Plastics

Plastics are natural/synthetic materials. They are produced by chemically modifying natural substances or are synthesized from inorganic and organic raw materials. On the basis of their physical characteristics, plastics are usually divided into thermosets, elastomers and thermoplastics. These groups differ primarily with regard to molecular structure, which is what determines their differing thermal behaviour. The following Table lists the characteristics of the various types of plastics:

Plastics are versatile and flexible materials and they may be very suitable for use in your project. This may be an area of materials research that you need to investigate in detail. It is important that you read the information below and consider the type of plastic that will best suit your project, here you have some examples of plastics used in actual life:

EXAMPLES OF THERMOSETTING PLASTICS

Many adhesives (glues) are thermosetting plastics. A good example is ‘Araldite’ which is an epoxy resin that hardens when a second chemical is added (a catalyst). It will bond most materials including woods and metals as well as some plastics.

Polyurethane. This forms the basis of many paints and varnishes because it is very tough and has water resistant qualities.

Melamine Formaldehyde. Used in the production of plastic laminates because of its smooth surface and hygienic qualities. It is also used in electrical plugs and sockets because it can be cast and it is an excellent insulator.

Polyester resins. If resins are combined with a material such as fibre glass the result is a very tough material that can resist impact. This type of material is known as a glass reinforced plastic (GRP) and is used in car body repairs, sailing boats, corrugated sheet because of its lightness, toughness and resistance to water.

SOME EXAMPLES OF THERMOPLASTICS         

These plastics possess a common property, they soften when heated and are often used in schools to vacuum form shapes. Usually, when heated and formed into a shape - if reheated they return to their original shape.

Acrylic. (Known also as PERSPEX) This is the most common plastic in a school workshop. It is purchased usually in the form of sheets and comes in a range of colours. It can be translucent (e.g. smoked), transparent or opaque. It is resistant to most acids and weather conditions.

Polythene. Can be moulded into almost any form due to its excellent moulding qualities. Used for the production of bottles, bowls, toys, tube etc... It is available in large sheets. There are two types: High density which is rigid and hard, and low density which is tough and flexible. Machine parts are generally made from high density polystyrene whilst bottles are made from the low density polystyrene.

Polyvinyl Chloride. Better known as PVC. It is a tough material which can be purchased as a hard material or alternatively a flexible form. It can be welded or bonded with an adhesive. It has a range of uses including water pipes, raincoats, long play records, coating on electrical wires and many more.

 Expanded Polystyrene. An efficient insulator used in cavity walls and as decorative tiles and covering on ceilings. It can also be used for basic model making.

Nylon. Is used in engineering to make gears and bearings. It’s oily nature means that friction is reduced between moving parts made from nylon.

HOW DO WE RECOGNIZE DIFFERENT TYPE OF PLASTICS?

 In the following table you can find different ways of recognizing thermoplastics by burning them and observing things such as the smell and the smoke.