Name: experimental implementation of a new composite fabrication method: exposing bare fibers on the composite surface by the soft layer method
Uploaded: 2017-10-06T12:30:00
Description: Watch this Scientific Journal Video about Experimental Implementation of a New Composite Fabrication Method: Exposing Bare Fibers on the Composite Surface by the Soft Layer Method at JoVE.com

This research was supported by the Climate Change Research Hub of KAIST (grant No. N11160012), the Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT and Future Planning (grant No. 2011-0030065), the Leading Human Resource Training Program of Regional Neo Industry through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (grant no. NRF-2016H1D5A1910603). Their support is greatly appreciated.

1. Material Preparation
<ol>
	<li>Preparation of the composite material 
	NOTE: CAUTION, Please consult all relevant material safety data sheets (MSDS) before use. Several of the chemicals used in these methods may be toxic and carcinogenic. Nanomaterials may have additional hazards compared to their bulk counterparts. Please use all appropriate safety practices when performing an experiment, including the use of engineering controls (fume hood, glove box) and personal protective equipment (safety...

<ol>
	<li>Hwang, I. U., 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=Bipolar+plate+made+of+carbon+fiber+epoxy+composite+for+polymer+electrolyte+membrane+fuel+cells.">Bipolar plate made of carbon fiber epoxy composite for polymer electrolyte membrane fuel cells.</a> J Power Sources. 184 (1), 90-94 (2008).</li><li>Avasarala, B., Haldar, P. <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+surface+roughness+of+composite+bipolar+plates+on+the+contact+resistance+of+a+proton+exchange+membrane+fuel+cell.">Effect of surface roughness of composite bipolar plates on the contact resistance of a proton exchange membrane fuel cell.</a> J Power Sources. 188 (1), 225-229 (2009).</li><li>Yu, H. N., Lim, J. W., Kim, M. K., Lee, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasma+treatment+of+the+carbon+fiber+bipolar+plate+for+PEM+fuel+cell.">Plasma treatment of the carbon fiber bipolar plate for PEM fuel cell.</a> Compos Struct. 94 (5), 1911-1918 (2012).</li><li>Lim, J. W., Lee, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+composite-metal+hybrid+bipolar+plates+for+PEM+fuel+cells.">Development of composite-metal hybrid bipolar plates for PEM fuel cells.</a> Int J Hydrogen Energy. 37 (17), (2012).</li><li>Kim, B. G., Lee, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electromagnetic-carbon+surface+treatment+of+composite+bipolar+plate+for+high-efficiency+polymer+electrolyte+membrane+fuel+cells.">Electromagnetic-carbon surface treatment of composite bipolar plate for high-efficiency polymer electrolyte membrane fuel cells.</a> J Power Sources. 195 (6), 1577-1582 (2010).</li><li>Kim, B. G., Lim, J. W., Lee, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+single-type+aluminum/composite+hybrid+bipolar+plate+with+surface+modification+for+high+efficiency+PEMFC.">A single-type aluminum/composite hybrid bipolar plate with surface modification for high efficiency PEMFC.</a> Int J Hydrogen Energy. 36 (4), 3087-3095 (2011).</li><li>Yu, H. N., Lim, J. W., Suh, J. D., Lee, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+graphite-coated+carbon+fiber+epoxy+composite+bipolar+plate+for+polymer+electrolyte+membrane+fuel+cell.">A graphite-coated carbon fiber epoxy composite bipolar plate for polymer electrolyte membrane fuel cell.</a> J Power Sources. 196 (23), 9868-9875 (2011).</li><li>Kim, K. H., Kim, B. G., Lee, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+carbon+composite+bipolar+plate+(BP)+for+vanadium+redox+flow+battery+(VRFB).">Development of carbon composite bipolar plate (BP) for vanadium redox flow battery (VRFB).</a> Compos Struct. 109, 253-259 (2014).</li><li>Lee, D., Lim, J. W., Nam, S., Choi, I., Lee, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gasket-integrated+carbon/silicone+elastomer+composite+bipolar+plate+for+high-temperature+PEMFC.">Gasket-integrated carbon/silicone elastomer composite bipolar plate for high-temperature PEMFC.</a> Compos Struct. 128, 284-290 (2015).</li><li>Lee, D., Lee, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electro-mechanical+properties+of+the+carbon+fabric+composites+with+fibers+exposed+on+the+surface.">Electro-mechanical properties of the carbon fabric composites with fibers exposed on the surface.</a> Compos Struct. 140, 77-83 (2016).</li><li>Lee, D., Lim, J. W., Nam, S., Choi, I., Lee, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Method+for+exposing+carbon+fibers+on+composite+bipolar+plates.">Method for exposing carbon fibers on composite bipolar plates.</a> Compos Struct. 134, 1-9 (2015).</li><li>Lee, D., Lee, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Carbon+composite+bipolar+plate+for+high-temperature+proton+exchange+membrane+fuel+cells+(HT-PEMFCs).">Carbon composite bipolar plate for high-temperature proton exchange membrane fuel cells (HT-PEMFCs).</a> J Power Sources. 327, 119-126 (2016).</li><li>Lee, D., Choe, J., Nam, S., Lim, J. W., Choi, I., Lee, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+non-woven+carbon+felt+composite+bipolar+plates+using+the+soft+layer+method.">Development of non-woven carbon felt composite bipolar plates using the soft layer method.</a> Compos struct. 160, 976-982 (2016).</li><li>Lee, D., Lim, J. W., Lee, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cathode/anode+integrated+composite+bipolar+plate+for+high-temperature+PEMFC.">Cathode/anode integrated composite bipolar plate for high-temperature PEMFC.</a> Compos Struct. 167, 144-151 (2017).</li><li>Lee, D., Oh, Y., Nam, S., Choe, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adhesion+Characteristics+of+Fiber-exposed+Glass+Composites.">Adhesion Characteristics of Fiber-exposed Glass Composites.</a> Compos Struct. 165, 9-14 (2017).</li></ol>

The soft layer method provides significant advantages compared with the conventional methods, and with a lower manufacturing cost. All three types of composites manufactured by the soft layer method show unique characteristics in terms of the electrical properties, mechanical properties, gas permeability, and adhesion properties.
For the measurement of the electrical property, a four-point probe method was used. ASR was measured 5 times and the average value was taken as a representative value...

The bipolar plate is a multi-functional key component of energy conversion systems and energy storage systems such as fuel cells and batteries. The key functional requirements of the bipolar plate are as follows: high electrical conductivity in the through-thickness direction to reduce ohmic-loss, high mechanical properties to withstand high compaction pressure and external impacts, and high productivity for mass production.
Compared with the graphite and metals that were conventionally adopted as materials for the bipolar plate, carbon fiber/epoxy composites have a higher specific strength and stiffness, which indicates that the weight of the system can be greatly reduced by replacing the conventional bipolar plate materials with composites1. However, conventional carbon/epoxy composites have poor electrical conductivity in the through-thickness direction, which results in a large areal specific resistance (ASR), due to the resin-rich layer that is formed on the composite surface. The insulating resin-rich layer prevents direct contact between the conductive carbon fibers and adjacent components, such as another bipolar plate, gas diffusion layer (GDL), and carbon felt electrode (CFE). 
Many studies were conducted to resolve the high ASR due to the resin-rich layer. The first approach was surface treatment methods to selectively remove the resin-rich layer. For example, mechanical abrasion was attempted to remove the resin on the surface2. However, the carbon fibers were also damaged, which resulted in a poor ASR. Plasma treatment3,4 and microwave treatment methods5,6 were also developed to avoid fiber damage, but they resulted in low productivity and uniformity. The second approach, conductive layer coating methods, includes expanded graphite coating7,8. This method successfully reduced the ASR and has been regarded as a standard method to manufacture a composite bipolar plate. However, it is costly and has durability and delamination issues due to the low mechanical strength.
In this study, the "soft layer method", a novel manufacturing method that can expose carbon fibers on the composite bipolar plate surface, is demonstrated. The main purpose of this method is to obtain a low ASR with a low manufacturing cost. The soft layer method adopts a thin soft layer such as a polymer release film between the compression mold and bipolar plate. After curing in the compression mold and the detaching of the soft layer, the fabricated bipolar plate displays carbon fibers exposed on the surface without any post-surface treatment. This method not only decreased the ASR but also significantly increased the mechanical properties and solved the gas permeability issue. This method can be applied for many other purposes: the development of an electrically conductive plate, the manufacture of a thin composite, and the fabrication of an adhesive joint without surface treatment.

<table width="891">
	<tbody>
		<tr height="21" style="height:15.75pt">
			<td class="xl63" height="21" style="width:223pt;height:15.75pt" width="297">Unidirectional carbon/epoxy prepreg</td>
			<td class="xl63" style="width:72pt" width="96">SK Chemicals</td>
			<td class="xl63" style="width:110pt" width="146">USN020</td>
			<td class="xl66" style="width:264pt" width="352">Used to fabricate unidirectional carbon composite</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl63" height="21" style="width:223pt;height:15.75pt" width="297">Plain weave carbon fabric/epoxy prepreg</td>
			<td class="xl63" style="width:72pt" width="96">SK Chemicals</td>
			<td class="xl63" style="width:110pt" width="146">WSN 1k</td>
			<td class="xl66">Used to fabricate fabric carbon composite</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl63" height="21" style="width:223pt;height:15.75pt" width="297">Plain weave carbon fabric</td>
			<td class="xl63" style="width:72pt" width="96">SK Chemicals</td>
			<td class="xl63" style="width:110pt" width="146">C-112</td>
			<td class="xl66">Used to fabricate fabric carbon composite</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl63" height="21" style="width:223pt;height:15.75pt" width="297">Non-woven carbon felt</td>
			<td class="xl63" style="width:72pt" width="96">Newell</td>
			<td class="xl63" style="width:110pt" width="146">Graphite felt 3 mm</td>
			<td class="xl66">Used to fabricated felt carbon composite</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl63" height="21" style="width:223pt;height:15.75pt" width="297">Film type epoxy resin</td>
			<td class="xl63" style="width:72pt" width="96">SK Chemicals</td>
			<td class="xl63" style="width:110pt" width="146">K51</td>
			<td class="xl66">Used as a matrix of the composite</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl63" height="21" style="width:223pt;height:15.75pt" width="297">Acetone 99.5%</td>
			<td class="xl63" style="width:72pt" width="96">Samchun</td>
			<td class="xl63" style="width:110pt" width="146">67-64-1</td>
			<td class="xl66">Used to cleanse the carbon fiber and the soft layers</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl63" height="21" style="width:223pt;height:15.75pt" width="297">Mold release</td>
			<td class="xl63" style="width:72pt" width="96">ShinEtsu</td>
			<td class="xl63" style="width:110pt" width="146">KF-96</td>
			<td class="xl66">Used to coat the mold</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl63" height="21" style="width:223pt;height:15.75pt" width="297">Release film</td>
			<td class="xl63" style="width:72pt" width="96">Airtech</td>
			<td class="xl63" style="width:110pt" width="146">A4000V</td>
			<td class="xl66">Used as a soft layer</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl63" height="21" style="width:223pt;height:15.75pt" width="297">Compression mold</td>
			<td class="xl63" style="width:72pt" width="96">N/A</td>
			<td class="xl63" style="width:110pt" width="146">N/A</td>
			<td class="xl66">Machined in lab. Material: NAK80</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl63" height="21" style="width:223pt;height:15.75pt" width="297">Hot press</td>
			<td class="xl63" style="width:72pt" width="96">Hydrotek 100</td>
			<td class="xl63" style="width:110pt" width="146">N/A</td>
			<td class="xl66">Used to apply pressure and heat</td>
		</tr>
		<tr height="21" style="height:15.75pt">
			<td class="xl63" height="21" style="width:223pt;height:15.75pt" width="297">Scanning electron microscope</td>
			<td class="xl63" style="width:72pt" width="96">FEI Compnay</td>
			<td class="xl63" style="width:110pt" width="146">Magellan 400</td>
			<td class="xl66">Used to investigate the surface of the composite</td>
		</tr>
	</tbody>
</table>

experimental implementation of a new composite fabrication method: exposing bare fibers on the composite surface by the soft layer method

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional component that should have high electrical conductivity, high mechanical properties, and high productivity.
In this regard, a carbon fiber/epoxy resin composite can be an ideal material to replace the conventional graphite bipolar plate, which often leads to the catastrophic failure of the entire system because of its inherent brittleness. Though the carbon/epoxy composite has high mechanical properties and is easy to manufacture, the electrical conductivity in the through-thickness direction is poor because of the resin-rich layer that forms on its surface. Therefore, an expanded graphite coating was adopted to solve the electrical conductivity issue. However, the expanded graphite coating not only increases the manufacturing costs but also has poor mechanical properties.
In this study, a method to expose fibers on the composite surface is demonstrated. There are currently many methods that can expose fibers by surface treatment after the fabrication of the composite. This new method, however, does not require surface treatment because the fibers are exposed during the manufacture of the composite. By exposing bare carbon fibers on the surface, the electrical conductivity and mechanical strength of the composite are increased drastically.

The fabricated specimens are observed using scanning electron microscopy (SEM) (Figure 1). Because the resin-rich layer that covers the top of the fibers is only a few micrometers thick, an optical microscopic image observed at the top of the specimen is not appropriate. A SEM image observed by tilting the specimen by 5&#176; provides a more representative image. Compared to the composites fabricated by conventional compression molding, which has its surface ...

Watch this Scientific Journal Video about Experimental Implementation of a New Composite Fabrication Method: Exposing Bare Fibers on the Composite Surface by the Soft Layer Method at JoVE.com

Experimental Implementation of a New Composite Fabrication Method: Exposing Bare Fibers on the Composite Surface by the Soft Layer Method

A protocol to expose bare fibers on the composite surface by eliminating resin rich area is presented. The fibers are exposed during fabrication of the composites, not by the post surface treatment. The exposed carbon composites exhibit high electrical conductivity in the through-thickness direction and high mechanical property.

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional ...

The overall goal of this procedure is to fabricate a fiber-reinforced composite with bare fibers exposed on the surface without any surface treatment. This technique can expose bare fibers on a composite surface without the use of expensive and inefficient surface treatments. The main advantage of this technique is that it improves the electrical conductivity and mechanical strengths of the composite.This technique also has high productivity. To prepare unidirectional carbon fiber fabric, pre-impregnated with epoxy, stack squares of prepreg with a fiber volume fraction of 50 to 60%in a sequence including zero degree and 90 degree orientations to avoid splitting of the laminate. To prepare each square of prepreg plain-weave carbon fiber fabric, first cleanse the fabric with acetone or ethanol.Place the fabric on a clean surface or on a lint-free laboratory wipe, and allow the acetone to evaporate under ambient conditions. Peel off one backing of a sheet of film-type epoxy resin with a curing temperature of 125 degrees Celsius. Apply a single sheet of epoxy resin film to the clean carbon fabric.Place the fabric epoxy side down on a hot plate at 70 degrees Celsius. Heat the fabric for 10 seconds to pre-impregnate the fabric with epoxy. Allow the prepreg fabric to cool under ambient conditions for 10 minutes.Then, remove the remaining backing sheet from the epoxy-coated side. Stack the plain-weave prepreg fabric in the desired stacking sequence to form the plain-weave carbon fiber fabric laminate. To prepare non-woven carbon fiber felt laminate, apply triple-layered epoxy sheet to each side of a piece of clean, dry carbon felt.Heat the epoxy-coated sides of the felt at 70 degrees Celsius for 10 seconds each with mass applied on the top. Allow the prepreg felt to cool for 10 minutes, and then peel off the remaining backing sheets. Next, wash sheets of 25 micrometer thick, non-perforated, fluorinated ethylene propylene release film with ethanol or acetone.Carefully dry the FEP sheets with lint-free wipes without causing wrinkles or pinholes. Ensure that the sheets are free of contaminants and particulate matter. Then, place each clean, dry sheet between lint-free wipes, and store the sheets in a dust-free, clean, plastic case.To begin the composite fabrication, apply silicone mold release to the compression mold. Wipe the mold with lint-free wipes to leave only a thin layer of mold release. Then, trim a piece of prepared carbon fiber laminate to be slightly smaller than the mold cavity.Place a sheet of 25 micrometer thick clean FEP film on the lower mold. Place the laminate on the mold, and cover it with 25 or 100 micrometer thick FEP film, depending on the fiber type. Carefully smooth out the film so that no air bubbles remain between the soft layer and the laminate.Then, close the compression mold. Heat a hot press to 150 degrees Celsius, and place the compression mold in the press. For unidirectional fiber composite, constantly apply 20 megapascals for 30 minutes.For a woven composite, apply 20 megapascals for four minutes, release the pressure, and immediately reapply 20 megapascals. Purge the material in this way until the viscosity of the resin begins increasing. Then, hold the pressure at 20 megapascals until the composite has cured for 30 minutes in total.For a felt composite, slowly increase the pressure to three megapascals, being careful not to overshoot. Cure the material at three megapascals for 30 minutes. Once the sample is cured, without releasing the pressure, cool the compression mold to below 120 degrees Celsius.Then, release the pressure, remove the mold, and de-mold the fabricated specimen. Scanning electron microscopy images acquired at a five-degree tilt showed that fibers were visible in greater detail in composites fabricated with the soft-layer method than with conventional compression molding. This was attributed to the elimination of the resin-rich layer on top of the composite.Despite the elimination of the epoxy resin layer, the fibers did not show visible defects. The through-thickness electrical conductivity was greater in composites fabricated with the soft-layer method, with a corresponding decrease in area-specific resistance to below 20 milliohms per square centimeter at a compaction pressure of 1.38 megapascals. The measured tensile strengths of soft-layer composites were comparable to those fabricated by the conventional compression method.The woven fabric and felt composites showed increases of 22%and 15%respectively. These increases were attributed to the soft layer applying a uniform pressure across the composite surface. By following this procedure, you will be able to fabricate a fiber-exposed composite without difficulty.The mechanism is simple. And with a good understand of your material, the implementation is even simpler. While attempting this procedure, remember to fine tune it to fit your specific application.Consider the curing condition of the composite and the thermal properties of the soft layer, and adjust the procedure accordingly to obtain the desired results.

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