HEAT SETTING OF MANUFACTURED FIBRES

• SUBMITTED TO- PROF. MUKESH KR. SINGH

• SUBMITTED BY- ARUN KR. MISHRA

INTRODUCTION TO HEAT SETTING

Heat setting is carried out to bring the material to it’s thermal equilibrium the material wouldn’t changes it’s morphology it’s kept at that temperature for a long.

Heat setting is also known as ANNEALING.

The degree of set, a term often used to describe the extent of heat setting is the measure of how close the material has moved to a thermal equilibrium. A 100% set material is considered to be at its thermal equilibrium at a given temperature.

Mechanism of Heat Setting• The setting temperature used is above

Tg. In heat setting, inter-chain bonds, such as hydrogen and dipole bonds, break. This allows the molecular chains to move and adopt new, stress-free positions. New intermolecular bonds then form with the fabric in a relaxed condition at the setting temperature. After cooling, the polymer molecules in the filaments become frozen in place. The new bonds are stable up to the heat setting temperature. The reorganized internal polymer structure, and the material’s dimensions, will be stable.

Purpose of Heat Setting The purpose of heat setting is to dimensionally stabilize fabrics

containing thermoplastic fibers.

Polyester and nylon are the principal fibers involved. Blended polyester/cotton fabrics are produced in large quantities. These fabrics may shrink, or otherwise become distorted either during wet processing or in the consumer's hands. Heat setting is a way of reducing or eliminating these undesirable properties.

The process is relatively simple - pass the fabric through a heating zone for a time and at a temperature that resets the thermoplastic fiber's morphology memory.

Purpose of Heat Setting The new memory relieves the stresses and strains imparted to the fiber by the yarn -

making and weaving processes, and makes stable the configuration it finds itself in flat smooth fabric.

This newly imparted memory allows the fiber to resist fabric distorting forces and provides a way to recover from them.

The time and temperature needed for the heat treatment depend on fabric density and previous heat history of the polyester. Time and temperature must exceed that imparted by previous heat treatments.

Usually 15 - 90 seconds at temperatures of 385 – 415˚F. will suffice. The heat setting equipment can be hot air in a tenter frame, or surface contact heat from hot cans. While the process is simple, careful control is required.

WHY HEAT SETTING IS DONE ….?

Heat setting is a heat treatment by which shape retention, crease resistance & elasticity are imparted to the fibres.

It also brings changes in strength, stretchability, softness, dyeability & sometimes on the colour of the material.

All these changes are connected with the structural & chemical modifications occurring in the fibres.

TYPES OF HEAT SETTING

Heat setting

Temporary heat setting

Semi-permanent heat setting

Permanent heat setting

TEMPORARY HEAT SETTING-

This type of heat setting is destroyed by regular use of material. For ex:- A steam pressed cotton textiles.

SEMI-PERMANENT HEAT SETTING-

In this tye of heat setting material is raised above their glass transition temperature & then set into a new form.

This type of set is maintain in normal use of material however the setting is lost when the material is subjected to severe condition of use.

For ex:- hot washing or steaming of material above Tg.

PERMANENT HEAT SETTING

• This type of heat setting involves change of internal morphology of the material in such a way that it would not revers till the material is destroyed by taking it above it’s melting point.

Heat Set Temperature of some Fibres

Fibre Min T. °C Max. T. °C Time (in seconds)

Polyester (PE) 170 210 15-50

Polyamide PA 6.6 170 210 15-40

Polyamide PA 6 160 180 15-40

Triacetate 160 180 15-40

Acrylic (PAC) 160 180-200 15-40

Elastomers 170 180-200 15-40

Mechanism used for Heat SettingMachines used: Stenters. Fluctuating temperatures inside the stenter cause a consistent variation of

crystallinity in the fibre structure, which leads to different affinity for dyes.

The moisture in the fibre produces soft hand, but variable moisture percentages in the different fabric sections create the above mentioned defect (variable crystallinity).

Too low temperatures do not allow a good setting while too high temperatures and too long

setting times cause yellowing (PA and elastic fibres), stiff hand (acrylics), and loss of elasticity (elastic fibres).

Mechanism used for Heat Setting 5. The presence of combustion gas (NOx) produces a yellowing of

the elastomers.

6. The heat setting process carried out before scouring could fix the stains on the fabric or make the scouring process more difficult due to the modification of the lubricating products (cracking with emission of polluting gas).

7. Heat setting after dyeing could lead to the sublimation of disperse dyes (if not accurately selected).

Points of Concern

Heat setting reduces polyester's dye up take. Heat -set goods dye lighter and slower than non heat -set good.

For uniform shades, side to center, front to back and beginning to end exposure to heat must be controlled and uniform, otherwise these differences will show up in the dyed cloth.

Heat - setting can be done either at the end of wet processing or at the beginning.

At either point, the goods must be free of wrinkles and other distortions otherwise the distortions will be permanently set.

Care must be taken when heat -setting greige goods sized with polyvinyl alcohol.

Points of Concern At high temperatures, PVA will dehydrate, becoming discolored and

insoluble in water.

While greige heat -setting may be particularly beneficial when preparing easily distorted fabrics, one may have to settle for less than the full heat -setting benefit in order to still remove the size.

For these cases, alternate mechanical handling preparation equipment may be the answer.

Heat -setting harshen the hand and stiffens the fabric. The condition is more prone to happen when contact heat is used.

The fabric may become flatter and develop an unwanted gloss or sheen.

References

• Book- VB Gupta & VK Kothari.

• http://www.slideshare.net/sheshir/heat-setting?qid=51840e8d-4fdc-4c2f-a012-753c10478363&v=&b=&from_search=1

• file:///D:/Forms,%20Results%20&%20docs/SEMINAR/NPTEL%20__%20Textile%20Engineering%20-%20Textile%20chemical%20Processing_%20Theory%20and%20practice%20of%20Preparatory%20Processes.html

ThankYou!