Name: disentangling high strength copolymer aramid fibers to enable the determination of their mechanical properties
Uploaded: 2018-09-01T14:00:00
Description: Watch this Scientific Journal Video about Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties at JoVE.com

The authors would like to acknowledge Dr. Will Osborn for helpful discussions and assistance with preparation of the cardstock template.

1. Dissolution of Coating on Copolymer Fibers to Aid in Fiber Separation
<ol>
	<li>Wearing appropriately selected chemically resistant gloves to prevent contamination of the fiber, cut 160 mm to 170 mm from each yarn bundle extracted using ceramic scissors or a fresh steel razor blade. Reserve the remainder of the yarn if needed for further analysis in a labeled container.</li>
	<li>Knot or clamp the ends of the yarn to keep the yarn from tangling when immersed in the solvent. 
	NOTE: For this study, solvents of w...

<ol>
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The method described herein provides an alternate solvent-based protocol for removing coatings from aramid copolymer fibers without using water. Two previous studies3,4 showed the evidence of hydrolysis in the fibers of this chemical composition, with exposure to water vapor or liquid water. Avoiding hydrolysis during the sample preparation is critical for the next phase of experiments where these sets of fibers will be examined for their susceptibility to ageing...

Currently, significant focus in the field of personal protection is on reducing the mass of the body armor needed for personal protection for law enforcement and military applications1. Traditional armor designs have relied on materials like poly(p-phenylene terephthalamide) (PPTA), also known as aramid, and polyethylene to provide protection against ballistic threats2. However, there is an interest in exploring different high strength fiber materials for their potential to reduce the weight of armor required to stop a specific ballistic threat. This has led to the exploration of alternative materials such as aramid copolymer fibers. These fibers are made by the reaction of [5-amino-2-(p-aminophenyl)benzimidazole] (amidobenzimidazole, ABI) and p-phenylenediamine (p-PDA) with terephthaloyl chloride to form poly(p-phenylene-benzimidazole-terephthalamide-co-p-phenylene terephthalamide). In this study, we examine three different fibers, all of which are commercially produced materials obtained from an industry contact. One is a homopolymer fiber that is made by reacting ABI with p-phenylenediamine to form poly 5-amino-2-(p-aminophenyl)benzimidazole, or PBIA. The other two copolymer fibers examined in this study are expected to be random copolymers with different ratios of PBIA and PPTA linkages3. The relative ratios of these linkages could not be determined experimentally using solid-state nuclear magnetic resonance. These fibers are designated as PBIA-co-PPTA1, PBIA-co-PPTA3 to extend the designations used in a previous publication4. PBIA-co-PPTA3 was not previously studied, but has a similar structure. These fiber systems have also been the focus of several recently granted patents5,6,7.
Superior ballistic resistance of body armor is predicated on the mechanical properties of the materials that comprise it, such as ultimate tensile strength and strain to failure8,9,10. Significant efforts11,12,13 have been focused on examining the long-term stability of polymeric fibers used in body armor by investigating detrimental changes in these mechanical properties after exposure to environmental conditions. The effect of environmental conditions on aramid copolymer fibers has not been the subject of a lot of research3,4. One challenge to studying these materials is the difficulty in disentangling yarns for testing. Prior work by McDonough4 investigated a technique by which water was used to disentangle yarns prior to performing single fiber tensile testing. However, there was no complete understanding on whether the mechanical strength of the fibers was altered by this water exposure. An alternative to disentangling the fibers is to test the mechanical strength of the yarn bundle, however, this requires a large amount of material, and is considered to average the strength of the fibers in the yarn bundle, providing less specific information. The goal of this project is to examine the effect of elevated humidity and temperature on the mechanical properties of aramid copolymer fibers. Thus, it is essential to find an alternative solvent for coating removal and fiber disentanglement that will enable us to distinguish hydrolysis in the fibers due to the environmental exposure from that induced by sample preparation. The preparation of single fibers for testing is further complicated by their small size. In this work, we investigate several common solvents (water, methanol, and acetone) and select acetone as the best choice for the preparation of single fibers for testing. All fibers were rinsed with methanol before further testing. Fourier transform infrared (FTIR) spectroscopy is performed to determine if the coating dissolution and disentanglement step caused any chemical degradation in the material. The detailed video protocol showing the sample preparation steps of disentanglement, chemical analysis, and mechanical testing of copolymer aramid fibers is intended to assist other researchers in developing methodologies for performing similar studies of single fibers in their laboratories.

<table border="0" cellpadding="0" cellspacing="0" width="757">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Stereo microscope&#160;</td>
			<td style="width:83px;">National</td>
			<td style="width:119px;">DC4-456H</td>
			<td style="width:339px;">Digital microscope</td>
		</tr>
		<tr height="66">
			<td height="66" style="height:66px;width:216px;">RSA-G2 Solids Analyzer&#160;</td>
			<td style="width:83px;">TA Instruments</td>
			<td style="width:119px;"></td>
			<td style="width:339px;">Dynamic mechanical thermal analyzer used in transient tensile mode with Film Tension Clamp Accesory&#160;</td>
		</tr>
		<tr height="47">
			<td height="47" style="height:47px;width:216px;">Vertex 80</td>
			<td style="width:83px;">Bruker Optics</td>
			<td></td>
			<td style="width:339px;">Fourier Transform Infrared spectrometer used to analyze results of washing protocol, equipped with mercury cadmium telluride (MCT) detector.</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:216px;">Durascope</td>
			<td style="width:83px;">Smiths Detection</td>
			<td></td>
			<td style="width:339px;">Attenuated total reflectance accessory used to perform FTIR</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Torque hex-end wrench</td>
			<td style="width:83px;">M.H.H. Engineering</td>
			<td style="width:119px;">Quickset Minor</td>
			<td>Torque wrench</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Methanol</td>
			<td style="width:83px;">J.T. Baker</td>
			<td style="width:119px;">9093-02</td>
			<td>methanol solvent</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Acetone</td>
			<td style="width:83px;">Fisher</td>
			<td style="width:119px;">A185-4</td>
			<td>acetone solvent</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Cyanoacrylate</td>
			<td style="width:83px;">Loctite</td>
			<td style="width:119px;"></td>
			<td>Super glue&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">FEI Helios 660 Dual Beam FIB/SEM</td>
			<td style="width:83px;">FEI Helios</td>
			<td style="width:119px;"></td>
			<td>Scanning electron microscope</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Denton Desktop sputter coater&#160;</td>
			<td style="width:83px;"></td>
			<td style="width:119px;"></td>
			<td>sputter coater</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">25 mm O.D. stainless steel washers with a 6.25 mm hole</td>
			<td style="width:83px;"></td>
			<td style="width:119px;"></td>
			<td style="width:339px;">25 mm O.D. stainless steel washers with a 6.25 mm hole</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Silver behenate&#160;</td>
			<td style="width:83px;"></td>
			<td style="width:119px;"></td>
			<td>Wide angle X-ray scattering (WAXS) standard</td>
		</tr>
		<tr height="126">
			<td height="126" style="height:126px;width:216px;">Xenocs Xeuss SAXS/WAXS small angle X-ray scattering system</td>
			<td style="width:83px;">Xenocs Xeuss</td>
			<td style="width:119px;"></td>
			<td style="width:339px;">SAXS/WAXS small angle X-ray scattering system equipped with an X-ray video-rate imager for SAXS analysis with a minimum Q = 0.0045 &#197;-1, detector separate X-ray video-rate imager for WAXS analysis (up to about 45&#176; 2&#952;) sample holder chamber.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fit 2D software</td>
			<td style="width:83px;"></td>
			<td style="width:119px;"></td>
			<td>Software to analyze WAXS data</td>
		</tr>
	</tbody>
</table>

disentangling high strength copolymer aramid fibers to enable the determination of their mechanical properties

Traditionally, soft body armor has been made from poly(p-phenylene terephthalamide) (PPTA) and ultra-high molecular weight polyethylene. However, to diversify the fiber choices in the United States body armor market, copolymer fibers based on the combination of 5-amino-2-(p-aminophenyl) benzimidazole (PBIA) and the more conventional PPTA were introduced. Little is known regarding the long-term stability of these fibers, but as condensation polymers, they are expected to have potential sensitivity to moisture and humidity. Therefore, characterizing the strength of the materials and understanding their vulnerability to environmental conditions is important for evaluating their use lifetime in safety applications. Ballistic resistance and other critical structural properties of these fibers are predicated on their strength. To accurately determine the strength of the individual fibers, it is necessary to disentangle them from the yarn without introducing any damage. Three aramid-based copolymer fibers were selected for the study. The fibers were washed with acetone followed by methanol to remove an organic coating that held the individual fibers in each yarn bundle together. This coating makes it difficult to separate single fibers from the yarn bundle for mechanical testing without damaging the fibers and affecting their strength. After washing, fourier transform infrared (FTIR) spectroscopy was performed on both washed and unwashed samples and the results were compared. This experiment has shown that there are no significant variations in the spectra of poly(p-phenylene-benzimidazole-terephthalamide-co-p-phenylene terephthalamide) (PBIA-co-PPTA1) and PBIA-co-PPTA3 after washing, and only a small variation in intensity for PBIA. This indicates that the acetone and methanol rinses are not adversely affecting the fibers and causing chemical degradation. Additionally, single fiber tensile testing was performed on the washed fibers to characterize their initial tensile strength and strain to failure, and compare those to other reported values. Iterative procedural development was necessary to find a successful method for performing tensile testing on these fibers.

The copolymer aramid fibers studied here are difficult to separate from yarn bundles into individual fibers for testing. The fibers are entangled and coated with processing chemicals that make them very difficult to separate without damaging the fibers. Figure 3 shows the structural morphology of fibers within a yarn. Even as part of a larger bundle, the fiber surfaces show extensive roughness and tears that are likely caused by strong adhesion to adjacent fi...

Watch this Scientific Journal Video about Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties at JoVE.com

Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties

The primary goal of the study is to develop a protocol to prepare consistent specimens for accurate mechanical testing of high strength copolymer aramid fibers, by removing a coating and disentangling the individual fiber strands without introducing significant chemical or physical degradation.

Traditionally, soft body armor has been made from poly(p-phenylene terephthalamide) (PPTA) and ultra-high molecular weight polyethylene. However, to ...

This method can help answer key questions in the single-fiber testing field about methodologies for dissolving coatings and disentangling challenging fiber samples. The main advantage of this technique is that the water method of coating dissolution has been replaced with a solvent-based method that is less damaging to the fibers. Generally, individuals new to this method will struggle because of the difficulty in manipulating single fibers.Wearing the appropriate chemically resistant gloves for preventing contamination of the fiber, use a fresh steel razor blade to cut 160 to 170 millimeters from each extracted yarn bundle, reserving the remainder of the yarn in a labeled container for further analysis as appropriate. Secure the ends to keep the yarn from tangling, and immerse the fibers in two to three milliliters of solvent in a labeled Petri dish. Place the lid on the dish and allow the yarns to soak for 30 minutes.After the third immersion, submerge the samples in two to three milliliters of methanol for at least 30 minutes. Then allow the yarn to dry for at least 24 hours. The next day, place a 30 by 30 centimeter or larger transparent plastic board onto a dark background of the same proportions.And use a razor blade to cut five to 10 millimeter pieces of low-tack masking tape on a glass surface. Tape both ends of a 20-millimeter gauge rectangular paper template to the plastic board so that the template lies completely flat. And wearing nitrile gloves to prevent contamination, cut approximately 70 to 80 millimeters of the solvent-rinsed yarn.Place the cut yarn on a clean surface, and using a stereo microscope, use tweezers to carefully remove a single fiber from the yarn. Place a single fiber on top of the paper template, making sure that the fiber is aligned with the markers on the template. And tape both ends of the fiber to the board.Place a dark background under the plastic board to improve the visibility of the fiber. The fiber should lay straight and slightly taut across the template. When all of the samples have been mounted on a separate paper template for each type of fiber, add one small drop of cyanoacrylate adhesive to each end of the fibers, leaving one centimeter free of glue at the ends of the paper templates for gripping during the tensile testing.After allowing the glue to dry for at least 24 hours, install the tensile grips and calibrate the tensile testing instrument to provide a 30-millimeter gap. Next, use gloves, a small spatula, and tweezers to feed a template through both of the grips, using the marks on the template to assist with the placement. Gently align and close the top grip face while keeping the fiber supported so it does not slide down, and use a torque wrench to tighten the screws on the upper and lower grips until the screws are just tight.Then, use a torque wrench to tighten the screws securely in a cross-pattern, to balance the load of 30 centinewton meters on the fiber. After trimming both sides of the paper, program the tensile test instrument to deliver a constant 0.0125 millimeters per second extension rate, monitoring the display, and stopping the test when the fiber has broken. At the end of the test, loosen the grip faces to remove the fiber and note the break location.Then, preserve the broken fiber in a labeled container for further analysis. Fourier Transform Infrared Spectroscopy reveals some intensity changes after washing, but no major changes in spectra indicative of chemical degradation. Nearly all of the samples affixed to the paper templates with the epoxy adhesive exhibit an uncharacteristic slipping behavior and jagged stress strain curves.While fibers fixed with cyanoacrylate adhesive are predominantly devoid of sample slippage. In this representative experiment, 35 samples from each type of fiber were tested, between 15 to 26 of which, per type, were successful. Scanning electron microscopy imaging of the failed fibers indicated that all of the fibers underwent brittle fracture that resulted in fibrillation.However, the diffractograms of the meridonial scattering also revealed the present of two major brag peaks at two theta angles of about 26 and 28 degrees, indicating a very low degree of crystallinity overall for each of the fiber types along the chain axis. While attempting this procedure, it's important to remember to handle the fibers very carefully to avoid damaging them while they're being disentangled. After its development, this technique paved the way for researchers in the field of single-fiber tensile testing to explore artificial aging of aramid copolymer fibers, which is the next step in our research study.Don't forget that working with solvents such as acetone and methanol can be extremely hazardous and that precautions such as wearing gloves and working in a hood should always be taken while performing this procedure.

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