Carbon Fiber is a lightweight and durable material that has become common across the automotive, wind generation, aerospace, and robotics industries. This advanced composite material provides strength and can be molded to fit nearly any application. As such, it’s become a very popular option. Notably, it’s this popularity that has caused some issues regarding how to deal with the carbon fiber waste from products once discarded. Here’s everything you need to know.
Carbon Fiber-Reinforced Polymers (CFRPs)
Carbon fibers can be laid out in different patterns and coated in matrix resins to create carbon fiber-reinforced polymers. This material has an excellent strength-to-weight ratio that has helped it become a core component of today’s most advanced equipment, manufacturing, and energy creation processes.
Disposing of Carbon Fiber
Once a product that has carbon fiber in it becomes garbage, this long-lasting and still valuable material needs to be extracted. The complex structure of carbon fiber pieces and the inability to reshape epoxies once cured continue to make waste management a serious concern. As such, several novel recycling methods emerged over the last few years.
Traditional Recycling Methods
Sadly, many of the most popular traditional recycling methods either don’t work or require a huge amount of energy to complete, eliminating any cost benefits. Using chemicals to loosen the epoxy and remove the fibers is inefficient. Additionally, it results in a lot of environmental waste in the form of dangerous chemicals.
Other methods require the carbon fiber polymer to be placed under extreme heat to create separations. This method is energy-intensive and dangerous. Additionally, both methods reduce the tensile strength of the recovered carbon fiber strands by as much as 85%, making the material unusable for most applications.
Electrohydraulic Fragmentation
Currently, the most advanced way to recover carbon fiber strands from polymers is using the electro-hydraulic fragmentation method. This approach sends high-voltage discharges through a pool of water. The carbon fiber sits in this pool as the high-voltage pulses create plasma. The plasma waves operate in microsecond pulses that work to separate materials via shockwaves.
This approach is far more efficient and effective than other methods that rely on heat and chemicals. Additionally, it only uses around a third of the energy of traditional recycling methods and can effectively remove adhesive and resin. However, it does have some shortcomings, such as degraded tensile strength of carbon fibers.
Better Options Needed
While the Electrohydraulic Fragmentation method is a major leap forward over chemical processes, it still lacks. A better solution would retain fiber strength, enabling the stands to be reused multiple times without reducing their durability. Ideally, it would remove all resin and adhesive residue from the strands. Thankfully, an innovative team of researchers from Waseda University has introduced a new process that could revolutionize carbon fiber recycling, allowing this material to be used in more applications without environmental risks.
Direct Discharge Electrical Pulses for Carbon Fiber Recycling Study
Waseda University engineers introduced a more efficient and lower-cost recycling method for recycling carbon fiber polymers. The approach, called Direct Discharge, was explained in detail in a paper published in the Scientific Journal. In the paper1, the team introduced their new approach to recycling carbon fiber and tested it against the electrohydraulic fragmentation method.
Direct Discharge Electrical Pulses
The direct discharge electrical pulse method eliminates the need to apply current to a pool. Instead, it leverages Joule heating and vapor expansion to separate the material from the inside out. This method produces plasma along the material edges. In turn, thermal stress creates expansion forces, separating the fibers from the epoxy.
Source – Scientific Report
Direct Discharge Electrical Pulses for Carbon Fiber Recycling Test
To prove their new methods’ effectiveness, several tests were conducted. The tests compared both methods of carbon fiber recycling in detail. Specifically, the engineers monitored key metrics, including the carbon fiber strand’s length, tensile strength, the amount of resin residue not removed, and its overall degradation. Additionally, the team compared energy requirements to gain a full understanding of the capabilities of either.
CFRP Laminates
The scientist began their testing phase by creating CFRP laminates. The laminates were designed to represent common airplane parts, making them an ideal way to check effectiveness using a real-world scenario. The laminates were only 8mm thick and utilized a common carbon fiber plain weave layer. The material featured consecutively layers arranged with alternating orientations at 45-degree angles. This layout is common because it provides excellent resilience and durability.
Direct Discharge Method
To test the Direct Discharge method the team created two CF samples that were 100 mm long and 30 mm long. The engineers insulated the sample using rubber-plated clamps to ensure the current flow remained stable. From there, the entire setup was placed in tap water, and pulses were applied directly to the sample.
Specifically, the engineers tested the process using a charging voltage of 10 kV with a capacitance of 80 µF. This data was captured using an array of sensors and a high-speed video camera. The engineers then utilized X-ray tomography and electric field simulations to track what residue was left.
Electrohydraulic Fragmentation Method
To test the electrohydraulic method, the team created 20 mm square samples. The smaller samples allowed the engineers to utilize smaller testing vessels, allowing them to better track any changes. The samples were placed in water and electrical current was applied to the water, rather than the Carbon Fiber polymer directly like in the Direct Discharge method.
Measuring Fibers
Following the experimentation, researchers collected 100 strands of carbon fiber from each test. An HiROX RX-100 optical microscope was used to compare their lengths. From there, the strands were scanned for structural integrity using a TM4000 Plus scanning electron microscope. Additionally, the team weighed the strands at different temperatures to track degradation, and single fiber tensile strength tests using a SHIMADZU EZ-SX were conducted.
Carbon Fiber Recycling Test Results
The results of the study revealed that Direct Discharge is more effective for CF recovery versus the Electrohydraulic Fragmentation method. The researchers determined that their new approach was capable of recovering longer fibers with higher strength. Additionally, it was successful at fully separating longer stands and removing residue. Impressively, the team found that this method of recovery left 81% of tensile strength intact.
Direct Discharge is more Efficient.
The Direct Discharge method was found to be more efficient across the board. When electrical pulses were applied, the team tracked immediate changes from the first pulse. These effects occurred quickly because potions of the resin broke down and became plasma, creating an internal shockwave that separated the strands.
Electrohydraulic Fragmentation Method
Interestingly, the researchers discovered that the Electrohydraulic Fragmentation method needed at least 100 charges before it showed any effect on the material. As such, the costs of operating Electrohydraulic Fragmentation recycling processes are much higher than Direct Discharge options. Additionally, there was more resin left on the CF strands versus the Direct Discharge process.
Benefits
This research brings many benefits to the table. For one, it opens the door for more carbon fiber and polymer uses. These lightweight materials will become more common in your vehicles as more efficient manufacturing methods appear. As such, it’s vital to recover this valuable material efficiently.
Efficient
There are several reasons why the Direct Discharge recycling approach is more efficient than Electrohydraulic Fragmentation options. For one, joule heating can be generated in microseconds, providing near-instant separation. The team discovered that the Direct Discharge method improved energy efficiency by at least 10 times.
Effective
Another major benefit of this research is that it is more effective. The ability to accurately separate carbon strands from residue is a game changer. This method reduces fragmentation while retaining +80% tensile strength.
Environmentally Friendly
In terms of environmental impact, the Direct Discharge approach reduces all the risks. It doesn’t require harmful chemicals or a lot of heat. As such, there are minimal storage and application requirements, allowing this method to be deployed in more regions.
Researchers
The Carbon Fiber recycling research was conducted at Waseda University. Professor Chiharu Tokoro from the Department of Creative Science and Engineering led the study. Keita Sato, Manabu Inutsuka, and Taketoshi Koita also contributed to the research. Now, the team will expand their efforts to see how to enhance the Direct Discharge method further.
Companies that can Benefit from Carbon Fiber Recycling
Several firms have the products and positioning to benefit from the research found in this study. Carbon Fiber can be used to replace many different materials and as its price lowers and manufacturing capabilities increase, there’s sure to be some serious winners. Here’s one company properly positioned to reap the benefits of this study.
Clearway Energy Inc. (CWEN -1.75%) is a leading renewable tech and infrastructure provider. The company is headquartered in New Jersey where it provides global clientele with wind, solar, and thermal energy solutions. Notably, Clerway is one of the most reputable renewables providers. It currently operates +350 clean energy products across the US.
Clearway Energy, Inc. (CWEN -1.75%)
Investors find Clearway to be an attractive option due to its stability and the company’s dedication to transparency and innovation. If Clearway Energy Inc. integrates recycled carbon fiber into its products, it could see substantial savings. These savings could be passed onto consumers, driving renewable adoption and pushing Clearway Energy ROIs up.
Recycling Carbon Fiber is the Key to Many Industries
When you look at the results of the recycling carbon fiber study, it is easy to see that the new method will open the door for cheaper and more available carbon fiber. In the future, pieces on your car that used to weigh pounds may become as light as ounces while retaining their strength. All of these factors and much more are possible thanks to the innovative researchers pushing for more efficient carbon fiber recycling methods.
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Study Reference:
1. Tokoro, C., Sato, K., Inutsuka, M. et al. Efficient recovery of carbon fibers from carbon fiber-reinforced polymers using direct discharge electrical pulses. Sci Rep 14, 29762 (2024). https://doi.org/10.1038/s41598-024-76955-0
