POLYESTER FIBRES PRODUCTION

MANUFACTURING OF POLYESTER FIBRE:

Polyester fibre is produced as follows:

SYNTHESISATION OF POLYMER:

The polyethene terephthalate is used as a condensation polymer. The polyester polymer is commercially produced by condensation polymerization of ethylene glycol with either dimethyl terephthalate or terephthalic acid. -

1- Terephthalic acid. 

2 - Dimethyl terephthalate. 

3 - Ethylene glycol. 

CONDENSATION POLYMERISATION:

PRODUCTION OF POLYETHYLENE TEREPHTHALATE BY USING PTA:

In condensation polymerisation, during the joining of monomers together a small molecule is eliminated. “A polyester is made by a reaction involving an acid with two -COOH groups, and an alcohol with two -OH groups”. The reaction follows below chemical equation:

This reaction takes place in two main stages, a pre-polymerisation stage and the other actual polymerisation. In the first stage, before polymerization takes place, a fairly simple ester is results between the acid and two molecules of ethane-1,2-diol.

In the actual polymerisation stage, this is heated. The temperature of about 260°C gets achieved. The pressure is kept very low (almost vacuum) during actual polymerization. A catalyst is used to accelerate the speed of the reaction. Antimony oxide is used as a catalyst in this reaction. The polyester polymer is formed. Half of the ethane-1,2-diol is also regenerated. This is removed and recycled.

PRODUCTION OF POLYETHYLENE TEREPHTHALATE BY USING DMT:

   

Condensation Polymerization:

When acid and alcohol get reacted in a vacuum at very high temperatures. The polythene terephthalate results in condensation polymerization. Once the polymerization has occurred the material is extruded onto a casting trough in the form of a ribbon. When the polymer gets cool, the polymer ribbon gets hardened.  Now, this is cut into polymer chips.

FIBRE FORMATION:

The polymer chips need to dry well before using them for melt-spinning. A hopper reservoir is used to melt the polymer chips. The chips are heated, and extruded through spinnerets and are cooled by bringing the filaments in contact with the air. It is then loosely wound on the spools.

SPINNING PROCESS:

The degree of polymerization of polyester polymer is controlled, depending on its end-uses. Polyester polymer being to be used in industrial fibres has a higher degree of polymerization, high molecular weight and high viscosity. “The normal molecular weight ranges between 15,000 and 20,000”. With the normal extrusion temperature (280°C-290°C), it has a low shear viscosity is 1000-3000 poise. Low molecular weight polyester polymer is spun at 265°C, whereas ultrahigh molecular weight polyester polymer is spun at 300°C or above. Generally, the degree of orientation is directly proportional to the wind-up speeds in the spinning process. Theoretically, the maximum orientation along with the increase in productivity is obtained at a wind-up speed of 10,000metres/minute. Although due to a voided skin, adverse effects may appear at wind-up speeds above 7000metres /minute.

DRAWING PROCESS:

The fibres obtained after melt-spinning are coarse and uneven. Thus these fibres need to draw. The drawing process is carried out at a temperature above the glass transition temperature (80°C-90°C). The fibres coming out from spinnerets are stretched in hot condition to about five times their original length with the help of drawing rollers. The diameter of filaments is reduced to the required extent. In this way, the desired denier of filaments is achieved. These filaments are wound onto the spools. The filaments are also passed through creeping rollers to obtain a creeping effect in the fibre. After creeping fibres pass through the heat-setting process then cut into pieces of required staple length. Since the drawing process provides an extra orientation to filaments so that the draw ratio (3:1-6:1) vary according to the final end-uses. “The higher draw ratio is used to achieve high tenacity”. In addition to orientation, crystallinity may be developed during the drawing at the temperature range of 140°C-220°C 

(FLOW CHART OF POLYESTER FIBRE PRODUCTION)

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