Now You Know Modern Developments in Sizing

Modern Developments in Sizing
Sherin Parmar
VJTI, Mumbai, India
Email: shrnparmar8@gmail.com

Sizing is the process of giving a protective coating on the warp yarn to minimize yarn breakage during weaving. It is called heart of weaving. Sizing is the most important operation in preparing warp yarn for weaving especially with cotton yarn. The primary purpose of sizing is to produce warp yarns that will weave satisfactorily without suffering any consequential damage due to abrasion with the moving parts of the loom. Besides it develops properties to the fabric, such as weight, feel, softness, and handle. To prevent warp yarns from excessive breakage under such weaving conditions, the threads are sized to impart better abrasion resistance and to improve yarn strength.

Modern sizing process is based on various factors: modern control system for reproducible, optimal quality and easy handling. In this article I will discuss about modern developments in sizing.

Two needs of the modern times:

1) Conservation of energy

Rising prices of fuels

2) Keep environment clean and pollution free

Reclaiming water and the sizing materials from desizing wash water
Sizing in a medium other than water or no medium at all

Method to Save Energy:

Energy requirements:

1. Normal slasher operating at 83m/min, energy consumption comes to be about 1500 kilo calories per kg of warp sized.

2. This energy is required

Preparation of size
Storage at a warm temp
Heating the size paste
Drying the sized yarn

Steps for the conservation of energy:

1. In the size preparation, a lower temp, 80 c instead of 100 c for cooking save 25% of energy (8% of total energy required for sizing)

2. 10% of the total energy require to store the size at high temp. this can be min by

Arranging the very short period of storage
By using non retrogradable size (store at low temp)

3. Use of one squeeze roller instead of two (save 3% - 7% of total energy)

A harder squeeze roll can save 5 % - 10%
The high pressure roll system (save 20 – 50% of energy required for drying )
High viscosity size mixture require more energy than low viscosity sizes
Mechanical energy required for stirring during cooking and storage.
In the preparation of size more energy is required for stirring than heating.

Emulsion size mixture:

Advantages claimed:

1. Liquid emulsions of ready made sizes,

Not require cooking
Not need to be heated during sizing

2. In their manufacture no step of

Drying a solid
Grinding into fine powder

Hot melt sizing:

As pey has mentioned a product in his research called Beveloid 6554, which has a low melting point and quick setting properties.
In this method, the warp receives size during warping of a section beam ( done at 550 m/min), then rewound on weavers beam.
Need grooved metal roller ( heated 205 c )
Each groove has one warp end passing through it.
Size in the form of solid block presses against the roller.(melting point 125 – 155 c)
It melts in contact with the hot roller and coats the warp end.
Molten size has low viscosity so it penetrates into yarn.
When warp is detached from roller, size quickly sets.
At least three separate grooved roller are required ( 12 to 120 tex )

***Size has:

Good strength
Elongation
Desized by usual aqueous wash

Advantages:

Very economical in energy consumption
Requires 80% less energy than conventional system
Simple to operate
Require low investment cost

Disadvantages:

Slow average speed of application
12% less than conventional sizing
Need to assemble sized warpers beam into weavers beam.
Difficulty in reclamation of size from aqueous solution after desizing
High water contamination after desizing

High squeeze pressure system:

Use of high pressure squeezing decrease in the energy requirement for drying.
Idea is to use higher concentrations of size mixture and higher squeezing pressure to give normal size add on.
Heat energy (HE)required for drying is several times more than mechanical energy( ME ) required by squeeze roll for pressing.
Low squeezing pressure - high HE & low ME
Cotton yarn, slow speed running and high squeezing pressure gives best squeezing effect and requires least energy for drying of the yarn. (more ME)
Polyester yarn or poly/ cotton blend yarn high pressure, high speed system was found more economical in respect of sum of HE & ME.
High pressure squeezing, Ensure better add on regularity, which allow lower add on, thus lead to further saving in size consumption.
As high concentrated size mixture is to be used, the adhesive used such that viscosity of paste will not be too high.

***High pressure squeezing allows use of more concentrated size paste than use for conventional one

To get same % of size add on
Same quality of size warp
This leaves less water to be evaporated
Thus effecting a saving in heat energy
22% of total

***As the speed of the yarn passage increases, energy consumption per kg of yarn decreases.

Low pressure – 1/7 its value
High pressure – 1/8 its value

***For this purpose modern synthetic adhesives like

Vinyl acetate copolymer
Acrylic copolymers
Blend of two
With polyvinyl alcohol

Comparison of normal and high pressure squeezing:

is the process of giving a protective coating on the warp yarn to minimize yarn breakage Now You Know Modern Developments in Sizing

Table: Comparison of normal and high pressure squeezing

Advantages:

Decrease in the energy required for drying (save energy)
Ensure better add on regularity, which allow lower add on, thus lead to further saving in size consumption.
Higher tensile strength
Abrasion resistance is at least same, if not better
Improves weaving efficiency by better size penetration
Economical process
When high pressure squeezing coupled with the device to automatically vary the squeezing pressure with change in speed, gives much economy in sizing material consumption.
This method involves a special design of the squeezing roller
Smaller diameter and harder surface give more effective squeezing pressure.
After long use, because of heavy pressure there is bowing of roller.
This bowing results in uneven and inadequate squeezing effect.
To avoid this, specially designed squeezing roller are advised.
Central shaft of lower squeezing rollers is quite broad at the centre and tapered at both end.
There is also a central metallic support, gives support to central position of rubber cover.
Prevent the formation of cavity at centre.

*** Squeezing effect depends on two properties of roller

The diameter
Hardness of the rollers

Foam sizing:

Objectives of foam sizing:

Reduce wet pick up
Conserving energy for drying
Increase production speed in sizing
Small volume of water required for making the paste.

General features of foam sizing:

The foam has advantage of having a large bulk with a very light density.
Some of new synthetic sizes, when blow through with air, produce quite a stable bulky foam through which the warp sheet can be passed and then squeezed.
With the high concentration of size paste, add on can be obtained with a very small pick up.
Ex. Instead of using 13.3% concentration (90% wet pick up) 25% conc. (48% wet pick up) was used. There was saving of nearly 54% of the drying energy.
Polyester type of sizes form bulky foam, but are too costly.
Mixture of conventional sizes with PE size and sodium lauryl sulphate as a foam stabiliser are found to be quite convenient.
Partially hydrolyzed PVA
Cellulose and starch derivatives
Sodium carboxymethyl cellulose
Polyester resins

***From sizing point of view, important properties of foam are

Viscosity of the foam
Its density
Stability

Advantages of foam sizing:

No size cooking required
No size box needed
Energy saving in drying
Increased production speed
Use of shorter drying ovens instead of cylinders
Improved size utilization
Ease of removal in desizing
Less colour bleeding on dyed yarns
Less yarn hairiness
Higher weaving efficiency
Higher productivity in sizing
Improved chemical utilisation

Use of silica dispersion:

Introduction of a new additive to the size mixture to further improve the sizing performance
The additive is a colloidal dispersion of silica in rubber latex emulsion
Siotexise is the name given to the additive.
It improves the abrasion resistance of the size film also the softness and pliability of the film.
The idea has been adopted from the finishing technology, where it has been used to improve the softness and wearability of the fabrics made from cotton, rayon, jute.
The rubber latex film has good adhesive strength
When applied in sizing, gives good fibrelay and improves strength of yarn, prevent fiber slippage.
When colloidal silica is added to the latex the microfine fibres of silica get embedded in the film and further improve its performance.
The quantity of the auxiliary in sizing is 4 – 6% on the weight of the adhesives in size mixture
Not only strength of the warp increased but also the surface characteristics of the yarn are improved, reducing the hairiness and imparting lubricity.
On cotton warp the breakage rate is found to be reduced by 25 – 33%.
In spite of the new addition the cost of the size mixture has been slightly reduced ( reduction in the proportion of CMC, gum, tallow)
The same firm introduced a similar product called Forcylor.
Which is meant to be added to the last wash after dyeing of yarn
It is well known that, coloured threads in a warp sheet do not behave well during sizing as compare to gray ones.
Forcylor addition to the yarn, to the extent 1% on the weight of the yarn, improves their performance
The coloured threads, without this addition, gives more breakages on the loom.

Heat shock treatment:

If the warp yarn is passed around a heated roller before entering into the size, the sizing effect is further enhanced
Increase strength of the yarn
Warp breakages reduced by 29%
Loom productivity increased by 6%
Elongation is some what decrease

Fusion of the yarn surface fibers:

This technique use for thermoplastic fibres like nylon or polyester, whether 100% or blended.
It is proposed to subject such a yarn to a momentary heat treatment, at a temp just above the melting point of the fibre, so that the surface fibres melt and get fused together to make a compact, resistance surface layer.
Increase abrasion resistance
Strength and dyeing properties are not affected.

Combining sizing with other wet processes:

Combined dyeing and sizing
The milnerised system of dyeing, resin finishing and sizing
Combined sizing and bleaching

Combined dyeing and sizing:

Dyeing and sizing in the same bath
One after other in two baths
Azoics, vats, reactives, pigments, disperse dyes etc. are dyed simultaneously with sizing.
In BTRA has successfully formulated methods for sizing and dyeing azoic combinations simultaneously.
Combining the dyeing of cold dyeing reactive dyes along with sizing with P.V. alcohol
Here reactive dye retains its fastness properties, the P.V. alcohol size also becomes more lasting.
The system using Padazoic colours ( azoic colour combination mixtures, like Rapid Fast colours) in which use of two slashers in tandem.
In the first padding through a solution of the Padazoic colour is taken. ( sol is made with colour, caustic soda, methanol and little gum to prevent the migration of colour during drying)
After that dried.
In second box is a mixture of starch, tallow and a buffer, like a mixture of sodium acetate and acetic acid.
If CMC is used only acetic acid is requied
Temp 96 c
Then dried
Another is the open width indigo dyeing ad sizing range
Scouring, rinsing, padding through indigo sol, squeezing, oxidation by airing, then repeated padding and airing several times, washing with water several times, drying, passing through the size paste, drying winding on loom beam.
The Milnerised system of dyeing, resin finishing and sizing
Combined sizing and bleaching

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