Understanding the Differences Between Carbon Kevlar and Carbon Fiber: A Comprehensive Guide

Carbon Kevlar and carbon fiber are both high-performance materials widely used in various industries. While both offer impressive mechanical properties, they differ in their composition, structure, and specific applications. This article delves into the differences between these materials, providing a comprehensive overview that covers their composition, properties, and applications in detail.

Composition and Production

Carbon Fiber

Composition: Carbon fiber is primarily made from carbon atoms bonded together in a crystalline structure. It is typically produced through a process that involves heating polyacrylonitrile (PAN) or pitch to form carbon fibers. This process involves several steps, starting with the polymerization of acrylonitrile to form polyacrylonitrile (PAN), followed by heat treatments to further develop the material's properties.

Production Steps:

Polymerization: Acrylonitrile is polymerized to form polyacrylonitrile (PAN). This is depicted in and . Heat Treatment: The synthesis involves a heat treatment process, during which structural changes occur at different temperatures. This process is visualized in . Cyclization: Further chemical reactions, such as cyclization, occur at temperatures between 600 and 1300°C. This step is illustrated in .

Finalizing the Material: Further heat treatment at temperatures above 2000°C to 3000°C graphitizes the material. This is shown in .

Structure-Property Correlations: The structure of carbon fibers consists of a large number of graphite-like hexagonal carbon units organized in layers, with delocalized electrons contributing to electrical conductivity. The strength of carbon fibers is due to their layered structure, where covalently bonded carbon atoms in each layer interact through weak intermolecular forces (London dispersion forces), resulting in a significant internal force within the fibers. This is illustrated in .

Kevlar

Composition: Kevlar is a type of aramid fiber made from long-chain synthetic aromatic polyamide. The production involves polymerization and spinning into fibers. The basic polymer in Kevlar is formed by the reaction between a diacid and a diamine, with the most popular type being Nylon 66. In Kevlar, the monomers reacting with the diamine are aromatic, providing a significant difference from Aliphatic Nylon 66.

Synthetic Reactions:

Intermolecular Forces and Strength: Kevlar's strength is attributed to intermolecular interactions, particularly hydrogen bonding. These interactions are strong and can occur between H and O atoms as shown in . Additionally, the highly symmetric, almost linear polymer chains contribute to their strength. This is illustrated in .

Properties and Applications

Carbon Fiber: Carbon fiber excels in stiffness and weight, making it ideal for aerospace, automotive, and sporting goods applications. Its properties include high tensile strength, low thermal expansion, excellent fatigue resistance, and good chemical resistance.

Kevlar: Kevlar is renowned for its impact resistance and flexibility, making it suitable for applications such as bulletproof vests, helmets, and various protective gear. Its properties include high tensile strength, great impact resistance, excellent thermal stability, lightweight, and good abrasion resistance.

Carbon Kevlar: Carbon Kevlar is a composite material that combines carbon fiber and Kevlar fibers, leveraging the strengths of both materials. It offers improved toughness and reduced brittleness compared to pure carbon fiber. Carbon Kevlar is often used in applications requiring a balance of rigidity and impact resistance, such as in certain automotive parts, sporting goods, and aerospace components.

Summary and Table Comparisons

In summary, carbon fiber excels in stiffness and weight, while Kevlar is renowned for its impact resistance and flexibility. Carbon Kevlar combines these properties, making it suitable for specialized applications that require a balance of these characteristics.

FiberBulk StrengthPolymer TypeStrength FactorApplication Carbon FiberHighPAN or PitchExcellent mechanical properties for aerospace and automotive applications KevlarHighAromatic PolyamideExcellent impact resistance for protective gear and ballistic applications Carbon KevlarHighCarbon Kevlar FibersApplications needing a balance of rigidity and impact resistance

Table 1 below provides a more detailed comparison of the breaking strength properties of several fibers, including Kevlar, Nylon 66, and Nomex. As shown in the table:

Table 1: Breaking Strength Properties of Several Fibers

Fiber TypeBreaking Strength (N/den) KEVLAR7550 Nylon 662700 NOMEX6580

The table shows that Kevlar has a higher breaking strength than both Nylon 66 and Nomex. Additionally, the molecular structure of Nomex is very similar to Kevlar; the main difference is that the connections to the aromatic ring are in the "meta" position, resulting in less symmetry and decreased strength.

Further Reading

For a more complete comparison between Kevlar and carbon fiber, you may refer to the following resources:

Difference Between Kevlar and Carbon Fiber: Kevlar vs Carbon Fiber Comparing the Characteristics of Glass Fiber, Kevlar, Aramid, and Carbon Fibre