Alignment Of Carbon Nanofibers Research Articles

Carbon nanofibers in polyurethane foams: Experimental evaluation of thermo-hygrometric and mechanical performance

Polymer nanocomposites synergistically combine the good thermal properties of the hosting polymer matrix with the high mechanical performance of the fillers, providing a new class of materials with superior properties.The present study aims to evaluate in a multidisciplinary way the enhancement in mechanical and thermal-hygrometric properties of low and medium density nanophased polyurethane (PUR) foams with either randomly oriented or aligned nanofibers as compared to the neat ones.To this aim, 1% weight of carbon nanofibers (CNFs) were homogeneously dispersed into polyol of PUR foam by an ultrasonic cavitation method. In parallel, a small amount of CNFs was functionalized in advance by a co-precipitation method so as to align them into the polymer matrix through an external low intensity magnetic field.SEM analyses were used to compare the microstructure of the neat and nanophased samples.Results have shown that the addition of carbon nanofibers in the foams products a closer structure with a more uniform size and shape. Moreover, functionalized CNFs play a significant role in regulating cells shape as well as strengthening cells walls.Mechanical test results also demonstrated that CNFs increase both strength and stiffness of the samples. The alignment of carbon nanofibers within medium density nanophased foams determines the highest mechanical properties. However, the more noticeable improvement in samples performance occurred in low density nanophased foams.Finally, carbon nanoparticles decrease the thermal conductivity and increase the resistance against water adsorption.

Polyacrylonitrile nanocomposite fibers from acrylonitrile-grafted carbon nanofibers

Abstract For the first time, uniform distribution of surface functionalized carbon nanofibers (CNFs) has been achieved in low molecular weight (≈120,000 g/mol) textile grade-polyacrylonitrile (PAN)-based composite filaments. Surface grafting of CNFs with acrylonitrile enhances the dispersion of nanofibers in PAN fiber matrix. XPS study reveals high atomic nitrogen content (7%) on the CNF surface due to the grafting reaction. The solution-spun filaments have been characterized for distribution of CNFs in the PAN matrix by electron microscopy. PAN composite filaments containing 3.2 wt.% CNF and processed at draw ratio of ≈6.3 exhibit enhanced tensile strength and modulus by more than three folds compared to the control PAN filament. Because of chemically compatible surface modification of the nanofibers, better dispersion and improved mechanical properties were accomplished in the reinforced PAN fibers. This should allow the production of CNF reinforced carbon fibers with improved tensile properties. An increase in CNF loading (6.4 wt.%), however, reduced performance due to inefficient alignment of CNF along the fiber axis. Nevertheless, hot stretching (at draw ratio ≈ 10) of the filaments enhanced tensile strength and elastic modulus of PAN composite filaments by 20–30% compared to the control hot stretched PAN filaments.

Fluid‐Induced Alignment of Carbon Nanofibers in Polymer Fibers

Carbon nanofiber/polycaprolactone (CNF/PCL) composite fibers are fabricated using a microfluidic approach. The fibers are made with different content levels of CNFs and flow rate ratios between the core and sheath fluids. The electrical conductivity and tensile properties of these fibers are then investigated. It is found that at a CNF concentration of 3 wt%, the electrical conductivity of the composite fiber significantly increases to 1.11 S m−1. The yield strength, Young's modulus, and ultimate strength of the 3 wt% CNF increase relative to the pure PCL by factors of 1.72, 2.88, and 1.23, respectively. Additionally, the results show that a microfluidic approach can be considered as an effective method to align CNFs along the fibers in the longitudinal direction. image

Characterization and Alignment of Carbon Nanofibers under Shear Force in Microchannel

This work presents a novel method to align CNFs by using shear forces in microchannels. Effect of two different microchannel sizes (1 mm × 0.1 mm and 1 mm × 0.2 mm) on CNFs alignment is investigated. SEM images of CNFs preform display significant alignment by both microchannels, which can be interpreted using a second-order alignment tensor and a manual angle meter. In the second-order alignment tensor description, an elongated ellipse can signify high degree of alignment in the direction of the major axis. When the microchannel size is 1 mm × 0.2 mm, the lengths of major and minor axes of the ellipse are 0.982 to 0.018. An angle meter manually shows that 85% of the CNFs are aligned in the direction between 60° and 90° when the microchannel is 1 mm × 0.2 mm. Both methods can demonstrate that better alignment of CNFs can be obtained using the 1 mm × 0.2 mm microchannel.

Reinforcing polyamide 1212 nanocomposites with aligned carbon nanofibers

In this study, the mechanical properties and structure orientation of pure polyamide 1212 (PA1212) were compared with those of PA1212–carbon nanofibers (CNFs) nanocomposites. The tensile strength of the composite containing 0.3wt.% modified CNFs was improved from 328MPa (pure PA1212) to 373MPa after drawing. The reinforcing effect was investigated in terms of crystallization behavior, crystal morphology, alignment of CNFs, and crystal orientation degree. Spherulites developed into oriented crystals after drawing, and the CNFs aligned along the drawing direction. The heterogeneous nucleation effect of the aligned CNFs improved the crystal orientation degree, which produced the reinforcing effect. The oriented fibril structures with rigid nanofibers acting as nuclei reinforced the entire oriented crystals in the composites.

Alignment of Carbon Nanofibers in Water and Epoxy by External Magnetic Field

Alignment of Carbon Nanofibers in Water and Epoxy by External Magnetic Field

Alignment of Carbon Nanofibers in an Uncured Polymer using Traveling Electric Field

Alignment of Carbon Nanofibers in an Uncured Polymer using Traveling Electric Field

Alignment of Carbon Nanofibers in the Al<SUB>2</SUB>O<SUB>3</SUB> Matrix under a Magnetic Field

A stable suspension of multi-walled carbon nanofibers (CNFs) in Al2O3 was prepared by adding ammonium polycarboxylate as a dispersant in an aqueous solution. A strong magnetic field of 12 T was applied to the CNFs/Al2O3 suspension to investigate the alignment of the CNFs. The result was that the CNFs in the matrix showed good alignment with the direction of the magnetic field. It was found that 0.5 mass% CNFs showed isolated alignment; in contrast, with 5 mass% CNFs there were mainly aligned bundles. The alignment was only seen with straight CNFs; curved CNFs showed no alignment in a magnetic field.

Fabrication and Characterization of High Temperature Resin/Carbon Nanofiber Composites

Multifunctional composites present a route to structural weight reduction. Nanoparticles such as carbon nanofibers (CNF) provide a compromise as a lower cost nanosize reinforcement that yields a desirable combination of properties. Blends of PETI-330 and CNFs were prepared and characterized to investigate the potential of CNF composites as a high-performance structural medium. Dry mixing techniques were employed and the effect of CNF loading level on melt viscosity was determined. The resulting powders were characterized for degree of mixing, thermal and rheological properties. Based on the characterization results, samples containing 30 and 40 wt.% CNF were scaled up to approximately 300 g and used to fabricate moldings 10.2 cm ′ 15.2 cm ′ 0.32 cm thick. The moldings were fabricated by injecting the mixtures at 260-280°C into a stainless steel tool followed by curing for 1 h at 371°C. The tool was designed to impart high shear during the injection process in an attempt to achieve some alignment of CNFs in the flow direction. Moldings were obtained that were subsequently characterized for thermal, mechanical and electrical properties. The degree of dispersion and alignment of CNFs were investigated using high-resolution scanning electron microscopy. The preparation and preliminary characterization of PETI-330/CNF composites are discussed.

Nanoscaled Reinforcement of Polystyrene Foams using Carbon Nanofibers

Carbon nanofibers (CNFs) are used as both the nucleants and the reinforcements for polystyrene (PS) foams in both batch and continuous extrusion processes with CO2 as the blowing agent. The inclusion of CNFs exhibits substantial impact on the morphology and properties of PS foams. The presence of CNFs results in a decrease in the cell size and an increase in the cell density. Macroscopic strength enhancement of PS foams due to the incorporation of CNFs is experimentally observed. These results are qualitatively explained via a series of nanoscaled observations. Through scanning electron microscopy (SEM), the alignment of CNFs and the polymer-sheathing phenomenon are identified. The protective CNF layers around the cell wall and the substantial polymer-fiber interactions resulted in the enhancement of foam strengths. Thermal properties (heat conductivity, infrared transmission, and thermal expansion coefficient) of the PS foams can also be influenced by CNFs. Intensive shear force exerted by the twin-screw extruder broke the fibers in lengths. The impact of the fiber length on the foam structures (cell size and cell density) is also studied.

Magnetic Alignment of Carbon Nanofibers in Polymer Composites

ABSTRACTCarbon nanofibers were well aligned in polymer composite magnetically at moderate fields up to 3 T. Due to the NiO-coating, carbon nanofibers exhibited strong magnetic moments that lead to alignment. Both TEM and SEM results showed the well-aligned nano-fibers in a polymer matrix. Mechanical testing showed a pronounced anisotropy in tensile strength in directions normal (12.1MPa) and parallel (22MPa) to the applied field, resulting from the well-aligned nanofibers in the polymer matrix. The mechanism of magnetic alignment due to coating of NiO on the nano fiber surface is discussed.

Alignment mechanism of carbon nanofibers produced by plasma-enhanced chemical-vapor deposition

We report experimental evidence showing a direct correlation between the alignment of carbon nanofibers (CNFs) prepared by plasma-enhanced chemical-vapor deposition and the location of the catalyst particle during CNF growth. In particular, we find that CNFs that have a catalyst particle at the tip (i.e., growth proceeds from the tip) align along the electric-field lines, whereas CNFs with the particle at the base (i.e., growth proceeds from the base) grow in random orientations. We propose a model that explains the alignment process as a result of a feedback mechanism associated with a nonuniform stress (part tensile, part compressive) that is created across the interface of the catalyst particle with the CNF due to electrostatic forces. Furthermore, we propose that the alignment seen recently in some dense CNF films is due to a crowding effect and is not directly the result of electrostatic forces.