676
autoclave, observed formation of a white, waxy, and light substance. Apparently, a
drop in pressure due to an inadvertent leak and presence of trace amount of oxygen
facilitated the polymerization and formation of this plastic material. This revolutionary plastic substance was later termed as PE. Soon PE found its first commercial
application, and a patent on this polymer was filed by ICI in 1936. In 1944, the real
commercial implementation of PE commenced. Both DuPont and Bakelite
Corporation obtained the license from ICI to start large-scale commercial production of PE. PE possessing excellent commercial value owing to its moisture and
chemical and electrical resistance is one of the major petrochemical products.
Currently, PE is synthesized in a large scale in several countries all over the world
with around 90 million metric tons of production per year. The C2 and C3 olefin
side products emanating from the fluid catalytic cracking units have promoted the
large-scale production of PE.
However, the PE synthesized under free radical condition was low-density PE
(LDPE) and exhibited inferior mechanical properties with low tensile strength and
Young’s modulus along with low melting point and low crystallinity (Table 1). In
presence of a free radical initiator such as peroxides and azobisisobutyronitrile
(AIBN) and under high pressure and temperature conditions, inter- and intramolecular chain transfer to polymer chain resulted in long- and short-chain branching
(Fig. 1). Occurrence of these chain transfer reactions increased the polydispersity
index (PDI), broadened the molecular weight distribution, and lowered the packing
efficiency and density of the samples. As a result, the mechanical properties of
LDPE were compromised to certain extend.
Table 1 Mechanical and thermal properties of HDPE, MDPE, LLDPE, and LDPE
Properties
HDPE
MDPE
LLDPE
LDPE
UTS (psi)
2200–6530
1810–5080
1150–6600
1500–2600
Young’s modulus (10
5 psi)
0.90–2.10
1.16
0.20–2.27
0.28–0.75
Ultimate elongation (%)
3–1900
50–1100
8–1100
100–850
Melting point (°C)
130–140
126–128
75–128
108–121
Flexural modulus (10
5
psi)
0.7–7.0
0.86–1.74
0.02–1.10
0.22–3.20
Density (g/cm
3
)
0.93–1.27
0.93–1.05
0.87–0.96
0.91–0.95
The properties were collected from matweb.com
UTS ultimate tensile strength
HDPE
MDPE
LLDPE
LDPE
Fig. 1 Schematic representation of the polymer chains of high-density PE (HDPE), mediumdensity PE (MDPE), linear LDPE (LLDPE), and LDPE
A. S. K. Sinha and U. Ojha
autoclave, observed formation of a white, waxy, and light substance. Apparently, a
drop in pressure due to an inadvertent leak and presence of trace amount of oxygen
facilitated the polymerization and formation of this plastic material. This revolutionary plastic substance was later termed as PE. Soon PE found its first commercial
application, and a patent on this polymer was filed by ICI in 1936. In 1944, the real
commercial implementation of PE commenced. Both DuPont and Bakelite
Corporation obtained the license from ICI to start large-scale commercial production of PE. PE possessing excellent commercial value owing to its moisture and
chemical and electrical resistance is one of the major petrochemical products.
Currently, PE is synthesized in a large scale in several countries all over the world
with around 90 million metric tons of production per year. The C2 and C3 olefin
side products emanating from the fluid catalytic cracking units have promoted the
large-scale production of PE.
However, the PE synthesized under free radical condition was low-density PE
(LDPE) and exhibited inferior mechanical properties with low tensile strength and
Young’s modulus along with low melting point and low crystallinity (Table 1). In
presence of a free radical initiator such as peroxides and azobisisobutyronitrile
(AIBN) and under high pressure and temperature conditions, inter- and intramolecular chain transfer to polymer chain resulted in long- and short-chain branching
(Fig. 1). Occurrence of these chain transfer reactions increased the polydispersity
index (PDI), broadened the molecular weight distribution, and lowered the packing
efficiency and density of the samples. As a result, the mechanical properties of
LDPE were compromised to certain extend.
Table 1 Mechanical and thermal properties of HDPE, MDPE, LLDPE, and LDPE
Properties
HDPE
MDPE
LLDPE
LDPE
UTS (psi)
2200–6530
1810–5080
1150–6600
1500–2600
Young’s modulus (10
5 psi)
0.90–2.10
1.16
0.20–2.27
0.28–0.75
Ultimate elongation (%)
3–1900
50–1100
8–1100
100–850
Melting point (°C)
130–140
126–128
75–128
108–121
Flexural modulus (10
5
psi)
0.7–7.0
0.86–1.74
0.02–1.10
0.22–3.20
Density (g/cm
3
)
0.93–1.27
0.93–1.05
0.87–0.96
0.91–0.95
The properties were collected from matweb.com
UTS ultimate tensile strength
HDPE
MDPE
LLDPE
LDPE
Fig. 1 Schematic representation of the polymer chains of high-density PE (HDPE), mediumdensity PE (MDPE), linear LDPE (LLDPE), and LDPE
A. S. K. Sinha and U. Ojha