UTSI Fiber Spinning Process
Low cost, pitch-based carbon fiber has already been developed and demonstrated in the UTSI’s spin lab. The UTSI carbon fiber spinning processes include the following steps:
Pitch precursor properties and identified softening point temperatures as one of the most important parameters to be controlled. The specific mesophase pitch used in the Lab is from ConocoPhillips (COP).
Pitch Fiber (Green Fiber) Spinning
The fiber spinning device comprises a filament former, such as a spinning pack where exit orifices forms filaments, a venturi adjacent the capillaries or spinneret that receives the filaments from the spinning pack, a diffuser downstream of the venturi that receives the filaments, one or more air exhaust ports that create in the diffuser an airflow having a direction normal to the direction of flow of the filaments, and a fiber collection bed or a spool winder that receives the filaments. The bed may comprise of a moving screen belt.
The device is equipped with various air supplies: 1- Primary gas supply provides gas around the fi1ament at the exit of the capillary or spinneret. The primary gas is comprised of a pair of opposing gas streams in the spinning pack. 2- Secondary gas supply which is comprised of a symmetric gas supply ducts having flow straighteners and openings on opposing sides of the filament. The diffuser has a contour increasing in width from its throat in both directions. The filaments are attenuated, cooled from a liquid state to a solid state in the spinneret neighborhood and the venturi.
This process includes devolitization and stabilization under oxidative atmosphere. Oxidative stabilization is an important step to avoid softening and melting of carbon fibers at higher temperatures. This step is time extensive, possibly taking several hours and forms a major part of the total energy costs and a time consuming component of continuous processing of fibers.
Important parameters involved in the oxidation process includes: 1) final oxidation temperature, 2) rate of heating and the total time taken for oxidation, 3) softening point of mesophase pitch and the green fiber, and 4) concentration of oxidant.
This step is to remove non-carbon elements from the stabilized pitch fiber. During carbonization, fibers are heated in inert atmosphere and volatiles such as the pitch solvent, H2O, CO2, CO and H2 evolve. The heating rate is very critical and has to be slow enough to limit the rate of mass transfer which otherwise could result in to surface irregularities.