Carbon fiber composite recycling: An industry perspective
While carbon fibers and the composites made from them have been around for a good many decades, they continue to gain public attention through the marketing efforts of aircraft companies, such as Airbus and Boeing, as well as Formula 1 racing teams and OEMs of high-end consumer goods. Today, most carbon fiber still finds its way into aerospace applications, such as the new A380 and 787 Dreamliner, but carbon fiber use is increasing in industrial applications. As a result, there is a current shortage, which is being remedied by the world's fiber manufacturers, who are building more production lines to meet the new demand.
The current world capacity is said to be on the order of 25,000 metric tonnes (about 55 million lb) per annum. As the new capacity comes on line over the next few years, worldwide capacity could reach 35,000 metric tonnes (about 77 million lb) per annum. It could reasonably be assumed that most of this carbon fiber will find its way into composites of one form or another and, if one were to take the waste figures being bandied about - anything up to 40 percent - the math is easy. If all the waste were recycled and reintroduced to the market, it could go a long way toward alleviating shortages.Few people doubt the value of recycling in terms of resource conservation, but when many see the label "recycled,"they think "second quality."In the case of recycled carbon fiber composites, this is far from accurate. Methods exist today by which carbon fibers and prepregs can be recycled, and the resulting recyclate retains up to 90 percent of the fibers' mechanical properties. In some cases, the method enhances the electrical properties of the recyclate because the carbon recyclate can deliver performance near to or superior to virgin material. All that remains is to create demand for recycled fiber by packaging it in a form useful to end-users. Because the recyclate is completely unsized, that is, there remains no resin or original finish, my company is currently evaluating the production of pelletized milled fibers with various binders as well as compressed milled fibers in tablet form, without binders. We also have successfully chopped the recyclate at 6 mm and 12 mm lengths (nearly 0.25 inch and 0.47 inch, respectively).
To make such recycled products viable, of course, there must be an infrastructure established for collecting and identifying the waste, and the end-user must have confidence in product quality. This has been done successfully in the plastics industry - it was not long ago that some form of identification was required on plastic parts to facilitate collection and segregation. Now, such marking and segregation is almost second nature to businesses and individuals alike. In 2001 - in the U.K. alone - 295,000 metric tonnes/650 million lb of recycled plastic were reused in products such as street furniture and construction materials. Most composites manufacturers are already engaged in waste management procedures, and could be counted on to recycle waste materials on the shop floor when collection and processing links are in place.
I have made no mention, thus far, of the end-of-life problems associated with composite parts. I have attended many conferences and seminars where advances in composites manufacture have been displayed, but never once have I heard mention of what we are to do when these composites reach the end of their useful life. It behooves designers to consider now the thorny issue of how recycling companies can be confident that they know what types of parts they are recycling. It could be a basic epoxy matrix composite, or it could be a brominated resin matrix, with all the associated toxic complications - typically we have no way of knowing. An ideal way of overcoming this is to embed an RFID (radio-frequency identification) tag in each part. This not only gives us information about the composite's makeup, but it also could inform engineers about the life of the component.
Glass fiber composites exist in greater volume than carbon parts. While we can recycle glass, the recyclate is not commercially viable due to the already low price for virgin material and the fact that no bulk end-use market yet exists that can accommodate recycled material in the quantity likely to be available. The industry must resolve this issue as well.
Here in the U.K., we now have the most stringent waste laws in Europe (possibly, in the world), and it is only a matter of time before other countries follow suit. It takes a few years for the practical capabilities of waste generators to catch up and, in the odd case, some regulations are completely impractical. It is already difficult to put composite waste into landfills, and the situation will get worse. Incineration is an appalling waste of resources, in my opinion, and even more expensive than disposal. It will take time and effort for the industry to adjust, but we should be positioning ourselves - now - for the inevitable end-of-life regulations by adopting waste composite recycling efforts.
Fast-reacting resins and speedier processes are making economical volume manufacturing possible.
Commercial production of recycled carbon fiber currently outpaces applications for it, but materials characterization and new technology demonstrations promise to close the gap.
Fiber-reinforced plastic (FRP) replacing coated steel in more reinforced-concrete applications.