Textile Finishing

 

STAIN RESISTANCEThe development of stain repellent general wearing apparel has taken place in response to the consumers’  desire for easy-care garments.

Stain Repellent (or Resistant) Finish: 

Prevents water and/or oils from penetrating the fabric causing potential aqueous and oily stains to bead up and roll off.

Stain/Soil Release Finish:
 Enhances the ability of a fabric to release stains during laundering. For a release finish, liquids may not bead up, but usually soak into the fabric.

Combination Repellent/Release Finish: 

Provides limited stain repellency plus soil release with the objective of overall stain management.
Stain repellants are used on a variety of cotton fabrics from apparel to home furnishings. The main advantage is that the fabrics resist soiling during use. When a spill occurs, it can usually be spot cleaned easily, since the stain is confined to the surface rather than penetrating deep into the fabric.

SOIL RELEASE:

Soil release is the term used to describe the cleanability of fabrics by the laundering process. Even though stain resistance finishes made fabrics more resistant to soiling; however, in practice it has been found that soils have a way of penetrating even the best of repellent finishes, the textile item must be cleaned anyway.

Type of Soils:

Soils can be defined as unwanted substances at the wrong place. Most common soils fall into one of four categories:

01.Water borne stains : Water borne stains are not much of a problem; the stains are soluble in the wash water. Food stains and dried blood, although not water soluble, are responsive to proteolytic enzymes found in most commercial detergents.
 02.Oil borne stains, Oily soils, e.g. salad oil, motor oil, food grease are particularly difficult to remove from synthetic fabrics such as polyester. The sorption forces between the oils and the synthetic fiber surfaces are so strong that it is virtually impossible to completely remove them by conventional laundering.
04.Dry particulate soils: Dry particulate soils such as flour, clay and carbon black are mechanically entrapped in the yarn interstices and reside on the surface of the fiber.
05.Composite soils involving oil and grease adsorbed on particulate matter.

How Fabrics are soiled:

Soil can be airborne particles that settle by01. Gravitational forces or are
02. Electrostatically attracted to the fabric.
03. Airborne: Soot is a troublesome airborne particulate that is difficult to remove from fabrics. Drapes, carpets and upholstery are items prone to being soiled by airborne soils.
04. Contact with a dirty surface and they can be ground in by pressure or rubbing.
05. By wicking; liquid soils in contact with fabrics will wick into the structure by capillary action.
06. Redeposition: Soils removed in the laundering process may redeposit back onto the fabric, emulsified oily soils may break out of solution unless the emulsion is well stabilized.

Soil Removal:The adhesion between particulate soil and the fiber depends on the location within the fabric structure, the forces of attraction between the soil and fiber, and the area of contact. The greater the area of contact, the more difficult it is to break the adhesive bond. Fine particles have a greater area of contact. The tighter the fabric, the smaller are the interfiber voids which make also make the outward transport more difficult.

Roll-up Mechanism:

Oily-soil removal will depend on the three phase boundary interaction that occurs in the detergent solution. The roll-up mechanism first postulated by Adams argues that for removal to take place, the surface forces generated at the three phase boundary of fiber/detergent solution/oily soil results in progressive retraction of the oil along the fiber surface until it assumes a contact angle of 180 degrees. The various phases of the roll-up mechanism is shown in figure

Soil Release Chemicals:

01. Acrylic Soil Release Finishes:
The chemical composition of acrylic SR finishes may be generalized as follows:
02. Polymethacrylic Acid PMAA:Poly(methacrylic) acid is completely water soluble and functions as a soil release finish. However the proper amount of cross-linking is necessary before the finish to functions properly.

03. Methacrylic Acid - Ethyl Acrylate Co-PolymersCo-polymers of methacrylic or acrylic acid and ethyl acrylate have been found to be particularly useful as soil release agents. A particularly good combination for soil release is 70% methacrylic acid and 30% ethyl acrylate.

Practical Considerations and Fabric Properties:

01. About 6 to 10% acrylic soil release agent is needed to give good results. The polymeric films are stiff and brittle, giving the fabric a stiff and harsh hand. Being brittle and stiff, the finish tends to cause dusting, excessive needle and sewing thread breakage.

02. Most of the finish is lost after the first wash; however, the small amount remaining is effective for many launderings. The fabric is considerably softer after washing.

03. Excellent soil release results can be obtained when the optimum conditions are met. It is the most effective finish against dirty motor oil.

04. The finish is temperamental. It takes precise condition at the finishing plant to give reproducible results.

05. The finish is cost-effective for work clothing when dirty motor oil release is a significant quality.

Fluorochemical Soil Release:
A unique block co-polymer, developed by the 3M company (Scotchgard Brand Dual-Action Fabric Protector) combines oil repellency with soil release. The hybrid polymer backbone is comprised of segments based on polyoxyethylene united with segments containing long-chain perfluoroaliphatic groups. Figure shows the structure of the H portion (the hydrophilic portion), the F portion ( the perfluoroaliphatic portion) and the block co-polymer. The individual segments alone do not confer effective soil release; however, when combined into a single molecule, the new composition is effective both as a soil release agent and an oil repellent finish.

Figure Fluorochemical Soil Release Agent



Recipe
A suggested formulation for a woven fabric is shown below (percent on weight of bath):6% - 8% Fluorochemical repellent
5% Extender (optional)
0.2% Non-rewetting, wetting agent
5% Glyoxal (DMDHEU) resin
1.5% MgCl2 catalyst

Extender: An extender is less expensive aliphatic or wax water repellent that is used to boost performance and help reduce the amount of fluorochemical needed.

Non-rewetting, wetting agent: A non-rewetting, wetting agent will then evaporate or “flash off” during curing. If a regular wetting agent is used, it may remain on the fabric after curing and interfere with water repellency.

Hydrophilic Soil-Release Finishes for 100% Polyester:

Effective soil release finishes have been developed for 100% polyester fabrics which are best applied during the dye cycle and are often called Exhaustible SR finishes.

These finishes work best on loosely structured, textured polyester fabrics. Fabrics made from continuous filament or spun 100% polyester yarns are not responsive to these finishes.

Water quickly penetrates treated fabrics and is transported away from the source. This quality has been promoted as improved summer comfort, the ability to adsorb and wick away body perspiration. The finish is not effective at all on polyester/cotton blends. The finish imparts good soil anti-redeposition protection to treated fabrics and a modest measure of antistatic protection.