As more composites and composite parts and systems are nearing end of life, the recycling of composite materials has become a rather large business. Several companies have recognized the need to recycle end of life composites because the economics of recycling to get at least the fiber back make sense for several types of composite materials that don’t need to be continuous fiber airplane wings.
Composites are inherently difficult to recycle or to reduce down to their original components like metal cans, glass bottles, and newspapers are. Since these materials were intentionally mixed together to form something that when well bonded was stiffer, stronger, and lighter than either of its starting materials (string and glue – right?) they are difficult to separate. They are bonded together strongly enough that it takes quite a bit of energy or fancy chemistry to get them separated so that each component can be reused.
Most of the recycling is done by either burning off or dissolving the resin to get at the fibers so that they can be reused. This is much better than incinerating the composites or just sending them to the landfills, because the recycled fiber is several orders of magnitude less expensive than making new fiber, and it is also much less energy intensive to get. Recycling to get back the carbon fiber saves more than half the energy required to make it in the first place, and the recycled fibers can be made into fairly high performance products for things like sheet molding compound and other discontinuous fiber composites.
Burning the plastic matrix away from the fiber is the most energy intensive and least environmentally friendly way of recycling carbon fiber composites. And it is inherently polluting because of the nature of the resin systems used to bind the fibers together. Dissolving the resin out of the composite is more environmentally friendly, and there is always the possibility of refining the dissolving agent to get back some of the chemistry of the resin and potentially reuse that as well.
But by far the best solution is to re-use or re-purpose the end of life composite part for some other purpose. Currently, recycled ground up fiberglass is used as a filler in resins for some applications, tires to increase wear resistance, plastic wood products, asphalt and asphalt roofing materials, and cast polymer countertops. And the fibers if they are extracted in a little bit longer form have been used in concrete to make bendable concrete and to make concrete shrink less when it cures. This has also been true of the incorporation of CO2 into concrete. Some of the strongest and most durable building materials used today are the result of the incorporation of glass fibers and CO2 into the concrete mix. This serves the dual purpose of enhancing the concrete and sequestering the carbon.
There is one company in Poland that started out as a metals recycling center and got involved in the recycling of wind turbine blades. Anmet started out as a metals recycler, but soon began to recognize the need to recycle composites – specifically wind turbine blades as they were nearing their end of life. Today Anmet’s main business is recycling these blades into useful products and not only burning out the resin to get the fiber, but actually cutting up the wind turbine blades themselves and making something out of them. The picture to the right at the top of this post is a section of a couple of the ends of wind turbine blades that have been made into supports for a bridge. They have made other products out of these blades as well, rather modern chairs, attractive pedestrian bridge supports across smaller waterways, outdoor furniture that will last a long time, even a chaise lounge. They have even made carports out of recycled carbon fiber composites.
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