➢ Polyethylene was first synthesized by the German chemist Hans von Pechmann, who prepared it

by accident in 1898 while investigating diazomethane…

，

➢ When his colleagues Eugen and Friedrich characterized the white, waxy substance that he had
created, they recognized that it contained long −CH2− chains and termed it polyethylene

02
➢ Polyethylene has become the most important polyolefin plastic with excellent mechanical
properties, processing properties and chemical stability. It is used in the production of film,
packaging and pipe.，

➢ It is a thermoplastic polymer with variable crystalline structure and an extremely large range of
applications

➢ It is available in a variety of grades and formulations to suit different needs. In general,

polyethylene's offer excellent chemical and impact resistance, electrical properties and low
02
coefficient of friction.
➢ Polyethylene is prepared by heating ethylene to 473K under a pressure of 1500 atm. This
occurs as free radical mechanism which is initiated by oxygen.
Polymerization of ethylene to polyethylene is described by the following
chemical equation:

n CH2=CH2 (gas) → [−CH2−CH2−]n

ΔH/n = −25.71 ± 0.59 kcal/mol (−107.6 ± 2.5 kJ/mol)

Initiation
➢ Dissociation of the peroxide's oxygen bonds leads to a temporary intermediate, which
then is quickly converted into carbon dioxide and 2 radicals

➢ These radicals can then act as electrophiles and attack the double bond of ethylene
forming a stabler intermediate:
Propagation
➢ The newly formed radical can add on to itself by attacking another ethylene molecule:

Termination
➢ Finally the reaction is terminated when two radicals react with each other to produce a
product with paired electrons:
Mechanical

➢ Polyethylene is of low strength, hardness and rigidity, but has a high ductility and impact
strength as well as low friction.
➢ It shows strong creep under persistent force, which can be reduced by addition of short
Mechanical
fibers. It feels waxy when touched
Thermal
➢ The commercial applicability of polyethylene is limited by its low melting point
compared to other thermoplastics.
➢ For common commercial grades of medium- and high-density polyethylene the
melting point is typically in the range 120 to 130 °C (248 to 266 °F).
➢ The melting point for average commercial low-density polyethylene is typically 105 to
115 °C (221 to 239 °F).
➢ These temperatures vary strongly with the type of polyethylene, but the theoretical
upper limit of melting of polyethylene is reported to be 144 to 146 °C (291 to 295 °F).
Combustion typically occurs above 349 °C (660 °F)
Chemical
➢ Polyethylene consists of nonpolar, saturated, high-molecular-weight hydrocarbons. Therefore, its
chemical behavior is similar to paraffin. The individual macromolecules are not covalently linked.
Because of their symmetric molecular structure, they tend to crystallize
➢ Most LDPE, MDPE, and HDPE grades have excellent chemical resistance, meaning that they are
not attacked by strong acids or strong bases and are resistant to gentle oxidants and reducing
agents.
➢ Polyethylene absorbs almost no water; the gas and water vapour permeability (only polar gases)
is lower than for most plastics. Oxygen, carbon dioxide and flavorings, on the other hand, can
pass it easily.
➢ PE can become brittle when exposed to sunlight.
➢ Polyethylene burns slowly with a blue flame having a yellow tip and gives off an odour of paraffin
Electrical
➢ Polyethylene is a good electrical insulator.
➢ It offers good electrical treeing resistance; however, it becomes easily electrostatically charged
(which can be reduced by additions of graphite, carbon black or antistatic agents).
➢ When pure, the dielectric constant is in the range 2.2 to 2.4 depending on the density and the
loss tangent is very low, making it a good dielectric for a capacitor
 LDPE LLDPE HDPE

Linear Low Density

Polymer Full Name Low Density Polyethylene High Density Polyethylene
Polyethylene

High Degree of short chain branching + High Degree of short chain Linear (or Low degree of short
Structure
long chain branching branching chain branching)

Ziegler-Natta catalyst in:

Using radical polymerization using Using Ziegler-Natta catalyst or - Single-stage polymerization
Catalyst and process
tubular method or auto clave method metallocene catalyst - Multi-stage polymerization
or a Cr or Phillips-type catalyst

Density 0.910-0.925 g/cm3 0.91-0.94 g/cm3 0.941-0.965 g/cm3

 High crystalline and low
Low crystalline and high amorphous (less Semi-crytalline, level
Crystallinity amorphous (>90%
than 50-60% crystalline) between 35 to 60%
crystalline)

•Flexible and good transparency •Excellent Chemical

•Good moisture barrier properties •As compared to LDPE, it Resistance
•High impact strength at low has:higher tensile strength •High tensile strength
Characteristics
temperature •higher impact and •Excellent moisture
•Excellent resistance to acids, bases puncture resistance barrier properties
and vegetable oils •Hard to semi-flexible

Recycling Code
Commercial Products LDPE Grades LLDPE Grades HDPE Grades

✓ Molecular weight
distribution is relatively
✓ High performance bags,
narrow, has applications
cushioning films,
➢ Shrink wrap in injection moldings or
✓ Tire separator films,
➢ Films flat yarns, and the latter
industrial liners
➢ Squeezable bottles type
General Applications ✓ Elastic films
➢ Garbage bags ✓
✓ Ice bags
➢ Extrusion moldings, and Molecular weight
✓ Bags for supplemental
laminates distribution is wide, is
packaging and garbage
used to make film
bags
products, hollow plastic
products and pipes
➢ PE is a thermoplastic; however, it can become a thermoset plastic when modified (such as cross-
linked PE)
➢ PE is classified by its density and branching. Its mechanical properties depend significantly on
variables such as the extent and type of branching, the crystal structure, and the molecular
weight.
➢ Mechanical properties such as hardness and tensile strength can be improved by the addition of
the fiber/filler.
➢ It is available in a variety of grades and formulations to suit different needs.
➢ Polyethylene plastic production process
August 2018
Insight - Material Science 1(1):1
https://www.researchgate.net/publication/335656841_Polyethylene_plastic_production_process

➢ Polyethylene: Preparation, Structure, And Properties

Sundar L. Aggarwal
and Orville J. Sweeting
Cite this: Chem. Rev. 1957, 57, 4, 665–742
Publication Date:August 1, 1957
https://doi.org/10.1021/cr50016a004
➢ Polyethylene fibers-polyethylene matrix composites: Preparation and physical properties
Albert Teishev,Silvia Incardona,Claudio Migliaresi,Gad Marom
First published: 15 October 1993
https://doi.org/10.1002/app.1993.070500314

➢ Compendium of Polymer Terminology and Nomenclature – IUPAC Recommendations 2008 (PDF).

Retrieved 28 August 2018
➢ Geyer, Roland; Jambeck, Jenna R.; Law, Kara Lavender (1 July 2017). "Production, use, and fate of
all plastics ever made". Science Advances. 3 (7):
e1700782. Bibcode:2017SciA....3E0782G. doi:10.1126/sciadv.1700782. PMC 5517107. PMID 2877
6036