TOPIC: PRODUCTION OF MATERIALS IV
SUB-TOPIC : PLASTICS AND RUBBER
PRODUCTION OF PLASTICS
Plastic is made from the raw materials called “Synthetic Resins” obtained from Petroleum, but some resins are obtained from Coal, Cotton, Wood and Natural Gas. STAGES OF PLASTIC PRODUCTION
POLYMERIZATION : is a process of making solid polystyrene from resins by heating. Additives are added to improve the properties of the plastic resins.
Common additives are:
Reinforcement : used to give extra strength and unbreakable quality to plastic.
Filler : used to improve plastic quality.
Plasticizer : used to make resins softer, flexible and easier to shape inside moulds.
Pigment : used to give beautiful appearance to make plastic available in variety of colours.
SHAPING : This is the process of forming plastic into different shapes. Shaping is done when the raw materials soften at very high temperature inside the moulding machine. The methods mostly used are :
Compression Moulding : used for moulding thermosetting plastics like pot handles, spoon handles, knife handles, etc.
Injection Moulding : used for moulding thermoplastics like rulers, set-squares, etc
Extrusion : is the same as injection moulding with exception that the molten resin is forced out through a shaping die. This method is used to produce pipes, rods, wire sheathing, garden house, etc.
Blow Mouding : Here, molten resin is placed inside a mould, compressed air or steam is forced into the molten resins. It expands and forces the resin against the walls of the mould. The product is allowed to set and the mould is opened for the product to be out. This method is used to produce hollow objects like bottles, kegs, etc.
Calendering : used to produce a continuous plastic sheets by pressure molten plastics between pairs of heated rollers, e.g. table cover.