BY:- ANUP CHAURASIA , SANDEEP MUKIM

SHRINK PROOF OF WOOL

Structure of wool

• FELTING SHRINKAGE :- Caused by the progressive entanglement of wool fibers through mechanical action during washing.

• RELAXATION SHRINKAGE :- occurs when the stresses or strains introduced during the processing of textile materials relaxed in water.

TYPES OF SHRINKAGE

CAUSES OF WOOL SHRINKAGE

The physical structure of scaly cuticle layer of the wool is responsible for the shrinkage.

Alternatively, we call it due to :-

1. DFE (differential frictional effect).2. ELASTICITY OF WOOL.

• Caused by the difference in friction between µa and µw .

where µa = friction coefficient when rubbing

in against - scale direction. µw = friction coefficient when rubbing

in with – scale direction. • Hence there is crimp i.e. springiness• This behavior pronounces due to agitation in

aqueous solution.

Directional Frictional Effect”(DFE)

Elasticity of WoolWhen alternative compression and relaxation are applied the compressive forces packs the wool fibre more tightly and on relaxation the DFE prevents many of them from reverting to their original position.

METHODS OF SHRINK PROOFING

a) By modifying the scale structure in such a manner that DFE is reduced or eliminated.

b) By introducing intermolecular cross-link there by decreasing the elasticity.

c) By covering the fibre with a film- i.e. Mask the surface, Hence removing the causes of DFE.

SHRINK RESIST TREATMENT

• The loose fibre treatment rely on reducing the DFE either by degrading the scale structure or by masking the scales.

• The fabric treatment rely on at least a degree of interfibre bonding to reduce interfibre movement.

Technologies currently being developed for shrink resist finish :-

• For loose fibre :-1. Combination of oxidation and additive polymer

process. e.g.- Chlorine-Hercosett shrink resist technology.• For fabric :-1. Additive polymer only process.• e.g.- Bunte salt finishing.1. Plasma treatment followed by resin polymer or

softener finishing.2. Enzymatic finishing.

LOOSE FIBRE SHRINK RESIST TRETMENT

CHLORINE-HERCOSETT RESIN PROCESS:-I. Top is first chlorinated, usually with

dichloroisocyanuric acid(DCCA).II. Then, anti chlorinated with bisulphite.III. Finally finished by a substantive treatment with a

cationic resin such as hercosett,basolan F or Dylan GRB.

Drawbacks:• yellowing is associated with chlorination.

Therefore to avoid Yellowing hydrogen peroxide is used as a antichlor agent, instead of bisulphite.

BUNTE SALT POLYMER FINISH.

Applied by pad-dry-cure procedure. reaction between bunte salt groups and wool

cystine occurs at the curing stage. form polydisulphide X-linked polymer. X-linking is performed intermolecularly. The result is “Elasticity is reduced”.

ADVANTAGES:• Reduces energy costs.• Elimination of thermal yellowing.

FABRIC SHRINK RESIST TREATMENT

PLASMA TREATMENT

• Plasma is an ionized gas composed of charged and neutral particles.

• Disrupts the outermost lipid layer of the epicuticle.

• Also attacks one-third of the highly X-linked disulphide bonds in the exocuticle.

• The shrink resist effect of the plasma treatment is due to the oxidation of disulphide groups and new hydrophilic groups created on the fibre surface.

ADVANTAGE

• Eco-friendly.• Use lower volume of water.• No chemicals required.

pictures of plasma-treated wool after resin application

Influence of the pretreatment on the area felting shrinkage of knittedfabrics after 50 simulated washing cycles in a domestic washing machine

Treatment Area felting shrinkage (%)

Untreated 69

Plasma-treated 21

Plasma/resin-treated 1.3

Chlorine/Hercosett-treated 1

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