Student Engineer  



Plastics are of a synthetic make up, which means that they are made up of two or more parts, typically its polymers that make up a plastic however additives can be used to alter properties or reduce cost.

Types of plastic
There are two types of plastic, thermoplastic and thermosetting, so what’s the difference?
Thermoplastics are made up of polymers that once heated turn into a soft pliable state which can be shaped, if left to cool in a desired shape the thermoplastic will hold this shape until heated again.

Thermosetting plastics however are permanently cured into shape once heated, re-heating the plastic again will not allow it to be re-shaped, this is caused by cross-linking bonds being formed between the polymers. The cross-linking bonds form molecules with a larger molecular weight which in turn increases the plastics melting point beyond its decomposition temperature, this change means that the plastic will end up destroying itself before it melts which gives the reason why it can’t be re-shaped.

Polystyrene is a cheap, colourless, rigid and brittle plastic, it can be cast into moulds with fine detail. Solid polystyrene is used to make cd cases, disposable cutlery or plastic models. Foamed polystyrene can be used to make packaging, foam cups or insulation.

Bakelite is an early thermosetting plastic which is comprised of a phenol formaldehyde resin. It was used primarily for its ability to resist heat and for its electrical insulation properties. Bakelite-type products are still used today within the electronics and aerospace industry and is produced in sheet, tube and rod form. Bakelite has been altered with additives to form many different commercial grades; these additives have been used to alter its mechanical, electrical and thermal requirements.

Nylon which is referred to as a polyamide is one the most commonly used polymers today.  It is a thermoplastic which was intended to be a synthetic replacement for silk and while prominent in many items of clothing, bedding and carpets, solid engineering grade nylon is used to construct gears, machine screws and other mechanical parts to reduce cost or weight.

Natural rubber is an elastomer made from the milky sap or latex of various tropical plants especially the rubber tree, natural rubber was used mainly for waterproofing cloth in early 1800’s, it wasn’t until Charles Goodyear created vulcanised rubber in 1839. Vulcanised rubber is still used today and is basically natural rubber heated with sulphur which creates cross links between polymers. The addition of these cross links improved the elastic properties and durability of the natural rubber. This kind of rubber is used in, hoses, matting, belts, anti vibration mounts; it is also used as adhesives in some manufacturing industries.

Synthetic rubber acts mainly as a substitute for natural rubber, the benefit of synthetic rubber is that properties can be altered to suit with additives. Synthetic rubber can be made from the polymerization of a variety of monomers including isoprene. © 2019