FAQs in cotton Spinning-2

FAQs in Cotton Spinning

Question: What are the causes of Cotton Fibre degradation

Light in the presence of moisture has a degrading effect on cotton fibres. Heat also affects strength, stretch and life of cotton.

Q: What are neps. How they are formed

Neps are fine specks in the form of tiny balls of entangled fibres. They are formed due to bad mechanical processing conditions. Longer and immature cottons are more prone to neppiness.

Q: What are naps. Hw they are different from neps


Naps contain fibres whcih are entangled together, but much more loosly than those in neps. A nap can open out while it is not possible to open out a nep.

Q. What is the necessity of a blowroom.

Textile mills are generally located far away from the fields where cotton is grown. Therefore, compressing loose cotton into a compact bale form is unavoidable for economic transportation. This cotton has to be opened in the blowroom.

Also during picking and ginning quite a number of impurities get associated with such cotton, to remove all such impurities from the cotton, blowroom sequence of machines is quite necessary.

Q. Why there are so many machines in the blowroom sequence

The real work of opening, cleaning and blending is done by the blowroom machines. The action of opening and cleaning should be gradual. Therefore, a number of machines are required which gradually open and clean the cotton. The machines in the beginning of the line are mostly expected to reduce the lump size, and the latter machines are expected to open out or still reduce the size of fringes or tufts.

Q. What are lattices in blow room line, what is their purpose

Lattices are made up of wooden legs which are either plain or spiked. Horizontally arranged lattices are mostly plain while spiked ones are meant for lifting purposes. They help to move the cotton ahead in regular and uniform quantities.

Q. What is the purpose of beaters.

The object of beating is to shake out the impurities and force them through specially arranged gridbars and perforated sheets.

Q. Why a three bladed beater is better than a two bladed beater

It is heavier in weight and each blow is more forcible than a two bladed beater. Besides, it gives 50% more beats, which means that this can be run at a lower speed than a two bladed beater and incidently reduces vibrations, wear and tear in the machine.

Introduction to textile sizing

Necessity of Warp Sizing
During the weaving process, the yarns are subjected to three basic physical stresses. These are stretch, strain and abrasion. Although these forces exist in varyiing proportions depending upon the type of loom and the fabric styling,all three are forces that must be considered in all cases.Therefore, the ideal sizing material would produce a smooth, tough, elastic film which would adhere to the yarn. It should smooth to friction and abrasion. It should be tough to endure the load or strain and it should be elastic to allow flexibility and sufficient stretch.

Advantage of using Polyvinyl Alcohol in Warp Sizing

PVA is an excellent film provider. Its tough film is easily removed (desized) with hot water. It leads to the following benefits:

-Superior Abrasion resistance
- Adhesion to synthetic fibres
-flexibility/ elongation
-strength
- user friendly slashing performance.

Yarn sized with PVA can run at lower add-on because of the adhesion and strength advantage PVA provides over natural binders. It requires in quantity only 1/3 rd of the starch.

The excellent abrasion resistance means less shedding on the slasher and in the weave room.

The inherent flexibility of films of PVA resins eliminates the need for high Relative humidity in the weave room. A RH of 65-75% are recommended

PVA solutions are thermally stable and can be maintained for lower periods of time at high temperature.

PVA are widely reclaimed and reused for sizing, thus reducing effluent levels from the finishing plant.

PVA and wax together will provide the optimal size performance. Wax is needed to reduce dryer can sticking, weaker film for easier split, minimize clinging on looms and improved lubrication for the size coating. However, excessive use of waxes can lead to poor adhesion, brittleness, roughness and decreased abrasion resistance. Also waxes can be difficult to remove at desizing stage which can lead to quality problems in desized fabrics. It is important to select a wax that contains an effective emulsifier. It will act to prevent wax from redepositing back on the fabric during desizing. Common wax is tallow.

Starch is primarily used as an extender for PVA to reduce formulation cost. However antistats are needed with starch containing formulations to minimize static on warp yarns. Generally they are not needed with 100% PVA sizes. Antistats funciton as humectants, helping to retain moisture in the film while simulatneously plasticising the film. It includes urea, ethylene glycol and glycerol. Recommended level is 3-7%.

Defomers: Size solution can exhibit foam. For this we need defoamers in the levels of 0.25 to 1.00% based on the weight.

Binders- They are used for synthetic fibres- two major types are polyester or polyacrylic solution.

To avoid lappets warp density: For ring Spun 100% cotton - Spacing between adjecent ends should not be less than the diameter of the yarn. For Ring spun P/C blend spacing should not be less than 1.5 times the yarn diameter. For open end yarns, number of yarns per inch should be 10% less than the ring spun yarns of comparable count.

Viscosity: A properly sized warp will have completely encapsulating (360o) the yarn surface to hold down loose fibres. Internal penetration must be sufficient (15-25%) to anchor the size film to the surface of the yarn. Too low a size viscosity allows liquid to penetrate too deeply into the yarn. Too high a viscosity will not allow sufficient penetration to anchor the size. If ends are tightly packed in the size box, viscosity should be lowered to improve penetration.

Temperature of the size box is important for the right viscosity. High temperature may cause PVA to form skin- causing hard size formation when the slasher is stopped. Recommended temperature is 160-185 o F.

Drying can temperature should be set at the minimum to dry the yarn to hte desired moisture content of 5-8%.

Yarn stretch in cotton should be 1-6%, PC should be 1-1.5%, and Rayon/ Acrylic should be 3-5%.

Desizing agents: Can be water for PVA, NaoH for oils/waxes, HCL for starch, Enzyme for starch, Solvents for oils/waxes or peroxide for PVA.

For more details about textile sizing please click here.

Dyeing of silk with lac dye

Dyeing of Silk with Lac Dye

To extract dye, stick lac is crushed into pieces but not into powder form because at the time of boiling, the sticky resin substance melts and sticks to silk fiber thus damaging the material. These small pieces of stick lac are wetted with water overnight and then churned by which dyes with water come out easily in the form of solution as the dyes are water soluble. It is filtered well and care should be taken that even a small piece of resin is not present in the solution. Depending upon conditions, dyes are extracted from 50% to 98%.

Silk is treated with 2-5% solution( on the weight of the material) of mordant (generally alum) at the boiling temperature for 45-60 minutes. Some times the dyer add turmeric powder (curcuma longa) to get the orange tone. Silk is squeezed only, not washed by fresh water, at this stage. If potash alum is used as mordant then purple color is produced. If copper oxide with ammonia is used then bluish violet is obtained. To get dark red, lead acetate is used, to get reddish yellow, pot. dichromate is used. Copper sulphate produces violet. Barium Hydroxide gives dark red, Tinchloride with Oxalic acid gives pink. Ferrous Sulphate gives a color ranging from grey to black. K2SO4 with Cream of tartar gives violet color.

Dye bath is prepared with the extracted dye solution and rest with water with material to liquor ratio of 1:30. Dyeing is carried out for one hour at boiling temperature. A little solution of myrobalan (Terminalia Chebula retz) is added during the process to achieve greater fastness.

Acidic pH is maintained throughout the process of dyeing and if required the pH is maintained by use of acetic acid. Now dyed material is taken out from the dye bath and washed with fresh water.

About 4-5 kg of stick lack is required for dyeing 1 kg of silk.

Kullu Shawls

Kullu is a place in Himachal Pradesh. It is famous not only for entertainment and beautiful sceneries but also for its traditional textiles named Kullu Shawls throughout India. Kullu shawls are pure woollen shawls having traditional designs.

Kullu shawls are made from woollen yarns. The fibres for this yarn are collected from sheep and then sorted out (near front legs and neck, best quality of wool is found on a sheep) according to color, length, quality and feel. The fibres are processed by domestic methods. Under these methods, the fibres are sorted, scoured  and radical impurities are removed and then these fibres are dyed by tub dyeing method. Then the fibres are spun into yarn by charkha and Takhli. Now-a-days few quantities of silk and cotton are also used for borders, pallau and centre motifs. Somethimes greige fibres are also used to produce produce patterning and motifs.

Though Kullu shawls are produced in different colors like china blue, olive green, maroon coffee etc. but beauty of Kullu Shawls stands only in black shades.

Because Kullu Shawls are not made by big machines, this is an art of hand woven technology. Sometimes Zig-zag effects are also produced.

In Kullu shawls small diamonds, small dots, small squares, small triangles, plus marks etc. are found on the body of the shawls. there may be small lines of patterning on the selvedge or border with matching colors.

Kullu shawls are of woollen yarn of high count and shape just like 10s of cotton yarn. This is optimum to have better quality.