Saturday, January 4, 2020

POLYPROPYLENE FIBRE, HISTORY OF POLYPROPYLENE FIBRE, CHEMICAL FORMULA OF POLYPROPYLENE FIBRE

POLYPROPYLENE FIBRE:



Polypropylene, is a thermoplastic fibre. It has wide range of applications. It gets used to make the bags for packaging of material. It is used to make fabric for car sheeting, curtains, ropes, carpet, and upholstery fabric.


The polypropylene is   an addition polymer. The propylene is used to manufacture the polypropylene polymer. “ The polypropylene is normally tough and flexible, specially when it gets copolymerized with ethylene”.

The Polypropylene is comparatively very  economical fibre. It  can be made semi-transparent when uncoloured. It can not be as transparent as acrylic and polystyrene.

HISTORY OF POLYPROPYLENE FIBRE

Propylene was first polymerized to a crystalline isotactic polymer by Giulio Natta as well as by the German chemist Karl Rehn in March 1954.
This  pioneer discovery changed the scenario of packaging industries.

The commercial production of isotactic polypropylene started  by the Italian firm Montecatini from 1957 onwards. Later on  Syndiotactic polypropylene was also first synthesized by Natta and his coworkers.

SYNTHESIS OF POLYPROPYLENE POLYMER

When the propylene gets polymerized, the monomers can arrange themselves along the polymer chain in three differents ways. If we denote the CH2 side of the propylene  as head of the monomer and the CH(CH3) side as the tail of the monomer, then following three types of molecular structures get possible during the day polymerisation of the propylene:

Head-to-tail polymerization:

It the polymerization gets occurred in head to tail way, the methyl group (CH3) get located on alternate  carbon atoms.



head-to-head or tail-to-tail polymerisation:

If the polymerization occurred in a head-to-head  or tail-to-tail way, the methyl groups get located on adjacent carbon atoms in pairs.



Random polymerisation:

 In this kind of polymerisation pattern , random orientation of monomer units along the polymer chain takes place. 



These three different structural forms of polypropylene fibre have  different physical properties.

The head-to-tail polymer is produced using heterogeneous Ziegler-Natta or homogeneous cyclopentadienyl-zirconium catalysts. 

There is another type of structural variability in polypropylene that is perhaps a bit more subtle. The  groups around each carbon atom in a polyolefin chain are tetrahedrally oriented. Hence, the chain has three-dimensional structure. Even if we assume a regular head-to-tail polymerization pattern for polypropylene, “the methyl groups (which will be situated on alternating carbon atoms) can adopt different relative orientations with respect to the polymer backbone”. 

ISOTACTIC POLYPROPYLENE:

If all the methyl groups lie on the same side of the chain, the polymer is called isotactic polypropylene. The chemical structure of isotactic polypropylene is given in below figure.


( ISOTACTIC POLYPROPYLENE POLYMER)

SYNDIOTACTIC POLYPROPYLENE:

If the methyl groups alternate in a regular pattern from one side of the chain to the other, the polymer is syndiotactic polypropylene. The chemical structure of syndiotactic polypropylene is given in below figure.


ATACTIC POLYPROPYLENE:

If the orientation of the methyl groups is random, it is called  atactic polypropylene polymer. The chemical structure of atactic polymer is given in below figure.


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