In this Part we will be dealing with fabric finishes based on Aesthetics point of view.
- Aesthetics:- The appearance of the fabric is conventionally thought to be a result of the combination of yarn, weave, per-treatment, dying and printing. But now a day a lot of mechanical and chemical processes have evolved over time that effect the aesthetics of the fabric/garment. Aesthetics finishes influence the luster, texture, drapability, hand and surface appearance of fabric.
In the previous article we have discussed the name of few aesthetics finishes. We will now study them here in depth.
A. Calendering:- Calendering is a mechanical process the finishes fabric by passing them between a series of rollers. It generate smooth, polished or embossed effects depending on the roller surface properties and relative speeds. A calender is a mechanical device consisting of two or more large rotating cylindrical rollers stacked on top of each other and usually heated. The cylindrical rollers are in contact with each other under pressure. Fabric being calendered passes around and between these cylinders. The specific type of calendered finished fabric varies with the nature of the cylinder surface, the speed of the cylinders and the nature of the fabric being finished.
- To give soft and smooth surface to the fabric
- To give luster and glaze to the fabric
- To give silk like appearance
- To decrease air permeability
- To flatten Slubs
B. Parchmentizing:- The literal meaning of parchmentizing means to make anything like paper in terms of the crispiness that paper holds. In finishes it means crispiness or ody given to fabric (mainly to cotton one). It uses an acid wash (sulphuric acid) to make cotton almost transparent, and yet permanently stiff such as organdy. The treatment process is carried out in a very timed and precised manner i.e. split second timing precision to prevent fabric from weakening. After the acid treatment, the cloth is nutralized in a weak alkali, washed and calandered to improve surface gloss. With this method we can provide the fabric an all over, a localized or a plisse effect.
C. Fulling:-According to Britannica fulling is a process that increases the thickness and compactness of woven or knitted wool by subjecting it to moisture, heat, friction, and pressure until shrinkage of 10–25% is achieved. Shrinkage occurs in both the warp and weft see weaving), producing a smooth, tightly finished fabric that is light, warm, and relatively weather proof.
The Fulling or Tucking process consists of the closing together of the threads of newly woven woollen fabric with the assistance of soap or acid liquor.Fulling consists of vigorous methods to make the cloth become a felt. It is the late stages of the felt-making process.Earlier in 11th century the person performing fulling were known as fullers. Mechanization of this finishing process in the 11th century made life much easier for the fuller. Water power was used to work fulling stocks, a machine with two large wooden hammers raised on tappets. The cloth was contained in a trough – the stock – and was repeatedly beaten by the rising and falling hammers. Such hammers did generate heat and heavily felted cloth was produced. Fulled fabric are denser and more compact on both warp and filling directions.
D. Mercerization:- It is the treatment of cellulosic material with higher concentrated alkali for short period at lower temperature.
Objectives:-
- to improve lusture of cotton materials
- to improve strength and mechanical properties
- to improve dyeability and moisture absorbancy
- to improve dimensional stabilty of materials
- to improve elasticity
How does alkali helps in mercerization?
Since cotton is having high resistance to alkali solutions, so mild alkali like sodium carbonate have no action on cotton. But strong alkalis with higher concentration induce structural and physical changes in cotton fibre. During mercerization swelling of fibre takes place and the initial cross-sectional shape of cotton fibre changes from bean shape to circular shape. Thus Cylindrical longitudinal shape increases luster of the fibre. It Also increases the strength of the fibre.
E. Napping :- A mechanical finishing process that raises the short fibers on the face of the fabric by utilizing teasels, rollers or revolving cylinders with fine bristle, wire or metal points. Protruding nap is clipped or sheared to a uniform length and brushed.
- Applied to` woven, knitted, tufted or nonwoven fabric structures
- Produced on one or both sides of the goods
- Surface may he brushed in one direction (single napping) or in opposite directions (double napping)
- Changes and/or modifies appearance or hand of fabric
- Softens fabric
- Increases durability
- Creates insulating air cells in the nap, increasing warmth of fabric
- Hides the weave of the fabric
- Hides weaving imperfections and defects in the cloth
- Cotton of man-made fiber fabrics may be treated to resemble wool texture
- Increases pilling action
- May abrade with wear and cleaning
- Flattens with wear
Brushing finish combined with steam is used to fix in position or lay the nap or pile structure of napped and pile fabrics in one direction.
The depth of pile developed on a napper can be much greater than can be obtained by sueding, assuming the fabric construction is correct. For example fleeces, velours, high-pile fur-like effects, flannels and bed blanket finishes are produced by napping. Proper fabric construction is a prerequisite to napping. It is important that the yarns acted on by the napper are not the ones responsible for the strength and integrity of the fabric. The reason for this is that the napped yarns are weakened by the napping action. Fabric to be napped should have a napping lubricant or softener applied prior to napping to allow the fibers in the yarn to slide more freely during the napping operation.
F. Sueding :- A surface finish imparted to fabric as it passes over rapidly revolving rollers covered with abrasive paper of desired grit for the fabric being processed. The height and direction of the low pile created on the surface of the fabric depends on the selection and manner of programming the multi -cylinder or a single-cylinder sanding/sueding machine.
- Used on both woven and knitted fabrics
- Softens hand of fabric
The degree of roughening the surface is determined by the
1. speed of the sandpaper roller;
2. coarseness of the sandpaper;
3. speed at which fabric is passed between the roller .
4. amount of space between the rollers.
Hand of fabric after processing differs depending on the:
• Fiber content of the fabric
• Filament count in the yarn
• Intensity with which fabric is worked.
According to Dr. Charles “A sueder is sometimes referred to as a sander since the machine consists of one or more rolls covered with sand paper as the abrasive. Fabrics traveling over these rolls develop a very low pile and the material’s surface can be made to feel like suede leather. The hand will depend on the fiber composition, the filament count in the yarn and the intensity with which the fabric is worked. Filament fabrics can be made to feel like a spun fabric and generally speaking, all fabrics will have a softer hand.”
G. Plisse:-Plisse is the name of a finish as well as the name of a fabric treated with this finish. It is a permanent finish, produced on cotton by the action of sodium hydroxide; but unlike mercerizing, no tension is used. The sodium hydroxide is printed on the fabric in the form of a paste.The fabric shrinks only where the sodium hydroxide is applied, producing a puckered effect.
OR
A mechanical finishing process producing a textured, pebbly or crinkly effect on fabrics and plisse fabrics. Finish is accomplished by one of the following methods. It is also known as creeping finish.
1. Passing cloth between hot rollers in the presence of steam, matching roller designed with indentations. This method is nonpermanent and will wash out or iron out.
2. Rolling caustic soda paste onto cloth in striped or figured patterns and subjecting fabric to wash bath. Treated areas create a puckered or crepe effect; untreated areas will shrink.
Degree of permanency depends on thermoplastic qualities of the fabric.
H. Shearing:- A mechanical process applied to natural or man-made staple length fiber fabrics. Utilizing a multi-blade machine, undesirable loose surface fibers are cut or sheared producing different surface looks.
- Evens and levels the surface of the fabric producing a uniform appearance
- Applied to one or both sides of fabric
- Allows weave of fabric to show
- Produces uniform pile for plushes, velvets, velours and cut-loop fabrics
- May be manipulated to produce cut designs and sculptured effects
- Changes hand, drapability and creasing properties of fabric
- Improves color and appearance of fabric
Shearing is the process where a raised fiber is cut at an even height. Some spun fabrics are sheared close to the fabric as a means of removing the raised hairs giving the fabric a clear, smooth surface. Shearing is an alternative to singeing.
More often however, shearing follows napping to:
1. clear out random lengths of fibers and produce a uniform and level pile.,
2. reduce the height of wild fibers and prevent pilling,
3. to produce a certain hand,
4. improve color and appearance and
5. produce sculptured effects.
Knitted and woven fabrics with loops on the face or back are not necessarily napped first – they can be sheared directly to cut off the tops of the loop and produce plushy velours such as knit velours and plush towels. Terry looped bath towels can be sheared on one or both faces to produce a plush pile surface.