22 Finishing agents – soil release, moth-proof, mildew proof agents

S. Ariharasudhan

1. SOIL-RELEASE FINISHES

Soil release is the term used to describe the cleanibility of fabrics by the laundering process. The finishes that 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. From a consumer point of view, a stain is perceived to be the worst case of soiling. With use fabrics tend to develop an overall grey and dingy look and this too is undesirable. But unless the consumer has the original fabric to compare with, the loss of whiteness is not objectionable unless it is severely discolored. A visual stain on the other hand, even a mild one, is more objectionable.

1.1. SOILS

Soils can be defined as unwanted substances at the wrong place. Most common soils fall into one of four categories: 1. water borne stains, 2. oil borne stains, 3. dry particulate soils and 4. composite soils involving oil and grease adsorbed on particulate matter. 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. 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. Removal of particulate soils depends on overcoming the work of adhesion between the particle and the fiber surface, facilitating the transport of detergent solution to where they reside and transporting the particle into the wash water. Mechanical energy (agitation) is important for latter.

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. For this reason oily soils, as a group, are particularly difficult to remove from many washable fabrics made from 100 % polyester and polyester blends. Lipstick, make-up, printing ink, used motor oil and atmospheric soot are examples of composite soils where bonding to the fiber is a function of the oily component. The removal of these stains is accomplished byovercoming the sorptive forces between the oil carrier and the fiber.

A. How Fabrics are Soiled

Soil can be airborne particles that settle by gravitational forces or are electrostatically attracted to the fabric. 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. Soils can transfer by contact with a dirty surface and they can be ground in by pressure or rubbing. Soils can also transfer by wicking, liquid soils in contact with fabrics will wick into the structure by capillary action. 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. Also the ionic charge of the emulsified soil may be attracted to an opposite charge on the fiber.

1.2. SOIL REMOVAL

A. Particulate Soil

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. Studies have shown that as more energy is used to grind the particulate soil into the fabric, the more difficult will it be to remove it. Both the area of contact and the location within the fabric are influenced by the force. Removal of particulate soil is brought about by breaking the adhesive bond between the particle and the fiber, wetting out the particle to make a stable dispersion, and then carry off the dispersed particle into the bulk of the wash water. 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.

B. Oily Soils

It was shown that the thermodynamic work of adhesion is given by the Young/Dupree equation, From this it follows that liquids that spread on a surface will have a zero contact angle. Since the cosine of zero is 1, the work require to remove that liquid will two times the surface tension of the liquid. Most oils have a surface tension of about 30 dynes/cm so they will completely spread on nearly all fibers except teflon.

1.3. SOIL RELEASE CHEMICALS

The introduction of polyester/cotton blends in the early 1960’s brought to light the need for soil release chemicals. Up until that era, most all washable fabrics were constructed of 100% cotton. The laundry processes included high wash temperatures, harsh chemicals (caustic, lye, bleach) and starch. Most all normal stains could be removed from these fabrics. When polyester entered the picture, oily stains became more difficult to remove. About the same time, home laundry procedures were changing; lower wash temperatures and less harsh chemicals evolved to prolong the life of durable press finishes. Also starching became unnecessary as the garment didn’t require ironing. Milliken can be credited for being first to introduce soil release durable press fabrics to the consumer. They incorporated an acrylic acid copolymer into their electron beam curable DP finish and merchandised the fabric under the VISA label. Shortly thereafter, the rest of the industry followed suit with a host of different soilrelease finishes. In general, soil release finishes are film forming polymers capable of imbibing water. Today the number has stabilized into three distinct varieties.

Two types work well on durable press finished cotton/polyester blends, e.g. acrylics and dual-action fluorochemicals. These are added into the final DP finish bath. A third type is engineered specifically for 100% polyester fabric, e.g. exhaustibles. They are best applied in the dye cycle (thus the name exhaustible) although they may be applied by pad-dry-cure.

A. Acrylic Soil Release Finishes

The chemical composition of acrylic SR finishes may be generalized as follows:

1. 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. The soil release rating are influenced by the inclusion of a diepoxide crosslinking agent. When PMAA is crosslinked with only the diepoxide, marginal SR ratings are obtained. However if a small amount of diepoxide is added with DMDHEU, the soil release ratings are vastly improved. Increasing the amount of diepoxide causes the SR rating to drop again. This data supports the contention that the ultimate properties of the cured film deposited on the surface of the fiber determines soil release.

2. Methacrylic Acid – Ethyl Acrylate Co-Polymers

Monomers containing carboxylic groups can be polymerized with vinyl and acrylic co-monomers to yield a range of co-polymers with varying carboxyl content. Co-polymers of methacrylic or acrylic acid and ethyl acrylate have been found to be particularly useful as soil release agents. An acid content of 70% or less give relatively high molecular weight emulsion polymers whereas higher proportions of acid renders the polymer water soluble and of lower molecular weight. A particularly good combination for soil release is 70% methacrylic acid and 30% ethyl acrylate. The effectiveness of co-polymers can be seen in Table 19. The data shows that when a 70/30 MAA/EA co-polymer is added to a typical durable press finish containingDMDHEU, the fabric possesses excellent soil release with fair durability. The data also shows that the SR ratings are substantially lowered if a diepoxide over crosslinks the polymer.

B. Dual Action 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. While conventional fluorochemical water and oil repellent finishes have an adverse affect on soil release, the co-polymer overcomes this deficiency. The hybrid polymer backbone is comprised of segments based on polyoxyethylene united with segments containing long-chain perfluoroaliphatic groups. The structure of the H portion (the hydrophilic portion), the F portion ( theperfluoroaliphatic portion) and the block co-polymer. The H section is a sulfhydryl-terminated co-polymer of tetraethylene glycol dimethacrylate and hydrogen sulfide containing 50% by weight of recurring ethylene oxide units. The F section contains poly(N-methyl perfluorooctanesulfonamido ethyl acrylate). The block co-polymer has recurring units ofperfluoro acrylate portion attached to the sulfhydryl-terminated glycol dimethacrylate.

C. 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. They are also called Co-Crystallizing SR finishes. This class of SR chemicals are composed of water dispersible, low molecular weight block co-polymers which have recurring blocks of hydrophilic segments attached to short blocks of PET. The hydrophilic segment is either polyoxyethylene or sulfoisophthalic acid. The PET portion provides attachment to the polyester fiber surface through secondary forces. The most effective application conditions are the same as those for exhaust dyeing polyester fibers with disperse dyes. This method results in a uniform deposition of the finish on the fiber surface. Pad applications are sometimes used; however, thermosoling temperatures are needed to get fixation.

2. Moth Proofing:

“Moth proofing is a finishing which is given to prevent the growth of moth.” It is one kind of special finishing process of textile. It is a chemical and property giving finish.

2.1. Purpose of Moth Proofing:

It is mainly carried out on wool fabrics as the keratin molecules are consumed by moths as food. Since woolen fabrics are costlier, they have to be protected from moth.Moth is a small insect that feeds on substances like keratin and fibroin and so animal fibres are more susceptible to the attack of moth.

Moth proof finished bag

Woolen and worsted materials are attacked by moth and quickly eaten away and the housewives have to be very careful in preserving such garments.

2.2. Requirements:

The finish should not affect the strength, drape, handle, softness, fastness property of dyed fabric and it should not cause any irritation to the human skin.

The finish should be fast to wash, light and laundering.

2.3. Process of Moth Proofing

Moth proofing can be done in the following ways:

    1.By exposing the material to sunlight or sulphur-di-oxide.

2.Using Naphthalene balls and para dichloro benzene.

3.Using some substances containing fluorine such as Sodium fluoride, Aluminium fluoride, Potassium fluoride, and Sodium antimony fluoride.

4.Using soluble solvents such as DichloroBeneze, Sulphomethylamid and DichloroTrichloro ethane.

5.  Evlan-BL and Mittin FF also produce moth proofing. These are the bet mothicides.

3.  MILDEW PROOF

It is as universal truth, every boat, no matter how carefully maintained will get a case of mildew eventually, but no one likes to talk about it. Eyeing the dark blotches on charts, under bunk cushions, or on the bulkhead, they simply hope it will go away, which it often does if the weather turns fair. The boat owner sighs with relief and forgets about it until opening the hatch weeks later to find that mildew has been very hard at work.

Mildew needs five things to grow and flourish:

• A food source. Soap scum is a real good one, for instance.

• A temperature range in which you and I would be comfortable

• Moisture.

•Darkness.

• Dead (unmoving) air.

Mildew is one of many forms of fungus present everywhere in the world. A very primitive plant form feeds on other plants and produces microscopic seed like spores that float freely around the cabin. These spores are always present, but it takes a particular set of conditions to encourage their growth into the black and smelly blight. Unfortunately, the ideal conditions for mildew are in a dark, damp location, just like your boat.

Mildew is whitish, grayish-white or gray-green fuzz that loves to grow in warm, dark and damp places. The fuzz is really the visible portion of the fungus which makes up what we call mildew. It particularly likes to grow in natural fabrics such as cotton and linen where it leaves easily recognized stains.

Mildew is much like Count Dracula it cannot survive light and warmth. So, take everything outside and spread them in the sun. Open all the curtains and let sunlight warm the interior. Your boat may look like an old-fashioned laundry, but you will kill the mildew. Expose all sides to the sunlight, and turn items like jackets inside out for full effect. Most of us, however, are not lucky enough to have year-around sunny weather, so you will probably have to rely on man-made assistance.

When it comes to mildew, prevention is the best cure. Since mildew is easier to prevent than to eliminate, your first concern should be prevention. The first line of defense is to provide good ventilation throughout the boat. The second is to keep everything clean and dry, and the last is to reduce the interior humidity level. None of these projects are small tasks in the marine environment, of course, but they are not impossible.

Heat, properly used, can also prevent mildew. The idea is to use a small source of heat to create convection currents in the cabin air. These currents cause the air in the cabin to circulate. Warming the air slightly also reduces its relative humidity, so the air is better able to dry up damp areas.

The most common chemical used to combat moisture is silica gel, which is usually encountered as the white packets tucked into camera and stereo equipment to absorb moisture during shipment. Both silica gel and a similar product, activated alumna, are porous granules that absorb up to half their weight in moisture from the atmosphere and which can be purchased inexpensively in bulk at hardware or drug stores. Using a double thickness of nylon stocking as a container, suspend these granules in lockers and around your cabin. Best of all, they can be reused after drying for about an hour in a 300 degree vented oven. A more potent chemical for removing moisture is calcium chloride, but it is highly caustic to both skin and fabric, and requires special care.However, even the best preventative measures sometimes are not enough, and you have to rid your vessel of mildew. There are two ways to approach the problem: with natural cures and with man-made products.

To rid yourself of mildew in a damp climate, you should start with a complete cleaning and airing. Be wary of strong laundry detergents, however, since phosphates are a delicacy for mildew. Any residue left after you scrub the mildewed area will only bring back an increased growth. Use low-phosphate soap for normal scrubbing and a mild alkali, such as washing soda or trisodium phosphate, for stubborn mildew, but be sure to rinse the area thoroughly.

Most traditional remedies rely on sodium hypochlorite (household bleach) to remove mildew. You can add TSP (tri-sodium phosphate, available at most hardware stores) to the formula to make it more effective. A good, strong, all-around solution is: 1/2 cup (4 oz.) Clorox per gallon of water

Special “mildew removers” are available in the house wares section of most supermarkets. Some marine stores also carry these products. If you cannot find a commercial mildew remover, youcan make your own by mixing 5 1/2 tablespoons of calcium hypochlorite into a quart of water. Spray this mixture onto the affected area, and then rinse with fresh water.

Always put the calcium hypochlorite into the water, never the other way around. Pouring water onto the chemical can cause a rapid, almost explosive reaction, so be sure to keep it away from children. Test this solution on an inconspicuous portion of the affected material to be sure it will not discolor. Do not use on clothing.

The most popular mildew remover is household chlorine bleach (sodium hypochlorite) sold in the U.S. in 5.25% solution. Manufacturers recommend diluting it further. Tilex® and other “mildew removers” are sodium hypochlorite solutions of about 3%.

4. Summary

Enhancement of existing properties and the creation of new material properties are the most important reasons for the functionalization of textiles. To impart the required functional properties to the fiber or fabric, it is customary to subject the material to different types of physical and chemical treatments. These days due to specific use and requirements of the consumer’s special purpose finishes are gaining importance, of these soil release, moth proof and mildew proff are some finishes which are very specific.

REFERENCES and URLs

1. Shenai, V.A., “Technology of Textile Finishing”, Sevak Publications, Bombay, 1995.
2. Marsh, J.T., “An Introduction to Textile Finishing”, Chapman and Hall Ltd., London, 1979.
3. W.D.Schindler and P.J.Hauser, Chemical finishing of Textiles, CRC Pr LIC Publication,2004.
4. Charles Tomasino, Chemistry and Technology of Fabric Preparation and Finishing, Department of Textile Engineering, Chemistry and Science College of Textiles, North Carolina State University, 1992
5. Heywood, “Textile Finishing”, Woodhead Publishing Limited, 2003.
6. Feighenbaum., A.V., “Total Quality Control”, McGraw Hill, New York, 1993.