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STARCHES AND POWDERS
Historically, starches and powders have been the base for textile thread sizing; nowadays, powders are less used than in the past, while starches are still extremely important, above all thanks to their derivatives that have significant advantages, even if higher costs. Among these, let's mention oxidized, etherized, esterized and carboxymethyled starches. These products offer the following advantages:
easy and fast preparation
lower and steady viscosity
stability and fluidity even at low temperatures
CMC (CarboxyMethylCellulose)
Type of products that, after the category of starches, is remarkably important for the yarn sizing.
Those available on the market differ in their pureness degree (pure cmc - technical cmc) and are classified according to their viscosity in low, medium, medium/high and high.
They are mixtures of polymers and additives suitably studied to prevent the user from wasting time, and are divided in 2 categories: reinforcing and ready to use.
The first ones correct a recipe already studied by the sizing operator and are usually adopted in small quantities, taking the recipe viscosity to the wished values to ensure a correct thread coverage.
The second ones contain all the ingredients needed for processing certain yarns containing additives such as softeners, antistatic products, as well as PVA, CMS, CMC...
SIZES BASED ON SYNTHETIC POLYMERS
These products are used for sizing the warp continuous threads and significantly aid also the treatment of discontinuous yarns (cotton, wool, viscose and their blends) mixed with products such as modified starches, carboxymethylates, guaro, etc...
Synthetic polymers can be roughly divided into mPolyVinyl Alcohol (PVA) - acrylic copolymers - vinyl copolymers - styrene copolymers - water-soluble or water-dispersible polyurethane polyesters; obviously, combinations of the families of the above mentioned polymers can be obtained with special procedures, for example polyvinylacrylates and acrylate polyesters, etc...
To sum up and avoid treating special products too long, we will deal with what is actually considered the size par excellence, namely PVA.
Marketed since 1939, it is a synthetic resin and the products available on the market are generally featured by a number indicating their hydrolysis degree, ranging from 80% to 99%, and by viscosity that, like for cmc, is divided in low, medium, medium / high, high. The main feature of PVAs is their high solubility, featured by the polymerization degree. They can be easily removed by washing at high temperature and have an outstanding tensile strength compared to other sizing products.
Just consider that a film made up of maize starch has a resistance of 700 - 800 psi, whereas for a cmc the value reaches 7000 psi and for PVA the value rises to 22000 psi.
Another very important point for the environmental impact and above all for water pollution is the low BOD (biological oxygen demand): a generic starch has a value of 477 ppm of a 0.1% solution, PVA has a BOD of 16 ppm, equal to the one of a solution with the same cmc concentration.
A further positive feature of PVA is that, with the same resistance of the sizing films, the usage quantity is definitely lower compared to the one of starch-based products. Polyvinyl alcohols absorb and release humidity to balance the room relative humidity; the balance of humidity content of the PVA film depends on the crystallizing and orientation degree of the molecules, and thus on the hydrolysis degree. The modern textile technology requires increasingly demanding performance: what was considered an almost unsurpassable limit as a weft introduction of 1500 m/min is nowadays widely surpassed.
The warp preparation is thus more and more refined and studied according to the company needs. PVA, too, is going to be gradually replaced by its derivatives, the modern acrylic or vinyl resins that, suitably selected for the different yarn types, guarantee an excellent result, above all for oe yarns that, due to their nature, tend to absorb high size quantities; with high viscosity products at low usage concentrations (5% - 6%) a perfect outer coverage can be achieved (elastic protective coating, resistant to abrasion). The same result is achieved also for sizing linen, where the use of a purified cmc with high viscosity enables to work with concentrations of 4% - 5%. In the shirt sector, the use of PVA derivatives with cmc mixtures and the addition of soaking and smoothing agents (compounds) enable processing with looms at 600 rpm, with high output and quality.
A special remark must be made for the use of the modern working method called PRE- WET, namely prewetting; this system enables (on raw yarns) to work with a coverage of 100% and over, to increase by 1-2% the output of the weaving room, to obtain significant savings on sizing products and energy, as well as on waste water purification costs.
Obviously, the sizing technician must consider (when formulating the sizing recipe) the humidity contribution due to the soaking in hot water, thus he shall increase the recipe by about 1.5-2% to balance the decrease of the concentration in the size box, because of the thread water contribution.
Generally, the yarn is calculated to acquire 30-35% of humidity and therefore there will be a load of dry sizing agent of 65-70%, that being a film applied outside the thread will get a higher residual elongation.
Example of calculation for adjusting the cotton and staple tensions
Description
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Chain weight (g/m)
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Cotton (tension %)
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Staple
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dry (tension %)
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wet (tension %)
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Unwinding tension FA
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2.5 – 5
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2.5 – 5
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2.5 – 5
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Introduction tension FE
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1 – 2.5
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1 – 2.5
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1 – 1.5
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Drying entry tension FN
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2 - 3
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2 - 3
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2 - 3
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Dividing table tension FT
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30 – 100
100 – 150
150 – 300
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8 – 11
6.5 – 8.5
6 - 8
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7 – 9
6 – 7
4 - 6
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6 – 8
5 – 6
3.5 – 5
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Winding tension
FW
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30 – 100
100 – 150
150 – 300
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10 – 14
9 – 12
8 - 10
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9 – 12
6 – 9
5 - 7
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8 – 10
5 – 8
4 – 5
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Pressure on beam FP
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30 – 100
100 – 150
150 – 300
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Factor A
2 – 2.5
1.5 – 2
1 – 1.5
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Factor A
1.3 – 1.5
0.9 – 1.3
0.7 – 0.9
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Factor A
1.3 – 1.5
0.9 – 1.3
0.7 – 0.9
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Breaking resistance of cotton yarn 12 km = 12 cN/tex
Breaking resistance of staple yarn 14 km = 14 cN/tex
SUITABLE OR RECOMMENDED PRODUCTS FOR THE VARIOUS FIBER TYPES
Cotton, cellulose and Liberian fibers starches, pva, acrylates, cmc
Wool pva, cmc, acrylates
Silk acrylic and vinyl copolymers
Staple viscose rayon acrylic copolymers, cmc
Continuous fiber viscose rayon acrylic and vinyl copolymers, pva
Cupro thread acrylic and vinyl copolymers, pva
Acetate rayon styrene copolymers, acrylic copolymers, pva
Triacetate rayon acrylic and vinyl copolymers, pva
Polyamide polyacrylic acids, polimetacrylic acids,
copolymeracrylic acids
Continuous polyester acrylic and vinyl copolymers, soluble pes
Polyacrylic acrylic and vinyl copolymers
Polypropylene acrylic and vinyl copolymers, soluble pes
Polyvinyl acrylic and vinyl copolymers
USEFUL TABLES
Dry substance on some widely used sizing products
POLYVYNIL ALCOHOL (type LAMOVIL - CARBOVOL - POLYNOL) 95%
CMC (type CARBOCELL - FINFIX) 92%
CMS (type QUICSOLAN - EMSIZE CMS 60) 88%
MODIFIED STARCHES - eterized esterized (type KOLLOTEX - EMSIZE) 82%
COMPOUNDS (type LAMCOL 750 - C 190 - CARBOTEX) 92%
Calculation of the dry substance on the sized yarn
[(Final weight - Initial weight) / initial weight] * 100 = dry substance %
Load on thread % = l /size kg * % RS recipe
Elongation = [ (final m - initial m ) / initial m ] * 100
Size recipe preparation
Sizing product kg = [ (tot. l * wished conc.) / product RS % ]
Initial water l = (tot. l - product kg) * 0.85
0.85 as 15% of the total volume will be composed of condensate
For example: total l 700 - wished concentration 11% - product RS % 85
( 700 * 11) / 85 = 90.6 kg of sizing product
( 700 - 90) * 0.85 = 518.5 l initial water
Size concentration check
[(Product tot. kg - product RH % ) / size final vol. ] * 100 = recipe RS %
Just to give a few useful indications, according to the experience we gained with our customers, some examples of sizing recipes for different types of fibers and yarns follow here below.
1. Sizing of wool
Ne 12
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4000 threads
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recipe = 10% PVA - 0.3% wax
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Ne 16
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4500 threads
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recipe = 8% PVA - 0.3% wax
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Ne 18
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5000 threads
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recipe = 10% PVA - 0.3% wax
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2. Sizing of viscose and its blends
Ne 18
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4050 threads
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recipe = 5% PVA - 0.3% wax
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Ne 12
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4200 threads
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recipe = 4% PVA - 0.2% wax
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Ne 24
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5120 threads
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recipe = 3% PVA - 0.2% wax
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Ne 10.6
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3000 threads
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recipe = 3% PVA - 0.2% wax
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Ne 12
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2860 threads
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recipe = 6% PVA - 0.2% wax
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Ne 12
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5600 threads
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recipe = 7% PVA - 0.3% wax
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3. Sizing of cotton
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• Ne 20/1
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6430 threads
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Single size box
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PVA
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35 kg
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Liq. resin (RS % 25)
grease
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1301 t
3 kg
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refractometer = 8.2% TF 4 mm = 10 "
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final vol. 850 liters
• Ne 45 7500 threads
• Ne 60 8500 threads
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double size box
double size box
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PVA
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20 kg
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cmc
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10 kg
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refractometer = 6
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anti-static wax
grease
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2 kg
0.2 kg
| |
final vol. 500 liters
Ne 40 4570 threads single size box
PVA
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30 kg
| |
cmc
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40 kg
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refractometer = 10.5
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grease
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5 kg
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final vol. 600 liters
4. Sizing of thread dyed cotton (e.g. denim)
· Ne 6.8 OE continuous line with 1 size box, double squeezing
Modified starch 75 kg
Wax 15 kg refractometer = 9
Hardener 25 kg
final vol. 1000 l
5. Sizing of a blended cotton yarn
· Ne 30 4500 threads pes / cotton 65 / 35 recipe PVA 8% wax 0.3
· Ne 45 8378 threads pes / cotton 65 / 35
Starch 25 kg
PVA 50 kg
CMS 5 kg
Grease 3 kg refractometer = 9.5%
Soft 10 kg
final vol. 830 liters
Sizing recipe for Ne 16 /1 100%co ring 3556 threads no. 6 beams flange 800*2000
Item = sponge terry cloth
Eterized starch 10 kg first squeezing 800/1000 KN
Carboxymethylate starch 2 kg second squeezing 1800/2500 KN
Antistatic wax 2 kg
Grease 1kg speed 50 m/min
Water 500 l RH % = 6.5
Tensions: classifying 175 KN
Winding 275 KN
Carriage pressure 300 KN