphene content and porosity. The corresponding specific EMI SE measured against the composite density is 833dBcm3/g. These values are among the highest for all carbon filler/polymer composites reported thus far. Significant synergy arises from the hybrid reinforcement structure of the composites: the GFs drive the incident microwaves to be attenuated by dissipation of the currents induced by electromagnetic fields, while the CNTs greatly enhance the dissipation of surface currents by expanding the conductive networks and introducing numerous interfaces with the matrix.

Characterization of thermoelectric properties of multifunctional multiscale composites and fiber-reinforced composites for thermal energy harvesting

Abstract We have fabricated two types of multifunctional composites, carbon nanotube (CNT)/glass fiber (GF)/epoxy composites and carbon fiber (CF)/epoxy composites, and evaluated thermoelectric properties of the composites for applications as n/p type thermoelectric materials as well as load carrying structural composites. Several test samples of CNT/GF/epoxy composites with various CNT concentrations were fabricated using a three-roll mill and hand-layup process on a hot plate, while CF/epoxy composite samples were manufactured using a hand-layup process. Experimental results demonstrated that the electrical resistivity of the CNT/GF/epoxy composite (multiscale composite) samples decreased as the CNT concentration increased. In-plane samples showed higher electrical and thermal conductivities due to partial alignment of CNTs in the multiscale composites and continuity of carbon fibers in CF/epoxy composites. Generally, CF/epoxy composites had better electrical and thermal conductivities than those of multiscale composites. In the Seebeck coefficient test, the multiscale composites showed n-type thermoelectric behavior, whereas the CF/epoxy composites showed p-type behavior. When temperature gradients were applied to closed circuits comprised of multiscale composites and CF/epoxy composites as n-type and p-type materials, respectively, an electric current was successfully generated.

Synergetic effects on the mechanical and fracture properties of epoxy composites with multiscale reinforcements: Carbon nanotubes and short carbon fibers

ABSTRACTThe ball‐milling/liquid‐phase oxidation (BMLPO) method was used to fabricate surface‐modified short carbon fibers (SCFs). Multiscale epoxy composites reinforced with a combination of SCFs and multiwalled carbon nanotubes (MWNTs) were prepared. Atomic force microscopy observations and contact angle measurement were used to investigate the modification effect of the BMLPO method. Mechanical tests and scanning electron microscopy observations were used to study the effects of the SCFs, MWNTs, and their combination on tensile properties, impact strength, and fracture toughness of the epoxy composites. The results show that the surface roughness of the SCFs after BMLPO treatment increased, and the wettability of the SCFs was improved as well. The combined use of the SCFs and MWNTs had a synergetic effect on the tensile strength, fracture toughness, and impact strength of the epoxy composites. The addition of MWNTs promoted the plastic deformation of the epoxy matrix and decreased the stress‐concentration level near the SCF/matrix interface; these were considered the main causes of the synergetic effect. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43500.

New Multi-Scale Hybrid System Based on Maple Wood Flour and Nano Crystalline Cellulose: Morphological, Mechanical and Physical Study

In the first part of this work, composites based on polypropylene (PP) and maple wood flour (MF) were prepared by melt compounding using twin-screw extrusion followed by compression molding. The morphological and mechanical properties of the composites were analyzed for three samples: PP, MF/PP and MF/PP containing maleic anhydride grafted polypropylene (MAPP) as coupling agent. The results showed that MF/PP composites have improved mechanical properties, especially tensile modulus (+33 %), with only 8 % increase in density. The addition of MAPP further improved the mechanical properties, in particular tensile modulus (up to 51 %), which could be related to better fiber/matrix adhesion. In the second step, nano crystalline cellulose (NCC) was added to all samples to produce NCC-MF/PP hybrid composites. From the mechanical analysis performed, the hybrid composites with MAPP have improved properties, especially tensile (+53 %) and flexural (+40 %) moduli. These results confirmed that multi-scale hybrid NCC-MF composites can substantially improve the mechanical properties of polyolefins with limited increase in density (14 %) leading to high specific properties.

In situ process monitoring of hierarchical micro-/nano-composites using percolated carbon nanotube networks

We report a method to monitor the manufacturing process of hierarchical micro-/nano-composites that uses integrated and percolated multi-walled carbon nanotube (MWCNT) networks with the aim of reducing part-to-part variability. Composites were fabricated by VARTM. Fiber textiles were spray-coated with MWCNTs, electrodes were embedded prior to vacuum bagging. In situ process monitoring was achieved by measurement of the electrical resistance of electrode pairs. The effects of MWCNT density and length on the ability to monitor the manufacturing process were evaluated. Experiments showed that monitoring the changes in resistance between electrode pairs on the conductive MWCNT network allowed various events during the manufacturing process, including part infusion, onset of crosslinking, and gel point of the resin, which are necessary for accurate evaluation of part quality. Our simple yet effective method to monitor the manufacturing processes and predict the final-part quality of multiscale composites can be integrated into existing processes with minimal modifications.

Organo-Montmorillonite Modified Bismaleimide as Matrix in Carbon Fibre-Reinforced Composites

Two types of organo-montmorillonite (OMMT) modified bismaleimide (BMI) nanocomposites based on 4,4'-bismaleimide diphenyl methane (BDM) and O,O'-diallyl bisphenol A (DBA) have been synthesized. A compression moulding process was used to fabricate carbon fibre-reinforced OMMT/BMI multiscale composites. X-ray diffractometry (XRD) and transmission electron microscopy (TEM) indicated that the silicate layers of OMMT were partially exfoliated and dispersed uniformly in the nanocomposites. The study showed that the interlaminar shear strength (ILSS) and flexural properties of the carbon fibre composites were improved by the incorporation of OMMT. The maximum increment of the ILSS, flexural strength and elastic modulus of carbon fibre composites were 19.09%, 38.26% and 26.97%, respectively. Scanning electron microscope (SEM) photographs revealed that the destruction modes of carbon fibre composites were also changed after the OMMT was introduced into the composites system.

Mechanical properties of carbon nanotube/carbon fiber reinforced thermoplastic polymer composite

Carbon nanotube (CNT)/carbon fiber (CF) hybrid fiber was fabricated by sizing unsized CF tow with a sizing agent containing CNT. The hybrid fiber was used to reinforce a thermoplastic polymer to prepare multiscale composite. The mechanical properties of the multiscale composite were characterized. Compared with the base composite (traditional commercial CF), the multiscale composite reinforced by the CNT/CF hybrid fiber shows increases in interlaminar shear strength (ILSS) and impact toughness. Laminate containing CNTs showed a 115.4% increase in ILSS and 27.0% increase in impact toughness. The reinforcing mechanism was also discussed by observing the impact fracture morphology. POLYM. COMPOS., 38:2001–2008, 2017. © 2015 Society of Plastics Engineers

An Assessment of the Role of Fiber Coating and Suspending Fluid on the Deposition of Carbon Nanotubes onto Glass Fibers for Multiscale Composites

Multiwall carbon nanotubes (MWCNTs) were ultrasonically deposited onto glass fibers by using either distilled water or a hydrolyzed silane. The role of the fiber coating (sizing) was investigated by depositing MWCNTs onto glass fibers with and without sizing. The interfacial shear strength (IFSS) between the MWCNT‐modified fibers and a vinyl ester matrix was analyzed by the microbond test. Increased electrical conductivity and surface roughness was achieved upon MWCNT deposition on the fibers. The use of a silane as suspending fluid renders moderate benefits with respect to distilled water, and its role is more critical in improving the IFSS between the MWCNT‐modified fibers and the matrix.

Damage Mechanisms of Hierarchical Composites: Computational Modelling

Computational studies of damage mechanisms in hierarchical composites, including biocomposites, nanoparticle reinforced polymer composites and other materials are discussed. Different methods of the analysis of hierarchical effects in the multiscale composites are demonstrated, among them, hierarchical fiber bundle model, 3D multiscale finite element models, analytical studies. Considering wood as a gradient, cellular material with layered composite cell walls, one analyzed the effect of wood structure on damage resistance of wood. The influence of nanoparticles distribution in unidirectional polymer matrix composites with secondary nanoreinforcement on the strength and damage resistance of the composites is demonstrated. The concept of nanostructuring of interfaces and grain boundaries as an important reserve of the improvement of the materials properties is formulated.

In-plane shear behaviour of multiscale hybrid composites based on multiwall carbon nanotubes and long carbon fibres

Both in-plane shear modulus and in-plane shear strength of multiscale hybrid composites have been studied. Carbon fibre-based laminates have been fabricated including functionalized multiwall carbon nanotubes by means of solvent spraying method and hot compression process. Mechanical in-plane shear characterization has been carried out using off-axis three-point flexure test. Fibre volume fraction of multiscale hybrid composites has been determined through thermogravimetric analysis and fracture surfaces after testing have been imaged by scanning electron microscopy. Results reveal that the inclusion of functionalized multiwall carbon nanotubes on laminates has a small influence on in-plane shear modulus, although it increases up to 15% of the in-plane shear strength. Multiwall carbon nanotube functionalization improves shear stress transmission between matrix and carbon nanotubes, which represents a reinforcement effect responsible for the increase in in-plane shear strength. Scanning electron micrographs have confirmed in-plane shear tests results.