Understanding Thermoplastics, Thermosetting Plastics, and Composites

1. Task • What is the definition of a thermoplastic (2 marks) • Give an example of a thermoplastic and a product it is used in (2 marks) • What is the definition of a thermosetting plastics (2 marks) • Give an example of a thermosetting plastic and a product it is used in (2 marks)

2. Composites. • Formed when two (or more) different materials are combined by bonding. • The main advantage of this is that the properties from each of the materials can be enhanced and utilised. • For example: • Plastics have useful strength and rigidity with lightweight and good electrical insulation properties. These characteristics can be enhanced by adding other materials.

3. Composites. • There are three main groups of composites materials: • Fibre-reinforced composites (made up of resins and fibres - Carbon fibre, glass fibre, Kevlar) • Particle-based composites (Consist solely of particles from two or more materials - Concrete, cermets) • Sheet-based composites (Man-made boards, ALU composite) • The most important of these are the fibre-reinforced composites, since these are more commonly used in the manufacture of products

4. Particle-Based Composites. • The general characteristics of particle-based composites: • High strength in compression • Good stability • Uniform structure ensuring consistent strength • Generally free from surface defects

5. Concrete. • Concretes are made up of materials known as aggregates (gravel & stone), as well as sand and cement. • The properties of concrete are determined by the ratio of the constituent parts. • Concrete is thoroughly mixed while its is dry. Water is then added and continually mixed until every particle of aggregate is coated with the cement paste. • The concrete is then cast into shape whether it is used for garden ornaments, foundations of a building or other structural means.

6. Concrete. • The proportion of the strength is governed by the ration of the mix. • A “lean” mixture of 1:10 would not be as strong as a “rich” mix of 1:3. • During hardening, the temperature of the mix will rise due to the chemical reaction that takes place. • Different pigments can also be added either as a liquid or powder form. • Additives are also available to combat corrosion due to sea water and acid attack.

7. Applications of concrete. • Concrete is often used as a material in the building and construction industry. • It has many uses such as foundations, structural load bearing columns, lintel above doors and windows. • Street furniture and garden ornaments. • Paving slabs, roadways and path surfaces

8. Applications of concrete.

9. Applications of concrete.

10. Applications of concrete.

11. Applications of concrete.

12. Advantages of concrete. • Can be moulded into a variety of complex shapes. • It has similar properties to stone but is more easily obtainable by combining the readily available constituents. • It can be cast on site whereas stone has to be cut and transported from a quarry at a cost. • It is very strong in compression. • It has a uniform structure ensuring consistent strength.

13. Disadvantages of concrete. • It is poor in tension, making it necessary to reinforce the concrete when spanning large distances. • Cement can be irritant causing skin complains e.g. dermatitis.

14. Reinforced concrete. • Concrete is very good when in compression (e.g foundations for a building) but very poor in tension (e.g. beams that span for a distance). • It can be made stronger under tension by adding metal bars, wires, mesh or cables to the composite. • The concrete is cast around the bars combat the possibility of failure under tension. • As there is still some potential for cracking, the reinforcing bars need to be under tension while the concrete is casting. • Once set the tension is removed from the bars. • Using reinforcing bars in this way allows it to withstand heavier loads when spanning a large area.

15. Exam Question • Pick a concrete product • Explain why concrete has been used • Explain how it has been made.

16. Task • Most public buildings and large architectural structures include concrete either in foundations or in the building itself. • Find out how concrete structures are produced. • Give at least three examples of where concrete has played a major part in a structure.

17. Task • For each of the following composites, list as many applications that you can think of where they are used: • Glass-reinforces plastic • Concrete • Carbon fibre • Kevlar • Laminated glass • Describe how concrete is used and strengthened. Give an example of an industrial application of concrete. (5 marks)

18. Composites. • Formed when two (or more) different materials are combined by bonding. • The main advantage of this is that the properties from each of the materials can be enhanced and utilised. • For example: • Plastics have useful strength and rigidity with lightweight and good electrical insulation properties. • These characteristics can be enhanced by adding other materials.

19. Composites. • There are three main groups of composites materials: • Fibre-reinforced composites (made up of resins and fibres - Carbon fibre, glass fibre, Kevlar) • Particle-based composites (Consist solely of particles from two or more materials - Concrete, cermets) • Sheet-based composites (Man-made boards, ALU composite) • The most important of these are the fibre-reinforced composites, since these are more commonly used in the manufacture of products

20. Cermets • These are another group of particle-based composites. • These are mixtures of both metal and ceramic particles. • An example of a common Cermet is tungsten carbide – combination of ceramic tungsten and metal cobalt. • This material is used extensively for cutting tools, as it keeps its cutting edge. • Other examples of cermets include a mixture of aluminium oxide and cobalt, used in the manufacture of components for jet engines.

21. Advantages and Disadvantages of Cermets

22. Tungsten carbide • Combination of ceramic tungsten and metal cobalt. • Approximately three times stiffer than steel, and is much denser than steel or titanium. • It can only be polished and finished with diamond wheels and compounds. • In its most basic form, it is a fine gray powder, but it can be sintered (pressed and formed into shapes) for use in industrial machinery, tools, abrasives, as well as for use in the military, sports equipment, jewellery and some domestic applications.

23. Applications of Tungsten carbide • Tools • Machining through hard materials such as carbon or stainless steel. • Used in situations where other tools would wear away for example equipment used in high-quantity production runs. • Can produce a better finish cut and allows for faster machining. • Can also withstand higher temperatures than standard high speed steel tools. • Military • It is a highly effective penetrating material due to its high hardness value combined with a very high density. • Sports equipment • Used by athletes, generally on poles which impact hard surfaces. (i.e Trekking poles) carbide tips last much longer than other types of tips.

24. Sintering • Sintering is the process used in the manufacture of materials that are difficult to process in any other way (i.e very high melting points). • Sintering is the process of using heat to turn powdered substances into solids without using melting and liquid casting processes.

25. Sintering • A suitable powder mix is produced with the right amounts and any additives. • The powder is compacted in a shaped die under extreme pressure, giving its final shape. • Sintering the compacted shape in a controlled-atmosphere furnace to fuse the particles together, forming strong bonds • Sizing and finishing. Diagram showing stages of particles fusing together

26. Sintering. • Sintered products are often used for bearings where, because of their porous nature, they are able to retain lubricating oil. • This allows certain products and components self oiling, sometimes lasting the lifetime of a product such as electric power tools like drills and jigsaws.

27. Kitchen Knives • Traditionally knives for use in the kitchen have been made from a range of materials, including stainless steel. • They are very tough and corrosion-resistant but do not keep their sharp edge, resulting in the need for re-sharpening

28. Advantages and Disadvantages of tungsten carbide on the cutting edge

29. Composites. • Formed when two (or more) different materials are combined by bonding. • The main advantage of this is that the properties from each of the materials can be enhanced and utilised. • For example: • Plastics have useful strength and rigidity with lightweight and good electrical insulation properties. These characteristics can be enhanced by adding other materials.

30. Composites. • There are three main groups of composites materials: • Fibre-reinforced composites (made up of resins and fibres - Carbon fibre, glass fibre, Kevlar) • Particle-based composites (Consist solely of particles from two or more materials - Concrete, cermets) • Sheet-based composites (Man-made boards, ALU composite) • The most important of these are the fibre-reinforced composites, since these are more commonly used in the manufacture of products

31. Common fibre-reinforced Composites • The general characteristics of fibre-reinforced composites: • Good strength to weight ratio (i.e light in weight with low density and strong compared to their weight) • Resistant to corrosion • Have good fatigue resistance • Possess a low thermal expansion

32. FibreglassGlass-reinforced plastic (GRP) Glass-fibre reinforced plastic (GFRP) • Glass used in glass-reinforced plastic (GRP) is spun to produce a fibre that is then coated to aid bonding to the resin. • Fibres of glass are available in a variety of gauges (thicknesses) from coarse (30µm) to very fine (5µm). (Note: 1µm = 0.001mm) these are woven to form a flexible fabric. • The pattern of weave determines the strength and weight of the Glass Reinforced Plastic, after resin has been added. Different weaves have been developed for different practical applications.

33. Glass-reinforced fibre • A mould is required for GRP. This can be produced quite cheaply from a range of materials including woods, metals and polymers. • The GRP fabric is placed into this mould, a polyester resin is added, followed by a catalyst (to speed up the reaction). • The process is repeated so that there are many layers of fibre glass and resin and allowed to dry/cure. This is called ‘Laying up’. • The resulting material is strong and light. Glass Reinforced Plastic can be sanded for a smooth finish and painted. 

34. Applications of GRP Other Examples: Water tanks, Surfboards, Canoes, Small boat hulls etc.

35. Properties of GRP. • Lightweight • Good thermal insulation properties. • High strength to weight ratio

36. Carbon Fibre Reinforced Plastic (CFRP) • Similar to Fibre glass (GRP). It is an improvement on GRP, although much more expensive • Woven into a textile material and resin such as epoxy resin is applied and allowed to cure. • More well known in recent years in its association with a variety of sports, e.g. Formula One racing cars, tennis racquets, fishing rods, etc. • F1 video

37. Carbon Fibre • The fibres are produced by heating polyacrylonitrile filaments through a range of temperatures up to 2000’c. • This effectively removes all other elements, leaving long chains of carbon atoms ensuring a high strength, lightweight material. • Initially carbon fibre-based products were expensive to produce due to the processes required to product the fibres. However, as these processes continue to develop, manufacturing costs continue to fall.

38. Processing with Carbon Fibres Stages of the process: • Carbon fibres are available in the form of woven matt, which is cut to shape of a pattern using ceramic scissors. • The material is placed into a mould half, where it is covered with resin and forced into the shape of the mould. • The mould halves are fixed together and everything is placed in an oven, where it is held at a temperature of 170’c for up to 8 hours to promote the rigid cross-links in the resin.

39. Properties of Carbon Fibre • Very strong • Very good strength to weight ratio • Carbon Fibre Reinforced Polymers tend to be used in the manufacture of expensive sports cars, where strong and light materials are required. • Expensive, competition bicycles and motorbikes tend to have CFRP frames, forks, handlebars to keep weight to a minimum and yet retain great strength. • The aerospace industry has embraced the use of CFRP in the manufacture of planes. • Eurofighter aircraft. The airframe is 70% Carbon Fibre Composite (CFC), resulting in a plane that is 30% lighter than if it had been constructed from modern metals.

40. Applications of Carbon Fibre • Sports cars, Formula 1 cars • Expensive, competition bicycles and motorbikes. • Planes

41. Kevlar • Mixture of aromatic and aramid (nylon-like) molecules. • These are melted and spun into fibres. • The long chain molecules are held together by strong hydrogen bonds. • These fibres giving the material its very high strength. Weight for weight, Kevlar is five times stronger than steel and about half the density of fibreglass.

42. How does Kevlar work? • Kevlar fibres are woven into a ‘cloth’, which can then be fashioned into protective equipment. • It protects the wearer by operating essentially as a net – in the same way that a goal net will absorb the force of a football being kicked into it. • All the horizontal and vertical fibres absorb some of the impact. • Kevlar can absorb impacts that would cause serious injury to an unprotected human body. The wearer is still affected by the impact, but saved from serious injury.

43. Uses of Kevlar • Body protection – such as bulletproof vests where lightweight properties, comfort and flexibility are important • Sports equipment – such as skis, helmets and racquets, where lightweight properties and strength are important • Sails for windsurfing – materials has to withstand high speeds • Run flat tyres – will not damage the wheel trims • Gloves – for use in the glass and sheet-metal industry

44. Properties of Kevlar • High strength to weight ratio • Low electrical conductivity • High chemical resistance • High toughness • High cut-resistance • Flame-resistant and self extinguishing

45. Application for fibre-reinforced composites