Fiber Length and Spinning Performance

Fiber length in spinning is important because it influences spinning limit, yarn strength, evenness and hairiness. It also contributes to the handle and luster of the product by influencing the number of turns of twist required. It influences productivity via the end breakage rate and end breakage rate.

In general, fibers less than 4 to 5 mm are lost at the spinning stage. Fibers from 12 to 15 mm do not contribute to strength but only to the fullness of the yarn. It is only fibers greater than 15mm in length that produce other positive characteristics in the yarn.

Fiber length after carding is most important. Conditions at card and fiber characteristics should be such that the fibers survive carding without noticeable shortening in length.

The fiber lengths can be assessed with the help of a staple diagram.

Remember that the fibers in the boll do not show extremely great length differences. Noticeable differences arise even before the spinning starts. This happens due to mechanical working on the fibers at the ginning and

cleaning stage.

Rectangular Staple

Such diagram is achievable with synthetic fibers.

However such lengths can cause problems in drafting as in drafting stage fibers do not move individually but in bunches, thereby producing a high degree of unevenness.

Triangular Staple

It lends itself to better processing than rectangular staple diagram. However, it produces too many short fibers which cannot be maintained under control. Thus it produces hairy yarn.

Trapezoidal Staple

The fibers depicting such diagram are ideal for processing.

Stepped Staple

It indicates that fiber materials of different lengths are mixed in wrong proportions. It has the disadvantage that fibres move only in bunches which produce a high degree of unevenness.

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Influence of Fiber Fineness and Maturity in spinning Process

Influence of Fiber Fineness and Maturity on spinning Process

Fiber Fineness

Fiber fineness determine how many fibers are present in the cross section of a yarn of given thickness. Additional fibers in the cross section not only provide additional strength but also a better distribution in the yarn. Minimum 30 fibers are needed, usually over 100 fibers are required. Fiber fineness influences spinning limit, drape of the fabric, yarn strength, luster, yarn evenness, handle, yarn fullness and productivity. Productivity is influenced by reduced end breakage rate.

In a conventional spinning process, fine fibers accumulate to the core and coarse fibers in the periphery.

Fiber fineness is measured in dtex which is equal to ratio of mass in dgrams and length in km. Decitex is equal to the product of Micronaire value of the cotton and 0.394.

Cotton fibers are generally classified as very fine if they have a micronaire value upto 3.1; fine if they have value between 3.1 to 3.9; medium if they have it between 4.0 to 4.9; slightly coarse between values of 5 to 5.9 and coarse if they have a micronaire value above 6.

Fiber Maturity

Cotton fiber consists of cell wall and lumen. The maturity index depends upon the thickness of the cell wall. The fibers are considered ripe if they have maturity index between 50-80 percent, unripe if they have MI between 30 to 45% and dead when they have it less than 25%.

Unripe fibers have neither adequate strength nor adequate longitudinal thickness. They lead to loss of yarn strength, neppiness, high proportion of short fibers, varying dyeability, processing difficulties mainly at the card.

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Fiber Identification - Burning Test- Man-made Fibers

Viscose Rayon 

All viscose including High Wet Modulus scorch and ignite quickly when brought near the flame. Like cotton they burn quickly with yellow flame when in the flame. When removed from the flame they continue to burn. There is no afterglow unlike cotton. The smell is that of burning paper. They leave a light gray and feathery ash.

Acetate Rayon  ( And Triacetate Rayon)

When brought near the flame, it fuses away from flame turning black. When in the flame, it flames quickly. The fabric puckers, sputters and melts. It drips like burning tar. When removed from the flame, it continues to burn and melt. It smells like vinegar. It leaves a brittle hard, irregular black ash which is difficult to crush.

Nylon 

Image via Wikipedia

Nylon fuses and shrinks away from the flame when brought near the flame. In flame, it burns slowly without melting. When removed from flame the flame diminishes and tends to die out. It has somewhat pungent odor. It leaves a hard, round, tough and gray bead.

Aramid  ( Nomex)

When brought near the flame, it shrinks away from the flame. When in the flames it puckers and chars. When removed from flame, it extinguishes by itself. It has no smell and it leaves a hard black bead.

Polyester  

Image via Wikipedia

Polyester fuses and shrinks away from flame. When in flame, it burns slowly with melting. When removed from the flame, it burns with difficulty. It has slightly sweetish smell. It leaves a hard round brittle, black bead.

Acrylics 

Orlon, Acrilan and Creslan and Zefran fuse and melt away from Flame when brought near the flame. When in flame Orlon flames rapidly. The fiber puckers, sputters and melts. Acrilan flames rapidly and melts. Creslan flames and melts and Zefran sputters slightly and flames. When removed flame all of acrylics continue to burn and melt. Orlon has a slightly burning meat-like smell. Acrilan has a buring steak smell. Creslan has sharp sweet smell and Zefran has a turmeric like smell. Orlon, Acrilan and Cresla have hard, brittle and irregular black bead. Zefran has irregular black ash that can be crushed easily.

Modacrylics

Verel and SEF fuse and shrink away from the flame when approached near a flame. When in flame, Verel burns very slowly with melting. SEF shrinks, melts and smolders. When removed from flames, all modacrylics are self extinguishing. Verel has a gunpower smell whereas SEF has a sharp sweet smell. Verel leaves a hard and irregular black bead whereas SEF leaves a hard and irregular black bead.

Spandax 

Fuses but doesn’t shrinks away from the flame when approached near the flame. When in flame, it burns with melting. It has an acrid smell. It leaves a soft, fluffy black bead.

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Identification of Natural Fibers by Burning Test

Identification of Natural Fibers by Burning Test


Cotton

When cotton is brought near the flame it scorches and ignites readily. In the flame it burns quickly with yellow flame. Upon removing from flame it continues to burn rapidly and shows afterglow. It emits a smell of burning paper. The Ash is light, feathery and grayish. If the ash is black it denotes mercerized cotton.

Linen

Linen like cotton when brought near the flame scorches and ignites easily. In the flame it burns slower than cotton with yellow flame. Upon removing from flame it continues to burn with a smell of burning paper. The ash residue is feathery and gray.

Wool

Wool when brought near the flame smolders. In flame it burns with small and slow flickering flame. Also in flame it sizzles and curls. When removed from flame it ceases to burn. The Odor is like that of burning feather or hair. It gives crisp, dark and irregular shaped ash that can be crushed easily.

Pure Silk

Pure silk smolders when brought near the flame. In the flame it burns slowly with sputtering. When removed away from flame it continues to burn but with difficulty and ultimately extinguishes. The smell that is emitted is like that of burning feathers or hair but it is less pronounced than wool. It gives out a round, crisp, shiny black beads that can be crushed easily.


Weighted Silk

Weighted Silk smolders when brought near the flame. In the flame it burns with a glow. When removed from flame the burned part becomes briefly incandescent then it slowly chars. The smell is like that of pure silk i.e. burning feather or hair. The ash brings a screen like skeleton of original sample.

The following guide is very handy in identifying the fibers by burning test:

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Suitability of a fiber for a blend

Fibers in a blend are chosen keeping in mind various properties of the constituent fibers. Thus a blend is chosen which gives the best of properties of the different constituents of the blend. The properties that are considered can be strength, absorbency,crease resistance, resistance to abrasion, resistance to heat, bulkiness,resistance to pilling and Dimensional stability.All the fibers do not have all the properties that are desired. This is the very reason why blend is chosen.

Cotton has moderate strength and dimensional stability. However, it is excellent in absorbency, resistance to heat and pilling. It has an average resistance to abrasion and poor bulkiness properties and crease retention.Thus it is added in the blend to have excellent absorbency properties.

Viscose Rayon has excellent absorbency, resistance to heat and pilling. Thus it is similar to cotton in these properties.It has however, poor resistance to abrasion, bulkiness, crease retention and stability. It has an average strength. It has absorbency properties similar to cotton. It is also cheaper than cotton.

Acetate Rayon has excellent resistance to pilling and stability. It has moderate resistance to heat and average absorbency, crease retention and stability. However its resistance to abrasion is very poor.

Wool has excellent absorbency, bulk and wrinkle resistance. However, it has poor stability. It has moderate abrasion and heat resistance. Its crease retention, resistance to pilling and strength can only be considered as average.

Nylon has excellent strength, stability and abrasion resistance. However, It has poor absorbency and bulk. It has moderate crease retention and average resistance to heat and pilling.

Polyester has excellent strength, stability, crease retention and abrasion resistance. However it has poor absorbency, bulkiness properties and resistance to pilling. Its resistance to heat is average.

Acrylic has excellent bulk and stability. It has moderate resistance to heat and average crease retention and strength. Its resistance to abrasion and pilling and absorbency are very poor.It is similar to wool in most of the properties. It is also cheaper than wool.

Modacrylic has excellent stability and bulk properties. However its absorbency, resistance to heat and pilling is very poor. It has average strength, resistance to abrasion and crease retention.

Polypropylene and Polyethylene have excellent stability and strength. They have poor absorbency, bulk and heat resistance. The have average crease resistance and resistance to pilling.

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Polyurethane Fibres ( Spandax, Lycra)

Polyurethane Fibres ( Spandax, Lycra)

Polyurethane is produced by action of butanediol and hexamethylene diisocyanate.

The polyurethane thus formed has rubber like properties. It gives an elastomeric fibre, which displays elasticity associated with natural rubber and hence can be stretched several times its original length and on releasing the stretching loads it will snap back quickly to recover its original length almost completely. Therefore polyurethane fibres are called snap back or elastomeric fibres.

Different Steps in Fiber Manufacture

Prepolymer Production:

The soft segments of the final polymer are formed in this step. The segments are the source of amorphous regions which permit unfolding of the molecular chains leading to the extension of the fibre under tensile stresses. These segments are made by normal condensation polymerisation techniques. These segments have hydroxy groups at the end.

Reaction Between prepolymers and Diisocyanate

The first prepolymer is reacted with excess of diisocyanate to form urethane groups in the molecular chains.

Segmented polyurethane production

In this step the hard segment is created by chain extension in which second prepolymer is treated with glycols or diamines.

Spinning

When the final polymer contain essentially linear macromolecules then it is dissolved in the solvent ( eg. DMF- Dimethyl Formamide) and extruded through spinnerettes into a coagulating bath ( water) as in wet spinning or into an atmosphere to remove the solvent as in dry spinning.

Properties

Strength: 0.55-1.0 gpd

Extension at Break: 520-610 %

Specific Gravity: 1.20-1.25

Set % at 600% stretch: 70%

Moisture Regain: 0.8-1.2

It is a thermoplastic fibres which sticks at 170 deg C and melts at 230 deg C

It has an excellent resistance to sunlight

It is resistant to insects and microorganisms.

It is resistant to common solvents such as dry cleaning solvents and saturated hydrocarbons.

Chemical Properties

It has good resistance to cold dilute Acids, Hot concentrated acids slightly yellow it.

It has a good resistance to weak and cold alkalies. It has good resistance to cosmetic oils and lotions. Chlorites and hypochlorites attack the fibre.

When heated the fibres fuse and do not shrink from the flame. They burn and produce soft fluffy black ash.

Polypropylene Fibres- Manufacturing Process

Polypropylene Fibres

Propylene is one of the constituents obtained from thermal or catalytic cracking of petroleum. Under suitable polymerising conditions, propylene produces fibres forming polypropylene.

Polymerisation: It is done by dissolving propylene in heptane using TiCl3Al(C2H5)3 catalyst system at about 100 deg C under a pressure of 30 Atm for 8 hours. The polymer has a molecular weight of about 80000.

Spinning : Polypropylene is melt spun. The filaments are extruded at 100 deg C above the melting point, cooled in air chamber and collected on bobbins. The filaments are hot drawn (polyethene- cold drawn) and twisted into yarns.


Properties:

1. PP fibres are colorless and have a smooth surface, with round cross section.

2. Tenacity- 4.5-6 gpd
Elongation at Break: 17-20 %
Elastic Properties at 2% extenstion: Instantenous
Stretch for 30 Seconds: 91%, delayed - 9%
Moisture Regain: Nil

3. Boiling water shrinks PP by about 15-20% in 20 minutes

4. Specific Gravity: 0.85-0.92

5. Softening point- 150 deg C, Melting Point: 160-170 deg C

6. PP is also attacked by atmospheric oxygen in presence of sunlight

7. It has excellent resistance to common organic solvents

8. It is resistant to insects and microorganisms

9. PP is generally resistant to common chemicals.

Polyethylene Fibres

Polyolefin fibres

Fibres made from polymers or copolymers of olefin hydrocarbons such as ethylene, propylene are called polyolefins.

Polyethylene: Of all the fibre forming polymers, polyethylene (made by addition polymerisation) Ch2==Ch2 has the simplest structure.

Manufacture: Ethylene is the principal raw material for producing polyethylene fibres. Ethylene gas is obtained by cracking petroleum.

Polymerisation: Ethylene is polymerised under severe conditions in autoclaves at 200 deg C and 1500 atmospheric pressure in the presence of traces (0.01%) of oxygen acting as a catalyst. The polymer resembles paraffin wax and is characterised by low density.

Spinning : Spinning of polyethylene is carried out by melt spinning. The polymer with a molecular weight of about 15,000 is spun from the melt at about 205 deg C and extended through a spinnerette of 0.1 mm diameter into a current of cooling gas. The filaments are cooled to 15 -60 deg C and stretched 4 to 10 times their original length. The drawn monofilaments are wound on spools.

Properties of polyethylene

a. Polyethylene fibre has a round cross section and has a smooth surface. Fibres made from low molecular weight polyethylene have a grease like handle.

b. Specific Gravity- 0.92
Tenacity - 1.0-1.5 gpd
Elongation at Break %- 45-50
Tensile Strength psi - 15000
Softening Range: deg C- 85-90

c The moisture regain of polyethylene is practically nil and hence moisture does not affect the mechanical properties of the fibres.

d. Polyethylene is insoluble in most of the common organic solvents at room temperature.

e. Polyethylene fibres have a high degree of resistance to acids and alkalies at all concentrations even at high temperature.

f. The fibre is generally inert and is resistant to wide range of chemicals at ordinary temperatures. They are attacked by oxidising agents.

Manufacturing Process and Properties of PVA

Polyvinyl Alcohol Fibres

Polyvinyl alcohol (water soluble compound) can be described as a polyhydric, having secondary alcoholic groups on alternate carbon atoms of an aliphatic macromolecule.

Because of the presence of a large number of hydroxy groups, in its molecular structure, it is soluble in water. This is solublised in water by a treatment with formaldehyde.

Manufacture of Polyvinyl Alcohol


1. Production of acetic acid from acetylene

For this purpose, limestone is calcinated to give quicklime (CaO) which is treated with coke at elevated temperature to form calciium carbide. Acetylene is generated by treating calcium carbide with water. A part of acetylene is converted into acetic acidby combined hydration and oxidation.

Synthesis of Vinyl Acetate

The acetic acid formed in the above step is reacted with acetylene in the presence of zinc acetate catalyst when vinyl acetate is formed.

Polymerisation of Vinyl Acetate

A solution of vinyl acetate in methanol is used for the polymerisation of vinyl acetate in the presence of a peroxide or azo compound as a catalyst.

Conversion of PVAcetate into PVA

NaOH is added in PV Acetate solution in methanol, when alcoholysis of the acetate groups takes place.

Spinning

The precipitated PVA as obtained in the preceding step is pressed and dried. It is then dissolved in water to give a 15% solution of the polymer. This solution is extruded into a spinning bath containing sulphuric acid ( 20%), Glauber's Salt ( 25%), formaldehyde (5%) and water (50%)

Properties

Shrinkage Properties: 10% at 220-230 deg C.

At 220 deg c, It begins to turn yellow and shrinks.

The fiber is inert to animal, vegetable and mineral oils and to most common organic solvents.

It has good resistance to acids under normal conditions, Hot or concentrated mineral acids cause swelling and shrinkage. Its resistance to alkali is generally good. Strong alkalies cause yellowing without affecting the tenacity.

Fabrics made from this fibre do not get solied easily. They are easy to wash and quick to dry. They have good crease retention.


Specific Gravity: 1.28

	Staple	Filament
Tenacity ( GPD)
Dry	3.8-6.2	6.0-8.5
Wet	3.2-5.0	5.0-7.6
Elongation at Break
Dry	13-26%	9-22%
Wet	14-27%	10-26%
Elastic Recovery	65-85%	70-90%
Moisture Regain	4.5-5%	3-5%

How to Identify Constituent Fibre Percentage in a Blend-2

Blend of Acrylic with Wool, Silk, Cotton, Viscose, Polyester or Nylon

1. Dissolve the acrylic fibres with (Dimethyl Formamide - DMF). Acrylic Fibres will dissolve in DMF.

2. Filter, rinse and weigh carefully to get the ratio of Acrylic Fibres.

Blend of Protein Fibres ( Wool or Silk) with cotton, polyester, nylon or acrylic

1. Take the blended fibres ( Carefully weighed) in a conical flask.

2. Add a solution of 5% (w/w) solution of Sodium Hydroxide or Potassium Hydroxide and boil for 10 minutes. Protein fibres will dissolve in Sodium Hydroxide or Potassium Hydroxide.

3. Rinse the leftover fibres with water and neutralise with dilute Acetic Acid.

4. Weigh the fibres after drying and find the ratio of protein fibres.

Blend of Polyester with Cotton or Viscose

1. Weigh the blend and heat it with Meta cresol. Polyester fibres will dissolve.

2. Weigh the residual fibres after rinsing thoroughly and drying and find the percentage of polyester fibres.

Blend of Elastane ( Spandex or Lycra) with Cotton or Viscose

1. Treat the blend with DMF. Elastane will dissolve in DMF.

2. Filter, Rinse, dry and get the weight of residual fibres to get the percentage of elastane.

How to Identify Constituent Fibre Percentage in a Blend-1

Blend of Polyester/Cotton (viscose)

1. Take 0.5 to 1.0 gms of blend sample, carefully weighed, and put it in a flask.

2. Add 75% (w/w) Sulphuric Acid (M:L::1:200).

3. Put in a water bath for one hour at 50+-5 deg C.

4. Filter it, whatever is left is polyester.

5. Wash it thoroughly.

6. Neutralise it with Dilute solution of Ammonia

7. Dry at 110 deg C, cool and weigh to find the Percentage of Polyester and the other cellulosic component.

Blend of Cotton/Viscose

1. Take 0.5 to 1.0 gms carefully weighed sample and put it in 60% w/w Sulphuric Acid. Keep material to Liquor ratio as 1:100.

2. Stir this solution mechanically for 30 minutes. Viscose fibres will dissolve by this process and cotton fibres will be left.

3. Filter the cotton fibres and wash it in Sulphuric Acid.

4. Again wash it with water and neutralise it with a dilute solution of Ammonium Hydroxide.

5. Dry and Weigh. Note that cotton fibres lose weight by 5% in this process. Apply this correction factor in finding the blend percentage .

Blend of Polyester/Cotton/Viscose

1. Put the fibres in 60% w/w sulphuric acid (after weighing). Viscose will dissolve in 60% w/w sulphuric acid.


2. Dry and weigh carefully the rest of the fibres.

3. Put these fibres in 75% sulphuric acid. Cotton will dissolve.

4. The fibres left will be of polyester, which are weighed after thorough washing and drying.

Polyvinyl Chloride- Manufacturing Process and Properties

Polyvinyl Chloride (Vinyon)

Fibre Manufacture:

Vinyl Chloride is the principal raw material from which polyvinyl chloride is made by addition polymerisation. There are two methods commonly used for the production of vinyl chloride:

1. Ethylene+ chlorine--> Ethylene Dichloride--600 deg C--> Vinyl chloride +HCl

or

Cl-CH2-CH2-Cl--300deg C +Charcoal--> Vinyl Chloride + HCl

or

Cl-CH2-CH2-Cl--CH3OH+NaOH (60 deg C)--> vinyl Chloride + NaCl+ H2

2. Acetylene +HCL--150 deg C, HgCl--> CH2=CHCl (Vinyl Chloride)

Polymerisation

the vinyl chloride monomer is polymerised in the emulsion form in an autoclave at a pressure of 50 Atm and at a temperature of 65 deg C. A suspension of the polymer is obtained which is then spray dried.

Spinning

This may be done by dry spinning or wet spinning.

1. Dry Spinning: In the dry spinning process the polymer is dissolved in a mixture of CS2 and acetone, filtered and pumped at 70 deg to 100 deg through spinnerettes into a chamber, provided with heated walls, and into which air is introduced. The solvent evaporating from the extruded filaments is carried away by the air. At the bottom of the chamber the solvent free filaments are removed through a fine orifice and wound on a bobbin. The solvent is recovered and used again. the filaments are stretched to ensure that the molecular chains get oriented and the fibres become stronger and attain less extension at break, increased brightness, transparency etc.

2. Wet Spinning: In the wet spinning process, PVC is dissolved in THF (Tetra Hydro Furon) to give a highly concentrated solution, which is spun into water, through a stretch spinning funnel. The filaments ar stretched and cut into staple fibres.

Properties

1. Tenacity: Wet or Dry: 2.7-3 gpd
2. Elongation at BreaK: Wet or Dry: 12-20 %
3. Moisture Content: 0
4. Specific Gravity: 1.4

v. Effect of Heat: It contracts at temperatures above 78 deg C and shrinks to half its original length at 100 deg C.

vi. It has an excellent resistance to sunlight. It is completely resistant to insects and microorganisms. It is inherently non-flammable.

vii. It is exceptionally resistant to caustic soda, nitric acid and sulphuric acid. It has outstanding resistance to many chemicals including bleaching agents, reducing agents.

Acrylic- Manufacturing Process and Properties

Polyacrilonitrile ( Acrylic)

vinyl Cyanide, more commonly known as acrylonitrile, can under go addition polymerisation to form polyacrylonitrile.

Raw Material

Acrilonitrile is the main main raw material for the manufacture of acrylic fibres. It is made by different methods. In one commercial method, hydrogen cyanide is treated with acetylene:

acetylene + Hydrogen cyanide --> Acrilonitrile

2nd Method

Ethylene--Air Oxidation--> Ethylene oxide + HCN--> Ethylene cyanahydrin--Dehydration at 300 deg C (catalyst)--> Acrylonitrile

In a continuous polymerisation process, 95% acrylonitrile and 6% methyl acrylate (400 parts) 0.25% aqueous solution of K2S2O8(600 parts), 0.50 % Na2S2O5 solution ( 600 Parts) and 2N sulphuric acid (2.5 Parts) are fed into the reaction vessel at 52 deg C under nitrogen atmosphere giving a slurry with 67% polymer. The slurry is continuously withdrawn, filtered and washed till it is free from salts and dried.

Acrilonitrile is dry spun. The material is dissolved in dimethyl formamide, the solution contains 10-20 polymers. It is heated and extruded into a heated spinning cell. A heated evaporating medium such as air, nitrogen or steam moves counter current to the travel of filaments and removes the solvent to take it to a recovery unit. The filaments are hot stretched at 100 to 250 C depending on the time of contact in the hot zone, to several times their original length.

Properties of Acrylic Fibres

1. Acrylic has a warm and dry hand like wool. Its density is 1.17 g/cc as compared to 1.32 g/cc of wool. It is about 30% bulkier than wool. It has about 20% greater insulating power than wool.

2. Acrylic has a moisture regain of 1.5-2% at 65% RH and 70 deg F.

3. It has a tenacity of 5 gpd in dry state and 4-8 gpd in wet state.

4. Breaking elongation is 15% ( both states)

5. It has a elastic recovery of 85% after 4% extension when the load is released immediately.

6. It has a good thermal stability. When exposed to temperatures above 175 deg C for prolonged periods some discolouration takes place.

7. Acrylic shrinks by about 1.5% when treated with boiling water for 30 min.

8. It has a good resistance to mineral acids. The resistance to weak alkalies is fairly good, while hot strong alkalies rapidly attack acrylic.

9. Moths, Mildew and insects do not attack Acrylic.

10. It has an outstanding stability towards commonly bleaching agents.

Uses

1. Knit Jersey, Sweater, blankets
2. Wrinkle resistant fabrics.
3. Pile and Fleece fabrics
4. Carpets and rugs.

Properties of Polyester

Tenacity (gpd)	High Tenacity	Normal Tenacity	Staple
Dry	6-7	4.5-5.5	3.5-4
Wet	6-7	4.5-5.5	3.5-4
Elongation (%)
Dry	12.5-7.5	25-15	40-25
Wet	12.5-7.5	25-15	40-25
Density	1.38	1.38	1.38

Moisture Regain

At 65% RH and 70 deg F--> 0.4%

Because of low moisture regain, it develops static charge. Garments of polyester fibres get soiled easily during wear.

Thermal Properties

Polyester fibres are most thermally stable of all synthetic fibres. As with all thermoplastic fibres, its tenacity decreases and elongation increases with rise in temperature. When ignited, polyester fibre burns with difficulty.

Shrinkage

Polyester shrinks approx 7% when immersed in an unrestrained state in boiling water. Like other textile fibres, polyester fibres undergo degradation when exposed to sunlight.

Its biological resistance is good as it is not a nutrient for microorganisms.

Swelling and Dissolving

The fibre swells in 2% solution of benzoic acid, salycylic acid and phenol.

Alcohols, Ketones, soaps, detergents and drycleaning solvents have no chemical action on polyester fibres.

Chemical Resistance

Polyester fibres have a high resistance to organic and mineral acids. Weak acids do not harm even at boil. Similarly strong acids including hydrofluoric acids do not attack the fibres appreciably in the cold.

Uses of Polyester

1. Woven and Knitted Fabrics, especially blends.
2. Conveyor belts, tyre cords, tarpaulines etc.
3. For filling pillows
4. For paper making machine
5. Insulating tapes
6. Hose pipe with rubber or PVC
7. Ropes, fish netting and sail cloth.

Manufacturing Process of Polyester

Manufacture of Polyester

These fibres are also known as Terylene, Terene, Dacron etc.

These fibres are synthetic textile fibres of high polymers which are obtained by esterification of dicarboxylic acids, with glycols or by ester exchange reactions between dicarboxylic acid esters and glycols.

Thus Terylene is made by polymerising using ester exchange reation between dimethyl teraphthlate and ethylene glycol.

Raw Materials

The main raw materials required for the manufacture of Terylene polyester fibres are p-xylene ethylene glycol and methanol.

or Dacron ( Du Pont ) is produced by polycondensation reaction using Teraphthaleic Acid (TPA) and Ethylene Glocol

Manufacture of TPA

P-xylene-- Air, nitric Acid-->P-Toluic Acid--> Teraphthaleic Acid

Manufacture of DMT

p-xylene--Air 200 degC, co-toluate--> Toluic Acid--Ch3OH--> Monomethyl toluate--oxidation--> Monomethyl teraphthalate--CH3OH--> DMT

The use of Dimethyl Teraphthalate is preferred instead of Teraphthalic acid as the purity of the reacting chemicals is essential and it is easier to purify DMT than teraphthalic acid.

Manufacture of Ethylene Glycol

Ethylene--Oxidation with air-->Ethylene Oxide--Hydrolysis-->Ethylene Glycol
or
Ethylene--Hypochlorous Acid HOCl--> Ethylene Chlorohydrin--Alkaline Hydrolysis--> Ethylene Glycol

Production


The polymer is made by heating teraphthalic acid with excess of ethylene glycol ( Both of high priority) in an atmosphere of nitrogen initially at atmospheric pressure. A catalyst like hydrochloric acid speeds up the reaction.

The resulting low molecular weight ethylene glycol teraphthalate is then heated at 280 deg C for 30 minutes at atmospheric pressure and then for 10 hours under vacuum. The excess of ethylene glycol is distilled off. the ester can polymerise now to form a product of high molecular weight. The resulting polymer is hard and almost white substance, melting at 256 deg C and has a molecular weight of 8000-10000. Filaments are prepared from this.

Spinning of Polyester Fibres

The polymer is extruded in the form of a ribbon. This ribbon is then converted into chips.

The wet chips are dried and fed through a hopper, ready for melting. This molten polymer is then extruded under high pressure through spinnerettes down to cylinder.

Each spinnerette contains 24 or so holes. A spinning finish is applied at this stage as a lubricant and an antistatic agent. The undrawn yarn is then wound onto cylinders.

This yarn goes to the drawing zone, where draw twist machines draw it to about four times their original length. This is hot drawn in contrast to cold drawing of nylon filaments.

For the production of staple fibres, the filaments are first brought together to from a thick tow. These are distributed in large cans. The tow is drawn to get correct strength. Then it is passed through a crimping machines, the crimps being stabilized by heating in ovens. It is then cut into specified lengths and baled ready for despatch.

Properties of Nylon 6

Properties of Nylon 6

Nylon 6 has certain advantages over Nylon 6,6,. Firstly the systheisi fo caprolectum is easier than that of Hexamethylene Diamine and Adipic Acid. Therefore it is cheaper to make Nylon 6 than Nylon6,6. Secondly Nylon 6 has greater affinity for acid dyes than Nylon6,6,

Mechanical Properties

Density: 1.14 g/cc
Tenacity: Dry= 4.2-5.8 gpd, Wet=4.0-5.3 gpd
Elongation at Break--> Dry = 24-40, Wet=28-43
Elastic Recovery at 4% extension= 100%
Moisture Regain= 4%
Because of low MR, wet nylon dries quickly.
Melting Point= 215 deg C ( Nylon 66-250 deg C)
It is weakened by prolonged exposure to sunlight.

Chemical Properties

1. It is resistant to most organic acids such as benzene, chloroform, acetone, esters ethers etc.

2. It dissolves in phenol, cresol and strong mineral acids.

3. good resistant towards alkalies.

4. Resistant to inorganic acids

These fibres are cylinderical in shape, with smooth surfaces and without having any markings. The fibres are unifrom in diameter and appear round in cross section.

Uses


a. Tyre Cord Manufacturing
b. Fishing Lines
c. Luxury Yachts
d. Stockings with good fit, sheerness, quick washing and drying properties.

Manufacturing Process of Nylon 6

Manufacturing Process of Nylon 6

Nylon Manufactured in India at present is of this type. This is made from Caprolactum which is made by a series of reactions using products obtained from coal tar

Coal Tar--> Benzene--Chlorine--> Chlorobenzene--> Sodium Phenate--HCL--> Phenol--H2 (Nickel)-->Cyclohexanol--Oxidation Air Fe, Zn Catalyst--> Cyclohexanone--> Cyclohexanone Oxime--H2SO4--> Caprolectum

Polymerisation

Caprolectum is a white flaky solid, melting at 68 deg C and is soluble in water. the polymerisation is carried out in stainless steel cylinders.

Hot Caprolectum is mixed with a suspension of pigment, acid promotor and acid chain stopper. The extent of polymerisation depends upon the temperature of polymerisation. The purpose of acid chain stopper is to stop furthur polymerisation so that a desired density of molten polymer may be obtained.

The molten polymer is extruded into ribbons and cut into chips. These chips are used for the production of continuous filaments.

Melt Spinning

Continuous filaments are made by melt spinning. Dry polymer chips are fed to a melt spinning apparatus, wherein one section of the chips fall, into a melting region where they are heated electrically to 250-260 deg C. The molten polymer flows into a conical section to form a pool, which feeds a spinning pump and spinnerette. The pool is kept under an atmosphere of nitrogen to prevent decomposition by air.

The molten polymer leaving the pump is filtered before entering the spinnerette which is a stainless steel disc having a number of holes, the number and diameter of which determine the type of yarn formed. Before reaching the machine in which cheese is build up, the filaments are moistened with water to ensure dimensional stability of the final packages.

The yarn thus formed is not strong enough and has a very high extensibility. the yarn contains a large number of macro molecules which are unoriented and these must be oriented so as to lie parallel to the length of the fibre to develop full strength. This is done by stretching the yarn to 3-4 times its original length.

Properties of Nylon 6,6

Properties of Nylon 6,6

Strength

The most outstanding property of nylon is its strength and elasticity. The tenacity varies from 8.8-4.3 gpd while corresponding elongation at break varies from 18-45%. The wet strength of nylon is 80-90% of its dry strength and the elongation at break increases by 5-30% on wetting.

Density: 1.14 g/cc

Elastic Recovery

When nylon yarn is stretched 1,2 and 4% with a load of 0.25 gpd for 30 seconds and then released the recovery after 60 seconds is 38, 63 and 73% respectively.

Moisture Regain

Nylon has a moisture regain of about 4% at 65% RH and 70 deg F.

Action of Light

Like other fibres, nylon undergoes degradation and weakens when exposed to lights.

Appearance

Nylon is dull and semi opaque before cold drawing, but on orientation its lustre is greatly incresed. Delustering is done by adding TiO2 in the polymerisation mixture.

Action of Heat

Nylon melts at 262 deg C in an atmosphere of Nitrogen and at 250 deg C in air. When a very hot iron is used for ironing nylon garments, sticking or even fusion may take place. Therefore ironing should not be done above 180 deg C. Permanent set may be applied to Nylon by heat setting with 25 psi pressure with saturated steam. The pleats thus set remian on wearing and washing even in hot water.

Chemical Properties

Nylon is extremely stable chemically. For example dry cleaning solvents, alcohols, aldehydes, ketones, ethers, hydrocarbons, chlorinated hydrocarbons, soaps and synthetic detergents and water including sea water do not affect Nylon.

Also it has got a remarkable stability towards alkali.

Biological Properties

Nylon is not a nutrient for Mildew or bacteria and is not eaten up by moth larvae. But they bite their way up when imprisoned in nylon cloth. It is harmless to human skin.

Manufacturing Process of Nylon 6,6

Manufacturing Process of Nylon 6,6

Nylon 6,6 is made from Hexamethylene diamine and adipic acid as shown in the figure below.



Spinning of Nylon 6,6



The chips of nylon polymer are fed through a hopper A, into a spinning vessel B, on an electrically heated grid ( perforated plate) C. The perforations are so small that the chips do not pass through, but when melted, the liquid can pass.

The molten nylon collects as a pool D, at the bottom of the vessel. This liquid should not come into contact with oxygen or air and hence nitrogen is introduced into the vessel. The molten polymer is kept at a temperature of about 288 deg C and sucked by a pump F, into a spinnerette E. The molten polymer solidifies as soon as it emerges out of the spinnerette. The filament thus formed pass through a colloing zone, in which cold air G circulates directed towards the filaments. The filaments are then passed through a steam chamber H, to wet them before winding on the bobbin L.

Drawing

Nylon filaments as obtained are not very strong. They have to tbe drawn 4-7 times their original length. This is done by cold drawing. The yarn in pulled off from bobbin L through guides M and N, between a pair of rollers O. The speed of rotation of these rollers determines the initial speed. The yarn then goes over a deflector P, and two to three times around roller Q, running at five times the speed than that of O. The yarn subsequently courses through another guide R, and wound on another bobbin which rotates at very high speed, to impart twist in the yarn before being wound.

Properties of Acetate Rayon

Properties of Acetate Rayon

55/20/3s means 55 denier yarn, 20 filament and 3 TPI S side.

Moisture content of sec. Cellulose acetate is 6.5% at 70 deg F and 65% RH.
( Moisture Content= Wt of water in a material /Total wt of material) ( Moisture Regain= wt of water in a material/ oven dry wt of material)
( RH= actual humidity/ humidity of air saturated in water).

Tenacity of Acetate rayon is 1.4 gpd at dry state and 0.9 gpd at wet state.

Elongation at break is 25% in dry state and 35% in wet state

Acetate Rayon is more sensitive to heat. It begins to weaken at 93 deg C. At 175 deg C it becomes sticky and melts at 260 deg C. Like nylon and polyester it is thermoplastic. Thus permanent crimp, pleats and creases can be imparted to the garment under carefully controlled conditions.

Acetate rayon is soluble in acetone, methyl ethyle ketone etc.

Some degeneration takes place when this fiber is exposed to light but not very serious.

It is stable to hot water.

It can also withstand treatment with soap or alkali solution having a pH of not more than 9.5 at temp upto 100 deg C. Therefore it can undergo normal scouring and dyeing operations without affecting the lustre.

It is unaffected by dilute solutions of weak acids but attacked by strong acids. Concentrated organic acids cause swelling

It is resistant to attack by bacteria and fungi. Its low moisture content contributes to resistance to mildew.

It is non toxic and non irritating to skin

Only a few striations ( 2-3) are present in the fibre as can be seen from the longitudinal view. The cross section of the fiber have individual lobes and are round and smooth. It is the smaller number of lobes or serrations of acetate fibres that distinguish the fibre from more numerous serrations of viscose rayon.