-28 May, 2017
Carbon fiber is a strong, light weight and highly heat resistant material, and because it possesses these qualities it is a sought after substance for use in the aerospace and motor sports industries. Carbon fibers themselves are invisible to the naked eye, as they have a diameter of just 5-10 micrometres, and they are used to make everything from motorbikes to racing (pedal) bikes and from aeroplane wings to parts for space ships. Carbon fibers were first used in 1860 by Joseph Swan, who made the first electric lightbulbs. Since then, large quantities of carbon fiber material have been manufactured. Unfortunately, all too often they have been thrown into landfill at the end of their useful lifespan. Add to this the fact that the production of carbon fiber is expensive and energy intensive, and carbon fiber recycling becomes a very attractive prospect.
Working with carbon fiber.
Recycling carbon fiber begins with heating the scrap material to temperatures of between 400 and 600 degrees Celsius. This is because almost all carbon fiber materials are in fact composite materials; rather than consisting of pure carbon fiber, 40-60% of these materials will be made up of other materials, such as glass and aluminium. Heating the material up to these high temperatures dissolves the epoxy resin holding the composite together and enables us to reclaim the fibers. This process uses a mere 5% of the energy used by the original carbon fiber manufacturing process. Boeing uses a specific type of this heat treatment, called ‘prolysis’, which removes the resin to produce what technicians have described as a ‘fluffy’ type of carbon fiber. The reclaimed carbon fibers can then be reshaped into new materials, though it is important to note that the recycling process shortens the fibers and makes them less suitable for use a structural parts as their tensile strength and load bearing abilities will be diminished. An alternative method of recycling carbon fiber simply involved grinding it up into a powder and mixing it with other materials for use in road building projects. This recycling method is also much less energy intensive than manufacturing new carbon fiber from scratch. Some of the residues produced through this process can also be reclaimed. For instance, any aluminium used in a composite material can be reshaped into a new aluminium object. Crucially, the recycling process does little to diminish the quality of aluminium and so these residues can also be used to create new carbon fiber composites.
Carbon fiber applications.
Now that we know how to recycle carbon fiber: let’s look at how that recycled fiber could be used. As mentioned above, this material is widely used in the biking, motor sports and aerospace industries. It is also used in the electronics industry, for instance to make laptop covers. Let’s look more closely at the bike industry. As it is strong and light weight, carbon fiber is the perfect material for using in high performance racing bike frames. It can be used to make handlebars, helmets and even wheel spokes, too. As we have already seen, the shorter, discontinuous fibers of recycled carbon, do not have the amazing levels of structural strength of the longer continuous virgin carbon fibers that are mixed with composites and used as key structural parts in bikes, planes, cars and more. Nevertheless, many bicycle frame manufacturers are using recycled carbon fiber to produce new sub-structural parts for bike frames. A key example is the prominent brand Trek, which works with a company called Carbon Conversions to heat treat (‘pyrolise’) scrap carbon (often from old Trek bike parts) to extract the raw carbon fibers. Subsequently, this raw carbon is immersed in water to make moulds. The water itself can be reused, further reducing the carbon footprint of the carbon recycling process. These moulds can produce anything from a new laptop case to a decorative or sub-structural part for a bike, and from a pair of sunglasses to a non load bearing part of an aeroplane. In sum, recycling carbon fiber is not only easy to do, it also helps us to tread more lightly on our precious green planet.