By: Noopur Shalini

What is stain?

A stain is a discoloration that distinguishes itself from the material on which it is found. It can be unintentional, in the case of domestic stains on fabric, cloth, or other material, or it can be intentional.

Synonyms: dirt, filth, grime, soil, grease, grunge

Various laundry techniques exist to attempt to remove or minimize existing stains, and stain removers are an important type of chemical in laundry detergents.
Stain resistance is an important characteristic in modern textile engineering.

What is repellency?

It forms a molecular barrier around the individual fibers to lower the critical surface tension (CST) so that the fabric does not attract stains or soil.
It results in-
 Liquids bead up and roll off the fabric.
 Spills can be blotted up quickly with a clean, dry, absorbent cloth.
 Provides unmatched resistance to oil- and water-based stains.

WHAT IS RELEASE?

Release allows stains to be removed more easily during laundering than most common untreated fabrics.
It results in-

� Stains temporarily soak into the fabric.
� Hydrophilic �water-loving� portion of finish draws in detergent and water.
� Stains wash out more easily.

Introduction

Chemical finish that permit relatively easy removal of soils with ordinary laundering.
These finishes are necessary because hydrophobic fibers and resins have very low water absorbency. It accomplishes the result of making the fiber more absorbent (hydrophilic), thus permitting better wettability for improved soil removal.

These finishes are applied at the same time the resins are applied to the textiles.

Most are durable to 40 to 50 launderings.

Soiling generally means smearing or staining of a large surface of the fabric with dust or dirt and oil or grease or both. The problem of soiling is not a new one. Natural fibers and synthetic fibers both attract dirt and get soiled but synthetic fibers attract soil to a grater extent than natural fibers; apart from this, they do not release soil easily during washing. Due to absorption and retention of soil, the whiteness and brightness of a fabric is spoiled and it appears yellowish and dirty.

Mechanism of Soiling

A fabric gets soiled mainly by three types of mechanism.

1. By mechanical adhesion of soil to the cloth by direct contact with a soiled surface or by rubbing of the garments against the skin or picking up dirt from liquors or from air; fabric construction facilitates such adhesion as the soil gets entrapped in inter fiber and inter yarn spaces or even into the capillary spaces of the fiber where it gets firmly deposited. Also soil which is oily in nature can diffuse into the fiber.
2. By adhesion by electrical forces due to attraction of dust particles from air by electrically charged fiber surface. This phenomenon occurs mainly with synthetic fibers because of their low moisture regain. Positively charged fabric surface is soiled more than negatively charged surface.
3. By redeposition of soil during washing which occurs particularly with nylon and polyester fabrics; the redeposition on these fibers takes place because of their oleophilic nature. Another aspect of soiling is the effect of time lag between soiling and washing. When a soiled fabric is allowed to lie unwashed for many days, the soil diffuses inside the fiber and it becomes difficult to remove it.

Factors influencing Soiling

Moisture regain of the fiber is the most important factor that influences soiling. Natural fibers and regenerated cellulose rayons have high moisture regain and have little tendency to accumulate static electricity. Even if static electricity is generated, it is quickly dissipated to the atmosphere. Therefore, the problem of soiling and soil removal is not very acute in the case of fibers having high moisture regain. Synthetic fibers have low moisture regain, therefore they accumulate static electricity which attracts dirt and dust from atmosphere. Lower the moisture regain, higher is the attraction of soil. When the moisture regain of the fibers drops below 4%, soiling increases rapidly. Polyester has the lowest moisture regain (0.4%) among synthetic fibers; therefore it attracts maximum soil. Since these fibers are hydrophobic, they do not swell in water and the removal of soil from the fiber becomes difficult. In the case of blends with cellulosic fibers, whatever soil is removed from the cellulosic component during washing, gets redeposited on the synthetic fiber because the synthetic fiber being oleophilic, attracts oily matter from the dirty wash waters.

Electrostatic charge

This is also an important factor which influences soiling. Synthetic fibers accumulate static charge during manufacture and during wear. Charged fibers attract soil from the atmosphere, positively charged fabric attracting more soil than the negatively charged one.

Fabric Structure

Fabric construction, yarn count, twist and the cross section of the fiber influence soiling. Smaller the denier, greater is the tendency to soil. A circular cross sectional fiber retains less soil than one with an irregular cross section. Higher the twist in the yarn, greater the soil retention. Fabric with protruding fibers assists soiling. Loosely woven and open knitted fabrics are more prone to soiling than closely woven fabrics but removal of soil from loosely woven fabrics is easy. Fabrics made from filament yarn do not get soiled as fast as those made from spun yarns.

Particle size of Soil

The smaller the size of the soil particles, grater is the soil retention by the fabric.

SOIL RELEASE FINISH

All fibers get soiled but most of them can be washed clean because soap, water or the detergent penetrates the fiber; but this is not so with polyester or polyester blended cotton. They are hydrophobic and often oleophilic or oil attracting. A soil release finish does not prevent soil from entering the fabric but it simply allows it to leave faster. It removes soil from the fabric and transfers it to the detergent; it protects the fiber from attack by soiling matter; it prevents redeposition of soil which has been dissolved or dispersed and lastly it prevents dust from being attracted and held by electrical charges on the fabric surface.

There are two types of soil release treatments available

1. Oleophobic treatments
2. Treatment with hydrophilic substances

In the first group it uses fluorocarbons which are oil repellent, soil resistant and release soil easily from the textile materials; one such compound is perfluoro-alkyl methacrylate used together with melamine formaldehyde condensate and paraffin wax. Many soil release finishes are based upon the use of organo silicon compounds which are applied by pad-dry-cure process. Thus the fabric may be padded with a mixture of methyl hydrogen polysiloxane and acetyl dimethyl benzyl ammonium chloride together with zinc acetate followed by drying and curing at 160 C for a few minutes. The new breed of soil release finishes confers hydrophilic character to the fiber surface.

Copolymers of ethyl acrylate with acrylic acid are used for soil release. Permalose T of ICI is applied (1-3%) to polyester and its blends by the pad-dry-cure process; it helps soil removal, prevents redeposition of soil during washing and prevents accumulation of static charges thereby reducing attraction of dust from the air. The finish is fast to washing and dry cleaning.

SOIL-RELEASE CHEMISTRY

Finishes providing soil release can be classified in numerous ways, by method of application, by fiber type, by chemical structure, electrical charge and so on. Here chemical structure is listed down-

Carboxy-based finishes

The composition of this finish is based on acrylic and methacrylic acid and ester copolymers. An ester to acid ratio of 70:30 is typical. This ratio seems to provide the proper blend of hydrophilicity and oleophobicity (hydrophilic-lipophilic balance, HLB) required for a soil release finish. The HLB scale is often used or the pre-selection of surfactants and ranges from about 0 (very hydrophobic) to nearly 20(very hydrophilic). For good soiling performance, HLB values of about 15 are favored. But this is only for rough orientation, because the important copolymer block arrangements are not expressed by these HLB values. Greater hydropilicity would strongly reduce durability to laundering. The ease of incorporating different acrylic monomers into copolymers has led to a wide variety of available finishes.other carboxy polymers that have been used as soil-release finishes include styrene-maleic anhydride copolymers and sodium carboxymethyl cellulose.

Hydroxy-based finishes

One of the earliest soil-release materials was starch, which functioned as a sacrifial treatment. Other starch- and cellulose based products that have been used as soil release agents include methyl cellulose, ethyl cellulose, hydroxypropyl starch, hydroxyethyl cellulose, hydroxypropylmethyl cellulose and hydrolyzed cellulose acetates. With some expectations these finished lack the laundering durability desired in finish expected to last of a garment and must be applied in combination with a binder or cross-linking agent.

Ethoxy-based finishes

One important group of soil-release agents for polyester fibers is based on condensation copolymers of terephthalic acid with ethylene glycol and polyethylene glycol. The structure of this polyester �ether copolymer contains blocks of polyethylene terephthalate and polyxyethylene terephthalate that provide a structure that has regions of hydrophilicity interspersed with hydrophobic regions that have a strong attraction for the polyester surface. These products can provide extremely durable soil-release properties for polyester fabrics by either exhaust or pad applications with about 0.5% solids add-on. It is possible to exhaust apply these products during the dyeing process. A modification of the condensation copolymer compounds involves incorporating anionic character into the polymer chain by use of sulfonated monomers. High soil-release performance, excellent softness and combinability with fluorocarbon finishes may be achieved by special silicone/polyalkylene oxide copolymers.

Fluorine-based finishes

These unique polymers have the unusual property of being hydrophobic and oleophobhic in air and hydrophilic and oil-releasing during laundering process. This is called �dual-action� mechanism. The hydrophilic blocks are shielded by the fluorocarbon segments when dry, presenting a repellent surface. After immersion in the wash bath, the hydrophilic blocks can swell and actually reverse the interfacial characteristics of the surface, yielding the hydrophilic surface necessary for oily soil release. Typically, these modified fluoropolymers are pad applied to fabrics in combination with the durable press crosslinking agents to increase the durability of the finish. The higher cost of the fluorochemical soil release agents compared to the acrylic copolymers is somewhat compensated by the low add-on required for soil-release performance. Mixtures of both polymers types provide a common compromise between efficiency and costs.

EVALUATION OF SOIL RELEASE

The ideal evaluation method for a soil-release finish would be to stain the fabric with the same material that will soil�s consumer�s clothes and then to wash the fabric with the detergents in the washing machine at the water temperatures that consumers will use. The American Association of Textile Chemists and Colorists (AATCC) has developed standardized procedures for evaluating soil-release finished that provide a strong indication of the actual finish performance in the real world. Evaluation of soil-release effects after washing is mostly visually done by comparison with photographic standards, but also by reflectance measurements and other instrumental techniques, including microscopy.

Oily soil-release testing

It specifies all the parameters that strongly influence soil release of oily soils.

Soil redepositon

It is used to estimate the degree of soil redeposition likely to occur during laundering. The fabrics to be tested are exposed to a soiling medium during a laundering simulation with a standard detergent. The change in reflectance of the fabric before and after the testing is an indication of the redeposition potential of the fabric.

Moisture transport

The procedure is used to determine the degree of absorbency of fabrics finished with soil-release agents. Typically, near instantaneous wetting of the fabric with water (<1s) is expected from non-fluorine-containing soil-release finishes.

Chemical mechanisms of soil-release finishes


FACTORS AFFECTING SOIL REALESE FINISH

� Nature of the soil
� Kind of fibers
� Nature of textile
� Effects of preparation
� Effects of dyeing and printing
� Effects of other finishes
� Washing conditions

PROPERTIES ACHIEVED BY SOIL RELEASE

� Add care to garments.
� Permits better wearability for improved soil release and soil removal.
� Permits relatively easy removal of oil borne stains from permanent press garments.
� Resists redepositing of soil when laundering.
� Aids in making fabric more absorbent.
� Provides greater comfort in hot weather.
� Provides improved anti static properties.

ADVANTAGES OF SOIL RESISTANT

� It protects the fibre from attack by soiling matter.
� It prevents redeposition of soil which has been dissolved or dispersed
� It prevents dust from being attracted and held by the electrical charges on the fabric surface.
� The finish is fast to washing and dry-cleaning.

FINISHING AGENTS USED

� FLUOROCARBONS
� FLUOROCHEMICALS
� PYRIDINUM COMPOUNDS
� RESINS
� SILICONE
� TRIAZINE COMPOUNDS
� WAX AND ITS DERIVATIVES

STAIN RESISTANT FINISH

Stain resistant fabric technology provides permanent stain repellency and stain release properties. Not only does this fabric repel stains, but it also releases the dirt and oils that cause stains. It helps garments stay cleaner, longer, because of the dual action of two robust and balanced technologies, working in the fabric for the life of your garment.

The stain repellent is applied on the outside of the fabric to allow most water- and oil-based stains to roll off.
The release is applied within to prevent ground-in oil-based stains from remaining in the fabric. During laundering, the release component pulls water and detergent through the fabric to wash out the stain It allows liquid and food-based spills to bead up and be wiped right off. It allows oil-based stains to be easily released in the wash cycle.

PROPERTIES ACHIEVED BY STAIN RESISTANT

� reduces rate of soil absorption, deposit and detention in fabric
� Provides for good soil release properties
� Prevents stains from spreading
� Allows water and spills to form globules on fabric surface preventing penetration into the fiber
� Resists water and water born stains
� Adds soft silicone hand
� Improves tear strength

ADVANTAGES OF STAIN RESISTANT

� The Stain resistant treatment does not affect the hand of the fabric.
� The Stain resistant treatment offers permanent protection to a variety of knitted and woven fabrics, including nylon, polyester, cotton, and cotton/poly blends.

MECHANISM COMMONLY USED IN INDUSTRY

1. USE OF FLUOROCARBONS


A durable stain resistant and soil release finish.

This finish imparts a fabric protector that enables the fabric to repel spills and stains on contact. The stain resistant finishes apply a coating to the fibers. This treatment gives fabric a stiffer hand as well as some other performance problems. The fluorocarbon stain resistant finish penetrates the individual fiber, becoming the part of the fiber. The surface properties of the fabric are not altered. Liquids can be blotted and soils wiped off and soils released during laundering.

2. NANOTECHNOLOGY

Nanotechnological processes for making stain-resistant fabric.

It involves a chemical treatment of the fabric to create a surface that repels water and also repels oil. Most stains come as liquids (like orange juice). The liquid dries up and develop a stain. If the liquid can be kept from getting sucked up, a stain can be prevented from happening.

Using nanotechnology, unique and permanent stain resistant finishes are being developed. Nanotechnology is defined as the precise manipulation of individual atoms and molecules to create layered structures. Nanosize particles can exhibit unexpected properties� different from those of the bulk material. The basic premise is that properties can dramatically change when a substance�s size is reduced to the nanometer range.

It uses chemistry to make little tiny whiskers and other things that help to repel liquids.
First the fabric is treated with some acid and some hydrophobic polymers are pressed into the fabric. The fabric is then baked to make the whiskers.

Supposedly, little tiny whiskers of which about one-thousand can fit across a thread of fabric. The whiskers make the fabric hydrophobic. So, it is part of the fabric and makes the fabric stain repellent. Stains don�t stay and the whiskers don�t wash away either.

APPLICATIONS

� High performance active apparel
� Work wear
� Military
� Uniform
� Travel apparel
� Casual men's and women's.sportswear
� Wall spaces for hospitality and commercial interior design use--fabrics for this market are possess flame retardant and stain release/repel properties.
� Nurses scrubs


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