CO2 technology for water free dyeing………….


CO2 Technology

People are more familiar with the practical uses of carbon dioxide (CO2) than they realize. CO2 is the same stuff that puts the fizz in your soda at every restaurant, and dry ice is nothing more than the solid form of carbon dioxide.

CO2 can exist as a gas, solid, liquid or supercritical fluid, depending on pressure and temperature. We develop applications which use CO2 in its liquid or supercritical states.

As a solvent CO2 has gas-like viscosity and liquid-like density. It’s low surface tension and high diffusivity allow for exceptional penetration and material / particle transportation properties. It’s gentle processing is ideal for delicate or sensitive materials.

CO2 is becoming a key commercial and industrial solvent, largely due to its highly effective solvency powers and low environmental impact. Alternative solvents, such as hazardous chemicals or water, are rapidly being phased out. CO2 is the 21st century solvent.

No new CO2 is generated from our processes. We use CO2 that’s already there – it’s been recaptured from other industrial processes and recycled, so there is zero greenhouse gas effect. CO2 is non-toxic, non-hazardous, non-flammable, in-exhaustible and inexpensive. It leaves no residues or secondary wastes behind after processing and and has zero potential for soil or groundwater contamination. In most cases process costs are lower than comparable conventional processes.

Our solutions are implemented across the processing spectrum, including the food, pharmaceutical, flavors & fragrances, renewable energies and textiles sectors. Here’s a few of the most exciting successes:

Dyeing Textiles Without Water
The textile industry is believed to be one of the biggest consumers of water. In conventional textile dyeing large amounts of water are used, both in terms of intake of fresh water and disposal of waste water. On average an estimated 11 – 14 gallons of, otherwise drinkable, water is needed to process 1 lb of textile. FeyeCon, together with partners, developed a process to dye textiles with CO2. It’s a completely water-free dyeing process with considerably lower operational costs compared to conventional dyeing processes.
For more information visit www.dyecoo.com

Fast Diagnoses Without Toxic Solvents
In medicine certain diseases are detectable only through the sampling and testing of tissue. Conventional tissue processing techniques rely on the use of toxic chemicals and is an overnight process. FeyeCon developed a process that eliminates the need for hazardous chemicals and processes quick enough for same-day diagnosis. Laboratory staff are not exposed to toxic chemicals, no hazardous wastes are produced, laboratory efficiency is increased and patients get fast results – unprecedented improvements in histological processing.
For more information visit www.tispamedical.com

Clean Clothes, Clean Environment
Cleaning clothes, professional garments and other textile are traditionally water and/or chemical intense. “Eco friendly” and “organic” cleaning solutions have been marketed recently, none of them however are truly sustainable. Together with partners FeyeCon has developed the next generation of fabric and textile cleaning methods that use liquid CO2 as a cleaning solvent. Washing is gentle and requires no heat (to wash or dry), which translates into longer lasting garments. No water, no toxic chemicals – just clean clothes.
For more information visit www.co2nexus.com

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Dyeable Polypropylene Fiber


The ability to dye polypropylene fibers using conventional disperse dyes makes the fibers more attractive for apparel end-uses.

TW Special Report

Polypropylene fibers possess a number of attractive properties when compared to other fibers (See Table 1). Despite desirable properties, polypropylene fibers traditionally have suffered from a major drawback that has limited their adoption in textile apparel applications: In contrast to other fibers, conventional polypropylene fibers cannot be dyed. Instead, the color has to be imparted at the fiber extrusion step through mass coloration or solution dyeing. The process involves adding a relatively thermally stable pigment color during the melt spinning of the fiber. The pigments used are not usually miscible with polypropylene. Thus, the pigments are present as discrete particles in the fiber, and the color imparted becomes permanent in the fiber. While this has the benefit of very good colorfastness, there are two significant disadvantages. The first is that introducing new colors involves a relatively complex color-matching step. The second is the absence of greige goods to be dyed. This means that relatively large lots of fiber are made for every new color, and the time required to go from a new color concept to the final fabric or garment can be long.

There has been a long-standing interest in commercializing a dyeable polypropylene fiber. Ideally, it should have a dyeing profile similar to or compatible with large-volume fibers such as polyester, nylon or cotton, so that it is compatible with the dyeing and related processes that are already well-established. Furthermore, it should not change the essential benefits of polypropylene fibers presented in Table 1, especially its low density and its low surface energy. There have been several attempts to make dyeable polypropylene fibers, but they have not been successful because the resulting product did not meet these criteria.
FiberVisions has developed a revolutionary new polypropylene fiber, CoolVisions™ dyeable polypropylene fiber, that meets the needs of facile dyeing and polypropylene fiber characteristics by incorporating an additive within the polypropylene fiber. The fiber can be dyed using conventional disperse dyes in a manner similar to that used for polyester fibers. The fibers feature a wide array of inherent benefits and properties including:

  • light weight and comfort;
  • cottony softness;
  • easy care, easy wear;
  • moisture management;durability;
  • breathability;
  • thermal insulation; and
  • stain resistance.

FWfeaturechart

Lightweight And Comfortable

Polypropylene fibers are among the lightest in weight of all commercial fibers. The increased number of polypropylene fibers per kilogram of fabric offers added value compared to many other fibers, resulting in improved coverage for the same weight range or equal coverage in lighter-weight fabrics for comfortable garments. In addition, CoolVisions fibers are inherently softer than traditional polypropylene fibers, resulting in greater comfort, according to FiberVisions. This combination of attributes makes garments made from these new fibers inherently easy care, easy wear.

Moisture Management

According to FiberVisions, CoolVisions polypropylene fibers outperform all other dyeable fibers in low-moisture-absorption tests. In addition, garments made from polypropylene tend to have a high moisture-vapor-transmission rate. This is important in comfort, especially when one wants the skin to stay cool and dry. The mechanical properties of polypropylene fibers are not affected when the fabric is wet an inherent advantage compared to fibers like rayon, which can lose strength substantially.
As with traditional polypropylene, CoolVisions offers excellent chemical resistance and aqueous stain resistance. Bleach and other household cleaning chemicals do not affect the fibers, which also are not attacked by microbial organisms such as mold, mildew and bacteria.

windsurfers
Dyeable polypropylene fibers are suitable for apparel end-uses including sports applications.

Dyeing Characteristics

CoolVisions dyeable polypropylene fibers can be dyed using commonly available polyester high-energy disperse dyes and in standard high-pressure dyeing processes used for polyester fibers, but with lower dyeing temperatures possible. The color range and color-matching process are similar to those for polyester fibers.
The ability to dye fabrics results in many benefits over the use of fabrics made with traditional solution-dyed fibers, including value chain and styling benefits. Some of the value-chain benefits include the ability to store greige goods, match colors quickly, produce smaller lot volumes and serve niche or fashion-related color lines, respond rapidly to market demand, and offer a wider range of colors without greatly increasing inventory costs. There are added financial benefits from reduced working capital needs and shortened production times. Styling benefits include reduction in barré found in solution-dyed garments and the ability to print with dye inks rather than pigment inks. Dye-printed fabrics exhibit a softer hand and better colorfastness than pigment-printed fabrics. CoolVisions fibers also have been engineered to have an inherently soft hand and cotton touch not found in traditional polypropylene fibers.
As noted previously, CoolVisions fibers contain an additive that acts as a dye receptor. The additive is present in the fibers as small domains into which the disperse dyes dissolve during the dyeing process. At dyeing temperatures greater than the boiling point of water, the disperse dyes diffuse readily through the polypropylene fiber into the encapsulated domains of the additive. Under actual garment use conditions — which include much lower temperatures — the diffusion of the disperse dyes back out of the fiber is greatly diminished, resulting in good colorfastness. As with polyester fibers, high-energy disperse dyes should be used to obtain optimum colorfastness.
The approach of encapsulating the additive within the polypropylene fiber has many benefits. The surface of the fiber is essentially unchanged, resulting in excellent aqueous stain resistance and low water absorption. The polypropylene fiber also serves to protect the dyes from chemicals such as chlorine, resulting in excellent bleach fastness.
Since the ability to dye the polypropylene fiber is imparted by the incorporation of an additive, the level of the additive affects the depth of shade. This has a couple of benefits, according to FiberVisions: The additive level can be controlled quite well, resulting in reduced shade sensitivity to processing conditions. In addition, the level can be intentionally changed to produce fibers that dye to different depths, thereby offering an additional styling tool.
FiberVisions officially launched CoolVisions dyeable polypropylene fibers at the recent Outdoor Retailer Show in Salt Lake City. A number of partner companies are currently working with these fibers to develop new fabrics and apparel styles. Activities are underway to develop air-jet spun and filament-type products to broaden the range of styling tools.

September/October 2006

REEF:- TEXTILE WORLD

Wood Fibres


Lumber from eco-friendly managed forests in the Americas are processed through an electrolysis process which separates the Wood fiber from oil and sugar. The result is
100% pure and natural Wood Fiber which contain no additive and chemicals.

FEATURES OF WOOD-FIBERimage

Because Wood Fiber is an all natural material, Wood Fiber products contain many of the natural characteristics of Wood in nature.

SMOOTH AS SILK These silky Fibers are the finest we have seen in a long time. It looks and feels like silk but washes and wears like cotton!

STATIC-FREE Wood-Fiber products are static free because it is 100% pure fiber and contains no chemical impurities.

ECO-FRIENDLY/ DETERGENT FREE Made entirely from the wood of sustainably harvested forests

Wood-Fiber is an eco-friendly alternative to the cotton industry. Using a process that continuously recycles 99.6% of the bleach-free solvent and the water used to make this fiber makes this product Eco-friendly and Nature Loving.

Wood Fiber are so silky smooth that dusts just falls off its surface. Detergent is not required and not recommended to clean it. Just gently rinse/ machine wash and tumble dry. Easiest cleaning instructions ever.image

ALLERGEN-FREE & DERMATOLOGICAL FRIENDLY Did you know that your bedding/towels may behosting millions of dust mites/allergen? If you suffer from burning eyes, a runny nose, and morning headaches you may have these tiny creatures and the allergen in their feces invading your bathroom. The allergen thrives in warm moist environments such as mattresses, pillows, face/bath towels and causes allergic reactions when inhaled. What is an Allergic ? An Allergy is your body’s reaction to certain substances. Different people have different tolerance towards the allergens. For allergic people only a small amount of allergens can cause the various symptoms above.Wood fiber products are 100% pure fibers without the sugar or oil. As a result bacterias do not multiply in Wood Fiber products. Together with the fact that Wood Fiber is all natural it is dermatologically friendly and suitable for allergy prone people.

SMELL-FREE Wood Fiber products are Smell resistant because it is resistant to smell causing bacterias.

HIGHLY ABSORBANT Wood-Fiber absorbs moisture, water, sweat and oil better than cotton. Products made from Wood Fiber such as socks are extremely breathable and does not trap moisture in the feet. This prevents many foot related diseases
and smell.

COLORFASTNESS OF COTTON TEXTILES


INTRODUCTION

Today’s consumer is more sophisticated than ever. They are conscious not only of style and comfort, but also of care and durability. They demand a quality product. Market studies show that consumers make many purchase choices based on color. Therefore, a fabric’s ability to retain its original color is one of the most important properties of a textile product.

The colorfastness or color retention of cotton textiles is influenced by a number of variables that occur both pre-consumer and post-consumer. This report summarizes how variations in raw materials, chemicals, manufacturing processes and consumer practices all have an effect on the performance characteristics of a fabric. Manufacturers must understand how the many variables affect colorfastness to achieve the ultimate goal of consumer satisfaction.

COLORFASTNESS AND TEST METHODS

Colorfastness is defined by the American Association of Textile Chemists and Colorists as “the resistance of a material to change in any of its color characteristics, to transfer its colorant(s) to adjacent materials, or both, as a result of the exposure of the material to any environment that might be encountered during the processing, testing, storage, or use of the material.” In other words, it is a fabric’s ability to retain its color throughout its intended life cycle. There are many types of colorfastness properties that must be considered to provide the consumer with an acceptable product. The American Association of Textile Chemists and Colorists has over thirty test methods that evaluate different colorfastness properties. These include, but are not limited to wash, light, crock, dry cleaning, perspiration, abrasion and heat. The type of product being manufactured determines which types of colorfastness are important and therefore which test methods are relevant. For example, upholstery fabrics must have excellent lightfastness and crockfastness properties, whereas washfastness is important for clothing fabrics. Manufacturers must know a fabric’s intended end use in order to make processing decisions that will produce a product of acceptable performance.

TEXTILE MANUFACTURING PROCESSES AFFECTING COLORFASTNESS

1. Preparation

Many aspects in the textile manufacturing process of taking a loom state fabric to a finished product have an effect on the colorfastness properties. Preparation is the first stage of textile wet processing. Cotton fibers are approximately 95% cellulose. The non-cellulosic portion consists of natural products such as waxes, sugars, metals, and man-made products such as processing aids, grease, plastic, and rubber. To achieve optimum dyeing and finishing conditions, it is important that these impurities are thoroughly removed with minimal damage to the cotton fiber.

2.Dye Selection

Dyeing is the crucial step in determining the colorfastness performance of a fabric. The American Association of Textile Chemists and Colorists define a dye as “a colorant applied to or formed in a substrate, via the molecularly dispersed state, which exhibits some degree of permanence.” Dyeing is accomplished by immersing the textile in a dye bath, applying heat and chemicals to drive the dye onto the textile, and then rinsing the substrate to remove the surface dye. These principles are illustrated below.

Different dye classes are used for each fiber type. The table below shows which dyes can be used for which fibers.

Dye Classes Available for Different Fibers

Fiber Dyestuffs
Cotton & manmade cellulosics Direct, Vat, Sulfur, Naphthol, Reactive, Pigment
Polyester Disperse, Basic
Nylon Disperse, Acid, Premetallized
Acetate Disperse
Wool & Silk Acid, Premetallized
Acrylic Dispersed, Basic

Dye selection must be based on desired performance criteria, manufacturing restrictions and the costs a market can bear for each end product. Every dye has unique colorfastness properties. Some dyes are known for their excellent washfastness characteristics and others are known for their lightfastness properties. The structure of the dye, the amount of dye, its method of bonding to the fabric and dyeing procedures all contribute to a dye’s performance characteristics. Dye combinations in a specific formulation must also be evaluated for their effect on colorfastness. Heavy shades often have reduced fastness properties. When high concentrations of dye are required, proper rinsing and washing off procedures are essential. However, due to entrapped dye particles within the cellulose structure, some unbound dye molecules can still remain and contribute to color loss and dye transfer

DYES FOR COTTON

Dyes can be categorized based on the mechanism by which they become fixed to a fiber. Dyes used for cotton fibers can be categorized into the surface bonding, adhesion, or covalent bonding mechanisms.

Pigments are sometimes used to color cotton fabrics, however they are not considered dyes. They are completely insoluble in water and have no affinity for cotton fibers. Some type of resin, adhesive, or bonding agent must be used to fix them to the cotton fiber. Typically, they exhibit good colorfastness to light and poor colorfastness to washing.

Direct dyes are water soluble and categorized into the surface bonding type dye because they are absorbed by the cellulose. There is no chemical reaction, but rather a chemical attraction. The affinity is a result of hydrogen bonding of the dye molecule to the hydroxyl groups in the cellulose. After the dyestuff is dissolved in the water, a salt is added to control the absorption rate of the dye into the fiber. Direct dyes are fairly inexpensive and available in a wide range of shades. Typically, they exhibit good lightfastness and poor washfastness. However, by applying a fixing agent after dyeing the washfastness can be improved dramatically.

Vat, sulfur, and naphthol dyes are fine suspensions of water insoluble pigments, which adhere to the cotton fiber by undergoing an intermediate chemical state in which they become water-soluble and have an affinity for the fiber. Typically, vat dyes exhibit very good colorfastness properties. Sulfur dyes are used to achieve a low cost deep black. They exhibit fair colorfastness properties, although the lighter shades tend to have poor lightfastness. Naphthol dyes are available in brilliant colors at low cost, but application requirements limit their use. They exhibit good lightfastness and washfastness, but poor crockfastness.

Reactive dyes attach to the cellulose fiber by forming a strong covalent (molecular) chemical bond. These dyes were developed in the 1950’s as an economical process for achieving acceptable colorfastness in cellulosic fibers. Bright shades and excellent washfastness properties are the trademark of reactive dyes. One concern regarding reactive dyes is their susceptibility to damage from chlorine. Another is that lighter shades tend to have reduced lightfastness properties.

The following table summarizes the fastness properties of the dye categories or classes available for dyeing cotton fabrics. Keep in mind that these are generalizations. Every dye is unique and some dyes within a particular class may behave differently.

Finishing

Finishing is the final stage of textile wet processing. Different types of finishes can be utilized depending on the desired performance characteristics of the end product. Resin and enzyme treatments are common finishing techniques that can influence the colorfastness of textile fabrics. Crosslinking resins are used to improve the durable press or wrinkle resistance of a fabric. Generally, resin treated fabrics demonstrate improved color retention to laundering. However, this increase in color retention comes at the expense of reduced physical properties of the fabric. Silicone softeners incorporated into the resin finish bath may further improve color retention for some fabrics. Softeners and resins play a key role in reducing surface abrasion and therefore improved overall wash performance. Cellulase enzymes are used to remove surface fibers that can create a fuzzy appearance on the surface of a fabric. Generally, enzyme treated fabrics show improved ability to maintain their original color and appearance after multiple home launderings. The degree of improvement from any of these finishing techniques is highly dependent on the individual dyes used in a particular formulation to achieve a given shade

CONSUMER PRACTICES

Manufacturers can follow every recommendation and precaution to produce a fabric with optimum performance characteristics. However, colorfastness properties are also influenced by consumer practices. These include laundry detergent selection and wash procedures. Therefore, when evaluating colorfastness properties of a product it is important to use the appropriate test method that accurately reflects the consumer laundry practices. Due to higher energy costs consumers are laundering clothes at lower temperatures. For this reason detergent with “color safe” or activated peroxy bleaching agents, which improve cleaning efficacy at lower wash temperatures, are one of the fastest growing segments of the home laundry market. Some fabrics may fade a little when home laundered with standard detergent, but fabrics laundered with detergents containing activated bleach can show significant losses in color strength as determined by the sensitivity of the dye to those detergents. Another type of detergent available to consumers is those containing enzymes, which remove surface cellulosic fibers from the fabric. Many times the loss or apparent loss of color can be attributed to surface changes in the fabric caused by abrasion during laundering. Detergents containing enzymes generally reduce the color change associated with home laundering by decreasing the fuzziness of a fabric’s surface. Wash procedures also influence a fabric’s ability to retain its color. Consumer practices such as washing clothes inverted, reducing the wash load size, adding softener to the final rinse and reducing the tumble dry time minimize color loss.

CONCLUSIONS

The colorfastness of cotton textiles can be a complicated subject. Fiber quality, yarn formation, fabric construction, textile wet processes and consumer practices can all have an influence on the performance characteristics of a fabric. Of these variables, the choices made during textile wet processing have the most significant effect on the colorfastness properties. Dye selection is of the utmost importance. Consumer practices such as detergent selection and laundering techniques also play a major role in the color retention of a fabric. Customer satisfaction should improve as manufacturers gain experience and knowledge in understanding and controlling the many aspects that influence colorfastness.

REf. TECHNICAL BULLETIN( www.cottoninc.com)

Chemical forces responsible for dyeing


The internal surface of fibers and its importance

The nature fibres, i.e. the cellulosic and protein fibres have exceedingly large internal surfaces, which are the walls of the channels between the bundles of long-chain molecules composing the fibres. The number of such channels is immense, of the order of ten million in the cross-section of, e.g. cotton or a wool fiber, and the total surface of their walls is of the order of 100 m2 or five acres per lb. This is about one thousand times as the outer surface of the fiber.

Whets the fiber is wetted, water rapidly penetrates and swells a large proportion of these channels, and Dyes in solution are then able to diffuse into the channels or pores. They can however enter only a relatively s proportion of the total internal space, because the remainder is in pores too small to admit a dye molecule. Many of the synthetic polymer fibres have much less internal surface than the natural fibres, but the dye used with such fibres are able to penetrate between the fiber molecules even though water cannot always do so.

Dyes are surface-active substances, that is, when dissolved in water their molecules tend to concentrate more closely together at a surface than in the body of the solution .the surface (or interface) can be that between the solution and either air or a fibre. The first action in any dyeing operation is the concentration of dye molecules at as much of the
internal surface of the fibre as they can reach. The concentration so produced is not usually sufficient to give a useful deep coloration to the fibre, and for such coloration other factors must be brought into play. These are the chemical forces, which can operate between a dye molecule, and fibre molecule, which are classified below, and also those between the dye molecules themselves. Which can cause their association into larger units?

The main physical and chemical effects between fibres and dyes

Broadly, four main chemical effects subsequently responsible for the substantively of the dye for the fibre are list below:

· Hydrogen bonds
· Non-polar or van der Walls’ forces
· Electrostatic or ionic forces –
· Covalent bonds.

These seldom act in isolation; usually at least two operate in any dyeing process.

· The hydrogen bond

This is the ‘secondary valency’ by which a hydrogen atom in e.g. a hydrogen group can form a weak association with another atom. Most fibres and dyes contain groups that can take part in this form of combination. There is evidence for the importance of hydrogen bonds in dyeing some man-made fibres. e.g. cellulose acetates and possible cellulosic protein fibres.

· Non-polar forces

This is a manifestation of the universal tendency, of atoms and molecules to attract one another. They seem to be particularly effective in attracting a dye to a fibre when the two have certain special characteristics, e.g. either when they both have long and fairly flat molecules, as with cellulose and direct or vat dyes and also with cellulose acetate and disperse dyes, or when they both contain a considerable proportion of purely hydrocarbon groups (aliphatic or aromatic) as with some dyes applied to wool and most dyes applied to polyester. In the latter cases the presence of the water of the dye bath assists the dye-fibre attraction because hydrocarbon groups tend to escape from water and associate together. This effect is known as ‘hydrophobic bonding’.

· Ionic forces

The third form of attraction between dye and fibre is due to difference of electric charge between them. In water, fibres become negatively charged and. Since most water soluble
dyes are anionic, their coloured ion carrying a negative charged, adsorption does not occur readily. It is then necessary to reduce or even reverse the charge on the fibre before the dye ion can approach closely enough, for the non-polar forces to become effective. (This does not apply with the u of cationic, i.e. positively charged dyeing of acrylic fibres.)
Adding salt to the bath can have the required effect with cellulose fibre, a suitable with protein fibres and nylon. In the latter case, the reaction for wool dyeing in presence of acid can be illustrated by a series of simple chemical equations.

· Covalent bonds

Only reactive dyes are attached to the fibre by a covalent bond, which is much stronger than the previously mentioned forces and difficult to break down. Some degree of breakdown, shown by bleeding of the dye from the fibre, can with some types of reactive dye be produced to small extent by drastic treatment with acid or alkali, and almost completely by a treatment For 3 h in boiling 49% aqueous hydrazine solution.

Choice of Dyes


REUTLINGEN, GERMANY - NOVEMBER 17:  A student ...

Image by Getty Images via @daylife

One reason for the existence of the great number of commercial dyes that any textile material may be have to withstand one or more of a wide variety of processes of manufacture and later be subjected to a variety of different types of wear and tear in use. The correct of choice of dye for any given circumstance, in fact, requires considerable knowledge and experience, and nothing more than a bare outline of the underlying principles can be given here. A few typical examples, selected at random, of some of the matters to he considered in making the choice are given below under four main headings:

1 Nature of wear and Tear in Use

Many textiles must withstand severe exposure to sunlight or to repeated washing. Thus curtains and fabrics for outer garments must have good fastness to light. And fabrics for awnings and deck chair must withstand sunlight and also rain: knitted wool material should be fast to washing; shirting and handkerchiefs must withstand boiling in soap solution; and so on.

2 Nature of Manufacturing Processes

Cotton fabric having colored threads on a white ground may have to be subjected to boiling, with alkali under pressure (kier boiling) and bleaching after weaving. The first kind of dye chose for bland fabrics should be withstood the dyeing conditions of the second kind of dye.

3 Nature of Dyeing Process

Apart from the above treatments to which the already dyed materials are subjected, the nature of the dyeing process is important in determining the choice of dye, Thus in the dyeing of fabric only the most level-dyeing dyes can be used, because the slightest inequality in colour in different areas of the cloth would spoil the appearance. If loose fiber is being dyed, however, levelness is of less importance, because any portions of uneven appearance in the mass will be evenly distributed when the fiber is subsequently manufactured into yarn. Again, in using package dyeing machine, which the dye-liquor is pumped through a container packed tight with loose fiber, or through a cake or thick reel
of yarn. it is important for the dye to be either in true solution or present as extremely fine particles.

4 Dyeing Costs

The prices of different dyes are quite different. It is better to choose the economic dyes in Practice if all above mentioned requirements are conformed.

MIXING(COTTON)


Once Valledupar's main economic produce; Cotton
Image via Wikipedia

Cotton is a hygroscopic material , hence it easily adopts to the atmospheric airconditions. Air temperature inside the mixing and blowroom area should be more than 25 degree centigrade and the relative humidity(RH%) should be around 45 to 60 %, because high moisture in the fibre leads to poor cleaning and dryness in the  fibre leads to fibre damages which ultimately reduces the spinnability of cotton.

Cotton is a natural fibre. The following properties vary very much between bales (between fibres) fibre micronaire fibre length fibre strength fibre color fibre maturity   Out of these , fibre micronaire, color, maturity and the origin of growth results in dye absorption variation.
There fore it is a good practice to check the maturity , color and micronaire of all the bales and to maintain the following to avoid dye pick up variation and barre in the finished fabric.

BALE MANAGEMENT :

Bale Management

In a particular lot

  • Micronaire range of the cotton bales   used should be same for all the mixings of a lot
  • Micronaire average of the cotton bales used should be same for all the mixings of a lot
  • Range of color of cotton bales used should be same for all the mixings of a lot
  • Average of color of cotton bales used should be same for all the mixings of a lot
  • Range of matutrity coefficient of cotton bales used should be same for all mixings of a lot
  • Average of maturity coefficient of cotton bales used should be same for all mixings of a lot

Please note, In practice people do not consider maturity coefficient since Micronaire variation and maturity variation are related to each other for a particular cotton.

It the cotton received is from different ginners, it is better to maintain the percentage of cotton from different ginners throught the lot, even though the type of cotton is same.

It is not advisable to mix the yarn made of out of two different shipments  of same cotton. For example , the first shipment of west african cotton is in january and the second shipment is in march, it is not advisable to mix the yarn made out of these two different shipments.  If there is no shadevariation after dyeing, then it can be mixed.

According to me, stack mixing is the best way of doing the mixing compared to using automatic bale openers which picks up the material from 40 to 70 bales depending on the length of the machine and bale size, provided  stack mixing is done perfectly. Improper stack mixing will lead to BARRE or SHADE VARIATION  problem.  Stack mixing with Bale opener takes care of short term blending and two mixers in series takes care of long term blending.

why?

  • Tuft sizes can be as low as 10 grams and it is the best way of opening the material(nep creation will be less, care has to be taken to reduce recyling in the inclined lattice)
  • contaminations can be removed before mixing is made
  • The raw material  gets   acclamatised to the required temp and R.H.%, since it is allowed to stay in the room for more than 24 hours and the fibre is opened , the fibre gets conditioned well.

Disadvantages:

  • more labour is required
  • more space is required
  • mixing may not be 100% homogeneous( can be overcome by installing double mixers)

If automatic bale opening machine is used the bales should be arranged as follows

let us assume that there are five different micronaires and five different colors in the mixing, 50 bales are used in the mxing. 5 to 10 groups should be made by grouping the bales in a mixing so that each group will have average micronaire and average color as that of the overall mixing. The position of a bale for micronaire and color should be fixed for the group and it should repeat in the same order for all the groups

It is always advisable to use a mixing with very low Micronaire range.Preferably .6 to 1.0 . Because

  • It is easy to optimise the process parameters in blow room and cards
  • drafting faults will be less
  • dyed cloth appearance will be better because of uniform dye pickup etc

It is advisable to use single cotton in a mixing , provided the length, strength micronaire ,maturity coefficient and trash content of the cotton will be suitable for producing the required counts.  Automatic bale opener is a must if more than two cottons are used in the mixing, to avoid BARRE or SHADE VARIATION problem.

It is better to avoid  using the following cottons

  • cottons with inseparable trash (very small size), even though the trash % is less
  • sticky cotton (with honey dew or sugar)
  • cotton with low maturity co-efficient

Stickiness of cotton consists of two major causes. Honeydew from Whiteflies and aphids and high level of natural plant sugars. The problems with the randomly distributed honey dew contamination often results in  costly production interruptions and requires immediate action often as severe as discontinuing the use of contaminated cottons.An effective way to control cotton   stickiness in processing is to blend sticky and non-sticky cotton.  Sticky cotton percentage should be less than 25%.

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