Fastness Properties of Dyed and Printed Textiles

ð  Fastness, that is the resistance of dyeing and prints to external influences, is of decisive importance for the practical use of any dyestuff.

ð  Fastness of dyestuffs is a very important property to satisfy the consumers of different societies.

ð  Technical committee 38, Sub-committee of the International Standards Organisation (ISO) has to date defined 45 different testing methods.

ð  The purpose for which a dyed material is to be used must always be born in mind when dyestuffs are selected and the results of fastness tests are evaluated.

ð  Fastness properties such as resistance to light, washing, rubbing, ironing and dry cleaning must be tested for everyday use, while resistance to boiling soda, bleaching, potting and milling must be ascertained when dyed yarns are submitted to process.

ð  Every test of fastness properties is made up three basic processes:-

(a)    Its implementation carried out in accordance with the pertinent standard fastness tests;

(b)   The evaluation of its results, effected with the gray scale used to determine changes of shade and staining;

(c)    The practical application of test results with regard to the end use of a dyeing or print.

ð  The quantitative assessment of the colour changes is done by comparison with standard S.D.C. grey scale, one for assessing colour changes and the second for assessing staining.

ð  Except for fastness to light, the first scale consists of five pairs of grey scale strips showing five extents of colour differences from nil to maximum and the second shows five pairs of white and stained strips show no staining to maximum staining.

Sample Preparation:-

ð  A 10 X 4 cm of the dyed/printed test specimen is sandwiched between two adjacent fabric pieces. i.e. an undyed cutting of the same material and another as specified in standard.

ð  In the case of blended material this piece should be of the material predominant in the blend.

ð  Specifications for these adjacent fabrics are shown in the Table.

If First Piece is	Second Piece to be
Cotton	Wool
Wool	Cotton
Linen	Cotton or Viscose
Silk	Cotton
Viscose	Wool
Acetate	Viscose
Polyamide	Wool or Viscose
Polyester	Wool or Cotton
Acrylic	Wool or Cotton

ð  This type of sample preparation is required practically for all fastness tests except for light, rubbing and scrubbing.

Fastness to Washing

ð  Machine :- Wash wheel or Launder – o – meter

ð  The dyed sample, sandwiched between and undyed cutting of the same sample and another as stated in the standard are placed in washing solution at appropriate temperature in the steel jars with tight fitting lids of the machines.

ð  These jars are rotated in a constant temperature water bath for the length of time as per the ISO standard.

ð  There are five test methods for evaluating fastness to washing. Test method no. 1 is a mild method whereas no. 5 is a severe one as can been seen from the test condition given in Table.

Summary of test conditions for Fastness to Washing

ISO Test Method No.	Washing Solution		Temperature °C	M : L	No. of steel ball	Time Minute
	Saop (g/l)	Soda ash (g/l)
1	5	---	40	1:50	Nil	30
2	5	---	50	1:50	Nil	45
3	5	2	60	1:50	Nil	30
4	5	2	95	1:50	10	30
5	5	2	95	1:50	10	240

ð  The specimen are taken out, rinsed and dried below 60°C.

ð  The change in colour of the specimen and the staining on white fabrics is assessed with reference to the two grey scales and ratings are given.

ð  If the sample is in the form of loose fibres, it is combed and pressed into sheet and stitched between two necessary undyed fabrics.

ð  If the sample is in the form of the yarn it is either made into a sheet or knitted into a fabric and then stitched between the undyed fabrics.

ð  The soap used for washing must be free from optical brightening agents (OBA) as their presence may sometimes cause serious error in the evaluation of colour difference i.e. in giving the rating.

Fastness to Rubbing   

ð  This test is carried out on a Crockmeter and is particularly important for azoic dyed and pigment printed materials.

ð  A strip of the specimen is mounted on the instrument.

ð  A piece of undyed cloth (about 5 sq cm) is clamped on the finger of the rubbing device of the instrument.

ð  The undyed piece is rubbed to and fro 10 times against the specimen along a track of 10 cm with a pressure of 900 g on the finger.

ð  The speed of rubbing is adjusted to one stroke (to and fro) per second.

ð  The colour transferred to white fabric (undyed piece) is then assessed by using the grey scale for staining.

ð  For the evaluation of wet rubbing fastness, the white fabric is wetted with water and excess water is squeezed off before clamping on the finger.

ð  When it is necessary to evaluate the rubbing fastness property of printed fabric samples with small motifs, a rotary type crockmeter is used.

ð  When evaluating this fastness property for “Khadi” printed materials, where titanium dioxide pigment is used in the paste, rubbing should be carried out with a black dyed fabric, or else the white titanium dioxide pigment which will be transferred on the white fabric will not be seen.

Fastness to Perspiration

ð  Human perspiration may be acidic or alkaline in nature depending on one’s metabolism.

ð  The preparation of the sample is similar to that in fastness to washing.

ð  Fastness to perspiration is therefore carried out at two different pH, viz. 8.0 and 5.5 using the perspiration liquor as given in Table:-

Composition of Perspiration Liquors

Liquor Composition	Solution
	A	B
1 – Histidine mono – hydrochloride monohydrate	0.5 g	0.5 g
Sodium chloride	5.0 g	5.0 g
Disodium hydrogen orthophosphate dodecahydrate	5.0 g	---
Sodium dihydrogen orthophosphate dihydrate	---	2.2 g
Volume (adjusted with distilled water)	1000 ml	1000 ml
pH (adjusted with 0.1 N NaOH/Acetic acid)	8.0	5.5

ð  The composite sample is wetted out in the above perspiration solutions and distilled water at room temperature for 30 min, material to liquor ratio being 1:50.

ð  Solution is then drained and the specimen is placed between two glass or Perspex plates under a load of 10 lbs. (Perspirometer)

ð  The apparatus containing the composite specimen is placed in an air oven at 37 + 2°C.

ð  Specimens are then separated and dried below 60°C.

ð  In the plate method, the composite specimen after wetting out in perspiration solutions (M : L :: 1 : 20) is placed on a flat bottomed dish and covered with a thick glass plate weighing about 50 g.

ð  The plate is pressed lightly to drain out the liquor and the whole is placed in the oven for 4 hours at 37 + 2°C.

ð  Assessment is done with reference to the two grey scales.

Fastness to Light

ð  The traditional method of determining this fastness property is by exposing the specimen to daylight under a defined condition, behind glass.

ð  However, this is not only requires longer time particularly for samples of good light fastness but it also becomes almost impossible to carry out these tests during monsoons.

ð  This has led to the development of fading lamps, viz. carbon arc, xenon arc, etc.

ð  The use of a xenon arc lamp has been recognised by the ISO and ISI as the energy distribution of this lamp is nearest to sun light whereas the carbon arc lamp is extensively used in USA.

ð  However, these instruments are costly and cheaper instruments eg. Suntest (Hanau) and Microscal are available which can be used for routine testing though these are not yet accepted by the ISI.

ð  Instrument :- Fed – O – Meter

ð  For this purpose wool fabric samples, dyed with specific colours (known as Blue Wool Standard (BWS)) having known light fastness property are used.

ð  During exposure, apart from the light source, the temperature and humidity are to be controlled as they have significant bearing to the fading time.

ð  A portion of the specimen and BWS are covered and exposed to the light.

ð  These are then periodically inspected till sufficient fading occurs on the specimen.

ð  The extent to which the fading must be allowed to proceed i.e. the point at which exposure to be terminated is determined by assessing the colour contrast between the exposed and unexposed portions which should be grade 2 on a grey scale.

ð  In the case of samples having exceptionally high light fastness, it may so happen that BWS NO. 7 may fade to grey scale contrast 4 before the sample fades.

ð  The test may then be terminated at this point.

ð  The BWS which fades along with the sample is the light fastness rating for that specimen, e.g. if the BWS NO. 5 fades along with sample the fastness rating is 5.

ð  When a large number of samples are regularly tested, it may not be possible to use the BWS every time.

ð  In such cases the number of hr required to fade different BWS under defined conditions of the temperature and humidity are standardised and rating are given on the basis of exposure hr.

ð  However, in such cases, the instrument has to be periodically standardised has to be periodically standardised using fresh BWS.

Fastness to Hot Pressing

ð  It is the resistance of the colour to ironing and processing on hot cylinders.

ð  This test may be carried out as dry pressing and wet pressing on a Scorch tester.

ð  The iron should be capable of giving a pressure of 0.43 lb/sq inch or 30 g/cm² and temperature of :-

Cotton and Linen                                190 - 210°C

Wool, Silk and Viscose                       140 - 160°C

Cellulose acetate, Polyamide              115 - 120°C

Polyester                                             180 - 190°C

ð  The cloth is pressed for 15 seconds with a hot iron in three conditions:-

(a)    Dry pressing – Dry specimen placed on dry cotton cloth.

(b)   Wet pressing – wet squeezed specimen on wet squeezed cotton cloth.

(c)    Damp pressing – Dry specimen placed on dry cotton cloth. Another wet squeezed is placed on the dry specimen.

ð  Change in colour is assessed by reference to grey scale for assessing colour change. Samples are conditioned before assessing.

Fastness to Sublimation

ð  This test is particularly important for fabrics of polyester and its blends as they are dyed with disperse dyestuffs, many of which may migrate and/or sublime during heat treatment.

ð  The presence of certain finishing auxiliaries may enhance this problem.

ð  This test may be carried out on a scorch tester or sublimation fastness tester as described for hot pressing.

ð  The difference between these tests is that, in the case of hot pressing only one plate i.e. the top plate is heated whereas in the case of sublimation, both the plates are heated.

ð  Further, in the case of the letter, generally the test temperature is higher i.e. 150, 180 and 210°C and the time of treatment is 30 seconds.

ð  The composite dry specimen is subjected to the desired condition and subsequently evaluated for change in colour and staining of the adjacent fabric.

Fastness to Bleaching

ð  Many textiles containing dyed cellulosics, wool, acetate and silk may at some stage be treated with hydrogen or sodium peroxide or sodium hypochlorite for bleaching main material.

ð  It is therefore necessary to know resistance of dyes used to these bleaching agents.

Hydrogen Peroxide

ð  A composite specimen is prepared by placing the specimen between an undyed specimen of itself and the other cotton (if the first piece is wool, silk, linen or viscose) and viscose (if the first piece is cotton or acetate).

ð  The 10 X 4 cm specimen is placed in a roll form in a test tube under 30 times its own weight of the bleaching solution.

ð  The test tube is fitted with a refluxing arrangement to reduce evaporation of bleaching liquor. Four types of bleaching liquors are used.

ð  The treated specimens are then taken out, rinsed, opened on three sides and dried below 60°C.

ð  Colour changes and staining are evaluated by reference to two grey scales.

Recipes of Peroxide Bath for Fastness Test

Starting Bath (per litre of distilled water)	(For Natural and Regenerated Cellulose)		(For Wool and Acetate Rayon) Bath 3	(For Silk) Bath 4
	Bath 1	Bath 2
30 % Hydrogen Peroxide (ml)	5	---	20	20
100 % Sodium Peroxide (g)	---	3	---	---
Sodium Silicate (35°Be) (ml)	5	5	---	5
Sodium Phosphate (g)	---	---	5	---
Magnesium chloride (g)	0.1	0.1	---	0.1
pH at start	10.5	11.5	9.3	10.0
Temperature	90°C	80°C	50°C	70°C
Duration (hours)	1	1	2	2
Liquor Ration	1 : 30	1 : 30	1 : 30	1 : 30

     Sodium Hypochlorite

ð  This test is specially suggested for natural and regenerated celluloses.

ð  Specimens are wetted out in distilled water (or in 0.5 % soap solution if the specimen has been treated with water repellent finish) and then treated in a bleaching solution containing 2 g/l available chlorine brought to pH 11 with 10 g/l sodium carbonate.

ð  The container is kept covered for 1 hour after which the samples are rinsed and treated with a solution of 2.5 ml of 30 % H₂O₂ per litre or 5 g sodium bisulphate per litre.

ð  Finally after rinsing, specimen is dried below 60°C and colour change is assessed by reference to the appropriate grey scale.

Fastness to Wet Scrubbing

ð  This test is particularly recommended for pigment dyed/printed materials as it evaluate, the fastness property of the binder film which ultimately holds the coloured pigments on the fabric surface and therefore can easily differentiate the quality of binders.

ð  At present though there is no ISO for this test, ISI will shortly come out with a standard test procedure for scrubbing fastness.

ð  The wet scrubbing fastness is suggested by Colur-Chem. The instrument for this purpose is similar to that of crockmeter, but instead of a rubbing device there is a scrubbing device which is fitted with a brush.

ð  The specimen is dipped in a bath containing 5 g/l soap and 2 g/l soda ash at 60°C and is secured on the instrument and subjected to scrubbing for a definite number of strokes (generally 100 strokes).

ð  After half the number of strokes, fresh soap soda solution at 60°C is poured on the specimen and scrubbed for the remaining strokes.

ð  It is then washed and dried and the change in colour is evaluated by using grey scale.