(a) Two polymer manufacturing processes are shown at A and B below - Leaving Cert Engineering - Question 6 - 2009

A - Sheets of acrylic, mats and floor coverings, etc. B - Thermoplastic products with uniform section such as pipes, curtain rails, tubes, gutters, etc.

A - Calendering: Continuous lengths of sheets are produced in thermoplastics by calendering. The material passes through a series of heated rollers to gradually produce the desired thickness of material. These sheets may then be cut to size or collected in a roll.

B - Extrusion: This process is used to produce items of uniform profile such as curtain rails and plumbing pipes. Plastic granules are fed from a hopper through a tube by a rotating screw. The plastic is heated in the chamber before it enters the die and can be may jet or forced out as it leaves the die. The extruded products can be cut into lengths or cooled. Polythene, PVC and nylon are commonly extruded.

Addition polymerisation produces polyethylene. Long chainlike molecules are formed by the addition of large numbers of mers. The ethylene molecule consists of a strong and weak bond between the carbon atoms. A catalyst or a free radical with an unpaired electron initiates the process, allowing the attachment of ethylene molecules to structurally repeat until termination takes place.

i. Blow moulding: A moulding process used to create hollow shapes, such as bottles. An extruded thick-walled tube, called a parison, is placed in the mould. The mould closes and air is blown into the parison, causing it to take the shape of the mould.

ii. Elastomers: A group of polymers consisting of linear chains that are coiled, entangled, and are subject to minimal cross-linking. This irregular internal structure and bonding arrangement allows these materials to be very elastic at room temperature.

iii. Catalyst: These are substances that speed up or slow down a chemical reaction; they are used to initiate the polymerisation process.