Textile Bleaching | Object of Bleaching | Bleaching Agent | Recipe forBleaching

Bleaching

Bleaching is chemical treatment employed for the removal of natural coloring matter from the substrate. The source of natural color is organic compounds with conjugated double bonds , by doing chemical bleaching the discoloration takes place by the breaking the chromophore , most likely destroying the one or more double bonds with in this conjugated system. The material appears whiter after the bleaching.

Natural fibres, i.e. cotton, wool, linen etc. are off-white in colour due to colour bodies present in the fibre. The degree of off-whiteness varies from batch-to-batch. Bleaching therefore can be defined as the destruction of these colour bodies. White is also an important market colour so the whitest white has commercial value. Yellow is a component of derived shades. For example, when yellow is mixed with blue, the shade turns green. A consistent white base fabric has real value when dyeing light to medium shades because it is much easier to reproduce shade matches on a consistent white background than on one that varies in amount of yellow.

Bleaching may be the only preparatory process or it may be used in conjunction with other treatments, e.g. desizing, scouring and mercerizing. The combination of such treatments for an individual situation will depend on the rigorousness of the preparation standard and economic factors within the various options. Other chemicals will be used in addition to the bleaching agent. These serve various functions such as to activate the bleaching system, to stabilize or control the rate of activation, to give wetting and detergent action, or to sequester metallic impurities. This section gives consideration to the selection of bleaching agents and to the role of the various chemicals used in conjunction.

The purpose of bleaching is to remove coloured impurities from the fibre and increase the whiteness level of fabric.

The aim of bleaching can be described as following:

• Removal of coloured impurities. 
•  Removal of the seed coats. 
•  Minimum tendering of fibre. 
•  Technically reliable & simple mode of operation. 
•  Low chemical & energy consumption. 
•  Increasing the degree of whiteness.

Bleaching Agent
A bleaching agent is a substance that can whiten or decolorize other substances.Bleaching agents essentially destroy chromophores (thereby removing the color), via the oxidation or reduction of these absorbing groups. Thus, bleaches can be classified as either oxidizing agents or reducing agents .

Type of Bleaching Agents
a.Oxidative Bleaching Agents
b.Reductive Bleaching Agents
c.Enzymatic Bleaching Agents

Recipe for Bleaching:
 

  NaOH                               17ml/kg

SOAP (DTC)                    2ml/kg

STABILIZER                    5ml/kg

 H2O2                               30ml/kg

Reaction time                     25min.

       speed                                50-70m/min

Importance of Textile Testing | Reasons for Testing of Textile

The testing of textile products is an expensive business. A laboratory has to be set up and furnished with a range of test equipment. Trained operatives have to be employed whose salaries have to be paid throughout the year, not just when results are required. Moreover all these costs are nonproductive and therefore add to the final cost of the product. Therefore it is important that testing is not undertaken without adding some benefit to the final product. There are a number of points in the production cycle where testing may be carried out to improve the product or to prevent sub-standard merchandise progressing further in the cycle.  

Reasons for Textile Testing

1. Checking Raw Materials
2. Monitoring Production
3. Assessing the Final Product
4. Investigation of Faulty Material
5. Product Development and Research

Checking Raw Materials
The production cycle as far as testing is concerned starts with the delivery of raw material. If the material is incorrect or sub-standard then it is impossible to produce the required quality of final product. The textile industry consists of a number of separate processes such as natural fibre production, man-made fibre extrusion, wool scouring, yarn spinning, weaving, dyeing and finishing, knitting, garment manufacture and production of household and technical products. These processes are very often carried out in separate establishments, therefore what is considered to be a raw material depends on the stage in processing at which the testing takes place. It can be either the raw fibre for a spinner, the yarn for a weaver or the finished fabric for a garment maker. The incoming material is checked for the required properties so that unsuitable material can be rejected or appropriate adjustments made to the production conditions. The standards that the raw material has to meet must be set at a realistic level. If the standards are set too high then material will be rejected that is good enough for the end use, and if they are set too low then large amounts of inferior material will go forward into production.

Monitoring Production
Production monitoring, which involves testing samples taken from the production line, is known as quality control. Its aim is to maintain, within known tolerances, certain specified properties of the product at the level at which they have been set. A quality product for these purposes is defined as one whose properties meets or exceeds the set specifications. Besides the need to carry out the tests correctly, successful monitoring of production also requires the careful design of appropriate sampling procedures and the use of statistical analysis to make sense of the results.

Assessing the Final Product
In this process the bulk production is examined before delivery to the customer to see if it meets the specifications. By its nature this takes place after the material has been produced. It is therefore too late to alter the production conditions. In some cases selected samples are tested and in other cases all the material is checked and steps taken to rectify faults. For instance some qualities of fabric are inspected for faulty places which are then mended by skilled operatives; this is a normal part of the process and the material would be dispatched as first quality.

Investigation of Faulty Material
If faulty material is discovered either at final inspection or through a customer complaint it is important that the cause is isolated. This enables steps to be taken to eliminate faulty production in future and so provide a better quality product. Investigations of faults can also involve the determination of which party is responsible for faulty material in the case of a dispute between a supplier and a user, especially where processes such as finishing have been undertaken by outside companies. Work of this nature is often contracted out to independent laboratories who are then able to give an unbiased opinion.

Product Development and Research
In the textile industry technology is changing all the time, bringing modified materials or different methods of production. Before any modified product reaches the market place it is necessary to test the material to check that the properties have been improved or have not been degraded by faster production methods. In this way an improved product or a lower-cost product with the same properties can be provided for the customer. A large organisation will often have a separate department to carry out research and development; otherwise it is part of the normal duties of the testing department.

Introduction of Glass Fiber | Types of Glass Fiber | Properties ofGlass Fiber | Manufacturing Processes of Glass Fiber | Uses of GlassFiber or Glass Yarn

Glass fiber

Glass fiber also called fiberglass. It is material made from extremely fine fibers of glass Fiberglass is a lightweight, extremely strong, and robust material. Although strength properties are somewhat lower than carbon fiber and it is less stiff, the material is typically far less brittle, and the raw materials are much less expensive. Its bulk strength and weight properties are also very favorable when compared to metals, and it can be easily formed using molding processes. Glass is the oldest, and most familiar, performance fiber. Fibers have been manufactured from glass since the 1930s.



Types of Glass Fiber
As to the raw material glass used to make glass fibres or nonwovens of glass fibres, the following classification is known:

1. A-glass: With regard to its composition, it is close to window glass. In the Federal Republic of Germany it is mainly used in the manufacture of process equipment.

2. C-glass: This kind of glass shows better resistance to chemical impact.

3. E-glass: This kind of glass combines the characteristics of C-glass with very good insulation to electricity.

4. AE-glass: Alkali resistant glass.

Generally, glass consists of quartz sand, soda, sodium sulphate, potash, feldspar and a number of refining and dying additives. The characteristics, with them the classification of the glass fibres to be made, are defined by the combination of raw materials and their proportions. Textile glass fibres mostly show a circular

Properties of Glass Fiber
Glass fibers are useful because of their high ratio of surface area to weight. However, the increased surface area makes them much more susceptible to chemical attack. By trapping air within them, blocks of glass fiber make good thermal insulation, with a thermal conductivity of the order of 0.05 W/(mK).

The strength of glass is usually tested and reported for “virgin” or pristine fibers those which have just been manufactured. The freshest, thinnest fibers are the strongest because the thinner fibers are more ductile. The more the surface is scratched, the less the resulting tenacity. Because glass has an amorphous structure, its properties are the same along the fiber and across the fiber. Humidity is an important factor in the tensile strength. Moisture is easily adsorbed, and can worsen microscopic cracks and surface defects, and lessen tenacity.

In contrast to carbon fiber, glass can undergo more elongation before it breaks. There is a correlation between bending diameter of the filament and the filament diameter. The viscosity of the molten glass is very important for manufacturing success. During drawing (pulling of the glass to reduce fiber circumference), the viscosity should be relatively low. If it is too high, the fiber will break during drawing. However, if it is too low, the glass will form droplets rather than drawing out into fiber.

Glass Fiber Manufacturing Processes
After the initial process of melting glass and passing it through spinnerets, continuous filaments or staple fibers of glass are manufactured by two different methods.

Continuous Filament Process
In this process, continuous filaments of indefinite length is produced. The molten glass passes through spinnerets having hundreds of small openings. These strands of multiple filaments are carried to winder revolving at very high speed of more than 2 miles per km. This process draws out the fibers in parallel filaments of the diameter of the openings. A sizing or a binder is applied to facilitate the twisting and winding process and to prevent breakage during yarn formation. After winding, filaments are further twisted and plied to make yarns by methods similar to those for making other continuous filament yarns. The sizing is removed through volatizing in an oven. These yarns are used for making such items as curtains and drapes.

Staple Fiber Process
Fibers with long-staple qualities are manufactured through staple fiber process. There are many methods for producing such fibers.

In one of such methods, the molten glass flows through the small holes of bushing, where jets of compressed air shake the thin streams of molten glass into fine fibers. These fibers vary in length ranging from 8 to 15 inches. The fibers fall through a spray of lubricant and a drying flame onto e revolving drum where they form into a thin web. These fibers in the form of web are gathered from the drum into a sliver. Yarn is then made from this sliver by similar methods that are adopted for making cotton or wool yarns. These yarns are used for fabrics for industrial purposes where insulation is required.

In yet another method, the ends of the glass rods are melted from which drops of glass fall away drawing off glass filaments after them onto a speedily revolving cylinder where they are wound parallel to each other. A web of sliver is formed if the cylinder moves sideways. Sometimes, the staple may be thrown off the cylinder onto a stationary sieve where it forms a sliver. In either conditions, the sliver is then converted into spun yarn.

The staple fiber, if subjected to oven, is compressed to the desired thickness and the binder which was earlier applied, is cured. This permanently binds the fibers.

Production:
The subsequent manufacture of glass fibres may be executed to the direct melting process. However, in most cases glass rods or balls are made first which then may undergo a variety of further processes.

Nozzle-Drawing:
As can be seen in Fig. 1-50, the glass fed in is melted in a heated melt tub at 1250–1400oC. Then, it emerges at the bottom of the melt tub from nozzle holes of 1–25 mm diameter and it is taken off and drawn. The filaments solidify and are finished and wound. One can find them in the shops as various kinds of “glass silk”. To make them into webs, the filaments are cut to length (mostly, between 6 and 25 mm).

Manufacture of glass melt

Processes to make glass fibres

Nozzle-Blowing:
The same as with nozzle-drawing, glass balls are melted in the tub. The melt emerging from the nozzle holes is then taken by pressed air, which draws the liquid glass so as to make fibres of 6–10 um diameter. A fluttering effect is caused by the flow of pressed air, which results in fibres of lengths from 50 to 300 mm. A lubricant is put on and the fibres are laid down on a sieve drum which sucks them in. The dry web received is held together by the long fibres, the short ones lying in between them as a filling material. Then, the slivers of glass fibre material are cut.

Rod-Drawing:
By means of a burner, bundles of glass rods are melted at their bottom ends. This results in drops which, as they fall down, draw filaments after them. The filaments are taken by a rotating drum, a squeegee laying them down onto a perforated belt. Thus, a dry web is received which can be wound as glass fibre slivers. – Machine performance being limited by the number of glass rods fed in, the rotating drum may be combined with nozzle-drawing, which results in drum-drawing. This multiplies machine performance. The dry web is again laid down onto a perforated belt and solidified or, after winding it so as to receive slivers, cut for further processing on machines producing wetlaid nonwovens. Using and processing glass fibres is not without any problems. For example, fine pieces of broken fibres may disturb if the work place is not well prepared for the purpose. Using the nonwovens to manufacture glass-fibre reinforced plastics, it is important the surface of the plastic material is fully even. Ends of fibre looking out may be pulled out or loosened by outward stress (temperature, gases, liquids), which may influence material characteristics. In some cases, it is
advisable to cover up such layers of glass fibre with suitable chemical fibres.

Uses of Glass Fiber or Glass Yarn
Glass fiber is manufactured in a wide range of fine diameters. Some of them are so fine that they can be seen only through a microscope. This quality of fineness contributes greatly to the flexibility of glass fibers. Various manufacturers produce different types of glass fibers for different end uses. Glass fibers them are used for various purpose.

1. For making home furnishings fabrics;
2. For making apparels and garments; and
3. For the purpose tires and reinforced plastics.

There are certain glass fibers that can resist heat upto 7200oC and can withstand forces having speed of 15,000 miles per hour. These types of glass fibers are used as

1. Filament windings around rocket cases;
2. Nose cones;
3. Exhaust nozzles; and
4. Heat shields for aeronautical equipment

Some other types of glass fibers are embedded into various plastics for strength. These are used in

1. Boat hulls and seats;
2. Fishing rods; and
3. Wall paneling

Some other types of glass fibers are used for reinforcing electrical insulation. Yet other types are used as batting for heat insulation in refrigerators and stoves.

What is Hardness of Water? | Potential Problem Caused by Hard Water inTextile Wet Processing Industry

Hardness of Water:
The presence of Calcium, Magnesium salt i.e bi-carbonates, sulphates, Chloride in water is called causes of hardness of water. The water which contains these salt is called hard water. Soft water is relatively free of calcium and magnesium ions. It produces a rich foamy lather with soap. This is essential for the soap to be an effective emulsifying agent for oils and dirt. With hard water, the soluble sodium salt of soap reacts with the alkaline earth metal ions and precipitates as the useless and undesirable calcium or magnesium soap. The cleaning ability is lost.

Hardness is defined as the presence of soluble calcium and magnesium salts in the water. If these are present in the form of bicarbonates, the hardness is temporary. Heating hard water containing bicarbonates eliminates dissolved carbon dioxide and the causes precipitation of calcium carbonate. Magnesium carbonate is slightly soluble in water but heating will cause its hydrolysis into the much less soluble magnesium hydroxide . Simply boiling and filtering the water therefore eliminates temporary hardness. In regions where water has high temporary hardness, and is used directly without treatment, it is not uncommon to see hot water rinsing and washing baths with a generous crust of chalk (CaCO3) on the inner surfaces. This type of precipitation inside a boiler is also undesirable because the scale reduces the efficiency of heat transfer.

Mg(HCO3)2(aq) =  MgCO3(s) + CO2(g) + H2O

MgCO3(aq) + H2O = Mg(OH)2(s) + CO2(g)

Consequences of Using Hard Water:
The use of hard water in a textile dyeing or finishing mill can have some serious consequences. 
These include:

(1) precipitation of soaps;
(2) redeposition of dirt and insoluble soaps on the fabric being washed – this can cause yellowing and lead to unlevel dyeing and a poor handle;
(3) precipitation of some dyes as calcium or magnesium salts;
(4) scale formation on equipment and in boilers and pipelines;
(5) reduction of the activity of the enzymes used in desizing;
6) decreased solubility of sizing agents;
(7) coagulation of some types of print pastes;
(8) incompatibility with chemicals in finishing recipes.

Basic Knitting Action of a Needle

The basic action of a needle are shown in below. Except for the manner in which the hook is closed (in this case by pressing the beard), the knitting action is similar for all needles.The arrows indicate the relative movement of the loops along the needles. (Whether the needle moves through the loops or the loops are moved over the needle by some other elements depends upon the machine design.)

1. The needle is in the (so-called) rest position, with the previously formed loop (a) held on its stem and covered by the hook.

2. The loop is cleared from the needle hook to a lower position on the needle stem.

3. The new yarn (b) is fed to the needle hook at a higher position on the needle stem than the position of the previous (‘old’) loop.

4. The yarn is formed into a ‘new’ loop.

5. The hook is closed, enclosing the new loop and excluding and landing the old loop onto the outside of the closed hook.

6. The new loop (b) is drawn through the head of the old loop (a). Simultaneously the old loop slides off the closed hook of the needle and is cast-off or knocked-over.

7. The old loop now hangs from the feet of the fully formed new loop and the knitting cycle starts again.

Fig. Basic knitting action of a needle.

Introduction of Latch Needle | Advantages of Latch Needle

Latch Needle:

The needle which have a right hook and a latch easily around the axis is called latch needle.Pierre Jeandeau patented the first latch needle (also known as the tumbler needle) in 1806 but there is no evidence of its practical use.There is also no evidence that the pivoting of a broken pocket knife blade led to the development of the latch spoon.The latch needle was a more expensive and intricate needle to manufacture than the bearded needle. It was more prone to making needle lines as it slides in its trick, particularly if the latch was damaged or there was dirt in the trick. Latch needle action is comparatively easy.

Advantages of Latch Needle:

The latch needle has the major advantage of being self-acting or loop-controlled, so that individual movement and control of the needle enables stitch selection to be achieved. It is ideally suited for use with computer-controlled electronic selection devices. For that reason, it is the most widely used needle in weft knitting and is sometimes termed the ‘automatic’ needle (provided there are loops on the needle).

The old loop is cleared from the hook automatically when the needle is lifted because the loop slides down inside the hook and contacts the latch or tumbler, causing it to pivot open allowing the loop to slide off the latch down onto the stem.

The hook is closed automatically after yarn feeding by lowering the needle because the old loop, which was on the stem, slides upwards contacting and pivoting the latch tightly closed and drawing and enclosing the newly fed loop inside the hook.

Latch needles thus knit automatically as they are reciprocated and draw the length of the new loop as they descend to knock-over. Except in raschel warp knitting machines, they are arranged to move independently in their tricks or grooves.

They can operate at any angle but often require a latch-guard or latch-opening facilities as there is a tendency for latches to spring closed as tightly-knitted loops are cleared from the open latches.

Individually moving latch needles can draw and form their own needle loops in succession across the needle bed, unlike bearded needles and needles in warp knitting machines which move as a unit and thus require sinkers or guides to form the loops around their stems. The Germans classify the first method as ‘Strickerei’ or loop drawing and the second method as ‘Wirkerei’ or loop forming.

Variation of the height of vertical reciprocation of a latch needle at a feeder can produce either missing, tucking or knitting, and depth of descent normally determines loop length. Specially designed latch needles are capable of facilitating rib loop transference by selective lifting to a height above clearing height. Doubleended purl needles can slide through the old loops in order to knit from an opposing bed and thus draw a loop from the opposite direction to the previously knitted loop.