Yaa Aramid Fibers - An Overview

Aramid Fibers-An Overview

Muhammad Imteaz Anjum
School Of Textile And Design
University Of Management And Technology Lahore, Islamic Republic of Pakistan
Email:- anjum5270@gmail.com
Cell: +92332-2424424

Introduction
All fibers used inwards polymer technology scientific discipline composites tin live divided into ii categories, namely synthetic fibers in addition to natural fibers. Synthetic fibers are the most common. Although in that location are many types of synthetic fibers, glass, carbon in addition to aramid fibers stand upwards for the most important.Kevlar is an aromatic polyamide or aramid fiber introduced inwards early on 1970s past times DuPont. It was the outset organic fiber amongst sufficient tensile strength in addition to modulus to live used inwards advanced composites. It has roughly 5 times the tensile strength of steel amongst a corresponding tensile modulus. Originally developed equally a replacement for steel inwards radial tires, aramid is immediately used inwards a broad arrive at of applications. It is a merchandise call of aramid fiber. (vigotsky, 2002)

Definition
The U.S. Federal Trade Commission gives a expert definition of an aramid fiber equally "a manufactured fiber inwards which the fiber forming core is a long chain synthetic polyamide inwards which at to the lowest degree 85% of the amide linkages are attached straight to ii aromatic rings. (comparison of aramid fibers, 2003)

History
First fourth dimension aramid fibers commercially introduced past times an American companionship DuPont inwards 1960 amongst merchandise call of Nomex. These Nomex fibers was good known due to their expert thermal in addition to electrical insulations properties. In 1971 DuPont introduced a much higher tenacity in addition to modules fiber amongst merchandise call of Kevlar. Scientists inwards the fields of liquid crystals, polymers, rheology in addition to fibre processing, equally good equally procedure in addition to scheme engineers, spent several years prior in addition to during the early on phase of its marketplace seat introduction establishing the basics in addition to telephone commutation agreement necessary to accept total wages of this novel grade of high-performance materials. (Hearle, 2001)

Basic Structure in addition to chemic composition of aramid fibers

Tho monomers of aramid fibers are consist of 1,4-phenyl-diamine (para-phenylenediamine) in addition to terephthaloyl chloride. The consequence is polymeric aromatic amide amongst altering benzene band in addition to amide groups. When they produced these polymer strand aligned randomly. Technically, aramid fibers are long-chain synthetic polyamides. Aramid fibers take keep extremely high tensile strength, which is why they are commonly used inwards armor in addition to ballistic protection applications. With a distinctive xanthous color, aramid fibers are oft used inwards advanced composite products which require high-strength in addition to light-weight properties.

The chemic composition of aramid is poly para-phenyleneterephthalamide (PPD-T) in addition to it is to a greater extent than properly known equally a para-aramid. It is oriented para-substituted aromatic units. Aramids belong to the identify unit of measurement of nylons. Common nylons, such equally nylon 6,6 practice non take keep real expert structural properties, in addition to thus the para-aramid distinction is important. Aramid fibers similar Nomex or Kevlar, however, are band compounds based on the construction of benzene equally opposed to linear compounds used to brand nylon. The aramid band gives thermal aramid stability, spell the para construction gives it high strength in addition to modulus. Like nylons, aramid filaments are made past times extruding the precursor through a spinneret. The rod shape of the para-aramid molecules in addition to the extrusion procedure brand Kevlar fibers anisotropic--they are stronger in addition to stiffer inwards the axial management than inwards the transverse direction. In comparison, graphite fibers are also anisotropic, but drinking glass fibers are isotropic.

Figure1: Chemical composition of Kevlar

It is made from a condensation reaction of para-phenylene diamine in addition to terephthaloyl (PPD-T) chloride. The resultant aromatic polyamide contains aromatic in addition to amide groups which makes them stiff rod similar polymers. The stiff rod similar construction results inwards a high drinking glass transition temperature in addition to hapless solubility, which makes fabrication of these polymers, past times conventional drawing techniques, hard Instead, they are melt spun from liquid crystalline polymer solutions equally described later. The Kevlar fiber is an array of molecules oriented parallel to each other similar a bundle of uncooked spaghetti. This orderly, untangled organization of molecules is described equally a crystalline structure. Crystallinity is obtained past times a manufacturing procedure known equally spinning, which involves extruding the molten polymer solution through minor holes.

When PPD-T solutions are extruded through a spinneret in addition to drawn through an air gap during fiber manufacture, the liquid crystalline domains tin orient in addition to align inwards the time period direction. Kevlar tin larn a high grade of alignment of long, straight polymer chains parallel to the fiber axis. The construction exhibits anisotropic properties, amongst higher strength in addition to modulus inwards the fiber longitudinal management than inwards the axial direction. The extruded stuff also possesses a febrile structure. This construction results inwards hapless shear in addition to compression properties for aramid composites. Hydrogen bonds shape betwixt the polar amide groups on side past times side chains in addition to they agree the private Kevlar polymer chains together [8]. It is shown equally inwards the next figure:

Figure 2: Hydrogen bonds shape betwixt the polar amide groups (A history of torso armour-bullet proof vasts, 1993)

Types of aramid fibers
There are ii chief types of aramid fibers.

1. Meta- aramid
2. Para- aramid

The term meta in addition to para refers to the location of chemic bonds inwards the construction of aramid fibers. The chemic bonds of a para-aramid fibers are to a greater extent than aligned inwards the long management of the fibers. The meta-aramid fibers are non aligned they are inwards zigzag blueprint in that location for they are non developed the higher tensile strength of the para-aramid bonds.

1. Meta-aramid
Fibers made from the meta aramid take keep the splendid thermal, chemic in addition to radiations resistance in addition to are brand the give notice retardant textiles such equally outer have on for give notice fighters in addition to racing auto drivers. Nomex in addition to teijiconex are examples of meta aramids.

2. Para-aramids
Fibers which are made from the para-aramid take keep higher strength. These are to a greater extent than commonly used inwards fibers reinforcement plactics for civil technology scientific discipline structures, Stress peel panels, in addition to other highly tensile strength applications. Kevlar in addition to technora are instance of para-aramid fibers. (Hearle, 2001) (Properties of Aramid Fibers, 2015)

Different merchandise call of aramid fibers
Aramid fibers are available amongst unlike merchandise names. There properties are create upwards one's hear past times the manufacturing process, atmospheric condition inwards which fibers are prepared in addition to destination uses. Different merchandise names of aramid fibers are Kevlar, Technora, Tawron, Nomex etc. (Aramid Fibers, merchandise names)

Manufacturing Process of aramid fibers
The polymer poly-metaphenylene isophthalamide is used to brand meta- aramids in addition to the polymer p-phenylene terephthalamide to brand para-aramids. Because the aramids decompose earlier they melt they are produced past times wet in addition to dry out spinning methods. Sulphuric acid is the normal solvent used inwards the spinning processes. In wet spinning a potent solution of the polymer, which also contains inorganic salts, is spun through a spinneret into weak acid or water. In this bathroom the salts leach out. In the dry out spinning procedure the salts are to a greater extent than hard to take in addition to this procedure is only used to make the weaker meta-aramid fibres. In both processes post handling of the fibres past times additional drawing is used to optimise fibre properties. Aramid products are available equally filament yarn, staple fibre or pulp. (Aramid fibers manufacturing method)

(Man-made Fibres, 2015)

Characteristics of Aramid Fibers

Fiber Structure
In aramid fibers a serial of synthetic polymers inwards which repeating units take keep large phenyl rings are linked together past times amide groups. Amide groups (CO-NH) shape potent bonds that are resistant to solvets in addition to heat. Phenyl rings are bulky six-sided groups of carbon in addition to hydrogen atoms that forestall polymer chains from rotating in addition to twisting around their chemic bonds.

Fiber Properties
Aramid fibers take keep medium to ultra-high strength, medium to depression elongation in addition to moderately high to ultra-high modulus amongst the densities ranging from 1.38g/cm3. Heat-resistant in addition to flame-retardant fibers comprise high proportion or meta-oriented phenylene rings, whereas ultra-high strength high-modulus fibers comprise mainly para-oriented phenylene rings.

Chemical Properties
All aramids comprise amide links that are hydrophilic. However, non all aramid products absorb the same moisture. The PPD-T (poly-phenylene terephathalamide) fiber has real expert resistance to many organic solvents in addition to salt, but potent acids tin drive substantial loss of strength. Aramid fibers are hard to dye due to their high Tg. Also, the aromatic nature of para-aramid is responsible for oxidative reactions when exposed to UV light, that leads to a alter inwards color in addition to loss of some strength.

Themal Properties
Aramid fibers practice non melt inn the conbentional feel but decompose simultaneously. They give notice only amongst difficulty because of express oxygen Index values. It should live mentioned that at 300 degrees celcius some aramid types tin soundless retain well-nigh 50% of their strength. Aramid fibers present high crystallinity which results inwards negligible shrinkage at high temperature.

Mechanical Properties
Aramid yarn take keep breaking tenacity of 3045 MPa, inwards other words to a greater extent than than 5 times than this steel (under water, aramid is iv times stronger) in addition to twice than this of drinking glass fiber or nylon. High strength is consequence of its aromatic in addition to amide grouping in addition to high crystallinity. Aramid retains strength in addition to modulus at temperatures equally high equally 300 degrees celcius. It behaves elastically nether tension. When it comes to severe bending, it shows non-linear plastic deformation. With tension fatigue, no failure is observed fifty-fifty at impressively high loads in addition to wheel times. Creep strain for aramid is only 0.3%.

To amount up, aramid full general characteristics are:

• v High strength
• v Resistance to absorption
• v Resistance to organic solvent
• v Good chemic resistance
• v No electrical conductivity
• v No melting betoken depression flammability
• v Excellent heat, in addition to cutting resistane
• v Sensitive to acids in addition to ultraviolet radiations (ARAMID FIBER CHARACTERISTICS, 2015)

Advantages of aramid fibers
Aramid chief advantages are high strength in addition to depression weight. Like graphite, it has slightly negative axial coefficient of thermal expansion, which agency aramid laminates tin live made thermally tabular array inwards dimensions. Unlike graphite, it is real resistant to touching in addition to abrasion damage. It tin live made waterproof when combined amongst other materials similar epoxy. It tin live used equally a composite amongst condom retaining its flexibility. High tensile modulus in addition to depression breakage elongation combined amongst real expert resistance to chemicals larn far the correct pick for unlike composite structural parts inn diverse applications.

Disadvantages of aramid fibers
On the other hand, aramid fiber has a few disadvantages. The fibers assorb moisture, in addition to thus aramid composites are to a greater extent than sensitive to the surroundings than drinking glass or graphite composites. For this reason, it must live combined amongst wet resistance materials similar epoxy systems. Compressive properties are ralativly hapless too. Consequently, aramid fiber is non used inwards duet edifice or whenever this manly soul monarch of resistance inwards needed. Also, aramid fibers are hard to cutting in addition to to grind without special equipments ( e.g special pair of scissors for cutting, special drill bits). Finally, aramid endure some corrosion in addition to are degradated past times UV light. For this argue they must live properly coated. (ADVANTAGES - DISADVANTAGES, 2015)

Key Applications of Aramid Fibre

• Some applications for aramid fibres are listed below. It is normally used equally fibre reinforcement for polymer matrix composites.
• Ballistic protective applications such equally bullet proof vests
• Protective wearing clothing such equally gloves, motorbike protective habiliment in addition to hunting gaitors, chaps in addition to pants.
• Sails for sailboats, yachts etc
• Belts in addition to hosing for industrial in addition to automotive applications
• Aircraft torso parts
• Boat hulls
• Fibre eye in addition to electromechanical cables
• Friction linings such equally clutch plates in addition to brake pads
• Gaskets for high temperature in addition to pressure level applications
• Adhesives in addition to sealants (Aramid Fibre ( Kevlar / Twaron ) – Properties in addition to Applications, 2015)

Comparison of aramid fiber amongst other high functioning fibers

*** Aramid fibers take keep High Strength to Weight Ratio
Force per unit of measurement surface area at failure / Density = is the Strength to Weight ratio of this material. Kevlar is real potent in addition to is slightly stronger than Carbon Fiber per unit of measurement weight.

MATERIAL	Strength to weight KN.m/kg.	Ultimate Strength MPa	Density g/cm3
Spectra fiber (UHMWPE)	3619	2300-3500	.97
Kevlar (ARAMID)	2514	2757	1.44
Carbon Fibre	2457	4137	1.75
Carbon laminate	785	1600	1.5
E Glass Fibre	1307	3450	2.57
E Glass laminate	775	1500	1.97
Polypropylene	89	19.7-80	.91
S Glass Fibre	1906	4710	2.47
Spider Silk	1069	1000	1.3
Balsa axial load	521	83	.16
Steel alloy ASTM A36	254	400	7.8
Aluminium alloy	222	248-483	2.63-2.8
Oak	87	65	.75
Epoxy	26	12-30	1.23
Nylon	69	75	1.15

 

*** Kevlar (ARAMID) is Much Stiffer than Glass but Not equally Stiff equally Carbon Fiber.

The Rigidity of a stuff is measured past times its Youngs' Modulus.

Kevlar is quite stiff in addition to has depression stretching at break.

Material	Young's Modulus GPa
PTFE (Teflon)	0.5
Rubber (small strain)	0.01-0.1
PTFE (Teflon)	0.5
Low density polyethylene	0.2
UHMWPE (such equally Dyneena or Spectra)	.7
Polypropylene	1.5-2
Nylon	2-4
Pine forest (along grain)	8.963
Oak forest (along grain)	11
Aluminium	69
Aramid (such equally Kevlar in addition to Twaron)	70.5-112.4
Brass in addition to bronze	100-125
Glass-reinforced plastic (70/30 past times weight fibre/matrix, unidirectional, along grain)	40-45
Carbon fiber (depends on management in addition to type)	300-400
Carbon fiber reinforced plastic (70/30 fibre/matrix, unidirectional, along grain)	181
Steel	200
Single-walled carbon nanotube	1,000+

 

*** Tensile Strength of Kevlar is lower than E Glass
This tabular array is offered equally a comparing only since in that location are a great issue of variables.

Material	MPa units
Carbon steel 1090	650
High density polyethylene (HDPE)	37
Polypropylene	19.7-80
High density polyethylene	37
Stainless steel AISI 302	860
Aluminium alloy 2014-T6	483
Aluminium alloy 6063-T6	248
E-Glass alone	3450
E-Glass inwards a laminate	1500
Carbon fiber alone	4127
Carbon fiber inwards a laminate	1600
Kevlar	2757
Pine forest (parallel to grain)	40

(Aramid fibers, 2015)

Conclusion
The electrical current production of continuous aramid fibres (both depression in addition to high modulus) worldwide is estimated at well-nigh 60,000 metric tons (MT)/year, only 4% of which goes into composite applications. This represents 2,400 MT/year, compared to 40,000 MT/year of carbon in addition to 5 meg MT/year of drinking glass fibre.

The evolution of para-aramid fibres (especially high-modulus) has been slowed downwardly past times for sure disadvantages that take keep turned upwards gradually amongst their use. These disadvantages include hapless compression strength, microcracking due to the high thermal expansion coefficient inwards the width direction, high wet regain, in addition to problems amongst processing (cutting, machining, finishing, surface aspect).

In addition, these fibres human face upwards stiff contest from carbon, which has much ameliorate mechanical properties in addition to is available at lower cost. As a result, in that location is currently footling to written report inwards the way of major developments for composites applications.

References

1. A history of torso armour-bullet proof vasts. (1993, august 25). Retrieved from www.inventore.about.com: www.inventores.about.com
2. ADVANTAGES - DISADVANTAGES. (2015, november 15). Retrieved november sunday, 2015, from http://www.aramid.eu/: http://www.aramid.eu/advantages---disadvantages.html
3. ARAMID FIBER CHARACTERISTICS. (2015, november 15). Retrieved november sunday, 2015, from http://www.aramid.eu/: http://www.aramid.eu/characteristics.html
4. aramid fibers. (2015, 10 15). Retrieved 10 sunday, 2015, from http://www.christinedemerchant.com: http://www.christinedemerchant.com/aramid_characteristics.html
5. aramid fibers manufacturing method. (n.d.). Retrieved from http://www.aramid.eu/: http://www.aramid.eu/manufacturing-methods.html
6. Manufacturing Process of Aramid, /search?q=production-process-of-synthetic-fiber_9386
7. Aramid Fibers, merchandise names. (n.d.). Retrieved from http://www.christinedemerchant.com/: http://www.christinedemerchant.com/aramid_characteristics.html
8. Aramid Fibre ( Kevlar / Twaron ) – Properties in addition to Applications. (2015, 10 15). Retrieved 10 sunday, 2015, from http://www.azom.com: http://www.azom.com/article.aspx?ArticleID=1384
9. comparison of aramid fibers. (2003, october 13). Retrieved from carb.com: www.rarb.com " comparing of aramid fibers
10. Hearle, J. W. (2001). High Performance Fibers. USA: Woodhead publishing limited.
11. Man-made Fibres. (2015, 10 15). Retrieved 10 sunday, 2015, from http://www.cirfs.org/: http://www.cirfs.org/manmadefibres/fibrerange/Aramid.aspx
12. Properties of Aramid Fibers. (2015, 10 15). Retrieved 10 sunday, 2015, from http://www.build-on-prince.com/: http://www.build-on-prince.com/aramid-fibers.html#sthash.RHkSA5Pn.YMwuoGQd.dpbs
13. vigotsky, v. (2002). “ANTEC fundamentals forum volition focus on innovative products in addition to processes”, Plastics Engineering. novel yark: brookfield center. 

 

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