Sunday, 31 May 2009
Determination of Abrasion Resistance of Fabrics
Plain Abrasion Resistance
Apparatus - Universal Wear Tester
Prior to test, the fabric should be Conditioned to moisture equilibrium from the dry side, in the standard atmosphere of 65+-2% relative humidity and 27+-2 deg C temperature. The test should be carried under standard atmospheric conditions.
Method for determination of plane Abrasion Resistance
1. Cut five circular test specimens of 112 mm in diameter, taking care to take specimens from areas containin the same wales or courses in knitted fabric or the same warp or weft yarn in woven fabric.
2. Set the instrument for inflated diaphram test.
3. Place the specimen over the rubber diaphram in smooth condition and clamp the specimen in place without disturbing it.
4. Place the abrasive paper on the abradent plate under sufficient tension to be held smooth and in such a position that the contact pin, reaching through a hole in the abradent is even with the surface of the abradent. In the absence of any specific material specification , zero emery polishing paper should be used as the abradent.
5. Set the air pressure under the diaphram and load on the abradent plate. In the absence of any specific material specifications, the air pressure should be 0.3kg/sq.cm (4 p.s.i.) and the load on the abradent should be 454 gm. Ensure that the air pressure control and contact between the inflated specimen and loaded abradent is in a state of equilibrium before abrasion is started. To ensure consistent inflation of the diaphragm, inflate to a higher air pressure ( 25 per cent) and then reduce the testing pressure.
6. If the unidirectional abrasion is desired, disengage the rotation mechanism of the specimen clamp and bring the specimen into the direction by turning and setting the clamp after the diaphragm has been inflated.
7. In the event that multi-directional abrasion is required, or if no specific indication as to the abrasion direction is given in the fabric specification, engage rotation mechanism of the specimen clamp.
8. Remove pills of matted fibres interfering with proper contact between specimen and abradent during the test if they cause a marked vibration of the abradent plate.
9. If the specimen slips in the clamp or the air pressure does not remain constant during the test or anomalous wear pattern is obtained, discard such individual measurements and test an additional specimen..
10. One of the following methods is selected for determination of end point as per test specifications:
a. Breakage of Thread: Abrade the specimen until all fibres in the centre of the abraded area are worn off so that the diaphragm and abradent head come into contact and the instrument automatically stops.
b. Removing a predetermined thickness of the material. Abrade the specimen using the electrical depth micrometer to determine the automatic end-point for removing a predetermined thickness of the material from the specimen.
11. Unless the continuous changing abrasion head is used, abradent paper is changed after every 300 cycles.
12. Report shall include the following information :
a. Type of abradent
b. Type of abrasion ( unidirectional or multi directional)
c. No. of cycles to reach the end point as determined by electrical contact.
Testing Abrasion Resistance For Socks
|Tenacity (gpd)||High Tenacity||Normal Tenacity||Staple|
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.
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.
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.
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.
Saturday, 30 May 2009
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.
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
Ethylene--Hypochlorous Acid HOCl--> Ethylene Chlorohydrin--Alkaline Hydrolysis--> Ethylene Glycol
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.
Friday, 29 May 2009
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,
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.
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.
a. Tyre Cord Manufacturing
b. Fishing Lines
c. Luxury Yachts
d. Stockings with good fit, sheerness, quick washing and drying properties.
Thursday, 28 May 2009
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
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.
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.
Wednesday, 27 May 2009
Properties of Nylon 6,6
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
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.
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.
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.
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.
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.
Tuesday, 26 May 2009
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.
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.
Saturday, 23 May 2009
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.
Friday, 22 May 2009
We know that
Alcohol + Acid --> Ester
If the cellulose is treated with acetic acid under certain conditions the free hydroxyl groups of cellulose are converted into ester groups.
Manfacture of cellulose acetate
Unlike inthe case of viscose rayon and cuprammonium rayon, where cellulose is dissolved and regenerated, cellulose acetate is manufactured by converting cellulose into a chemical compound of cellulose ( or chem modified cellulose) which is then dissolved in a suitable solvent ( chloroform or acetone) and spun by evaporating the solvent. Thus while viscose and cuprammonium rayons are regenerated fibres, acetate rayon is regenerated modified fibre.
Cotton linters and wood pulp are the most common employed raw materials for the manufacture of acetate rayon
The pretreated purified cotton linters are fed into an acetylator ( closed vessel) containing a mixture of acetic anhydride, glacial acetic acid and a small amount of concentrated sulphuric acid. For every 100 kg of cotton linters, 300 kg of glacial acetic acid, 500 kg of acetic anhydride and 8-10 kg of concentrated su;phuric acid may be used. The acetylator consists of a metal tank having a circular door at the top. The door is sealed after adding the mixture of chemicals and cotton linters. A stirrer having many blades rotates in the acetylator to mix the ingredients thoroughly. The acetylation reaction is an exotherimic reation. Heat is removed by circulating cold water through a jacket fitted to the acetylator. The acetylation reation is completed in 7-8 hours at 25-30 deg c. Triacetate is formed at this stage and it is in the form of a suspension in the acetylation mixture called the acid dope.
Hydrolysis ( Partial Deacetylation)
The acid dope from the above process is stored in jars for ageing. Acetic acid, water and sulphuric acid are added and allowed to stand for 10-20 hours. During this period, called ripening period, partial conversion of acetate groups to hydroxy groups takes place. The mixture is then diluted with water and stirred continuously when white flakes of acetate rayon get precipated. The flakes are placed in a centrifuge and the excess water is forced out of the cage through perforations. The flakes are then dried.
Spinning Solution or Dope
Acetate rayon is manufactured by dry spinning. It is dissovled in a volatile solvent (Acetone) to form the spinning solution or dope. This solution is forced through a spinnerette into a chamber in which hot air is circulated. The solvent evaporates leaving filaments of acetate rayon.
The details are as follows. Dried acetate flakes are mixed with three times the weight of acetone in enclosed tanks which are provided with powerful stirrers. The acetate dissolves slowly in the solvent. It takes about 24 hours for the complete dissolution to give a thick clear liquid called dope. The solution is filtered and deareated.
The dope is spun into acetate rayon filaments on the dry spinning process. The dope is fed from a spinning tank into spinning cabinets. The dope coming out of the spinnerette travels a distance of 2-5 meters vertically downwards to a feed roller, from where it is guided on to a bobbin at a much greater speed than the speed of spinning. This imparts twist to the filaments.
Sunday, 17 May 2009
These two websites - one of which is a commercial exporter's and the other is about hand painted silk, provide some valuable information about silk.
First of all, definitions. One can go through the definitions here. However, I was always looking for the definitions of the following types of Silk.
1. Mulberry Silk
I was not particularly looking for this definiton. Silk produced by silk worm (Bombyx Mori) fed on Mulberry Leaves.
2. Tussar Silk
I was particularly looking for this:
Larvae of several species of moth such as Antheraea mylitta, Antheraca proylei, Antherea pernyi and Antheraca yamamai produce this silk.The insects mostly live in the wild on bushes and trees on which they feed.
3. Katiya Silk
A big one for me.
The portion of Tussar cocoons leftover after about 60% reelable silk is spun into Katiya yarn.
4. Balkal Silk
The peduncles (silk that anchors the cocoon, it is very weak) are utilised for production of Balkal yarn.
5. Muga Silk:
It belongs to same family as Tussar. It is popular for its natural golden colour, glossy fine textures and durability. Muga silk is produced by Antheraea assama westwood which is an endemic species prevalent in the Brahmaputra valley and adjoining hills.
Muga silkworm is a polyhageous insect which feeds on leaves of Som, Soalu and other plants which grows abundantly in Brahmapautra valley.
Eri Silk :
The word Eri is a derivative from Sanskrit nomenclature for Castor Plant, eranada. Castor leaf is the main food for the Eri silkworms and so named as Eri. This is the only completely domesticated non-mulberry variety. Its silk is spun as it can not be reeled.
A Silk yarn made of short lengths of silk obtained from silk wastes, pierced cocoons or floss which gives yarn its characteristic brilliance. There are two grades of yarn Schappe and Bourette. It is spun on special machinery which in some ways is akin to cotton and worsted.
Noil Short fibres removed in combing operation of yarn making of Spun silk is spun into Noil yarn. Noil is mostly produced in Karnataka and Madras.
An irregular, rough silk reeled from double cocoons or cocoons spun side-by-side which are interlocked, making it necessary to reel them together. The unevenness of the yarn confines its use.
A raw silk which is reeled by machine as distinct from silk prepared by hand in cottage industry.
Another Big One.
Matka Silk is obtained from waste Mulberry silk by hand spinning without removing the gum (sericin). Cocoons required to produce Matka are mainly obtained from Karnataka and Kashmir but spinning is mostly done in the villages of Malda and Murshidabad districts in West Bengal by women by hand spinning.
Filaments of the cocoons of this silk from Bihar were originally unwound and plied together on a mud pot, or Matka ( Today, they are alikely to be reeled on a woman's thigh)
Though not a silk fabric yet very important from the point of view of traditional textiles. It is a veg based fabric. A satin weave with rayon warp and cotton weft, creates a high glossy surface.
Gajji Silk is satin weave done on silk fabric. Used in Tie-Dye Sarees in Gujarat state of India
Care of Silk Fabric: This site gives it comprehensively among other resources.
such as Interesting Facts about silk Fabrics and Scarf Tying Techniques
I am still looking for the following definitions of Silk
Some other Snippets
* All tussar is wild silk which is produced from an unraptured cocoon.
* Ghicha and Matka are produced from Raptured cocoon.
* Korea Silk is also known as 33/37 fiber. Generally we have fabrics of korea x korea , korea x china and korea x desi. Korea x Korea can be made on powerloom. The other two qualities are not possible to make on powerloom because of their marked evenness.
* When a supplier talks about 2x1 Korea x China, it means he has taken two threads of Korea together in warp (not twisted, but just taken together) .
* Generally reed in these fabrics is always 72
* China silk is also known as 50/70 fiber. It is paler and coarser in appearance than Korea.
* Desi is a raptured silk from India. Very uneven yet brilliant when worn.
Friday, 15 May 2009
Properties of Cuprammonium Rayon
1. The one important characteristic of these fibres is their extreme fineness. Filaments as fine as 1.33 deniers are produced regularly ( as compared to viscose rayon which have a usual denier of around 2.5). This increased fineness is due to the stretch that is applied to the filaments during spinning.
2. Because of its fineness, cuprammonium rayons produce a soft silk like handle.
3. It has all the properties of cotton except that the average DP is lower and a larger portion of this fibre is occupied by amorphous regions. Hence the rayon swells to a greater extent and hence chemical reactions take place faster in the case of rayon than in case of cotton.
4. Like viscose rayon it burns rapidly and chars at 180 deg C. It is degraded and weakened by exposure to sunlight in the presence of oxygen and moisture. On ignition, it leaves behind ash containing copper.
5. The average tensile strength of cuprammonium rayon is 1.7-2.3 in dry and 0.9-2.5 in wet state.
6. It has an elongation at break of 10-17% when dry.
7. Moisture content at 70 deg F and 65% RH is about 11% as in case of Viscose Rayon.
8. Dye absorption power for direct dyes of cuprammonium rayon is greater and shades obtained are deeper than viscose rayon.
9. The filaments appear uniform with surfaces having no markings, in the longitudinal view. Cross sections are round and smooth with occasionally slightly oval.
Thursday, 14 May 2009
Like Viscose Rayon, cuprammonium rayon is also a regenerated cellulose fibre. Cotton linters are used as the source of cellulose for this rayon.
Ammonical copper oxide solution is also known as cuprammonium hydroxide solution. Cuprammonium hydroxide solution is a solvent for cellulose. When a solution of cellulose in cuprammonium hydroxide is diluted with water or treated with dilute sulphuric acid, the cellulose is regenerated or reprecipitated. By using a spinnerette, filaments of this regenerated cellulose can be produced.
Manufacture of Cuprammonium Rayon
The source of cellulose for this rayon is cotton linters, the purification of cotton linters is carried out in two stages:
a. Mechanical Treatment
b. Chemical Treatment
The cotton linters are transported in bales in highly compressed state and the object of the mechanical treatment is to loosen them and to remove mechanically admixed and loosly bound impurities such as dust sand, seed residues etc.
The mechanically opened and purified cotton linters are boiled under pressure for several hours with dilute sod ash ( Na2Co3) solution (2%) to which a little amount of caustic soda may be added. The natural fatty matter present in the cotton is converted into soluble substance by the action of soda ash and thus removed from cotton linters.
Dissolution of Cellulose
In this, a solution of hydrated copper sulphate in 300-400 liters of water is introduced in a vessel at ordinary temperature with stirring. Some sugar is also added followed by caustic soda solution to form copper hydroxide.
Ground linters suspended in water are added to the above mixture to form copper cellulose.
The copper cellulose is filtered to remove the liquid, well ground and dissolved in a solution of ammonia in water.
By adding certain compounds to the cuprammonium cellulose solution, the solution is made more suitable for spinning. These compounds include glycerine, glucose, tartaric acid, citric acid, oxalic acid, can sugar etc.
In the spinning process, the cuprammonium cellulose solution is discharged through nozzles ( spinnerette) into a solution of sulphuric acid in the form of relatively thick threads which are subsequently pulled( stretched ) to very fine filaments.
Wednesday, 13 May 2009
Properties of Viscose Rayon
It absorbs more moisture than cotton. Moisture Content of Coton is 6% at 70 deg F and 65% RH, and for Viscose Rayon it is 13% under the same conditions.
The Tensile Strength of the fibre is less when the fibre is wet than when dry. It is 1.5-2.4 gpd in the dry state and 0.7-1.2 gpd in the wet state. For high tenacity variety the values are 3-4.6 gpd and 1.9 to 3.0 gpd.
The elasticity of Viscose Rayon is less than 2-3%. This is very important in handling viscose yarns during weaving, stentering etc when sudden tensions are applied.
Elongation at Break
Ordinary Viscose rayon has 15-30% elongation at break, whule high tenacity rayon has only 9-17% elongation at break.
The density of Viscose rayon is 1.53 g/cc. Rayon filaments are available in three densities: 1.5, 3.0 and 4.5
Action of Heat and Light
At 300 deg F or more, VR loses its strength and begins to decompose at 350-400 deg F. Prolonged exposure to sunlight also weakens the fibre due to moisture and ultraviolet light of the sunlight.
Viscose rayon consists of cellulose of lower DP than cotton cellulose. Also amorphous region of Viscose rayon is present to a greater extent, therefore, Viscose rayon reacts faster than cotton with chemicals. Acids like H2SO4 HCL breaks the cellulose to hydrocellulose. Oxidising agents like Na(OCl)2, Bleaching powder, K2Cr2O7, KMnO4- form oxycellulose. Cold acid solutions for a short time do not attack viscose rayon.
Action of Solvents
Textile solvents can be used on Viscose rayon without any deteriorating effect. Viscose rayon dissolves in cuprammonium hydroxide solution.
Effect of Iron
Contact with iron in the form of ferrous hydroxide weakens viscose rayon yarns. Therefore staining, marking or touching of rayon to iron or iron surface should be avoided.
Action of Microorganisms
Microorganisms ( moulds, mildew, fungus, bacteria) affect the colour, strength, dyeing properties and lustre of rayon. Clean and dry viscose rayon is rarely attacked by moulds and mildew.
The longitudinal view of these fibres show many striations running parallel to the long axis of the fibre. The cross section of viscose has striated periphery, having many sharp indentations, and cross sectional contours vary from circular and oval to ribbon-like forms.
Tuesday, 12 May 2009
Here is a site which gives some details about the fabrics sold in Indian markets ( although the language is a bit colloquial)
2x2 Rubia Cotton
Lizzy Bizzy Cotton:50% cotton 50% Polyster
Small Pleads cotton
Medium Pleads cotton
Crepe Back Satin
Artificial Silk Sari fabric
Silk Sari fabric
It is a regenerated cellulosic fibre and cellulose is the raw material for producing this man made fibre.
The raw material is obtained from a special variety of wood called spruce.
a. Purification of Cellulose:
The manufacture of viscose rayon starts with the purification of cellulose. Spruce trees are cut into timber. Their barks are removed and cut into pieces measuring 7/8" x 1/2" x 1/4". These pieces are treated with a solution of calcium bisulphite and cooked with steam under pressure for about 14 hours.
The cellulosic component of the wood is unaffected by this treatment, but the cementing material called lignin, which is present in the wood, is converted into its sulphonated compound which is soluble in water. This can be washed off, thereby purifying the remaining cellulose. This cellulose is treated with excess of water. After this it is treated with a bleaching agent (sod hypochlorite) and finally converted into paper boards or sheets. This is called wood pulp, which is normally purchased by the manufacturers of viscose rayon.
b. Conditioning of Wood Pulp:
The pulp sheets are cut by a guillotine to the required dimension and are kept in a special room. Air moves freely among the divisors by means of ventilatorys, the temperature is maintained at 30 deg celcius. In this way the desired moisture content can be had.
c. Steeping Process:
The conditioned wood pulp sheets are treated with caustic soda solution ( about 17.5%). It is called mercerising or steeping. The high DP cellulose (1000) is converted into soda cellulose. The sheets are allowed to soak (steep0 until they become dark brown in colour. This takes about 1-14 hours. The caustic soda solution is drained off and sheets are pressed to squeeze out excess caustic soda solution. 100 kg of sulphite pulp gives about 310 kg of soda cellulose.
4. Shredding or cutting process:
The wet, soft sheets of soda cellulose are passed through a shredding machine which cuts them into small bits. In 2-3 hours the sheets are broken into fine crumbs.
5. Ageing Process:
To obtain almost ideal solution of cellulose, the soda cellulose is stored in small galvanised drums for about 48 hours at 28 deg C. This process is called ageing process.The ageing process is essential. During This process, the DP od soda cellulose is decreased from 1000 to about 300 by oxygen present in the air, contained in the drum.
6. Churning Process or Xanthation:
After ageing, the crumbs of soda cellulose are transferred to rotating, air tight, hexagonal churners or mixers. Carbon disulphide ( 10% of the weight of the crumbs) is added to the mixer and churned together for 3 hours by rotating the mixers at a slow speed of 2 rev per minutes. Sodium cellulose xanthate is formed during this process and the colors of the product changes from white to reddish orange.
7. Mixing or dissolving Process:
The orange product i.e. sod.cell.xanthate is in the form of small balls. These fall into a mixer called dissover which is provided with a stirrer. A dilute solution of caustic soda is added, and the contents are stirred for 4-5 hours and at the same time, the dissovler is cooled. The sod.cell.xan. dissovles to give a clear brown thick liquor, similar to honey. This is called 'viscose' and it contains about 6.5% caustic soda and 7.5% cellulose.
8. Ripening Process:
This viscose solution requires to be ripened to give a solution having best spinning qualities. Ripening is carried by storing the viscose solution for 4-5 days at 10 to 18 deg. The viscosity of the solution first decreases and then rises to its original value. The ripened solutoin is filtered carefully and is now ready for spinning to produce viscose rayon filaments.
9. Spinning Process:
The viscose solution is forced through a spinnerette, having many fine holes ( 0.05-0.1mm) diameter. The spinnerette is submerged into a solution containing the following chemicals.
10% --> sulphuric acid, 18%- Sod sulphate, 1% - Zinc sulphate, 2% glucose, 69% water.
The spinning solution is kept at 40-45 deg celcius.
Sodium sulphate precipitates the dissoved sod. cell.xanthate. Sulphuric Acid converts xanthate into cellulose, carbon disulphide and sod. sulphate. the glucose is supposed to give softness and pliability to the filaments whereas zinc sulphate gives added strength.
The quality of viscose rayon filament formed depends upon:
1. The temperature of the spinning bath
2. The composition of the spinning bath.
3. The speed of coagulation
4. The period of immersion of the filament in the spinning bath.
5. The speed of spinning.
6. The stretch imparted to the filaments.
As a number of filaments emerge from the spinnerette, they are taken together to an eye at the surface of the spinning bath and then guided to two rollers from where they are wound on to a spindle.
Sunday, 3 May 2009
Common Yarn Faults in manmade fibres
Slub like thick faults seriously mar the appearance of fabrics made from manmade fibres. The following measures can be taken
A. In Blends with cotton
a. properly select the cotton component
b. ensure proper grinding of wirepoints at cards
c. regularly check the ringframe drafting system.
B. In 100% manmade fibres
a. Ensure adequate number of doublings
b. avoid too wide a roller setting and inadequate weighting on rollers.
c. Select correctly the fibres in regard to their compatibility in length.
This defect is characterised by the cracking sound produced when the yarn is pulled. The sound is produced due to sudden rupture of fibres curled around the yarn.
- Crackers are caused mainly by the presence of very long fibres due to improper cutting of the two.
- They can also be caused due to high vairability in the elongation of the constituent fibres in the blend.
- Ensure wider roller setting in the back zone, adequate roller weighting and avoid too narrow a spacing between the aprons.
- It is helpful to have low roving twist and higher spinning tension through the use of heavier traveller.
This can also mar the appearance of a fabric
- In man made fibres longer and finer fibres tend to produce more neps.
- Other reasons of neps are
- Excessing beating of fibres in the blow room
- Loading of licker-in or cylinder at card
- Blunt wire points on various carding elements
- excessive lap weight
4. Fluffy Yarn
In general presence of short fibres and proneness to static accumulation tend to produce this defect.
The fault can be corrected by maintaining proper atmospheric conditions and reducing the fluff on roving.
5. Smoky Yarn
- The yarn containing synthetic fibres get smoky through long exposure of the running bobbin in a dirty atmosphere in the ring spinning system.
- Installation of smoke filters in H-plant can correct the problem
- Use of roving build can check this defect.