Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

Contents

01. Basic Terms To Understand Aramids

02. Meaning of Aramids

03. Types of Aramids

04. Short History of Aramids

05. Chemical Structure

06. Properties

i. Physical Properties

ii. Chemical Properties

07. Manufacturing

08. Uses

Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

Basic Terms to Understand

Aramids

Poly-Amide Fibers:

“Synthetic fibers of polymers containing amide linkages.”

Exception:

Types of Poly-Amide Fibers:

There are two types of poly-amides;

1. Nylons2. Aramids

If only one carbon is between alternateamide linages then it is protein.

Amide

Amide LinkageLinkage is used to connecttwo things together that’swhy it has two valency.

Nylons

This definition is not applicable forsome nylons like Nylon 6,T and Qiana.

Poly-amides containing less than 85% amidelinkages directly attached two aromaticrings.

TFPIA Definition:

Aramids

Poly-amides containing atleast 85% amidelinkages directly attached two aromaticrings.

TFPIA Definition:

Or

Poly-amides containing (CH2)n chainbetween two alternate amide linkages.

General Definition: Or

Poly-amides containing aromatic ringbetween two alternate amide linkages.

General Definition:

Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

Amide linkages attached with two aromatic rings also calledaromatic polyamides.

Meaning of Aramids

Ar – amid

Origin: Aromatic Amides

Meaning:

Types of Aramids

There are many types of aramids, some of them are following:

Nomex (Meta-Aramid)

Kevlar (Para-Aramid)

Twaron

Technora

Heracron

etc…

} These two are the mostcommon types of aramids.

Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

Short History of Aramids

Polish-American chemist Stephanie Kwolekinvented the 1st Para-Aramid fiber which wasKevlar.

On the other hand Dr. WilfredSweeny, a Scottish-born scientistwas responsible for thediscoveries leading to Nomex theMeta-Aramid fiber.

In 1960, DuPont introducedmeta-aramid incommercial applications

under the trade name Nomex.

They were also the 1st one tointroduce Para-Aramid fibers under thetrade name Kevlar.

Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

Chemical Structure

Kevlar:

1. Polymer Structure:

2. Charge DistributionOver Polymer:

3. Monomers:

Amide Linkage

These Linkages are attached to para positions ofaromatic rings that’s why called as para-aramids.

Negative Charge

Positive Charge

Structure Shows there is greater amount of negative charge on polymer

>

Due to these monomers IUPAC name of polymer is poly(para-phenylene terephthalamide).

Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

Nomex:

1. Polymer Structure:

2. Charge DistributionOver Polymer:

3. Monomers:

Amide Linkage

These Linkages are attached to para positions ofaromatic rings that’s why called as para-aramids.

Negative Charge

Positive Charge

Structure Shows there is greater amount of negative charge on polymerBut its electro positive hydrogen is more exposed unlike Kevlars, due to

this more water molecules can attract over positive center.

>

Isophthaloyl Chloride m-phenylene diamine

Due to these monomers IUPAC name of polymer is poly(meta-phenylene isophthalamide).

Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

Properties Of Aramids

Physical Properties

01.Optical Properties:

a. Color:Nomex = whiteKevlar = golden

b.Lustar:Depends upon cross section shape.Circular: more luster.Dogbone: less luster as compared to circular.Note: Luster can be controlled by finishes.

c. Effect of Some Rays:Beta = No effectGamma = No effectUV rays = Starts to Degrade and lose strength

02.Mechanical Properties:

a. Tenacity(g/d):Nomex Kevlar

Dry 4.0 - 5.3 18 – 26.5Wet 3.0 – 5.3 17 – 25.0

Very high as compared to nylons.

Easy to Break one joint. Hard to Break more than one joint.

Simple logical Reason:

Kevlar Nomex

Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

b.Stress-Strain Relaion:The initial modulus of aramid fibers ishigher than that of nylons as shown ingraph.The rato of stress to strain (slope ofcurve) is used to measure the stiffnessof the fiber.Kevlar = most stiffNomex = less stiffer than Kevlar.

c. Density(g/cm3):Kevlar = 1.44 – 1.47 g/cm3

Nomex = 1.38 g/cm3

03.Thermal Properties:

a. Melting Point:Kevlar = above 500oC (930oF)Nomex = 350oC (660oF)Note: At these temperatures they not only melts but also starts to decompose.

b.Glass Transition Temperature:Kevlar = starts from 170oCNomex = from 120 – 220oC

c. Specific Heat Capacity:Kevlar = 1420 J/K.KgNomex = 1200 J/K.Kg

d.Highly Flame Resistant:

Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

04.Other Properties:

a. Moisture Regain:

Kevlar = 1.2 – 4.3%

Nomex = 6.5%

Non-flexible chains.

Reason: Two alternate rings try to oppose each

other by repulsion of aromatic rings which keepsthe fiber straight and non-flexible.

Hydrogen-bonding between chains there byforming a sheet like structure (of fibrils).

Reason: Shown in Picture.

Fibrils (sheets) separated by elongated voids.

Reason: Because each sheet is a plane whose both faces are negatively

charged because of Aromatic Rings (similar to graphite sheets) due to thiselongated void is created between fibril sheets.

Aramid Fiber

Fibrils Sheets Chemical Structure.

Gaps between Fibril Sheets

Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

Chemical Properties

a. Resistance To Alkalies:

Nomex Kevlar

Dilute(at Room Temp.) No effect No effect

Conc.(high Temp.) Degrades Weaken

b.Resistance To Alkalies:

Nomex Kevlar

Dilute(at Room Temp.) No effect No effect

Conc.(high Temp.) Weaken Weaken

Strong Acids Degrades Weaken

c. Resistance To Dye:Because of high negative charge repulsion its hard to dye but inextreme conditions support electrophilic substitution reaction.

d.Resistance To Bleach:

Resistant to bleaches that’s why its hard to change the naturalgolden color of Kevlar.

Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

Manufacturing

Steps For Manufacturing:

1. Polymer Formation:

We normally use suspension polymerization technique for aramids. Thedi amine is dissolved in water, with an acid acceptor (Na2CO3). The acidchloride is dissolved in a solvent (CTC or cyclohexanone).

Two solutions are then mixed intensively which cause rapid polymerizationreaction at liquid interface. This technique is known as interfacialpolymerization.

2. Spinning:a. Dope Formation:

Nomex: Its polymer is dissolved in a mixture of dimethylformamideand lithium chloride.

Kevlar: Its polymer is dissolved in Sulphuric Acid.

b. Extrusion:

Then dope is extruded through spinneret’s hole to give shape offilament.

Important PointAromatic polyamides should be prepared from aromatic dicarboxylic

acid and aromatic diamines. But aromatic dicarboxylic acid areunreactive that’s why we use more reactive aromatic acid chlorides.

Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

c. Solidification:Nomex: It is solidified in hot air and the solvents are recovered bydistillation. (Dry Spun)Kevlar: It is solidified in water or dilute sulphuric acid bath.(Wet spun)

Uses

Technical Textile:

1. Buildings: Aramids are used for fire proofing of

walls because of their flame resistant property.

Also used as insulation of electric wires used in

buildings to prevent breakage by heat because of high specific heat.

2. Protective Textile: Used to prepare protective

products like uncut able gloves, helmets, bullet proof

waist, suits of fire fighters, suits of astronauts etc.

Aramid Fibers

By; Syed Ahmed Khizar TEXT-176 Submitted to; Sir Imran Raza

3. Sports: Used in sports products like rackets, tires

of formula one cars, boats, whole bicycles are made

up of aramids because of its light weight and

strength.

Also ropes and cables because of its strength.

Worldwide usage of synthetic fibers