Question

Answer the following

How is polythene manufactured? Give their properties and uses.

Answer 1

i. LDP is prepared by polymerization of ethylene under high pressure (1000 - 2000 atm) and temperature (350 - 570 K) in presence of traces of O₂ or peroxide as initiator.

\[\ce{{n} CH2 = CH2->[Traces of O2 or][peroxide at 350-570 K, 1000 - 2000 atm] LDP}\]

ii. The mechanism of this reaction involves free radical addition and H-atom abstraction. The latter results in branching.

iii. Polymeric chains are loosely held due to branching and the polymer has low density.

iv. Properties of low-density polyethylene:

a. LDP films are extremely flexible but tough, chemically inert, and moisture resistant. b. It is a poor conductor of electricity with a melting point 110 °C.

v. Uses of low-density polyethylene:

a. It is mainly used in the preparation of pipes for agriculture, irrigation, domestic water line connections as well as insulation to electric cables.

b. It is also used in submarine cable insulation.

c. It is used in producing extruded films, sheets, mainly for packaging and household uses like in preparation of squeeze bottles, attractive containers, etc.

vi. HDP is a linear polymer with high density due to close packing.

vii. It is obtained by polymerization of ethene in presence of Zieglar-Natta catalyst, which is a combination of triethyl aluminium with titanium tetrachloride.

viii. Polymerization of ethene is carried out at a temperature of 333 K to 343 K and a pressure of 6-7 atm.

\[\ce{\text{n} CH2 = CH2 ->[333K - 343K][6-7 atm, catalyst] HDP}\]

ix. Properties of high-density polyethylene:

a. HDP is crystalline, melting point in the range of 144 - 150 °C.

b. It is much stiffer than LDP and has high tensile strength and hardness.

c. It is more resistant to chemicals than LDP.

x. Uses of high-density polyethylene:

a. HDP is used in the manufacture of toys and other household articles like buckets, dustbins, bottles, pipes, etc.

b. It is used to prepare laboratory wares and other objects where high tensile strength and stiffness is required.