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There are several polyamides, which have been developed as fibres. The generic word for

these products is Nylon. Nylon is defined as a generic term for any long chain synthetic

polymeric amide which has recurring amide groups as an integral part of the main polymer

chain and which is capable of being formed into a filament in which the structural elements

are oriented in the direction of the axis.

DuPont researchers led by Dr. Wallace Carothers, invented nylon-66 polymer in the 1930s.

Nylon, the generic name for a group of synthetic fibers, was the first of the miracle yarns

made entirely from chemical ingredients through the process of polymerization. Nylon 66

polymer chip can be extruded through spinnerets into fiber filaments or molded and formed

into a variety of finished engineeredstructures.Nylon-66 fibre is a member of the large group

of polycondensation products of dicarboxylic acids and diamines with fibre forming

properties. The individual member refers to the number of carbon atoms respectively in the

diamine and dicarboxylic acid chains.

Nylon-66 (polyhexamethylene diamine adipamide) is a polyamide made from adipic acid andhexamethylenediamine by polycondensation. The resulting polymer is extruded into a wide

range of fiber types. The fibers are drawn, or stretched, in a process that increases their length

and reorients the materials molecules parallel to one another to produce a strong, elastic

filament. The thermo-plasticity of nylon permits permanent crimping or texturing of the

fibers and provides bulk and stretch properties.

The nylon developed by Carothers at Du Pont was nylon 66. Because of the importance of

starting out with equal amounts of the two reactants, salts of the diamine and of the diacid are

made and then used in the commercial synthesis of nylon 66.

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Table 12.1 Raw materials of different Nylons

3. The Nylon Fiber Design Advantage

In 1939, the introduction of nylon into sheer stockings revolutionized the womens hosiery

market. Silk and cotton were quickly replaced by this more durable and easy-care product.

Nylon soon found its way into other end uses. In parachutes and fishing line, nylon provided

a moisture- and mildew-resistant replacement for silk. In flak vests, nylon offered a strength

and durability previously unattainable for protection against shell fragments. And, when used

as aircraft tire reinforcement, nylon enabled heavy bombers to land safely on improvised air

strips. Today, as the global leader in nylon polymer, DuPont offers a wide range of nylon-66

polymer types for use in industrial, textile, and furnishing/floor covering applications.

4. Advantages of Nylon-66

Nylon 66 is superior in many applications to nylon 6the other large volume nylondue toits outstanding dimensional stability, higher melting point, and more compact molecular

Nylon Raw materials

Nylon 4,6Nylon 6,6 Nylon 6, 1

0 Nylon 6,12

Nylon 3

Nylon 4

Nylon 6 Nylon

7 Nylon 11

Nylon 12

1 ,4 diamino butane, Adipic acid

Hexamethylene diamine, Adipicacid Hexamethylene diamine, Sebacic

acidHexamethylenediamine, Dodecanedioic acid

Acrylamide

2-pyrolidane

Caprolactum

Lactum of heptonoic acid

W-amino-cendecanoic acid

Dodelactum

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structure (see Figure 1). Nylon 66 exhibits only about half the shrinkage of nylon 6 in steam,

for instance. And, with a less open structure, the 66 fiber has good dye wash fastness and UV

light-fastness, and excellent performance in high-speed spinning processes. Typical

advantages of nylon 66 over nylon 6 are its

Higher tensile strength in use,

Excellent abrasion resistance, and

Higher melting point.

Nylon 66 provides high tensile strength for

Tough fibers at fine deniers,

Excellent performance for tyre applications, and

High-speed mill processing.

Excellent abrasion resistance makes nylon-66 polymer ideal for use in

Carpets,

Upholstery, and

Conveyor belts.

The rubber industry takes advantage of the higher melting point of nylon 66 in high-

temperature tire curing. A high melting point also results in a fiber with

High stretch and recovery in false-twist textured Yarns (e.g., hosiery and socks) and

Thermal stability in high-temperature coating operations.

5. Use of Nylon-66 in Fiber Manufacturing

The processing of nylon usually begins by conditioning the received chip, with or without an

increase in the asreceived molecular weight. The chip is then melted, usually in a screw-type

extruder, and spun into filament form. The filamentsare then packaged in a process that may

include drawing, bulking, or cutting into lengths of staple.

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6. Preparing Nylon-66 Chip

Chip is normally conditioned in an inert atmosphere at temperatures in the 120180C (248356F) range. Processors may employ higher temperatures to increase molecular weight,

especially for industrial uses. Both batch- and continuous-type conditioners may be used. It is

important to avoid excessive exposure of the chip to oxygen, which may lead to degradation

and yellowing of the product.

7. Remelting Nylon 66 Chip

Remelting is normally performed in a single or twin screw-type extruder, although the

melting can be done in a heated grid-type melter. Single screws are preferred for smaller

spinning plants because of their simplicity. Twin screws are preferred for larger installations

or when more extensive mixing during remelt is required. Equipment must have thecapability of heating the polymer to 280290C (536554F). Handling of the Molten

Polymer Nylon 66 may produce undesirable cross-linked material (gel) if processing

temperatures and holdup times are not properly maintained. Care must be taken to eliminate

areas of stagnation in the screw and in the polymer piping. Good engineering practices

require the application of optimum shear rates and frequent mixing of the melt. Conversion

Molten Polymer to Final Product Form Due to the wide variety of nylon 66 products that can

be produced and the range of processing equipment available, it is beyond the scope of this

bulletin to specify ideal processing conditions. In general, most modern filament-producing

equipment will process nylon 66 polymer adequately.

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8. PREPARATION of the Monomer

Adipic Acid (ADA) and Hexamethylene diamine (HMD) are used as raw materials for

Nylon-66 Polymer. The schemes of preparation of adipic acid and hexamethylene diamine

are shown in Figure.

8.1. ADIPIC ACID MANUFACTURE

8.1.1 FROM CYCLOHEXANOL

Mostly cyclohexane (CH), cyclohexanol (CHL) and cyclohexanone (CNH) are used to obtain

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adipic acid (ADA). For oxidation, only nitric acid and oxygen can be used economically. The

most important process is the oxidation of cyclohexanol with 50% nitric acid at 60-70C. In a

stainless steel kettle the cyclohexanol is added to the acid under cooling and stirring, the acid

is crystallized from water. The yield exceeds 85%.

8.1.2. From Cyclohexanone

The oxidation of cyclohexanone with nitric acid requires higher temperatures. Also

cyclohexanone is oxidized in the presence of acetic acid as diluent and with 0.1% manganese

acetate or nitrate at 80-1.00C. The yield is about 70%.

8.1.3 From Cyclohexane

The simplest method for the production of adipic acid is direct oxidation of cyclohexane.

Most useful is the catalytic oxidation with air by soluble Mn or Co catalysts at 120-150C.

The reaction is interrupted at a conversion of 10-15% and leads away to a mixture of

cyclohexanol and cyclohexanone in equal amounts with adipic acid, cyclohexanol adipate,and lower aliphatic acids. The unchanged product is recycled and the crude oxidation product

fractionated. Since cyclohexane is an important petrochemical product, production of

cyclohexanol and cyclohexanone is based on this process.

8.2. ADIPONITRILE Manufacture

Adiponitrile is the intermediate for the production of hexamethylene diamine. It can be

produced by different methods:

8.2.1. VAPOUR PHASE FROM ADIPIC ACID AND AMMONIA

This method involves condensation from ammonia and adipic acid in the vapor phase. Adipic

acid is vaporized with an excess of ammonia gas (mol. ratio 20:1) at 350C over a catalyst of

boron phosphate. The reaction is endothermic at 57 cal/mole. The yield is 88%.

8.2.2. Liquid Phase Process

In a liquid phase process, ammonia is introduced in molten adipic acid at 200-250 in the

presence of such alkyl or alkyl phosphates catalysts like 0.1 -0.5% phosphonic acid or boron

phosphate. The yield is around 88%.

8.3. 1, 4 DlCHLOROBUTANE AND SODIUM CYANIDE1, 4 Dichlorobutane can be obtained by addition of chlorine to butadiene. This can be

converted to 1, 4 dicyanobutane by NaCN. Dry NaCN is mixed with adiponitrile as diluent

and the calculated amount of 1, 4 dichlorobutane is added at 185-190C. By addition of

water, the oily layer is distilled. The yield is about 95%.

8.4. ELECTROHYDRO DIMERISATION OF ACRYLONITRILE

By electrohydro dimerisation, yield will be 82%. The pH will be 9 and the current density

will be 2 to 30 MA/dm2. The cathode potential was found to be independent of pH above 2.5.

The overall reaction will be

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2 CH2 CHCN + 2 H+ + 2e- NC (CH2)4CN

8.5. Hexamethylene Diamine Manufacture

HMD is manufactured exclusively by the hydrogenation of the dinitriles. Palladium is used as

catalyst. Another effective catalyst is cobalt oxide mixed with calcium oxide. In all cases, the

reaction must be carried out in the presence of excess ammonia. Pure HMD is a colourless

crystal, melting at 40C, B.P. 100C, soluble in water, and alcohol.

9. POLYMERISATION

Nylon-66 production from adipic acid and hexamethylene diamine comprises four steps: (1)

Salt preparation (2) Polycondensation (3) Melting. (4) Extrusion. A schematic diagram of

Nylon 66 polymer formation process is shown in Figure.

10. Nylon 66 Salt (NH salt)

High molecular weight nylon 66 is only obtained if equimolecular amounts of the

components are used. An excess of the components would terminate the chain by formation

of an acid or amino end group. So stoichiometric portions of hexamethylene diamine and

adipic acid must be used (amine to acid of 1:1). For this reason, the salt of 1 mole adipic acidand hexamethylene diamine (AH salt) is used as intermediate. The hexamethylene diamine is

used as a 60-70% solution and the adipic acid as a 20% solution. The monomers are fed and

mixed in the mixer and transferred to the prepolymeriser. Methanol is added and the reaction

takes place. Methanol can be refluxed. The separated salt is centrifuged and washed with

methanol. It is stored as a 60% solution in distilled water. It is a snow white crystal (mp

190C). Owing to all these constraints, batch processing is used.

11. POLYCONDENSATION

The concentrated salt solution is then fed to the polymerisation reactor, where the second-

stage of the reaction begins (Fig 12.5 c). 60% Aq. Solution of the salt in distilled water, 0.5%

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acetic acid (stabilizer) is pumped into an autoclave. Increased temperature and pressure are

used to initiate the polymerisation reaction. So the autoclave is heated to 275C. The pressure

is generally kept constant (1.8 MPa). Before the reaction, the autoclave is purged with very

pure nitrogen (less than 0.005% oxygen) to avoid degradation and discoloration of the

polymer. When the temperature of the batch reaches 275C, the pressure is allowed to fall to

atmospheric pressure. The batch is held at 270C and atmospheric pressure for half an hour to

allow removal of the water vapor. The heating is continued until all water has been distilled

off. Towards the end of the distillation, the autoclave is evacuated. The polymer is obtained

as a clear, low-viscous melt which is removed from the autoclave by pressure with pure

nitrogen. The melt is extruded through the bottom of the reactor to form a ribbon. It is

solidified and cooled in cold water cut into chips and dried. The dried chips are stored in a

storage hopper in a similar manner like that of Nylon 6.

12. SPINNING

Nylon has sufficient stability of the melt and adequate viscosity. So it can be spun in themolten state with usual velocity (upto 2000 m/min). The polymer chips are fed to the hopper

and then it is melted and homogenized in an extruder. The molten polymer after filtration is

passed to the spinnerets. The melt is pumped through this system and solidifies immediately

on contact with air. Cross air flow is used for solidification. The melting temperature for

spinning is around 300C. After spinning like nylon 6, the flows are stretched to get the

desired elongation. Details of spinning and stretching processes are discussed in Chapter 2

(Fig 2.1 and 2.6). The different parameters which can be varied to influence fibre properties

are: (a) Mass output, (b) Winding speed, (c) Spin draw ratio, (d) Draw ratio and (e) Draw

temperature. The properties which will be considered are: tensile strength, elongation,

modulus, crystallinity and orientation.

13. PROPERTIES

13.1. PHYSICAL PROPERTIES

Like Nylon 6, different types of Nylon 66 fibre exhibit different physical properties.

Physical

Properties Staple Fibre Normal Filament

High Tenacity

Filament

Density (gm/cc) 1.13 1.14 1.15

Moisture (%) at

65% rh

100% rh

4.0-4.56.0-8.0

4.0-4.5

6.0-8.0

4.0-4.5

6.0-8.0

Tenacity (g/d)

Dry

Wet

3.0-6.8

2.5-6.1

2.3-6.0

2.0-5.5

6.0-10.0

5.1-8.0

Elongation (%) 16-75 25-65 15-28

Stiffness (g/d) 10-45 5-24 21-58

13.2. Thermal PropertiesBecause of different structure, the melting point will occur in the range of 249C to 260C.

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The glass transition temperature of this fibre is in the range of 29C- 42C. The softening

temperature i.e., the sticking temperature is 230C. The fibre discolors, when kept at 150C

for 5 hours. The heat deflection temperature is 70C. The decomposition of this fibre starts at

350C.

13.3. Chemical Properties

Nylon 6, 6 fibres is more resistant to acids or alkalis in comparison with nylon 6 fibre

because of light intermolecular forces present in the structure. The fibre is unaffected by most

mineral acids, except hot mineral acids. The fibre dissolves with partial decomposition in

concentrated solutions of hydrochloric acid, sulphuric acid and nitric acid. The fibre is

soluble in formic acid. In a similar way, the fibre is attacked by strong alkalies under extreme

conditions otherwise it is inert to alkalis. The fibre can be bleached by most of the bleaching

agents. The fibre is mostly insoluble in all organic solvents except some phenolic

compounds.

The fibre has excellent resistance to biological attacks. Prolonged exposure to sunlight causes

fibre degradation and loss in strength.

The fibre can be dyed by almost all type of dyestuffs like direct, acid, metal-complex,

chrome, reactive, disperse and pigments. However only acid and metal complex dyes are

preferred because of higher fastness properties.

14. Types of Nylon-66 products Manufactured

1.

Nylon 66/6

2. Nylon 66/6, 10% Glass Fiber Reinforced

3. Nylon 66/6, 20% Glass Fiber Reinforced

4.

Nylon 66/6, 30% Glass Fiber Reinforced5. Nylon 66/6, 40% Glass Fiber Reinforced

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6. Nylon 66/6, Mineral Reinforced

7.

Nylon 66/6, 60% Glass Fiber Reinforced

8. Nylon 66/Nylon 6 Blend, Glass Fiber Filled

9. Nylon 66, Unreinforced

10.

Nylon 66, Impact Grade

11.

Nylon 66, Unreinforced, Flame Retardant

12.Nylon 66, Heat Stabilized

13.Nylon 66, Extruded

14.Nylon 66, Film

15.

Nylon 66, Nucleated

16.Nylon 66, PTFE Filled

17.Nylon 66, MoS2 Filled

18.

Nylon 66, Glass Bead Filled

19.

Nylon 66, 30% glass filled, extruded

20.Nylon 66, Mineral Filled, NCG Fiber Filled

15. Advantages of DuPont Nylon 66 in Specific Fiber Applications

When processed into fiber form, nylon 66 polymer offers many advantages for customer

applications.

Hosiery

Excellent high-speed processing

High stretch and recovery

High durability and strength

Good handWeaving and Warp Knitting

High fiber modulus

minimizes yarn distortion possible during winding, warping, knitting, and weaving

processes

minimizes barr and streaks during dyeing

Wide operating window for heat setting, dyeing, and processing, this is especially

important for fabric combinations with spandex

Very good resistance to photo degradation

Good dye light-fastness

Good dye wet-fastness

Tires and Conveyor Belts

Heavy-duty tires and belts reinforced with nylon 66 polymer are capable of withstanding high

temperatures and fast curing cycles. The superior performance is due to the high strength and

modulus of nylon 66. Woven and modified nylon 66 tire cord provides aircraft and off-road

vehicle tires with long life and high fatigue resistance. Nylon 66 has particular advantages in

industrial products as a result of the polyamides

High melting point,

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Superior dimensional stability, and

Reduced moisture sensitivity.

Coated Fabrics

Nylon 66 fabrics withstand coating temperatures with PU, PVC, and rubber up to 200C

(392F) and display good dimensional stability for coating integrity.

Carpeting

During the late 1950s, two new developments opened up a new era for the carpet industry.

First, equipment was developed to tuft carpet yarn into a backing material to produce pile

carpeting. At the same time, DuPont invented a technique to impart bulk or loft to nylon by

a fluid-texturing process called Bulk Continuous Filament (BCF). The combination of nylon

66 yarns, textured by the BCF process, yields carpets with

High abrasion resistance,

High resistance to pile crushing and Matting,

Ease of level dyeing,

High dye light-fastness, and

High dye wet/wash-fastness.

Carpets of nylon now account for nearly 70% in a market that was once the exclusive domain

of wool yarns.

Furnishings/Floor Coverings

Nylon 66 offers the furnishings/floor coverings industry

A complete line of luster (from 0.0 to 1.0% TiO2),

Products for direct use and post-polymerization Feed,

Products intended for color addition during remelt, and

A full line of dye variant polymers for yarn styling formulations.

Nylon is a material that runs from combs to ship propellers to ladies stockings. The

applications can be summarized as follows:

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Values quoted in specifications are those measured in 90% formic acid. Figure.6 shows the

typical relationship between RV in 90% formic acid versus 98% sulfuric acid.

Amine End Groups (AEG)

A major nylon asset is its ability to accept a wide range of dyestuffs. These include both acidand premetallized dyestuffs that associate with the terminal amine groups of the polymer. The

concentration of these end groups is an important factor in controlling dye ability (see

Figure7).

Analysis Method

The technique commonly used for measuring AEG involves dissolution of polymer in 68/32

wt% phenol/methanol solvent and potentiometric titration with 0.05 m hydrochloric acid

using commercially available equipment. Results are corrected for moisture and titanium

dioxide content.

For typical textile grade products, amine end Group concentration is usually within the range

of 3550 and is expressed as gram equivalents/106 g of polymer.

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Moisture Content

Nylon is a relatively hygroscopic polymer. Nylon 66 leaves our production plant with low

moisture content (typically

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