Multi-scale Hybrid Composites Research Articles

Unidirectional spread‐tow carbon fiber/polypropylene composites reinforced with mechanically aligned multi‐walled carbon nanotubes and exfoliated graphite nanoplatelets

We investigated efficient methods to maximize the mechanical properties of carbon fiber/polypropylene (PP) composites by combining unidirectional spread‐tow carbon fibers (USCFs) and mechanically stretched PP films reinforced with aligned carbon nanomaterials (CNMs), such as multi‐walled carbon nanotubes (MWCNTs) and exfoliated graphite nanoplatelets (xGnPs). CNM/PP composite films were fabricated using film extrusion process, which resulted in tension‐induced orientation of CNMs. The influences of CNMs and their orientations in the films, the speed of the drawing rollers (take‐up speed), and the degree of crystallinity on the mechanical properties of nanocomposites were investigated. Multiscale hybrid composites (MHCs) consisting of USCFs and PP films reinforced with MWCNTs and xGnPs were manufactured by hot pressing. As compared with neat USCF/PP composites, USCF/PP composites containing 1 wt% aligned CNMs showed up to 18.3 and 77.3% increases in tensile modulus and strength, respectively, and 68.4 and 36.1% increases in flexural modulus and strength, respectively. In parallel, modeling and simulation of CNM/PP composite films and CNM/USCF/PP composites were performed to predict the tensile properties, taking into account the effects of CNM orientation. The mechanical properties of both nanocomposite films and MHCs were most dominantly affected by the degree of polymer crystallinity and CNM orientation. POLYM. COMPOS., 39:E1251–E1261, 2018. © 2018 Society of Plastics Engineers

Prediction of thermal conductivities of carbon-containing fiber-reinforced and multiscale hybrid composites

Abstract An effective analytical modeling method to predict the thermal conductivity of a multiscale hybrid composite, consisting of nano-sized filler, micron-scale continuous fiber and polymer matrix, has been proposed. The method combines the modified Mori-Tanaka method and woven fiber composite modeling, which are used to predict the thermal conductivities of carbon nanotube(CNT)/polymer composites and CNT/woven fiber/polymer multiscale composites, respectively. The thermal-electrical circuit analogy was applied to the unit cell of a multiscale woven fiber composite, which allowed predictions of conductivities in both in-plane and through-thickness directions. The experimental validations on woven fiber composites and multiscale composites revealed that thermal conductivity predictions based on the proposed modeling approaches agreed well with the experimental results, taking into account the effects of CNT content, fiber volume fraction, constituent conductivities, and fiber undulation.

Comparison of two different carbon nanotubes-based hybrid multiscale composites with respect to mechanical and electrical properties

ABSTRACTPristine and carboxylic acid functionalised carbon nanotubes (CNTs-P and CNTs-COOH) hybrid composites based on ultrasonically processed nanocomposite epoxy matrix have been prepared. The thermodynamic interactions between CNTs and epoxy components are evaluated through solution experiment. The measurements of mechanical properties and volume electrical resistivity are performed to characterise the structure-property interplay of CNTs hybrid composites. A 0.3 wt-% CNTs-COOH loading significantly enhances the glass transition temperatures (Tg) of the resultant hybrid composites. The re-agglomeration of CNTs-P has been ascribed to the thermodynamic and kinetic factors, which determine the morphological characteristics of CNTs within the overall composites. CNTs-P network enables a continuous conductive path to be present in the composites at lower CNTs-P concentration. An analysis of the effects of the functionalisation of CNTs on the structure and properties of their hybrid composites has been carried out.

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.

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.

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.

Impact behavior and fractographic study of carbon nanotubes grafted carbon fiber-reinforced epoxy matrix multi-scale hybrid composites

Carbon nanotubes are the most promising reinforcement for high performance composites. Multiwall carbon nanotubes were directly grown onto the carbon fiber surface by catalytic thermal chemical vapor deposition technique. Multi-scale hybrid composites were fabricated using the carbon nanotubes grown fibers with epoxy matrix. Morphology of the grown carbon nanotubes was investigated using field emission scanning electron microscopy and transmission electron microscopy. The fabricated composites were subjected to impact tests which showed 48.7% and 42.2% higher energy absorption in Charpy and Izod impact tests respectively. Fractographic analysis of the impact tested specimens revealed the presence of carbon nanotubes both at the fiber surface and within the matrix which explained the reason for improved energy absorption capability of these composites. Carbon nanotubes presence at various cracks formed during loading provided a direct evidence of micro crack bridging. Thus the enhanced fracture strength of these composites is attributed to stronger fiber–matrix interfacial bonding and simultaneous matrix strengthening due to the grown carbon nanotubes.

Preparation and properties of hierarchical composites based on carbon nanotubes‐coated glass babric preform

A strategy based on carbon nanotubes (CNTs)‐containing sizing dispersion has been implemented to fabricate nanocomposite preforms and their hybrid multiscale composites. The state of pristine CNTs and carboxylic acid functionalized CNTs (CNTs–COOH) in sizing dispersion was effectively monitored by on‐line measuring electrical conductivity. The effects of different CNTs coating applied onto glass fabric on wettability of nanocomposite fibrous reinforcement with epoxy matrix were evaluated using scanning electron microscopy and capillary experiment. A CNTs‐COOH loading of 0.5 wt% gave rise to 97% and 30°C increases in the storage modulus (G′) and glass transition temperature of the resulting hybrid composites, respectively. The enhanced thermomechanical properties of the CNTs hybrid composites are closely related to the stable CNTs sizing dispersion and uniform coating onto fiber reinforcement. The mechanism for reinforcing composites through toughening resin region with CNTs desorbing from primary fiber surface during impregnation has been identified. POLYM. COMPOS. 37:979–986, 2016. © 2014 Society of Plastics Engineers

Electrophoretic deposition of different carbon nanoscale reinforcements on carbon fiber fabrics and mechanical properties of the resulting hybrid multi-scale epoxy composites

Three types of carbon nanoscale reinforcements (CNRs) including the shortened electrospun carbon nanofibers (ECNFs, with diameters and lengths of ∼200 nm and ∼15 µm, respectively), carbon nanofibers (CNFs), and graphite nanofibers (GNFs) were electrophoretically deposited on carbon fiber (CF) fabrics for the fabrication of hybrid multi-scale epoxy composites. The results indicated that the electrophoretic deposition (EPD) of CNRs onto CF fabrics led to substantial improvements on mechanical properties of hybrid multi-scale epoxy composites; in particular, the hybrid multi-scale epoxy composite containing surface-functionalized ECNFs (with amino groups) exhibited the highest mechanical properties. The study also indicated that some agglomerates of CNRs (particularly GNFs) could form during the EPD process, which would decrease mechanical properties of the resulting composites. Additionally, the reinforcement mechanisms were investigated, and the results suggested that continuous (or long) ECNFs would outperform short ECNFs on the reinforcement of resin-rich interlaminar regions in the composites. POLYM. COMPOS., 35:1229–1237, 2014. © 2013 Society of Plastics Engineers

Nano-epoxy resins containing electrospun carbon nanofibers and the resulting hybrid multi-scale composites

For the first time, electrospun carbon nanofibers (ECNFs, with diameters and lengths of ∼200nm and ∼15μm, respectively) were explored for the preparation of nano-epoxy resins; and the prepared resins were further investigated for the fabrication of hybrid multi-scale composites with woven fabrics of conventional carbon fibers via the technique of vacuum assisted resin transfer molding (VARTM). For comparison, vapor growth carbon nanofibers (VGCNFs) and graphite carbon nanofibers (GCNFs) were also studied for making nano-epoxy resins and hybrid multi-scale composites. Unlike VGCNFs and GCNFs that are prepared by bottom-up methods, ECNFs are produced through a top-down approach; hence, ECNFs are more cost-effective than VGCNFs and GCNFs. The results indicated that the incorporation of a small mass fraction (e.g., 0.1% and 0.3%) of ECNFs into epoxy resin would result in substantial improvements on impact absorption energy, inter-laminar shear strength, and flexural properties for both nano-epoxy resins and hybrid multi-scale composites. In general, the reinforcement effect of ECNFs was similar to that of VGCNFs, while it was higher than that of GCNFs.

Influence of Surfactant Modification on Structure and Properties of CNT Hybrid Multiscale Composites

Hybrid composites with hierarchical structure, simultaneously reinforced by microscale glass fibers and CNTs, are fabricated using resin transfer molding. Processing/structure/property relationships of the resulting hybrid multiscale composites are studied. Loading of the CNTs with surfactant are crucial for structures and properties of composites. Microscopic observation confirms the formation of a CNT percolation network and its roles in mechanical reinforcement and electrical amelioration. The dependence of the CNT morphology on surfactant concentration is responsible for the variation in the mechanical and electrical responses of composites. The hierarchical structure influenced by several competing factors bears great potential for tuning the performance of the hybrid composites.

Structure and properties of aeronautical composites using carbon nanotubes/epoxy dispersion as nanocomposite matrix

The structure and properties of hybrid multiscale composites containing carbon nanotubes (CNTs) was reported. CNTs were dispersed in epoxy by using high energy ultrasonication, followed by the fabrication of CNT hybrid composites via resin transfer molding (RTM) processing. The processability of CNTs/epoxy systems was explored by a capillary experiment. The dependences of mechanical and electrical properties of the hybrid composites on CNT content were investigated. Microscopic observation confirms the formation of CNTs percolation network. The different roles of CNT networks in mechanical reinforcement and electrical amelioration were analyzed. One explanation based on the dispersion and distribution of CNTs is proposed. It is found that the variations of the hybrid composites with respect to mechanical and electrical properties are attributed to the hierarchical structure in the hybrid composites. As far as the hybrid multiscale composites produced via RTM process is concerned, the formation of CNT percolation network, subjected to dynamic impregnation, is hindered by the presence of continuous fibrous reinforcement. The hierarchical structure influenced by several competing factors reveals great potential in being able to tailor the structural and functional performance of the CNT hybrid composites. The effects of CNTs on the dimensional stability of polymer based composites are also assessed. POLYM. COMPOS., 34:1690–1697, 2013. © 2013 Society of Plastics Engineers

Microwave properties of carbon nanotube/microwire/rubber multiscale hybrid composites

A novel microwire/carbon nanotube (CNT)/rubber multiscale hybrid composite is reported here. Compared to CNT composites, the hybrid composite shows enhanced conductivity and permittivity and decreased intrinsic impedance, giving rise to significant improvement of absorption yet along with the increase of reflection loss. The hybrid composite also shows a field tunable effect with a featured critical bias, which divided two opposite frequency dispersion trend with the field due to the different biasing mechanism decided by the field magnitude. The counter-influence of wires and CNTs plays an important role in formulating the resulting electromagnetic responses.

Fabrication and properties of CNTs/carbon fabric hybrid multiscale composites processed via resin transfer molding technique

Carbon nanotubes (CNTs) are effective fillers/reinforcements regarding improving the properties of polymer. In the present paper, carboxylic acid functionalized CNTs were used to modify epoxy with intent to develop a nanocomposite matrix for hybrid multiscale composites combining benefits of nanoscale reinforcement with well-established fibrous composites. CNTs were dispersed in epoxy by using high energy sonication. At low contents of CNTs, hybrid multiscale composites specimens were manufactured via resin transfer molding (RTM) process. The processibility of CNTs/epoxy systems was explored with respect to their viscosity. The dispersion quality and re-agglomeration behavior of CNTs in epoxy were characterized using optical microscope. A CNTs loading of 0.025wt% significantly improved the glass transition temperatures (Tg) of the hybrid multiscale composites. Scanning electron microscopy (SEM) was used to examine the fracture surface of the failed specimens. It is demonstrated that the addition of small amount of CNTs (0.025wt%) to epoxy for the fabrication of multiscale carbon fabric composites via RTM route effectively improves the matrix-dominated properties of polymer based composites. Hybridization efficiency in carbon fiber reinforced composites using CNTs is found to be highly dependent on the changes in the dispersion state of CNTs in epoxy.

Fabrication and mechanical properties of hybrid multi-scale epoxy composites reinforced with conventional carbon fiber fabrics surface-attached with electrospun carbon nanofiber mats

This paper reports the fabrication and mechanical properties of hybrid multi-scale epoxy composites reinforced with conventional carbon fiber (CF) fabrics surface-attached with electrospun carbon nanofiber (ECN) mats. The ECNs were prepared via thermal treatments of polyacrylonitrile copolymer nanofibers, which were produced by the electrospinning technique and collected as overlaid mats on the T300 CF fabrics. The ECN-CF fabrics/mats were used as innovative reinforcement fillers for the fabrication of hybrid multi-scale composites (with SC-15 epoxy resin) through the composite-manufacturing technique of vacuum assisted resin transfer molding. Three-point bending test and short-beam shear test were carried out to evaluate the strengthening/toughening effects of ECNs on mechanical properties of the novel composites. The results indicated that out-of-plane mechanical properties of the ECN-CF/epoxy composites were considerably higher than the control sample of traditional CF/epoxy composites.

Experimental assessment on potential for processiblity of carbon nanotubes/epoxy system used as nanocomposites

In this study, carboxylic acid functionalized carbon nanotubes (CNTs) were used to modify epoxy with intent to develop a nanocomposite matrix for hybrid multiscale composites combining benefits of nanoscale reinforcement with well-established fibrous composites. CNTs were dispersed in epoxy by using high energy sonication, followed by the fabrication of epoxy/CNTs composites. The processibility of CNTs/epoxy systems was explored with respect to their dispersion state and viscosity. The dependences of viscosity, mechanical and thermomechanical properties of nanocomposite system on CNTs content were investigated. The dispersion quality and reagglomeration behavior of CNTs in epoxy and the capillary infiltration of continuous fiber with the epoxy/CNTs dispersion were characterized using optical microscope and capillary experiment. As compared with neat epoxy sample, the CNTs nanocomposites exhibit flexural strength of 126.5 MPa for 1 wt% CNTs content and impact strength of 28.9 kJ m−2 for 0.1 wt% CNTs content, respectively. A CNTs loading of 0.1 wt% significantly improved the glass transition temperatures, Tg, of the nanocomposites. Scanning electron microscopy (SEM) was used to examine the fracture surface of the failed specimens. It is demonstrated that the properties of CNTs/epoxy system are dispersion-dominated and interface sensitive. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

The effect of surface modification with carbon nanotubes upon the tensile strength and Weibull modulus of carbon fibers

Carbon fibers are widely used as reinforcements in composite materials because of their high specific strength and modulus. Today, a number of ultrahigh strength polyacrylonitrile (PAN)-based (more than 6 GPa), and ultrahigh modulus pitch-based (more than 900 GPa) carbon fibers have been commercially available. In contrast, carbon nanotube (CNT) with the extremely high tensile strength have attracted attention as reinforcements. An interesting technique to modify the carbon fiber is CNT grafting on the carbon fiber surface. CNT-grafted carbon fibers offer the opportunity to add the potential benefits of nanoscale reinforcement to well-established fibrous composites to create micro-nano multiscale hybrid composites. In the present study, the tensile properties of CNT grown on T1000GB PAN- and K13D pitch-based carbon fibers have been investigated. Single filament tensile test at gauge lengths of 1, 5, and 25 mm were conducted. The effect of gauge length on tensile strength and Weibull modulus of CNT-grafted PAN- and pitch-based carbon fibers were evaluated. It was found that grafting of CNT improves the tensile strength and Weibull modulus of PAN- and pitch-based carbon fibers with longer gauge length (≥5 mm). The results also clearly show that for CNT-grafted and as-received PAN- and pitch-based carbon fibers, there is a linear relation between the Weibull modulus and the average tensile strength on log–log scale.

Investigation on some matrix‐dominated properties of hybrid multiscale composites based on carbon fiber/carbon nanotube modified epoxy

AbstractContinuous fiber reinforced polymer‐based composites have outstanding fiber‐dominated properties but unsatisfactory matrix‐dominated performances. In this investigation, carbon fiber reinforced epoxy composites modified with carbon nanotubes (CNTs) were fabricated to evaluate the effects of CNTs on some matrix‐dominated properties of the resulting hybrid multiscale composites. Carboxylic acid functionalized multiwalled CNTs were dispersed in epoxy by using high energy sonication, followed by the fabrication of the composites laminates with the epoxy/CNTs dispersion. The dispersion quality of CNTs in epoxy and the capillary infiltration of continuous fiber with the epoxy/CNTs dispersion were characterized using optical microscope and capillary experiment to optimize the processing parameters. A CNTs loading of 1 wt % significantly improved the flexural strength and interlaminar shear strength of the composites containing varying scale reinforcements by 51.8% and 34.2%, respectively, as compared to the control carbon/epoxy composites. Scanning electron microscopy was used to examine the fracture surface of the failed specimens. The moisture absorption behavior of the carbon fiber/epoxy composites with and without CNTs was investigated by comparing the weight gain and shear properties degradation in distilled water and 1.5 wt % brine. The integration of CNTs in composites is found to contribute to the medium‐dependent moisture adsorption behavior. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Fabrication and Mechanical Properties of a Micro/Nanoscale Hybrid Composite

Abstract Microscale SiC particles with multiwalled carbon nanotubes grow on were filled in epoxy resin to construct multiscale hybrid composite. Static and dynamic compressive responses of composites were investigated. A dynamic experimental technique, split Hopkinson press bar (SHPB), was introduced to study the constitutive laws of materials at high strain rates. SEM observations show good dispersion of carbon nanotubes and SiC particles, but bad link between SiC particles and carbon nanotubes exists. Experimental results of static and dynamic tests verify that increase of strength happens with SiC/CNT as reinforcement Increment of strength under dynamic loading is bigger than under static loading.