How to prepare polyester cotton blended fabric for dyeing?

If the fabric contains polyeset and cotton blends then we have to scour it as we do in the case of cotton scouring. For this purpose 2-3% owf sodium hydroxide  may be used depending upon the percentage of cotton in the blends at boil for 45 minutes. For example if the blend contain 50% Polyester and 50% cotton and total weight of the fabric is 100 grams. Then there will be 50 gram of cotton in the blend. If we used 3% Sodium hydroxide on weight of fabric (owf) then the total NaOH required will be 1.5 gram.


How to prepare polyester viscose blended fabric for dyeing?

As polyester and viscose both are manmade fibres, there is no need to do vigrous scouring like cotton, which has natural impurties. In that case light scouring is needed, in which detergent may be used to remove oil stains. 

How to test scoured cotton material:

As we understand cotton is scoured using alkali at boiling temperature. During or after scouring, it is must to know whether the material scoured properly or not. To ascetain that a simple drop test can be performed. In such type of test, if the material is under scouring process, a small piece of fabric is cut from the lot of fabric which is running in the machine say jigger (after stoping it). The piece is washed properly under tap water (Soft water) and dried using iron or placing the fabric piece on hot steam pipe line. After cooling the fabric, a drop of water is allowed to fall on this piece of fabric. If the drop is absorb whithin few seconds say 3 seconds, one can be assured that scouring is perfectly done. However, if the drop is taking much time to absorb, there is a need to continue the scouring process untill the fabric acquire optimum absorbency. If the fabric is being scoured for printing process, it is required that the water drop should be absorbed within 1 second. There are standard tests are also availabe for testing absorbency of fabric in the laboratory e.g IS 2349 and AATCC 79.

How to test desized material (Starch based size):

To test the presense of sizing material i.e starch based sizing material in the fabric iodine test is conducted. In which the fabric is spotted or treated with  Iodine solution —Iodine dissolved in an aqueous solution of potassium iodide, which reacts with the starch and produce a bluish-purple-black colour. If there is no starch the colour may be brownish-yellowish.  In the below figure, it is explained that if the iodine solution is added in the solution ( which you want to know whether there is a starch or not) if there is a starch then you may get purple/bluish colur solution. If there is no starch the colour remain same. 

TEGEWA solution is also used for the identification of starch.  For making this solution potassium iodide 10 g of KI (100%) in 100 ml of water is added with 0.6358 g of iodine (100%) and shake this well to disslove iodine crystals. Then make it up to 800 ml using distilled water and finally make it up to 1000 ml with ethanol.

High Pressure Kier with multitubular heater:

The modern high pressure kier with multitubular heater is also known as  Walsh's kier and one of the best kier. The 2 ton capacity kier is most common which is about 9 ft high and 6.5 ft in diameter and mounted on R.C.C Coloumn. The kier works at working pressure 40 lb/sq inch at 141 degree C and is composed of mild steel plates. The kier is provided with pressure gauge, safety valve, blow off valve for air, steam trap, liquor level indicator, drain cock etc.

The goods in rope form are plaited either manually or mechanically plaiting on the perforated false bottom. The cloth can be saturated with alkaline solution containing the recipe as given above with figure.

During piling sufficient scouring liquor is   added to the kier from the below to remove entrapped air from the goods to avoid the formation of oxycellulose. The lid is then closed but air valve is kept open. Steam is turned on and the liquor is circulated by centrifugal pump coupled to an electric motor. High pressure kier operate at about 8 to 10 hours with liquor ratio 1:3 to 1:5 (MLR). After scouring the drain cock is opened at reduced pressure (5 to 6 lb/sq meter) and equivalent amount of hot water is added from the top. After circulating cold water the goods are removed and washed in a rope washing machine. The liquor is withdrawn from the bottom of the kier and forced through the heater and spread over top of the load by distributor. Fabric which are to be sold in white state are given two boils and the fabric intended for printing single boil is sufficient.

 Precaution:

 Following precaution should be taken while using kier:

• Kier should be clean
• Material should be packed evenly.
• No air packed should be formed
• The fabric should be in liquor completely.

Souring:

The fabric after bleaching contains metallic salts such as calcium carbonate, magnesium carbonate etc., and other mineral matter. These salts, if left on the fabric, will not only give a harsh feel but also affect the uniformity of the shade during dyeing. In order to make these salts soluble in water, the fabric is treated with either dilute hydrochloric acid or sulphuric acid, the former is used for fabrics meant for dyeing whereas latter, being cheap, is used for fabrics meant for white finish. Hydrochloric acid which forms soluble calcium salts is better then sulphuric acid. The concentration used is about 0.5 to 1.0% on the weight of fabric.

Making a lot size for preparation or dyeing:

Grey stage fabric usually 60-70 m in length so that  several pieces are stitched together to make a processable length ( Lot size ).  Normally Polyester (Sewing thread ) yarn is used for stitching. Marked each piece properly for sort number, lot number etc. so that pieces can be identify at any stage of the processing. Two pieces are arranged selvedge to selvedge and the ends are stiched on a special end to end stitching machine so that pieces are joined without overlapping: Some of the important poits are given below:

•         Cotton threads: 3/40s, 4/30s, 4/36s, 6/28s and 6/36s are popular

•         Polyester threads are also used when carbonising is required

•    Stitches per inches:  6 to 7 for coarse, 7 to 8 for poplin and 8 to 10 for cambric

Stitching defects: Stitching defects are described below:

i)  Protruding Selvedge: It mostly occurs due to difference in width of the pieces. Some time careless handling also lead to a protruding selvedge.

It Causes: Fold or selvedge crease and the fold portion either less dyed or       remain undyed

ii)  Open End: Pieces are not locked in the stitch at and near the selvedge and due to careless handling.

It Causes: Such stitch will open out more and more every pull around guide roll during processing. It may induce Fold or crease formation at the selvedge, undyed/unprinted folds will result.

iii) Loose Thread: It occurs due to careless handling of stitching process.

It Causes: It may cause thread mark in dyeing and printing, lead entanglement in machine parts, etc. The loose thread may pick up soil and damage long lengths

iv) Fold: If the large folds are inserted in the stitch to accommodate width difference of two pieces, it will surely lead to damage

It Causes: It may cause warp stripes in dyeing and creases in dyeing and printing

v)Broken Stitch: It may be due to poor machine condition, poor quality of thread or poor method of operation.

It Causes: It may cause damage in dyeing and printing

Human Visual System

 Retina uses special cells called “rods” and “cones”. Rods “sees” in black, white & shades of grey and tell us the form or shape(Super-sensitive allowing us to see when it's very dark).Cones “senses” colour but need more light. Three types and each is sensitive to one of three different colours - red, green, or blue. Together these can sense combinations of light waves (To see millions of colours). Rods and cones together process the light to give you the total picture.

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PERCEPTION OF COLOUR

•         It involves a series of events which are interdisciplinary in nature. Perception of colours includes source of light, object that is illuminated and eye and brain that perceive the colour.

METAMERISM: It is a phenomenon observed when two specimens appears to have the similar colour under one set of viewing conditions, but different under another. The change in viewing conditions refers to change in source, observer or geometry of the observation.

TYPES OF METAMERISM

•         illuminant metamerism

•         observer metamerism

•         geometry metamerism

ILLUMINANT METAMERISM

•         When the colour of two specimens match under one illuminant but not with another illuminant, it is said to be illuminant metamerism.

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OBSERVER METAMERISM

•         When colour of two objects appear to match to one observer but not to the other, it is said to be observer metamerism. In this case observer may not be colour blind but the spectral sensitivity of colour receptors of one observer may be slightly different than the other.

GEOMETRY METAMERISM

•         Two objects which match in one arrangement of illumination, sample and observer may mismatch by altering the positions.