Kevlar fabric | Properties, Types, Applications | Kevlar synthesis process

 

Kevlar fabric

Kevlar fabric is a heat-resistant and strong synthetic fiber fabric that is related to other aramids like Nomex and Technora. It was developed by Stephanie Kwolek in Dupont in 1965 and this high-strength material was used commercially in the early 1970s as a replacement for steel in race tires. It is generally spun into ropes or fabric sheets that can be used as an ingredient in composite material components.

Polish-American chemist Stephanie Kwolek, while working at Dupont, feared a shortage of gasoline when she discovered a poly-para phenylene terephthalamide (K29) branded Kevlar. In 1964, her team began looking for new lightweight strong fibers for lighter, but stronger tires. The polymers he was working with at the time, poly-p-phenylene-terephthalate and polybenzamide, formed liquid crystals during that solution, which was unique to the polymers of that time.

Kevlar fabric has many applications that are ranged from bicycle tires and racing sails to bulletproof vests, due to its high strength-to-weight ratio. For this reason, it is five times stronger than steel items. It is used to make modern marching drumheads that resist high impact. It has been also used for mooring lines and other underwater applications.

Properties of Kevlar fabric

i. Kevlar fabric is a heat-resistant and very strong synthetic fiber fabric

ii. It has high tensile strength, which is five times stronger than steel.

iii. It is a high modulus of elasticity;

iv. It is very low elongation up to breaking point;

v. It is low weight fabric;

vi. It has high chemical inertness;

vii. It is a very low coefficient of thermal expansion;

viii. It has high fracture toughness;

ix. It has high cut resistance;

x. It has textile processability power

xi. It has flame resistance ability.

Kevlar synthesis process

Kevlar fabric is synthesized in a solution by producing hydrochloric acid as a byproduct from monomers 1,4-phenylene-diamine and terephthaloyl chloride in a condensation reaction. The resulting liquid-crystal behavior and mechanical drawing are in the polymer chains on the fiber side. At the initial time, hexamethylphosphoramide was the solvent used for polymerization, but for protection, Dupont replaced it with a solution of N-methyl-pyrrolidone and calcium chloride. Since this process was patented by Akzo in the production of Twaron, the patent war ensued. Kevlar production is expensive because of the inconvenience caused by using concentrated sulfuric acid, which needs to be kept in a water-insoluble polymer solution during synthesis and spinning.

Types of Kevlar

i. Kevlar K-29 – It is used for industrial purposes, such as cables, asbestos replacement, tires, and brake linings.

ii. Kevlar K49 – It has a high modulus that is used in cable and rope products manufacturing.

iii. Kevlar K100 – It is a colored version of Kevlar that is used in ropes and cables, tapes and strappings, gloves, and other protective apparel, and sporting goods manufacturing.

iv. Kevlar K119 – It is higher-elongation, flexible, and more fatigue resistant

v. Kevlar K129 – It has higher tenacity for ballistic applications

vi. Kevlar K149 – It is the highest tenacity for ballistic, armor, and aerospace applications

vii. Kevlar AP – It has a 15% higher tensile strength than K-29 type Kevlar.

viii. Kevlar XP – It is a lighter weight resin and KM2 plus fiber combination

ix. Kevlar KM2 – It is enhanced ballistic resistance for armor applications.

Applications of Kevlar products

i. Kevlar is used in cryogenics for lower thermal conductivity and higher strength than other materials for suspension purposes.

ii. To reduce any heat leakage in paramagnetic elements it is mostly used to suspend the perimeter of paramagnetic salts from a superconducting magnet mandrel.

iii. It is used as a thermal standoff or structural support where low heat leakage is needed.

iv. It is used in personal armor like combat helmets, ballistic face masks, and ballistic vests.

v. It is used to make gloves, sleeves, jackets, chaps, and others for protecting users from cuts, abrasions, and heat.

vi. Kevlar sail is used for high-performance racing boats.

vii. It is also used as -an inner lining for some bicycle tires, shoelaces, musical instruments, non-stick frying pans, and smartphone backplate making.