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As an excellent candidate for lightweight structural materials and nonmetal electrical conductors, carbon nanotube reinforced carbon matrix (CNT/C) composites have potential use in technologies employed in aerospace, military, and defense endeavors, where the combinations of light weight, high strength, and excellent conductivity are required. Both polymer infiltration pyrolysis (PIP) and chemical vapor infiltration (CVI) methods have been widely studied for CNT/C composite fabrications with diverse focuses and various modifications. Progress has been reported to optimize the performance of CNT/C composites from broad aspects, including matrix densification, CNT alignment, microstructure control, and interface engineering, etc. Recent approaches, such as using resistance heating for PIP or CVI, contribute to the development of CNT/C composites. To deliver a timely and up-to-date overview of CNT/C composites, we have reviewed the most recent trends in fabrication processes, summarized the mechanical reinforcement mechanism, and discussed the electrical and thermal properties, as well as relevant case studies for high-temperature applications. Conclusions and perspectives addressing future routes for performance optimization are also presented. Hence, this review serves as a rundown of recent advances in CNT/C composites and will be a valuable resource to aid future developments in this field.

Carbon fiber reinforced polymers (CFRP) are becoming increasingly used in aerospace applications which require lightweight and stability at high temperatures. This paper discusses a systematic design of a carbon nanotube/phenolic thermal protection layer (TPL) with heat shield functionality while maintaining designed mechanical strength compared to traditional CFRP composites. These TPLs were integrated onto the surface of carbon fiber/bismaleimide composites to act as a heat shield for hybrid composites. A bonding layer of ultra-thin unidirectional carbon fiber was introduced between the TPLs and CFRP to improve the constituent interface. Hybrid composites with different TPL volume fractions were produced. The TPLs resulted in a 17% decrease of the through-thickness thermal conductivity for hybrid composites. A flame torch test was used to evaluate the thermal shield effectiveness, and the hybrid composites showed a noticeable increase in residual flexural strength and modulus when compared to the control samples under a heat flux of 20 W/cm2. The retention of the strength and modulus of the hybrid composites after burning was 39% and 70% of the initial value, respectively, as compared to 11% and 21% of the CFRP control. This paper also discusses the effects of TPLs’ coefficient of thermal expansion and protection mechanisms.

Carbon nanotube/carbon (CNT/C) composites show potential for lightweight structural materials and non-metal electrical conductors for aerospace, military, and other industries where the combination of lightweight, high strength and excellent conductivity are required. Most research attempts have been reported to fabricate CNT/C composite focusing on the high CNT alignment and dense carbon matrix. However, simultaneous improvement of strength and electrical conductivity in materials still presents a great challenge. In this study, pyrolyzed polydopamine (py-PDA) with selected surface treatments is introduced as an interface enhancer between CNTs and the carbon matrix. Due to the presence of py-PDA, the effective physical interlocking and conductive pathways are rebuilt at the interface area between CNTs and carbon matrix, resulting in better load transfer and electron transport. The CNT/py-PDA/C composite fibers demonstrated remarkable improvements in electrical conductivity (2.1 × 103 S cm−1 or 228 S m2 kg−1) and tensile strength (up to 727 MPa or 790 MPa/(g·cm−3)), which should prove to be vastly advantageous as compared to the previously reported CNT/C composites. The outstanding thermal stability of fully carbonized materials is also an attractive feature. Coupled with scalable manufacturing methods, these integrated characteristics of CNT/py-PDA/C composite fiber can potentially have broad applications for lightweight structural materials and non-metal conductors.

Using a floating catalyst synthesis process, carbon nanotubes (CNTs) can be produced to form randomly oriented networks. However, to realize their potential high structural performance, the nanotubes must be aligned and closely packed to eliminate molecular and microscale defects, which would be similar to carbon fiber microstructures. This paper describes a mechanical stretching technique using bismaleimide (BMI) resin to transform the randomly oriented networks into aligned networks. The BMI resin acts as a lubricant to decrease the friction between the nanotube bundles within the network during the stretching process. The unique flattening and self-assembling behaviors and the resultant graphitic crystal packing of CNTs were observed. The nanotubes' degree of alignment, measured by Raman and X-ray scattering drastically increased at approximately 40% stretch strain, plateaued at a 60% stretch strain, and achieved a maximum of 0.92 degree of alignment with noticeable graphitic crystal packing at 80% stretch strain. Both TEM and SEM observations indicate that as the stretch strain increased, the CNTs started to align along the stretched direction and self-assembled into large bundles. Additionally, high-resolution TEM analysis indicated that the CNTs exhibited flattening and polygonization self-assembling to form graphitic crystal packing. Tensile testing on the stretched CNT/BMI composite samples revealed an increase in Young's modulus, with a maximum of 252 GPa at 80% stretch strain, while an ultimate tensile strength of 1.58 GPa was reached at 70% stretch strain. The high degree of alignment and polygonization packing resulted in a better load transfer among CNTs, and thus a higher mechanical performance in the resultant CNT composites. Furthermore, this stretching process is scalable and has the potential to realize greater performance for applications using CNTs.

A hybrid ceramic-polymer composite is fabricated by a co-curing lay-up process by combining a carbon nanotube (CNT) reinforced ceramic composite thin film with a carbon fiber reinforced polymer (CFRP) composite substrate. The ceramic nanocomposite thin film has good flexibility, thermal conductivity and high temperature tolerance. The polymer composite substrate is a carbon fiber reinforced bismaleimide composite that is widely used in aerospace and automotive industries. Finite element analysis (FEA) is used to investigate the maximum survival temperature with different thicknesses of the ceramic nanocomposite. The resultant hybrid composite shows good structural integrity and displays a pull-off bonding strength up to 8.3 MPa. In addition, thermal study illustrates that such a flexible CNT reinforced ceramic composite can effectively protect CFRP in an elevated temperature environment by delaying transient thermal conduction.

We report the synthesis and characterization of (Ph4P)2SbCl5, a novel ionically bonded organic metal halide hybrid with a zero-dimensional (0D) structure at the molecular level. By cocrystallization of tetraphenylphosphonium (Ph4P+) and antimony (Sb3+) chloride salts, (Ph4P)2SbCl5 bulk single crystals can be prepared in high yield, which exhibit a highly efficient broadband red emission peaked at 648 nm with a photoluminescence quantum efficiency (PLQE) of around 87%. Density functional theory (DFT) calculations reveal the origin of emission as phosphorescence from the excitons localized at SbCl52– with strong excited-state structural distortion. Interestingly, (Ph4P)2SbCl5 bulk crystals with a PLQE of around 100% can be prepared via a rapid crystal growth process within minutes, followed by a spontaneous structural transformation. It was found that the rapid growth process yielded a yellow emitting kinetically favored metastable product containing solvent molecules, which turned into the red emitting the...

Composite materials for bipolar plate applications in proton exchange membrane fuel cells were fabricated from synthetic graphite (SG), natural graphite (NG), or expanded graphite (EG) and novolac phenolic resin using compression molding. In comparing the resultant samples, the EG composite exhibited the best properties with a density of ∼1.55 g/cm3, flexural strength of 109 MPa, and modulus of 24 GPa even with a high graphite loading of 80 wt % and a low plate thickness of ∼0.9 mm, as well as in-plane conductivity of 182 S/cm. The EG content was further varied to find the optimal composition. The effects of using carbon nanotube sheets (buckypapers) or multiwalled carbon nanotubes as reinforcements to the EG-resin composite were investigated. A modified approach of measuring through-plane electrical conductivity capable of separated analysis of bulk resistance and interfacial contact resistance was attempted. The corrosion resistance, thermal conductivity, and gas permeability of EG-based composites were...

Carbon nanotube (CNT) electrically conductive cables, fibers, or tapes are undergoing extensive research. However, the research conducted on these materials with high conductivity has been primarily limited to small samples, such as fibers around 5–10 μm in diameter or sheets less than 1 μm thick. The need for scaling up these samples to manufacture CNT lightweight conducting materials is urgent, yet challenging. This paper reports on our study to produce large-scale continuous CNT sheets with ultra-high electrical conductivity. After mechanical stretching to achieve a high degree of CNT alignment, iodine doping and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) capping was performed, resulting in high electrical conductivity in the range of 10,000 S/cm (the highest value achieved as ∼13,000 S/cm). High CNT alignment and carrier concentration after iodine doping significantly improved the overall conductivity. The superior open air stability of samples, benefiting from the capping layer of PEDOT:PSS, was demonstrated by the very small changes of the conductivity during test period. Additionally, this doping process is scalable for producing continuous highly conductive and lightweight CNT sheets. Metallic conduction behaviors of the aligned and doped large size CNT sheets could provide lightweight conductor applications of CNT materials.

Composite materials for bipolar plates in proton exchange membrane fuel cells were fabricated from synthetic graphite (SG), natural graphite (NG), or expanded graphite (EG) and phenolic resin and compared. EG turned out to be the best candidate, exhibiting density of ~1.55 g/cm3, flexural strength of 109 MPa and modulus of 24 GPa even with a high graphite loading of 80 wt% and a low thickness of ~0.9 mm, and in-plane conductivity of 182 S/cm. A sandwich structure of buckypaper-composite-buckypaper was created to explore the effects of buckypaper. Multi-walled carbon nanotubes (MWCNTs) were incorporated into EG-resin composite to seek potential benefits through nanostructuring. A modified approach of measuring through-plane conductivity capable of separating bulk resistance from contact resistance was proposed. Corrosion resistance of EG-based composites was also assessed. The EG composite offering low thickness and density with competitive properties demonstrates great potential for weight and volume reduction of fuel cell stacks.

Honeycomb structures have been used extensively in lightweight sandwich structure and impact energy absorption applications. Recently the research has been carried out on auxetic honeycombs that have negative Poisson's ratio (NPR). Auxetic structures are attractive for various engineering applications because of their unique mechanical properties, volume change control and excellent impact energy absorption performance. In this study, novel design and performance improvement of new auxetic-strut structures were presented. A comparative study of in-plane uniaxial compression loading behavior of regular honeycomb, re-entrant auxetic honeycomb, locally reinforced auxetic-strut structure and a hybrid structure of combining regular honeycomb and auxetic-strut structure was conducted on 3D printed samples. The deformation and failure modes of the different cells were studied and their performance was also discussed. The new auxetic-strut structure showed better mechanical properties than the honeycomb and auxetic structure. For example, the compressive strength of the auxetic-strut design is ~ 300% more than that of honeycomb structure and ~ 65% more than that of auxetic structure. With lower values of the Poisson's ratio, the new design can absorb more energy when compared to the other structures. Hybrid structure of auxetic-strut and honeycomb cells allows us tailor the deformation paths to provide desired failure modes.

Conductive metals such as copper are heavily used as conductors or lightning protection materials in aircrafts and other industrial areas. But the high bulk density and corrosion problem make non-metal conductors with low density and corrosionresistance more promising such as carbon nanotubes (CNTs). However, the small sample size of previously reported highly conductive CNT fibers (1-2 μm in diameter) or films (less than 1 μm in thickness) limits the practical engineering applications. In this work, a macroscopic continuously stretched CNT tape was prepared with excellent CNT alignment, high conductivity, and large dimensional size (~ 9 mm in width and ~ 30 μm in thickness). Through combined post-treatments of mechanical stretching, iodine doping and polymer capping layer, the macroscopic CNT tape shows high conductivity in the range of 10,000 S/cm (the highest is ~ 13,000 S/cm) and this excellent performance is stable in open air without any sign of degradation. Various characterizations were conducted including SEM observation, Raman, TGA, PPMS, electrical, and mechanical measurements. Overall, the high conductivity was ascribed to better CNT alignment after stretching and high carrier density after iodine doping. More importantly, the substantial stability of electrical property was demonstrated, benefitting from the polymer capping layer. Additionally, this process is based on commercially available raw materials and scalable for industrial production. And the proposed method here can be readily transferred to our buckypaper (CNT sheets) with roll-to-roll production capability. Furthermore, these highly conductive CNT tape and sheet can be directly incorporated into fiber-reinforced composite to improve the conductivity which could serve multiple functionalities as structural, electromagnetic interference shielding and lightning protection materials in aircrafts. This work opens a new path to optimize the electrical performance of CNT assemblies with a wide range of engineering applications including conductive composites..

Carbon fiber reinforced polymers (CFRP) are increasingly used in aerospace applications which demand lightweight and stability at elevated temperatures. This paper discusses a method of fabricating a novel carbon nanotube (CNT)/phenolic nanocomposite and using it as a thermal protection layer (TPL) to improve the performance of CFRP. Hybrid composites of different volume fractions of TPL and bonding interfaces were evaluated. The presence of TPLs in the hybrid composites resulted in as much as a 17% decrease of through-thickness thermal conductivity. Residual flexural strength and modulus after a flame torch test were 39% and 70% respectively of the initial value, a substantial improvement over 11% and 21% of a control sample. We also discuss the effects of TPLs on the coefficient of thermal expansion (CTE) and protection mechanisms. This research could lead to scalable manufacturing of CFRPs with enhanced performance characteristic at elevated temperatures for aerospace applications.

Carbon nanotubes (CNTs) can be produced from floating catalyst synthesis to form random networks. However, the CNTs must be aligned and closely packed to eliminate molecular and microscale defects to reach levels of mechanical performance similar to carbon fiber systems. Previous research has shown that strain-induced alignment methods using bismaleimide (BMI) infiltration can effectively modify randomly oriented CNT networks. The BMI resin lubricates the network decreasing the friction between the CNT bundles and assists with load transfer between CNT bundles during the stretching process. This process yields unique CNT collapsing, self-assembling behaviors, and graphitic crystal packing at the nanoscale. In this study, the CNTs’ alignment degree was measured by Raman spectroscopy and X-ray scattering. Alignment degree analysis results showed a considerable increase at 40% stretch ratio with a plateau at 60% stretch ratio. An 80% stretch ratio achieved the highest alignment degree of 0.93 with noticeable graphitic crystal packing. Both scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) images of the CNT sheet surfaces and cross-sections show that as the stretch ratio increased, the CNTs started to align along the stretching axis and self-assembled into large bundles. Additionally, HRTEM analysis indicated that the CNTs exhibited collapsing and self-assemblage to form graphitic crystal packing. Tensile testing on the aligned CNT/BMI composite samples measured an increase in tensile properties. The ultimate tensile strength (UTS) and Young's modulus reached maximums of 1.58 GPa at 70% stretch ratio and 252 GPa at 80% stretch ratio, respectively. The high alignment degree and graphitic packing improved load transfer throughout the CNT network, and consequently, better mechanical performance in the CNT composites were achieved. Furthermore, this alignment process proved its scalability and potential to transcend into industrial-scale applications that utilize CNT material systems.

Stretchable materials are indispensable for applications such as deformable devices, wearable electronics, and future robotics. However, designs for new elastomers with high stretchability have undergone only limited research. Here we have fabricated highly stretchable Ag+/polyacrylonitrile elastomer with nanoreservoirs of lubricant using cyano-silver complexes. The prepared products feature nanoconfinement structures of lubricant surrounded by polymer chains with coordination bond through chelates of cyano-silver, resulting in an enhanced stretchability of more than 600% from 2%. The elastomeric properties were investigated, and a mechanical response model was proposed, which explained the structural evolution including the polymer chain fluidity under external deformation. Also, the easy breakage and dynamic reformation of cyano-silver coordination complexes promises a strain recovery under various stretching conditions. This elastomer itself can directly work as sensors and open paths to alternative substrates for soft electronics development.

Carbon nanotube/carbon (CNT/C) composites show potential for lightweight structural materials and non-metal electrical conductors for aerospace, military, and other industries where the combination of lightweight, high strength and excellent conductivity are required. Numerous research attempts have been reported to fabricate CNT/C composite focusing on high CNT alignment and dense carbon matrix. However, simultaneous improvements for mechanically strengthening and electrically improving properties of strength and conductivity in materials still presents a great challenge. In this study, pyrolyzed polydopamine (py-PDA) with selected surface treatments is introduced as an interface enhancer between CNTs and carbon matrix. Due to the presence of py-PDA, the effective physical interlocking and conductive pathways are rebuilt at the interface area between CNTs and carbon matrix, resulting in better load transfer and electron transport. The CNT/py-PDA/C composite fibers demonstrated remarkable improvements in electrical conductivity (2.1 × 103 S cm-1) and tensile strength (up to 727 MPa), which should prove to be vastly advantageous as compared to the previously reported CNT/C composites. The outstanding thermal stability of fully carbonized materials is also an attractive feature. Coupled with scalable manufacturing methods, these integrated characteristics of CNT/py-PDA/C composite fiber can potentially have broad applications for lightweight structural materials and non-metal conductors.

Modern electronics and communication systems are subject to high levels of electromagnetic interference (EMI). Due to the increasing demands for miniaturized devices with reduced weight, lightweight and flexible EMI shielding materials with high performance have driven the requirements for developing conductive polymers and other conductive composites. Carbon nanotube (CNT)-filled polymeric matrix composites and sandwiched CNT film/polymer hybrid composites have shown great potentials to achieve these goals. This chapter summarizes the importance of developing CNT-based nanocomposites for EMI shielding applications and how to tune the properties of materials to meet various requirements by varying the filler contents and structure of nanocomposites. Other nanocarbon-based materials such as graphene and carbon black nanocomposites are also discussed.

In this paper, a novel three-dimensional-linked (3D-linked) carbon fiber-carbon nanotube (C f -CNT) hybrid structure is presented to improve the through-thickness thermal properties of polymer derived silicon carbonitride matrix composites. Comparing with pristine plain woven carbon fiber, the pores in the criss-cross position are fully filled with carbon nanotubes (CNT) in the presented C f -CNT hybrid structure. CNT can be integrated in between the plain woven carbon fibers and generate a 3D-linked C f -CNT hybrid network structure. Thanks to the percolating network of CNT and the densification effect, the through-thickness thermal conductivity of the resultant ceramic matrix composites is improved significantly, which is enhanced by 10% with short CNT and by 31% with long CNT, respectively. The thermal conductivity is found to increase with temperature from 100 to 900 °C for these composites. Multiphysics simulation is conducted to reveal the effects of the 3D-linked C f -CNT hybrid structure on the thermal conductivity at various temperatures, which are consistent with experimental results.

Carbon nanotube (CNT) yarns have demonstrated promising mechanical properties and scalability for composite applications. In this study, a commercially available continuous CNT yarn and two modified versions at large gauge lengths (~110 mm) were tested to reveal engineering properties. The as-received yarns with a large cross-section demonstrated the highest specific tensile strength (0.911 ± 0.137 N/tex), while the highly densified yarns showed the lowest specific tensile strength (0.337 ± 0.217 N/tex). Results suggest that alignment governs the ultimate tensile strength, while defects dictate how yarns fail and the harnessed strength potential. Of the two failure modes detected, brittle edge failures experienced greater ultimate tensile strengths ranging from ~8 to 20% depending on the yarn type. The test results were fitted to 2-parameter Weibull distributions to further confirm the failure behavior. These results indicate valuable properties for industrial CNT yarn applications and provide a baseline for large gauge length CNT studies.

The Floating Catalyst Chemical Vapor Deposition (FCCVD) method has attracted extensive research interests from both academia and industry due to its high potential for carbon nanotube (CNT) mass production. As aerospace aims become increasingly demanding, there is an ever growing need for mass producing lightweight structural composites. By infiltrating bismaleimide (BMI) resin and curing under pressure, CNT/BMI nanocomposites with high CNT loading are exhibiting excellent mechanical properties. By further integrating CNT into carbon fiber (CF), the mechanical and electrical improvements in axial, transverse and through-thickness direction demonstrate potential for multifunctional applications. In this work, a FCCVD reactor designed and assembled at the High-Performance Materials Institute was used for CNT synthesis. The CNT aerogel formed was continuously spun onto a rotating mandrel while continuously spraying a BMI/acetone solution, forming an ultra-thin prepreg material ranging from 1-5 μm in thickness. The quality of the CNTs collected was characterized using Raman Spectroscopy, Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), and Transmission Electron Microscopy (TEM). To evaluate the ultra-thin FCCVD-CNT prepregs, six layers were stacked in the same alignment direction, and cured using a vacuum-assisted bagging system and hot press. Electrical conductivity tests were conducted in both the aligned and the transverse directions. Furthermore, the ultra-thin CNT prepregs were integrated into the aerospace-grade unidirectional IM7/CYCOM® 5250-4 prepregs following an alternating order. The assembly was finally vacuum-bagged to expel air and cured with a hot press. The microstructure and interface of CF/CNT hybrid composites and CNT/BMI composites were observed under SEM. This paper reports on a fabrication process of CNT prepregs, which could be potentially used to scale-up the CNT/BMI composites and CF/CNT interply hybrid composites manufacturing.

Large scale manufacturing of electrically conductive carbon nanotube (CNT) sheets with production capability, low cost, and long-term electrical performance stability is still a challenge. A new method to fabricate highly conductive continuous buckypaper (CBP) with roll-to-roll production capability and relatively low cost is reported. The electrical conductivity of CBP can be improved to 7.6 × 104 S m−1 by using an oxidant chemical (i.e. HNO3 and I2) doping method. To compensate for the conductivity degradation caused by the instability of the oxidant chemical doping, a polymer layer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) was coated on the chemically doped CBP. The fabricated highly conductive CBP showed stable electrical performance in air for more than a month. This CBP material with high electrical conductivity, relatively low cost, and roll-to-roll manufacturing capability could enable a wide range of engineering applications including flexible conductors, electromagnetic interference (EMI) shielding materials, and electrodes in energy devices.

While the mechanical properties of highly aligned carbon nanotube (CNT) thin films and their nanocomposites have been widely studied, the load transfer mechanisms and failure modes of aligned CNT composites have not been sufficiently explored and understood. In this research, super-aligned CNT thin films with a measured alignment fraction of up to 0.93 are fabricated by mechanical stretching. High concentration (50–60 wt% CNT) CNT reinforced bismaleimide (CNT/BMI) nanocomposites are fabricated from the aligned network to study mechanical properties and microstructures. Atomic resolution transmission electron microscopy (TEM) analysis reveal unusual CNT crystal packing and permit the observation of interesting structural features of the CNTs and their assemblages, including collapse, flattened packing, preferred stacking, folding and twisting phenomena, as well as CNT pullouts from bundles and the resin matrix. The large surface-to-surface contact areas between aligned and flattened nanotubes, driven by van der Waals interactions, give rise to a high density packing of the flattened CNTs in the nanocomposite, resembling a graphitic material. Molecular dynamics (MD) simulations are performed to model the packing structure and understand the dependence of density on the relative content of flattened nanotube and void space. The modeling results support the conclusions drawn from the experimental observations.

Due to the nanoscale size of carbon nanotubes (CNTs), observing the CNT/CNT and CNT/resin interactions in nanocomposites requires a high resolution transmission electron microscope (TEM) analysis. This research focuses on developing a protocol to provide an effective and reliable approach to obtain ultra-thin ( Two CNT nanocomposite samples made with different resins were studied for both microtome cutting and TEM analysis and it revealed the alignment direction of the nanotubes and numerous stacks of CNT bundles. In addition, there was visible flattening of CNT packing into dumbbell shapes similar to results obtain in CNT yarn materials. TEM for the 3-layer CNT BP/BMI nanocomposite revealed uniform cutting in the resin areas. However, when the diamond knife reached graphite crystalline regions, the nanotubes either became deformed into a cone-like structure, were cut thicker than the resin, or folded over onto itself. This is most likely due to the high mechanical properties of CNT in response to the stress of cutting.

This paper has studied the open-hole and pin filled-hole effects on the tensile properties of Kenaf/Polypropylene Nonwoven Composites (KPNCs) in production of automotive interior parts. The influence of specimen width-to-hole diameter (W/D) ratios of 6, 3, and 2 on failure load was studied. Two sample thicknesses of 3 mm and 6 mm were evaluated. Mechanical properties of the KPNCs in terms of uniaxial tensile, open-hole tensile (OHT), and pin filled-hole tensile (FHT) were measured experimentally. A preliminary model by extended finite element method (XFEM) was established to predict the failure load and simulate crack propagation of 3 mm thick open-hole and pin filled-hole specimens. Good agreement was found between experimental and simulation results. By calculating the stress concentration factor Kt for brittle materials, the net section stress factor Kn for ductile materials, and the strength reduction factor Kr, it was found that KPNC was relatively ductile and insensitive to the notch.

This paper reports on a study of carbon nanotube (CNT) thin film, or buckypaper (BP), integrated into carbon fiber (CF) prepreg composites to create hybrid composite materials with high CNT content. The autoclave process of manufacturing hybrid composite laminates was investigated to gain an understanding of nano/micro dual-scale resin flow characteristics. The study found that resin bleeding along the through-thickness direction was inhibited due to extra-low permeability and high resin absorbing capacity of the BP. Resin matrix-impregnated BP layers were much thicker than dry pristine BP due to high resin absorbency and swelling effects. The BP/unidirectional carbon fiber (UD-CF) hybrid composites with local fiber volume fraction of 61.46 vol% in CF ply and local CNT volume fraction of 26.57 vol% in BP layer, had a tensile strength of 2519 ± 101 MPa and modulus of 149 ± 18 GPa. The dramatic improvements in both in-plane and through-thickness electrical conductivities demonstrate potential for both structural and multifunctional applications of the resultant hybrid composites.

Higher concentrations of long carbon nanotubes (CNTs) that are aligned and functionalized can improve the mechanical properties of CNT composites. For this purpose, pristine/random CNT sheets were mechanically stretched at different strains of 40 %, 60 % and up to 80 %. The higher degree of CNT alignment was confirmed by scanning electron microscope (SEM) images and the degree of alignment was quantified by X-ray scattering and polarized Raman spectroscopy. The highest degree of alignment of 0.93 was achieved by using this method. Aligned CNT sheets were functionalized and CNT/bismaleimide (BMI) composites were fabricated. The mechanical properties of the composites were improved with a higher degree of alignment achieving a modulus of 252 GPa and tensile strength of over 1.4 GPa for an 80% stretched CNT/BMI composite. To understand the internal CNT packing and the CNT/resin interface, thin composite cross sections that are perpendicular to the alignment direction were prepared using focused ion beam (FIB) with a lift-out process. Using a high-resolution transmission electron microscopy (HRTEM), relatively large diameter CNTs (> 5 nm) cross sections and double-walled CNT bundles were observed. An increased number of densely packed and collapsed CNT structures were also observed with higher stretch ratio, which confirmed the CNT alignment and dense packing along the stretch direction. The CNT/resin interface was also analyzed by electron energy loss spectroscopy (EELS). Carbon K-edge peak was used to identify the functionalization of CNT, and a ratio of 1s-* to 1s-* transition was mapped by a scanning TEM. A decreased */* transition ratio was observed at the edge of CNT packing and could be related to the reduced sp2 bonding after functionalization. This leads efficient load transfer between CNT and resin, thus higher mechanical properties.

This study focused on the influence of different filler loadings on the elongation at break and flammability properties of the PA11/FR/HNTs nanocomposites. Polyamide 11 (PA11)/flame-retardant (FR) additives/halloysite nanotubes (HNTs) nanocomposites were melt compounded via twin-screw extrusion for all the compositions. Three FR additive loadings (15, 20, and 25 wt%) and three HNTs loadings (2.5, 5, and 10 wt%) were selected. The formula with 25 % FR and 2.5 % HNT had the lowest additives content and the highest elongation at break of 10.22 % among all UL-94 V-0 rated formulas. A homogeneous dispersion of HNTs in PA11 matrix was observed by transmission electron microscopy. Differential scanning calorimeter measurements indicated that HNTs behaved as nucleating agents by accelerating the rate of crystallization, thus increasing crystallization temperature. The young’s modulus of the PA11 nanocomposites was enhanced with the addition of HNTs. Micro-scale combustion calorimeter results demonstrated that the addition of HNTs also decreased the peak heat release rate of the nanocomposites. These results indicate the effectiveness of HNTs on the mechanical, thermal, and flame-retardant performance of PA11/FR/HNTs nanocomposites.

The kenaf/polypropylene nonwoven composites (KPNCs), with 50/50 blend ratio by weight, were produced by carding and needle-punching techniques, followed by a compression molding with 6-mm thick gauge. The uniaxial tensile, three-point bending, in-plane shearing, and Izod impact tests were performed to evaluate the composite mechanical properties. The thermal properties were evaluated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The performance of sound absorption and sound insulation was also investigated. An adhesive-free sandwich structure was found to have excellent sound absorption and insulation performance. Based on the evaluation of end-use performance, the best processing condition combination of 230 °C and 120 s was determined, and the correlation between mechanical properties and acoustical behavior was also verified by the panel resonance theory.

Functionalization is critical for improving mechanical properties of carbon nanotubes (CNTs)/polymer nanocomposites. A fundamental understanding of the role of the CNT/polymer interface and bonding structure is key to improving functionalization procedures for higher mechanical performance. In this study, we investigated the effects of chemical functionalization on the nanocomposite interface at atomic resolution to provide direct and quantifiable information of the interactions and interface formation between CNT surfaces and adjacent resin molecules. We observed and compared electronic structures and their changes at the interfaces of nonfunctionalized and functionalized CNT/polymer nanocomposite samples via scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) spectrum imaging techniques. The results show that the state of sp2 bonding and its distribution at the CNT/resin interface can be clearly visualized through EELS mapping. We found that the functionalized CNT/polymer samples exhibited a lower fraction of sp2 bonding and a lower π*/σ* ratio compared with the nonfunctionalized cases. A good correlation between near-edge fine structures and low-loss plasmon energies was observed.

With an industrial trend of going green, the use of natural fibers in polymer composites is growing rapidly, especially in the automotive industry. The objectives of this research are to investigate mechanical performance of kenaf/polypropylene nonwoven composites (KPNCs) in production of automotive interior parts, and to develop preliminary linear models for quantifying elastic range of the KPNCs under various loading conditions. Using polypropylene (PP) fiber as bonding fiber, the KPNCs were fabricated with 50/50 blend ratio by weight. Unlike the manufacturing method of fiber reinforced plastics, all KPNCs were produced by carding and needle-punching techniques and thermally bonded by a panel press with 3-mm thickness gauge. Mechanical properties of the KPNCs in terms of uniaxial tensile, open-hole tensile, tensile at different strain rates, flexural, and in-plane shear were measured instrumentally. It was found that sample which was processed at higher temperature (230 °C) but shorter time (60 s) had the best mechanical performance. KPNCs were relatively insensitive to the notch but sensitive to strain rates. The linear elastic finite element model of KPNCs agreed well with the experimental results in the valid strain range of 0–0.5 % for uniaxial tensile test and 0–1 % for flexural test.

Regenerated cellulose fibers from bagasse and wood were produced under various processing conditions using the ionic liquid 1-butyl-3-methylimidazolium chloride (BMIMCl) as a solvent. Two different ionic liquid solutions were prepared with 6 wt% of bagasse cellulose and 6 wt% of wood cellulose. The solutions were extruded with a dry-jet and wet-spinning method using water as a coagulation bath. A thermogravimetric analyzer (TGA) was used to measure the thermal properties of these regenerated fibers. Dynamic mechanical analysis (DMA) was used to determine the thermal mechanical property of the regenerated cellulose fibers and wide-angle X-ray diffraction (WAXD) was used to measure the degree of crystallinity, as well as the degree of crystal orientation for those experimental fibers. To evaluate the quantity of ionic liquid residue in the regenerated fibers, the instrumental methods of FT-IR and mass spectrometry were applied to test the residues of BMIMCl in the regenerated fibers. Research results indicated increases in the degree of crystallinity and storage modulus under a higher fiber drawing speed. Both regenerated bagasse film and regenerated wood film had similar thermal properties. However, the regenerated bagasse fibers showed a higher degree of crystallinity, and higher tenacity than the regenerated wood fibers obtained under the same condition. The study also revealed that water treatment would be helpful for eliminating the ionic liquid residue in the regenerated fibers.

The quasi-static indentation and transverse impact behavior of 3-D orthogonal woven composite T-beam were investigated with a universal material tester (MTS 810.23) and a modified split Hopkinson pressure bar (SHPB), respectively. The load–displacement and energy–displacement curves were obtained to analyze the damage of the composite T-beam under three kinds of impact velocities. Finite element analysis which based on unit-cell model of the 3-D orthogonal woven composite and user-defined material subroutine was conducted to calculate the dynamic responses. The good agreement between experimental and FEM results reveals the composite damage mechanisms and energy absorption features of the T-beam with different flange height.

Microcellular foaming of biodegradable and biocompatible PLA/starch composites in supercritical/compressed CO2 has been studied. The purpose of this study is to explore the potential application of this kind of materials in medical materials or drug containers. The rate of CO2 uptake and CO2 equilibrium concentration in PLA/starch composites were studied by performing sorption and desorption experiments. The effects of a series of variable factors, such as saturation time and saturation temperature on the foaming morphology were studied through SEM observation and density measurement. The experimental results show that, while keeping other variables unchanged, longer saturation time leads to reduced bulk foam densities and different saturation pressures result in different bulk foam densities. The crystallinity of PLA–starch sample was characterized by differential scanning calorimetry. It indicates that the foaming treatment with supercritical CO2 increased the crystallinity of PLA/starch composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Combinations of nanoscale and microscale silver particles were used to construct heterogeneously conductive paths in graphite composites for improving through-thickness thermal conductivity. Composites with four different pitch-based graphite fibers were studied and compared to realize the improved thermal conductivity with adequate mechanical performance. The test panels of EWC300X graphite fibers and sliver fillers achieved a through-thickness thermal conductivity of ~10.0 W/m·K at 25 °C. The rheological behavior of Epon862/curing agent resin and silver flakes filled Epon862/curing agent resin was studied for the standardization and quality control of large panel fabrication. By adding 40wt% silver flakes in the resin system, the viscosity greatly increased. The lowest viscosity of 40% silver flakes filled Epon862/curing agent resin system occurred at 65 °C; therefore, the curing process was modified accordingly to ensure resin/fiber wetting and reduction of voids. The hybrid composites with IM7 and pitch-based carbon fiber were also made in order to optimize the composite performance with a balanced thermal conductivity and mechanical properties. The failure mechanisms of laminated composites with and without silver fillers were investigated. The IM7/EWC300X hybrid composite with a density of 2.31 g/cm showed a thermal conductivity of 5.29 W/ m·K and adequate mechanical properties for structural applications.

This work presents a new method for fabricating thermal devices, such as heat sinks, using a 3D printing technique and lightweight composite ink. The method focuses on formulating composite inks with desired properties and direct ink writing for manufacturing. The ink undergoes two phases: phase one uses low viscosity epoxy to provide viscoelastic properties and phase two provides the fillers consisting of carbon fiber and graphite nanoplatelets to provide high thermal conductivity and structural properties. By combining these functional materials, 3D structures with a high thermal conductivity (≈2 W m−1 K−1) are printed for thermal management applications with the storage modulus of 3000 MPa and a density only 1.24 g cm−3. The results show that by carefully tailoring functional properties of the ink, net-shape multifunctional structures can be directly printed for thermal management device applications, such as heat sinks.

Featuring high efficiency and power density, relatively low operating temperature (60-80°C), quiet operation, and environmental friendliness, proton exchange membrane fuel cells (PEMFCs) have become promising power sources for transportation, stationary, and portable applications (1, 2). Bipolar plate is a vital and multifunctional component in PEMFCs, accounting for 60-80% of fuel cell stack weight and 30-45% of stack cost (3). While conventional bipolar plate materials are graphite or metal, graphite-polymer composites have recently been investigated as bipolar plate materials to maximally utilize the electrical conductivity of graphite and the mechanical strength of polymers and to exploit the benefits of smaller size, lighter weight, easier fabrication, and reduced cost. In this study, different polymer composites for bipolar plates based on synthetic graphite (SG), natural graphite (NG), and expanded graphite (EG) at a fixed graphite to polymer weight ratio were prepared by compression molding and compared in terms of three main properties: flexural strength, flexural modulus, and in-plane electrical conductivity. Novolac phenolic resin was chosen to form the composite because of its low cost and easy processing. EG turned out to be the best candidate, exhibiting flexural strength of 109 MPa and flexural modulus of 24 GPa even with a high graphite loading of 80 wt% and a low plate thickness of 0.9 mm, as well as in-plane conductivity of 182 S/cm. The EG content was then varied in a range of 60-85 wt% to find out the optimal composite composition. After this, a sandwich structure of buckypaper-composite-buckypaper was created to probe the effects of adding buckypaper on the mechanical and electrical properties. In addition, carbon nanotubes (CNTs) were incorporated into the EG-novolac resin composite for the first time, to the best of our knowledge, at low concentration of 0.5-2 wt% in the hope of potential benefits through nanostructuring. Through-plane electrical conductivity and corrosion resistance were also assessed for the composites with MWNTs 0-2 wt%. Previous research efforts on through-plane conductivity measurement either involved use of a reference material (4, 5), or calculated the sample bulk resistance roughly by assuming that all the contact resistances were the same (6), or did not provide specific description capable of separated analysis of interfacial contact resistance and bulk resistance (7). Herein a modified approach is suggested for detailed and reliable evaluation of through-plane resistance and contact resistance. As to corrosion behavior studies, a majority of them concentrated on metallic plates, some emerged in recent years to delve into the corrosion stability of graphite composites (8, 9), while the field of corrosion characteristics of EG-based bipolar plates and the influence that CNTs would have on their corrosion properties remains unexplored. The present work thus aims to shed some light on this aspect as well. References: 1. P. Chaiwan and J. Pumchusak, Electrochimica Acta, 158, 1 (2015) 2. K.H. Kim, J.W. Lim, and M. Kim, Composite Structures, 98, 103 (2013) 3. F. Dundar, E. Dur, S. Mahabunphachai, et al., Journal of Power sources, 195(11), 3546 (2010) 4. US Fuel Cell Council: Through-plane electrical conductivity testing protocol for composite materials. 2004 5. N. Cunningham, M. Lefèvre, G. Lebrun, et al., Journal of power sources, 143(1), 93 (2005) 6. L. Du and S.C. Jana, Journal of Power Sources, 172(2), 734 (2007) 7. R. Yeetsorn and M. Fowler, KMUTNB International Journal of Applied Science and Technology, 7(4), 13 (2014) 8. M.C.L. de Oliveira, G. Ett, and R.A. Antunes, Journal of Power Sources, 221, 345 (2013) 9. R.A. Antunes, M.C. Lopes de Oliveira, and G. Ett, International Journal of Hydrogen Energy, 36(19) (2011) Figure 1

This article reports an exploratory study on the creep and recovery behavior of kenaf/polypropylene nonwoven composites (KPNCs), serving as a bio-based substitution for polypropylene (PP) plastics in the automotive industry due to the environmental concern. The creep and recovery behavior of KPNC and solid virgin PP were performed by dynamic mechanical analyzer (DMA) which allowed it to be studied extensively. The linear viscoelastic limit (LVL) was found at 1 MPa. Two popular creep models, the four-element Burgers (FEB) model and the Findley power law (FPL) model, were used to model the creep behavior in this study. The FEB model was found only appropriate for characterizing short-term creep behavior. In contrast, the FPL model was satisfactory for predicting the long-term creep performance. The long-term creep behavior of KPNC in comparison to virgin PP plastic was predicted using the time-temperature superposition (TTS) principle. The 1-year creep strains were estimated to be 0.32% for KPNC and 1.00% for virgin PP at 40°C. A three-day creep test was conducted to validate the effectiveness of the TTS prediction. KPNC showed a better creep resistance and higher recoverability than the virgin PP, especially in a high-temperature environment. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40726.

The use of natural fibers in polymer composites is growing rapidly, especially in the automotive industry, due to the environmental concern. In this research, the open-hole effects on the tensile property of kenaf/polypropylene nonwoven composites (KPNCs) in production of automotive interior parts have been investigated. KPNCs were fabricated using kenaf fiber as reinforcement and polypropylene (PP) fiber as bonding fiber. All KPNCs were produced by carding and needle-punching techniques and thermally bonded by a panel press with 6-mm thickness gauges. Unlike the traditional fiber reinforced composites, KPNCs are produced by nonwoven technique with a 50% fiber weight ratio. Mechanical properties of the KPNCs in terms of uniaxial tensile and open-hole tensile (OHT) were measured instrumentally. By calculating the stress concentration factor Kt for brittle materials, the net section stress factor Kn for ductile materials, and the strength reduction factor Kr, we found that KPNC was relatively ductile and insensitive to the notch.

In recent decades, the energy resource and environment pollution is becoming a main challenge for the sustainability of global economic development as a result of population growth and industrial development. Costs of the synthetic materials are rising due to the short supply of fossil oil. Meanwhile the synthetic materials are not biodegradable and renewable. So the materials with biodegradable and renewable properties need to be investigated. With an annual yield of about 7 × 1011 tones, cellulose is the Earth’s most abundant natural organic material [1]. Many methods and chemicals have been developed to process cellulose into different products [2–6].Copyright © 2012 by ASME