Sunday, December 15, 2019

POLYESTER FIBRES PRODUCTION

MANUFACTURING OF POLYESTER FIBRE:

Polyester fibre is produced as follows:

SYNTHESISATION OF POLYMER:

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

1- Terephthalic acid. 

2 - Dimethyl terephthate. 

3 - Ethylene glycol. 

CONDENSATION POLYMERISATION:

PRODUCTION OF POLYETHYLENE TEREPHTHELATE 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 vaccume) during actual polymerization. A catalyst is used to accelerate the speed of reaction. The antimony oxide is used as a catalyst in this reaction. The polyester polymer is formed. The half of the ethane-1,2-diol is  also regenerated. This is removed and recycled.

PRODUCTION OF POLYETHYLENE TEREPHTHELATE BY USING DMT:
   


Condensation Polymerization:

When acid and alcohol get reacted in a vacuum at very high temperatures. The polythene terephthate 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 of  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  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 weigh 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 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 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 required extent. In this way desired denier of filaments are achieved. These filaments are wound onto the spools. The filaments are also passed through creeping rollers to obtain creeping effect in the fibre. After creeping fibres pass through heat-setting process then cut into pieces of required staple length. Since the drawing process provides extra orientation to filaments, sothat  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)


You may also be interested in following articles:

Production process of nylon 66

Elastane or spandex fibre production ( lycra and dorlastane

Soy protein fibre ( a renewable fibre

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1 comment:

  1. Polymerisation is a chemical process that combines several monomers to form a polymer or polymeric compound. But polymerization is an important chapter if you want to perform good marks in exams. There are a lot of ways to learn if you are not good in this subject. Online Chemistry Tuition is one of them. You can easily get the study material from online websites. Chemistry Tuition provides notes with video tutorials also.

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