Research

4429 KiB

Open AccessArticle

Scaling up the Fabrication of Mechanically-Robust Carbon Nanofiber Foams

by William Curtin, Pedro J. Arias-Monje, Charliean Dominguez, Jonathan Phillips and Claudia C. Luhrs

Fibers 2016, 4(1), 9; https://doi.org/10.3390/fib4010009 - 15 Feb 2016

Viewed by 6430

Abstract

This work aimed to identify and address the main challenges associated with fabricating large samples of carbon foams composed of interwoven networks of carbon nanofibers. Solutions to two difficulties related with the process of fabricating carbon foams, maximum foam size and catalyst cost, [...] Read more.

This work aimed to identify and address the main challenges associated with fabricating large samples of carbon foams composed of interwoven networks of carbon nanofibers. Solutions to two difficulties related with the process of fabricating carbon foams, maximum foam size and catalyst cost, were developed. First, a simple physical method was invented to scale-up the constrained formation of fibrous nanostructures process (CoFFiN) to fabricate relatively large foams. Specifically, a gas deflector system capable of maintaining conditions supportive of carbon nanofiber foam growth throughout a relatively large mold was developed. ANSYS CFX models were used to simulate the gas flow paths with and without deflectors; the data generated proved to be a very useful tool for the deflector design. Second, a simple method for selectively leaching the Pd catalyst material trapped in the foam during growth was successfully tested. Multiple techniques, including scanning electron microscopy, surface area measurements, and mechanical testing, were employed to characterize the foams generated in this study. All results confirmed that the larger foam samples preserve the basic characteristics: their interwoven nanofiber microstructure forms a low-density tridimensional solid with viscoelastic behavior. Fiber growth mechanisms are also discussed. Larger samples of mechanically-robust carbon nanofiber foams will enable the use of these materials as strain sensors, shock absorbers, selective absorbents for environmental remediation and electrodes for energy storage devices, among other applications. Full article

(This article belongs to the Special Issue Carbon Fibers)

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1514 KiB

Open AccessArticle

Carbon Fiber Biocompatibility for Implants

by Richard Petersen

Fibers 2016, 4(1), 1; https://doi.org/10.3390/fib4010001 - 08 Jan 2016

Cited by 53 | Viewed by 11254

Abstract

Carbon fibers have multiple potential advantages in developing high-strength biomaterials with a density close to bone for better stress transfer and electrical properties that enhance tissue formation. As a breakthrough example in biomaterials, a 1.5 mm diameter bisphenol-epoxy/carbon-fiber-reinforced composite rod was compared for [...] Read more.

Carbon fibers have multiple potential advantages in developing high-strength biomaterials with a density close to bone for better stress transfer and electrical properties that enhance tissue formation. As a breakthrough example in biomaterials, a 1.5 mm diameter bisphenol-epoxy/carbon-fiber-reinforced composite rod was compared for two weeks in a rat tibia model with a similar 1.5 mm diameter titanium-6-4 alloy screw manufactured to retain bone implants. Results showed that carbon-fiber-reinforced composite stimulated osseointegration inside the tibia bone marrow measured as percent bone area (PBA) to a great extent when compared to the titanium-6-4 alloy at statistically significant levels. PBA increased significantly with the carbon-fiber composite over the titanium-6-4 alloy for distances from the implant surfaces of 0.1 mm at 77.7% vs. 19.3% (p < 10⁻⁸) and 0.8 mm at 41.6% vs. 19.5% (p < 10⁻⁴), respectively. The review focuses on carbon fiber properties that increased PBA for enhanced implant osseointegration. Carbon fibers acting as polymer coated electrically conducting micro-biocircuits appear to provide a biocompatible semi-antioxidant property to remove damaging electron free radicals from the surrounding implant surface. Further, carbon fibers by removing excess electrons produced from the cellular mitochondrial electron transport chain during periods of hypoxia perhaps stimulate bone cell recruitment by free-radical chemotactic influences. In addition, well-studied bioorganic cell actin carbon fiber growth would appear to interface in close contact with the carbon-fiber-reinforced composite implant. Resulting subsequent actin carbon fiber/implant carbon fiber contacts then could help in discharging the electron biological overloads through electrochemical gradients to lower negative charges and lower concentration. Full article

(This article belongs to the Special Issue Carbon Fibers)

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1062 KiB

Open AccessArticle

Properties of PAN Fibers Solution Spun into a Chilled Coagulation Bath at High Solvent Compositions

by E. Ashley Morris, Matthew C. Weisenberger and Gregory Wilson Rice

Fibers 2015, 3(4), 560-574; https://doi.org/10.3390/fib3040560 - 15 Dec 2015

Cited by 32 | Viewed by 9579

Abstract

In this work, multifilament, continuous polyacrylonitrile (PAN) fiber tow was solution spun mimicking industrial processing at the small pilot scale (0.5 k tow), while carefully altering the composition of the coagulation bath, in order to determine the effect on the resulting fiber shape, [...] Read more.

In this work, multifilament, continuous polyacrylonitrile (PAN) fiber tow was solution spun mimicking industrial processing at the small pilot scale (0.5 k tow), while carefully altering the composition of the coagulation bath, in order to determine the effect on the resulting fiber shape, density, orientation, and tensile properties at varying points in the spinning process. Novel here are the abnormally high coagulation bath solvent compositions investigated, which surpass those often reported in the literature. In addition, the coagulation bath was maintained at a slightly chilled temperature, contrary to reported methods to produce round fibers. Further, by altering the composition of the bath in a step-wise fashion during a single spinning run, variations in all other process parameters were minimized. We found that with increasing solvent composition in the coagulation bath, the fibers not only became round in cross section, but also became smaller in diameter, which persisted down the spin line. With this decrease in diameter, all else equal, came an accompanying increase in apparent fiber density via a reduction in microvoid content. In addition, molecular orientation and tensile properties also increased. Therefore, it was found that inadequate understanding of the coagulation bath effects, and spinning at low coagulation bath solvent compositions, can hinder the ability of the fiber to reach optimum properties. Full article

(This article belongs to the Special Issue Carbon Fibers)

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967 KiB

Open AccessArticle

Using Mechanical Alloying to Create Bimetallic Catalysts for Vapor-Phase Carbon Nanofiber Synthesis

by Laura Guevara, Crystal Wanner, Roger Welsh and Mark A. Atwater

Fibers 2015, 3(4), 394-410; https://doi.org/10.3390/fib3040394 - 05 Oct 2015

Cited by 9 | Viewed by 7615

Abstract

Carbon nanofibers were generated over bimetallic catalysts in an atmospheric pressure chemical vapor deposition (APCVD) reactor. Catalyst compositions of Fe 30 at%, Cu and Ni 30 at% and Cu were mechanically alloyed using high-energy ball milling over durations of 4, 8, 12, 16, [...] Read more.

Carbon nanofibers were generated over bimetallic catalysts in an atmospheric pressure chemical vapor deposition (APCVD) reactor. Catalyst compositions of Fe 30 at%, Cu and Ni 30 at% and Cu were mechanically alloyed using high-energy ball milling over durations of 4, 8, 12, 16, and 20 h. The catalyst powders were then used to produce carbon nanofibers in ethylene and hydrogen (4:1) at temperatures of 500, 550, and 600 °C. The microstructures of the catalysts were characterized as a function of milling time as well as at deposition temperature. The corresponding carbon deposition rates were assessed and are correlated to the microstructural features of each catalyst. The milling process directly determines the performance of each catalyst toward carbon deposition, and both catalysts performed comparably to those made by traditional co-precipitation methods. Considerations in miscible and immiscible nanostructured alloy systems are discussed. Full article

(This article belongs to the Special Issue Carbon Fibers)

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339 KiB

Open AccessArticle

Polyethylene-Based Carbon Fibers by the Use of Sulphonation for Stabilization

by Gisa Wortberg, Andreas De Palmenaer, Markus Beckers, Gunnar Seide and Thomas Gries

Fibers 2015, 3(3), 373-379; https://doi.org/10.3390/fib3030373 - 23 Sep 2015

Cited by 28 | Viewed by 9309

Abstract

Polyethylene has great potential as an alternative material for carbon fiber production. Polyethylene can be processed in the economic melt spinning process. These precursors are prepared for the subsequent process step of carbonization by using chemical stabilization (sulphonation). The strategy is to adjust [...] Read more.

Polyethylene has great potential as an alternative material for carbon fiber production. Polyethylene can be processed in the economic melt spinning process. These precursors are prepared for the subsequent process step of carbonization by using chemical stabilization (sulphonation). The strategy is to adjust these precursor properties by the melt spinning process, thus resulting in a precursor, which can be stabilized sufficiently by sulphonation. The objective is to find the correlation between precursor properties and the results of the sulphonation. In this paper, the chemical stabilization is described and the results of the chemical stabilization are discussed. The novelty in this paper is that the results of the sulphonation are brought in correlation with the precursor properties. It can be shown that the filament diameter and the polymer structure (e.g., the crystallinity) of the precursor have an influence on the sulphonation process. Full article

(This article belongs to the Special Issue Carbon Fibers)

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627 KiB

Open AccessArticle

Carbon Fibers from UV-Assisted Stabilization of Lignin-Based Precursors

by Meng Zhang, Jing Jin and Amod A. Ogale

Fibers 2015, 3(2), 184-196; https://doi.org/10.3390/fib3020184 - 18 Jun 2015

Cited by 42 | Viewed by 8879

Abstract

Production of high strength carbon fibers from bio-derived precursors is of topical interest. Recently, we reported on dry-spinning of a partially acetylated softwood kraft lignin to produce carbon fibers with superior properties, but the thermo-oxidative stabilization step required a long time due to [...] Read more.

Production of high strength carbon fibers from bio-derived precursors is of topical interest. Recently, we reported on dry-spinning of a partially acetylated softwood kraft lignin to produce carbon fibers with superior properties, but the thermo-oxidative stabilization step required a long time due to a slow heating rate needed to prevent the fibers from being heated too rapidly and sticking to each other. Here we report a rapid strategy of dual UV-thermoxidative stabilization (crosslinking) of dry-spun lignin fibers that significantly reduces the stabilization time. The fibers undergo reaction close to the surface such that they can be subsequently thermally stabilized at a rapid heating rate without fibers fusing together, which reduces the total stabilization time significantly from 40 to 4 h. Consequently, the glass transition temperature of UV irradiated fibers was about 15 °C higher than that of fibers without UV treatment. Stabilized fibers were successfully carbonized at 1000 °C and resulting carbon fibers displayed a tensile strength of 900 ± 100 MPa, which is amongst the highest reported for carbon fibers derived from softwood lignin-based precursors. These results establish that UV irradiation is a rapid step that can effectively shorten the total stabilization time for production of lignin-derived carbon fibers. Full article

(This article belongs to the Special Issue Carbon Fibers)

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965 KiB

Open AccessArticle

Improvement by Nanofibers of Load Transfer in Carbon Fiber Reinforced Composites

by Alexandre Vivet, Willy Leclerc, Bessem Ben Doudou, Jun Chen and Christophe Poilâne

Fibers 2015, 3(2), 134-150; https://doi.org/10.3390/fib3020134 - 29 Apr 2015

Cited by 4 | Viewed by 7491

Abstract

This paper focuses on the load transfer improvement caused by nanofibers (NF) in carbon fiber reinforced composites. Load transfer is defined as the ability to transfer the mechanical loading between two adjacent fibers through the surrounding matrix. NF action is explored with a [...] Read more.

This paper focuses on the load transfer improvement caused by nanofibers (NF) in carbon fiber reinforced composites. Load transfer is defined as the ability to transfer the mechanical loading between two adjacent fibers through the surrounding matrix. NF action is explored with a finite element model representing two carbon fibers separated by a layer of a NF reinforced matrix. It appears that the role of the NF network is to strengthen the matrix by increasing matrix shear rigidity, and thus to improve the load transfer between the carbon fibers. NF network morphology, defined by NF orientation, NF spatial distribution or NF diameter, governs the NF network efficiency. Full article

(This article belongs to the Special Issue Carbon Fibers)

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2359 KiB

Open AccessArticle

Improving Fatigue Performance of GFRP Composite Using Carbon Nanotubes

by Moneeb Genedy, Sherif Daghash, Eslam Soliman and Mahmoud M. Reda Taha

Fibers 2015, 3(1), 13-29; https://doi.org/10.3390/fib3010013 - 15 Jan 2015

Cited by 34 | Viewed by 10079

Abstract

Glass fiber reinforced polymers (GFRP) have become a preferable material for reinforcing or strengthening reinforced concrete structures due to their corrosion resistance, high strength to weight ratio, and relatively low cost compared with carbon fiber reinforced polymers (CFRP). However, the limited fatigue life [...] Read more.

Glass fiber reinforced polymers (GFRP) have become a preferable material for reinforcing or strengthening reinforced concrete structures due to their corrosion resistance, high strength to weight ratio, and relatively low cost compared with carbon fiber reinforced polymers (CFRP). However, the limited fatigue life of GFRP hinders their use in infrastructure applications. For instance, the low fatigue life of GFRP caused design codes to impose stringent stress limits on GFRP that rendered their use non-economic under significant cyclic loads in bridges. In this paper, we demonstrate that the fatigue life of GFRP can be significantly improved by an order of magnitude by incorporating Multi-Wall Carbon Nanotubes (MWCNTs) during GFRP fabrication. GFRP coupons were fabricated and tested under static tension and cyclic tension with mean fatigue stress equal to 40% of the GFRP tensile strength. Microstructural investigations using scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR) spectroscopy were used for further investigation of the effect of MWCNTs on the GFRP composite. The experimental results show the 0.5 wt% and the 1.0 wt% MWCNTs were able to improve the fatigue life of GFRP by 1143% and 986%, respectively, compared with neat GFRP. Full article

(This article belongs to the Special Issue Carbon Fibers)

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