vest pocket book of sizing

8/3/2019 Vest Pocket Book of Sizing

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Sizing Agents and SizingOperation

Edited byWoraphot Wattanaphan


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General Review

Among the preparatory processes of weaving, warp sizing can be

regarded as the most important process. It has a great impact on the production efficiency of weavinglooms, operation cost and quality of the woven fabric.

A properly sized warp achieves already half the goal of a good

weaving operation.


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Functions of Sizing

1. Spun yarn ( natural fiber ) Increased yarn strength - size film Glue down protruding fibers less hairy High and stable viscosity less penetration easy removal Low friction and good extensibility

2. Filament yarn Bind all filaments together (need penetration for better adhesion) Antistatic no repulsion between single filaments Even add on to the whole beam

3. Blends of synthetic and natural fibers Hydrophobic nature of synthetic fiber adhesion Suppleness Smoothness Antistatic


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General requirements of a good size

Tensile strength;

Abrasion resistance;

Good adhesion;

Good extensibility;

Inexpensive;

Not support mildew growth; Easy to remove;

Flexible.


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Warp Sizing Agents

Vegetativeorigin

Animalorigin

Grease

Starch

Potato,sago,wheat,corn,

tapioca

SeaweedNatural

gums

GumArabic

Animal

protein

Boneglue

Dry oil

Linseedoil


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Warp Sizing Agents

Natural derivative

Processedstarch

Starchderivative

Cellulosederivatives

Electrolyte

Soluble starch,roasted starch,

starchStarchacetate

PhosphatedStarchCationicstarchCM starchCE starchHE starch

Methylcellulose

EthylcelluloseCMCHyroxylethylcellulose

Sodiumalginate


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Warp Sizing Agents

Synthetic Sizes

Vinyl Vinyl copolymer Acrylic Petroleum

PVA Mod PVA

Partiallyhydro' PVAFully

Hydro' PVA

PVAester

PVM

PolyacrylamidePolyacrylester Polyolefin

PVAc acrylicacid


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Starch

Historically, starches and flours are the traditional film former of the sizing process. Starches are flours with the gluten (gummy substance) removed.

Natural sources of starches applied in sizing:

Wheat starch x300Potato starch x300Tapioca starch

Rice starch x300 Maize starch x40


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Sources of starches used in textile sizing

Corn (maize) Tapioca ( cassava) WheatSweet potato

Sago Rice Yucca Potato

Chemical constitution of starches


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Chemical constitution of starches

Amylose is a linear polymer, MW range 100,000 to 300,000 found in the interior ofthe starch granule and account for 19 26% of the weight. It is soluble in hot water,however , when the solution is cooled, it will form strongly H - bond betweenadjacent chains making it difficult to re-solubilize.

Amylopectin is the major component of starch and comprises the outer sheathof the granule. A highly branched high MW polymer (1.6M), less water soluble

than amylose.

Starch polymers are carbohydrate composed of repeating anhydroglucose unitslinked together by an alpha glucosidic linkage. The alpha linkage is an acetalformed by the linkage of the hydroxyl group at the -1- position with the -4-position of another. This gives rise to linear polymer called Amylose. Branchingcan occur when an acetal linkage between the -1- position of one ring forms withthe -6- position of another. Highly branched polymers are called Amylopectin.


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Amylose AmylopectinStructure linear branched

Molecular weight 100,000 ~ 300,000 1,600,000

Average DP Several hundreds 10,000 ~

Content % 20% 80%

Solubility Soluble in warm water Less soluble in warm water

Test paper Blue Red purple

Enzyme easy difficult

Retrograding happen Not happen

Viscosity low high

Oil influence influence Not influence

Properties of amylose and amylopectin


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Natural starches are not very soluble in cold water. Cooking is necessary

to get the starch granules to form a homogenous solution. Typically thestarch granules are stirred in cold water and kept suspended by highspeed mixing.

As the temperature is raised, water penetrates through the amylopectinmembrane to solubilize the amylose. The granules swell, as more andmore water diffuses in, to many times of their original dimensions. The

viscosity of the solution increases as the granules swell, reaching amaximum at the point where the swollen granules press against eachother.

Prolonged heating and mechanical shearing rupture the swollen granulemembrane allowing the solubilized amylose to spill into the bulk of thesolution. At this point the viscosity begins to fall off, and stabilized if the

temperature is kept there.

The starch solution can be considered as solubilized amylose moleculesintermingled with ruptured swollen fragments of the amylopectinmembrane.

Starch solution


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Gelatinizationprocess

Initialswellingphase

MainSwelling

phase

Gelatinizingphase

Ripeningphase

Stabilizingphase

Change ofstarch particle

Water in,penetrationstart

Amylosedissolve,swelling

Rupture ofmembrane

Temperature ofgelatinization

55 ~ 60C > 85C ruptureofamylopectin

General 88C,90 ~ 95C, HT115 ~ 120C

Establishpastestability

Keep temp toavoidretrograding

Viscositychange

Temperature1007550250

Preparation of starch solution


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In warp sizing, about 60% to 65% corn starch, and about 25 to 30% wheatstarch were used.

1. Corn starch: Very hard particles, higher cooking temperature is needed tooptimize the gelatinization, otherwise long time is needed. High pressurecooking can compensate this inconvenience. Adhesion is strong, uniformpenetration and resilient makes a good sized yarn. But the sizing, on comparedwith other starch, is more rigid and more difficult to be desized. Cookedsolution of corn starch cannot be kept for too long without decay but cornstarch is still the most extensively used. Its quality specifications are asfollows:

Item Specification

Moisture content % 12.4 +/- 1.0%

Crude protein < 0.35%

Whiteness 98.0 +/- 0.5%

pH 4.5 ~ 4.8

Viscosity cps 1700 +/- 100

Sulfite residue < 0.005%

Soluble protein < 0.04 +/- 0.01%

Crude fat < 0.20%

Corn starchgeneralspecification


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2. Sweet potato starch: viscosity varies with different sources; Need to beboiled for more than 2 hours to obtain stable viscosity; Film strength weakerthan the other starches; Elongation similar to corn starch and potato starch;

Other features in between that of potato starch and wheat starch .

3 potato starch: flexibility and abrasion resistance of film are excellent; Goodpenetration of the starch solution; Rapid increase in viscosity when cooking,but then gradually drop into unstable state; Mostly applied in mixture with cornand wheat starch.

4 Wheat starch: viscosity lower than corn starch, but more stable; betterpenetration, good film smoothness; due to not so good film forming andextensibility, use in mixture with synthetic sizes.

5 Wheat flour starch: Wheat flour contains bran protein (9 ~ 14%); Strongadhesion but viscosity not stable as wheat starch; tends to foam duringgelatinization; mildew grows easily.

6 Processed starches: also known as modified starch; altogether about fivecategories, namely: thin boiling starch; dextrin; British gum; oxidized starch;and starch ether.


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Starch type Particle size Particle shape

Corn 14 polygonWheat 21 Spherical, polygonSweet potato 30 ovalPotato 40 oval

Size and shape of starch particle

Starch type Gelatinizing temp Highest viscositytemp

Corn 71C 92CWheat 83C 95C

Sweet potato 68C 84C

Potato 58C 69C

Rice 65C 95C

Tapioca 66C 73C

Gelatinizing temp. and highest viscosity temp. of starches (7%)


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Example 1 Example 2Amylose Amylopectin Amylose Amylopectin

Corn 25 75 10 90

Wheat 12 88 32.5 67.5

Potato 3 97 27 73

Rice 24 76 31.5 68.5

Ratio of amylose and amylopectin in various starches source and types

Starch type Adhesiveness Index

Rice 100

Corn 85

Wheat 75

Potato 68

Adhesiveness Index of various starches


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Film type Film properties

Potato starch Transparent, strong and soft

Corn starch Similar to potato but more brittle

Sweet potato starch Better than corn, less strength

Soluble starch Transparent, colorless, brittle

CMC Uneven thickness, rough, not sobrittle as starches

PVA fully hydrolysed 2300Partially hydrolysed 1800

Evenness, good strength, goodextensibility but with sticky feeling

Properties of various sizing films


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Thin boiling starches are made by adding a small amount of acid to a starchsuspension that is held just below its gel point. The acid cleaves the polymerat the glucosidic linkage thereby lowering the viscosity of the solution.

Hydrolysis occurs within the granule without breaking the granule. Mostlycorn starch is used to make thin boiling starches. Their solutions stillretrograde

Processed starches1. Thin boiling starch

2. Dextrin

Dextrin are made by heating dry starch with a mineral acid. White dextrinis made by heating at moderate temperature and yellow dextrin is made by

heating at higher temperature with less acid. The degree of hydrolysis ishigher than thin boiling starch so dextrin solutions have lower viscosity.

Hydrolysis ofstarch


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British gums are made by dry heating starch granules at 180oC withoutacid. Some of the 1-4 acetal linkages are broken and 1-6 are formed. A

more highly branched, lower molecular weight product is formed withmore reducing end groups. British gums are more water soluble andproduce higher solution viscosity. They are mainly used as thickeners.

3. British Gum

Processed starches (cont'd)

4. Oxidized starch

Starch granules are oxidized with sodium hypochlorite which convertsthe 2-3hydroxyl into -COOH groups breaking the ring at that point. Five to

seven -COOH groups per 100 anhydroglucose are introduced. Sodiumbisulfite is added to destroy excess hypochlorite. The granular structureis retained and films from oxidized starch are better than those formedfrom thin boiling starch.


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Processed starches (cont'd)

5. Starch ethers

Starch ethers are made by reacting the hydroxyl groups in the anhydro

glucose ring with appropriate reagents. These reactions increase thehydrophilic nature of the starch and decrease the ability to form hydrogenbonds between polymers, thus modifying solution and dry film properties

General Properties of Starches


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``

Sweetpotato

Potato Corn(Maize)

Wheat WheatFlour

ProcessedStarches

Moisturecontent % 16.6 17.8 13.3 13.9 12.3 various

Proteincontent %

0.83 1.20 1.13 7.0

Particlevolume

15 45 17 21 25

Particle sizedistri~

even Not even even Not even Not even even

Viscosity Stablemedium

unstable Stablehigh

Stablelow

Stablelow

Usuallylow

Penetrationmm

100 218 105 52 vary Usuallygreat

Film forming good good good UsuallyNot good

Not good good

Tenacity (g) 25.7 39.9 40.7 48.4 43.1 23.9

Extension % 5.1 3.9 5.6 3.4 3.6 3.3

Flexibility(no. of fold) 21.9 45.2 30.7 15.3 18.4 9.4

General Properties of Starches


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Swelling of starch particle

Soaking the starch,allowing full swelling, before cooking, can shorten thetime ofgelatinizing of the starch suspension. Approximately one hour is

needed for fully gelatinizing the starch suspension and bring it to a stableviscosity.

Swelling temp Swelling

Room temp 6.0%

40 o C 7.0%

45 o C 7.0%

50 o C 7.5%

55 o C 10.5%

60 o C 40.0%

5.13 Effect of Soaking temp and swelling of starch

Conditions: wheat starch 7g / 50ml water

Water temp 12oC


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Temp of

oiling

Temp of

starch

Swelling

60oC 38oC 24%

70oC 42oC 30%

80oC 48oC 35%

90oC 52oC 38.5%

100oC 55oC 48.5%

5.14 Effect of temp of oiling added to swelling of starch

Conditions: wheat starch 7 g / 50ml; oiling D 0.161g

Water temp 16oC

Addition of oiling facilitates swelling of starch


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5.15 Effect of oiling type and temp of swelling of starch

Conditions: wheat starch 7g / 50mlOiling 0.525g; water temp 12.5oC

Swellingtemp

Swelling volume

Oiling A Oiling B Oiling C Oiling D

40oC 21mm 21mm 23mm 21mm




Different oiling type has effect on swelling of starch


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Oilingquantity

7.5% 10% 12.5% 15% 18%

Oiling A 19mm 17.5mm 15mm 15mm 12.5mm

Oiling B 18mm 13.5mm 11mm 11mm 10.5mm

Oiling C 21mm 18mm 15mm 13mm 15mm

Oiling D 18mm 17mm 14mm 10.5mm 8mm

Oiling E 21mm 21mm 21mm 20mm 20mm

5.16 Effect of oiling quantity on swelling of starch

Conditions: Wheat starch 7g / 50ml ; 51oC ~ 52oC

Oiling 91oC; Water Temp: 14oC

Increase in oiling quantity decreases swelling volume of starch


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Polyvinyl alcohol (PVA, POVAL)

Manufacturing process of polyvinyl alcohol

hydrolysis


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Polyvinyl acetate is dissolved in methanol to form a 20% solution. Sodiummethoxide is added while the solution is being stirred by a high speed mixer.The solution is poured onto a conveyor and passed through a gelling zone.Polyvinyl alcohol is not soluble in methanol so as the hydrolysis proceeds, agel is formed. The gel, consisting of polyvinyl alcohol, methyl acetate, methanoland catalyst is chopped-up, the catalyst neutralized with acetic acid, squeezedto remove the excess liquids and the solids purified by washing with more

methanol. The solids are dried and pulverized into relatively pure polyvinylalcohol.

Industrial manufacturing method of PVA

Commercial PVA comes in grades which reflect the molecular weight anddegree of hydrolysis. For textile size applications, three grades are mainly used.

Degree of hydrolysis Solution temp

Fully hydrolyzed 98 ~ 99% Boiling water

Intermediately hydrolyzed 95% 60oC

Partially hydrolyzed 85 ~ 90% 49oC


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Water solubility, solution viscosity and film properties are influenced by themolecular weight and degree of hydrolysis. As the acetate ester, the polymer

does not have hydrophilic groups to assist in water solubilization. However -OHgroups are able to form hydrogen bond with water; therefore, as the number ofacetate groups are converted to the corresponding -OH group, the hydrophilicnature of the polymer increases up to a point where 88 % of the ester groupsare hydrolyzed. Beyond this, the hydrophilic nature drops off rapidly as thepolymer nears the fully hydrolyzed state. Fully hydrolyzed polyvinyl alcohol(PVA) form strong hydrogen bonds with neighboring chains. Being linear, the

chains can align themselves to form a tightly packed array. Higher energies areneeded for water molecules to penetrate the network so fully hydrolyzed gradesrequire very hot water to solubilize them.

When acetate ester groups remain, the ability of the polymer chains to formH-bonds is interrupted by the pendant nature of the ester group. This allows watermolecules easier access to the -OH groups and at 88 % hydrolysis, a balance

between the number of hydrophilic groups and chain separation is struck foroptimum water solubility.

White powder Specific gravity: 1.295 fully hydrolyzed; 1.275 partially hydrolyzed Water solubility: varies according to DP and degree of hydrolysis

Properties of PVA


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Viscosity: low viscosity group, very stable viscosity

A, 7881 mol% hydrolyzed, DP = 20002100; B,8789 mol% hydrolyzed, DP = 500600; C, 9899 mol% hydrolyzed, DP = 500600; D, 9899 mol% hydrolyzed, DP =17001800


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For PVA of a certain molecular weight, the extent of both inter and intrachain hydrogen bonding, and the solute-solvent hydrogen bonding aremainly determined by the degreeof hydrolysis of PVA and the solutiontemperature [17]. For PVA of low % hydrolysis,due to the bulky size and

hydrophobic character of the remaining acetate groups in the molecules,OH groups on neighboring chains are prevented from getting close enoughto form inter chain hydrogen bonds [12,17]. The solubility of partially-hydrolyzed PVA is thus high at room temperature while fully-hydrolyzedPVA is essentially insoluble in water at the same situation. On the otherhand, in the solution of higher temperature, the extent of inter andintrachain hydrogen bonding is disrupted by the higher mobility of themolecules and the ones between PVA and water are thus enhanced. As aresult, the solubility of highly-hydrolyzed PVA increases dramatically


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