Name: disentangling high strength copolymer aramid fibers to enable the determination of their mechanical properties
Uploaded: 2018-09-01T14:00:00.000+00:00
Duration: 6 min 2 s
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 wide ranging polarity (from the polarity series) were initially explored. Based on qualitative results, a more in-depth examination was conducted using acetone, water, and methanol. Finally, acetone was selected as the best solvent for fiber separation based on the ease of detangling and the scanning electron microscopy (SEM) results (described later).</li>
	<li>Immerse the fiber in 2 mL to 3 mL of the solvent in a labeled Petri dish and cover with the Petri dish lid.</li>
	<li>Allow the yarns to soak in acetone for 30 min, then discard the solvent.</li>
	<li>Repeat steps 1.3 to 1.4 at least two additional times and then allow the solvent to evaporate.</li>
	<li>To remove any acetone residue and to aid in drying, immerse the sample in 2 mL to 3 mL of methanol.</li>
	<li>Allow the yarns to soak in methanol at least 30 min.</li>
	<li>Remove the yarn from the solvent and allow to dry for at least 24 h.</li>
</ol>
2. Analysis of Coating Dissolution Step by Scanning Electron Microscopy
<ol>
	<li>Separate the individual fibers with tweezers, which are previously washed using different solvents from the yarn bundle, for analysis under a stereo microscope if necessary.</li>
	<li>Mount the fibers on a stainless-steel stub (1 cm diameter) by adhering them with tweezers onto double-sided carbon tape.</li>
	<li>Coat the fibers with a conductive material such as Au/Pd to mitigate the surface charging effects under the SEM.</li>
	<li>Load the fiber samples into a scanning electron microscope and image them at 2 kV accelerating voltage and 50 pA &#8211; 100 pA electron current. Apply charge neutralization settings to counter charging effects where necessary.</li>
</ol>
3. Analysis of Coating Dissolution Step by Fourier Transform Infrared Spectroscopy
<ol>
	<li>Cut approximately 30 mm to 40 mm of the washed yarn bundle.</li>
	<li>Obtain an adhesive IR sample card and remove the protective backing.</li>
	<li>While wearing gloves to protect the sample from contamination, slightly twist the fiber bundle to coalesce the sample for analysis and place the sample over the window in the card.</li>
	<li>Prepare the FTIR for analysis according to the manufacturer&#39;s specifications. Turn on the purge gas, fill the detector with liquid nitrogen, and install the ATR accessory using the magnetic alignment plate in the sample compartment.</li>
	<li>Program the parameters for number of scans and instrument resolution in the advanced measurement tab of the instrument software, in this case, 128 scans are averaged at a resolution of 4 cm-1.</li>
	<li>Clean the window of the ATR accessory with a low lint wipe and methanol.</li>
	<li>Collect a background by pressing the collect background button in the basic measurement window of the software with the parameters selected in step 3.5.</li>
	<li>Align the fiber sample over the window in the ATR accessory, using the microscope and video monitor to help position the fiber.</li>
	<li>Collect a sample spectrum by pressing the collect sample button in the basic measurement window of the software using the parameters selected in step 3.5.</li>
	<li>Repeat steps 3.6-3.9, collecting at least 3 spectra per sample until all samples have been analyzed.</li>
</ol>
4. Analysis of Fibers by Wide Angle X-Ray Scattering
<ol>
	<li>While wearing nitrile gloves, cut approximately 25 mm of the yarn from the yarn spool using a razor blade.</li>
	<li>Center each bundle of the yarn over the 6.25 mm inner hole of a 25 mm stainless steel washer.</li>
	<li>Tape the yarn bundle to the washer to hold it in place using cellophane tape.</li>
	<li>Repeat steps 4.1 to 4.3 for the other two types of yarn.</li>
	<li>Tape the washers containing the yarn bundles to a stainless-steel sample holder block (which contains metallic rods for positioning) as shown in Figure 1. The fibers should be in the vertical configuration for analysis.</li>
	<li>Mount a silver behenate control sample to the sample holder block in the same position as the washers.</li>
	<li>Open the door to the instrument and mount the sample holder block to the analysis stage using the magnetic alignment system.</li>
	<li>Close the door to the sample holder chamber and activate the vacuum pump to evacuate the sample analysis chamber. Monitor the vacuum gauge mounted next to the instrument until the vacuum reaches approximately 1600 Pa.</li>
	<li>Open the instrument software, activate the beam, and perform a horizontal scan to determine the x-location of each sample on the sample holder.</li>
	<li>After identifying x-location of each sample, perform a vertical scan to optimize the y-location to obtain the maximum signal intensity for each sample.</li>
	<li>Once the x and y-locations are determined, begin the measurement by analyzing the silver behenate control sample to determine the distance between the sample and each detector.</li>
	<li>Analyze the first fiber sample using a 10 min exposure time.</li>
	<li>Repeat step 4.13 two additional times for a total scan time of 30 min. 
	NOTE: This protocol is used instead of one long 30 min scan case because there are issues with the sample exposure to minimize wasted instrument time.</li>
	<li>Average the 3 scans to obtain the final result using the average function in Fit 2D software.</li>
	<li>Repeat steps 4.13-4.15 for each additional sample.</li>
</ol>
5. Yarn Disentanglement and Preparation for Tensile Testing
<ol>
	<li>Obtain a 30 cm x 30 cm or larger transparent plastic board (polycarbonate sheets are used in these experiments) that can be placed on a dark background, or a dark plastic board of the same dimensions.</li>
	<li>Cut pieces of low tack masking tape (approximately 10 mm 5 mm) and have them available for the following steps. Perform this step on a glass surface and cut the tape with a razor blade.</li>
	<li>Tape both ends of a 20 mm gauge rectangular paper template to the plastic board so that it lies completely flat. 
	NOTE: 20 mm is selected as the optimal gauge length for these tests based on previous work and the available jaw separation of the instrument.</li>
	<li>Wearing nitrile gloves to prevent contamination, cut approximately 70 mm to 80 mm of rinsed yarn and place it on a glass slide or other clean surface (Figure 2a-b).</li>
	<li>Using a stereo microscope to assist disentanglement, carefully remove a single fiber from the yarn using tweezers. Take care to avoid snagging or damaging the fiber during this process. Discard any fibers that are damaged (Figure 2c).</li>
	<li>Place a single fiber on top of the paper template, making sure that the fiber is aligned with the markers on the template (Figure 2d-f).</li>
	<li>Tape both ends of the fiber to the board. In order to improve the visibility of the fiber, put a dark background underneath the transparent plastic board or use a black plastic board. The fiber should lay straight and slightly taught across the template (Figure 2f).</li>
	<li>Repeat steps 5.3 to 5.7 until approximately 35 to 45 fibers are mounted on separate paper templates for each type of fiber. In this case, there are three types of fibers: PBIA-co-PPTA1, PBIA, and PBIA-co-PPTA3.</li>
	<li>Once all fibers are taped to the plastic board, add one small drop of cyanoacrylate adhesive to each end of the fiber aligned to the paper template. Leave 1 cm free of glue at the ends of the paper templates for gripping during tensile testing. 
	NOTE: Cyanoacrylate was found to be the best adhesive for this material, an unsuccessful attempt with a 24 h cure epoxy is shown in the Representative Results.</li>
	<li>Allow the adhesive to cure for at least 24 h before testing.</li>
</ol>
6. Single Fiber Tensile Testing
<ol>
	<li>Determine the gage length and the rate of extension that provides the most consistent results for the specimen of interest. These parameters may be dictated by the amount of available sample and by the limitations of the experimental setup.</li>
	<li>Prepare the instrument for testing by installing tensile grips and calibrating the gap.</li>
	<li>Program the instrument to move the grips to provide a gap of 30 mm, which is the gage length selected based on the size of the paper template and the 10 mm space left at each end for the jaw.</li>
	<li>Loosen the grip faces to create a gap for loading the paper template that contains the single fiber.</li>
	<li>Move one of the samples prepared in step 5 to the instrument. Using gloved hands, a small spatula, and tweezers, feed the template through both grips, using the marks on the template to assist the placement. Make sure that the glue is outside of the grip area.</li>
	<li>Gently align and close the top grip face, while still supporting the fiber so that it does not slide down.</li>
	<li>Tighten the top and bottom screws with a torque wrench until the screws are just tight.</li>
	<li>Repeat step 6.7 for the bottom screws.</li>
	<li>Tighten the screws on the upper and lower grips using a torque wrench. Take care to tighten the screws in a cross pattern to balance the load on the fiber. 
	NOTE: The appropriate torque to use may vary and must be experimentally determined. 30 cN&#183;m was used in these experiments.</li>
	<li>Trim both sides of the paper template with scissors.</li>
	<li>Program the instrument to perform the tensile test at a constant rate of extension of 0.0125 mm/s, monitor the display and stop the test when the fiber has broken.</li>
	<li>At the end of the test, remove the fiber from the grips by loosening the grip faces. Observe the break location and preserve the broken fiber in a labeled container for further analysis. 
	NOTE: Fibers that break at the grip face are discarded from analysis as &#34;jaw breaks&#34; as described in ASTM D3822.</li>
	<li>Return the gap to 30 mm and repeat steps 6.4-6.12 until all samples are tested.</li>
	<li>Save the broken fiber fragments in the template for further microscopic analysis.</li>
</ol>

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	<li>Joseph, A., Wiley, A., Orr, R., Schram, B., Dawes, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+impact+of+load+carriage+on+measures+of+power+and+agility+in+tactical+occupations:+A+critical+review.">The impact of load carriage on measures of power and agility in tactical occupations: A critical review.</a> International Journal of Environmental Research and Public Health. 15 (1), (2018).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> High-performance fibres. , (2001).</li><li>Messin, G. H. R., Rice, K. D., Riley, M. A., Watson, S. S., Sieber, J. R., Forster, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+moisture+on+copolymer+fibers+based+on+5-amino-2-(p-aminophenyl)-+benzimidazole.">Effect of moisture on copolymer fibers based on 5-amino-2-(p-aminophenyl)- benzimidazole.</a> Polymer Degradation and Stability. 96 (10), 1847-1857 (2011).</li><li>McDonough, W. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Testing+and+analyses+of+copolymer+fibers+based+on+5-amino-2-(p-aminophenyl)-benzimidazole.">Testing and analyses of copolymer fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole.</a> Fibers and Polymers. 16 (9), 1836-1852 (2015).</li><li>De Vos, R. E. T. P., Surquin, J. E., Marlieke, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> US patent. , (2013).</li><li>Lee, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> US patent. , (2014).</li><li>Mallon, F. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> US patent. , (2014).</li><li>Cunniff, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dimensionless+Parameters+for+Optimization+of+Textile-Based+Armor+Systems.">Dimensionless Parameters for Optimization of Textile-Based Armor Systems.</a> 18th Int Symp Ballist. , 1302-1310 (1999).</li><li>Cuniff, P. M., Song, J. W., Ward, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Investigation+of+High+Performance+Fibers+for+Ballistic+Impact+Resistance+Potential.">Investigation of High Performance Fibers for Ballistic Impact Resistance Potential.</a> Int SAMPE Tech Conf Ser. 21, 840-851 (1989).</li><li>Cheng, M., Chen, W., Weerasooriya, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+Properties+of+Kevlar&#174;+KM2+Single+Fiber.">Mechanical Properties of Kevlar&#174; KM2 Single Fiber.</a> Journal of Engineering Materials and Technolog. 127 (2), 197 (2005).</li><li>Forster, A. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrolytic+stability+of+polybenzobisoxazole+and+polyterephthalamide+body+armor.">Hydrolytic stability of polybenzobisoxazole and polyterephthalamide body armor.</a> Polymer Degradation and Stability. 96 (2), 247-254 (2011).</li><li>Forster, A. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long-term+stability+of+UHMWPE+fibers.">Long-term stability of UHMWPE fibers.</a> Polymer Degradation and Stability. , 45-51 (2015).</li><li>Holmes, G. A., Kim, J. -. H., Ho, D. L., McDonough, W. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Role+of+Folding+in+the+Degradation+of+Ballistic+Fibers.">The Role of Folding in the Degradation of Ballistic Fibers.</a> Polymer Composites. 31, 879-886 (2010).</li><li>ASTM International. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> ASTM D3822/D3822M-14 Standard Test Method for Tensile Properties of Single Textile Fibers. , 1-10 (2015).</li><li>Levchenko, A. A., Antipov, E. M., Plate, N. A., Stamm, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparative+analysis+of+structure+and+temperature+behaviour+of+two+copolyamides+-+Regular+KEVLAR+and+statistical+ARMOS.">Comparative analysis of structure and temperature behaviour of two copolyamides - Regular KEVLAR and statistical ARMOS.</a> Macromolecular Symposia. 146, 145-151 (1999).</li><li>Jenket, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Failure Mechanisms Of Ultra High Molar Mass Polyethylene Single Fibers At Extreme Temperatures And Strain-Rates. , (2017).</li></ol>

The full description of the procedures used in this paper requires the identification of certain commercial products and their suppliers. The inclusion of such information should in no way be construed as indicating that such products or suppliers are endorsed by NIST or are recommended by NIST or that they are necessarily the best materials, instruments, software or suppliers for the purposes described.

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><tbody><tr><td>Stereo microscope</td><td>National</td><td>DC4-456H</td><td>Digital microscope</td></tr><tr><td>RSA-G2 Solids Analyzer</td><td>TA Instruments</td><td></td><td>Dynamic mechanical thermal analyzer used in transient tensile mode with Film Tension Clamp Accesory</td></tr><tr><td>Vertex 80</td><td>Bruker Optics</td><td></td><td>Fourier Transform Infrared spectrometer used to analyze results of washing protocol, equipped with mercury cadmium telluride (MCT) detector.</td></tr><tr><td>Durascope</td><td>Smiths Detection</td><td></td><td>Attenuated total reflectance accessory used to perform FTIR</td></tr><tr><td>Torque hex-end wrench</td><td>M.H.H. Engineering</td><td>Quickset Minor</td><td>Torque wrench</td></tr><tr><td>Methanol</td><td>J.T. Baker</td><td>9093-02</td><td>methanol solvent</td></tr><tr><td>Acetone</td><td>Fisher</td><td>A185-4</td><td>acetone solvent</td></tr><tr><td>Cyanoacrylate</td><td>Loctite</td><td></td><td>Super glue</td></tr><tr><td>FEI Helios 660 Dual Beam FIB/SEM</td><td>FEI Helios</td><td></td><td>Scanning electron microscope</td></tr><tr><td>Denton Desktop sputter coater</td><td></td><td></td><td>sputter coater</td></tr><tr><td>25 mm O.D. stainless steel washers with a 6.25 mm hole</td><td></td><td></td><td>25 mm O.D. stainless steel washers with a 6.25 mm hole</td></tr><tr><td>Silver behenate</td><td></td><td></td><td>Wide angle X-ray scattering (WAXS) standard</td></tr><tr><td>Xenocs Xeuss SAXS/WAXS small angle X-ray scattering system</td><td>Xenocs Xeuss</td><td></td><td>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 &amp;Aring;-1, detector separate X-ray video-rate imager for WAXS analysis (up to about 45&amp;deg; 2&amp;theta;) sample holder chamber.</td></tr><tr><td>Fit 2D software</td><td></td><td></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 ...

disentangling-high-strength-copolymer-aramid-fibers-to-enable

Research

JoVE Journal

Chemistry

7.1K Views.  National Institute of Standards and Technology. 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.

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

A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs and condition-based maintenance. These materials are adopted in a wide range of engineering applications, from aircraft and ship structures, to bridges, wind turbine blades, biomaterials and biomedical implants. Polymers are viscoelastic materials, and their response may be highly nonlinear and thus make it challenging to predict and monitor their in-service performance. The laboratory-scale testing platform presented herein assists the investigation of the influence of concurrent mechanical loadings and environmental conditions on these materials. The platform was designed to be low-cost and user-friendly. Its chemically resistant materials make the platform adaptable to studies of chemical degradation due to in-service exposure to fluids. An example of experiment was conducted at RT on closed-cell polyurethane foam samples loaded with a weight corresponding to ~50% of their ultimate static and dry load. Results show that the testing apparatus is appropriate for these studies. Results also highlight the larger vulnerability of the polymer under concurrent loading, based on the higher mid-point displacements and lower residual failure loads. Recommendations are made for additional improvements to the testing apparatus.

The durability of polymers and fiber-reinforced polymer composites in service is a critical aspect for their designs and condition-based maintenance. We present a novel low-cost laboratory testing platform for the investigation of the influence of concurrent mechanical and environmental loadings, and may help design more efficient yet safer composite structures.

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs ...

Engineering

Environmentally-controlled Microtensile Testing of Mechanically-adaptive Polymer Nanocomposites for ex vivo Characterization

Implantable microdevices are gaining significant attention for several biomedical applications1-4. Such devices have been made from a range of materials, each offering its own advantages and shortcomings5,6. Most prominently, due to the microscale device dimensions, a high modulus is required to facilitate implantation into living tissue. Conversely, the stiffness of the device should match the surrounding tissue to minimize induced local strain7-9. Therefore, we recently developed a new class of bio-inspired materials to meet these requirements by responding to environmental stimuli with a change in mechanical properties10-14. Specifically, our poly(vinyl acetate)-based nanocomposite (PVAc-NC) displays a reduction in stiffness when exposed to water and elevated temperatures (e.g. body temperature). Unfortunately, few methods exist to quantify the stiffness of materials in vivo15, and mechanical testing outside of the physiological environment often requires large samples inappropriate for implantation. Further, stimuli-responsive materials may quickly recover their initial stiffness after explantation. Therefore, we have developed a method by which the mechanical properties of implanted microsamples can be measured ex vivo, with simulated physiological conditions maintained using moisture and temperature control13,16,17. 
To this end, a custom microtensile tester was designed to accommodate microscale samples13,17 with widely-varying Young's moduli (range of 10 MPa to 5 GPa). As our interests are in the application of PVAc-NC as a biologically-adaptable neural probe substrate, a tool capable of mechanical characterization of samples at the microscale was necessary. This tool was adapted to provide humidity and temperature control, which minimized sample drying and cooling17. As a result, the mechanical characteristics of the explanted sample closely reflect those of the sample just prior to explantation.
The overall goal of this method is to quantitatively assess the in vivo mechanical properties, specifically the Young's modulus, of stimuli-responsive, mechanically-adaptive polymer-based materials. This is accomplished by first establishing the environmental conditions that will minimize a change in sample mechanical properties after explantation without contributing to a reduction in stiffness independent of that resulting from implantation. Samples are then prepared for implantation, handling, and testing (Figure 1A). Each sample is implanted into the cerebral cortex of rats, which is represented here as an explanted rat brain, for a specified duration (Figure 1B). At this point, the sample is explanted and immediately loaded into the microtensile tester, and then subjected to tensile testing (Figure 1C). Subsequent data analysis provides insight into the mechanical behavior of these innovative materials in the environment of the cerebral cortex.

Environmentally-controlled Microtensile Testing of Mechanically-adaptive Polymer Nanocomposites for ex vivo Characterization

A method is discussed by which the in vivo mechanical behavior of stimuli-responsive materials is monitored as a function of time. Samples are tested ex vivo using a microtensile tester with environmental controls to simulate the physiological environment. This work further promotes understanding the in vivo behavior of our material.

Implantable microdevices are gaining significant attention for several biomedical applications1-4. Such devices have been made from a range of materials, ...

Bioengineering

Manufacturing Of Robust Natural Fiber Preforms Utilizing Bacterial Cellulose as Binder

A novel method of manufacturing rigid and robust natural fiber preforms is presented here. This method is based on a papermaking process, whereby loose and short sisal fibers are dispersed into a water suspension containing bacterial cellulose. The fiber and nanocellulose suspension is then filtered (using vacuum or gravity) and the wet filter cake pressed to squeeze out any excess water, followed by a drying step. This will result in the hornification of the bacterial cellulose network, holding the loose natural fibers together.
Our method is specially suited for the manufacturing of rigid and robust preforms of hydrophilic fibers. The porous and hydrophilic nature of such fibers results in significant water uptake, drawing in the bacterial cellulose dispersed in the suspension. The bacterial cellulose will then be filtered against the surface of these fibers, forming a bacterial cellulose coating. When the loose fiber-bacterial cellulose suspension is filtered and dried, the adjacent bacterial cellulose forms a network and hornified to hold the otherwise loose fibers together.
The introduction of bacterial cellulose into the preform resulted in a significant increase of the mechanical properties of the fiber preforms. This can be attributed to the high stiffness and strength of the bacterial cellulose network. With this preform, renewable high performance hierarchical composites can also be manufactured by using conventional composite production methods, such as resin film infusion (RFI) or resin transfer molding (RTM). Here, we also describe the manufacturing of renewable hierarchical composites using double bag vacuum assisted resin infusion.

We present a novel method of manufacturing rigid and robust short natural fiber preforms using a papermaking process. Bacterial cellulose acts simultaneously as the binder for the loose fibers and provides rigidity to the fiber preforms. These preforms can be infused with a resin to produce truly green hierarchical composites.

A novel method of manufacturing rigid and robust natural fiber preforms is presented here. This method is based on a papermaking process, whereby loose ...

Cutting Procedures, Tensile Testing, and Ageing of Flexible Unidirectional Composite Laminates

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, where the yarns in each layer are oriented parallel to each other and held in place using binder resins and thin polymer films. The armor is constructed by stacking the unidirectional layers in different orientations. To date, only very preliminary work has been performed to characterize the ageing of the binder resins used in unidirectional laminates and the effects on their performance. For example, during the development of the conditioning protocol used in the National Institute of Justice Standard-0101.06, UD laminates showed visual signs of delamination and reductions in V50, which is the velocity at which half of the projectiles are expected to perforate the armor, after ageing. A better understanding of the material property changes in UD laminates is necessary to comprehend the long-term performance of armors constructed from these materials. There are no current standards recommended for mechanically interrogating unidirectional (UD) laminate materials. This study explores methods and best practices for accurately testing the mechanical properties of these materials and proposes a new test methodology for these materials. Best practices for ageing these materials are also described.

The goal of the study was to develop protocols to prepare consistent specimens for accurate mechanical testing of high-strength aramid or ultra-high-molar-mass polyethylene-based flexible unidirectional composite laminate materials and to describe protocols for performing artificial ageing on these materials.

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, ...

Artificial Thermal Ageing of Polyester Reinforced and Polyvinyl Chloride Coated Technical Fabric

Architectural fabric AF9032 has been subjected to artificial thermal ageing to determine changes of the material parameters of the fabric. The proposed method is based on the accelerated ageing approach proposed by Arrhenius. 300 mm x 50 mm samples were cut in the warp and fill directions and placed in a thermal chamber at 80 &#176;C for up to 12 weeks or at 90 &#176;C for up to 6 weeks. Then after one week of conditioning at ambient temperature, the samples were uniaxially tensioned at a constant strain rate. Experimentally, the parameters were determined for the non-linear elastic (linear piecewise) and viscoplastic (Bodner&#8211;Partom) models. Changes in these parameters were studied with respect to the ageing temperature and ageing period. In both cases, the linear approximation function was successfully applied using the simplified methodology of Arrhenius. A correlation was obtained for the fill direction between experimental results and the results from the Arrhenius approach. For the warp direction, the extrapolation results exhibited some differences. Increasing and decreasing tendencies have been observed at both temperatures. The Arrhenius law was confirmed by the experimental results only for the fill direction. The proposed method makes it possible to predict real fabric behavior during long term exploitation, which is a critical issue in the design process.

Here, we simulate accelerated thermal ageing of technical fabric and see how this ageing process influences the mechanical properties of the fabric.

Architectural fabric AF9032 has been subjected to artificial thermal ageing to determine changes of the material parameters of the fabric. The proposed ...

Twin-Screw Extrusion Process to Produce Renewable Fiberboards

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pre-treatment on lignocellulosic biomass before using it as source of mechanical reinforcement in fully bio-based fiberboards was developed. Various lignocellulosic crop by-products have already been successfully pre-treated through this process, e.g., cereal straws (especially rice), coriander straw, shives from oleaginous flax straw, and bark of both amaranth and sunflower stems.
The extrusion process results in a marked increase in the average fiber aspect ratio, leading to improved mechanical properties of fiberboards. The twin-screw extruder can also be fitted with a filtration module at the end of the barrel. The continuous extraction of various chemicals (e.g., free sugars, hemicelluloses, volatiles from essential oil fractions, etc.) from the lignocellulosic substrate, and the fiber refining can, therefore, be performed simultaneously.
The extruder can also be used for its mixing ability: a natural binder (e.g., Organosolv lignins, protein-based oilcakes, starch, etc.) can be added to the refined fibers at the end of the screw profile. The obtained premix is ready to be molded through hot pressing, with the natural binder contributing to fiberboard cohesion. Such a combined process in a single extruder pass improves the production time, production cost, and may lead to reduction in plant production size. Because all the operations are performed in a single step, fiber morphology is better preserved, thanks to a reduced residence time of the material inside the extruder, resulting in enhanced material performances. Such one-step extrusion operation may be at the origin of a valuable industrial process intensification.
Compared to commercial wood-based materials, these fully bio-based fiberboards do not emit any formaldehyde, and they could find various applications, e.g., intermediate containers, furniture, domestic flooring, shelving, general construction, etc.

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pretreatment on lignocellulosic biomass was developed, which leads to an increased average fiber aspect ratio. A natural binder can also be added continuously after fiber refining, leading to bio-based fiberboards with improved mechanical properties after hot pressing of the obtained extruded material.

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pre-treatment on lignocellulosic biomass before using it as ...

Solution Blow Spinning of Polymeric Nano-Composite Fibers for Personal Protective Equipment

Light-weight, protective armor systems typically consist of high modulus (&#62;109 MPa) and high-strength polymeric fibers held in place with an elastic resin material (binder) to form a non-woven, unidirectional laminate. While significant efforts have focused on improving the mechanical properties of the high-strength fibers, little work has been undertaken to improve the properties of the binder materials. To improve the performance of these elastomeric polymer binders, a relatively new and simple fabrication process, known as solution blow spinning, was used. This technique is capable of producing sheets or webs of fibers with average diameters ranging from the nanoscale to the microscale. To achieve this, a solution blow spinning (SBS) apparatus has been designed and built in the laboratory to fabricate non-woven fiber mats from polymer elastomer solutions.
In this study, a commonly used binder material, a styrene-butadiene-styrene block-co-polymer dissolved in tetrahydrofuran, was used to produce nanocomposite fiber mats by adding metallic nanoparticles (NPs), such as iron oxide NPs, that were encapsulated with silicon oil and thus incorporated in the fibers formed via the SBS process. The protocol described in this work will discuss the effects of the various critical parameters involved in the SBS process, including the polymer molar mass, the selection of the thermodynamically appropriate solvent, the polymer concentration in solution, and the carrier gas pressure to assist others in performing similar experiments, as well as provide guidance to optimize the configuration of the experimental setup. The structural integrity and morphology of the resultant non-woven fiber mats were examined using scanning electron microscopy (SEM) and elemental X-ray analysis via energy-dispersive X-ray spectroscopy (EDS). The goal of this study is to evaluate the effects of the various experimental parameters and material selections to optimize the structure and morphology of the SBS fiber mats.

The primary goal of this study is to describe a protocol to prepare polymeric fiber mats with consistent morphology via solution blow spinning (SBS). We aim to use SBS to develop novel, tunable, flexible polymeric fiber nanocomposites for various applications, including protective materials, by incorporating nanoparticles in a polymer-elastomer matrix.

Light-weight, protective armor systems typically consist of high modulus (&#62;109 MPa) and high-strength polymeric fibers held in place with an elastic ...

Fabrication and Mechanical Property Assessment of Fiber Composite Laminates

Measuring the Mechanical Properties of Glass Fiber Reinforcement Polymer Composite Laminates Obtained by Different Fabrication Processes

The traditional wet hand lay-up process (WL) has been widely applied in the manufacturing of fiber composite laminates. However, due insufficiency in the forming pressure, the mass fraction of fiber is reduced and lots of air bubbles are trapped inside, resulting in low-quality laminates (low stiffness and strength). The wet hand lay-up/vacuum bag (WLVB) process for the fabrication of composite laminates is based on the traditional wet hand lay-up process, using a vacuum bag to remove air bubbles and provide pressure, and then carrying out the heating and curing process. 
Compared with the traditional hand lay-up process, laminates manufactured by the WLVB process show superior mechanical properties, including better strength and stiffness, higher fiber volume fraction, and lower void volume fraction, which are all benefits for composite laminates. This process is completely manual, and it is greatly influenced by the skills of the preparation personnel. Therefore, the products are prone to defects such as voids and uneven thickness, leading to unstable qualities and mechanical properties of the laminate. Hence, it is necessary to finely describe the WLVB process, finely control steps, and quantify material ratios, in order to ensure the mechanical properties of laminates. 
This paper describes the meticulous process of the WLVB process for preparing woven plain patterned glass fiber reinforcement composite laminates (GFRPs). The fiber volume content of laminates was calculated using the formula method, and the calculated results showed that the fiber volume content of WL laminates was 42.04%, while that of WLVB laminates was 57.82%, increasing by 15.78%. The mechanical properties of the laminates were characterized using tensile and impact tests. The experimental results revealed that with the WLVB process, the strength and modulus of the laminates were enhanced by 17.4% and 16.35%, respectively, and the specific absorbed energy was increased by 19.48%.

Author Spotlight: Enhancing Fiber Composite Laminate Quality with the Wet Hand Lay-Up/Vacuum Bag Process 

This paper describes a fabrication process for fiber-reinforced polymer matrix composite laminates obtained using the wet hand lay-up/vacuum bag method.

The traditional wet hand lay-up process (WL) has been widely applied in the manufacturing of fiber composite laminates. However, due insufficiency in the ...

Characterizing Viscoelastic Properties of 3D-Printed Polymer Metamaterials

Characterizing Dissipative Elastic Metamaterials Produced by Additive Manufacturing

Viscoelastic behavior can be beneficial in enhancing the unprecedented dynamics of polymer metamaterials or, in contrast, negatively impacting their wave control mechanisms. It is, therefore, crucial to properly characterize the viscoelastic properties of a polymer metamaterial at its working frequencies to understand viscoelastic effects. However, the viscoelasticity of polymers is a complex phenomenon, and the data on storage and loss moduli at ultrasonic frequencies are extremely limited, especially for additively manufactured polymers. This work presents a protocol to experimentally characterize the viscoelastic properties of additively manufactured polymers and to use them in the numerical analysis of polymer metamaterials. Specifically, the protocol includes the description of the manufacturing process, experimental procedures to measure the thermal, viscoelastic, and mechanical properties of additively manufactured polymers, and an approach to use these properties in finite-element simulations of the metamaterial dynamics. The numerical results are validated in ultrasonic transmission tests. To exemplify the protocol, the analysis is focused on acrylonitrile butadiene styrene (ABS) and aims at characterizing the dynamic behavior of a simple metamaterial made from it by using fused deposition modeling (FDM) three-dimensional (3D) printing. The proposed protocol will be helpful for many researchers to estimate viscous losses in 3D-printed polymer elastic metamaterials that will improve the understanding of material-property relations for viscoelastic metamaterials and eventually stimulate the use of 3D-printed polymer metamaterial parts in various applications.

Additively manufactured polymers have been widely used for producing elastic metamaterials. The viscoelastic behavior of these polymers at ultrasonic frequencies remains, however, poorly studied. This study reports a protocol to estimate the viscoelastic properties of 3D-printed polymers and show how to use them to analyze the metamaterial dynamics.

Viscoelastic behavior can be beneficial in enhancing the unprecedented dynamics of polymer metamaterials or, in contrast, negatively impacting their wave ...

Tension Tests of Polymers

Source:&#160;Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA
Polymeric materials are widely used in civil structures, with uses ranging from very soft sealants to more rigid pipes in water and wastewater systems. The most basic definition of a polymer is a molecular structure with repeating subunits. The term polymer comes from Greek, where &#34;poly&#34; means many, and &#34;-mer&#34; means basic unit. Monomers, or single mers, are the specific repeating units. With polymers, the structure, including the length of the carbon backbone and the varying flexibility, will dictate the properties of the polymer. Polymers are classified into 3 subcategories: plastics, elastomers, and rigid rod polymers. Plastics are further subdivided into thermosets, which do not soften on heating, and thermoplastics, which do soften when heated and harden on cooling. Additionally, thermoplastics are mostly linear or branched polymers with little to no cross-linking, whereas thermosets exhibit 3D structure and have extensive cross-linking. Elastomers, or rubbers, are long, coiled chains and can be stretched to twice the original length, but will contract back to the original size when released, whereas rigid rod polymers do not stretch and are strong, crystalline structures.
In this laboratory, we will look at several different polymeric materials, including high density polyethylene (HDPE), polyvinyl chlorides (PVC), nylon, and methyl methacrylate (acrylic) in order to understand the breadth and diversity of the stress-strain curves for these materials and how their mechanical properties affect their performance.

Uniaxial Tensile Test Strength for Polymers

Source:&#160;Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA
Polymeric materials are widely used in civil ...

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

Summary

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Chapters in this video

A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli

Environmentally-controlled Microtensile Testing of Mechanically-adaptive Polymer Nanocomposites for ex vivo Characterization

Manufacturing Of Robust Natural Fiber Preforms Utilizing Bacterial Cellulose as Binder

Cutting Procedures, Tensile Testing, and Ageing of Flexible Unidirectional Composite Laminates

Artificial Thermal Ageing of Polyester Reinforced and Polyvinyl Chloride Coated Technical Fabric

Twin-Screw Extrusion Process to Produce Renewable Fiberboards

Solution Blow Spinning of Polymeric Nano-Composite Fibers for Personal Protective Equipment

Measuring the Mechanical Properties of Glass Fiber Reinforcement Polymer Composite Laminates Obtained by Different Fabrication Processes

Characterizing Dissipative Elastic Metamaterials Produced by Additive Manufacturing

Tension Tests of Polymers