A Mr BTec Book Plastics
3 Plastics 25 recycled bottles are enough to make one pupil blazer. Anon
What are Plastics? Plastics are the most widely used material in commercial production. Plastics can be created from two main sources which are natural and synthetic materials. Source One - Natural plastics: includes amber which is fossilised tree resin, latex which is a form of rubber. Source Two - Synthetic plastics: are chemically manufactured from carbon based materials such as crude oil, coal and gas. Image: Fossilised Amber. Image: Extracting Rubber from a rubber tree. Movie 1.1 Tapping Rubber from a Tree Pinch to expand and watch this video fullscreen. 2
Plastics, Fuels and Chemicals Made from Crude Oil. Oil refineries refine oil in massive quantities, to produce the fuels we need. These include diesel, petrol and heating oil. However, some of the raw materials we need to manufacture plastics, are also extracted from oil at the refinery. When crude oil is refined, four percent ends up as raw materials for the production of plastics. Oil is used widely for the production of plastics as it is composed of carbon and hydrogen. This is why oil is called a hydrocarbon. Oil and natural gas are the most important raw materials for plastics manufacture. To the plastics industry, Naphtha is the most important fraction distilled from crude oil. It is used in the production of a range of plastics. 3
The Oil Refinery. Crude oil is virtually unusable in its unrefined state. It is composed of a mix of hydrocarbons, each with a different number of carbon atoms. The hydrocarbons are different in weight, with the lightest being propane (gas) and heaviest asphalt (used on roads). Extracting the various hydrocarbons from crude oil is a formidable challenge and this process takes place in an oil refinery. The process is called distillation. The distillation process takes place at an oil refinery in a distillation Tower. An example is seen on page 5. When crude oil is refined it is distilled into fractions. Each hydrocarbon extracted from crude oil, is called a fraction. The refining process is also called the cracking process. Crude oil is heated to over 370 degrees Celsius and tit is pumped into the base of the distillation tower. The crude oil vaporises and rises up the tower. As it cools the molecules condense, with heavier molecules of asphalt, bitumen and tar at the bottom and lighter molecules such as diesel, petrol and aviation fuel at the top. At each level, the condensed hydrocarbons are siphoned off. 4
The fractions / hydrocarbons produced include gas, petrol, diesel, heating oils, naphtha (important for plastics), ethylene and polyethylene. Bitumen / asphalt is also produced, as a residue. A Distillation Tower Example Cracking Process in a Distillation Tower Movie 1.2 How Crude Oil Cracking Works. Pinch to expand and watch this video fullscreen. 5
The Science Behind Plastics Remember, all Plastics are Polymers. Plastics are versatile and flexible materials and they may be very suitable for use in many projects in school. This may be an area of materials research that you need to investigate in detail. All plastics are based on polymers and they are created by bonding molecules together. A monomer is a relatively small molecule that can chemically bond to other monomers, forming a polymer. Remember, all plastics are polymers. The terms monomer and polymer are very important in the plastics industry. 6
A MONOMER is a small molecule that combines chemically to other monomers to form a polymer. Groups of Plastics. There are two groups of plastic, thermosetting plastics and thermoplastics. Thermoplastics Thermoplastics can be heated and shaped many times. Thermoplastics will soften when it is heated and can be shaped when hot. The plastic will harden when cooled, but can be reshaped because their is no links between the polymer chains. Example - derived from oil - a hydrocarbon ethylene molecule(seen above). Many modern plastics are manufactured from oil. An ethylene monomer forms a long chain monomer due to individual ethylene monomers joining together. This produces the polymer - polyethylene. Thermosetting plastics Thermosetting plastics can only be heated and shaped once. If re-heated they cannot soften as polymer chains are interlinked. Separate polymers are joined in order to form a huge polymer. The main thermosetting plastics are epoxy resin, melamine formaldehyde, polyester resin and urea formaldehyde. This is a thermoplastic and is useful in the manufacture of 'plastic' bottles. If this science stuff is in here it must be important! 7
Example Thermosetting Plastics. Many adhesives (glues) are thermosetting plastics. An 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. 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. 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. Urea Formaldehyde (UF): Urea Formaldehyde has physical properties of high hardness and high toughness, making it suitable for strong, knock-resistant electrical fittings. It is also scratch resistant and a very good electrical insulator, making electrical fittings manufactured from this polymer safe to use. 8
Example 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. 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. 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. Polyethylene. The most common plastic in everyday life. Used in the manufacture of 'plastic' bottles, grocery bags, shampoo bottles and children's toys. Polycarbonate. This is a thermoplastic which means it can be shaped and formed through a number of manufacturing processes. It machines well and can be solvent bonded and welded. It is tough and resistant to damage which is an ideal property for a mobile phone. If dropped, a mobile phone with a polycarbonate casing is likely to survive undamaged. It is an insulator, often used to insulate electrical circuits.it is supplied in a range of colours. 9
Other Useful Plastics. Styrofoam. This is a light-weight dense foam. It is easy to shape with saws, files and abrasive paper and is ideal as a model Nylon. Is used in engineering to make making material. gears and bearings. It s oily nature means Expanded Polystyrene. An efficient insula- parts made from nylon. that friction is reduced between moving tor used in cavity walls and as decorative tiles and covering on ceilings. It can also be used for basic model making. Gallery 1.1 Plastics and their Uses. Polyurethane Floor Varnish (Thermoset) 10
Summary & Quick Guide Plastics can be a complicated area to grasp and remember. Their are loads of types of plastics and this book should help with any research or revision you may have. Manufacturing processes will be covered in another book later in the series. Plastics are all around us and their production and use has really changed the way our world is in a big way. Look at the labels on your blazer, tie or jumper. See any words you now recognise from this book? Recycling and sustainability is an important area to consider when we think of using plastics for products. Coal, Oil and Gas are not renewable resources so, like trees and metal ore s, the environmental impact from production to disposal MUST be considered in the design of any product. 11
Common Thermosetting Plastics 12
Common Thermoplastics 13
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