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Desizing: Objective, acid and enzymatic desizing processes. Their merits and demerits. Measurement of Desizing efficiency.

PREPARATORY PROCESSES FOR COTTON

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SINGEING SCOURING

MERCERIZING

BLEACHING

DE-SIZING

DESIZING

Onto de-sizing…

PRE-TREATMENT

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The reason for de-sizing because during the spinning and weaving process, the fabric goes through sizing.

DESIZING

SIZING is when SIZE is applied to the fabric to protect it from the abrasive

action of the loom.

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WHAT IS SIZE?

Natural sizing agents are

mostly based on starch and

starch-derivatives.

There are also

synthetic sizing agents

such as modified polyesters

DESIZING

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DESIZINGDe-sizing is the removal of sizing agents from the fabric using enzymes, acid, oxidative agents, etc. Enzymatic de-sizing is the most common.

STARCH (AMYLOSE)

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ROT STEEPINGThe fabric is steeped in warm water at 35° to 40°C for 24 hours or overnight at 60° C

ACID STEEPINGThe fabric is steeped in a solution containing 0.5 to 1.0% hydrochloric acid or

Sulphuric acid at room temperature or at 40° C. The acid reacts with starch and

degrades it which is removed during washing., but fabric can be degraded

ENZYME DESIZINGEnzymes are biocatalysts. Enzymes which degrade starch are called amylases.

There are three types of enzymes : bacterial, malt and pancreatic. These

enzymes are the starch degrading agents of the fermentation process which

occurs when starched fabrics stored in wet condition at slightly elevated

temperature become infected by micro organisms.

TYPE OF DESIZING

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STARCHβ- Amylase

α- AmylaseAttack randomly

and produce

Attack at particular places

and produce

dextrinsFAST REACTION

maltose

SLOW REACTION

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Amylase Optimum Optimum Effect of Effect of

PH Temp(°C) NaCl CaCl2

Pancreas 6.8-7.0 40-55 + +

Malt ∝ 4.6-5.2 55-65 — +

Malt β 4.6-6.2 40-50 — __

Bacterial 5.0-7.0 60-70 O +

OPTIMUM OPERATIONAL CONDITIONS OF AMYLASES

ENZYME DESIZING

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Irrespective of what kind of de-sizing, the process includes:

Washing out the degradation products

Impregnation of fabric with

de-sizing agentAllowing the de-sizing agent to solubilize or degrade the size

DESIZING

Process route

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DESIZING

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OXIDATIVE DESIZING

Starch is oxidised to degraded products, and removed during washing

(1) Sodium Hypochlorite 2 g/l at room temperature

(2) Hydrogen Peroxide 1 to 2 volume

Sodium Hydroxide 7 to 15 g/l

pH 10.0

Steamed for 2 to 3 minutes

Temperature 30° to 40° C

Pad cold and store overnight

The residual starch content on the weight of the fabric after desizing should be less than 1.0%

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DESIZING EFFECIENCY

CONVENTIONAL METHOD

TEGEWA RATING

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Total size = W1-W3

Residual size = W2-W3

Desizing Efficiency = (Total size – Residual size)/Total size X 100

CONVENTIONAL METHOD

take the weight of the sized fabric let it be W1

WEIGHING

Desize the fabric, dry & take the weight, let it be W2

DESIZING

Treat the fabric with 3gpl (35%) HCl at 700 C for 30 min. dry & take the weight of the fabric. Let it be W3.

TREATMENT WITH HCl

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TEGEWA METHODPREPARTION OF TEGEWA SOLUTION

Potassium iodide (10 gm. Of KI (100%) in 100 ml water

Add 0.6358 gm of iodine (100%) stir and shake

Fill up to 800 ml with water then complete to 1000 ml with ethanol

Shelf life approx 6 months only