High Aspect Ratio Fibers Research Articles

The effect of steel fiber aspect-ratio and content on the fresh, flexural, and mechanical performance of concrete made with recycled fine aggregate

In order to solve the problem of low toughness and easy cracking of recycled aggregate concrete, steel fibers were incorporated to recycled fine aggregate concrete (RAC) to prepare a sustainable fiber-reinforced concrete. Steel fibers of various contents (20, 35, 50 and 65 kg/m3) and aspect ratios (l/d = 40 and 55) were incorporated to the RAC, and their fresh properties, mechanical properties and microstructure were investigated. The results show that the slump of RAC decreases with increasing fiber aspect ratio and content. Meanwhile, incorporating a small amount of steel fibers (l/d = 40, 20 kg/m3) improves the 28-d compressive strength of RAC, but with further increase in fiber aspect ratio and content, the compressive strength of RAC decreases. The incorporation of steel fibers greatly improves the splitting tensile strength and flexural strength of RAC, and the steel fibers with high aspect ratio have a higher gain in strength. The 28-d flexural strength of concrete with 65 kg/m3 steel fibers (l/d = 40) increases by 148.11 % relative to plain RAC, while the 65 kg/m3 steel fibers with an aspect ratio of 55 makes RAC with increases by 243.78 %. The mass loss of fiber-reinforced RAC under abrasion is also lower than that of plain RAC, and the steel fiber with high aspect ratio performs better. For the load–deflection response, the incorporation of fibers increases the peak load, and also increases the flexural toughness and post-cracking toughness, with the greatest gain for high aspect ratio fibers.

Processing of nanocellulose sheet for capturing fine particulate matter

Nanofibers have gained more interest in recent times due to their high surface area. One such class of fibers being nanocellulose fibers are biodegradable and hydrophilic depending on the amount of lignin present. In this work, wood chips were subjected to Kraft cooking and the resulting pulp was refined using Lab Valley Beater (LVB) and Super masscolloider (SMC). Refining was carried out using three different parameters to obtain the high aspect ratio fibers. LVB refining yielded short-length, micron diameter fibers (<1000 µm) whereas SMC refining yielded longer length, smaller diameter fibers (<900 nm). The properties of the refined slurry were analyzed using consistency and Canadian standard freeness (CSF) tests to gauge the structure–property relationship, especially the drainability of sheets. Sheets consisting of micro and nanocellulose fibers were prepared using a Whatman filter of 10 µm pore size. LVB refining of 60 mins was sufficient to obtain sheets with optimum porosity, consistency, CSF, and tensile elongation. SMC sheet made from 0.01 clearance revealed high aspect ratio fibers, high tensile strength, low elongation, low CSF, low consistency, and low porosity. Therefore, this sheet was used to capture fine particulate matter (PM2.5) from the air at 25–500 µg/m3 concentration and was concluded as a possible alternative to Teflon sheets to capture fine dust (PM2.5).

Nanofiber‐Carbon black dual filler reinforced sustainable high‐performance Natural Rubber nanocomposites

AbstractIn the present work, uncured and cured properties of high‐performance, sustainable Natural Rubber nanocomposites developed by leveraging the unique synergy between carbon black and fibrous nanofillers such as silicon carbide, carbon nanotubes, and aramid nanofibers were investigated. Reinforcement in these composites was analyzed using the properties of the unvulcanized compounds, which were then correlated with those of the vulcanized compounds. A 50% increment was recorded for the bound rubber content of the nanocomposites, which resulted in tremendous improvements in the reinforcement index and tensile strength of the unvulcanized nanocomposites. In contrast, the die swell index came down compared with the control compound. The formation of a percolating network due to the presence of high aspect ratio fibers resulted in a higher Payne effect in hybrid nanocomposites, which was confirmed from the scanning and transmission electron microscopy. The 100% modulus, 300% modulus, and tensile strength of the unvulcanized nanocomposites recorded an improvement of 80, 121, and 450%, respectively, by the incorporation of nanofibers. The molecular aspects of reinforcement were elucidated from theoretical calculations using Mooney–Rivlin plots. It was presumed that the improved reinforcing efficiency of the nanofibers resulted from restricted mobility of elastomer chains due to the presence of the dual filler system.

Instrument for tensile testing of individual collagen fibrils with facile sample coupling and uncoupling.

Collagen is the major structural protein in human bodies constituting about 30% of the entire protein mass. Through a self-assembly process, triple helical collagen molecules assemble into high aspect-ratio fibers of tens to hundreds of nanometer diameter, known as collagen fibrils (CFs). In the last decade, several methods for tensile testing these CFs emerged. However, these methods are either overly time-consuming or offer low data acquisition bandwidth, rendering dynamic investigation of tensile properties impossible. Here, we describe a novel instrument for tensile testing of individual CFs. CFs are furnished with magnetic beads using a custom magnetic tweezer. Subsequently, CFs are lifted by magnetic force, allowing them to be picked-up by a microgripper structure, which is mounted on a cantilever-based interferometric force probe. A piezo-lever actuator is used to apply tensile displacements and to perform tensile tests of tethered CFs, after alignment. Once the mechanical tests are finished, CFs are removed from the microgripper by application of a magnetic field. Our novel instrument enables tensile tests with at least 25-fold increased throughput compared to tensile testing with an atomic force microscope while achieving force resolution (p-p) of 10 nN at a strain resolution better than 0.1%.

An efficient computational approach for three-dimensional modeling and simulation of fibrous battery electrodes.

Fibrous electrodes are a promising alternative to conventional particle‐based lithium‐ion battery electrodes. In this contribution, we propose an efficient computational approach for the modeling and simulation of electrochemical phenomena taking place in fibrous electrodes during battery charge/discharge processes. Since each fiber is explicitly modeled by means of a dimensionally reduced embedded fiber model, the framework enables simulations in a three‐dimensional setting with relatively modest discretization and computational requirements compared to simulations with fully resolved fiber discretizations. The approach is applied to electrodes with high volume fractions of high aspect ratio fibers. Various local and global quantities are analyzed and results are compared to those obtained with the standard finite element method and the pseudo‐2D model.

3D fibrillated network of compatibilized linear low density polyethylene/polyamide with high melt strength and superior foamability

A new, efficient and easy to scale up approach to enhance the melt strength of linear low density polyethylene (LLDPE) through high aspect ratio polyamide (PA) fibrillar inclusions is presented. For the first time, the effect of the incorporation of compatibilizer in the blends on the efficiency of the in-situ fibrillation approach to improve rheological properties and foamability is discussed. The morphological analysis indicates high aspect ratio fibers were achieved for both compatibilized and non-compatibilized systems. Also, very fine fibers with nano-scale cross-sectional diameter were achieved for compatibilized blends. Comparable rheological responses and substantial improvement of the foaming ability with superior foam morphology and high cell density was obtained, for both fibrillated blends with and without compatibilizer. Investigation of the crystallinity of the blends through DSC and WAXD indicated that bimodal melting and crystallization of LLDPE is remarkably affected by the presence of PA inclusions, particularly for the blends containing fibrillated PA. Further investigation of the crystallinity through 2D-SAXS revealed formation of shish-kebab crystalline structures as a result of drawing and shear induced crystallization.

Comparative study on the mechanical, tribological, and thermal properties of POM composites filled with different PTFE

In this study, two different types of polytetrafluoroethylene (PTFE) fillers (i.e. fibrillar and particulate PTFE) were utilized to improve the tribological properties of polyoxymethylene (POM). POM/PTFE composites with various filler contents were tested on a commercial block-on-ring tester. To further probe the tribological properties of POM/PTFE composites under severe sliding conditions, a homemade pin-on-disc tester was employed. Results showed that the lowest coefficient of friction and wear rate are obtained from PTFE particle–filled POM composites at 20 wt%, which is attributed to the formation of uniform transfer film at the sliding interface thanks to the well distribution of PTFE particles. The mass wear rate of POM/PTFE fiber composites is lower than that of PTFE particle–containing counterparts due to the better load transfer of high aspect ratio fibers. The tensile properties of POM/PTFE composites deteriorate with the addition of PTFE fillers; however, the impact strength is significantly enhanced for PTFE fiber filled POM composites. Moreover, both the melting and crystallization properties of POM are affected by the morphology of PTFE fillers and filler concentration, as characterized by differential scanning calorimetry analysis.

Nickel Nanofibers Manufactured via Sol-Gel and Electrospinning Processes for Electrically Conductive Adhesive Applications

The electrospun fibers of poly(vinyl pyrrolidone) (PVP)-nickel acetate (Ni(CH3COO)2·4H2O) composite were successfully prepared by using sol-gel processing and electrospinning technique. Nickel oxide (NiO) nanofibers were obtained afterwards by high temperature calcinations of the precursor fibers, PVP/Ni acetate composite nanofibers, at 700 °C for 10 h. Following with the reduction of NiO nanofibers at 400 °C using hydrogen gas (H2) under inert atmosphere, the metallic nickel (Ni) nanofibers were subsequently produced. In addition, as-prepared Ni nanofibers were chemically coated with silver (Ag) nanoparticles to enhance their electrical property and prevent the surface oxidation. The characteristics of as-prepared fibers, such as surface morphology, fiber diameters, purity, the amount of NiO nanofibers, and metal crystallinity, were determined using a scanning electron microscope (SEM), a Fourier transform infrared spectrometer (FT-IR), a thermogravimetric analyzer (TGA), and a wide-angle x-ray diffractometer (WAXD). The volume resistivity of epoxy nanocomposite filled with Ag-coated short Ni nanofibers was lower than the one containing short Ni nanofibers with no coating due to the synergetic effect of Ag nanoparticles created during the coating process. We also demonstrated that the volume resistivity of epoxy nanocomposite filled with Ni nanofibers could be dramatically decreased by using Ni nanofibers in the non-woven mat form due to their small fiber diameter and high fiber aspect ratio, which yield a high specific surface area, and high interconnecting network.

In Silico Optimization of Fiber-Shaped Aerosols in Inhalation Therapy for Augmented Targeting and Deposition across the Respiratory Tract.

Motivated by a desire to uncover new opportunities for designing the size and shape of fiber-shaped aerosols towards improved pulmonary drug delivery deposition outcomes, we explore the transport and deposition characteristics of fibers under physiologically inspired inhalation conditions in silico, mimicking a dry powder inhaler (DPI) maneuver in adult lung models. Here, using computational fluid dynamics (CFD) simulations, we resolve the transient translational and rotational motion of inhaled micron-sized ellipsoid particles under the influence of aerodynamic (i.e., drag, lift) and gravitational forces in a respiratory tract model spanning the first seven bifurcating generations (i.e., from the mouth to upper airways), coupled to a more distal airway model representing nine generations of the mid-bronchial tree. Aerosol deposition efficiencies are quantified as a function of the equivalent diameter (dp) and geometrical aspect ratio (AR), and these are compared to outcomes with traditional spherical particles of equivalent mass. Our results help elucidate how deposition patterns are intimately coupled to dp and AR, whereby high AR fibers in the narrow range of dp = 6–7 µm yield the highest deposition efficiency for targeting the upper- and mid-bronchi, whereas fibers in the range of dp= 4–6 µm are anticipated to cross through the conducting regions and reach the deeper lung regions. Our efforts underscore previously uncovered opportunities to design the shape and size of fiber-like aerosols towards targeted pulmonary drug delivery with increased deposition efficiencies, in particular by leveraging their large payloads for deep lung deposition.

The influence of resin composite with high fiber aspect ratio on fracture resistance of severely damaged bovine incisors.

The aim was to determine the fracture-behavior of incisors restored with different post-core foundations and crown made of conventional composite (PFC, G-aenial Anterior). Forty bovine-incisors were cut and divided into 5 groups. Group A had teeth restored using fiber-post and Gradia Core as core build-up and crown of PFC. Group B contained teeth restored with fiber-post and core made of everX Flow and crown of PFC. In Group C, the teeth were restored with everX Flow as post-core and crown of PFC. Group D, post-core-crown restorations were indirectly made from CERASMART. Group E, teeth were restored with Gradia Core as post-core and crown of PFC. Restored teeth were statically-loaded until fracture. ANOVA revealed that restoration technique significantly affected load-bearing capacity (p<0.05). Restored incisors (Group B) had the highest load-bearing capacity (443 N) among all groups. Using everX Flow as core material with fiber-post is promising to strengthen structurally compromised incisors.

Laryngeal Lavage: A Potential Method of Evaluation of Amphibole Fiber Exposure.

Our objective is to propose a simple procedure for evaluating potential recent heavy exposure to tremolite. One day after an accidental exposure to tremolite in rock dust, sputum was sampled; 3 months later a laryngeal lavage was taken. The sputum was examined with scanning electron microscopy (SEM); the lavage was examined with transmission electron microscopy (TEM). The sputum was found to contain abundant tremolite while the lavage contained very thin, high aspect-ratio fibers, many in the "Stanton Fiber" range. The abundance of tremolite from the larynx suggests accumulation. The thin fibers exhibit splitting from thicker fibers that were in the lungs. Laryngeal lavage may be an important index of asbestos exposure and is a less complex and more diagnostic alternative to bronchoalveolar lavage or sputum sampling.

Evaluation of 3D Embedded Element Technique in the Finite Element Analysis for the Composite

RVE combined with finite element analysis (FEA) is a very popular method to predict the mechanical property of the composite reinforced by short fibers. In the conventional method, generally the “tie” approach is used. By this method, the FE model with high fiber aspect ratio can not be achieved and the non-convergence of the numerical calculation may appear because of the complex mesh. The embedded element techinique is considered to be a replaceable method . Using this method, the mechanical behavior of composite with high fiber aspect ratio would be simulated. Therefore, in this study, the 3D solid element was employed for the FE model with multi cylinder particles. The comparisions of the Mise stress and the displacement between the embedded and conventional method indicate that compared with the stress transfer, the simulated result of composite stiffness is more accurate. In addition, the effects of model size, fiber orientated angle, fiber volume fraction and fiber aspect ratio were investigated. The numerical results were compared with the Mori-Tanaka model and the good agreements verify the applicability of the embedded element technique we studied in this paper.

Template-Assisted Synthesis of Luminescent Carbon Nanofibers from Beverage-Related Precursors by Microwave Heating.

Luminescent carbon nanomaterials are important materials for sensing, imaging, and display technologies. This work describes the use of microwave heating for the template-assisted preparation of luminescent carbon nanofibers (CNFs) from the reaction of a range of beverage-related precursors with the nitrogen-rich polyethyleneimine. Highly luminescent robust carbon fibers that were 10 to 30 μm in length and had a diameter of 200 nm were obtained under moderate conditions of temperature (250–260 °C) and a short reaction time (6 min). The high aspect ratio fibers showed wavelength-dependent emission that can be readily imaged using epifluorescence. The development of these multi-emissive one-dimensional (1D) carbon nanomaterials offers potential for a range of applications.

Fiber motion in highly confined flows of carbon fiber and non-Newtonian polymer

Inks compounded of short carbon fibers suspended in polymer resin can be extruded to produce composite materials during additive manufacturing or 3D printing processes. The flow process induces anisotropic orientation of the fibers which is set into the matrix and significantly affects the mechanical and physical properties of the final product. Therefore, the flow of fiber suspensions needs to be understood in order to predict the orientation distribution of the fibers during such manufacturing processes. There is still a lack of knowledge for extrusion of the complex mixture of a non-Newtonian polymer containing a high-volume fraction of fibers with high fiber aspect ratio, where both inter-particle, fluid-particle and fiber-wall interactions are computationally evaluated. This paper presents predictive numerical simulations and experimental results of such confined flow in a concentrated regime. The code is based on Lagrange multiplier technique and resolves each particle and interaction between the fibers and surrounding fluid and nozzle walls. We investigate numerically how the fiber length impacts the fiber alignment during extrusion. We found that a fiber length above 67% of the nozzle's diameter induces dramatic change in the fiber flow, causing fibers to concentrate at the nozzle boundaries with very low concentration of fibers in the center of the nozzle. It was found that the best fiber alignment is reached for fiber lengths equal to 40–50% of the nozzle diameters. Numerical findings are supported by experimental results. This work improves understanding of fiber orientation during 3D printing and is an important milestone for the prediction of the complex mechanical properties of additively manufactured fiber composites.

Review of techniques and studies characterizing the release of carbon nanotubes from nanocomposites: Implications for exposure and human health risk assessment.

Composites made with engineered nanomaterials (nanocomposites) have a wide range of applications, from use in basic consumer goods to critical national defense technologies. Carbon nanotubes (CNTs) are a popular addition in nanocomposites because of their enhanced mechanical, thermal, and electrical properties. Concerns have been raised, though, regarding potential exposure and health risks from nanocomposites containing CNTs because of comparisons to other high aspect ratio fibers. Assessing the factors affecting CNT release from composites is therefore paramount for understanding potential exposure scenarios that may occur during product handling and manipulation. Standardized methods for detecting and quantifying released CNTs, however, have not yet been developed. We therefore evaluated experimental approaches deployed by various researchers, with an emphasis on characterizing free versus composite bound CNTs. From our analysis of published studies characterizing CNT releases from nanocomposites, we found that the qualitative and quantitative methods used across studies varied greatly, thus limiting the ability for objective comparison and evaluation of various release factors. Nonetheless, qualitative results indicated that factors such as composite type, CNT functionalization, and energy input during manipulation (i.e., grinding) may affect CNT release. Based on our findings, we offer several recommendations for future product testing and assessment of potential exposure and health risks associated with CNT nanocomposites.

충청북도 제천시 폐석면광산 주변 토양에서 검출되는 각섬석의 크기 분포

본 연구는 석면형태와 비석면형태의 구분을 위하여 충청북도 제천시에 소재한 한 폐석면광산 지역의 토양 중 트레모라이트와 악티노라이트 섬유의 크기 특성을 파악하였다. 폐석면광산 주변지역의 토양과 트레모라이트 석면 암석을 채취하고, 투과전자현미경으로 길이 <TEX>$5{\mu}m$</TEX> 이상이며 길이대너비 비율이 3:1 이상인 섬유의 크기를 측정하여 알려진 석면형태와 비석면형태를 보이는 트레모라이트의 크기 분포와 비교하였다. 연구 결과 섬유의 너비는 기하평균으로 토양시료 <TEX>$1.2{\mu}m$</TEX>, 석면 암석 <TEX>$0.3-0.6{\mu}m$</TEX>, NIST 트레모라이트 <TEX>$1.3{\mu}m$</TEX>, HSL 트레모라이트 <TEX>$0.2{\mu}m$</TEX> 이었다. 길이대너비 비율은 기하평균으로 토양시료 7.3, 석면 암석 13.7-30.1, NIST 트레모라이트 7.2, HSL 트레모라이트 37.8 이었다. 토양시료는 알려진 석면형태의 트레모라이트 뿐만 아니라 비석면형태의 트레모라이트에 비해서도 가늘고 길이대너비 비율이 큰 섬유를 적게 함유하였다. 따라서 연구 대상 토양시료 중의 트레모라이트-악티노라이트는 전형적 석면형태로 분류할 수 없으며, 대부분은 광산 및 채석장으로부터 바람에 의해 비산된 석면으로 인한 오염의 결과가 아닌 것으로 추정된다. 토양 중 석면의 관리를 위해서 석면 오염 여부를 조사 시에는 감섬석의 크기 분포가 함께 고려되어야 한다. This study is for discrimination between asbestiform and non-asbestiform based on size characteristics of tremolite-actinolite fibers in soils from a closed asbestos mine, Jecheon, Chungcheongbuk-do, Korea. Soils and tremolite asbestos rocks were collected from a closed asbestos mine area. The dimensions of fibers with minimum <TEX>$5{\mu}m$</TEX> in length and 3:1 in aspect ratio were measured using transmission electron microscopy (TEM) and compared to the known tremolite populations ranging from asbestiform to non-asbestiform. The geometric means of width of soils, asbestos rocks and National Institute for Standard and Technology (NIST) and Health and Safety Laboratory (HSL) reference samples were <TEX>$1.2{\mu}m$</TEX>, <TEX>$0.3-0.6{\mu}m$</TEX>, <TEX>$1.3{\mu}m$</TEX> and <TEX>$0.2{\mu}m$</TEX>, respectively. The geometric means of aspect ratio of soils, asbestos rocks and NIST and HSL reference samples were 7.3, 13.7-30.1, 7.2 and 37.8, respectively. The population of tremolite-actinolite fibers from soils compared to known asbestiform and non-asbestiform tremolite was lack of thin and high aspect ratio fibers. Upper results suggest that tremolite-actinolite fibers in soils cannot be classified into a commercial grade asbestos. The tremolite-actinolite fibers do not mainly appear to be the result of contamination from distance asbestos sources by wind. For the management and control of asbestos in soils, size distributions of amphiboles should be incorporated into asbestos survey results of soils.

In-plane deformation of shape memory polymer sheets programmed using only scissors

This paper describes an unconventional, yet simple method to program sheets of shape memory polymer into a variety of two dimensional (2D) structures. The final shape is “encoded” by physically cutting an initial design out of a pre-strained film. The orientation of the initial cut-out relative to the direction of strain and the subsequent relaxation of strain via heating defines the final shape. The appeal of the approach described here is that an easy, low-cost cutting method can achieve a similar shape memory effect attained by more complex processing techniques. Unlike conventional methods, where the final shape of a shape memory polymer must be defined a priori, the direction of cutting of the polymer defines its final shape without any complex pre-programmed strain profiles. A geometric model relating the resolved 2D polymer shape to the initial shape and strain orientation reveals linear correlation between the model-predicted and experimentally-observed shapes. In addition to demonstrating the principle with simple rectangular shapes, we suggest geometries related to encryption and high aspect ratio fibers.

A comprehensive validation of analytical homogenization models: The case of ellipsoidal particles reinforced composites

This paper presents a rigorous and exhaustive evaluation of the analytical homogenization models accuracy for the case of randomly distributed and oriented ellipsoidal fibers reinforced composites. Artificial random microstructures were generated using a molecular dynamics (MD) algorithm. Numerical effective properties were computed using a Fast Fourier Transforms (FFT) based technique. The numerical predictions were compared to those of the analytical models for a wide range of phases mechanical properties, fibers volume fractions and aspect ratios. The validation campaign involved a rigorous Representative Volume Element (RVE) determination process and approximately, 66,000 simulations were performed. The results show that the analytical models accuracy is more sensitive to the mechanical properties contrasts than to the fibers volume fraction and aspect ratio. Among all the studied models, Lielens’ model remains the most accurate, especially for high contrasts and volume fractions. For high aspect ratio fibers, Lielens’s model and Beveniste’s interpretation of the Mori–Tanaka model provide similar estimates, especially when predicting the effective shear modulus. In this case, the latter could be an alternative to Lielens’ model, especially for composites where the fibers are not completely stiffer than the matrix. All conclusions of this study apply to both prolate and oblate ellipsoidal fibers.

Understanding the Effects of High Aspect Ratio Fibers on the Mechanical Reinforcement of Soybean Based Polyurethane Foam

Understanding the Effects of High Aspect Ratio Fibers on the Mechanical Reinforcement of Soybean Based Polyurethane Foam

하이브리드 섬유로 보강된 콘크리트 포장의 역학적 특성 실험연구

Cement concrete pavement offers long-term service life and excellent applicability for heavy traffic. It is easier to purchase and more durable and economical than the asphalt pavement. However, it is difficult to repair and rehabilitate compared to the asphalt pavement when it comes to the maintenance problem. Since the crack is the main reason of the damage of concrete pavement, it is necessary to control the early and long-term crack in the concrete pavement. In this experimental study, the basic performance tests have been carried out to investigate the effect of hybrid fibers which were composed of micro fibers with small diameter and high aspect ratio and macro fibers with large diameter and low aspect ratio on the concrete pavement, in which lower water ratio and larger aggregates were used compared to the general concrete mixture. The test results showed that the flexural strength and toughness of concrete pavement mixture have been increased with the use of hybrid fibers in the concrete pavement mixture, even though they were less effective compared to the normal concrete mixture. It was found that the hybrid fibers were effective to control the early shrinkage of the concrete pavement which is one of the main reasons of the damage in the concrete pavement.