Review

Preparation, Properties and Applications of Nylon 6, 6 Fibres

By Mufaddal Bagwala

Department of Textile Technology

Shri Vaishnav Institute of Technology and Science, Indore

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CONTENT

Abstract…………………………………………………………………………………..….3

1. Introduction………………………………………………………………………...…3

2. History……………………………………………………………………………...…5

3. The Nylon Fiber Design Advantage………………………………………….…...…7

4. Advantages of Nylon-66……………………………………………………….…..…7

5. Use of Nylon-66 in Fiber Manufacturing…………………………………….…...…9

6. Preparing Nylon-66 Chip…………………………………………………….………9

7. Remelting Nylon 66 Chip……………………………………………………………9

8. PREPARATION OF THE MONOMER………………………………………………...…10

9. Polymerisation…………...……………………………........................................... 13

10. NYLON 66 SALT (NH SALT)………………………………………………………..…13

11. Polycondensation………………………………………………………………...…14

12. Spinning………………………………………………………………………….……14

13. Properties……………………………………………………………………………15

14. Types of Nylon-66 products Manufactured………………………………………16

15. Advantages of DuPont Nylon 66 in Specific Fiber Applications…………………17

16. Product Specification Parameters……………………………………………….…20

17. Conclusion………………………………………………………………………...…23

References………………………………………………………………………………...…24

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ABSTRACT

Here in this term paper description is given about a type of polyamide fibre i.e.

Nylon-66. Here in this paper the methods of preparation of monomers, polymerisation,

manufacturing methods of nylon-66, spinning process to obtain fibres, different properties

and wide range of applications and uses of nylon-66 are discussed. In this paper data are

represented in the form of flow charts, histogram and pie charts for easy understandings. This

paper covers all the processes related to nylon-66.

1. Introduction

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 engineered structures.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 and

hexamethylenediamine 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 material’s 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.

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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.

NYLON-66 YARN MONOMERS OF NYLON-66

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2. HISTORYThe development of nylon was started from 1927 by means of

many researchers, notably among them W.H.Carothers and

P.Schlack. The research activities preceding the manufacture of

nylon yarn can be divided into the following categories:

(a) Fundamental research activities which provided the

foundation

for the development.

(b) Different types of polyamides, their synthesis,

manufacture and

their suitability for use as a new fibre. This includes all

types of

polyamides like aliphatic, aliphatic-aromatic and fully aromatic

polyamides.

(c) Commercial production of the fibres.

(d) Development of the properties and serviceability of the fibres.

Polyamides are characterized according to the number of carbon atoms present in the

structural unit of the molecule. These are:

(a) Nylon made from condensation of a diamine and a dicarboxylic acid is

classified according to the number of carbon atoms present in the amine

and acid respectively. Thus nylon formed by hexamethylene diamine

(NH2 (CH2)6-NH2) having 6 carbon atoms and sebacic acid

(COOH-(CH2)8-COOH) having 10 carbon atoms is generally referred

to as nylon 6,10

(b) Nylon, made from amino acid, is classified according to the number of

carbon atoms present in the acid. It will have only one number. For

example, Nylon 6 can be made from amino acid having 6 carbon atoms

i.e., amino caproic acid or its condense product caprolactum.

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So the numbers indicate the number of carbon atoms in the monomer taking part in the

polymerisation. In general,

Table 12.1 Raw materials of different Nylons

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Nylon Raw materials

Nylon 4,6 Nylon 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 acidHexamethylene diamine, Adipic acid Hexamethylene diamine, Sebacic acid Hexamethylenediamine, Dodecanedioic acid Acrylamide 2-pyrolidane Caprolactum Lactum of heptonoic acid W-amino-cendecanoic acid Dodelactum

3. The Nylon Fiber Design Advantage

In 1939, the introduction of nylon into sheer stockings revolutionized the women’s 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-66Nylon 66 is superior in many applications to nylon 6—the other large volume nylon—due to

its outstanding dimensional stability, higher melting point, and more compact molecular

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.

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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.

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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.

6. Preparing Nylon-66 Chip

Chip is normally conditioned in an inert atmosphere at temperatures in the 120–180°C (248–

356°F) 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 the

capability of heating the polymer to 280–290°C (536–554°F). Handling of the Molten

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

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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.

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.

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8.1. ADIPIC ACID MANUFACTURE

8.1.1 FROM CYCLOHEXANOL

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

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 60-70°C. 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 80-1.00°C. 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 120-150°C. 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:

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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 350°C 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 CYANIDE

1, 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 185-190°C. 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

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 40°C, B.P. 100°C, soluble in water, and alcohol.

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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 acid and 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

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60% solution in distilled water. It is a snow white crystal (mp - 190°C). 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% 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 275°C. 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 275°C, the pressure is allowed to fall to atmospheric pressure. The batch is held at

270°C 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 the molten 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 300°C. 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.

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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

4.0-4.5

6.0-8.0

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 PROPERTIES

Because of different structure, the melting point will occur in the range of 249°C to 260°C. The

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

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

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

350°C.

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

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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 Reinforced

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5. Nylon 66/6, 40% Glass Fiber Reinforced

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 hand

Weaving and Warp Knitting

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• High fiber modulus

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

processes

– minimizes barré 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 polyamide’s

• High melting point,

• Superior dimensional stability, and

• reduced moisture sensitivity.

Coated Fabrics

Nylon 66 fabrics withstand coating temperatures with PU, PVC, and rubber up to 200°C (392°F) 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

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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:

Textiles Apparel, tooth brushes, Tyre cord

Automotive Bearings, slides, door handles, door & window stops.

Furniture Locks, hangers, chairs etc.,

Packaging Film sheet

Mech. Engg. Drive gears, bearings, fish plates for railways lines tubing.

16. Product Specification Parameters19

Relative Viscosity (RV)

The degree of polymerization of a polymer is directly proportional to molecular weight and is commonly measured by a solution viscosity technique. Methods of Measurement Common solvents used for viscosity measurements of nylon 66 include both formic and sulfuric acids. The details of these procedures are summarized in Table.

RV is determined by comparing the

time required for a specific volume of

polymer solution to flow through a capillary tube with the corresponding flow time of the

same volume of pure solvent. Results are corrected for moisture content of the sample;

alternatively, the sample is dried to a low moisture level.

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

and 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).

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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 35–50 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 <0.3 wt %). However, the product can absorb more moisture (up to8 wt %) depending on the relative humidity (see Figure 8) and length of exposure time (see Figure 9). Customers must take precautions to keep the product free of moisture.

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17. CONCLUSION

After all the research works and information in this term paper we conclude that Nylon 6,6

is a semi-crystalline, off-white engineering thermoplastic that is the strongest and most

abrasion resistant unreinforced aliphatic nylon with better low temperature toughness than

Nylon 6 or acetal. Its very low melt viscosity can give industrial processing difficulties and

weathering can cause embrittlement and color change unless it is stabilized or protected.

Available with a wide range of fillers notably glass fibre, which gives a marked increase in

stiffness, and solid and liquid (oil) lubricants. Super-tough grades are also available whose

impact properties and low notch sensitivity are amongst the best of all engineering

thermoplastics.

Applications include mainly engineering components eg gears, bearings, nuts, bolts, rivets

and wheels and power tool casings and rocker box covers. Widely used as monofilament for

brushes etc and fibre - notable for its resilience and high abrasion resistance - for apparel,

carpet and industrial end-uses.

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REFERENCES

1. Nylon 66, polyamide fibres, A Text Book of Fibre Science and Technology S.P.

Mishra, New Age Publishers.

2. Advances in nylon 6, 6 Fibre Science and Technology, By Premamoy Ghosh.

3. Nylon manufacturing, Modern Fibres edited by J.W.S HEARLE.

4. http://en.wikipedia.org/wiki/nylon 6,6 .

5. http://www.encyclopedia.com/topic/nylon.aspx .

6. http://www.polymerprocessing.com/polymers/PA66.html .

7. http://www.goodfellow.com/E/Polyamide-Nylon-6%2C-6.html.

8. http://www.slideshare.net/nashton/nylon-66-presentation-5487525.

9. DuPont Nylon, DuPont Singapore (PTE) Ltd, and 07-01 World Trade Center1

Maritime Square Singapore 0409, Telephone: 65-279-3497, Fax: 65-272-7494.

10. Properties of nylon 66, Textile research journal, http://trj.sagepub.com/.

11. Technical details of nylon 6, 6 fibres, http://www.btraindia.com/articles_indian.asp.

12. http://www.sciencedirect.com/nylon-66.

13. Chemistry of textile fibres, W.S. Murphy

14. Testing of textile fibres, by J.E. Booth.

THANK YOU!!

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