Soil Release Finish | Mechanism of Soil Release Finish | Factor Affecting the Soil Release Finish
B.Tech in Textile Chemistry
SSM College of Engineering, Tamilnadu, India
What is Soil Release Finish?
Soil or stain release is a chemical finish that permits relatively easy removal of soils with ordinary laundering. The finish that allow stains to leave the fabric faster and makes fabric cleanable without significant loss of soil release properties. Soil release is the term used to describe the clean ability of the fabric by the laundering process. Stain or soil release is the ability of a fabric to be cleaned easily by laundering. Soil release properties are important for those textiles that can be washed whereas stain resistant properties are important for upholstery, carpets or such other fabrics that cannot be conveniently laundered. Soil release, particularly of oily stains, is usually difficult in textiles made from hydrophobic fibers such as polyester. Soil release properties may be imparted by applying hydrophilic treatments to hydrophobic textiles.
For example, low molecular weight block copolymers of hydrophilic segments like polyoxyethylene can be used to improve soil release properties of polyester fabrics. Conventional soil resistance finishes deteriorate soil release properties of fabrics but dual action fluorocarbons comprising a block copolymer of fluorocarbon component and a hydrophilic polyoxyethylene component have good soil resistance as well as good soil release properties.
Soils are unwanted substances and they belong to one of the following four types:
- Water-borne stains,
- Oil-borne stains,
- Dry particulate soils and
- Composite soils involving oil and grease adsorbed on particulate matter
What is Soiling?
Soiling can be defined as smearing large surface of the fabric with dust or dirt or oil or grease or both.
What is Release Finish?
Release finish allows stains to be removed more easily during laundering compare to most common untreated fabrics.
Mechanism of Soiling:
A fabric gets soiled mainly by three types of mechanism.
1. By mechanical adhesion:
- The soil is adhere 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.
- The 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
- The soil is adhere to the fabric 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 take 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:
1. Moisture regain:
- 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.
2. Electrostatic charge:
- 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.
3. Fabric construction:
- Fabric construction, yarn count, twist and the cross section of the fiber influence soiling. Smaller the denier, greater is the tendency to soil because circular cross sectional fiber retains less soil than one with an irregular cross section.
- Higher the twist in the yarn, greater the soil retention. Because 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. Because Fabrics made from filament yarn do not get soiled as fast as those made from spun yarns.
4. Particle size of soil:
- The smaller the size of the soil particles, grater is the soil retention by the fabric.
Mechanical Work Lead in Soil Release Finish:
- Hydrodynamic flow of washing washing carrying away the removed soil.
- Fiber flexing to force soil from between fibers during washing.
- Surface abrasion to remove soil physically during washing.
- Swelling of finish to reduce inter-fiber spacing.
Factor Affecting the Soil Release Finish:
|Nature of the soil||Oily soil or particulate soil, hydrophobic or hydrophilic, liquid or solid|
|Kind of fibers||Type of fiber, hydrophilic or hydrophobic, smooth or porous fiber surface|
|Nature of textile||Textile construction; yarn (staple or filament), fabric (knit, woven or nonwoven)|
|Effects of dyeing and printing||Difference in binder films, residual hydrophobic dyeing auxiliaries|
|Effects of other finishes||
|Washing conditions||Detergents, hydrodynamic flow in the washing machine|
Mechanism of Soil Release Finish (DUAL ACTION):
- The flouro carbon polymers have the unusual property of being hydrophobic and oleophobic in air and hydrophilic and oil-releasing during the laundering process.
- This is called as ‘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 easy oily soil release during washing.
- So the detergent used during washing can easily penetrate inside the fabric and enhance the soil release.
- Typically, these modified fluoro polymers are pad applied to fabrics followed by drying and curing.
Development in Soil Release Finishes:
- Stain-repellency performance has been achieved by the fluorocarbon resins based upon C8 perfluoro acrylates.
- C8 fluorocarbon finishes produced via electrochemical fluorination, it is discontinued because PFOS (perfluorooctane sulfonate) can result as a breakdown product during the manufacturing process.
- At present only C6 fluorocarbon products are manufactured using this route because they do not involve PFOS, which is a does, not causes pollution that is also bioaccumulative.
Troubleshooting for Soil-release Finishes:
- The performance of a soil-release finish depends upon its ability to provide a hydrophilic surface during the laundering process.
- Therefore any material deposited on the fiber surface that would reduce this necessary hydrophilicity should be avoided.
- Softeners, lubricants and other products that modify surface properties should be carefully investigated in laboratory trials before being used with fabrics treated with soil-release finishes.
Properties Achieved by Soil Release:
- Add care to garments.
- Permits better wearability for improved soil release.
- Provides greater comfort in hot weather.
- Resists redepositing of soil when laundering.
Chemicals Used in Soil Release Finish:
- Pyridinum Compounds
- Triazine Compounds
- Wax and Its Derivatives
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.