Thermo-plastic materials like High Density Polythene (HDPE), Poly-Vinyl Chloride (PVC) can be blow moulded into containers of different sizes and shapes. Some of the common items that are produced include buckets, mugs and jerry cans. Buckets, cans and mugs are produced from PVC and that of Jerry cans from HDPE. Their light weight, flexibility, corrosion and chemical resistance have made these plastic products popular for storage and handling of water, petrol, diesel etc.
Combs are an item of daily necessity. In earlier days, combs were made out of ivory, horns of cows and a buffalo, which has now, becomes costly affairs. In recent years, plastic combs are being used increasingly it being convenient to handle and economic. Plastic combs are being produce by using injection moulding machine.
Polythylene is the simplest homo polymer and a thermoplastic. The structure of polyethylene is (CH2 – CH2)n
There are two commercial grades of polyethylene. They are
i) Low density polyethylene (LDPE)
ii) High density polyethylene(HDPE)
iii) Low density polyethylene (LDPE):
LDPE is prepared by polymerisation of ethylene under high pressure (1500 –50,000Psi) and high temperature (350oC) using a trace of oxygen or any peroxide such as benzoyl peroxide as initiator.
· LDPE has a linear structure with extensive branching
· It has a low degree of crystallinity (40%)
· It has a low density (0.912 – 0.935)
· It has a low melting point (110oC)
· It has lower tensile strength, stiffness and hardness
· Its chemical resistance is also poor
High Density polyethylene (HDPE):
HDPE is prepared by coordination polymerisation of ethylene using Ziegler Natta catalyst
[TiCl4 Al(C2H5) 3 in hydrocarbon solvent]
· HDPE is a linear polymer with no branching.
· It has relatively high degree of crystallinity (90%)
· It has high density (0.96)
· It has high melting point (140oC)
· It has high tensile strength, stiffness and hardness.
· It is not attacked by chemicals.
· Films and sheets: A large amount of polyethylene produced is used as packing materials for food and textile.
· Molded articles: It is used for the manufacture of molded articles such as bottles, cans, buckets, toys, tubs, pipes, squeeze bottles etc.
· Insulating material: It is used for wire and cable coating because of its excellent electrical insulation properties.