WATER REPELLENT FINISHESWATER REPELLENCE

Water repellent fabrics are those which resist being wetted by water, water drops will roll off the fabric. A fabric's resistance to water will depend on the nature of the surface, the porosity of the fabric and the dynamic force behind the impacting water spray.

DIFFERENCE BETWEEN WATER REPELLENT FABRIC AND WATER PROOF FABRIC

WATER REPELLENT FABRIC

Water Repellent Fabrics have open pores and are permeable to air and water vapour. Water-repellent fabrics will permit the passage of liquid water once hydro-static pressure is high.

WATER PROOF FABRIC

Water-Proof Fabrics are resistant to the penetration of water under much higher hydrostatic pressure than are water-repellent fabrics. These fabrics have fewer open pores and are less permeable to the passage of air and water vapour, with no bonding between the s and the coated product. The more waterproof a fabric, the less able it is to permit the passage of air or water vapour.

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A fabric is made water-repellent by depositing a hydrophobic material on the 's surface; however, water proofing requires filling the pores as well.

PHYSICAL CHEMISTRY OF WETTING

When a drop of liquid on a solid surface does not spread, the drop will assume a shape that appears constant and exhibits an angle, called the contact angle. The angle is characteristic of the particular liquid/solid interaction; therefore, the equilibrium contact angle serves as an indication of wettability of the solid by the liquid.

In theory, therefore, when the surface tension of the liquid is lower than the

surface free energy of the solid, the liquid will spontaneously wet the solid.

The surface free energies of typical textile solids are as follows:

Solid Surface Free Energy mN/m

Polyamide (Nylon 6.6 ) 46

Cotton 44

Polyester 43

PVC 39

Polyethylene 31

Thus a liquid with a surface tension lower than the surface free energy of cotton ( 44 mN/m) will spontaneously wet the cotton.

For fabrics to be water repellent, the Surface free energy of the 's surface must be lowered to about 24 to 30 mN/m. Pure water has a surface tension of 72 mN/m so these values are sufficient for water repellency.

WATER –REPELLENT FINISHES

Because of the different effectiveness of various finishes, the following degrees of water repellence can be found:

‘Shower-resistance’ garments which will protect the wearer from light rain ‘Rain-resistant’ garments which will provide protection for a few hours in moderate

rain

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‘Storm-resistant’ garments which will resist water penetration for many hours in heavy rain.

There are two types of water-repellent finish: non-durable and durable. The non-durable finish is usually based on paraffin wax and although it gives very good ratings of water repellence, it can only withstand very light laundering. The durable finish, on the other hand can endure both repeated washing and dry cleaning. Durable finishes are most expensive to produce and are usually based on silicone products, which are also used as fabric softeners can further improve the fabric handle.

WATER REPELLENTS

PARAFFIN WAXES

The oldest and most economical way to make a fabric water repellent is to coat it with paraffin wax. Solvent solutions, molten coatings and wax emulsions are ways of applying wax to fabrics.

Of these, wax emulsions are the most convenient products for finishing fabrics. An important consideration in making water repellent wax emulsion is that the emulsifying system not detracts from the hydrophobic character of paraffin.

Paraffin wax melts and wicks into the fabric when the fabric is heated. This will cause most of the s to be covered with a thin layer of wax and the fabric will have excellent water repellent properties.

The major disadvantage of wax water repellents is poor durability. Wax is easily abraded by mechanical action and wax dissolves in dry cleaning fluids. It is also removed by laundry processes.

WAX DISPERSIONS CONTAINING ZIRCONIUM SALTS AND PYRIDINIUM COMPOUNDS

SILICONE WATER REPELLENTS

The above products were temporary and lasted only for a few washes. This led to the development of Silicone compounds. Methyl Hydrogen Polysiloxane (MeSIOH) was a very popular water repellent 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 and resins. SIH products evolve hydrogen upon contact with strong bases, amines, primary alcohols.

Advantages

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Silicone water repellents are durable to washing and dry-cleaning. Silicones are more durable than wax repellents Less expensive than fluorochemical repellents. Silicone finishes resist water borne stains Fabric hand can be made soft and pliable.

Disadvantages

Durability is brought about by the formation of a sheath of finish around the . If the sheath cracks, durability is lost.

Adsorption of hydrophilic substances found in dry cleaning and laundry products also impair water repellency.

Less durable than fluorochemical finishes. Silicones are more expensive than wax repellents Silicones do not resist oil borne stains.

FLUOROCHEMICAL REPELLENTS

Silicone 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 repellent finishing operations. More over compounds based on Paraffin oil with Silicone water repellent finishing agents were not sufficient to protect textiles from grease and oil stains. This led to the development of FLURO CARBON POLYMERS. (FCP)

Fluorocarbon polymers are special class of polymers and represent an indispensable part of the technology of water and oil repellent 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 repellent and oil repellent polymer on its surface. A fluropolymer sheath around the s strongly reduces the textiles surface free energy, accompanied by the increase of the contact angle of liquids on its surface.

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 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.

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APPLICATIONS

Water repellent fabrics are used to make rainwear, umbrellas, garments that are comfortable as well as water repellent.

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WATER PROOF FINISHESWaterproof fabric is a natural or synthetic fabric that has been coated with a substance to repel water. Common waterproofing substances include polyurethane, polyvinyl chloride, silicone, and wax. The term "waterproof" applies to the fabric only, not the entire garment. Even if a fabric is entirely waterproof, the seams must be sealed or taped and the zippers must have storm flaps, or the garment is merely water-resistant.

Until quite recently, most waterproofs and tents were made from special close-woven cotton. As the fabric gets wet, the cotton threads swell and pack together, keeping out the water. There are small holes still left in the fabric and water vapour can pass through without condensing on the inside. Most cotton for tents and jackets also have some form of treatment which helps them to shed water without absorbing too much. They need re-spraying from time to time with this. In general, cottons are comfortable to wear and hardwearing, but they tend to be heavy, especially when wet, their waterproof qualities are limited, they take a long time to dry out and they are liable to rot. 

Most waterproofs and tents are nowadays made of nylon (or to some extent polyester). Nylon fabrics are very light and strong, packing away into a small bundle. They can be coated in a variety of ways to render them either totally waterproof or breathable-waterproof. For very light fabrics, thicker threads are scattered through the finer weave to strengthen it - "rip stop" fabric. Nylon doesn't absorb much water and so takes very much less time to dry out than cotton. It is also resistant to rot. All in all, nylon is more practical for fieldwork. The problem for manufacturers with nylon fabrics is that they deteriorate when exposed to sunlight, and are weakened when coated with the various waterproofing treatments, but these things have been largely sorted out.

Although there is a huge range of waterproofs with different names, and different levels of performance, they fall essentially into two different types:

COATED, BREATHABLE MEMBRANES - FABRICS CREATED WITH A PU COATING AND A MEMBRANE CONSTRUCTION FOR WATERPROOFING THEM

These are manufactured by spreading a thin layer of resin directly onto the inside face of the fabric, also known as a hydrophilic coating. Fabrics are sprayed with a PU (Polyurethane) coating before being made into a jacket.

The seams are then sealed to prevent moisture entering the garment in any way.

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Hydrophilic coatings rely on the behaviour of water molecules so heat generated by the body inside the garment drives body moisture downs the polymer chains in the coating to the external face.

This is also known as moisture management. Most membranes rely on a pore based construction, so as well as being waterproof, they can also vent out hot air and sweat.

GORE-TEX

This is the original breathable membrane, made of micro porous PTFE (polytetrafluoroethylene) plastic which will not let cold rainwater droplets in but allows warm water vapour to pass out through the tiny pores. It can be laminated (i.e. stuck on) to a variety of fabrics, or can also be sewn in as a separate drop lining between a non-waterproof outer and inner. Micro porous membranes need to be kept clean, because the pores can clog up and prevent the water vapour passing through - leading to condensation.

SYMPATEX

The next development of a breathable membrane, this is non-porous polyester which absorbs warm water vapour inside and passes it through to the cooler outside of the membrane. Sympatex membranes are completely water and windproof and do not needs to be kept clean - a major advantage on an archaeological site. They can be laminated to a variety of fabrics, but are normally found as a "drop liner".

BREATHABLE COATINGS

Nowadays there are also many breathable coatings which can be applied directly to the inside of a fabric. They are not generally thought to be as good as the membranes, but they are a lot cheaper. A wide variety of fabrics can be coated, including cottons and synthetics. Better makes of jackets etc. have an inner lining layer to protect the coating and make the jacket more comfortable.

DURABLE WATER REPELLENCY (DWR) - A WATERPROOFING TREATMENT SPRAYED ONTO THE FACE FABRIC

DWR is Durable Water Repellency, another way of coating the fabric after a laminate or membrane has been applied to form a protective wall from water droplets on the outer layer.

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DWR is a water repellent coating added at the manufacturing stage to a product. Usually DWR is used not only used to help repel water, but to increase breathability.

Typically a DWR treatment is used in conjunction with a weather-proof membrane (such as Gore-Tex or e-Vent) in order to achieve high levels of breathability and weather proofing.

DWR is a factory applied coating, but it is expected with any DWR treatment that over time you will need to re-proof it. Often, the breakdown of the DWR treatment, caused by oil build up and general wear causes a waterproofed item to begin to leak, even if it's made from a high quality membrane such as Gore-Tex.

DWR needs to be reapplied, and can be retreated to improve its performance. Due to DWR being applied to the face of the fabric, it is easily affected by dirt and oils, which soon coat the DWR layer, hindering the performance.

DWR can also be removed by regular cleaners, so DWR should always be treated with a specific product which can refresh it.

DWR is made using Fluro polymers in most cases, and these coated to the face fabric. They work in a way that is similar to Teflon in a non-stick pan, allowing moisture to bead off.

A garment made with a coating of DWR is usually cheaper than a pore based weather-proof membrane, and offers a good level of protection on slimmer items (e.g. packable jackets) which is why many choose it.

DWR is applied at the manufacturing stage, laying directly onto the individual s of a thread, which is crucial in helping the garment to allow water to bead off, without hindering breathability. The factory applications are more thorough than a home coating, and seams are typically sealed as well to allow 100% waterproofing.

FULLY WATERPROOF COATINGS

WAX

This is the waterproofing used on the Barbour thornproof jackets and their clones. It is heavy, slightly sticky and with a faint smell. The wax wears off and the fabric must be re-treated regularly to maintain its waterproof qualities.

POLYVINYL CHLORIDE (PVC)

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This is the traditional coating that replaced oilskins in boats. It is heavy to wear and quite tough (although surprisingly easy to tear if caught on something). Fine if you don't mind carrying it about.

NEOPRENE

Diving suits are out of this synthetic rubber. It's tough and very resistant to abrasion so, when coated onto a heavy duty nylon fabric it is almost indestructible. The best tents use neoprene coated nylon for their groundsheets.

POLYURETHANES (PU)

Very commonly used as a waterproof coating for a wide variety of weights of nylon. Not as hardwearing as neoprene, but can be to applied to lighter fabric.

SILICONE ELASTOMER

Used for the lightest tents, because it does not weaken the fabric as much as PU. So a lighter silicone coated fabric can be used to do the job of a heavier PU coated fabric.

SEALING SEAMS

One thing to check on waterproof clothes and tents is the seams. Even a good strong seam will still leave little holes through which the thread passes and through which water can enter. On a good quality product these should be sealed.

This is usually done with an appropriately coated tape covering the seam inside the garment or tent. Fully waterproof PU coated or neoprene tape for the non-breathable fabrics and breathable tape to match the breathable. The very best tents have hot-melt tape sealed seams on their PU coated flysheets. Silicone coated fabrics cannot be seam-sealed using tape or the proprietary compounds (or Bostick), because these simply don't stick to them.

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APPLICATIONS

Water proof fabrics are used to make clothing like raincoats, footwear, tents, waterproof outdoor sports clothing.

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SOIL RELEASE FINISHESIt is a chemical finish that permits relatively easy removal of soils on fabrics with ordinary laundering.

These finishes are necessary because hydrophobic s and resins have very low water absorbency. It accomplishes the result of making the 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.

Soiling generally means smearing or staining of a large surface of the fabric with dust or dirt and oil or grease or both. Natural s and synthetic s both attract dirt and get soiled but synthetics attract soil to a greater extent than natural s; 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.

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 fibre from attack by soiling matter; it

prevents re-deposition 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.

MECHANISM OF SOILING

A fabric gets soiled mainly by three types of mechanism.

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 and inter yarn spaces or even into the capillary spaces of the where it gets firmly deposited. Also soil which is oily in nature can diffuse into the.

By adhesion by electrical forces due to attraction of dust particles from air by electrically charged surface. This phenomenon occurs mainly with synthetic s because of their low moisture regain. Positively charged fabric surface is soiled more than negatively charged surface.

By re-deposition of soil during washing which occurs particularly with nylon and polyester fabrics; the re-deposition on these takes place because of their hydrophilic nature. Another aspect of soiling is the effect of time lag between soiling and washing. When a soiled fabric

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is allowed to lie unwashed for many days, the soil diffuses inside the and it becomes difficult to remove it.

FACTORS INFLUENCING SOILING  

MOISTURE REGAIN

Moisture regain of the fibre is the most important factor that influences soiling. The problem of soiling and soil removal is not very acute in the case of fibres having high moisture regain.

Synthetic fibres 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 fibres drops below 4%, soiling increases rapidly.

Polyester has the lowest moisture regain (0.4%) among synthetic fibres; therefore it attracts maximum soil. Since these fibres are hydrophobic, they do not swell in water and the removal of soil from the fibre becomes difficult.

In the case of blends with cellulosic fibres, whatever soil is removed from the cellulosic component during washing, gets re-deposited on the synthetic fibre because the synthetic fibre being oleophilic attracts oily matter from the dirty wash waters.

ELECTROSTATIC CHARGE

This is also an important factor which influences soiling. Synthetic fibres accumulate static charge during manufacture and during wear. Charged fibres 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 fibre influence soiling. Smaller the denier, greater is the tendency to soil.

A circular cross sectional fibre retains less soil than one with an irregular cross section. Higher the twist in the yarn, greater is the soil retention.

Fabric with protruding fibres assists soiling. Loosely woven and open knitted fabrics are more prone to soiling than closely woven fabrics but removal of soil from loosely woven

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fabrics is easy. Fabrics made from filament yarn do not get soiled as fast as those made from spun yarns.

SIZE OF THE SOIL PARTICLE

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

SOIL RELEASE FINISH

There are two types of soil release treatments available

Oleo-phobic treatments

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 organic silicon compounds which are applied by pad-dry-cure process.

Treatment with hydrophilic substances

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 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. Other starch- and cellulose based products that have been used as soil release agents include methyl cellulose, ethyl cellulose.

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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.

EHTHOXY-BASED FINISHES

One important group of soil-release agents for polyester fibres is based on condensation copolymers of terephthalic acid with ethylene glycol and polyethylene glycol.

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. High soil-release performance, excellent softness and combinability with fluorocarbon finishes may be achieved by special silicone/polyalkylene oxide copolymers.

FLOURINE-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.

NON-POLYMER SOIL RELEASE TREARMENTS

Alkali and plasma treatments of polyester generate a more hydrophilic fibre surface by forming new carboxyl and hydroxyl groups.

Under alkaline washing conditions the carboxyl structures become anionic carboxylate groups, giving rise to high electrostatic repulsion of the negatively charged soil particles both in pure form and those enclosed in anionic surfactant micelles.

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APPLICATIONS

Soil release finishes are applied to Bag, Curtain, Home Textile, Industry, Lingerie, Mattress, Raincoats, Tents, and Toys where soil release is a desirable product feature.

It is also used in uniforms and active wear.

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ANTI-STATIC FINISHESStatic electricity is most commonly found in synthetic fibres- natural fibres do not normally accumulate static charges. An exception to this rule is resin finished natural fibres; hence it is quite common to apply an antistatic finish to wash-and-wear and permanent press cotton fabrics, to improve their serviceability.

Anti-static finishes are chemical substances applied at the textile finishing mill for the purpose of reducing or eliminating static. These chemicals are actually substances which absorb small amounts of moisture from the atmosphere, thus reducing the dryness of the fabric.

Antistats or antistatic agents are finishes that can be applied to a fabric to aid in the dissipation of static charge build-up on the fibres. Antistats can be applied to the fibre as a temporary finish or added in the spinning bath prior to fibre formation to give a more permanent finish. Chemical crosslinking of an antistatic applied to a textile structure will provide a permanent finish, also.

Most natural fibres and regenerated natural fibres are hydrophilic and possess charged or polar groups on the fibre surface that can dissipate static charge to the atmosphere and prevent static build-up.

Therefore antistatic treatments are confined to the synthetic fibres such as nylon, polyester, etc. The antistats are surface-active agents related to detergents, ethylene oxide derivatives, silicones, or polar polymers such as polyamine resins. Because of their polar nature, they are able to bleed static charge from the fibre and dissipate it into the air.

MECHANISM OFANTISTATIC FINISHES

The principal mechanisms of antistatic finishes are increasing the conductivity of the fibre surface (equivalent to lowering the surface resistivity) and reducing frictional forces through lubrication.

Antistatic agents that increase fibre surface conductivity form an intermediate layer on the surface. This layer is typically hygroscopic. The increased moisture content leads to higher conductivity. The presence of mobile ions on the surface is very important for increased conductivity.

The effectiveness of hygroscopic antistatic finishes depends greatly on humidity of the surrounding air during actual use; lower humidity leads to lower conductivity and greater problems with static electricity.

Most non-polymeric antistatic finishes are also surfactants that can orient themselves in specific ways at fibre surfaces. The hydrophobic structure parts of the molecule act as

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lubricants to reduce charge build-up. The main effect from anionic and non-ionic surfactants is increased conductivity from mobile ions and the hydration layer that surrounds the hydrophilic portion of the molecule since the surface orientation of these materials places the hydrated layer at the air surface.

NON DUARABLE ANTISTATIC FINISHES

Non-durable anti-static agents are preferred for fibre and yarn processing finishes since ease of removal is important. Other important requirements of spin finish and fibre lubricants are heat resistance and oil solubility. This group of mostly hygroscopic materials include surfactants, organic salts, glycols etc.

The general requirements for non-durable anitistats are low volatility, low flammability, non-yellowing and non-corrosive. Low foaming properties are also desired.

Esters of phosphoric acid form the largest group of non-durable antistats. Cationic anitistats have affinity for textile fibres and can be applied by exhaustion process.

Non-ionic materials provide increased moisture absorption and cationic products provide mobile counter ions.

DURABLE ANTISTATIC FINISHES

Obtaining antistatic properties that are durable to repeated launderings from a single finish application is difficult to achieve. The basic principle is to form a cross-linked polymer network containing hydrophilic groups. Typically, polyamines are reacted with polyglycols to make such structures. These polymers can be forms prior to application to fabrics or they can be formed in situ on the fibre surface after pad application. The amount of hydrophilic character in the final polymer can be varied to, meet individual requirements.

The larger the hydrophilic portion, the more moisture is absorbed and greater the antistatic effect obtained. However at higher levels of moisture absorbed, the polymer surface film softens and is more easily removed by abrasion during laundering.

High degrees of cross-linking will reduce the moisture absorption and subsequent swelling, and the antistatic effectiveness decreases.

Additional difficulties with cross-linked hydrophilic polymers include interferences with soil release and soil re-deposition properties. Owing to the difficulties in achieving the perfect balance of desired properties, the use of durable antistatic finishes is limited.

CONDUCTIVE FIBRES

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Electrically conductive fibres have been produced by several methods: dispersing carbon particles or antistatic agents in polymer melts prior to extrusion, depositing carbon (epitropic fibres) or metallic (Nano silver) coatings onto fibre surfaces, incorporating hydrophilic comomomers, or by fabricating fibres from stainless steel, aluminium or other metals.

Although excellent durable control of static electricity is achieved by incorporating these fibres into fabrics during spinning, knitting or weaving, the conductive fibres are always black or metallic in appearance and can be seen in most textiles even at low levels of use.

This drawback limits conductive fibres to industrial fabrics and much specialised apparel and carpeting.

APPLICATIONS

Antistatic fibres and textiles are used to make industrial wear, protective wear.

Anti-static garments or anti-static clothing is required to prevent damage to electrical components or to prevent fires and explosions when working with flammable liquids and gases.

Antistatic fabrics are used to make firemen’s uniforms; Antistatic garments are used in many industries such as electronics, communications, and telecommunications and defence applications.

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