Pre-oxidation Process of Polyacrylonitrile Based Carbon Fiber

Polypropylene is an important raw material for manufacturing carbobn fibers. Currently, 90% of carbon fibers are made from polypropylene, and pre-oxidation is a very important step. This process converts the original linear molecular chains into heat-resistand trapezoidal structures, which do not melt or ignite during high-temperature carbonization, maintaining the fiber morphology and obtaining high-quality carbon fibers.

During the pre-oxidation process, the color of polyprophlene fibers changes from white, yellow, and brown, gradually turning black. Complex chemical reactions occur on the surface and inside, including cyclization, dehydrogenation, and oxidation reactions. Uncyclic polymer chains or cyclic heterocycles can undergo dehydrogenation reactions due to the action of oxygen. In addition to deheydrogenation reactions, oxygen is also directly bound to the structure of pre-oxidized fibers.

The exothermic reaction is the main reaction in the pre-oxidation process, and the total amount of heat released can reach up to 1000kcal/kg. This heat must be dissipated immediately. If the temperature is too high, it will cause fiber fracture and production failure, so this is a critical technical issue. There will also be significant thermal shrinkage reactions during the pre-oxidation process. One reason is the shrinkage reaction of polypropylene precursor fibers themselves, and the other is chemical shrinkage during the cyclization process. In order to produce better performance carbon fibers from polypropylene precursor fibers, it is necessary to maintain the preferred orientaton of the molecular main chain structure towards the fiber axis. During the oxidation process, tession must be applied to the fibers and multi-stage stretching must be carried out.