Structural Polymer-Based Carbon Nanotube Composite Fibers: Understanding the Processing-Structure-Performance Relationship

Preparation and Characterization of Polyvinyl Alcohol (PVA)/Carbonized Waste Rubber Biocomposite Films

The technological properties of composite materials (thermal, strength, rheology, electrical and morphology) are very important parameters for high-performance applications. In this study, we aimed to improve the properties of PVA by using carbon materials obtained by the pyrolysis of waste tires, with the aim of recycling them instead of disposing of them. For this purpose, PVA biocomposite films containing carbonized waste rubber at different rates were prepared. The thermal properties of the prepared biocomposite films were examined via thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) methods. While rheological measurements were carried out with a rheometer, bulk conductivities were measured with a pico-ammeter. In addition, the morphology of biocomposite films was determined via field emission scanning electron microscopy. The nanomechanical properties of biocomposite film was investigated via XPM analyses. According to the rheological measurements and nanoindentation hardness results, it is understood that as the amount of carbonized waste rubber increases, flexibility decreases and harder and brittle structures are observed in biocomposite films. The electrical measurement results showed that electrical conductivity increased as the amount of carbonized waste rubber increased. When all the results obtained were evaluated, it could be concluded that biocomposite films obtained by increasing the electrical conductivity and hardness of PVA can be used in the electronics industry.

Improved Yield and Electrical Properties of Poly(Lactic Acid)/Carbon Nanotube Composites by Shear and Anneal

Shear and thermal processing can greatly influence nanoparticles' orientation and dispersion, affecting the nanocomposites' conductivity and mechanical properties. The synergistic effects of shear flow and Carbon nanotubes (CNTs) nucleating ability on the crystallization mechanisms have been proven. In this study, Polylactic acid/Carbon nanotubes (PLA/CNTs) nanocomposites were produced by three different molding methods: compression molding (CM), conventional injection molding (IM), and interval injection molding (IntM). Solid annealing at 80 °C for 4 h and pre-melt annealing at 120 °C for 3 h was applied to research the CNTs' nucleation effect and the crystallized volume exclusion effect on the electrical conductivity and mechanical properties. The volume exclusion effect only significantly impacts the oriented CNTs, causing the conductivity along the transverse direction to rise by about seven orders of magnitude. In addition, the tensile modulus of the nanocomposites decreases with the increased crystallinity, while the tensile strength and modulus decrease.

Review of Recent Developments of Glass Transition in PVC Nanocomposites

This review addresses the impact of different nanoadditives on the glass transition temperature (Tg) of polyvinyl chloride (PVC), which is a widely used industrial polymer. The relatively high Tg limits its temperature-dependent applications. The objective of the review is to present the state-of-the-art knowledge on the influence of nanofillers of various origins and dimensions on the Tg of the PVC. The Tg variations induced by added nanofillers can be probed mostly by such experimental techniques as thermomechanical analysis (TMA), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and dielectric thermal analysis (DETA). The increase in Tg is commonly associated with the use of mineral and carbonaceous nanofillers. In this case, a rise in the concentration of nanoadditives leads to an increase in the Tg due to a restraint of the PVC macromolecular chain's mobility. The lowering of Tg may be attributed to the well-known plasticizing effect, which is a consequence of the incorporation of oligomeric silsesquioxanes to the polymeric matrix. It has been well established that the variation in the Tg value depends also on the chemical modification of nanofillers and their incorporation into the PVC matrix. This review may be an inspiration for further investigation of nanofillers' effect on the PVC glass transition temperature.

3D Printing-Enabled Nanoparticle Alignment: A Review of Mechanisms and Applications

3D printing (additive manufacturing (AM)) has enormous potential for rapid tooling and mass production due to its design flexibility and significant reduction of the timeline from design to manufacturing. The current state-of-the-art in 3D printing focuses on material manufacturability and engineering applications. However, there still exists the bottleneck of low printing resolution and processing rates, especially when nanomaterials need tailorable orders at different scales. An interesting phenomenon is the preferential alignment of nanoparticles that enhance material properties. Therefore, this review emphasizes the landscape of nanoparticle alignment in the context of 3D printing. Herein, a brief overview of 3D printing is provided, followed by a comprehensive summary of the 3D printing-enabled nanoparticle alignment in well-established and in-house customized 3D printing mechanisms that can lead to selective deposition and preferential orientation of nanoparticles. Subsequently, it is listed that typical applications that utilized the properties of ordered nanoparticles (e.g., structural composites, heat conductors, chemo-resistive sensors, engineered surfaces, tissue scaffolds, and actuators based on structural and functional property improvement). This review's emphasis is on the particle alignment methodology and the performance of composites incorporating aligned nanoparticles. In the end, significant limitations of current 3D printing techniques are identified together with future perspectives.

Fibers of Thermoplastic Copolyamides with Carbon Nanotubes for Electromagnetic Shielding Applications

Polymer composites containing carbon nanofillers are extensively developed for electromagnetic shielding applications, where lightweight and flexible materials are required. One example of the microwave absorbers can be thermoplastic fibers fabricated from copolyamide hot melt adhesives and 7 wt% of multi-walled carbon nanotubes, as presented in this paper. A broadband dielectric spectroscopy confirmed that the addition of carbon nanotubes significantly increased microwave electrical properties of the thin (diameter about 100 μm) thermoplastic fibers. Moreover, the dielectric properties are improved for the thicker fibers, and they are almost stable at the frequency range 26-40 GHz and not dependent on the temperature. The variances in the dielectric properties of the fibers are associated with the degree of orientation of carbon nanotubes and the presence of bundles, which were examined using a high-resolution scanning microscope. Analyzing the mechanical properties of the nanocomposite fibers, as an effect of the carbon nanotubes addition, an improvement in the stiffness of the fibers was observed, together with a decrease in the fibers' elongation and tensile strength.

Thermal and mechanical characterization of high performance polymer fabrics for applications in wearable devices

With advances in flexible and wearable device technology, thermal regulation will become increasingly important. Fabrics and substrates used for such applications will be required to effectively spread any heat generated in the devices to ensure user comfort and safety, while also preventing overheating of the electronic components. Commercial fabrics consisting of ultra-high molecular weight polyethylene (UHMW-PE) fibers are currently used in personal body armor and sports gear owing to their high strength, durability, and abrasion resistance. In addition to superior mechanical properties, UHMW-PE fibers exhibit very high axial thermal conductivity due to a high degree of polymer chain orientation. However, these materials have not been widely explored for thermal management applications in flexible and wearable devices. Assessment of their suitability for such applications requires characterization of the thermal and mechanical properties of UHMW-PE in the fabric form that will ultimately be used to construct heat spreading materials. Here, we use advanced techniques to characterize the thermal and mechanical properties of UHMW-PE fabrics, as well as other conventional flexible materials and fabrics. An infrared microscopy-based approach measures the effective in-plane thermal conductivity, while an ASTM-based bend testing method quantifies the bending stiffness. We also characterize the effective thermal behavior of fabrics when subjected to creasing and thermal annealing to assess their reliability for relevant practical engineering applications. Fabrics consisting of UHMW-PE fibers have significantly higher thermal conductivities than the benchmark conventional materials while possessing good mechanical flexibility, thereby showcasing great potential as substrates for flexible and wearable heat spreading application.

Relationship between the Processing, Structure, and Properties of Microfibrillar Composites

The relationship between processing, morphology, and properties of polymeric materials has been the subject of numerous studies of academic and industrial research. Finding an answer to this question might result in guidelines on how to design polymeric materials. Microfibrillar composites (MFCs) are an interesting class of polymer-polymer composites. The advantage of the MFC concept lies in developing in situ microfibrils by which a perfect homogeneous distribution of the reinforcement in the matrix can be achieved. Their potentially excellent mechanical properties are strongly dependent on the aspect ratio of the fibrils, which is developed through a three-stage production process: melt blending, fibrillation, and isotropization. During melt blending, the polymers undergo different morphological changes, such as a breakup and coalescence of the droplets, which play a crucial role in defining the microstructure. During processing, various parameters may affect the morphology of the MFCs, which must be taken into account. Besides the processing parameters, the microstructure of the composite is dependent on the composition ratio of the blend and viscosity of the components, as well as the dispersion and distribution of the microfibrils. The objective here is to outline this importance and bring together an overview of the processing-structure-property relationship for MFCs.

Rheological Behavior of Polymer/Carbon Nanotube Composites: An Overview

This paper reviews the current achievements regarding the rheological behavior of polymer-based nanocomposites containing carbon nanotubes (CNTs). These systems have been the subject of a very large number of scientific investigations in the last decades, due to the outstanding characteristics of CNTs that have allowed the formulation of nanostructured polymer-based materials with superior properties. However, the exploitation of the theoretical nanocomposite properties is strictly dependent on the complete dispersion of CNTs within the host matrix and on the consequent development of a huge interfacial region. In this context, a deep knowledge of the rheological behavior of CNT-containing systems is of fundamental importance, since the evaluation of the material's viscoelastic properties allows the gaining of fundamental information as far as the microstructure of nanofilled polymers is concerned. More specifically, the understanding of the rheological response of polymer/CNT nanocomposites reveals important details about the characteristics of the interface and the extent of interaction between the two components, hence allowing the optimization of the final properties in the resulting nanocomposites. As the literature contains plenty of reviews concerning the rheological behavior of polymer/CNT nanocomposites, this review paper will summarize the most significant thermoplastic matrices in terms of availability and relevant industrial applications.

Inorganic Nanotube Mesophases Enable Strong Self-Healing Fibers

The assembly of one-dimensional nanomaterials into macroscopic fibers can improve mechanical as well as multifunctional performance. Double-walled aluminogermanate imogolite nanotubes are geo-inspired analogues of carbon nanotubes, synthesized at low temperature, with complementary properties. Here, continuous imogolite-based fibers are wet-spun within a poly(vinyl alcohol) matrix. The lyotropic liquid crystallinity of the system produces highly aligned fibers with tensile stiffness and strength up to 24.1 GPa (14.1 N tex^-1) and 0.8 GPa (0.46 N tex^-1), respectively. Significant enhancements over the pure polymer control are quantitatively attributed to both matrix refinement and direct nanoscale reinforcement, by fitting an analytical model. Most intriguingly, imogolite-based fibers show a high degree of healability via evaporation-induced self-assembly, recovering up to 44% and 19% of the original fiber tensile stiffness and strength, respectively. This recovery at high absolute strength highlights a general strategy for the development of high-performance healable fibers relevant to composite structures and other applications.

Fabricating Fibers of a Porous-Polystyrene Shell and Particle-Loaded Core

Polystyrene (PS) polymers have broad applications in protective packaging for food shipping, containers, lids, bottles, trays, tumblers, disposable cutlery and the making of models. Currently, most PS products, such as foams, are not accepted for recycling due to a low density in the porous structure. This poses a challenge for logistics as well as creating a lack of incentive to invest in high-value products. This study, however, demonstrated the use of a dry-jet wet-spinning technique to manufacture continuous PS fibers enabled by an in-house designed and developed spinning apparatus. The manufactured fibers showed porosity in the shell and the capability to load particles in their core, a structure with high potential use in environmentally relevant applications such as water treatment or CO2 collections. A two-phase liquid-state microstructure was first achieved via a co-axial spinneret. Following coagulation procedures and heat treatment, phase-separation-based selective dissolution successfully generated the porous-shell/particle-core fibers. The pore size and density were controlled by the porogen (i.e., PEG) concentrations and examined using scanning electron microscopy (SEM). Fiber formation dynamics were studied via rheology tests and gelation measurements. The shell components were characterized by tensile tests, thermogravimetric analysis, and differential scanning calorimetry for mechanical durability and thermal stability analyses.

Incorporation of F-MWCNTs into electrospun nanofibers regulates osteogenesis through stiffness and nanotopography

Nanotopography and stiffness are major physical cues affecting cell fate. However, the current nanofiber modifications techniques are limited by their ability to control these two physical cues irrespective of each other without changing the materials' surface chemistry. For this reason, the isolated effects of topography and stiffness on osteogenic regulation in electrospun nanofibers have been studied incompletely. Here, we investigated 1. how functionalized multiwall carbon nanotubes (F-MWCNTs) loaded in Polycaprolactone (PCL) nanofibers control their physical properties and 2. whether the resulting unique structures lead to distinctive phenotypes in bone progenitor cells. Changes in material properties were measured by high-resolution electron microscopes, protein adsorption and tensile tests. The effect of the developed structures on human mesenchymal stem cell (MSC) osteogenic differentiation was determined by extensive quantification of early and late osteogenic marker genes. It was found that F-MWCNT loading was an effective method to independently control the PCL nanofiber surface nanoroughness or stiffness, depending on the applied F-MWCNT concentration. Collectively, this suggests that stiffness and topography activate distinct osteogenic signaling pathway. The current strategy can help our further understanding of the mechano-biological responses in osteoprogenitor cells, which could ultimately lead to improved design of bone substitute biomaterials.

Reversible Self-Healing for Preserving Optical Transparency and Repairing Mechanical Damage in Composites

This research concentrates on the healing of optical properties, roughness, contact angle hysteresis, and shallow scratches in polymer/nanoparticle composites. A series of ternary composite blends [epoxy/halloysite nanotubes (HNTs)/cellulose acetate butyrate (CAB)] with various CAB concentrations were fabricated and subjected to a series of mechanical damages. The optimized concentration of a nanoparticle is 1.0 vol %, and the CAB concentration is 3.0 vol % based on the mechanical reinforcement and wear resistance. Nanoscale scratching, microlevel falling-sand test, and macrolevel Taber abrasions were utilized to damage the surfaces. The induced damage (roughness and surface scratch up to hundreds of nanometers in depth) healed upon heating. At any temperatures above the softening transition of the semi-interpenetrating network structure of the polymer composites, CAB migrates into the microcracks, and the essential mechanical parameters (modulus, strength, strain to failure) are recovered; in our particular epoxy/HNTs/CAB system, optical transparency is also recovered efficiently. CAB also moves to the macroscopic air/specimen interface and favorably modifies the surface properties, reducing the roll-off angles of water droplets from ∼90° to ∼20°. Through an appropriate choice of CAB additives with different molecular weights, the healing temperature can be tailored.

Polymer nanocomposites having a high filler content: synthesis, structures, properties, and applications

The recent development of nanoscale fillers, such as carbon nanotubes, graphene, and nanocellulose, allows the functionality of polymer nanocomposites to be controlled and enhanced. However, conventional synthesis methods of polymer nanocomposites cannot maximise the reinforcement of these nanofillers at high filler content. Approaches for the synthesis of high content filler polymer nanocomposites are suggested to facilitate future applications. The fabrication methods address the design of the polymer nanocomposite architecture, which encompasses one, two, and three dimensional morphologies. Factors that hamper the reinforcement of nanostructures, such as alignment, dispersion of the filler and interfacial bonding between the filler and polymer, are outlined. Using suitable approaches, maximum potential reinforcement of nanoscale fillers can be anticipated without limitations in orientation, dispersion, and the integrity of the filler particle-matrix interface. High filler content polymer composites containing emerging materials such as 2D transition metal carbides, nitrides, and carbonitrides (MXenes) are expected in the future.

Accelerated Curing and Enhanced Material Properties of Conductive Polymer Nanocomposites by Joule Heating

Joule heating is useful for fast and reliable manufacturing of conductive composite materials. In this study, we investigated the influence of Joule heating on curing conditions and material properties of polymer-based conductive composite materials consisting of carbon nanotubes (CNTs) and polydimethylsiloxane (PDMS). We applied different voltages to the CNT nanocomposites to investigate their electrical stabilization, curing temperature, and curing time. The result showed that highly conductive CNT/PDMS composites were successfully cured by Joule heating with uniform and fast heat distribution. For a 7.0 wt % CNT/PDMS composite, a high curing temperature of around 100 °C was achieved at 20 V with rapid temperature increase. The conductive nanocomposite cured by Joule heating also revealed an enhancement in mechanical properties without changing the electrical conductivities. Therefore, CNT/PDMS composites cured by Joule heating are useful for expediting the manufacturing process for particulate conductive composites in the field of flexible and large-area sensors and electronics, where fast and uniform curing is critical to their performance.

Graphene Oxide-Graft-Poly(l-lactide)/Poly(l-lactide) Nanocomposites: Mechanical and Thermal Properties

The surface modification of graphene sheets with polymer chains may greatly hinder its aggregation and improve its phase compatibility with a polymer matrix. In this work, poly(l-lactic acid)-grafted graphene oxide (GO-g-PLLA) was prepared via a simple condensation polymerization method, realizing its dispersion well in organic solvents, which demonstrated that the surface of GO changed from hydrophilic to hydrophobic. GO-g-PLLA can disperse homogeneously in the PLLA matrix, and the tensile test showed that the mechanical properties of GO-g-PLLA/PLLA were much better than that of GO/PLLA; compared with GO, only 3% GO-g-PLLA content can realize a 37.8% increase in the tensile strength for their PLLA composites. Furthermore, the differential scanning calorimetry (DSC) and polarized optical microscopy (POM) results demonstrated that GO-g-PLLA shows a nucleating agent effect and can promote the crystallization of PLLA.

Effect of graphite and silicon carbide fillers on mechanical properties of PA6 polymer composites

In this paper, the combined effect of different weight percentages of silicon carbide (SiC) and graphite (Gr) reinforcement on the mechanical properties of polyamide (PA6) composite is studied. Test specimens of pure PA6, 85 wt% PA6+10 wt% SiC+5 wt% Gr and 85 wt% PA6+5 wt% SiC+10 wt% Gr are prepared using an injection molding machine. The tensile, impact, hardness, morphology and thermal properties of the injection molded composites were investigated. The obtained results showed that mechanical properties, such as tensile and impact strength and modulus of the PA6 composites, were significantly higher than the pure PA6, and hybridization with silicon carbide and graphite further enhanced the performance properties, as well as the thermal resistance of the composites. The tensile fracture morphology and the characterization of PA6 polymer composites were observed by scanning electron microscope (SEM) and Fourier transform infrared spectroscopic methods. SEM observation of the fracture surfaces showed the fine dispersion of SiC and Gr for strong interfacial adhesion between fibers and matrix. The individual and combined reinforcing effects of silicon carbide and graphite on the mechanical properties of PA6 hybrid composites were compared and interpreted in this study. Improved mechanical properties were observed by the addition of small amount of SiC and Gr concurrently reinforced with the pure PA6. Finally, thermogravimetric analysis showed that the heat resistance of the composites tended to increase with increasing silicon carbide and graphite content simultaneously.

Electrical, Mechanical, and Thermal Properties of LDPE Graphene Nanoplatelets Composites Produced by Means of Melt Extrusion Process

Composites of LDPE filled with different amounts of graphene nanoplatelets (GnP) were prepared in form of films by means of precoating technique and single screw melt-extrusion using two types of screws, compression and mixing. This manufacturing process imposes strong anisotropy on the sample's morphology, in which the nanoplatelets become oriented along the extrusion direction. Such orientation of GnP in LDPE matrix is confirmed by scanning electron microscopy observations and it yields unique electrical properties. As compared to pure LDPE, significant reductions of the through-plane conductivity are found for the composites at relatively low electric fields (<20 kV/mm) at low filler concentrations. Above the field level of 20 kV/mm, a crossover effect is observed that results in a strong field dependency of the conductivity where the non-linear behavior starts to dominate. Moreover, differential scanning calorimetry (DSC) results indicate a decrease in polymer crystallinity of the composite matrix with increasing filler content, whereas thermogravimetric (TG) analysis shows a slight increase in the material's thermal stability. Application of GnP also leads to improvement of mechanical properties, manifested by the increase of Young's modulus and tensile strength in both types of samples.

Impact of size control of graphene oxide nanosheets for enhancing electrical and mechanical properties of carbon nanotube–polymer composites

The size effects of GOs on the dispersion behavior of multi-walled carbon nanotubes (MWCNTs) were evaluated, and the GOs were exploited to develop conducting film and polymer-CNT composites with excellent electrical and mechanical properties.

Enhanced Wear Resistance of Transparent Epoxy Composite Coatings with Vertically Aligned Halloysite Nanotubes

The influence of nanoparticle orientation on wear resistance of transparent composite coatings has been studied. Using a nozzle spray coating method, halloysite nanotubes (HNTs) were aligned in the in-plane and out-of-plane directions and in various randomly oriented states. Nanoscratching, falling sand, and Taber Abrasion tests were used to characterize the wear resistance at different length scales. Composites consistently displayed better wear resistance than pure epoxy. Samples with out-of-plane particle orientations exhibited better wear-resistant behavior than those with in-plane particle distributions. In nanoscratching tests, the out-of-plane orientation decreases the normalized scratch volume by as much as 60% compared to pure epoxy. In the falling sand and Taber Abrasion tests, out-of-plane aligned halloysite particles resulted in surfaces with smaller roughness based on stylus profilometry and SEM observations. The decrease in roughness values after these wear tests can be as large as 67% from pure epoxy to composites. Composites with higher out-of-plane particle orientation factors exhibited better light transmittance after sand impingements and other wear tests. This study suggests a useful strategy for producing material systems with enhanced mechanical durability and more durable optical properties.

Effect of Microwave Treatment of Graphite on the Electrical Conductivity and Electrochemical Properties of Polyaniline/Graphene Oxide Composites

Polyaniline (PANI)/graphene oxide (GO) composites were synthesized via in situ polymerization of aniline in the presence of GO. The effect of microwave treatment of graphite on the electrical conductivity and electrochemical properties of PANI/GO composites was highlighted, and the morphology and microstructure were subsequently characterized using transmission electron microscopy, scanning electron microscopy, Fourier-transformed infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis. The results demonstrated that microwave treatment of graphite imparted a well-dispersed, highly ordered layered structure to the as-prepared GO, and in turn facilitated strong bonding between the GO and PANI nanosheets, which may be responsible for the improved electrical conductivity and electrochemical properties of the resulting PANI/GO composites. The desired PANI/GO composites possessed an electrical conductivity of 508 S/m, an areal capacitance of 172.8 mF/cm², and a retained capacitance of 87.4% after cycling, representing percentage increases of 102, 232, and 112, respectively, as a result of the microwave treatment of graphite. The resulting composites are promising electrode materials for high-performance and ecofriendly electrical energy storage devices.

Carbon Nanotube (CNT) Honeycomb Cell Area-Dependent Optical Reflectance

The relationship between the physical structure of carbon nanotube (CNT) honeycomb structures and their total, diffuse, and specular reflectance is investigated for the first time. It is found that CNT honeycomb structures with average cell areas of smaller than 30 μm² show a higher total reflectance. Particularly, a thinner, highly packed CNT (buckypaper) film, along with a larger wall height and higher ratio of wall height to cell area, markedly increase the total reflectance for cell areas smaller than 30 μm², which means that a higher total area of buckypapers in CNT walls and bottom areas increases the total reflectance, including the diffuse reflectance. It is also found that the total reflection of non-absorbed light in CNT honeycomb structures consists primarily of diffuse reflectance.

Material Evaluation and Process Optimization of CNT-Coated Polymer Powders for Selective Laser Sintering

Multi-walled carbon nanotubes (CNTs) as nano-reinforcements were introduced to facilitate the laser sintering process and enhance the thermal and mechanical properties of polymeric composites. A dual experimental-theoretical method was proposed to evaluate the processability and predict the process parameters of newly developed CNT-coated polyamide 12 (CNTs/PA12) powders. The thermal conductivity, melt viscosity, phase transition and temperature-dependent density and heat capacity of PA12 and CNTs/PA12 powders were characterized for material evaluation. The composite powders exhibited improved heat conduction and heat absorption compared with virgin polymer powders, and the stable sintering range of composite powders was extended and found to be favourable for the sintering process. The microstructures of sintered composites revealed that the CNTs remained at the powder boundaries and formed network architectures, which instantaneously induced the significant enhancements in tensile strength, elongation at break and toughness without sacrificing tensile modulus.

Study of Polymer Matrix Degradation Behavior in CFRP Short Pulsed Laser Processing

Short pulsed laser is preferred to avoid the thermal damage in processing the heat sensitive material, such as carbon fiber reinforced plastic (CFRP). In this paper, a numerical model capturing both the material ablation and polymer matrix pyrolysis processes in pulsed laser processing is established. The effect of laser pulse length from ns order to μs order is studied. It was found that with shorter pulse length, ablation depth is increased and heat affected zone is remarkably reduced. Moreover the pyrolysis gas transport analysis shows that shorter pulse length results in a larger internal pressure. At pulse length in ns order, maximum pressure as high as hundreds of times atmospheric pressure in CFRP could be produced and leads to mechanical erosion of material. The predicted ablation depth of a single short laser pulse conforms well to the experiment result of the CFRP laser milling experiment.

Spray-Coated Halloysite-Epoxy Composites: A Means To Create Mechanically Robust, Vertically Aligned Nanotube Composites

Halloysite nanotube-filled epoxy composites were fabricated using spray-coating methods. The halloysite nanotubes (HNTs) were aligned by the hydrodynamic flow conditions at the spray nozzle, and the polymer viscosity helped to preserve this preferential orientation in the final coatings on the target substrates. Electron microscopy demonstrated a consistent trend of higher orientation degree in the nanocomposite coatings as viscosity increased. The nanoindentation mechanical performances of these coatings were studied using a Hysitron TriboIndenter device. Composites showed improvements up to ∼50% in modulus and ∼100% in hardness as compared to pure epoxy, and the largest improvements in mechanical performance correlated with higher alignment of HNTs along the plane-normal direction. Achieving this nanotube alignment using a simple spray-coating method suggests potential for large-scale production of multifunctional anisotropic nanocomposite coatings on a variety of rigid and deformable substrates.

Beads, beaded-fibres and fibres: Tailoring the morphology of poly(caprolactone) using pressurised gyration

This work focuses on forming bead on string poly(caprolactone) (PCL) by using gyration under pressure. The fibre morphology of bead on string is an interesting feature that falls between bead-free fibres and droplets, and it could be effectively controlled by the rheological properties of spinning dopes and the major processing parameters of the pressurised gyration system which are working pressure and rotating speed. Bead products were not always spherical in shape and tended to be more elliptical, therefore both their width and length were measured. The average bead width and length produced spanned a range 145-660μm and 140-1060μm, respectively. The average distance between two adjacent beads (i.e. inter-bead distance) and the bead size (width and length) are shown to be a function of processing parameters and polymer concentration. An interesting morphology i.e. beads with short fibre was observed when using a high polymer concentration. Bead on string structure agglomeration was promoted by a low polymer concentration. Formation of droplets or agglomerated bead on string is promoted below 5wt% polymer concentration, and beads with short fibre were present in the microstructure beyond a polymer concentration of 20wt%.

A Facile Route to Synthesize Nanographene Reinforced PBO Composites Fiber via in Situ Polymerization

The polymer matrix with introduced carbon-based nanofiber displays fascinating properties. They have inspired extensive research on the synthesis of polymer composites, which have been applied in catalysis, electronics, and energy storage. In this report, we reported a facile and efficient method to prepare poly(p-phenylene benzobisoxazole) (PBO)/nanographene (PNG) composites fibers via in-situ polymerization, accompanied by the reduction from (nanographene oxide) NGO to (nanographene) NG. By tuning the ratio of feeding PBO monomer to NGO, various composites fibers with 0.1–1 wt % contents of NG were obtained. The efficient PBO chains grafting made NG uniformly disperse in the PBO matrix, and it also increased the uniformity of the packing orientation of PBO chains. Consequently, the tensile strength, tensile modulus, and thermal stability of the obtained PNG composites fibers had been improved significantly. In addition, the composites fibers with 0.5 wt % NG exhibited a 25% increment in tensile strength, and a 41% enhancement in tensile modulus compared with neat PBO fibers. It reveals an excellent reinforcement to PBO composites fibers with NG.

Monotonic and Cyclic Bond Behavior of Deformed CFRP Bars in High Strength Concrete

Composite reinforcing bars (rebars) that are used in concrete members with high performance (strength and durability) properties could have beneficial effects on the behavior of these members. This is especially vital when a building is constructed in an aggressive environment, for instance a corrosive environment. Although tension capacity/weight (or volume) ratios in composite rebars (carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), etc.) are very high when compared to steel rebars, major weaknesses in concrete members reinforced with these composite rebars may be the potential consequences of relatively poor bonding capacity. This may even be more crucial when the member is subjected to cyclic loading. Although monotonic bond tests are available in the literature, only limited experimental studies exist on bond characteristics under cyclic loading conditions. In order to fill this gap and propose preliminary design recommendations, 10 specimens of 10-mm-diameter ribbed CFRP rebars embedded in specially designed high strength concrete (f’_c = 70 MPa) blocks were subjected to monotonic and cyclic pullout tests. The experimental results showed that cyclically loaded CFRP rebars had less bond strength than those companion specimens loaded monotonically.

Multiwalled Carbon nanotube – Strength to polymer composite

Carbon nanotubes (CNTs), a rather fascinating material, are among the pillars of nanotechnology. CNTs exhibit unique electrical, mechanical, adsorption, and thermal properties with high aspect ratio, exceptional stiffness, excellent strength, and low density, which can be exploited in the manufacturing of revolutionary smart nano composite materials. The demand for lighter and stronger polymer composite material in various applications is increasing every day. Among all the possibilities to research and exploit the exceptional properties of CNTs in polymer composites we focused on the reinforcement of epoxy resin with different types of multiwalled carbon nano tubes (MWCNTs). We studied mechanical properties such as stress, strain, ultimate tensile strength, yield point, modulus and fracture toughness, and Young's modulus by plotting and calculating by means of the off-set method. The mechanical strength of epoxy composite is increased intensely with 1 and 3 wt.% of filler.