A critical review of carbon fiber and related products from an industrial perspective

Because of their exceptional mechanical properties, carbon fibers are being used in composite applications where weight saving is key such as in the aerospace and sports sector, with increasing demands coming from wind energy, aerospace and defense. However, an even more significant increase in demand in automotive is foreseen if the cost price of carbon fiber could come down substantially. In 2012 the US Department of Energy set a target price level of 10 USD/kg to get carbon fiber into mainstream cars. These low-cost carbon fibers should possess a tenacity of at least 1.7 GPa with a corresponding elastic modulus of 170 GPa. Carbon fibers are currently predominantly based on polyacrylonitrile (PAN) precursor fibers, while pitch is used for some high-modulus fibers. The cost price of PAN-based carbon fibers is determined for at least 50% by the PAN precursor. Consequently, over the last decade huge R&D programs have been undertaken in search of cheaper and more sustainable precursors such as lignin and polyethylene. Despite major efforts no significant commercial successes have been obtained up to now in stark contrast with numerous claims in the scientific literature regarding so-called breakthrough technologies. Next to the recent revival in carbon fiber research another carbon allotrope, the carbon nanotube (CNT), has received huge attention as the ‘next generation’ reinforcing element for composites. Fibers and yarns have been made directly from CNTs or have been added into other high-performance fibers to boost their properties. However, also here despite major research efforts and numerous high impact publications the results obtained were at best interesting or doubtful with little commercial success.