Resistant Materials Plastics These icons indicate that teacher’s notes or useful web addresses are available in the Notes Page. This icon indicates that the slide contains activities created in Flash. These activities are not editable. For more detailed instructions, see the Getting Started presentation. 1 of 31 © Boardworks Ltd 2005 Learning objectives Learning objectives To understand the differences between thermoplastic and thermosetting plastics. To become familiar with the properties of different types of plastic, and know what each is typically used for. To be aware of the origins of plastics and with the range of industrial processes used to manufacture plastic products. 2 of 31 © Boardworks Ltd 2005 Plastics There are two main groups of plastics: thermosetting plastics thermoplastic plastics. Thermoplastic plastics: The word What does the ‘plastic’ means word ‘plastic’ ‘easily shaped or mean? moulded’. Formed by heat Soften when heated Made of long polymer chains with few cross links Can be reheated and reshaped Mostly recyclable 3 of 31 © Boardworks Ltd 2005 Plastics Thermosetting plastics: Initially set by heat Consist of polymer chains with strong bonds between each chain Strong and durable Cannot be reshaped once set Common in powder or resin forms What items do you have in your possession that are made of plastic? Are they made from thermoplastic or thermosetting plastics? 4 of 31 © Boardworks Ltd 2005 Plastics Thermoplastic plastics are made of long chains of polymers which don’t cross over very often. When heated, the molecules slip easily over one another. Thermosetting plastics also have lots of long chain molecules, but there are links between them. These cross links prevent the molecules from moving over one another. individual monomer molecule individual monomer molecule Which of these diagrams depicts a thermoplastic and which depicts a thermosetting plastic? 5 of 31 © Boardworks Ltd 2005 Thermoplastic plastics The majority of common plastics are thermoplastics. Thermoplastics can be heated and reshaped because of the ways in which the molecules are joined together. This can be repeated many times (as long as no damage is caused by overheating). Heat Harden Soften Cool 6 of 31 © Boardworks Ltd 2005 Thermoplastic plastics 7 of 31 © Boardworks Ltd 2005 Thermosetting plastics Thermosetting plastics are those which are set with heat and have little elasticity. Once set, they cannot be reheated and reformed. Burn They are heated and moulded during manufacture. Once cooled, they will not soften again when heated. This breaks the potentially unending cycle that thermoplastic plastics are capable of. If heated too much, they burn. 8 of 31 Heat Harden Soften Cool © Boardworks Ltd 2005 Thermosetting plastics 9 of 31 © Boardworks Ltd 2005 Uses of plastics (thermoplastics) Here are some common products made from thermoplastics. Can you say which type of thermoplastic each one is made of? Polystyrene Polypropylene High density polythene Low density polythene ABS Acrylic Why do thermoplastics make good materials for What other usesthese do these thermoplastics have? products? 10 of 31 © Boardworks Ltd 2005 Uses of plastics (thermosets) Thermosets have different qualities to thermoplastics. Can you say which thermoset each of these products is made from? Epoxy resin Melamine formaldehyde Phenol formaldehyde Urea formaldehyde GRP Why are thermosets good materials for these What other uses do these thermosets have? particular products? 11 of 31 © Boardworks Ltd 2005 Working with plastics – considerations 12 of 31 © Boardworks Ltd 2005 Why do we use plastics? Think of five reasons why we use plastics. How many of them are mentioned below? They can be shaped into very complex shapes. They are soft to the touch. They are tough and durable. They are strong. They can be shaped easily, quickly and cheaply. They are light in weight. They are available in a large range of colours. 13 of 31 © Boardworks Ltd 2005 Early and modern plastics Plastic materials were first used at around 2000BC. Plastics can occur naturally in trees or even milk; amber is an example (a resin from trees and insects). Amber was used by early Egyptians to make jewellery and is still used for this purpose today. Today, numerous different plastics are available. Some are still made from natural materials but most modern plastics are manufactured from chemicals obtained from crude oil. Plastics manufacturers convert chemicals into plastics. What implications do you think this has for the environment? 14 of 31 © Boardworks Ltd 2005 Oil - the raw material for plastics Pump Pipeline Oil well Layers of rock Gas Oil 15 of 31 We obtain crude oil from under ground, either on land or at sea. After it has been pumped, it is heated in a fractioning tower and broken down into chemicals. The chemicals consist of nitrogen, carbon, chlorine, sulfur and water. © Boardworks Ltd 2005 The birth of plastics 16 of 31 © Boardworks Ltd 2005 Acrylic Acrylic is available in many different colours. It comes in sheets or as round rods. Acrylic is stronger than glass, but scratches easily. It is also used to make many outer cases for toys. These properties make acrylic ideal for shop signs. Acrylic can resist the weather very well. It can be softened and bent, blown or twisted into many different shapes. 17 of 31 © Boardworks Ltd 2005 Polystyrene foam Polystyrene foam can be easily shaped and is very light. This makes it suitable for modelling three-dimensional objects. Which other uses for polystyrene can you think of? 18 of 31 © Boardworks Ltd 2005 Bakelite – a very early plastic Bakelite was one of the first artificial plastics and was created in 1909 by Leo Baekeland. It is used for telephones, radios and electrical equipment. Bakelite is a hard, brittle plastic that has a natural dark glossy colour. It resists heat without softening. It is a good thermal insulator and a good electrical insulator. When overheated, it burns and smells. 19 of 31 © Boardworks Ltd 2005 Melamine Melamine plastics have similar properties to Bakelite. However, they have the added advantage of being able to be coloured during processing. Melamine formaldehyde Urea formaldehyde Melamine formaldehyde and urea formaldehyde are two types of melamine plastics. 20 of 31 © Boardworks Ltd 2005 Polyester resin Polyester resin is a chemical hardener. Polyester resin can be reinforced with glass fibre. It will set at room temperature. Glass-reinforced polyester resin or glass-reinforced plastic (GRP) is used for making motor cycle fairings and boats. When set, the plastic is stiff, hard and brittle. When working with it in large projects, it is advised to use gloves and a chemical respirator to protect yourself from the fumes. 21 of 31 © Boardworks Ltd 2005 Vacuum forming When plastic is used to make a large number of identical products, industrial processes are used. Specialized machines are used to mass produce products. Press play to see a video of the vacuum forming process. 22 of 31 © Boardworks Ltd 2005 Injection moulding What similarities and differences can you identify between the vacuum forming and injection moulding processes? 23 of 31 © Boardworks Ltd 2005 Blow moulding What similarities and differences can you identify between the blow moulding and vacuum forming processes? 24 of 31 © Boardworks Ltd 2005 Line bending What products can you think of that have been manufactured using a strip heater? © Boardworks Ltd 2005 25 of 31 Compression moulding What is the difference between male and female moulds? 26 of 31 © Boardworks Ltd 2005 Extrusion Can you think of any other products that are manufactured using extrusion? © Boardworks Ltd 2005 27 of 31 Finishing techniques Plastics have excellent surface qualities. As they are self-finishing, plastics require little or no surface finish. However, when designers want a specific colour or texture, spray paints can be used. Use wet and dry paper (wet) to smooth the surface down and create a ‘key’ for the primer to grip to. Primer is used to create an undercoat to protect the plastic and provide a good surface finish for the top coat. The primer should be rubbed down using wet and dry paper between coats. Top coat is applied once the primer has completely hardened. There are different surface textures; gloss, matt and metallic being the most common. Top coat is applied in several layers to build up a thick, tough surface layer on the top of the primer. 28 of 31 © Boardworks Ltd 2005 Plastics combined with other materials Plastics are very useful materials. They are durable, easy to join, self-finishing, easy to mould and not susceptible to rot or sust. However, sometimes their properties are enhanced by combining them with other materials. Carbon fibre can be added to thermosetting plastics to improve their strength. Golf clubs, tennis racquets, cycle frames and fishing rods are made using carbon fibre composite. 29 of 31 © Boardworks Ltd 2005 Working with plastics – keywords 30 of 31 © Boardworks Ltd 2005 Key points Key points Plastics can come under the categories of thermoplastic and thermosetting plastics. Both have very different properties. Most modern plastics are manufactured from chemicals obtained from crude oil. Plastic can be shaped or formed using a variety of industrial processes such as vacuum forming, injection moulding, blow moulding, line bending, compression moulding and extrusion. There are also a number of finishing techniques that can be used to give a particular colour or texture to a plastic. 31 of 31 © Boardworks Ltd 2005
