Fraunhofer IAP is manufacturing bio-based carbon fibres with similar properties to those of petroleum-based fibres. The process relies heavily on a new ultra-high temperature oven.
At Fraunhofer IAP, bio-based fibres are graphitised from cellulose at a temperature of 2,900°C.
Fraunhofer IAP
The Fraunhofer Institute for Applied Polymer Research (IAP) has a new kind of oven that can use renewable materials to produce carbon fibres, whose strength and stiffness are sometimes close to those of conventional polyacrylonitrile-based (PAN) carbon fibres. To achieve this, scientists had a special ultra-high temperature oven built, in which the bio-based carbon fibres are post-treated for a few seconds at temperatures between 2,700°C and 2,900°C. In this temperature range, the carbon structures in the fibre are stretched so that they align along the fibre axis, making the fibres much stronger and stiffer.
A massive graphite tube inside of the oven serves as a heating element. Depending on the desired temperature, a current of up to 1,500 A is passed through it until it glows. The carbon fibre to be treated is continually transported through the tube and stretched in a precise way. An inert gas atmosphere protects both the oven and the fibre being transported through the tube from thermo-oxidative decomposition.
Carbon fibres are made from fibrous polymer precursors. According to Fraunhofer IAP, the mechanical properties of conventional carbon fibres from precursors based on cellulose, lignin or hemicellulose are very restricted, and therefore do not represent a serious alternative to their petroleum-based counterparts in high-performance applications.