Aramid fibers are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic-rated body armor fabric and ballistic composites, in bicycle tires and engine drive belts. The name “aramid” is a portmanteau of “aromatic polyamide”. Aramid fibers are synthesized from aromatic monomers that contain amino groups attached directly to two aromatic rings. Because the best-known aramids contain phenylene groups, they are generally called poly(p-phenylene terephthalamides).
Aramid fibers are commonly used in ballistic-rated body armors, cut-resistant gloves for industrial safety, military vehicles and aircraft, fiber-optic cables, ballistic fabric, and welding apparel due to their high temperature resistance and strength. They also find major application as reinforcement in automobile tires, conveyor belts, and brake pads in automobiles. It has been estimated that over 50% of aramid fiber produced is used in reinforcement applications.
Types of Aramid Fiber
Aramid fibers are categorized based on their chemical composition and properties. The two most commonly known types are:
Other examples include Twaron and Technora. Kevlar fibers are 5 times stronger than steel on an equal weight basis and have very high thermal stability. Due their high tenacity, para-aramids find application in bulletproof vests, cut-resistant gloves, fiber-reinforced plastics, auto brake pads, cables and other high-performance applications requiring cut, abrasion, and heat resistance.
Meta-aramid fibers, also known as MPTA fibers, are based on poly(m-phenylene isophthalamide) monomers. Compared to para-aramids, meta-aramids are not as strong but they are generally more elastic and tolerant to heat deformation. Examples include fibers marketed under the trade names Teijinconex, Conenxx, and Twaron. Meta-aramids are used in applications requiring greater flexibility and heat resistance like heat insulation, engine components, adhesive films and thermosetting laminates.
The manufacturing process of aramid fibers typically involves the following key steps:
The first step involves polymerization reaction to synthesize organic aromatic monomers containing amino groups attached to aromatic rings. For para-aramids like Kevlar, p-phenylenediamine and terephthaloyl chloride are reacted under controlled conditions.
Next, the monomers are polymerized into long chains or polymers through polycondensation reaction in a solution. For Kevlar, the polymer formed is poly(p-phenylene terephthalamide).
Spinning into Fibers
The spinning processconcentrates and aligns the linear polymer chains through extrusion. The concentrated polymer solution is spun through a spinneret into air or liquid to form fibers. The fibers solidify through evaporation or quenching.
Drawing and Winding
The as-spun fibers are drawn or stretched to further align the polymer chains along the fiber axis for optimum strength and properties. After drawing, the high strength fibers are wound onto packages.
The fiber packages may undergo additional processing like sizing, heating or chemical treatments to impart specific properties before final conversion into high performance materials, fabrics or components.
Properties and Advantages
Aramid fibers have several remarkable properties that have made them popular industrial materials:
– High tensile strength: They have tensile strength exceeding even steel and high performance plastics. Kevlar-29 has tensile strength of 3.6GPa.
– Low specific gravity: Though very strong, aramid fibers are light in weight with specific gravity around 1.45, much lower than steel.
– Heat resistance: They have excellent heat resistance up to 650°F due to their stable polymer structure.
– Chemical resistance: They retain properties in acidic or alkaline environments where other fibers deteriorate.
– Non-conductivity: Aramid fibers are generally non-conductive making them suitable for applications involving handling of electricity or static charges.
– Abrasion resistance: Their molecular chain structure makes them resistant to abrasive wear and cutting.
– Flexural rigidity: Aramid composites exhibit good flexural rigidity for lightweight applications needing dimensional stability.
– Processability: Aramid fibers can be easily converted into woven fabrics, tapes or non-woven mats and processed further for end use applications.
In summary, aramid fibers have revolutionized a number of industries with their versatile properties and characteristics. Their high strength, heat and cut resistance makes them ideal candidates for protective fabrics, ballistic applications and high performance reinforcement in advanced composites. The growth of aramid fiber market is expected to accelerate further with the expansion of automotive, aerospace and defense sectors in developing nations, and development of lighter and stronger materials. Continued research is also enhancing properties and exploring of new application areas for these super fibers.
1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it