An Overview of Kevlar Fiber
Abhijit R. Dhoke
JCT LTD. Phagwara, Punjab, India
Kevlar is the trade name of Dupont’s para-aramide fiber. The discovery of Kevlar Aramid fiber begins in1965. a DuPont research scientist synthesized a series of paraoriented aromatic polyamides.
Kevlar Aramid fiber was commercialized by DuPont in 1972. The word ‘Aramid’ is a generic term for a manufactured fibre in which the fibre forming substance is a long chain synthetic polyamide in which at least 85% of the amide linkages are attached directly to the two aromatic rings as defined by the U.S. federal trade commission. Kevlar fibre is based on poly (P-phenylene terephthalamide)
Aramid fibers are being considered for use in many structural engineering applications. Many of these would require knowledge of the long-term creep behaviour under constant loads. Creep tests at ambient conditions are considered to be the most reliable way of predicting the creep behaviour of
Aramid at the same time useful conclusions about the viscoelastic properties of the material can be made.
DuPont Kevlar Aramid fibre is used to make a variety of clothing, accessories, and equipment safe and cut resistant. It’s lightweight and extraordinarily strong, with five times the strength of steel on an equal-weight basis. Best known for its use in ballistic and stab-resistant body armor, Kevlar® brand Aramid fibre has shown its own heroism in helping to save the lives of thousands of people around the world.
The result Kevlar Aramid fibre is now successfully used in everything from vehicles and industrial clothing to fibre optics and city roads
What is Kevlar?
- Kevlar is an organic fiber in the aromatic polyamide family.
- Kevlar has unique combination of high strength, high modulus, toughness and thermal stability.
- It was developed for demanding industrial and advanced-technology applications.
- Currently, many types of Kevlar are produced to meet a broad range of end uses
- Higher tensile modulus than steel wire
- High breaking tenacity
- Very high kinetic energy absorption
- 4-5-time strength than steel
- It has a much higher tensile modulus than steel wire
- Low elongation to brake
- Low electric conductivity
- Low thermal shrinkage
PROCESS OF KEVLAR MANUFACTURING
P-phenylene diamine + terepthaloyl chloride
↓ (Condensation polymerization with lithium chloride with low temp)
Poly (p-phenylene terephthalamide) + HCL
Liquid crystal polymer (LCP)
Dry-Jet wet spinning2
Drawing at more than 300 ° c at 15-20 draw ratio
FDY or staple fibre of Kevlar
The two raw materials, p-phenylene diamine and terephthaloyl chloride will undergo low temperature polycondensation in alkyl amide solvent like dimethyl acetamide. The polymer from this reaction system is isolated by precipitation with water, neutralized and subsequently washed and dried.
The polymer and sulphuric acid solution will be subjected to dry-jet wet spinning for producing Kevlar fibre or filament yarns, the Kevlar polymer decomposes in heat before reaching melt temperature, so melt spinning is not used.
CHARACTERISTICS OF ARAMID FIBRES
Aramid fibres have unique properties that set them apart from other fibres. Aramid fibre tensile strength and modulus are significantly higher than those of earlier organic fibres and fibre elongation are lower. Aramid fibres can be woven on fabric looms more easily than brittle fibres such as glass, Carbon or ceramic. They also exhibit inherent resistance to organic solvents, Fuels, lubricants and exposure to flame.
Each type of aromatic polymer gives certain characteristic fibre properties. Because of its fibre and intrinsic polymer structure. Rather than going through an encyclopaedic description of the properties of the aromatic Polyamides, we propose in the following section to review some of the predominant studies that we believe are important in order to understand the unique properties of this class of fibre materials. The superimposed structures, such as the crystallites, the fibrils and the skin-core boundaries are definitely unique attributes that can be partially tailored through the fibre process engineering. This is worth examining in more detail. It is equally important to provide more insights into the pleated structure and the formation of the hydrogen bonds acting as zippers between the chains.
DIFFERENT TYPES OF KEVLAR
- Kevlar – Tire cord yarn
- Kevlar 29 – Multipurpose yarn
- Kevlar 49 – High modulus yarn
- Kevlar 68 – Moderate modulus yarn
- Kevlar 100 – Coloured yarn
- Kevlar 119 – High elongation yarn
- Kevlar 129 – High tenacity yarn
- Kevlar 149 – Ultra high modulus yarn
Kevlar fibre and filament come in a variety of types, each with its own unique set of properties and performance characteristics for different protection needs.
The original family of product types of Kevlar having similar tensile properties with many decitex and finishes. These yarns are used in ballistic applications, ropes and cables, protective apparel such as cut-resistant gloves, in life protection uses such as helmets, vehicular armoring and plates, and as rubber reinforcement in tires and automotive hoses.
High modulus type used primarily in fiber optic cable, textile processing, plastic reinforcement, ropes, cables, and composites for marine sporting goods and aerospace applications.
Producer colored Kevlar yarns, used in ropes and cables, tapes and strappings, gloves and other protective apparel, and sporting goods.
Higher elongation, flexible fatigue-resistant yarn types found in mechanical rubber goods, such as tires, automotive belts and hoses.
Lightweight, high-performance, and high tenacity type of yarns used in motorcycle racing gear, life protection accessories, ropes and cables, and high-pressure hoses used in the oil and gas industry.
Woven into fabric meeting performance requirements for helmets and vests for military and high-performing UDs for spall liners.
Kevlar KM2 plus
High tenacity, high toughness, finer decitex fiber used in vests and helmet for both military and enforcement officers.
Kevlar AP for advanced performance dramatically improves cost-effectiveness and design flexibility to help manufacturers build learner, more robust consumer and industrial products.
PROPERTIES OF KEVLAR FIBER
Kevlar Aramid fibre has a high breaking tenacity, which is several times that of steel wire; it also, has a much higher tensile modulus than steel wire, fibre glass. Kevlar fibre is inherently stable at relatively at relatively high temperature and has very small shrinkage at elevated temperature, low creep and high glass transition temperature. It is corrosion resistant, non-conductive and resistant to most chemicals except strong acids and bases. The typical properties of Kevlar Aramid fibre yarns are shown in table-4.
|Yarn properties||Kevlar and Kevlar 29||Kevlar 49||Kevlar 68||Kevlar 119||Kevlar 129||Kevlar149|
|Tensile strength gpd||23||23||23||24||26.5||18|
|Initial modulus gpd||550||950||780||430||750||1100|
APPLICATIONS OF KEVLAR FIBER
Brake pads made of Kevlar pulp are better equipped to withstand the wear and tear that friction creates with their enhanced thermal stability and inherent abrasion resistance; reinforced brake pads made of Kevlar are designed for long life and safe, quite braking.
Due to its chemical and thermal stability, reinforced made of Kevlar helps make gaskets strong and durable.
Kevlar is also effective in clutches, which are subject to severe frictional stress. Tests have shown that clutch linings with Kevlar do not require service or replacement as often as standard clutch linings.
Kevlar provides an effective, lightweight armor solution that helps protect against ballistic attack, allowing cars and light trucks to retain most of their original handling characteristics while stopping multiple rounds. Law enforcement agencies, cash security companies and people who live or work in hostile environments trust Kevlar armor to help increase security in vehicles where weight is a critical factor.
Kevlar reinforcement helps reduce weight without compromising strength in marine, energy, and maritime vessel composite
Armor systems of Kevlar Aramid fiber are designed for the protection of human lives and vital equipment against ballistic threats, the ballistic resistance of Kevlar Aramid can be attributed to its excellent thermal properties, high crystalinity, highly oriented fine structure and high tensile properties. The high glass transition temperature and thermal stability of Kevlar fibre ensure the integrity of ballistic structure at relatively high temperature in a ballistic event.
Aerospace, Marine, & Rail
DuPont Kevlar helps manufacturers in aerospace, marine, and rail industries to build aircraft, ships, and rail carriages. Le performance characteristics of Kevlar® and can help to increase fuel efficiency and decrease operating and maintenance costs.
Automotive Components Reinforcements
Kevlar fibers help to improve the safety, performance, and durability of automotive components for a wide variety of vehicles, from passenger cars and light trucks to professional race cars. Kevlar help provide inherent strength in automotive components, inside and out.
Automotive Hoses & Belts Reinforcements
DuPont Kevlar fiber helps improve the safety, performance, and durability of automotive components such as automotive hoses and automotive belts for a wide variety of vehicles, from passenger cars and trucks to professional race cars
Kevlar® provides high tensile strength, helping to safeguard fibre optic cables against mechanical stresses to ensure optimal performance. Learn how the inherent dielectric properties, light weight, small diameter, and flexibility of Kevlar® meet requirements for a wide variety of fibre optic cable applications.
Kevlar fiber is a very important part of the military’s assets. By incorporating its inherent protective technology into military helmets, it has helped to save thousands of lives.
Ropes & Cables
Kevlar ropes and cables help deliver performance and value to customers in the fine gauge cable industry by helping to provide excellent robustness, fatigue resistance, shrinkage, and durability. From land to sea to space, learn how Kevlar brand fibre has helped strengthen ropes and cables to stand up to temperature extremes and harsh environments.
Sporting Goods Apparel & Accessories
The quest for lighter, stronger, and safer sporting goods has made Kevlar® a popular choice for both equipment manufacturers and consumers. Learn how the same properties and performance attributes that have proven so effective in industrial and life-protection applications also appeal to athletes, outdoors enthusiasts and anyone else looking for better performance in sports products.
This research indicates that you can enjoy the superior protection and long wear life of protective clothing made of KEVLAR without undue concern about the effects of heat and heat stress.
The lighter weight of KEVLAR fabrics makes them less likely to cause heat stress in hot, humid environments than other heavier fabrics.
- High performance fibres by J.w.s. Hurl
- High Performance And High Temperature Resistant Fibers- Emphasis on Protective Clothing, William C. Smith, ITA, Greer, SC 9/21/99
- Viscoelasticity of Kevlar 49 fibres Ioannis P. GIANNOPOULOS1, Chris J. BURGOYNE2
- Du Pont (1991). “Data manual for fibre optics and other cables”, E. I. Du Pont de Nemours and Co. (Inc.).
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.