The document discusses polyethylene polymerization, defining polymers and their types, along with various classifications based on origin, structure, and polymerization methods. It details the production processes for low-density polyethylene (LDPE) and distinguishes between types of polyethylene such as high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE). Additionally, it outlines the applications of different polyethylene types in industries such as packaging and construction.

1. Polyethylene
Polymerization
Submitted By:
Muhammad Razzaq
Submitted To:
Prof. Dr. Ameer Fawad Zahoor
Roll No:
230805

2. Table of Content
1. What is Polymer and Polymerization?
2. Classification Of Polymers
3. Types of Polymerization
4. What is Polyethylene?
5. Types of Polyethylene
6. Manufacturing of LDPE
7. Applications of Polyethylene

3. Polymer
A polymer is any class of natural or synthetic
substances composed of very large molecules, called
macromolecules, which are multiples of simpler
chemical units called monomers. Polymers make up
many of the materials in living organisms and are
the basis of many minerals and man-made materials

4. Polymerization
It is a process by which monomer units are converted into
polymers. Polymerization reactions are mostly chain
reactions. Examples are polyethene from ethylene,
polystyrene from styrene, polyvinyl chloride (PVC) from
vinyl chloride, polypropylene from propylene, etc.

5. Classification
1) Based on Source of Origin
2) Based on Structure
3) Based on Mode of Polymerisation
4) Based on Molecular Forces

6. Based on Source of Origin
1. Natural polymers
Those polymers which occur in nature. i.e., in plants or
animals. are called natural polymers.
2. Synthetic polymers
The polymers which are prepared in the laboratory are known
as synthetic polymers or man-made polymers, e.g.,
polythene, synthetic rubber, PVC, nylon-66, teflon, orlon etc.
3. Semisynthetic polymers
Polymers obtained by making some modification in natural
polymers by artificial means, are known as semi synthetic
polymers, e.g., cellulose acetate (rayon), vulcanised rubber
etc.

7. Based on Structure
1. Linear polymers
These are the polymers in which the monomer units are
linked to one another to form long linear chains. These
linear chains are closely packed in space. The close
packing results in high densities, tensile strength and
high melting and boiling points. e.g., high density
polyethene, nylon and polyesters are linear polymers.

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2. Branched chain polymers
In such polymers, the monomer units are linked to form long
chains with some branched chains of different lengths with source.
As a result of branching, these polymers are not closely packed in
space. Thus, they have low densities, low tensile strength as well
as low melting and boiling points. Some common examples of
such polymers are low density polyethene, starch, glycogen etc.

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3. Cross-linked polymers or network polymers
In such polymers, the monomer units are linked together
to form three dimensional network. These are expected
to be quite hard, rigid and brittle. Examples of cross
linked polymers are bakelite, glyptal, melamine-
formaldehyde polymer etc.

10. Based on Mode of Polymerisation
1. Addition polymers
The polymers formed by the polymerisation of
monomers containing double or triple bonds
(unsaturated compounds) are called addition
polymers. Addition polymers have the same
empirical formula as their monomers. Addition
polymers can further be classified on the basis of
the types of monomers into the following two
classes:
• Homopolymers
• Copolymers

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2. Condensation polymers
The polymers which are formed by the combination of
monomers with the elimination of small molecules such
as water, alcohol, hydrogen chloride etc., are known as
condensation polymers, e.g., nylon 6,6 is formed by the
condensation of hexamethylene diamine with adipic
acid.

12. Based on Molecular Forces

13. Types of Polymerisation
A. Chain Growth Polymerisation or Addition Polymerisation
It involves formation of reactive intermediate such as free radical, a
carbocation or a carbanion. For this polymerisation monomers used are
unsaturated compounds like alkenes; alkadienes and their derivatives.
Depending upon the nature of the reactive species involved. chain growth
polymerisation occurs by the following mechanisms:
1. Free radical addition polymerisation
2. Cationic polymerisation
3. Anionic polymerisation

14. 1. Free radical addition Polymerisation
The monomers used are generally monosubstituted alkenes. The most
commonly used catalysts are benzoyl peroxide, hydrogen peroxide or t-
butyl peroxide etc. Mechanism The reaction involves the following steps
Chain initiation step:

15. Chain propagation step
Chain termination step

16. 2. Cationic Polymerisation

17. 3. Anionic Polymerisation

18. B. Step Growth Polymerisation
Condensation polymerisation which occurs
in a stepwise manner with elimination of
some smaller molecules like H2O, NH3,
HCI, ROH, etc., is concerned with step
growth polymerisation, e.g., adipic acid
and hexamethylenediamine phenol and
formaldehyde etc., undergo step Growth
Polymerisation.

19. Polyethylene

20. Types of Polyethylene
1. Low Density Polyethylene (LDPE)
2. High Density Polyethylene (HDPE)
3. Linear Low Density Polyethylene (LLDPE)
4. Ultrahigh Molecular Weight Polyethylene
(UHMW)

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1. Low Density Polyethylene (LDPE) –
First polyethylene produced. - As the name implied, it has a lower
density compared to High Density polyethylene. - LDPE has more
branching, hence the molecules are less tightly packed and less
crystalline due to the side branches. - LDPE is also frequently used in
comsumer packaging, bags, bottles, and liners.
2. High Density Polyethylene (HDPE) –
It is a polyethylene made from petroleum. - It is sometimes called
“alkathene” or “polythene” when used for pipes. - HDPE has little
branching, giving it stronger intermolecular forces and tensile
strength than LDPE. - It is also harder and more opaque and can
withstand higher temperatures.

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3. Linear Low Density Polyethylene (LLDPE) –
LLDPE is the most flexible type of polyethylene. - It is a
blended form of LDPE where the film has much more
flexibility, tensile strength, and more comfortability. -
LLDPE is used for films that need a tremendous amount of
strength to absorb impacts without tearing or puncturing.
4. Ultrahigh Molecular Weight Polyethylene (UHMWPE,
UHMW) –
Also known as high-modulus polyethylene (HMPE) or high-
performance polyethylene (HPPE). - It is odorless, tasteless
and nontoxic. - It has extremely long chains, which results in
a very tough material, with the highest impact strength of any
thermoplastic presently made.

24. Process Flow of LDPE Production

25. Individual Process Descriptions
1. Demethanization and Deethanization –
The feed for the process is a mixture of methane,
ethane, and ethylene. Since ethylene is the monomer
to be used ethylene has to be separated from
methane and ethane. High purity ethylene is used
(99.8%).

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2. Compression of Ethylene and Catalyst
Ethylene and the catalyst (free-radical yielding such as
oxygen or peroxide) are compressed to operating pressure
(150 MPa).

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3. Solution Polymerization –
In a tubular reactor maintained at 190°C, solution
polymerization occurs to convert ethylene to polyethylene.
About 30% conversion is achieved per pass.

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4. Pressure Separation –
At this stage, the unconverted
ethylene is removed and
recycled.

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5. Extrusion and Pelletizing –
The polyethylene is extruded and pelletized.

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6. Quench Cooling –
This hardens the polyethylene pellets by addition of cold
water.

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7. Water Separation and Drying –
These involve the removal of water from the pellets to
obtain the final product.

32. Applications
1. LDPE -
Milk, Carton, bowls and buckets, squeezable bottles such
as ketchup containers, cable jacketing, flexible water pipes

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2. HDPE-
Shopping plastic bags, food packing plastics, crates,
dustbin, drums, detergent bottle, , water pipe

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3. LLDPE-
Food and non-food packaging, extrusion coating
applications, garden products, kitchen accessories, luggage
and furniture parts, recreational products and toys

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4. UHMW-
Bulletproof vest, vehicular armor joint and ligament
reconstruction and spinal and maxillofacial implants.

36. References
1. Organic Chemistry by Dr. Younus CH# 14 (Synthetic
polymer)
2. Advance polymer Chemistry by Manas Chanda CH# 1
(Introductory Concepts)
3. https://www.slideshare.net/janapra/polymer-industries
4. https://www.slideshare.net/AlyshaJuguan/polyethylene-
78643472