Published on: Mar 4, 2016
Transcripts - Poly ethylene
MONOMER OF POLY ETHYLENE
• The ingredient
or monomer is ethylene (IUPAC name ethene),
a gaseous hydrocarbon with the formula C2H4,
which can be viewed as a pair of methylene
groups (=CH2) connected to each other.
• Because the compound is highly reactive, the
ethylene must be of high purity.
MONOMER OF POLYETHYLENE
STRUCTURE OF POLYETHYLENE
# Most LDPE, MDPE, and HDPE grades have excellent chemical
resistance, meaning that it is not attacked by strong acids or
# It is also resistant to gentle oxidants and reducing agents.
Polyethylene burns slowly with a blue flame having a yellow tip
and gives off an odour of paraffin.
# The material continues burning on removal of the flame
source and produces a drip.
# Crystalline samples do not dissolve at room temperature.
Polyethylene (other than cross-linked polyethylene) usually can
be dissolved at elevated temperatures in aromatic
hydrocarbons such as toluene or xylene, or in chlorinated
solvents such as tri-chloroethane or tri-chlorobenzen.
Polyethylene is a thermoplastic polymer consisting of
long hydrocarbon chains.
Depending on the crystallinity and molecular weight,
a melting point and glass transition may or may not be
The temperature at which these occur varies strongly
with the type of polyethylene.
For common commercial grades of medium- and high-
density polyethylene the melting point is typically in the
range 120 to 180 °C (248 to 356 °F).
The melting point for average, commercial, low-density
polyethylene is typically 105 to 115 °C (221 to 239 °F)
• Ethylene is a rather stable molecule that polymerizes only
upon contact with catalysts.
• The conversion is highly exothermic.
• Coordination polymerization is the most pervasive
technology, which means that metal chlorides or metal oxides
• The most common catalysts consist of titanium(III) chloride,
the so-called Ziegler-Natta catalysts.
• Another common catalyst is the Phillips catalyst, prepared by
depositing chromium(VI) oxide on silica.
• Ethylene can be produced through radical polymerization,
but this route has only limited utility and typically requires
high pressure apparatus
CLASSIFICATION OF POLYETHYLENE
• Polyethylene is classified into several different categories based mostly on
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. With regard to sold volumes, the most important
polyethylene grades are HDPE, LLDPE and LDPE.
• Ultra-high-molecular-weight polyethylene (UHMWPE)
• Ultra-low-molecular-weight polyethylene (ULMWPE or PE-WAX)
• High-molecular-weight polyethylene (HMWPE)
• High-density polyethylene (HDPE)
• High-density cross-linked polyethylene (HDXLPE)
• Cross-linked polyethylene (PEX or XLPE)
• Medium-density polyethylene (MDPE)
• Linear low-density polyethylene (LLDPE)
• Low-density polyethylene (LDPE)
• Very-low-density polyethylene (VLDPE)
• Chlorinated polyethylene (CPE)
BRIEF HISTORY ABOUT POLYETHYLENE
Polyethylene was first synthesized by the
German chemist Hans von Pechmann who
prepared it by accident in 1898 while
When his colleagues Eugen
Bamberger and FriedricH
Tschirner characterized the white, waxy
substance that he had created, they recognized
that it contained long -CH2- chains and termed
it poly methylene.
• #The first industrially practical polyethylene synthesis (diazomethane is a notoriously
unstable substance that is generally avoided in industrial application) was discovered
in 1933 by Eric Fawcett and Reginald Gibson, again by accident, at the Imperial
Chemical Industries (ICI) works in North wHich, England . Upon applying extremely
high pressure (several hundred atmospheres) to a mixture of ethylene and benz
aldehyde they again produced a white, waxy, material. Because the reaction had been
initiated by trace oxygen contamination in their apparatus, the experiment was, at
first, difficult to reproduce. It was not until 1935 that another ICI chemist, Michael
Perrin, developed this accident into a reproducible high-pressure synthesis for
polyethylene that became the basis for industrial LDPE production beginning in 1939.
Because polyethylene was found to have very low-loss properties at very high
frequency radio waves, commercial distribution in Britain was suspended on the
outbreak of World War II, secrecy imposed and the new process was used to produce
insulation for UHF and SHF coaxial cables of radar sets. During World War II, further
research was done on the ICI process and in 1944 Bakelite Corporation at Sabine, Texas
and Du Pont at Charleston, West Virginia, began large scale commercial production
under license from ICI.
• The breakthrough landmark in the commercial production of polyethylene began with the
development of catalyst that promote the polymerization at mild temperatures and
• The first of these was a chromium trioxide–based catalyst discovered in 1951 by Robert
Banks andJ. Paul Hogan at Phillips Petroleum.
• In 1953 the German chemist Karl Ziegler developed a catalytic system based
on titanium halides and organoaluminium compounds that worked at even milder
conditions than the Phillips catalyst.
• The Phillips catalyst is less expensive and easier to work with, however, and both methods
are heavily used industrially. By the end of the 1950s both the Phillips- and Ziegler-type
catalysts were being used for HDPE production.
• In the 1970s, the Ziegler system was improved by the incorporation of magnesiuM chloride.
• Catalytic systems based on soluble catalysts, the metallocenes, were reported in 1976 by
Walter Kaminsky and Hansjörg Sinn. The Ziegler- and metallocene-based catalysts families
have proven to be very flexible at copolymerizing ethylene with other olefins and have
become the basis for the wide range of polyethylene resins available today, including very
low density polyethylene and linear low-density polyethylene.
• Such resins, in the form of UHMWPE fibers, have (as of 2005) begun to replace aramids in
many high-strength applications.
SOME PRODUCT OF POLYETHYLENE