Wet Processing of Polyester Microfibres

8/4/2019 Wet Processing of Polyester Microfibres

1/12

W et Processing of Polyester MicrofibresEdward Menezes Rossari Biotech Ltd

[email protected] No 912261233800/802

Introduction

During the last few years, the comfort, fuller handle of the natural fibres has scored

heavily over the wash and wear properties of the synthetic fibres. The only viable

alternative to natural fibres is the polyester microfibre. The advantages of this product

include excellent durability and dimensional stability, in addition to a soft, full hand not

normally associated with synthetics.

Microfibres are termed as fibres having fineness of less than 0.0001 denier. Fibre

producers all over the world have continuously trying for finer and still finer fibres foralmost 20 25 years. The most popular definitions of microfibres and super microfibres

are,

Distinguishing

Properties

A fabric made of microfibre will contain four times

more filaments as compared to conventional fabric. It

will therefore has more surface area and bulk,

thereby giving distinguishing properties such as soft,

full handle with excellent drapabillity and comfort.

This is in addition to the inherent properties of

synthetic fibres like easy care and dimensional

stability. The tightly woven fabrics made of polyester microfibres, give good water

proofing and wind resistant effects, much better than those obtained with coated or

laminated or finished conventional fabrics. These tightly woven fabrics impede water

droplets from penetrating but allow water vapours to permeate, resulting in increased

comfort, especially for the sports wear.

Fibre Containing fibrils ofMicrofibres < 1 decitex/denier per

filamentSuper microfibre < 0.3 decitex/denier per

filament
mailto:[email protected]:[email protected]


2/12

Islands of PESIn a sea ofPolystyrene

Solvent

dissolving

0.1 dpf PESSuper-microfibre

Solvent

dissolving

Regular PES0.3 dpf PESSuper-microfibre

Alkali dissolvable PES

Microfibre production method

Conjugate technology

Developed by Kanebo Limited of

Japan, the method involves

spinning of bicomponent

filaments comprising of nylon 6

matrix with polyester fibrils.

After spinning and weaving stages, the fabric is subjected to a solvent swelling

treatment. The poor cohesion in solvent of the polyester fibrils and the nylon matrix

causes the individual wedge shaped polyester segments to move outwards. Each

polyester segment then acts as an individual super microfibre filament.

Sea island technology

The technology is developed by Toray industries of Japan. It

involves the spinning of islands of

polyester in a sea of polystyrene.

Following the weaving and spinning

steps, the polystyrene is dissolved

using chlorinated hydrocarbon solvent

to leave polyester super microfibre

filaments.

Direct melt spinning

In this method, single component

filaments are extruded through

spinerettes. By conventional melt spinning technology, it is possible to produce

microfibres of upto 0.4 dtexpf. Recently, Asahi Kasei and Unitika of Japan have patented

methods, which claims to produce microfibres of 0.1 dtexpf.

Applications of microfibres

The most popular areas of application of microfibres are,

Imitation of silk

Peach skin suedes

Worsted effects

Blends and mixtures with viscose

Air and moisture permeable water proofs

Blends and mixtures with cotton

Wiping cloths (lens wipes)


3/12

Imitation of silk

To produce a synthetic withal the qualities of silk has proved a continuing challenge to

the fibre scientists and technologists. It can be achieved by using combination of variety

of technological innovations.

Property of

silk

Technique used

Lustre Triangular cross sectionDrapability Lowering contact pressure between yarns by alkali weight

reductionSoft feel Ultrafine fibreBulkiness Mixed weaving and combining fibres with self extensionable yarnScrooping sound Introducing irregular shape and microgroovesNatural

appearance

Combining various deniers and modifying and touching shapes in

cross section and/or combining filaments and staples.

Enhancement of the silk like drape and aesthetics can be achieved by subjecting the

woven fabric to a caustic weight reduction process. The development of ultra fine

microfibre filaments has considerably increased the range and aesthetic scope of the

light weight woven polyester silks.

Peach skins and Suedes

A wide range of fabrics from delicate peach skin finishes through to heavy suedes,

similar in handle to chamois leather can be produced using micro-fibres and super micro-

fibres. Different combinations of physical characteristics are made use of to produce

these effects, like,

Combining yarns of widely differing shrinkage characteristics

Combining filaments of differing dtexpf and differing cross sectional shape in

special effect blends

The combined effect of differential shrinkage filaments is to form a micropile during

relaxation and shrinkage, which takes place during fabric processing.

Worsted effects

The combined effect of multi false twisting and air texturising techniques in warp and

weft blends produces interlaced or so called structured fabrics.

Blends with Viscose

High twist microfibres in both polyester and nylon are being used in blends with viscose

to imitate the unique drape and handle of 100% viscose to impart

Considerable reduced shrinkage

Anti crease characteristics


4/12

Tensile strength

Durability

Moisture vapour permeable waterproof effects

Breathable but showerproof effects for casual outwear can be produced by using high

density fibres. The fabrics are either fluorocarbon finished and/or alternatively

polyurethane coated from a solvent such as DMF or MEK, which is subsequently flashed

off. The evaporation of the solvent leaves micropores in the surface coating, which allows

breathability whilst still fully retaining the water proofing effect.

Blends with cotton

The aesthetics, which the microfibre offers like, softness of handle, warmth and moisture

absorbency has a considerable impact on polyester cotton blends. For high quality

shirtings, PES microfibre staple is being used and similar development is expected in

knitgoods particularly in apparel sector.

Wiping cloths (Lens wiping)

The combined effect of ultra fine filaments, very high surface area and the capillary

effect of conjugates which imparts moisture absorbency enables a wide range of wiping

clothes for lenses of cameras and spectacles.

Wet processing

Development of micro-fibre technology is continuing and application of micro-fibres is

increasing in woven and knitted constructions. Depending on the end use, the wet

processing recommendations will vary, however, there are certain factors in each of the

three stages of wet processes, i.e.

Preparation

Dyeing

Finishing

Stage Important factors Attention to

Preparatio

n

Efficient removal of large amounts of fibre

processing aids

Scouring stage invariably has to incorporate

tensionless relaxation to avoid creases and

crows feet marking

Method and machinery

used

Dyeing

Level dyeing and coverage

Light fastness

Build-up of disperse dyes

Fastness of disperse dyes

Dyeing method

Dyeing machinery

Disperse dye selection


5/12

Finishing Surface effects (suedes, peach skins)

Special effect finishes (coatings)

Method and machinery

used

Preparation

Includes three important stages

Desize scour / relax

Pre-setting

Caustic weight reduction

Desize scour / relax

A gentle but efficient preparation stage is very vital to optimise removal of fibre

processing aids and to minimise creasing and maintaining desired aesthetics.

In addition to, or even as a replacement of acrylate or polyester based sizes, largeamounts of oils and waxes are frequently applied to aid fibre processing and help protect

the delicate polyester microfibre fibrils.

The very large surface area of microfibre based fabrics also means that 2 to 5 times

more fibre processing aids need to be applied compared with conventional polyester

based fabrics.

To minimise creasing and maintain desired aesthetics it is necessary to control shrinkage

of microfibre filaments during scouring stage. During relaxation, it is important to

maintain minimum tension.

Important points to be monitored during processing,

Controlled shrinkage under relaxed conditions is vital during preparation

stage

Shrinkage commences at lower wet processing temperatures when fabrics

contain microfibres

Microfibre containing fabrics have a much higher loading of fibre

processing aids

Waxes have a high melting point and inefficient removal at he preparation

stage can cause subsequent spotting problems at the dyeing stage.

Identification of sizes

Before establishing procedure to optimise removal of the fibre processing aid, it is

important to identify the size.

Test Observation Inference

1. Dip sample of grey fabric in

solution of 0.5 % C. I. Basic Red

22

Light to dark red

colour developed

Polyacrylate or

Polyester or

polyvinyl acetate size

present


6/12

Wet out thoroughly

Take out fabric and leave

for 10 seconds in air and rinse in

cold water2. Wash stained fabric withDichloromethane Stain removed Polyester sizeMethanol Stain removed Polyacrylate size

The optimum conditions to remove size, oils and waxes depend on the type of size

present.

Polyester size Polyacrylate sizeAdjust pH to 7 9

With 0.2-0.5 gm/lit soda

ash

or

1.5-2.0 gm/lit disodium

hydrogen phosphate

Adjust pH to 14

With 2.0 5.0

gm/lit caustic

soda

Adjust pH to 10 11

With 1.0 3.0 gm/lit soda

ash

or

1.5 2.0 gm/lit trisodium

phosphate

At pH 7-9, polyester size is removed as a dispersion with the aid of auxiliaries, where as

at pH 14, it is saponified to produce the soluble monomer. The high concentration of

caustic soda is essential to ensure complete saponification of size.

Pre-settingPresetting conditions should be as advised by the fibre manufacturer. Many microfibre

based fabrics dyed without presetting to take account of such factors as high shrinkage,

which are controlled at the preparation or dyeing stage.

Caustic weight reduction

Since 1970s imitation of silks is been done via caustic weight reduction of polyester

filaments. In spite of the introduction of the true microfibres, there are still areas where a

caustic weight reduction is used to further enhance certain properties like, drape and

aesthetics, eliminating the stiffness.

In the caustic weight reduction, the polyester is hydrolysed to produce water soluble

sodium terephthalate and ethylene glycol.


7/12

+ HOCH2CH2OH

Sodium Terephthalate Ethylene Glycol

NaOH2

OCH2 CH2 CO OC

OO

CO OC Na

OO

Na

n

Factors affecting the quality of weight reduction and reproducibility include,

Treatment temperature

Treatment time

Purity of caustic soda

Liquor ratio

Type and concentration of auxiliaries

Cationic agents like quaternary ammonium compounds can be used to accelerate the

rate of weight reduction, but the care is needed to avoid,

Yellowing of treated goods

Lowering of tensile strength

Difficulty in removing cationic residues

Problems arising from very strongly cationic agents extinguishing bacilli in

activated sludge

Washing off techniques

After the weight reduction step, the woven fabric has large amounts of decomposition

products like oligomers, sodium terephthalate and ethylene glycol adhering to its

surface, which are to be efficiently removed. A soaping bath at 90 - 95C is recommended

before dyeing.

Preparation methods

There are number of options when polyester microfibre based woven fabrics are to be

prepared for dyeing, which includes batch-wise or continuous.

Option A: pad batch continuous scour/ relax dyeing

Pad Kleenox PSF liquidor Kleenox AAP liquid

5.0 gm/lit

Fibrolube HML liquid 2.0 gm/lit

Zywet PDG liquid 3.0 gm/litAlkali Depending on


8/12

sizeBatch Optional time between 3 12 hoursContinuous scour /relax

Kleenox PSF liquidor Kleenox AAP liquid

2.0 gm/lit

Zywet PDG liquid 0.5 gm/lit

Soda ash 1.0 gm/lit1st bath 95C

2nd bath 60C

3rd bath 40C4th bath cold rinse

Dye

Option B: continuous scour/ relax dyeing

Continuous scour /relaxPre-wetting tank Kleenox PSF

liquid or

Kleenox AAPliquid

5.0 gm/lit

Fibrolube HMLliquid

2.0 gm/lit

Zywet PDG liquid 3.0 gm/litAlkali Depending on

sizeSecond tank Water at 70C

Dye

Option C: jet scour/ relax - dyeing

Jet Scour /relax

Kleenox PSF liquidorKleenox AAP liquid

2.0gm/lit

Fibrolube HMLliquid

2.0gm/lit

Zywet PDG liquid 0.5gm/lit

Treat at 90C for 20min

Dye

Dyeing processesImportant factors to be considered during dyeing of polyester microfibres are,

Level dyeing

Microfibres have been found to commence dye uptake at lower temperatures than

conventional polyester and the uptake is also faster. This means that the temperature for

starting the dyeing has to be lower than for conventional fibres as well as the rate of rise

of temperature also has to be lower. The high twist yarns used in these high density

fabrics are often difficult to penetrate. Hence, it is important to choose compatible dye

combinations and dyeing auxiliaries, which assist the levelling properties of the dyes.


9/12

Creasing and Crows feet marking

Creasing and Crows feet marking occurs due to uncontrolled change of temperature

during heating and cooling. Good lubricating agent like Fibrolube HML liquid is an

invaluable assistant in avoiding unnecessary crease marks.

Light fastness

As the available surface area in case of microfibres is much higher compared to

conventional fibres, there is a higher exposure of dye to light. It is necessary to use a UV

absorber in addition to careful dye selection.

Dye coverage

Microfibres are often used in combination with conventional polyester. Flat filaments are

often mixed with textured filaments and frequently the cross sections of filaments in yarn

will differ. All these factors contribute to differential dye uptake, giving poor solidity of

shade. Careful selection of dye, control of the dyeing method and proper use of

appropriate dyebath auxiliaries leads to solve this problem to a greater extent.

Abrasion marks

Abrasion marks arise due to improper loading or incorrect selection of machine is or

inadequate removal of oligomers and processing aids during preparation. A good

lubricating agent like Fibrolube HML liquid is mandatory during preparation stage along

with good choice of machinery to obtain good results.

Build up properties

The finer the filaments, the more dye has to be applied to achieve a given depth of

shade. A dye having normal build up on normal polyester can have quite different build

up on microfibres.

Wash fastness

As the quantity of dye used on microfibre is much more compared to conventional

polyester to achieve same shade, the amount of dye to be wash off is also more. This

underlines the importance of proper dye selection and adequate washing off process to

achieve good fastness properties.

Thus, to obtain good level dyeing many factors are to be considered, some of these are,

Correct selection of machinery

Careful control of process parameters

Appropriate selection of dyes and auxiliaries


10/12

During dyeing, even on well-prepared microfibre based fabric, certain factors influence

the actual dyeing process. These are,

Disperse dyes exhaust on microfibres at a much faster rate than on conventional

polyester

Fabrics based on microfibres exhibit much greater shrinkage as the temperature

of dyebath rises

Exhaustion of dyes and shrinkage of yarns occurs at lower temperatures when

compared with conventional polyester based yarns.

Typical comparative dyeing methods are shown schematically as,

Dyeing process

Add at 40C,

Dispa HOT liquid 1.0 gm/lit (anionic dispersant for dye and oligomers)

Fibrolube HML liquid 1.0 gm/lit (lubricating agent with anticrease properties)

Greendye AI liquid 0.5 gm/lit (to maintain pH 4.5 5.5)

Krisil AB liquid or

Gritacol IO liquid 0.5 gm/lit (non-ionic levelling agent)

Add the chemicals and run for 10 mins. Then add dyes (1st portion), run for 5 min, start

raising the temperature from 40C to 90C at 0.5 1.0C per minute and add the

remaining 3 portions of dye at intervals of 2 3 min after 1st addition. Hold at 130C for

20 30 min more than used for normal PES.

Temperature

130oC

90oC

2-3oC/min

60oC

70oC

40oC

1.5oC

1.0oC 2.0oC

1.0oC

30-60 mins

Conventional

PolyesterPolyester microfibre

Time

1-2oC/min


11/12

Thermosol process

Even though PES microfibre articles for the functional sports and leisurewear as well as

fashion sectors are mostly dyed by the exhaust method, the special features of

Thermosol dyeing are also important. Extremely hard woven fabrics tend to result in

surface dyeings, which, provided they are level and fast, may be acceptable. In

laboratory matching this must be taken into account when defining the pick-up and

migration inhibitor. In cases where the dye is fixed at temperatures of 200C and over,

hardening of the woven fabric has been encountered in some cases. This can be

explained by the more rapid penetration of the heat through the very fine portions of the

fibre. Over fixation thus occurs. Temperatures of about 180C suffice to achieve adequate

dye diffusion and even to fix higher amounts of dye. In all cases when new article is to be

dyed it is recommended to carry out pre-trials in the laboratory.

Finishing

Most popular areas where microfibres are used include

Fashionable apparel and outerwear: in fashion sector, natural fibres and viscose

have been extensively used for washed out and emerised effects. Natural fibres, and

particularly viscose, have been popular because of the associated smooth and soft

handle, but potential has been severely restricted because of dimensional stability and

creasing problems. Microfibres play a vital role in overcoming these difficulties.

Application of silicone elastomers like Innersof GTX, Innersof Elasto and Terysil BRK

by padding or exhaust techniques followed by stentering at 170 - 180C is a popular

method of enhancing softness of handle.

Functional sportswear: the high density polyester microfibre based woven fabrics

comprising of flat filament or textured yarns are an ideal basis for water proof effects,

and performance is considerably better than similar constructions based on cotton or

PES/cotton. Microfibres with a fluorocarbon finish, like Hydrogard Conc. even without

coating, can achieve a resistance to water penetration equivalent to a water colulmn of

350 700 mm, which is generally sufficient for ordinary rainwear or skiwear. Their water

Rinse 60o

CR/C 80oCRinse 60oCOption for 2nd R/C for veryheavy shades

60 mins60 mins20 mins40oC

70oC

130oC


12/12

vapour permeability and associated wearer comfort is appreciably better than coated or

laminated fabrics.

Surface effect finishes: the formation of micropile and microloop surfaces, by using

differential shrinkage yarns, results in formation of peach skins and suedes.

Before emerising, it is better to pre-lubricate the fabric with a non permanent softener

and this is best done on fully scoured and relaxed fabric, as it ensures

Better visual appearance after dyeing

Closer control of the emerising operation

References

Sanjay Gupta, Textile Asia, January 1993, 53

Stan Davies, EIU Textile Outlook Internation, January 1990, 65

Documents

Wet Processing of Polyester Microfibres