- 1 Introduction To Advanced Functional Finishes
- 2 What is Functional Finishing?
- 3 Flameproof Finish
- 3.1 Need of Fire Proof Or Flame Retardant Fabric
- 3.2 Objective Of Flame Retardant Finish
- 3.3 Flame Retardant Finish Can Be Produced In Two Ways
- 3.4 Mechanism Of Flame Retardant Finish
- 3.5 Chemical Theory
- 3.6 Flame Retardants For Cellulosic Fibres
- 3.7 Flame retardants for polyester
- 3.8 Use of phosphorus-containing compounds
- 4 Soil Release Finish
- 5 Anti-pilling Finish
- 6 Anti-static finish
- 7 Antimicrobial / Antibacterial finish
- 8 Finishes impervious to water
- 9 Conclusion
Nowadays, the image of textile is changing from its conventional function to its special function i.e. from aesthetic properties to functional properties. Traditional textile is now becoming functional textile as it giving additional functional properties like flame retardancy, water repellency, soil release, easy-care or wash & wear, etc.
By applying functional finishes on the fabric. to explore their potential it is necessary to study these functional finishes. This paper presents an overview of some of the advanced functional finishes which used in textile for developing & improving functional properties of fabric as well as improve appearance, performance, handle, comfort, etc.
Introduction To Advanced Functional Finishes
The chemical finishing of textile refers to the application of specific compounds in order to improve physical or chemical properties of the textile material.
The textile material is subjected to many processes during the transformation of fiber to fabric & during manufacture of the final product be it garment, upholstery or whatever. During the many stages fiber undergo, they may be damaged & in some cases, natural fats may be removed from the fibres.
Resulting in the harsh & undesirable handle. The restoration of a satisfactory handle can be achieved through the addition of suitable chemical compounds. These compounds form a fatty film on the fibre surface, this film makes the fibre smoother & more slippery, so providing a sensation of greater softness. In the same way as compound are applied to achieve special functional properties.
The traditional image of textile as a low tech product is fast changing with the advent of textiles specially developed for high-performance functions.
In fact the modern day, textiles are doing, more functions in addition to their primary functions such providing flame retardancy, water repellency, soil release, easy-care or wash & wear, anti-pilling, etc. ‘Such specially developed textiles have already found their way to the consumer market, so it becomes all the more necessary to study these functional finishes. In this review paper, we study different functional finishes their functions, application methods and effect on fabrics.
What is Functional Finishing?
Textile finishing defines a series of processing operations applied to grey fabrics to enhance their appearance, handle & functional properties. Functional finishes change the internal performance properties of the fabric.
Objectives of finishing:
- To improve the appearance of the fabric.
- To improve the feel of the fabric.
- To import special properties to the fabric for special end uses such as waterproofing, flame-proofing etc.
Different Types Of Functional Finishes
1 Flameproof finish
2 Soil release finish
3 Anti-static finish
4 Anti-pilling finish
5 Antibacterial finish
6 Finishes impervious to water
8 Easy care /wash & wear/ Anti-crease finish etc.
The term “fireproof” or flameproof can only be applied to glass or asbestos fibres because only a material which undergoes no change when exposed to fire can be termed fireproof but in practice, fireproof finish means one which does not propagate flame beyond the charred area, there is as yet no known finish which can make textile material fireproof in the real sense of term.
Fireproof fabric or flame retardant fabric may be defined as one that does not propagate flame although it may burn or char when exposed to heat. Flame resistant or retardant fabric are those that ignite with difficulty, burn slowly. When the source of flame is removed.
There are different types of flame retardants, which are generally divided into classes that include the organic halogenated, (usually brominated or chlorinated), phosphorus-containing, nitrogen-containing & inorganic flame retardants.
Need of Fire Proof Or Flame Retardant Fabric
Fire safety is important for textile themselves where the risk of fire is involved. As in defense organization for tents, ropes, baggage, parachutes, industry uniforms, in coal mines, uniforms for a fire fighter.
Wool, silk & acetate rayon do not propagate flame readily. The cellulosic textile material will burn readily once they are ignited. The great danger with cellulosic fiber is afterglow, which may remain if the flame has been incompletely extinguished synthetic fibres may melt rather than burn nylon & polyester are poorly inflammable, but they cause injuries by melting & dripping when they ignited.
The risk of fire increased when such synthetic fibres are blended with cellulosic fibre because the combustion of cellulosic material which is non melting produces scaffolding effect since the use of blend increasing, there is need to make such blend flame retardant.
Objective Of Flame Retardant Finish
- Prevent the fire or retard its growth & spread i.e. the flash over.
- Control the fire properties of combustible items.
- Provide for suppression of the fire.
Flame Retardant Finish Can Be Produced In Two Ways
- 1 By making the use of fibres that do not burn.
- By chemically treating the fibres to produce the desired effect.
Mechanism Of Flame Retardant Finish
There are many theories have been postulated to explain how flame resistance is imparted to cellulosic material, but chemical theory most widely accepted. It is applicable to all types of flame retardants.
this theory applicable to nearly all types of flame-retardants, the flame retardant on burning reacts with cellulose & forms chemicals such as phosphoric acid & sulphuric acid which are dehydrating agents; these bring catalytic dehydration of cellulose which on combustion produces mainly carbon & water & not CO2 & water.
The flame resistance of cellulosic materials is brought about by dehydration of cellulose.
Flame Retardants For Cellulosic Fibres
THPC – Tetrakis (hydroxymethyl) phosphonium chloride is the most important commercial derivative & used as a durable flame retardant for years together is prepared from phosphine, formaldehyde & hydrochloric acid at room temperature. It contains 11.5% phosphorous & is applied to a pad dry cure oxidize process.
THPC, when applied along with cross-linking agents like Dimethylol urea (DMU), increases LOI values by 25 – 30%.but on washing LOI values decreases to 7% only which is due to the removal of unfixed resin from fabric. There is about 12-15% loss in tensile strength observed in treated fabric compared to untreated.
This loss in tensile strength is due to cross-linking between THPC cross-linking agent & cellulose. Cellulose with OH- groups react with methylol groups of a cross linking agent which act as a bridging agent between cellulose & flame retardant system.
Drawbacks / Disadvantage of THPC
- The loss in tensile strength.
- The release of formaldehyde which is harmful to the environment.
- Acid tendering of the fabric during curing.
- Harshening of fabric handle.
- Breakdown of flame resistant finish by laundering & dry cleaning.
Flame retardants for polyester
Polyester can be made flame retardant by following methods.
1 By using phosphorus-containing compounds in the fibre either through physical mixing with the polymer or through chemical reaction with the polymer
2 By using halogen-containing compounds in the fibre either through physical mixing with the polymer or through chemical reaction with the polymer
3 By using aromatic raw materials for producing wholly aromatic polyester with rigid chains.
Use of phosphorus-containing compounds
5-10% by wt. of phosphorus-containing compound is added either during esterification or polycondensation & complete mixing achieved during melt spinning.
Use of halogen-containing compounds
10-15% by wt. Is physically or chemically combined with the polyester. Delion PFR-501 is added at the beginning of polycondensation reaction. The compound tris(2,3-dibromopropyl) phosphate was once widely used as the flame retardant for polyester but was abandoned due to carcinogenic effect.
Flame retardants for Nylon
The nylon6,6 fabric has been widely used in the military and civilian area for many areas. However, the melting drip problem has not been effectively solved despite the efforts made in last two decades. An intumescent flame retardant system, containing ammonium phosphate, melamine & pentaerythritol, has been proved to be effective in preventing melting drip during the burning of nylon6,6 fabric.
Advantages of flame retardants based on Nitrogen compounds
Nitrogen compounds are a small but rapidly growing group of flame retardants (FR) which are in the focus of public interest concerning environmentally friendly flame retardants. their main common advantages are their low toxicity, their solid state & in case of fire, the absence of dioxin & halogen acids as well as their low evaluation of smoke.
Soil Release Finish
Generally soiling means smearing or staining of a large surface of the fabric with dust or dirt & oil or grease or both. The problem of soiling is not a new one. Natural & synthetic fibres both attract dirt & get soiled but synthetic fibres attract soil to a greater extent than natural fibres, also synthetic fibres do not release soil easily during washing. Due to absorption and retention of soil, the whiteness & brightness of a fabric is spoiled & it appears yellowish & dirty.
A soil release finish does not prevent soil from entering into the fabric but simply allows it to leave faster. It removes from the fabric and transfers it to the detergent; it protects the fibre from attack by soiling matter; it prevents redeposition of the soil.
Mechanism of Soiling
A fabric gets soiled mainly by three types of mechanism.
1. By mechanical adhesion of soil to the cloth
In this fabric comes directly in contact with the soiled surface or by picking up dirt from liquors or from the air; fabric construction facilitates such adhesion as the soil gets entrapped in inter fibre & inter yarn spaces or even into the capillary spaces of the fibre where it gets firmly deposited. Also, soil which is oily in nature can diffuse into the fibre.
2. By adhesion by electrical forces
It is due to the attraction of dust particles from the air by electrically charged fibre surface. This phenomenon occurs mainly with synthetic fibres because of their low moisture regain. Positively charged fabric surface is soiled more than the negatively charged surface.
3. By redeposition of soil during washing
This occurs with particularly with nylon & polyester fabrics; the redeposition on these fibres takes place because of their oleophilic nature. Another aspect of soiling is the effect of the time lag between soiling & washing if soiled fabric remains unwashed for many days then the soil diffuses inside the fibre & it becomes difficult to remove it.
Factors influencing soiling –
- Moisture regain –
The problem of soiling & soil removal is not very acute in the case of fibres having a high moisture regain. lower the moisture regain, higher is the attraction of soil. synthetic fibres have a low moisture regain, so they accumulate the static electricity which attracts dirt & dust from the atmosphere. If moisture regains drop below 4% soiling increases rapidly.
- Electrostatic charge –
Synthetic fibres accumulate static charge during manufacture & 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 & cross section of the fibre influence soiling.
- Coarser yarn greater tendency to the soil.
- Circular cross-sectional fibres retain less soil than one with an irregular cross section.
- Higher the twist in the yarn, greater the soil retention.
- Loosely woven & open knitted fabrics are easily soiled compared to closely woven fabrics.
- Fabric made from spun yarn is easily soiled than filament yarn.
- Particle size of soil
The smaller the size of the soil particles, greater is the soil retention of the fabric.
Soil release finishing treatment
There are two types of treatment for soil release finish
1 oleophobic treatment in this fluorocarbons are used; they are oil repellent, soil resistant & release soil easily from textile materials. ex- perfluoro-alkyl methacrylate used together with melamine formaldehyde & paraffin wax.
2 hydrophilic treatment
this is recently introduced technique for soil release it confers the hydrophilic character into the fibre surface. copolymers of ethyl acrylate with acrylic acid are used.
pilling is nothing but the formation of small knots on the surface of the fabric, is formed by the entanglement of the fibres on the surface of the fabric. It spoils the appearance of the fabric. One of the main reason for the formation of pills is high tenacity of fibre. high tenacity fibre like polyester, nylon faced piling problems. Fibre who has low tenacity like cotton, wool, silk, etc. has no pilling problem & even if they are formed, they are rubbed off or washed off during wear.
Factors influencing pilling are
Fibre characteristics longer
- staple length has low tendency to form pills. Finer count less pilling problem.
- Fibre crimp is high then less formation of pills are less. Fibres with circular cross-section have high tendency to form pills rather than irregular one.
- higher twist then pills formation low.
- Plied yarn shows less pilling than single yarn.
- High tenacity causes more pills formation.
- loosely woven fabric or fr fabric with open structure causes more pills formation.
- Plain woven fabrics are more pills resistant than twill or sateen.
The only way to reduce pilling is to adopt mechanical or chemical processes & apply anti-pilling finishes.
1 Mechanical treatment
it includes cropping, shearing & singeing process to make fabric pill free. The fabric is firstly sheared then cropped & then singed. Singing is the most important operation for reducing pilling. During singing, protruding fibres are burnt. Generally singeing is carried out after dyeing.
2 Chemical treatment
in this fabric is treated with 2 Gpl caustic soda solution at 600C for 30 min. or fabric is treated with 3.5% ammonia solution at 1300C for few minutes and then followed by washing , drying & heat setting.
anti-static finish mostly used for synthetic fibres.
Synthetic fibres accumulate static charges on their surface. Hydrophobic nature of synthetic fibres are helpful to develop static electricity & such static electricity creates lots of problem such as it can produce sparks which are dangerous to workers as well operators who operating machine may get an electric shock. Charged fibres attract dirt, dust from the air & get soiled.
By applying antistatic agent development of static electricity can be minimized. anti-static properties of fibres improved by incorporating an antistatic agent into the polymer during manufacture. Antistatic agent can be applied to filaments, yarns or fabrics.
These agents have to be polar (hygroscopic); it will attract water molecules so, that it helps to maintain a layer of moisture on the surface of fibre which is responsible for dissipating static electricity. Polyethylene glycol acrylate, melamine formaldehyde resin with polyethylene oxide, fatty acid condensed with glycerin & ethylene oxide, etc. are some of the chemicals used as the anti static agent.
Antimicrobial / Antibacterial finish
clothing & textile material are not only the carriers of micro-organism such as pathogenic bacteria, odour generating bacteria & mould fungi but also good media for the growth of the micro-organism & such microbes poses danger to both living & nonliving matters, like obnoxious smell from inner garments, spread diseases, staining & degradation of textile this are some detrimental effect of bad microbes.
The consumers are now increasingly aware of the hygienic lifestyle, there is a necessity & expectation for a wide range of textile products finished with antimicrobial properties. This finish prevents the growth of bacteria & it also guards garments against unpleasant odor.
Six link theory –
this is the main mechanism of the spread of infection by the microbes can be explained by the six link theory. According to this theory, six different links are formed between the pathogen, environment and the host in which all join to form a circular chain. Even if a single link fails to form the process of infection spread is interrupted & no infection occurs.
Methodologies for Antibacterial finishing
1. The surface application
This method is applicable to all fibres, but for cotton, it is the major mode of finishing.2. Chemical bonding
in this method, the chemical bond is formed between the antimicrobial agent & the fibre. Washing durability depends on the strength of the bond so formed.
in this, instead of antimicrobials making the chemical bond with fibres as in case of chemical bonding, microcapsules that contain the antimicrobials are covalently fixed on the fibres.
Finishes impervious to water
Textile fabrics treated with finishes impervious to water fall into two categories: water proof & water repellent finish.
in his fabric is coated with a synthetic resin or plastic, rubber, wax, fats or oil to prevent penetration of water into the fabric but also such coating make the fabric impermeable to air & moisture & it adversely affects comfort.
Water repellent finish
A water repellent finish is also water – proof but is not absolutely waterproof & is permeable to moist air so it gives comfort to wearer.
For natural fibres aluminum soaps, oils, fats, waxes, pyridinium compounds (Velan PF), esters & ethers of cellulose are used as water repellent agent. While wax dispersions, pyridinium compounds, silicones, fluorochemicals this used for synthetic fibre as water repellent agent.
The continuous research attempts are being made by scientist & industrialist to invent functional finishes for textile which are Eco-friendly & cost-effective to meet the standards. While meeting environmental & toxicity requirements, will continue to challenge those who work in this field. The interesting development is that the different functions can be combined together on to a single fabric/ textile to get what is known as a multi functional textile. There is great potential for these functional finishes as they are considered to be good enough as well as we have to focus on to overcome the demerits such as loss in strength, stiffness, poor handle, etc.
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