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How to Making Carbon Fiber

Tasuns Composite Technology Co.,Ltd | Updated: Jun 25, 2017

Did you know carbon fiber had its debut into the world as the filaments used in incandescent light bulbs?  Well, by baking cotton threads at very high temperatures, Thomas Edison made the first carbon fiber filament.  This was later replicated by Lewis Latimer in 1880.

light-bulb.jpg – Edison Light Bulb

70 years later, using a similar baking process, “high”-performance carbon fiber was manufactured by Union Carbide.  This version of carbon fiber only contained about 20% carbon and therefore had very low strength and stiffness properties. It wasn’t until 1963 that the potential of carbon fiber was better realized and advancements were made.  In the late 1960’s PAN-based carbon fibers were manufactured with 99% carbon.

The process used today can be summarized into three stages: stabilization, carbonization and graphitization.  The three steps are performed at increasing heat inputs performing critical processes that make carbon fiber the strong and light material that we know and love today.

Two types of polymer precursors can be utilized to make structural carbon fiber: Polyacrylonitrile (PAN) and Mesophase Pitch.  PAN degrades prior to melting causing it to loose the mechanical properties retained in Pitch.  Because pitch retains its properties approaching melting temperature its properties can be controlled during extrusion creating better properties in the final product.

pan.jpg – PAN Yarn

Before the precursors can be subjected to high temperatures they must be stabilized. The stabilization phase, also called oxidation, cross links the polymers to prevent relaxation and scission during the next step.  During stabilization the polymers are baked at 400 Deg F – 750 Deg F in air.

Carbonization is the second heating process the extruded Pitch or PAN goes through to become carbon fiber.  This process converts organic material into carbon fiber.  By heating the polymer the carbon atoms break their bonds with nitrogen and oxygen and form bonds with other polymers. This step takes place at 2,700 Deg F – 3,000 Deg F.

carbon-fiber-production1.png – Carbon Fiber Production Line

The final phase is graphitization. This step takes place at 4,500 Deg F – 5,500 Deg F in an inert atmosphere. During graphitization, the moleculare structure of the carbon bonds change to form “side-by-side” graphene sheets which merge to form columnar filaments.  Depending upon the temperature reached during carbonization and graphitization the manufacturer can alter the final mechanical properties like tensile strength and modulus of elasticity.

carbon-tow.png – Carbon Fiber Tows 

Keep an eye out for the next edition of Composites 101 to learn how these fibers get woven into the carbon fiber patterns we know and love!