Difference Between Kevlar and Carbon Fibre

The key difference between Kevlar and carbon fibre is that the Kevlar essentially contains nitrogen atoms in its chemical structure whereas the carbon fibre does not contain nitrogen atoms and mainly contains carbon atoms in its chemical structure.

Kevlar and carbon fibre are two forms of synthetic fibres. Both these materials have a high strength. Therefore, they have many applications in textile and other industries. Let us discuss more details on these materials.

1. Overview and Key Difference
2. What is Kevlar
3. What is Carbon Fibre
4. Side by Side Comparison – Kevlar vs Carbon Fibre in Tabular Form
5. Summary

What is Kevlar?

Kevlar is a strong synthetic fibre that has the chemical formula [-CO-C₆H₄-CO-NH-C₆H₄-NH-]_n. It is well-known for its heat resistance. This material is related to several other polymer compounds such as Nomex and Technora. In early times of its production, people used this material as a replacement for steel in racing tires. Manufacturers define this material as “five times stronger than steel” when we consider two equal portions of Kevlar and steel. This material is a super-strong plastic. We use two forms of monomers for the synthesis of this polymer material. The monomers are 1,4-phenylenediamine and terephthaloyl chloride. These monomers undergo condensation reactions. It yields a byproduct: HCl acid molecules.

Difference Between Kevlar and Carbon Fibre

Figure 01: Chemical structure of Kevlar

The resultant polymer has a liquid-crystalline nature. The solvent that the manufacturer used for this production is a mixture of N-methyl-pyrrolidone and calcium chloride. This production process uses concentrated sulfuric acid to keep the water-insoluble product (Kevlar) in the solution until the production ends. Therefore, this material is very expensive (because we use concentrated sulfuric for this production). This material has a high tensile strength, relative density, due to the intermolecular hydrogen bonds. The NH groups in this material form these hydrogen bonds. There are many uses of this material. For example, it is useful in producing bicycle tires, racing sails and bulletproof vests.

What is Carbon Fibre?

Carbon fibre is a synthetic fibre material these fibres have about 5-10 micrometer diameter. This material mainly contains carbon atoms. This material contains organic polymers which consist of long strings of molecules. These strings are held together by carbon atoms. Manufacturers mainly produce these fibres from polyacrylonitrile (PAN) process. In this manufacturing process, they draw the raw materials into long strands or fibres. Then they combine these strands with other materials to get desired shapes and sizes. In the PAN process, there are five main steps:

Spinning – Here, the mixture of PAN and other ingredients are spun into fibres. Then these fibres are washed and stretched.
Stabilizing – Here, we do chemical alteration for the stabilization of fibre.
Carbonizing – Here, we heat the stabilized fibre into very high temperatures. This forms tightly bound carbon crystals.
Treating the surface – Then we oxidize the surface of fibres to improve the properties.
Sizing – We use spinning machines to twist the fibres into different size yarns.

The applications of this material are in aerospace, civil engineering, military, and motorsports, etc. However, these fibres are relatively expensive than other fibre forms.

What is the Difference Between Kevlar and Carbon Fibre?

Kevlar is a strong synthetic fibre which has the chemical formula [-CO-C₆H₄-CO-NH-C₆H₄-NH-]_n. It essentially contains nitrogen atoms in its chemical structure. Moreover, it has hydrogen bonds. Carbon fibre is a synthetic fibre material and the fibres have about 5-10 micrometre diameter. It does not contain nitrogen and mainly contains carbon atoms in its chemical structure. These fibres are bound to each other via carbon atoms. This is the main difference between Kevlar and Carbon fibre.

Summary – Kevlar vs Carbon Fibre

Kevlar and carbon fibre are very important synthetic fibres. The difference between Kevlar and carbon fibre is that the Kevlar essentially contains nitrogen atoms in its chemical structure whereas the carbon fibre does not contain nitrogen atoms and mainly contains carbon atoms in its chemical structure.

Reference:

1. “Kevlar.” Wikipedia, Wikimedia Foundation, 3 July 2018. Available here
2. Johnson, Todd. “How Is Carbon Fiber Made?” ThoughtCo, ThoughtCo. Available here