Carbon Fibers in Plastic Materials

The use of carbon fibers in plastic materials has a long history.  As early as 1879, Thomas Edison was experimenting with carbon fibers made from cotton threads and bamboo slivers.  In fact, the first incandescent light bulb heated by electricity contained carbon fibers. 

In the 1960’s, Dr. Akio Shindo at the Agency of Industrial Science and Technology in Japan developed a carbon fiber based on polyacrylonitrile (PAN).  The resulting fiber contained 55% carbon.  

The PAN-based conversion process quickly became the primary method for producing carbon fiber.  Ninety percent of carbon fibers today are made from polyacrylonitrile (C3H3N)n  or PAN a synthetic, semi-crystalline organic polymer resin.  The remaining 10% are made from rayon or petroleum pitch. Fibers made from PAN are extremely strong and light. These fibers are bound by thermoset or thermoplastic polymers such as polyester, vinyl ester or nylon to make carbon fiber reinforced plastic, or carbon FRP. 

Adding Carbon Fiber to a Polymer Has Many Benefits

Tensile strength and flexural modulus are increased as is the heat deflection temperature or HDT.  Additionally, adding carbon fiber reinforcement diminishes shrinkage and warping.  

Each carbon fiber is a long thin strand made up of thousands of carbon filaments. A single fiber is about 5-10 μm in diameter and composed mostly of carbon.  Microscopic crystals in the carbon bond together in a structure that is more or less aligned parallel to the long axis of the fiber.  It is this alignment of crystals that make the fibers so strong.  

Classified by Tensile Modulus

Carbon fibers are classified by the tensile modulus* of the fiber.  The tensile modulus may range from 34.8 million psi to 72.5-145.0 million psi.  Steel has a tensile modulus of 29 million psi thus the strongest carbon fiber is five times stronger than steel.

“Low” modulus fibers have a tensile modulus below 34.8 million psi (240 million kPa). Fibers are also classified in ascending order of tensile modulus as “standard modulus,” “intermediate modulus,” “high modulus,” and “ultrahigh modulus.” Carbon fibers with a classification of ultrahigh modulus have a tensile modulus of 72.5-145.0 million psi (500 million-1.0 billion kPa).

Spinning, Stabilizing, Carbonizing, Surface Treatment and Sizing 

The manufacturing process for carbon fiber is partly chemical and partly mechanical.

  • Spinning:  The PAN is spun using one of a few spinning processes.  This step is important because it forms the internal atomic structure of the fiber.  The fibers are then washed and stretched to the required diameter.  The stretching also helps align the molecules to aid in the formation of the carbon crystals created by carbonization.
  • Stabilizing: In this step the fibers are treated with chemicals to change their linear bonding to a thermally stable ladder bonding structure.  The filaments are then heated in air so they pick up oxygen molecules and change their atomic bonding pattern.
  • Carbonizing: The fibers are then exposed to very high heat without oxygen present so the fiber cannot burn.  The atoms in the fiber vibrate violently expelling most of the non-carbon atoms in the precursor.  
  • Surface Treatment:  After carbonizing, the surface of the fibers does not bond well with the materials used in making composite materials.  In this step, the surface of the fibers are slightly oxidized by immersion in various gases or liquids.
  • SizingIn this process, the fibers are coated to protect them from damage during winding or weaving.

A few products made from carbon fibers are fishing rods, bicycles, golf equipment, tennis rackets, parts for aircrafts, bridges, and automobiles. 

*Tensile modulus is how much pulling force a fiber of a certain diameter can exert without breaking. Tensile modulus is described by pound per square inch or psi. 

Questions?  Let me know in the comments section below.

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6 responses to “The Rise of Carbon Fiber Reinforced Plastics

  1. Do you make a product for applying the product to the underside of a 6″ wide concrete beam to give it extra strength? Application would be under the beam using an epoxy ‘glue’. Beam spans 60 ft.

    1. Ted,
      Sorry, but our expertise is in machining and molding small plastic components. I’m not familiar with the type of product you refer to, but would suggest you research “concrete” or call a local concrete vendor.

  2. Hello! I should have come to this website a long time ago but here I am now and I think I could be well served to seek your advice. Without being specific right here, I want to form a horizontal fish-hook design more or less the neck of the hook would lie on the ground and a person might sit on the rounded edge where the hook would be (not) but the sitting part would have to be “flexible” so as to support a human up to 300# in weight. The straight part on the ground would be maybe 6′ in length from end of the rounded hook part to the front tip. The rounded end and seat (hook would flex). Can a form be made satisfying this idea?

    1. Will – Thanks for reading the Craftech Industries’ blogs. Could you forward a drawing of your device? That would give us a much better idea of what you need to accomplish.

  3. Hello from Wash. DC….. few questions….Great Blog by the way!

    1. What’s the customary ratio of Carbon Fiber to Plastic when making “CFRP”….70% carbon fiber to 30% plastic. etc.

    2. Retail cost per ton of CFRP vs. 100% Carbon Fiber

    3. Strength comparison of CFRP vs. 100% Carbon Fiber

    Thanks for your help on this…..Alex

    1. Hi Alex – Thanks for reading the Craftech Industries’ blogs! Carbon fiber can be added to plastic from 10 to 60% to our knowledge. The cost of carbon fiber is prohibitive compared to the cost of using it in plastic, and this is one reason it is reserved for very critical applications – such as aeronautical uses. I’m not sure what the going cost of carbon fiber is since we don’t buy it. Even as an additive to plastic, it is more expensive than glass fiber material, which is commonly used to strengthen resin. While carbon fiber has a high tensile strength, it is also brittle, so analyzing the exact requirements of the application is critical. Good luck!

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