Engineering Chemistry S Datta

450 ENGINEERING CHEMISTRY
Recycle ethylene
Ethylene
Primary
compressor
Hypercompressor
Catalyst
Cooling tower
High-pressure
separator
Low-pressure
separator
Polyethene
pellets
Dryer
Water
Cold water
Separator
Extruder and pelletizer
Quench cooler
Fig. 20.8 Low-density polyethylene by high-pressure processing (LDPE).
Compressor
Compressor
Fluid-bed
reactor
Ethylene
Cycle
cooler
690 to
2100 kPa
100°C
Purge
Comonomer
Catalyst
Lock
Separator and
product discharge
Ganular
Nitrogen
polyethylene
Fig. 20.9 High-density polyethylene by low-pressure resins (HDPE).
Polyethylene has highly symmetrical structure so it crystalizes easily. The degree of
crystallinity varies from 40-95% depending on degree of branching. LDPE has a branched
structure and hence is flexible and tough. It has low sp. gr. It has low hardness i.e., about 1/10th
of bakelite.
HDPE is a completely linear polymer, it has better chemical resistance, higher softening
point, greater rigidity but low impact strength and it is opaque and relatively brittle.
Uses. Polythene sheets, tubes are manufactured, which are used for domestic purpose.
It is also used to prepare toys, coated-wires and cables, bags for packing, bottles, caps, insulator
parts.