Water and oil repellant finishes

INTRODUCTION:

Home textile segment in textiles is growing by leaps and bounds with lot of young people buying homes. In addition they also have surplus income to buy premium products in the market. Water /oil repellant finishes can provide durable liquid repellency {Water and Oil}without compromising the natural feel of cotton. With proper chemical treatments, judicious selection of specialty chemicals, fabric construction,fabric/ garments, a host of benefits to the wearer such as staying clean for alonger period, faster drying and protection from rain can be produced.

During the last one decade, there has been a growing demand to provide stain repellency and or stain release properties to apparel goods. The development of these finishes has taken place in response to the consumers growing need for easy care fabrics. Water and oil repellant fabrics can be used for a variety of end uses such as outer wear, where the requirement is for high degree of water repellency and general wear such asexpensive silk sarees, where the focus is more both water and oil repellency.Other common end uses for these finishes include upholstery, rugs, carpets, protective clothing Filter fleece, Uniforms, Table cloths , wall paper etc etc.

During the last few years, easy care concept has expanded rapidly to include Oil and water resistant features in many apparel applications. Easy care concept now encompasses both minimization of ironing and easiness to clean garments that get stained in day to day use.Fabric manufacturers and chemical manufacturers have made significant advances in finishing processes to ease stain removal and prevent stain penetration Substrates that possess water and oil repellency are desirable for in many textile applications.Water repellant finishing on these fabrics is mostly imparted by theincorporation of low surface energy compounds

HISTORICAL DEVELOPMENTS: WATER REPELLANTS

1: Wax dispersions free of metalions

2: Metallic salts and soaps

3: Wax dispersions containingZirconium salts and Pyrdinium compounds.

4: Silicones

5: Organo Chronium compounds

6: Flurochemicals.

Products falling under 1 to 4 categories were purely temporary and lasted only a few washes. This led to the development of Silicone compounds. Methyl Hydrogen Polysiloxane {MeSIOH} was a very popular water repellant finish and had lot of risks associated with it. MeSIOH are reactive in nature and great care had to be taken while handling these materials. These materials came in many forms such as fluids, emulsions andresins. SIH products evolve hydrogen upon contact with strong bases, amines, primary alcohols. SIH compounds rapidly evolve hydrogen gas and form flammable and explosive mixtures in air. The inherent risk involved with these compounds made them unpopular and unattractive for water repellant finishing operations. More over compounds based on Parrafin oil with Silicone water repellant finishing agentswere not sufficient to protect textiles from grease and oil stains. This led to the development of FLURO CARBON POLYMERS. {FCP} Cellulose fibers, wool and silk are prone to stain faster than synthetic fibers because of their hydrophilic nature.

Natural fibers exhibit little or no water repellency, but when they get soiled they are readily cleaned, thus exhibiting a high degree of soil releasability many synthetic fibers notably polyester exhibit a low level of soil releasability. Thus the trend of producing textiles having a natural and synthetic blend of fibers tends to aggravate the situation, because these blends are easily soiled and the absorbed soil is difficult to wash out. Fluorocarbon polymers are applied to textiles in an attempt to solve this problem, however, they make soil release properties worse, because the aqueous washing medium cannot wet the substrate and hence cannot remove the stain, conversely, the addition of hydrophilic soil release polymers tends to enhance the soil release characteristics, but limits the ability of the textile to resist and repel water and oil based liquids.

FLUOROCARBON POLYMERS AND ITS CHEMISTRY:

Chemically fluorocarbon polymers, also known as Perfluroalkylacrylate copolymer and its fundamental structure resemble acrylic resins. Fluorocarbon polymers are special class of polymers and represent an indispensable part of the technology of water and oil repellant finishing and contain Carbon and Fluorine bonds. The relatively low reactivity and high polarity of the carbon- fluorine imparts unique characteristics to fluorocarbon polymers. FCP decreases the wettability but form water repellant and oil repellant polymer on its surface. A fluropolymer sheth around the fibers strongly reduces the textiles surface free energy, accompanied by the increase of the contact angle of liquids on its surface.

FCP are applied by the normal pad dry- cure technique, where in the substrate align the fluorocarbon segments of the polymers, there by reducing the tendency of soil, oil and water to adhere to the fibers of the substrates. Fluorocarbon polymers typically include a fluorinated component and a non fluorinated polymeric back bone. The fluorinated part called the Perfluoroalkyl group is common to all fluorochemical protectors. Greater the number of fluorine atoms attached to the carbon atoms and the more closely packed, they are, the better the water repellency. It has also been determined that the optimal number of linking carbon atoms is between 10 and 12. Linked carbon atoms that are linear rather than branched give better performance.

The non fluorinated part, in addition to being an extender by lowering the cost of the fluorochemical, serves two other useful purposes. It forms a backbone to the flurochemical making it more durable and acts as a glue to bond the flurochemical part to the fiber. The important feature of the polymeric back bone is that it is capable of forming a durable film on the surface of the fiber. The principle of fluorocarbon polymer finishing is similar to that of non stick frying pans. Fluorocarbon polymers act as a plastic sheet on top of the fabric and any liquid coming in contact is repelled and cannot pass through the barrier. The liquid beads up and roll off the fabric { as seen in the two photographs } and can be easily wicked or blotted off with a absorbent towel.

MECHANISM OF WATER AND OIL REPELLANCY:

If the critical surface tension of solid is greater than or equal to the surface tension of liquid, the liquid will wet the fabric. If the critical surface tension of the solid is less than the surface tension of the liquid, the fabric will repel the liquid. Thus water repellency can be obtained in case the critical surface tension of solid is smaller than the surface tension of liquid. When cotton is treated with FCP, water repellant in advance between them changes too. Critical surface tension of water repellant finished cotton is less than the surface tension of water.

Only FCP are the only class of chemicals, which impart both water and oil repellency. When a drop of oil is added on a textile surface it forms a contact angle with it, if the contact angle is > 90, there is drop formation and hardly any wetting of the surface.{ See Fig 2 and 4 } If the contact angle is < 90, there is wetting of the surface and if the contact angle is 0, there is complete wetting { See Fig 1 and 3} .The contact angle, thus, is dependent on the surface energy {SE } of the surface and the surface tension {ST} of the liquid. Wetting occurs only when ST <SE, energy of the surface depends on the presence of fluorocarbon groups on it.

In finishing, FCP can be used alone or in conjunction with other finishing agents when multiple function finishes are desired. They are applied in mixtures with durable press finishes in order to make cotton concurrently repellant as well as crease resistant and easy care. Other finishing auxiliaries used with flurochemical polymers are

1: Cross linker: These compounds can be resins like DMDHEU or others to provide durability of the finish.

2: Extenders: An extender is less expensive aliphatic or wax water repellant that can be used to boost the performance and reduce the amount of flurochemical.

3: Non Rewetting agent: A fugitive wetting agent such as Isopropyl alcohol is added along with flurochemical polymer to assist wetting of the substrate. These fugitive wetting agents evaporate or flash off during curing .Conventional wetting agents should not be used, as they will remain on the fabric after curing and interfere with water and oil repellency.

New Generation Flurochemicals: Conventional fluorinated polymers including esters or amides of polyacrylic acids are either stable emulsions or dispersions for addition to aqueous pad baths. While, these products impart good resistance to soiling and staining, these are easily removed after several launderings in water or by dry cleaning. Garments treated with these flurochemical finishes are subject to premature disposal, since once the finish is depleted on the garment, the garment is usually discarded. New generation products to produce water, stain and soil repellant repellency are based on flurosurfactants, which are capable of with standing numerous washing in water or dry cleanings. These new molecules are based on Perfluroalkyl hydroxyalkyl siloxane or the flurosilicone compounds.

The advantage of recent advancements in fluorocarbon chemistries is that the finish, when applied does not affect other properties of the fabric. For example, the technology adds stain repel/release functionality but permits cotton and cotton blended fabrics to maintain their wrinkle resistant and easy care properties. Some stain protection technologies that have been introduced provide dual action stain protection, as they impart soil repellency combined with stain release technologies. These advancements in stain protection have been introduced as the new generation water and oil repellant finishes. A dual action stain repellant /stain repellant technology function by repelling water based stains, at the same time, allowing soils that become stains when they penetrate the finish to be released.

Fluorocarbon polymers are used where very high performance and value added finishes are desired on 100% cotton fabrics. Other end uses of these polymers are acid and alkali protection, Alcohol and Petrol repellency, besides water and oil repellency. For end uses such as outer wear and rain wear, passing the rain test is required, which severely limits the fabrics that can be used to those with tighter construction. For technical outer wear tests more severe, than the rain test may be required such as Bundessmann and Hydrostatic pressure test.

AATCC test method 22- 2201 is used to evaluate water repellency while oil repellency is evaluated by using 3M Oil Alcohol tests.

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