An innovative process for carbon fiber recovery from epoxy carbon fiber composite

Primarily finding application in aerospace, auto racing and high-end sporting goods, carbon fibre reinforced plastic (CFRP) composites are increasingly being used in several new manufacturing applications where performance, high strength and reduced weight are important. In recent decades, carbon fibers have found wide applications in commercial and civilian aircraft, recreational, industrial and other markets as their price has come down and technologies have matured. Carbon fibre composites make aircrafts stronger, lighter, more fuel efficient and cheaper to fly, and hence aerospace is the largest market segment for carbon fibre at 21%. The global carbon fibre market has grown at double digits over the last five years and is expected to continue growing but at a slower pace, increasing from 2008�s level of US$1.5 bln to US$2.5 bln in 2014, according to a Lucintel report.
Disposal of a composite structure at end of its service life becomes difficult. While landfills remain the least expensive option, most European Union (EU) member states, in 2004, passed laws forbidding landfill disposal of composites. Landfill option is not good due to non degradability of carbon thermosets and the health and safety risks they would create. End-of-Life Vehicle (EEEV) Directive adopted by EU member nations in November 2003 requires that 95% of each vehicle manufactured after January 2015 must be reused or recovered. Also it is not economical to dispose off carbon composites. They should be recovered for better economic benefits.
Carbon fiber recycling is driven by the financials, by government research incentives, and by the desire for manufacturers to have green manufacturing processes and products. There are some commercially available methods of recovering carbon fiber. These are Pyrolysis, Microwave radiation used to enhance pyrolysis, Fluidized Bed. These methods can, however, result in shortening of fiber length and some degradation of fiber resulting in reduction of properties of fiber. A research team at University of Nottingham from UK has developed a method of recovering carbon fiber in the near virgin state which would retain almost 100% of the fiber properties. An economical solvent system has been developed to dissolve epoxy resin from the composite leaving carbon fiber in purer form without breaking of the length. The research team has exploited the dissolving power of supercritical fluids, a class of solvent that has proved effective in other industries. They investigated supercritical water, carbon dioxide and a number of organic solvents including ethanol, methanol and acetone, before selecting finally propanol, an affordable short-chain alcohol that is reasonably benign in its normal state. Alcohols are interesting because they require only moderate pressure (2-7 MPa), albeit with high temperature (200-450�C), to go supercritical. This makes them more convenient to use than water, which requires a pressure of 22.1 MPa and temperature of 374°C to reach its critical point. Ethanol and methanol are effective in dissolving polyester resin in glass fiber composite, but do not work well with epoxy. Propanol (Propyl alcohol) can successfully break down epoxy. Tests carried out showed that recovered fiber had a high (up to 99%) of original strength & stiffness. The experiments so far have been done at the laboratory scale. More research work is needed to make this process commercial
Carbon fiber recycling offers a threefold environmental benefit: It prevents the waste of virgin carbon fiber in landfills after its first use, while components produced using the recycled fiber are recyclable, because carbon can retain a significant portion of virgin properties even after a second reclamation. Further, the recycling process itself significantly reduces energy costs.
(Source Courtsey : www.compositesworld.com)