Chapter 5
Polyamide fibre:
Polyamide fibre:
Polyamides are a group of polymers characterized by repeating unit –NH—CO—link groups.
Synthetic polyamides are made by a condensation reaction taking place between small molecules
in which the linkage of molecules occurs through the formation of amide groups.
Types of polyamide —
I) Nylon
II) Aramide
Aramide :
Aramide is a long chain synthetic polymer in which at least 85% of amide linkages are directly
attached to two aromatic rings of a long chain synthetic polyamide.
Classification:
1. Kevler —
a) Kevler - 2g: — as filament.
— Used in parachute.
b) Kevler – 4g: — as filament and spun.
— Used for boat making.
2. Nomex —
As filament
as spun
Nomex 430
Nomex 450
Nomex 431
Nomex 451
Nomex 432
Nomex 452
Nomex 433
Nomex 453
Nomex 434
Nylon:
Nylon are polyamide in which less than 85% of the amide are linked to the aromatic rings.
There are different types of nylon —
Nylon-6, Nylon-6,6, Nylon-6,10, Nylon-11, Nylon-7, Nylon 9.
Nylon polymer:
Nylon is a linear polyamide polymer. The nylon 6,6 polymers has a linear but zig zag
arrangement of carbon atoms. The carbon atom can bear four single covalent bonds which are
arranged about the atom as the verticals of a triangular pyramid i.e. a tetrahedron. This
tetrahedral arrangement of bonds causes the carbon atoms to form a zig zag but linear polymer.
This polymer configuration is partly responsible for the very good elastic properties of nylon.
The polymer system of nylon is estimated to be about 65-85% crystalline and correspondingly,
about 35-15% amorphous. This gives nylon a very crystalline, very well aligned or oriented
polymer system. With the inter polymer distances on average about 0.3 nm.
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Chemistry involved:
I) Nylon 6,6:
Nylon 6,6 fibres is spun from Poly Hexa Methylene Adipamide, a polyamide made by the
condensation of Hexa Methylene Diamine and adipic acid.
NH2-(CH2)6-NH2
+
Hexa methylene
Di amine
HOOC-(CH2)4-COOH
Adipic acid
-CONH(CH2)6-NHCO-(CH2)4-CONH-(CH2)6-NHCO-(CH2)4-CO-Nylon 6,6
Why this amide is called Nylon 6,6:
Nylon 6,6 denotes that there are two monomers, each containing six carbon atoms, which is
required to form the polymer of this type of nylon.
II) Nylon 6:
Nylon 6 fibre is spun from Polycaproamide, a polyamide made by the self condensation of 6
Amino Caproic acid .
Caprolactam:
CH2(CH2)4CONH
-NH(CH2)5-CONH(CH2)5CONH(CH2)5Nylon 6
III)Nylon 11:
Nylon 11 fibres are spun from poly undecanamide made by the self condensation of 11 amino
undecanoic acids.
NH2(CH2)10COOH
-NH(CH2)10CONH(CH2)10CONH(CH2)10COIV)Nylon 6,10:
NH2(CH2)6NH2
HMD
+
HOOC(CH2)8COOH
Sebasic acid
-NH(CH2)6-CONH-(CH2)6-CONylon 6,10
V)Nylon 7:
NH2(CH2)6-COOH
-NH-(CH2)6-CONH-(CH2)6COAmino Heptanoic acid
Nylon 7
Raw materials for production of:
1. Nylon 6
: 6 amino caproic acid / caprolactam.
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2. Nylon 6,6
: Hexa-methylene diamine and adipic acid.
3. Nylon 6,10
: Hexa-methylene diamine and sebasic acid.
4. Nylon 11
: 11-Amino undecanoic acid.
5. Nylon 7
: Amino Heptanoic acid.
n
Difference bet nylon 6,6 and nylon 6:
Subject
Nylon 6,6
Nylon 6
1. Monomer
Hexa methylene diamine H2N
(CH2)6NH2 and adipic acid (HOOC
(CH2)4COOH).
Cyclic caprolactam.
CH2
CH2
H2C
NH
CO
CH2
CH2
2. Repeating unit
Hexa methylene diamine adipate [NH(CH2)6NHCO(CH2)4CO-]-
Linear caprolactam
-[-NH(CH2)5CO-]-
3. Estimated degree of
polymerization
N = 50 to 80
N = 200
4. Estimated polymer
length
90 to 140 nm
90 nm
5. Estimated polymer
thickness
0.3 nm
0.3 nm
Manufacturing of nylon 6,6:
Raw materials
:
Coat and petroleum oil. This raw mtls prepare Hexa methylene diamine and Adipic acid.
Process:
 In a typical continuous system, equimolar mixtures of hexa methylene diamine and adipic
acid after carbon treatment are passed into suitable mixing tank and then with a solid
content of 45-50% they flow through an evaporator.
 They are evaporated at a temp of 1050-1150C over a period of 20-30 min until a solid
content fo 60-75% is reached .
 They are then passed through a high pressure reactor at 240-260 psig with a temp of
235oC, residence time is 2 hrs. At this stage, the nylon salt solution is converted to a pre
polymer. Pressure is released at a temp of 260o-290oC in a flasher.
 The polymer is pumped to a finisher, a thin film evaporator. The nylon 6,6 is maintained
at temp of 2600-2900C for a period of 5-10 min in a finisher and is discharged from this
unit when the desired viscosity is reached for spinning into fibres.
Chemical reaction:
NH2(CH2)6NH2 + HOOC-(CH2)4-COOH
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-CONH(CH2)6-CONH-(CH2)4CONylon 6,6
Flow chart of continuous polymerization plant for nylon 6,6:
Equimolar mixture of hexa methylene diamine and adipic acid—
Mix Tank
Mix Tank
40-50%
Solid
Water vapor out
110o-115oC
Residence
time 20-30 min
240-260 PSIG
230oc
Residence
Time 2 hrs
Condensator
250o-290oC
Light charge
280o-290oc
Residence
Time 5-10min
Evaporator
High pressure steam
Condensate out
Reactor
Dowtherm in
Dowtherm out
Flasher
Dowtherm in
Dowtherm out
Flasher
Nylon 6,6 polymer to
spinning
Formation of adipic acid, hexa methylene diamine and nylon salt:
Adipic acid:
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OH
Coal tar
Hydrogenat
ion
Partial
distillation
Phenol
OH
Cyclo hexanol
[o]
HOOC(CH2)4COOH
Adipic acid
HNO3
Oxidation
Hexa methylene diamine:
NH3 vapor
HOOC(CH2)4COOH
Adipic acid
NC(CH2)4-CH
Catalyst Boron Phosphate Adiponitrile
Reduction
NH2(CH2)6-NH2
Hexamethylene diamine
Ni catalyst
Nylon salt:
By reacting adipic acid and hexa methylene diamine in the soln of methyl alcohol, we get nylon
salt. This salt is separated and purified at this stage.
H2N(CH2)6NH2
+
HOOC(CH2)4-COOH
Hexamethylene
Adipic acid
diamine
+ H2N(CH2)6-NH3 - OOC-(CH2)4-COOH
Nylon 6,6 salt
Features of Nylon:
I)
Diameter 14 µm to 24µm.
II)
Color slightly off – white.
III)
Moisture regains 3.5-5.0% (not absorbent due to crystallinity).
IV)
Hand feel- soft and smooth.
V)
Resiliency- Excellent.
VI)
Abrasion resistance- Excellent.
Properties of nylon:
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1.
2.
Physical properties:
 Tenacity
 Elasticity
 Stiffness
 Moisture regain
 Specific gravity
 Abrasion resistance
 Dimensional stability
 Resiliency
 Softening point
: 4-9 gm/den (dry), in wet 90% of dry.
: Breaking extension — 20-40%.
: 20-40 gm/den.
: 3.5-5%; (not absorbent due to crystallinity).
: 1.14.
: Excellent.
: Good.
: Excellent.
: Nylon 6,6 — 229oC, Nylon 6 — 149oC.
 Melting point
 Hand feel
: Nylon 6,6 — 252oC, Nylon 6 — 215oC.
: Soft and smooth.
Chemical properties:
 Acid: Nylon 6,6 is attacked by mineral acids is disintegrate or dissolve almost. But is
inert to dilute acetic acid and formic acids even of the boil. It is dissolved in the
concentrated formic acid. Nylon 6 is attacked by mineral acid but resistant to dilute
boiling organic acid.
 Bleaches: Not affected by oxidizing and reducing bleaches but may be harmed by
chlorine and strong oxidizing bleaches.
 Alkali: Nylon is substantially inert to alkalis.
 Organic solvent: Most organic solvent have little or no effect on nylon. Phenol
metacressol and formic acid dissolve the fibre but solvents used in stain removal and dry
cleaning do not damage it.
 Light: No discoloration. Nylon 6 gradually loss of strength on prolonged extension.
 Biological
: Neither micro organism nor moth, larvae attack nylon.
 Electrical : High insulating properties leads to static charges on the fibre.
 Flammability : Burns slowly.
Uses of Nylon:
I) Apparel use:
High tenacity nylons are used for parachute fabrics, cords and ropes. Having good dimensional
stability, nylons are used for ladies gloves, ladies hose, under wear, swimming wear, stocking,
hosiery fabric etc.
II) Domestic use:
Nylon is used for home furnishing, in carpets, in upholstery and in ropes and cords.
III).Industrial use: In fishing nets, tire cords, filtering cloths, sewing threads, tow ropes are made
of nylon. It is used in manufacturing of belts of various m/cs (Flat belt, V-belts).
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