1. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Summary of Material Science Chapter 1: Science of Materials Chapter 2: Properties of Materials Chapter 3: Material Testing Chapter 4: Alloys of Materials Chapter 5: Plain Carbon Steels Chapter 6: Heat Treatment Chapter 7: Cast Iron Chapter 8: Plastics/Polymers Chapter 9: Composite Materials Chapter 10: Ceramics Chapter 11: Semiconductors & Diodes Chapter 12: Biomaterials Chapter 13: Electrochemistry

2. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Plastic: Any substance, which can be moulded into a permanent shape under pressure. Polymer: A substance that has a high molecular weight built up chiefly or completely from a large number of repeating units bonded together. Polymers: transparent or opaque, hard or soft, rigid or flexible. Suitable insulating materials: poor conductors of heat and electricity. Three categories: 1.Natural Plastics 2.Modified Natural Plastics 3.Synthetic Plastics Plastics/Polymers

3. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Natural Plastics Used for household items from 1860's. Popular natural plastics are: Shellac (Insects) Amber (Pine tree sap) Animal Horn (Skin) Modified Plastics Natural materials that have been modified. Cellulose - From cotton fibre and wood pulp Casein - is obtained from cows milk Plastics/Polymers

4. Synthetic Polymers Produced entirely by chemical processes. First:1850, Professor Alexander Parks Two sources: 1. By-products of gas from coal. 2. By-products from the distillation of crude oil. Coal and oil are compounds of Carbon = organic substances. Carbon forms endless number of compounds by combining with other elements such as Hydrogen, Oxygen, Nitrogen, Chlorine and Flourine. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Plastics/Polymers

5. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Polymer substances are made up of very large molecules. These molecules are the result of a repetition of a single unit known as a “mer”. The mers join together to form long main structures. Polymerisation The process in which mers of the same kind are linked together is called polymerisation. The molecule produced in the process is called a polymer. Polymer comes from the Greek words meaning many parts. Structure of Polymers

6. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Structure of Polymers Copolymerisation The process in which mers of different kinds are linked together is called copolymerisation.

7. Two Production methods 1.Addition Polymerisation 2.Condensation Polymerisation Addition Polymerisation adding together ‘mers’ to form long chain-like molecules. E.g. Monomer of ethylene produces polyethylene: 1.Initiation: A double bond exists between carbon atoms. This is ‘opened’ to allow addition. 2. Propagation Many molecules join on to the ‘open’ monomer. 3. Termination The reaction stops due to a.)stiffening of the material, b.)lack of monomer or c.) combination of two polymer chains. Producing Polymers

8. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Producing Polymers

9. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Producing Polymers Condensation Polymerisation When two monomers are made to react in a certain way, they produce water as a by- product. When the water is eliminated polymerisation occurs. E.g. Polyamide

10. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Polymers Two types of Synthetic Polymers: Thermoplastic Polymers When heated they soften and can be molded. Chains are tangled together but not connected. Thermoset Polymers Once set can not be re-melted or softened. Chemically set.

11. Dr. Joseph Stokes School of Mechanical & Manufacturing Engineering Thermoplastic Polymers Thermoplastic Materials In these materials there are two molecular structures 1.Linear Chain Molecules 2.Branched Chain Molecules In both of these instances the bonding between adjacent molecules is secondary. Heating weakens secondary bonds causing softening, allowing moulded.

12. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Thermoset Polymers Thermosetting Materials Cross-linked  primary bonding Rigid non-reversible bonds Initiated by catalyst (chemical which doesn’t get used up) Assisted by heat and pressure Condensation process Curing E.g. Epoxy Resin for fibre glass

13. Polymers are often combined with other materials to gain certain desired properties. These other materials can be summarised as: Fillers - improve their mechanical properties E.g. Wood flour, calcium carbonate, Cloth fibre, Glass fibre, Plasticisers - to improve its flexibility Stabilisers Prevent degradation with heat, sunlight and weathering Colour Pigments-give the plastic the desired colour. 3 types of Pigment: Organic, Inorganic, Dyestuffs Lubricants Improve flow through a process The final products or compounds are commonly known as plastics. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Polymeric Additives

14. Polymeric Properties General Properties of Polymeric Materials Plastics are versatile and popular for the manufacture of objects. Important properties are: Strength - resistance to breaking under load Rigidity - ability to resist distortion when carrying loads Thermal - behaviour when heated Electrical - ability to insulate Durability - ability to resist degradation and corrosion

15. Recycling Plastics 1.PET or PETE – Polyethylene terephthalate of the Polyester family -Questionable – depending on the quality, repeated use may cause the leaching of DEHA or BPA, possible human carcinogen. 2.HDPE –High Density Polyethylene - not known to leach unwanted chemicals may leach BPA/BPS estrogen agonist 3.PVC or V – Bad –Shows leaching of DEHA. 4.LDPE – OK – not known to leach unwanted chemicals although not as widely recycled as #1 or #2. 5.PP – OK – not known to leach unwanted chemicals although not as widely recycled as #1 or #2. 6.PS – Bad – suspected to possibly leach harmful carcinogens 7.Other/Assorted but usually polycarbonate – Bad – may contain leaching BPA. (Bisphenol A – harmful to humans) DEHA is a plasticizer and can lead to cancer. BPA/BPS along with other leachates are estrogen agonists

16. Typical Thermoplastics Polyethylene: PE, LDPE, HDPE, UHMWPE This is one of the most versatile and widely used plastics Tough and flexible over a wide range of temperatures Easily moulded and is used in a wide range of domestic. It is resistant to most solvents and has good weathering. Degrades when exposed to strong sunlight unless it contains a UV filter pigment such as carbon black. Low density polyethylene - this has a branched molecular chain which makes the formation of crystallites difficult High density polyethylene - this has a simple linear chain which leads itself to the close packing essential for high density and for the orderly structure required to form crystallites. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering

17. Typical Thermoplastics Polypropylene: PP Tough, rigid, lightweight Similar properties to polyethylene but better heat resistance. Good mechanical properties Good acid, alkali and salt resistance even at high temperatures. Widely used for chemical plant and domestic hardware and for moulding hospital and laboratory equipment. Can be drawn into fibres for rope and net making and rolled into sheets for packaging. It is also a good moulding material for electrical insulators. Twine Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering

18. Typical Thermoplastics Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Polystyrene: PS This is a tough, dense plastic, which is hard and rigid and has good dimensional stability. It can be moulded to give a high surface gloss and is used for such articles as domestic hollowware and refrigerator trays. Tends to be brittle because of its high glass transition temperature. Unfortunately petrol and other organic solvents can attack it. Since it can be foamed, rigid foamed polystyrene is used for heat and sound insulation blocks in buildings and refrigeration. It can also be used for ceiling tiles, moulded packaging, and for buoyancy aids.

19. Typical Thermoplastics PolyVinyl Chloride: PVC Unplasticised PVC: hard and tough, can be moulded  Buckets, plant pots, guttering and drainpipes. Heated above its glass transition temperature of 87 °C to make it soft and flexible. Plasticised PVC: flexible and rubbery  waterproof clothing, hosepipes, electric cable insulation. Good resistance to attack by water, acids, alkalis and most common solvents. Hardens and becomes brittle with age. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering

20. Typical Thermoplastics PolyTetraFluoroEthytene: PTFE Suitable for the manufacture of tough mouldings Non-stick & anti-friction coating (Teflon) Temperature resistant (does not burn) Highly resistant to attack by solvents, acids or bases Lowest coefficient of friction of any known solid. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering

21. Typical Thermoplastics PolyMethyl MethAcrylate (PMMA) Light material excellent optical properties. strong and rigid excellent insulating properties easily scratched and softens in boiling water. Poor resistance to solvent attack Contact lenses, dentures, aircraft windows, sinks & baths. Polyamide (Nylon) First engineering or high strength thermoplastic. Strong, tough and flexible. Good resistance to abrasion, Easily moulded (gears, bearings, cams & surgical equipment) Easily extruded or drawn (textiles, fishing lines, ropes)

22. Phenol-Formaldehyde (PF) Always used in conjunction with fillers and other additives to: Reduce the intent of brittleness Improve the mechanical and electrical properties Electrical insulators, Electrical plugs and sockets, Handles, knobs & vehicle mouldings, Clutch & brake linings Urea-Formaldehyde (UF) Hard, brittle, rigid and scratch resistant. Resistant to most solvents and household detergents. Widely used for domestic electrical equipment. Melamine-Formaldehyde (MF) Similar to UF but more resistant to heat and less water absorbent. Suitable for electrical goods & tableware. Typical Thermosetting Polymers

23. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Typical Thermosetting Polymers Epoxides: Epoxy resins are used for bonding glass fibre fillers. They are resistant to water and most reagents Excellent electrical insulation properties widely used as a casting material for small components (model aeroplanes) "potting" material for sealing electrical equipment such as chokes and transducers.

24. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Typical Elastomers Elastomers Elastomers are substances, which permit extreme reversible extensions to take place at normal temperatures. Natural rubber is an important elastomer. E.g. Acrylic Rubbers, Butyl Rubbers, Nitrile Rubbers And Silicone Rubbers Although silicone rubber has a relatively low tensile strength, it has an exceptionally wide working temperature range of -80 to +235 o C. Thus it often outperforms other rubbers which are superior at room temperature but which can exist at such extreme temperatures. It can be used for mould linings and high- temperature seals. It is also used in space vehicles and artificial satellites.

25. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Typical Elastomers Elastomers Elastomers are substances, which permit extreme reversible extensions to take place at normal temperatures. Natural rubber is an important elastomer. E.g. Acrylic Rubbers, Butyl Rubbers, Nitrile Rubbers, Polyisoprene (natural rubber) And Silicone Rubbers Although silicone rubber has a relatively low tensile strength, it has an exceptionally wide working temperature range of -80 to +235 o C. Thus it often outperforms other rubbers which are superior at room temperature but which can exist at such extreme temperatures. It can be used for mould linings and high- temperature seals. It is also used in space vehicles and artificial satellites.