Textile Finishing

Chapter 1

STAIN RESISTANCE

The 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:

·        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.

·        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.

·        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.

·        Composite soils involving oil and grease adsorbed on particulate matter.

How Fabrics are soiled

Soil can be airborne particles that settle by

1.    Gravitational forces or are

2.    Electrostatically attracted to the fabric.

3.    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.

4.    Contact with a dirty surface and they can be ground in by pressure or rubbing.

5.    By wicking; liquid soils in contact with fabrics will wick into the structure by capillary action.

6.    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

1. Acrylic Soil Release Finishes

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

    a . 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.

    b . Methacrylic Acid - Ethyl Acrylate Co-Polymers

Co-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

1.           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.

2.           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.

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

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

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

2.  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.

3. 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.

Chapter 2

Protection from Micro-organism

Textile materials and clothing are known to be susceptible to microbial attack, as these provide large surface area and absorb moisture required for microbial growth. Natural fibers have protein (keratin) and cellulose, etc., which provide basic requirements such as moisture, oxygen, nutrients and temperature for bacterial growth and multiplication. This often leads to objectionable odor, dermal infection, product deterioration, allergic responses and other related diseases.

Microorganisms cause problems with textile raw materials and processing chemicals, wet processes in the mills, roll or bulk goods in storage, finished goods in storage and transport, and goods as they are used by the consumer. This can be extremely critical to a clean room operator, a medical facility, or a food processing facility, or it can be an annoyance and aesthetic problem to the athlete or normal consumers.

Antimicrobial finish

The term ‘Antimicrobial’ refers to a broad range of technologies that can provide varying degrees of protection for textile products against microorganisms. Antimicrobials are very different in their chemical nature, mode of action, impact on people and the environment, inplant handling characteristics, durability on various substrates, costs, and how they interact with good and bad microorganisms.

Q> What are microbes?

Q> How micro-organism works?

Cotton is biologically degraded by several microorganisms. Micro-organisms do not directly attack the substrate upon which they live. They are able to manufacture very complex non-living molecules called ‘enzymes’ which have the power to break down cellulose. These enzymes are solubilizing biocatalysts, proteinaceous, and highly specific. They enable complicated chemical reactions to occur under mild conditions even though the amount present at any time may be very small, for example, 0.001 to 0.01% on the weight of the substrate. Cellulolytic enzymes are not produced on the cellulose on the absence of cellulose. These enzymes are locally absorbed on the cellulose chains and it is proposed that different steps of degradation may occur.

Figure: How cellulose is broken down under the influence of an enzyme. The diagram illustrates cleavage of a "glycosidic" bond in cellulose (a polymer of glucose) by reaction with a molecule of water. This hydrolysis, the fundamental step in the biodegradation of cellulose, which would otherwise be immeasurably slow, is accelerated by the presence of an "enzyme", or biocatalyst. The insoluble polymer is converted into soluble sugars which can then be metabolized inside the bacterial or fungal cells.

Benefits of Antimicrobial Textiles

A wide range textile product is now available for the benefit of the consumer.

·        Initially, the primary objective of the finish was to protect textiles from being affected by microbes particularly fungi. Uniforms, tents, defense textiles and technical textiles, such as, geotextiles have therefore all been finished using antimicrobial agents.

·        Later, the home textiles, such as, curtains coverings, & bath mats came with antimicrobial finish.

·        The application of the finish is now extended to textiles used for outdoor, healthcare sector, sports and leisure.

·        Novel technologies in antimicrobial finishing are successfully employed in non-woven sector especially in medical textiles.

·        Textile fibers with built-in antimicrobial properties will also serve the purpose alone or in blends with other fibers. Bioactive fibers are not only used in medicine and health applications but also for manufacturing textile products of daily use and technical textiles. The field of application of the bioactive fibers includes sanitary materials, dressing materials, surgical threads, materials for filtration of gases and liquids, air conditioning and ventilation, constructional materials, special materials for food industry, pharmaceutical industry, footwear industry, clothing industry, automotive industry etc.

Necessity of Antimicrobial Finishes

Antimicrobial treatment for textile materials is necessary to fulfill the following objectives:

1.    To avoid cross infection by pathogenic micro-organisms;

2.    To control the infestation by microbes;

3.    To arrest metabolism in microbes in order to reduce the formation odor; and

4.    To safeguard the textile products from staining, discoloration and quality deterioration.

Requirements of Antibacterial finish

1.    Effective against a wide range of micro-organisms, particularly bacteria and microfungi.

2.    Active during the life of the product.

3.    Of low mammalian toxicity and non-toxic to humans at the concentrations used.

4.    Colorless and odorless.

5.    Effective at low concentrations.

6.    Inexpensive and easy to apply.

7.    Resistant to sunlight and heat.

8.    Not affecting fabric handle or strength.

9.    Compatible with water-repellent and flame-retardant agents, dyes, and other textile auxiliaries.

10.                     Does not sensitize the fabric to damage by light or other influences.

11.                     Should not produce harmful effects to the manufacturer, user and the environment.

Factors for micro-organism growth

1.    Moisture: micro-organism requires moisture for their growth and with the increase in moisture content (MC %) of the material, the microbial growth and attack increases. It has claimed that,

At 10% MC of sample, about 1.4 million organisms per gram of raw cotton

At 50% MC of sample, about 9000 million organisms per gram of raw cotton

2.    Temperature: Most of the organisms exhibit a rapid destructive action on cotton fabrics at a temperature from 25-30ºC.

3.    pH: the growth of micro-organism is highly affected by the pH and most cellulose destroying bacteria are active at pH 7-8

4.    Laundering: laundering also caused little observable surface damage to cotton fiber but it was observed that damage to cotton fiber by microbial attack increases with each laundering. Severe damage was noticed after 10th laundering, suggesting that possible physical breakdown may have made the fibers more accessible to microbial attack.

Mechanism of Antimicrobial Activity

Negative effect on the vitality of the microorganisms is generally referred to as antimicrobial.

The degree of activity is differentiated by the term “cidal” which indicates significant destruction of microbes and the term “static” represents inhibition of microbial growth without much destruction. The differentiation of antimicrobial activity is given in the diagram. The activity which affects the bacteria is known as antibacterial and that of fungi is antimycotic.

Methods of Proofing

1.    By physical barrier

2.    By the addition of toxic substances to the fiber

3.    By chemical modification of the cotton fiber

4.    by Silicone quaternary ammonium compound

By Physical barrier

The microbial degradation of cotton fibers is localized and it requires direct contact between the organism and the fiber. It should be possible to prevent microbiological attack on cellulose by imposing a continuous, inert physical barrier or film between the attacking agent and the substrate.

Coating materials such as paraffin, chlorinated paraffin, and rubber, have been used with cotton yarns, netting, ropes, canvas etc as a rot proofing agent. It was claimed that a net treated with such materials was found to retain its strength for over 54 months when immersed in water as compared to only 2.5 months for untreated net of the same type.

Proofing by toxic agents

To obtain resistance to microbial attack toxic inhibitors can be applied o fibers, silver, yarn or fabric at sizing, dyeing or other stages of manufacture. Toxic agents that are used for this purpose are

Inorganic inhibitors: The most popular are compound of copper. The copper compounds are normally applied from solution, for example, cuprammonium carbonate, cuprammonium hydroxide, cuprammonium fluoride to give copper concentrations on the fabric of 0.8% to 2%.

The compounds of zirconium, titanium, thorium, cerium, lanthanum and didymium can also be used which has been claimed to have very good mildew resistance together with some degree of water repellency.

Organic inhibitors: Phenolic compounds are one of the most popular mildew proofing agents used in the past including polychlorophenols, the diarylmethanes and the acrylamides. Among many phenolic compounds, chlorinated phenol is more popular as mildew and rot proofing agents. Pentachlorophenol is one of the most widely used and most active chlorinated phenolic compound. They are used in wide range of textiles including cotton, flax, and jute fabrics used as covers, tarpaulins, shop blinds, tents, etc.; also carpet backings, coated fabrics, hospital materials, mattress covers, pressed felts and woollen textiles.

The main drawback of pentachlorophenol is its lack of durability, but permanence can be increased by a resin coating.

Proofing by chemical modification:

Cellulosic fabrics have been made resistant to degradation by cellulolytic micro-organisms by chemical modifications. These modifications includes

·        Acetylation

·        Cyanoethylation

·        Phosphorylation

·        Reaction with formaldehyde

Acetylation: Acetylation is the earliest process and the degree of resistance depends on the amount of acetylation as the figure shows:

Cyanoethylation: Cyanoethylation involves introduction of cyanoethyl groups into some of the glucose units of the cellulose by an ether linkage. This occurs by reaction with hydroxyl groups in the cellulose:

cell-OH + CH₂=CHCN cell-OCH₂-CH₂-CN

cellulose acrylonitrile cyanoethyl cellulose

It has mentioned that the blocking of only one hydroxyl group per anhydroglucose unit brings about resistance to microbial degradation, which also brings resistance to heat and resistance to rotting.

Phosphorylation: Chemical modification is also done by treating fabric with an aqueous solution of phosphoric acid followed by drying and curing at temperature at 150 to 200ºC. The phosphate ester of cellulose produced has good flame and mildew resistance properties.

Reaction with formaldehyde: Treatment with formaldehyde can also protect cotton fiber from microbial degradation. The reaction goes:

2cell-OH + HCHO cell-O-CH2-O-cell

cellulose formaldehyde cross linked cellulose

Formaldehyde content synthetic resin finish also protects cotton fiber from bacterial and fungal attack. One important disadvantage of formaldehyde treatment of cotton fabric is the considerable loss in tensile strength.

Silicone quaternary ammonium compound

A significantly different & much more unique antimicrobial technology used in the textile industry does not leach but instead remains permanently affixed to the surface it is applied to.

Applied in a single stage of the wet finish process, the attachment of this technology to surfaces involves two means. First and most important is a very rapid process, which coats the substrate (fabric, fiber, etc.) with the positive ion. This is an ion exchange process by which the cation of the silane quaternary ammonium compound replaces protons from water or chemicals on the surface.

The second mechanism is unique to materials such as silane quaternary ammonium compounds. In this case, the silanol allows for covalent bonding to receptive surfaces to occur.

The technology stays on the substrate it does not cross the skin barrier and does not affect normal skin bacteria, cause rashes or skin irritations.

Commercial Antimicrobial Agents and Fibers

Evaluation of Antimicrobial Activity

Various test procedures have been used to demonstrate the effectiveness of the antibacterial activity. Some of the tests used are:

1.    Agar diffusion test: Agar diffusion test is a preliminary test to detect the diffusive antimicrobial finish. It is not suitable for non diffusive finishes and textile materials other than fabrics.

2.    Challenge test (Quantitative). Objective evaluation of the antimicrobial activity is arrived at by making use of the challenge test where in which the difference between the actual bacterial count of the treated and untreated material is accounted for. A series of test methods are available from AATCC (USA), DIN(International), JIS (Japan ) and SN(Switzerland).

3.    Soil burial test.

4.    Humidity chamber test.

5.    Fouling tests.

Chapter 3

FABRIC SOFTENERS

A Softener is a chemical that alters the fabric hand making it more pleasing to the touch. The more pleasing feel is a combination of a smooth sensation, characteristic of silk, and of the material being less stiff. The softened fabric is fluffier and has better drape.

Functions of softeners:

·        Increase aesthetics (drape and silkiness),

·        Improve abrasion resistance,

·        Increase tearing strength,

·        Reduce sewing thread breakage and

·        Reduce needle cutting when the garment is sewn.

Because of these functional reasons, softener chemicals are included in nearly every finish formulation applied to fabrics.

How softeners alters the handle of textile materials

·        Softeners act as fiber lubricants and reduce the coefficient of friction between fibers, yarns, and between a fabric and an object (an abrasive object or a person's hand). Whenever yarns slide past each other more easily, the fabric will be more pliable and have better drape.

·        Tearing resistance, reduced abrasion and improved sewing characteristics are also related to lower coefficients of friction.

·        Fabric tearing is a function of breaking yarns, one at a time, when tearing forces are applied to the fabric. Softeners allow yarns to slide past each other more easily therefore several yarns can bunch up at the point of tear. More fiber mass is brought to bear and the force required to break the bunch is greater than the force required to break a single yarn.

·        Sewing problems are caused by the friction of a needle rapidly moving through the fabric. Friction will cause the needle to become hot and soften thermoplastic finishes on the fibers.

Points of Concern

There are some important points to consider when selecting the appropriate material as a softener.

Viscosity: The viscosity of softener materials range from water like (machine oil) to semisolids (waxes). All are capable of reducing coefficient of friction and therefore are effective in overcoming sewing problems, improving tear, and improving abrasion resistance. However the lower viscosity oils are the ones that impart the soft silky feel and improve drape.

Color: Some softener materials are dark in color to begin with while others become dark when exposed to heat, light, oxygen, ozone, oxides of nitrogen or other airborne gases. These might not be a problem on dark shades but they are to be avoided for pastel shades and whites.

Odor: Some softeners develop odor with age. Fat based softeners develop a rancid odor (associated with aged fats) and should be avoided whenever possible.

Bleeding: Some lubricants are good solvents for surface dyes. Disperse dyes, as a class, are particularly prone to dissolve in softener materials. Color from darker yarns will migrate (bleed) to stain adjacent lighter yarns like might be found in a striped pattern.

Spotting: The volatility of softeners is also important. Softener materials that have low smoke points will condense and drip back onto the fabric causing unsightly spots. Smoke from heated oils and waxes are droplets of oil suspended in air. These droplets will condense when they come in contact with cooler surfaces and eventually drip.

Soiling: Cationic softeners tend to attract soils making them harder to remove. This tendency must be compensated for by the use of soil release finishes.

Light fastness: Certain softeners will diminish the light fastness of some direct and reactive dyes. This tendency must be checked out and compensated for.

Desirable properties of softener

·        Good compatibility with chemicals

·        Stable to high temperature, no volatile by water and water vapor

·        No effect on fastness

·        No change of shade of color and no yellowing

·        Low forming, stable to shearing, no deposit on rollers

·        Regular and complete bath exhaust

·        Non-toxic, non-caustic, non-corrosive

·        Easily biodegradable

·        Dermatologically harmless

·        Easy handling (liquid and stable) and no restriction of transport and storage

Raw Materials for Softeners

Hydrocarbon radicals having a total of 8 to 20 carbons are the most effective molecular group used in textile softeners. Commercially, there are two main sources of raw material supply that are inexpensive and available in large quantities:

1.    Fat derived Raw Materials: obtained from animal and vegetable fats and oils

i.       Fatty acids

ii.     Fatty acids monoesters

iii.   Fatty acids ethoxylates

iv.   Fatty amines

v.     Fatty alcohols

2.    Petrochemical derived Raw Materials: based on crude oil and natural gas

i.       Long chain hydrocarbons

ii.     Short chain hydrocarbons

iii.   Long chain alcohols

iv.   Alkyl aromatics

v.     Ethylene, propylene oxides

vi.   amines

Softener Classifications

Softeners are divided into four major chemical categories describing the ionic nature of the molecule,

1.    Anionic,

2.    Cationic

3.    Nonionic

4.    Amphoteric

Anionic Softeners

Anionic softeners and/or surfactant molecules have a negative charge on the molecule which come from either a carboxylate group (-COO^-), a sulfate group (-OSO₃^-) or a phosphate group (-PO₄^-). Sulfates and sulfonates make up the bulk of the anionic softeners.

Properties of Anionic Softeners

Anionic softeners impart pliability and flexibility without making the fabric feel silky. They are used extensively on fabrics to be mechanically finished, e.g. napped, and sheared or Sanforized. A good napping lubricant, for example, provides lubrication between the fabric and the napping wires yet at the same time provides a certain amount of cohesiveness between fibers. If the fibers are too slippery, the napping wires will overly damage the yarn.

Advantages

·        Most anionic softeners show good stability towards heat & some are resistant to yellowing.

·        Anionic softeners do not interfere with finishes to be foamed, in fact like defoamers and are deleterious for foam finishing.

·        Anionic softeners have good rewetting properties and are preferred for those fabrics that must adsorb water such as bath towels.

·        Cheaper compared to other types

·        In case of white finishes, it has been used.

Disadvantages

·        The degree of softness with anionic softeners is inferior when compared with cationic softeners and some nonionic softeners.

·        Anionic softeners have limited durability to laundering and dry-cleaning.

·        Anionic softeners will not exhaust from a bath, they must be physically deposited on the fabric.

·        Anionic softeners tend to be sensitive to water hardness and to electrolytes in finish baths.

·        Anionic softeners are incompatible in some finish baths containing cationically stabilized emulsions.

Cationic Softeners

Cationic softeners are ionic molecules that have a positive charge on the large part of the molecule. The important ones are based on nitrogen, either in the form of an amine or in the form of a quaternary ammonium salt. The amine becomes positively charged at acidic pHs and therefore functions as a cationic material at pH below 7. Quaternary ammonium salts (hereafter referred to as QUATS), retain their cationic nature at all pHs.

An important quality of cationic softeners is that they exhaust from water onto all fibers. Cationics are highly efficient softeners. The ionic attraction causes complete exhaustion from baths and the orientation on the fiber surfaces allows a monolayer to-be as effective as having more lubricant piled on-top.

Figure Adsorption on Fiber Surface

1.                    Amine Functional Cationic Softeners

They exhaust and become excellent softeners under acidic conditions. The cationic charge on a given hydrophobe is proportional to the number of amino groups, therefore the attraction of the cationic portion to the fiber surface increases as the number of amine groups’ increase.

i.       Primary Fatty Amines

ii.     Difatty Amines

iii.   Fatty Diamines

iv.   Cationic Amine Salts:

2.                    Fatty Aminoesters

3.                    Fatty Amidoamides

4.                    Quaternary Ammonium Salts

Quaternary ammonium salts are extremely important fatty acid derivatives. The quat's cationic charge is permanent, being maintained at all pHs. In addition to imparting softness, quats reduce the static charge on synthetic fabrics and inhibit the growth of bacteria. Quats are therefore used as antistats and germicides as well as softeners. Cationics containing two C18 fatty tails attached to the nitrogen impart very soft, fluffy hand to textile products.

1.    Synthesis of Monofatty Quats

2.    Synthesis of Difatty Quats

3.    Synthesis of Imidazoline Quats

Advantages

·        Cationic softeners impart very soft, fluffy, silky hand to most all fabrics at very low levels of add-on.

·        Cationics will exhaust from dyebaths and laundry rinse baths making them very efficient materials to use.

·        Cationics will exhaust from acidic solutions.

·        Cationics improve tear resistance, abrasion resistance and fabric sewability.

·        Cationics also improve antistatic properties of synthetic fibers.

·        They are compatible with most resin finishes.

·        They are good for fabrics to be napped or sueded.

b. Disadvantages

·        They are incompatible with anionic auxiliary chemicals.

·        They have poor resistance to yellowing.

·        They may change dye shade or affect light fastness of some dyes.

·        They retain chlorine from bleach baths.

·        They adversely affect soiling and soil removal and may impart unwanted water repellency to some fabrics.

C. Nonionic Softeners

They are not very good softener, however it can be used with any composition of the bath as they are nonionic. Now a days one of its class silicone softeners have been used extensively.

Nonionic softeners can be divided into three subcategories,

o        ethylene oxide derivatives,

o        hydrocarbon waxes based on paraffin or polyethylene.

o        Silicones

Dispersions with anionic, nonionic and cationic character are made by selecting appropriate auxiliary emulsifier. Selecting an emulsion with the proper ionic character is important otherwise the finishing bath will become unstable and break out.

Silicone Chemistry

Silicones are Polysiloxane Polymers and fall under the class of materials known as organometallics. The element silicon is considered a metal and is found in abundance in nature as silica, SiO₂. Silicon resembles carbon in that it is tetravalent and forms covalent bond with other elements. Simple tetravalent compounds are called silanes. Silicon forms a stable covalent bond with carbon leading to a class of materials known as organosilanes

1.    Formation of Organofunctional Reactive Silanes

Compound Name

[I] Dimethylchlorosilane

[II] Methylchlorosilane

[III] Methylhydrogendichlorosilane

[IV] Trimethylchlorosilane

Silicone Softeners

Four varieties of silicone polymers have found use as textile softeners. One variety is based on

o        Dimethyl Fluids

o        Methylhydrogen Fluids

o        Amino Functional Silicones

o        Epoxy Functional Silicones

a. Dimethyl Fluids

Dimethyl fluids are made from dimethyldichloro silane. Fluids are water clear and do not discolor with heat or age. They impart soft silky hands to fabrics. In addition to softening, dimethyl fluids render fabrics somewhat water repellent; however, being fluids, they are not durable.

Figure Orientation of Dimethyl Fluids on Fiber Surface.

b. Methylhydrogen Fluids

Methylhydrogendichlorosilane offers a route for making a linear polysiloxane These offer a way of improving durability.

c. Amino Functional Silicones

Amino functional silicones are made by incorporation the appropriate organofunctional chlorosilane to the reaction mix. Amino functional silicones become cationic at acid pHs and exhaust from aqueous baths.

d. Epoxy Functional Silicones

Epoxy functional groups can be incorporated into silicone polymers by incorporating the appropriate group into the silicone polymer back boneThese softeners are more durable to repeated laundering.

Advantages

·        Silicones are water clear oils that are stable to heat and light and do not discolor fabric.

·        They produce a slick silky hand and are preferred for white goods. They improve tear and abrasion resistance and are excellent for improving sewing properties of fabrics.

·        Amino functional silicones improve DP performance of cotton goods.

·        Epoxy functionals are more durable.

Disadvantages

·        The silicones are water repellent which make them unsuitable as towel softeners.

·        Silicones are expensive compared with fatty softeners.

·        Amino functional silicone discolors with heat and aging.

·        They may interfere with redyeing when salvaging off quality goods.

Amphoteric softener

Amphoteric softener have long alkyl chain which contain both acidic and basic group and their nature depends on pH. At

Low pH: cationic

pH 7: nonionic

high pH: anionic

They are expensive and used in novelty products in specialist application. Generally they are not used in textile industry but cosmetic industry.

The products are based on

·        Substituted amino acids: R-⁺NH₂CH₂CH₂COO^-

·        Sulphobetains: R₃N+ (CH₂)_n-SO₃^-

·        Betains: R CONH-C₃H₆N⁺(CH₃)₂CH₂COO^-

·        Imidazolines

Trade name of softener

BASF

o        Basosoft EUK (cationic)

o        Basosoft FA535 (cationic but mixed with silicone softener)

o        Siligen FA210 (normal silicone)

Chapter 4

Textile Finishing

Finishing has been defined by Textile Institute as ‘Descriptive of processes, physical or chemical, applied to a substrate to produce a desired effect.’ Finishing encompasses chemical or mechanical treatments performed on fiber, yam, or fabric to improve appearance, texture, or performance.

Mechanical Finishing

·        Heatsetting

·        Brushing and napping

·        Softening, Calendering, or ironing

·        Optical finishing

·        Shearing

·        Compacting

Chemical Finishing

·        Softener

·        Anionic, cationic, nonionic, silicone

·        Durable press / resin finish

·        Water repellency

·        Stain Resistance

·        Soil Release

·        Fire Retardancy

·        Antimicrobial finishes

·        Slow release of fragrance and odor absorption

Terminology

Antimicrobial Agent (AM): A chemical compound that either destroys or inhibits the growth of microscopic and submicroscopic organisms.

Calender: A machine in which heavy rollers rotate in contact under pressure; used to smooth and flatten fabric, to close the intersections between the yarns, and to confer a surface glaze.

Coated fabric: A material composed of two or more layers, at least one of which is a textile fabric and at least one of which is a substantially continuous polymeric layer.

Cross-linking: The creation of chemical bonds between polymer molecules to form a three-dimensional polymeric network, e.g., in a fiber. This generally restricts swelling, inhibits solubility and alters elastic recovery.

Curing: A process following application of a finish to textile fabrics in which appropriate conditions are used to effect a chemical reaction.

Durable press (permanent press): A finishing treatment designed to impart to a textile material or garment the retention of specific contours including defined creases and pleats resistant to normal usage, washing or dry cleaning.

Flame Retardant (FR): A substance used to impart improved flame resistance to a material.

Flame Resistance¹: The property of a material whereby flaming combustion is slowed, terminated or prevented.

Flammability: The ability of a material or product to burn with a flame under specified test conditions.

Fleece: A general term for any plain weft-knitted fabric which has been brushed or raised on one or both sides. A specific term for a plain, weft-knitted fabric with a ground yarn in which a yarn of low twist, laid-in and secured by a binder (yarn), appears on the back of the fabric and may be brushed or raised.

Foam finishing: The application of one or more liquid chemical finishes in the form of a foam to a textile material with the advantage of low wet pick-up.

Hydrophilic: Water loving; having a high degree of moisture absorption or attraction.

Hydrophobic: Water repelling; having a low degree of moisture absorption or attraction.

Limiting Oxygen Index (LOI): The minimum concentration of oxygen in a mixture of oxygen and nitrogen that will just support combustion of a material under specified test conditions.

Moisture Regain: The moisture in a material determined under prescribed conditions and expressed as a percentage of the weight of the moisture-free specimen.

Resiliency: Ability of a fabric to return to its original shape after compressing, bending or other deformation.

Sanforizing®: Commercial process in which a fabric is caused to shrink in length, e.g., by controlled compression

Soil Release: A textile finish which makes it easier to remove soiling or stains by ordinary domestic washing.

Spectroscopy: The branch of physics concerned with the production, measurement, and interpretation of electromagnetic spectra arising from either emission or absorption of radiant energy by various substances.

Surfactant: An agent, soluble or dispersible in a liquid, which decreases the surface tension of the liquid; contraction of “surface-active agent”

Stenter: An open-width fabric-finishing machine in which the selvedges are held by a pair of endless traveling chains maintaining tension; used for drying, heat setting, fixing dyes and finishes, and controlling fabric width.

Waterproof: Ability of a fabric to be fully resistant to penetration by water.

Wet pick-up: The weight of liquor taken up by a given weight of fabric after impregnation, spraying, or coating

Wicking: The passage of liquids along or through a textile material or along the interstices formed by the textile element and coating polymer of a coated fabric.

Wrinkle recovery: A laboratory test to measure the angle (degrees) of recovery from wrinkling or creasing.

1 Flame resistance can be an inherent property of the basic material or it may be imparted by a specific treatment. The degree of flame resistance exhibited by a material during testing may vary with test conditions.

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