Tuesday, 30 June 2009
Sunday, 28 June 2009
Monday, 22 June 2009
Why Cotton Shrinks
Why Cotton Shrinks
Cotton has the property of swelling in water and this effects shrinking when drying. Also the mechanical stresses, strain and tension, during spinning and weaving etc., when released causes the fabric to shrink.
The cotton fabric, when put in water, swelling occurs and rearrangement of internal forces takes place. The fibres will become free from tensionless state. These are the resons for shrinkage.
In case of a fabric, the warp yarns are under much strain due to interlacement than the weft yarns. The warp yarn shrinkage will be more than weft.
to overcome this, the fabric is extended in widthwise to some extent in the stenter machine during the finishing process. Then it is subjected to preshrink process.
How to Improve Colorfastness in Vat Dyeing
Colorfastness Problems in Vat Dyeing- Reasons and Remedies
Causes of Poor Colorfastness in Vat Dyeing
Frequent addition of colors in the dye bath to match the shade. It disturbs the equlibrium between colors and chemicals.
- Improper oxidation
- Improper washing
- Some peculiar colors such as blue and brown also leads to this defect.
- Hardness in the water used
- Mixing of incompatible colors
- Usage of large quantities of reducing agent and alkali
- Improper temperature
- Improper wringing of the cloth
- Faults in the machine
- Not using essential chemicals such as dispersing agent or leveling agents.
- Dyeing in a finished cloth ( Resin or Silicon Finish)
- Improper preparation of the cloth or thread for dyeing ( Like not removing impurities or size)
How to improve colorfastness in Vat Dyeing
1. Dont frequently add colors during dyeing
2. Ensure proper reduction clearance
3. Ensure proper oxidation
4. Choose right colors and chemicals
5. Control Temperarue
6. Use soft water
7. Add Dispersing or levelling agent as per need
8. Dont redye finished cloths
9. Ensure proper washing after dyeing.
10. Treat the material with small amount of Ammonia and Sodium Hydrosulphite
11. Treat the cloth with large amount of reducing agent and alkali. This method can be resorted to if there is some bleeding in the colors.
Sunday, 21 June 2009
The Measures of Fiber Length
The Measures of Fiber Length
1. Mean Length: Numerical Average length of fibres of given population of fibre.
2. Upper Quartile: Length for which 75% of all observed values are lower or 25% higher by weight or number
3. Modal Length: The most frequently occuring length of fiber.
4. Median Length: Length Below and above which 50% of fibres lie.
5. Half Fall Value: The fiber length higher than modal length having half the modal frequency by wt. (Group length longer than mode with frequency equal to 1/2 of mode.)
6. Effective Length: Upper quartile of numerical length distribution from which some of the shortest fibers, having length less than half of effective length are cutailed or eliminated.
7. short fiber %: It is the % of fibers having length less than 1/2 of the effective length value.
8. Uniformity Ratio: Ratio of 50% span length to 2.5 % span length.
9. Span Length: It is the distance that can be spanned by specified percentage of fibers in a test beard.
10. Irregularity: Percentage by weight fo fibers in a sample which are shorter than 3/4th of the mode.
11. Dispersion %: inter quartile range expressed as % of effective length.
How to Determine the Color Fastness of Textile material to Dry Cleaning
How to Determine the Color Fastness of Textile material to Dry Cleaning
Technical Specifications:
Apparatus:
1.To determine colorfastness to drycleaning a suitable mechanical device consisting of water bath containing a rotatable shaft which supports, radially, glass or stainless steel containers ( 75+-5mm diameter x 125+-10mm high) of approximately 550+-50 ml. capacity, being 45+-10mm high from the centre of the shaft should be used. The Shaft/container assembly is rotated at a speed of 40+-2 rev per minutes.The temperature of the water bath is thermostatically controlled to maintain the test solvent at 30 deg +-2 celcius.
2. Stainless stell disc of 30+-2mm x 3+-0.5mm, smooth and free from rough edges of mass 20+-2 gm.
3. Undyed cotton twill cloth of unit area 270+-70 gsm, free from finishing and cut into samples of size 12 cm x 12 cm
4. Grey scale for evaluating change in color and staining.
5. Glass tubes of diameter 25 mm
Preparation of the Specimen
For a fabric sample, take a specimen of size 10cm x 4cm from the sample representing the lot.
If the material to be tested is sewing thread, make a wick of parallel length 10 cm long and about 0.5 cm in diameter, tied near both ends.
Procedure
Prepare a bag with inside dimension of 10cm x 10 cm using the undyed cotton twill cloth by sewing together two squares of this cloth around three sides.
Place the specimen and 12 stell discs inside the bag and close the bag.
Place the bag in the container and add 200 ml of Perchloroethylene or any other suitable solvent at 30 +- 2 deg C
Fix the container in the mechanical device maintained at 30+-2 deg C and run the machine for 30 minutes.
Remove the bag from the container, withdraw the specimen and dry the specimen in air at a temperature not exceeding 60+-5 deg C.
Evaluate the change in color of the tested test specimen with grey scale, after attaining normal moisture content.
Filter the solvent remaining in the container through filter paper and compare the color of the filtered solvent with that of unused solvent in the glass tube placed in from the white card using transmitted light by means of grey scale for assessing staining.
In case of doubt in the color fastness rating as assessed by an observer, the assessment should be done by at least three observers and the overall average rating should be reported.
Report
Report the numerical rating for change in color of the test specimen and the numerical rating for staining of the solvent. Also report the solvent used for the test.
Saturday, 20 June 2009
Listing Defect in Vat Dyeing
Listing Defect in Vat Dyeing and the Precautions to Prevent the Defect
Listing is the variation in color of centre of the fabric with the selvedge. Some of the reasons for this defect are:
1. Improper batching.
2. Non Uniformity in the selvedge
3. Redyeing of the fabric
4. Foam on the two sides of the jigger.
5. Slippage of the fabric from the roller during dyeing.
6. Shortcomings in the machine such as malfunctioning of guide roll, expander roller or improper squeezing.
7. Improper filteration of the colors, improper circlation of the liquor during dyeing. Difference in temperature of liquor in the centre and at the ends.
8. Mixing of colors which are not properly compatible.
9. Improper singeing
The remedies are:
1. There should not be any mechanical fault in the machine.
2. Take proper care during dyeing, like filter the color solution before using, ensure that all the controlling instrument ( temperature, time) work properly. Circulate the liquor continuously during dyeing.
3. If some shade is not coming out proper, dye with a slighly heavy shade without taking out the earlier color.
4. Join the fabrics of the same width while making a lot.
Friday, 19 June 2009
How to Perform Test for Color Fastness to Rubbing
Colour Fastness to Rubbing: Why Fabrics Sometimes Leave Colour on Other Surfaces
A common complaint in textiles is: “The fabric is giving colour.” Sometimes the colour comes out during washing, sometimes during perspiration, and sometimes simply by rubbing. A dark saree rubbing against a light blouse, a printed dupatta staining the neck area, denim leaving blue marks on a bag, or upholstery fabric staining clothing are all examples of poor colour fastness to rubbing.
The Indian Standard IS 766:1988 gives a method for determining the colour fastness of textile materials to rubbing. It applies to textile materials in different forms, including fabrics, yarns, textile floor coverings and pile fabrics. The test is carried out in two ways: dry rubbing and wet rubbing.
What is colour fastness to rubbing?
Colour fastness to rubbing means the resistance of a dyed or printed textile to transfer its colour to another surface when rubbed.
In simple language, it answers one practical question:
If this fabric rubs against another fabric, skin, furniture, or garment part, will it stain it?
This is especially important in deep shades such as black, navy, maroon, red, indigo, bottle green and dark brown. It is also important in printed textiles, pigment prints, denim, sarees, dress materials, upholstery, carpets and pile fabrics.
Why rubbing fastness matters
A fabric may look attractive in the store, but if it stains another garment during use, the customer experiences it as a quality failure. Colour fastness depends not only on the nature and depth of the dye, but also on fibre type and the dyeing or printing method used. The same colouring matter may behave differently on different fibres or when applied by different processes.
For merchandisers, buyers and quality inspectors, this means one important thing:
Colour fastness cannot be assumed only from appearance. It has to be tested.
Principle of the rubbing fastness test
In this test, the textile specimen is rubbed with a standard white cotton rubbing cloth. After rubbing, the staining on the rubbing cloth is assessed using a grey scale for staining. Two tests are made: one using a dry rubbing cloth and another using a wet rubbing cloth.
The idea is very practical. If colour transfers to the white rubbing cloth, the fabric has lower rubbing fastness. If very little colour transfers, the fabric has better rubbing fastness.
Apparatus used
The test requires a rubbing testing device. For pile fabrics, including textile floor coverings, a larger rubbing finger is used: 3.2 cm diameter, with a downward force of 22 N, moving along a 10 cm track.
For all other textiles, a 1.6 cm diameter rubbing finger is used with a downward force of 9 N, again moving along a 10 cm track.
The rubbing cloth is a standard cotton cloth: desized, bleached, without finish, cut into 5 cm × 5 cm squares. A grey scale for evaluating staining is then used to rate the amount of colour transferred.
Preparation of the specimen
For fabrics and textile floor coverings, the specimen should be at least 14 cm × 5 cm. Separate specimens are taken for dry rubbing and wet rubbing.
One specimen is taken with its long direction parallel to the warp, or direction of manufacture, and another parallel to the weft, or at right angles to the direction of manufacture.
This is important because rubbing behaviour may differ in warp and weft directions. In woven fabrics, yarn structure, surface hairiness, floats, finishing and print placement may not be identical in both directions.
For yarn or thread, it may be knitted or woven into fabric, or arranged as parallel strands on a cardboard rectangle to prepare the test specimen.
Dry rubbing test
In the dry rubbing test, a dry rubbing cloth is fixed over the rubbing finger of the testing device. The specimen is rubbed in a straight line along a 10 cm track, 10 times to and fro in 10 seconds.
The force applied depends on the type of textile being tested:
- 22 N for pile fabrics
- 9 N for other textiles
After rubbing, the cotton cloth is examined for staining. Loose dyed fibres pulled out during rubbing should not be mistaken for actual dye staining. The assessment should consider colouration due to staining by dyestuff.
Wet rubbing test
The wet rubbing test is similar, but the rubbing cloth is first wetted with water. The cloth should have about 100% water take-up. After rubbing, the cloth is dried at room temperature and then assessed for staining.
Wet rubbing is often more severe than dry rubbing. Many fabrics that pass dry rubbing may show lower performance in wet rubbing, especially dark shades, pigment prints, indigo-dyed fabrics and poorly after-treated dyed materials.
Multicoloured fabrics
When testing multicoloured textiles, the specimen should be positioned so that all colours in the design are rubbed during the test. If the colour areas are large enough, separate specimens may be taken and each colour assessed separately.
This point is very useful for printed sarees, dress materials, dupattas and furnishing fabrics. A single rubbing result may not represent the whole design if one colour is fast and another colour is weak.
Rating and reporting
The staining of the rubbing cotton cloth is assessed using the grey scale for staining. The report should give numerical ratings separately for dry staining and wet staining, and for each direction of manufacture.
| Test condition | Direction | Rating |
|---|---|---|
| Dry rubbing | Warp direction | 4–5 |
| Dry rubbing | Weft direction | 4 |
| Wet rubbing | Warp direction | 3 |
| Wet rubbing | Weft direction | 2–3 |
In general interpretation, a higher grey scale rating indicates less staining and better fastness, while a lower rating indicates more staining and poorer fastness.
Special problem in pile fabrics
Pile fabrics can create a difficulty known as haloing, where heavier staining appears around the circumference of the stained area. The larger 3.2 cm rubbing finger can reduce haloing in many pile fabrics, although assessment may still be difficult for high-pile fabrics.
This is relevant for carpets, velvets, towels, blankets and certain upholstery fabrics. Their raised surface behaves differently from flat woven or knitted fabrics.
Practical meaning for textile buyers and merchandisers
For a buyer, rubbing fastness is not just a laboratory number. It has direct customer implications.
A dark saree with poor rubbing fastness can stain a blouse. A printed dupatta can stain the neck or kurta. A dark upholstery fabric can stain light garments. A poor pigment print can leave colour on hands. Denim with poor rubbing fastness can stain bags, shoes and car seats.
Therefore, rubbing fastness should be checked carefully in:
- Dark dyed fabrics
- Indigo and denim-like fabrics
- Pigment printed fabrics
- Sarees with strong contrast colours
- Upholstery and home textile fabrics
- Pile fabrics and carpets
- Fabrics expected to rub against skin or lighter garments
Common mistakes in understanding rubbing fastness
One mistake is to think that only washing fastness matters. A fabric may not bleed badly in washing but may still stain during rubbing.
Another mistake is to look only at dry rubbing. Wet rubbing is equally important because garments are often used in humid conditions, during perspiration, or after partial wetting.
A third mistake is to test only one part of a multicoloured fabric. In printed textiles, each colour may behave differently.
A fourth mistake is to ignore direction. Warp-way and weft-way rubbing results may differ, especially in fabrics with surface texture, floats or pile.
Knowledge nugget
Rubbing fastness is a surface-performance test. It tells us how well the colour is held on the textile surface when mechanical friction is applied.
This is why rubbing fastness is often a problem in dark shades, pigment prints and fabrics where dye fixation, washing-off or finishing has not been properly controlled.
Conclusion
The rubbing fastness test is one of the most practical colour fastness tests in textiles. It simulates a real-life action: one surface rubbing against another.
IS 766:1988 standardizes this test by defining the specimen size, rubbing cloth, rubbing force, rubbing distance, number of strokes, dry and wet conditions, and method of assessment.
For students, it teaches how laboratory testing connects to consumer use. For merchandisers and buyers, it gives a simple but powerful quality checkpoint. And for manufacturers, it reminds us that colour is not only about beauty — it is also about durability in actual use.
Suggested visuals to accompany this article
- Colour Fastness to Rubbing Test Overview: A labelled diagram showing fabric specimen, white rubbing cloth, rubbing finger, rubbing direction and grey scale assessment.
- Dry vs Wet Rubbing Fastness: A comparison visual showing dry rubbing cloth and wetted rubbing cloth, with examples of lighter and heavier staining.
- Grey Scale Interpretation Chart: A simple educational chart explaining that rating 5 means no or negligible staining, while rating 1 means heavy staining.
Source
Based on IS 766:1988, Indian Standard method for determination of colour fastness of textile materials to rubbing.
General disclaimer
This article is written for educational and general understanding purposes only. The explanations simplify the testing method for students, merchandisers and textile professionals. For official testing, certification, dispute resolution, legal compliance or commercial acceptance, the original relevant Indian Standard and accredited laboratory procedures should be referred to.
Thursday, 18 June 2009
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.
Wednesday, 17 June 2009
Natural Dyes and their Application Classes
Natural Dyes and their Application Classes
An excellent paper on the status of natural dyes in India can be downloaded from here
Here is a great blog talking about mordanting on wool.
| S. No. | Common Name | Dye Class |
| 1 | Indigo | Vat |
| 2 | Madder | Mordant/Disperse |
| 3 | manjeet | Acid/ Mordant/Disperse |
| 4 | Sappanwood | Mordant /Disperse |
| 5 | Lac dye | Acid/ Mordant |
| 6 | Berberine | Basic |
| 7 | Tesu | Mordant/ Disperse |
| 8 | Kamala | Mordant/ Disperse |
| 9 | Dolu | Mordant/Disperse |
| 10 | Gall Nuts | Acid/ Mordant |
| 11 | Cutch | Acid/ Mordant/ Disperse |
Here is a great blog talking about mordanting on wool.
Monday, 15 June 2009
Defects in Dyeing with Reactive Dyes
Defects in Dyeing with Reactive Dyes
Defect: Colors are not fast to washing, Abrasion;Staining in the fabric when transporting from place to the other, water marks on the fabric
Remedy : Wash the fabric with soap and soda ash at right temperature. Adding sequestering agent will yield good results. Treating with Ammonia will also give good results.
Defects in the fabric due to Printing- Need to take out full color
Remedy: Treat the dyed fabric with Sodium Hydrosuphite with 5-10 gm Sodium Hydrosulphite at 75 deg C for 30-45 minutes. Add 5-7 gms Caustic Soda for even removal of colors. The color becomes light yellow or brown after removal. Wash it thoroughly with soap.
The color can also be removed by solution of Sodium Hypochlorite. Treat the fabric with a sodium hypochlorite solution ( 3-5 gms Chlorine) for 20-30 minutes. Keep the pH between 9-10. The fabric is treated with Acetic acid after removal of color to remove chlorine and to neutralise the fabric.
The fabric can be redyed after removal of color
Defect: Bleeding in colors during washing, abrasion
Remedy: Boil the fabric with caustic, Treat the fabric with Hydrogen Peroxide ( 5-10 gpl, 60-70 deg C) to make the color fast.
Defect: The fabric has been dyed in darker shade, uneven dyeing
Remedy: To take out color from the fabric treat it with caustic for 45-60 min at 70 deg C. Thereafter treat the fabric with 10-20 gpl Acetic Acid for 40-60 min at 80-85 deg C.
Defect: Uneven dyeing, marks of water, marks of colors
Remedy: Wash the fabric in soap and redye in a darker shade
Defect : The fabric has become stiff and rough after dyeing
Remedy: Finish after adding right softner
Defect: Color staining of fabric, uneven dyeing
Remedy: Redye the fabric in darker shade.
Defect: Color staining in fabrics of darker shade, uneven undyeing
Remedy: Dye the fabric in Sulphur black
Caution: Please treat a small length fabric to check the effectiveness and any harmful effects before commencing a full treatment.
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.
Friday, 12 June 2009
Printing with Natural Dyes
Printing with Natural Dyes
In traditional methods in India, printing is essentially carried in three steps:
1. Preparation of the Cloth
2. Mordanting
3. Dyeing
1. First of all the cloth is prepared by applying tannin.
2. A thickened mordant is printed on this tannin treated cloth in the desired pattern.
3. The cloth is then dyed so that dyestuff attaches itself to those parts of the cloth to which mordant has been applied.
Thus the various processes are:
a. Tanning of fabric
b. printing of mordant
c. fixing of the modant
d. washing out the excess of fixing agent
e. dyeing
f. washing and soaping.
Harda or Myrobalan is used in India as a tanning agent for dyeing and printing with natural colours.
It is applied on scoured cotton fabric in cold ( 10-40 gpl) using conventional method of tub dip wherein the Harda powder is replenished with each piece added to the bath.
After drying various metallic salts such as alum or ferrous sulphate are printed on the fabric either separately or in mixtures.
It is then subsequently dyed with madder root ( Manjith), pometranate rind, kusum flowers and other vegetable dyes.
Thursday, 11 June 2009
Trade Names of Natural Dyes
| DYE SOURCE | BOTANICAL NAME/ SOURCE | TRADE NAME |
| Pomegranate | Punica granatium | Pacific |
| Myrobalan | Terminalia chebula | Kongo |
| Cutch | Acacia catechu | Thar |
| Kamala | Mallotus phillipinensis | Basant |
| Nut Galls | Quercus infectoria | Amber-M |
| Madder | Rubia cardifolia | Indus |
| Himalayan Rhubarb | Rheum emodi | Desert |
| Indigo | Indigofera tinctoria | Nile |
| Annato | Bixa orellana | Amazon |
| Lac | Coccus laccae | Rhine-M |
Common Causes of Dyeing Defects
Common Causes of Dyeing Defects:
It is important that the general precautions should be followed while dyeing a textile material. It is always helpful to keep a record of all the conditions (including temperature, time, conc of color, chemicals, material to liquor ratio) in order to get an even shade in each batch. In general the following are the common causes of dyeing defects across all the categories of dyes:
1. The material is not well prepared for dyeing and printing
a. Material having dead fibres or other defective fibres
b. Left over of Chemicals after bleaching etc.
c. Material not properly desized
d. Material not properly mercerised.
e. Absorbancy of the fabric not proper
f. Sticking of insoluble material on the fibres
g. Impurities are not removed properly
h. Uneven heat treatment.
2.Water Quality not Proper
a. More Hardness of water
b. Water has metal ions such as iron.
c. pH of water not proper
d. Water having more chlorine
3. Due to Shortcomings in making Dyeing Solution
a. Improper weight ratio of colors, material and chemicals.
b. Improper material to water ratio
3. Improper filtering of concentrated colors.
4. Due to Shortcomings in the dye machinery
a. Coming out of Dye liquor during dyeing
b. Defective instruments controlling temperature, pressure speed etc.
Wednesday, 10 June 2009
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.
How to determine Seam Strength
Seam strength is the strength of seam assembly in a garment. It is a function of the strength of the thread used for the seam, type of seam assembly in a garment and type of fabric used, among other factors.
Failure of seam assembly can occur either by breaking of sewing thread, tearing of the fabric at the seam, excessive yarn slippage adjacent to the stitches or a combination of the above mentioned conditions.
How to determine seam strength in laboratory
In a lab CRE type tensile testing machines such as INSTRON is used. Before testing the samples are prepared.The method is called Grab Test
If the specimens are from manufactured items such as garment then five speicmens are cut having a length of 270 mm on either side of the stitch line and a width of 100 mm parallel to the stitch line.
If the specimens are prepared from fabric then seam strength is measured in warp, weft and bias directions. In such cases swatches are cut in these three directions.
Also two such swatches from two different rolls are joined by the seam assembly- for which we want to test the strength- to measure the parameters.
Before testing the material is conditioned to standard temperature.
The specimen is mounted on the tensile tester. It is operated until the sewn seam or fabric ruptures. The observation is made whether the rupture is caused by Fabric yarn rupture, sewing thread rupture, sewn seam yarn slippage or a combination of two or more of the foregoing. This will give the seam strength.
Repeat this Grab Test for the fabric specimens from which seam failure test is carried out. The result will give the base fabric strength.
Seam strength ( for each direction) will be calculated by the formula:
Seam strength ( gms/cm)= ( Individual specimen seam breaking force in gms)/ Width of specimen in Jaws i.e. 2.5 cm.
Base fabric breaking strength of the individual specimens are calculated by the formula:
Base fabric strength (gms/cm)= (Base Fabric breaking force in gms of individual test specimen)/ Width of specimen in jaws i.e. 2.5 cm
Seam Efficiency= Seam Strength ( Seamed Fabric Strength) x 100)/ Base Fabric Strength
If this seam efficiency ratio falls below 80%, the fabric has been excessively damaged by the sewing operation.
Friday, 5 June 2009
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% |
Thursday, 4 June 2009
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.
Wednesday, 3 June 2009
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.
FAQ in textile dyeing
Here is an amazing site to answer the following ( and many more) frequently asked questions on Dyeing:
Which dyes are more lightfast?
How can I fix non-reactive dyes
Is there anything I can do to "set" the dye on purchased fabric?
How can I dye spandex (or Lycra or elastane)?
How can I dye nylon?
How can I dye rayon?
How can I dye satin or charmeuse?
How can I dye polyester?
What are mordants? What's the difference between mordants and other dye chemicals?
What is soda ash? What's it used for?
What temperature should the soda ash be?
What is the effect of pH? What is the optimal pH?
What is urea for? Is it necessary?
What is the effect of temperature?
Should I use distilled or spring water instead of tap water?
Do I need to use salt?
How are thickeners such as alginate used with dye?
How do you use Silk Salt or other large salt crystals to make bursts of color?
Help! I ruined clothing by spattering bleach. How can I fix it?
How do you "bleach" a screen print on a t-shirt?
Can you tie dye something that is already dark?
How can I neutralize the damaging effects of chlorine bleach?
What chemicals can be used to remove dye?
Which Procion MX dyes discharge the best? Which are good at resisting chlorine bleach?
Which Procion MX dyes are pure, and which are mixtures?
Which MX dyes at one supplier are the same as those at another?
How can I mix Procion MX dyes to get specific colors?
What is in Procion type dye powder?
What other brand names are Procion MX type dyes sold under?
What do the letters and numbers in the code name for a Procion MX type dye mean?
Which Procion MX dyes discharge the best? Which are good at resisting chlorine bleach?
Which Procion H dyes are pure unmixed colors, and which mixtures? How do they compare from one retailer to another?
Which Wash Fast Acid dyes are pure, rather than mixtures?
What are Kiton Levelling Acid Dyes?
My colors just washed out! What happened?
My colors are not very bright. What did I do wrong?
Why are there specks of color all over my fabric?
Why did the thread stay white when I dyed clothing?
How do you tie-dye a star or mandela pattern?
How do you tie-dye a spiral?
How do you tie-dye letters of the alphabet?
How can I tie-dye a peace sign?
How can I dye clothing or fabric in the washing machine?
Can I paint on clothing with oil paints?
Can I screenprint with a dye resist?
How do you tie-dye socks?
Is it safe to eat or breathe fiber reactive dyes?
Which dyes are the safest? Which are the most dangerous?
Aren't natural dyes always safer than synthetic dyes?
Is all-purpose dye safer than fiber reactive dye?
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.
Tuesday, 2 June 2009
Flex Abrasion Resistance- Determination
Method for determination of Flex abrasion resistance:
1. Cut five test specimens each 200mm. long and of 32 or 38mm width depending upon wheter the number of yarns/dm of the specimen is below or above 200. Ravel the specimen to 25 mm in width by removing from each side approximately the same number of yarns. Do not take two specimens fro the weft test from the same warp ends or any two specimens fro the weft test from the same picks. Take weft specimens at wide intervals.
2 After positioning the bar by means of the yoke holder, place the specimen between the pressure (upper) plate and the reciprocating (lower) plate of the apparatus and locate centrally. with the specified folding bar or folding blade inserted, after being clamped and loaded by removal of yoke holder, distribute the tension exerted by the bar or blade uniformly over the width of the specimen and align the long dimension both above and below the bar parallel to the direction of the reciprocating motion. Position the specimen with the fold at the centre of the upper plate, and the reciprocating plate at the rear of its stroke when the specimen is clamped.
3. Load the pressure plate and the folding bar or blade as required by the material specifications. In the absence of the material specification, the bar load sufficient to produce rupture in excess of at least 100 cycles and preferably in 300 cycles should be used, in combination with the lowest head load (pressure) sufficient to prevent vibration of the upper plate at the start of the test.
The ratio of the bar to head loads shall be 4:1
4. Check the bar alignment after the first 25 cycles. If shifting of bar from its normal position is noticed, discard the specimen and make the proper adjustment.
5. Remove the pills of matted fibres debris interfering with proper contact between the specimen and the folding bar or folding blade during the test if they cause a marked vibration of the pressure plate or otherwise interfere with proper abrasion. The pill should be removed by careful clipping. Do not correct the vibration of the pressure plate due to pilling by applying additional load. Check the position of the specimen after additional cycles to ensure that the removal of the pills has not altered the bar alignment.
6. If the specimen slips in the clamps or tension and pressure upon the folded specimen do not remain constant during the test, or an anomalous wear pattern is obtained, discard such individual measurements and test an additional specimen.
7. Before every test the blade is rinsed with degreasing agent.
8. The end point is determined by abrading the specimen until rupture and number of cycles is recorded.
9. The report should include the following information:
a. Abradent used, bar or blade
b. Average number of cycles required to produce rupture the specimen
Total No of cycles Report to the nearest cycle
Below 200 10
200 to 299 25
1000 to 4999 50
5000 and above 100
c. Tension and pressure used.
Monday, 1 June 2009
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.
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