Carbon fiber: Life Beyond the Landfill
When a composite structure reaches the end of its service life, disposal becomes an issue. Historically, composite components from retired aircraft and junked automobiles have been disposed of in landfills or incinerated. While landfills remain the least expensive option, in 2004, most European Union (EU) member states passed laws forbidding landfill disposal of composites. Further, incineration of plastics is suspect because of the potential release of toxic byproducts. The EU’s End-of-Life Vehicle (EEEV) Directive, issued in 2000 by the EU parliament on Sept. 18, 2000, and adopted by EU member nations in November 2003, requires that 95 percent of each vehicle manufactured after January 2015 must be reused or recovered. Given the current political pressure to develop renewable resources, not to mention growing concern over global warming, reuse and recovery rules similar to the EEEV are likely to be adopted by most industrialized nations.
A boost for recycling
Starting this year, the EEEV puts the onus of disposal on the original equipment manufacturer (OEM) and calls for OEMs to design in recyclability and design out hazardous substances. “In the U.K., product designers are being forced to consider how a component will be disposed of when it has reached the end of its lifespan,” says John Davidson, managing director for carbon fiber recycler Milled Carbon (Henley in Arden, U.K.), who notes that regulations like EEEV are gradually opening up the recycling market in Europe.
Recycling typically involves four basic steps: collection, identification/separation, reclamation and remarketing. Recycling is practical only if the value of the reclaimed raw materials exceeds the cost of the recycling process. Here, composites present some unique difficulties for recyclers because of the complex nature of the product. It is relatively easy to reclaim aluminum used in an aluminum alloy aileron from an aircraft wing by heating the alloy. The molten elements separate, and established processes can be used to reclaim those elements with predictable levels of purity. A composite, however, can be made from a number of materials that are much more difficult to separate and, in the case of thermoset composites, cannot be reclaimed through a melt process.
Since the idea of recycling composites was first conceived, the greatest challenge has been to develop a profitable recycling process. While technology advancements have made carbon recycling more practical, reclaimed fibers emerge from the recycling process in a chopped or milled form that prevents reuse in structural applications. Where in the market, then, does such a fiber fit?
And at what price? Although continuous virgin carbon fiber currently commands a price as high as $20/lb, chopped or milled virgin fiber is available today from most of the major carbon fiber suppliers at $11/lb to $14/lb. On the open market, recycled carbon fiber is unlikely to approach even the low figure of this nearest competitor. Still, a small group of pioneering carbon fiber recyclers believes it is not only possible, but probable that reclaimed carbon fiber can be sold at a significantly lower-than-virgin but still profitable price and expect market opportunities to expand as their recycling technologies are further refined and perfected.
One such firm is Adherent Technologies (Albuquerque, N.M.), which says that demand for chopped and milled carbon fiber is growing as carbon fiber is used in greater quantities outside the aerospace market, especially in applications where cost savings associated with fiber reuse are overcoming initial resistance to “recycled” materials.
Aircraft recycling initiatives
When looking for carbon fiber to recycle, the obvious starting point is the industry that uses the most carbon fiber today: aerospace. Between 2007 and 2025, about 200 commercial passenger aircraft per year are expected to meet their end of life, a fact that is driving recycling efforts by commercial aircraft giants Airbus Industrie (Toulouse, France) and The Boeing Co. (Seattle, Wash.).
In Europe, Airbus is spearheading the European Union’s sustainability project, called the Process for Advanced Management of End of Life of Aircraft (PAMELA). The €2.4 million ($3.2 million) project, initiated last year and funded in part by the European Commission’s LIFE (l’Instrument Financier pour l’Environnement) program, is designed to establish best practices for dealing with end-of-life aircraft. The PAMELA consortium includes Airbus, waste-management firm SITA (Maidenhead, Berkshire, U.K.), EADS CCR (Suresnes, France), Sogerma Services (Mérignac, France) and the Prefecture des Hautes-Pyrénées. A test facility has been established near Tarbes Airport in southwest France, where Airbus intends to prove that more than 85 percent of every aircraft can be recycled, reused or otherwise recovered.
Although Airbus is not directly involved in recycling process development, a retired Airbus A300 aircraft was flown to the PAMELA site in late summer 2006 to be used for experimentation. That plane, which contains less than 4 percent composites, will be joined by other A300s, A310s and older A320s, as they are taken out of service. As planes with greater composites content come in for recycling, PAMELA project leaders say that new processes will have to be investigated. To date, the only commercialized method for composites to come from PAMELA research is grinding of thermoset composites into granules for use as filler materials (e.g., in asphalt), while reclaimed short fibers are used to reinforce sheet molding compound and bulk molding compound (SMC and BMC).
Although U.S. regulations do not yet mandate recycling, Airbus rival Boeing is heavily involved in carbon fiber reclamation research. Bill Carberry, Boeing’s project manager for airplane and composite recycling, says that although a market exists for recycled carbon fiber, there is still a stigma attached to “recycled material” — something people associate with products like soda cans. But Carberry expects this perception will change as research validates the value and quality of recycled fiber.
With this in mind, Boeing helped form the Aircraft Fleet Recycling Assn. (ARFA) in April 2006, a consortium of U.S. and European companies, including Adherent, Milled Carbon, Air Salvage International (Alton, Hampshire, U.K.), Bartin Recycling Group and Châteauroux Air Center (both in Châteauroux, France), Evergreen Air Center (Marana, Ariz.), Europe Aviation (Orly, France), Huron Valley Steel (Belleville, Mich.) and WINGNet (a networking group founded by the Engineering and Physical Sciences Research Council, Swindon, U.K.). Rolls Royce’s membership in the consortium was pending as of January 2007. “One of the challenges as a large systems integrator is getting others in the field interested in meeting our objectives,” says Carberry, adding, “We are getting people together to work toward a common goal.”
ARFA is concentrating on recovery of carbon fiber from manufacturing waste and retired airplane scrap. The group currently processes more than 125 planes per year. As part of the effort, Boeing is involved in the development of a commercial carbon fiber recycling reactor in the U.S. Partners in the effort include Boeing’s AFRA partners Milled Carbon and Adherent Technologies and metal-recovery firm Huron Valley Steel’s Fritz West operation in Tucson, Ariz.
Players and processes
As carbon fiber reclamation work has progressed, Milled Carbon and Adherent Technologies have shared the spotlight in recycling process development.
Based in the U.K., Milled Carbon was established in 2003 and has developed a system that recycles cured and uncured carbon fiber composites using pyrolysis, a method of incineration that chemically decomposes materials by heating them in a near oxygen-free atmosphere. While an entirely oxygen-free process is a practical impossibility, the extremely oxygen-poor atmosphere maintained during pyrolysis retards oxidation, making it possible to recover materials in substantially the same condition as before they were incorporated into the composite. In Milled Carbon’s process, incineration burns off all the resin and additives, freeing the fiber reinforcement. “The art of our process is how we control the atmosphere,” says Davidson.
The process supports the recycling of cured parts up 2m/6.56 ft wide, 0.25m/0.82 ft high and 25 mm/1 inch thick, and uncured material in the form of manufacturing off-cuts or unused rolls of pre-impregnated material are processed in a similar fashion. The company does not need to pretreat the material before processing, according to Davidson. Milled Carbon has the ability to process the recyclate further by shredding, chopping and milling it for various applications.
“One of the biggest problems I have is the generators of waste don’t generally record what they are throwing away, so we are not always sure of the resin matrix,” says Davidson. “We are trying to get waste generators to segregate their waste, which helps introduce quality and control.” He points out, however, that some customers — notably, Formula 1 racing companies and the U.K. Ministry of Defence — are grappling with how to release materials data without compromising proprietary information.
In terms of resin, Milled Carbon typically handles basic epoxies, but Davidson says the company has the capability to work with others as well, including bismaleimides (BMIs) and phenolics.
Davidson believes the company’s progress has been hindered in the current regulatory climate in the U.K. “Legislation does not keep up with innovation,” Davidson contends, noting that the company has worked for three years to get its process included under existing legislation devised to cover disposal via incineration or landfill placement. He believes the company is now close to winning a license that will enable a ramp-up to commercialization on a large scale. Milled Carbon also is looking into contaminated end-of-life waste as well, such as scrapped airplanes from which any composites come in shredded form with varying degrees of detritus accompanying it. The company is working with U.K.-based Nottingham University on a fluidized bed process. “Exhaust gasses from our process could drive [provide energy for] new processes, such as the fluidized bed,” says Davidson. The latter immerses the composite in a chemical bath that helps break the material down into its constituent parts.
In the U.S., Adherent and its development partner, Titan Technologies (Albuquerque, N.M.), are developing a low-temperature, catalytic conversion process for recycling complex mixtures of thermoplastic and crosslinked thermoset polymers as well as automobile/truck tires and mixed electronics scrap. The 13-year effort has benefited from U.S. government support — about $3 million (USD) in for research and development — but the partners are now seeking investors to help move the company from its prototype work into a full commercial offering, which company president Ronald Allred hopes to achieve this year.
Adherent contends that a major cost barrier in composites recycling is that collected composite waste must be sorted — one of the more labor-intensive aspects of conventional recycling processes. Its reclamation process is designed to treat all materials at once in a three-step or tertiary process that includes thermal pretreatment and two wet chemical processes. Tertiary recycling, a term coined by the American Plastics Council, reclaims not only fibers but also thermoplastic and thermoset polymeric waste, the latter in the form of reusable hydrocarbon fractions (chemical building blocks) that may be used subsequently to make new polymers, monomers, fuels or other chemicals. The process does not require that materials be sorted and separated, thus removing transportation, labor and other related segregation costs from the equation. All scrap parts and other materials are introduced to the recycling process as a single feedstock. The various materials are separated by designated support unit operations during the process, both before and after entering the tertiary recycling reactor. The support units handle size reduction (crushing, chopping, etc.), drying, material classification, off-gas treatment and distillation, and the recovery of metals, fiber and carbon char.
Although the company’s process is able, at this point, to recycle only a few hundred pounds of scrap a day, according to Allred the reclaimed carbon fibers are 99.9 percent pure. Adherent has conducted single fiber tests to compare virgin carbon-fiber fabric with reclaimed fibers. Results indicate that reclaimed fiber exhibited an average reduction in tensile strength of only 8.6 percent, supporting Adherent’s contention that reclaimed fibers substantially retain their properties.
Once the company ramps up to full commercial capacity, Allred expects to erect a plant that will have the capacity to process 4,000 lb/1,814 kg a day. The company has forecast that it has the potential to recover about 435,000 lb/162,359 kg of high-purity carbon fiber from 660,00 lb/246,338 kg of carbon composite scrap in its first year. At this volume, the plant would be running at about 40 percent capacity, permitting significant growth in subsequent years.
Mid-year facility startup
Meanwhile, the first Boeing recycling facility is expected to be up and running in the U.S. by late 2007, or early 2008, in Tucson, Ariz., the site of a large U.S. aircraft “boneyard.” Boeing says Milled Carbon’s U.S. entity, Recycled Carbon Fibers (North Hollywood, Calif.), will run the reactor. Carberry notes that, at this facility, some of the resin can be reused (e.g., to make particleboard for the construction industry), but most of the resin will be burned to help facilitate the recycling process, saving energy. Both Milled Carbon and Adherent use a pyrolytic (heat) process, In Milled Carbon’s process, the resin burns, providing heat and thus reducing the external (or supplied) energy, explains Carberry. In Adherent’s process, however, the resin is not burned, but rather is broken down using a catalyst, and the resin’s components, therefore, can be reused. Carberry points out that although Boeing will maintain no direct control over the business end of the venture, it will provide the composite feedstock from its Puget Sound facilities in Washington State. The object is to have all of the Boeing facility’s recyclable composite parts going to the carbon fiber recycling reactor. In return, Boeing contractually will have the first right of refusal on the reclaimed carbon fiber, says Carberry.
When Boeing first looked into recycling, Carberry recalls, the company thought it would have to justify offering a lower-grade fiber with much reduced mechanical properties. In this light, the recycling effort has proved encouraging: Carberry asserts that the strength, modulus, surface activity and wetting ability of reclaimed fiber is remarkably close to virgin. For injection molding applications, he contends, the reclaimed fiber, in chopped form, is as good as virgin fiber.
One of the hurdles that must be cleared before aerospace market acceptance can be achieved is to make sure the fiber that was once classified for disposal can be reclassified for reuse. Carberry says Boeing is confident that legal hurdles can be surmounted: fibers reclaimed from retired Boeing 777 parts and a host of military jets have been used to make a single, nonstructural part for a military aircraft. Tests of the fibers and the part have confirmed their utility, according to Carberry.
Recycled fiber not purchased and reused by Boeing will be sold on the open market. The value of the carbon fiber depends on the grade, but Carberry estimates the recyclate will fetch about $5.50/lb to $6.00/lb on the open market — about one-third to one-half the cost of virgin chopped fiber.
Reuse in conductive materials
Outside aerospace circles, fiber recycling is primarily a matter of possibilities rather than probabilities. The one exception is YF International (Duiven, The Netherlands). Founded in 1998, this company began recycling carbon fiber from composites and other forms of waste in 2000 and has since begun to process para- and meta-aramid and glass fibers, as well as other fibrous waste derived from noncomposite sources, such as cotton, polyester and nylon 6/6. Waste sources for its carbon fibers include “all applications areas,” claims YF’s managing director Klaas Hauwert, noting that, “We are not using prepreg at this moment but, technically, we could recycle it.” Although the company collects discarded composite components, its feedstock also includes off-spec fiber and fabrics, selvedges, fabric cuttings and leftovers purchased worldwide. YF handles the collection of feedstock and sales/distribution of reclaimed fibers, while partner Apply Carbon (Languidic, France) processes the cured composites in its pyrolysis unit and then chops or mills the reclaimed fiber. According to Hauwert, the YF/Apply partnership can reclaim and remarket from 100 to 1,000 metric tonnes (almost 250,000 lb to more than 2.2 million lb) of carbon fiber per year. YF’s customers include suppliers of filled thermoplastic and thermoset compounds, such as SMC and BMC.
Like Carberry, Hauwert acknowledges that potential customers are initially skeptical, but says they are not reluctant for long. “Once we go through our quality procedure and our customers test the product,” he explains, “they are convinced. As one customer once said, ‘We are selling technical properties, not virgin or recycled compounds.’”
Most of the chopped/milled product goes to customers looking to cut cost in conductive applications. “Our customers have concluded that for their applications, recycled fiber is good enough.”
While carbon fiber recycling is still in its infancy in many industries, proponents are excited about its prospects. While Boeing’s stance is that it’s too soon to tell how and where reclaimed carbon fiber will find its markets, the airframer and its processing partners will continue to conduct research. Carberry believes the fruits of the research will prove recycled carbon fiber’s suitability for reuse.