Functional Finishes

8/7/2019 Functional Finishes

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Functional Finishes: The properties of synthetic fibers, most important among them being

polyamide, polyester and polyacrilonitrile, are essentially different from those of natural cellulosic

and wool fibers. Hence the sequence of finishing operations is likely to be different. While

cellulosic's require a resin finishing treatment to impart easy-care properties, synthetic fibers

already have these easy-care criteria and require only a heat setting operation. The use of 100%synthetic textiles has increased considerably since the arrival texurised yarns consisting of

filaments and the growing production of knit goods. The use of open weave has enabled

production of lighter, air permeable, fabrics to ensure better wearing comfort.

What is Heat Setting?

Heat setting of synthetic fabrics eliminates the internal tensions within the fiber generated during

manufacture and the new state can be fixed by rapid cooling. This heat setting fixes the fabrics in

the relaxed state and thus avoids subsequent shrinkage or creasing of fabric. Presetting of goods

make it possible to use higher temperature for setting without considering the sublimation

properties of dyes and also has a favorable effect on dyeing behaviorand running properties

of goods. On the other hand, post setting can be combined with some other operations such as

thermosol dyeing or optical brightening of polyester, post setting as a final finish is useful to get a

high dimensional stability along with desired handle.

The application of heat in heat setting can be done by hot air, on a pin stenter at 220c for 20-30

seconds for polyester goods and at a lower temperature range of 190-225C for 15 -20 seconds

for polyamides . Acrylics may be heat set partially at 170-190 c for 15-60 seconds to reduce

formation of running creases. but higher temperature should be avoided to prevent yellowing.

Hydro setting is so rarely used particularly to get fuller and softer handle on polyamides at 125-

135c in autoclaves for 20-30 minutes. It can be combined with dyeing or optical brightening.

Steam setting can be done by saturated or super heated steam. During steaming, uniform

treatment can be ensured by initial sequence of alternate short steaming and vacuum application

for 20-30 min at 130C under pressure. Super heated steam can be used in stenters and setting

time is 25% shorter than for hot air on account of quicker heating up rate. Acrylic fibers have to

be protested as some may under go excessive shrinkage or loss of handle. Before the material isheat set, it should be thoroughly washed to remove spin preparations, lubricants, sizing agents

and impurities as these are likely to be burned in drying heat setting making their removal difficult.

Filling and Stiffening finishes:
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A stiffening effect is desirable in certain polyamides and polyester materials for petticoats, collar

interlinings, etc., which can be done by reducing the mutual independence of structural element

of fabric by polymer deposition on coating as a fine film. Some special Urea-formaldehyde pre-

condensates have been found to be useful. Application of film-forming acrylates dispersions as

well as latex rubber emulsions gives a fuller effect with sufficient stiffness.

When softening is desired it can be achieved by reducing the frictional coefficient between

structural elements of fabrics, cationic long chain fatty derivatives and silicones may be used in

conjunction with polymer forming agents. Recently some cationic softeners having reactive

functional groups have been developed to get better fastness of finish.

Hydrophilic finishes:

On account of lower moisture and water absorption capacity synthetic fiber materials become

uncomfortable in contact with skin. Certain products based on modified (oxy-ethylated)

polyamides makes the wearing more pleasant by reducing the cohesion of water so that it

spreads over a larger area and thus evaporates more rapidly.

Anti-pilling finishes:

Pilling is an unpleasant phenomenon associated with spun yarn fabrics especially when they

contain synthetics. Synthetic fibers are more readily brought to the surface of fabric due to their

smooth surface and circular cross section and due to their higher tensile strength and abrasion

resistance, the pills formed take a long time to be abraded by wear. With knit fabric, two moreproblems occur, viz., "picking" where the abrasion individual fibers work themselves out of yarn

loops onto the surface when garment catches a pointed or rough object. These two effects are

more predominant in the weave, is more open and yarn is bulkier.

The finish has to cement the fibers within the yearn so that their dragging becomes more difficult,

without affecting the handle adversely. Special polymer formers of acrylate type or latex type are

useful but should form a film of good cohesion, should hydrophilic and should not form a tacky

surface. padding in polymer dispersion or emulsion followed by drying at moderate temperature

gives the desired effect.

Permanent Anti-static effects:

Anti-static effective chemicals are largely chemically inert and require Thermosol or heat

treatment for fixing on polyester goods. Agents of polyether type are found to be useful but

should not effect the dye-equilibrium on fiber otherwise the rubbing fastness is impaired. In


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general Thermsolable anti-static agents also have a good soil release action which is as

permanent as the anti-static effect. Anti-static finishes may also be of polyamide type being

curable at moderate temperatures.

Non-Slip finishes:

Synthetic warp and weft threads in loosely woven fabrics are particularly prone to slip because of

their surface smoothness when the structure of fabric is disturbed and appearance is no loner

attractive. To avoid this attempts are made to give the filaments a rougher surface. Silica-gel

dispersions or silicic acid colloidal solutions are quite useful and they are used with advantage in

combination with latex polymer or acrylates dispersions to get more permanent effect along with

simultaneous improvement in resistance to pilling or snagging. These polymer finishes are also

capable of imparting a soft and smooth handle to synthetic fabric without imparting water

repellency.

Fire Resistant finishes:

With synthetic fiber which melt on igniting by a flame, the molten moss is itself quite dangerous

and a fire resistant treatment is desirable for certain end uses. Polyester fabrics can be made

flame resistant by treatment with an aqueous emulsion of xylene soluble 2,3-dibromopropyl

phosphate in a pad-cure sequence. A semi-permanent effect can be produced by treating with a

mixture of ammonium bromide and brominated phosphoric acid esters.

Polyamides can be made flame resistant by applying phosphorous tri-chloride ammonia reactionproducts or ammonium bromide with amino-triazine condensation products. For acrylics tris-

dibromopropyl-phosphate as well as 2-cyanoethyl-tetramethyl-di-amino-phosphate is quite

effective.

Anti-microbial finishes:

With the increasing use synthetic fibers for carpets and other materials in public places, anti-

microbial finishes have assumed importance. A reduction in soiling tendency will along way in

keeping textiles free from germs and usual soil repellant as well as soil release finishes are

effective in some way. products which are commonly applied are brominated phenols, quaternary

ammonium compounds, organo-silver and tin compounds which can be applied as solutions or

dispersions. They can also be incorporated in a polymeric film deposited on the surface to get

controlled release. Some reactive systems similar to those for reactive dyes have been recently

tried to incorporate anti-microbial structural features.
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Finishing of Elastomeric textiles:

The heat sensitivity of electrometric fibers limits the choice of products and finishing process that

can be employed. In order to eliminate the latent tensions, these electrometric textiles are simply

steamed or treated with hot water. Dry curing or heat treatment is restricted to temperature below140C,. These fabric have e to be dried and curd with minimum tension with over feed stenter. To

groups of materials, viz., foundation fabric and knitted fabric for bathing snits are resin finished.

Water proofing can be imparted by using Zirconium salts containing wax emulsions as it does not

require a high temperature treatment. A filling treatment can be obtained with modified methylol-

urea type products.


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Functional Finishes

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