Group 6 Presentation Chapter 7, 8, and 9

1. Group 6 PresentationChapter 7, 8, and 9 Gavin Kurey Kevin Archibeque David Barboza Cedric Turcotte Marcos Gonzales

2. Overview of Presentation: Structure, General Properties, and Applications of: Polymers (Ch. 7) Ceramics, Graphite, and Diamonds (Ch. 8) Composite Materials (Ch. 9) Pictures from Accelrys

3. Chapter 7Structure, General Properties, and Applications of Polymers Background of Polymers Characteristics of Polymers The Structure of Polymers Types of Plastics and Rubbers Recycling Plastics

4. Background of Polymers Terminology: Polymer – Poly meaning many and mer meaning unit. Monomers – Basic building block of a polymer. Macromolecules – extremely large collections of molecules to form one unit. Plastics – a synonym for polymers. Synthetic – manmade.

5. Background of Polymers The word plastic comes from the Greek word plastikos, meaning capable of being molded and shaped. The earliest polymers, such as cellulose, were made from natural organic materials from animals and vegetable products.

6. Background of Polymers • Bakelite, the earliest synthetic polymer, is made from phenolformaldehyde, a thermoset developed in 1906.

7. Background of Polymers The development of modern polymer technology began in the 1920’s when raw materials necessary for making polymers were extracted from coal and petroleum products. Ethylene was the first example of such raw material.

8. Characteristics of Polymers Plastics contain large molecules Two common examples of how plastics can be shaped are: Forming Machine Casting

9. Characteristics of Polymers

10. Characteristics of Polymers

11. Characteristics of Polymers

12. Characteristics of Polymers Advantages of using plastics: Low Cost Low Electrical and Thermal Conductivity Low Density High Strength-to-Weight Ratio Resistance to Chemical Corrosion Amount of Noise Reduction Assortment of Colors and Transparencies Ease of Manufacturing Minimal Additional Surface Treatments Forms of Availability Such As: Tubes, Films, Sheets, Plates, Rods, etc.

13. Structures of Polymers Definitions: Molecular Weight Distribution (MWD), is the sum of the molecular weights of the mers in a chain Degree of Polymerization (DP), is the size of the polymer chain MWD and DP determines the tensile strength, impact strength, and viscosity of polymers.

14. Structures of Polymers An increase in MWD, increases: Tensile Strength Impact strength Resistance to cracking Viscosity The larger DP, the larger: Viscosity Cost (because harder to shape)

15. Structures of Polymers Polymers are very large molecules compared to most other organic materials They are long chain of molecules linked together by a process called polymerization. There are two important types of Polymerization: Condensation Polymerization Addition Polymerization

16. Structures of Polymers Condensation Polymerization: Known as Step-Growth or Step Reaction Is the process in which polymers are produced by the formation of bonds between two types of reacting mers. In better terms, the polymer grows step-by-step until all of one reactant is consumed. Example: Water is condensed out to make plastic.

17. Structures of Polymers Addition Polymerization: Known as chain-growth or chain-reaction Much faster than condensation method Is the process in which the chain-growth takes place without reactant by-products such as water An initiator is added to the reaction to open the double bond between the two carbon atoms

18. Structures of Polymers • Examples of the basic building blocks for plastics:

19. Structures of Polymers Linear Polymers Sequential structures Branched Polymers Increase resistance to deformation and stress cracking. Cross Linked Polymers (Thermosets) have a major influence in polymers. Imparting hardness, strength, stiffness, brittleness, and better dimensional stability. Networked Polymers (highly cross linked), have a higher strength when exposed to high energy radiation, UV light, x-rays, or electron beams.

20. Structures of Polymers Copolymers contain two types of polymers Ex: Styrene-butadiene, used in making tires Terpolymers contains three types of polymers Ex: Acrylonitrile-butadiene-styrene, used to make helmets

21. Structures of Polymers Amorphous, the polymer chains exist without order. Crystallites, the regions arrange themselves in an orderly manner.

22. Structures of Polymers As Crystallinity increases polymers become: Stiffer Harder Less ductile More dense Less rubbery More resistant to solvents and heat.

23. Thermoplastics Polymers that can undergo external shaping forces and return to their original state Ex: Acrylics, Nylons, Polyethylenes

24. Thermoplastics Characteristics and Effects on Thermoplastics: Effects of Temperature Rate of Deformation Orientation Creep/Stress Relaxation Crazing Water Absorption Thermal and Electrical Properties

25. Effects of Temperature Glass-Transition Temperature (Tg) Above the Tg, the thermoplastic gradually softens and eventually turns into a viscous fluid. Repeated heat-cycling causes thermal aging or degredation. Effects of Temp. on thermoplastics is similar to that of metals, (for increased T, Increased toughness, strength/modulus of elasticity decreases)

26. Rate of Deformation Thermoplastics can undergo large uniform deformation in tension before fracture. This characteristic allows for thermoforming. Complex shapes can be made, like bottles, meat trays, etc.

27. Orientation Under deformation, the molecules within thermoplastics align themselves in unison with the deformation. This is called Orientation. The specimen becomes anistropic Important for enhancing strength and toughness properties

28. Creep/Stress Relaxation Most thermoplastics are susceptible to Creeping and/or stress relaxation This can even occur at room temperature!

29. Crazing Localized, deformed areas that are wedge-shaped that occur under stress Sometimes appearing to be cracks, crazes are usually comprised of voids (50%). Caused by enviroment stress or other external forces, like solvents. Stress whitening

30. Water Absorption Polymers absorb water Water acts as a plasticizing agent Lubrication Tg, elastic modulus, and yeild stress are all lowered when water is absorbed Dimensional changes

31. Thermal/Electrical Properties low thermal/electrical conductivity and a high coefficient of thermal expansion Good as insulators and packaging for electronics Doping Electrically conducting Polymers (metal powders, iodides, salts) Thermally conducting Polymers (nonmetallic, conductive particles;100x more conductive)

32. Thermosets When long chain molecules in a polymer become one giant molecule with strong covalent bonds and is from then on permanently set. The curing reaction of a thermoset is irreversible, unlike thermoplastics No set Tg value, rate of deformation, or response to temperature.

33. Additives in Plastic Plasticizers Carbon Black Fillers Colorants Flame Retardants Lubricants

34. Plasticizers Adds Flexibility Adds Softness Achieved by reducing secondary bond strength Most common use of a plasticizer is found in PVC (Polyvinylchloride)

35. Carbon Black Soot Compounded into plastics and rubbers Protects against Oxidation and Ultraviolet Radiation

36. Fillers Reduces overall cost of a polymer May improve hardness, toughness, stiffness, abrasion resistance, etc Common fillers include: Saw Dust, silica flour, clay, mica, talc, asbestos, etc

37. Colorants Organic or Inorganic Dyes(organic) Pigments(inorganic) Colorant selection depends on service temperature and light exposure. Pigments have a higher tolerance to temp and light.

38. Flame Retardants Additives to reduce the flammability of a polymer Common additives include phosphorus, chlorine, and boron Cross-linking reduces flammability as well

39. Lubricants Added to reduce friction during processing. Typical lubricants are: Linseed oil, mineral oil, waxes, metallic soaps, etc Very important to keep thin polymer sheets from sticking to each other

40. General Applications of Thermoplastics and Thermosets

41. Biodegradable Plastics Biodegrability - microbial species can decompose the object over time Three different biodegradable plastics have been developed thus far: Starch-based, Lactic-based, and Fermented Sugar Systems.

42. Recycling Thermoplastics can be recycled by melting them down and reshaping them into new products Recycling symbols/numbers • PETE (polyethylene) • HDPE (high density polyethylene) • V (vinyl) • LDPE (low density polyethylene) • PP (polypropylene) • PS (polystyrene) • Other

43. Elastomers Also known as Rubber Ability to undergo large elastic deformations without rupture Highly kinked structure Stretch under load, but return to original shape without load Vulcanization (cross-linking w/ sulfur) Types of elastomers: Natural Rubber, Synthetic Rubber, Silicones, Polyurethane

44. Ceramics Definition: Ceramics are compounds of metallic and non-metallic elements Two Major Categories: Traditional such as whiteware, tiles, bricks, and pottery. Industrial uses: turbines, cutting tools, and aerospace applications.

45. Major types of oxide ceramics • Alumina: • Used both in its raw form or as an ingredient blended with other ceramics. • Are the most commonly used ceramic material • Used as an abrasive such as grinding wheels or sandpaper. • Affordable compared to other ceramics.

46. Major types of oxide ceramics • Zirconia: • Possesses high toughness and strength, resistance to thermal shock, wear, corrosion and low thermal conductivity. • Excellent or good for high heat applications such as dies for hot extrusions, aerospace coatings. • Definitions: • Thermal Shock-Refers to the development of cracks after a single thermal cycle. • Thermal conductivity- Rate at which heat flows within and through a material. Ionically or covalently bonded have poor conductivity

47. Tungsten Carbide • Made from tungsten-carbide particles with cobalt as a binder • The quantity of binder used has a major influence on the attributes of the final product. • Cobalt increases toughness, but hardness, strength, and wear resistance decreases Carbides • Titanium Carbide • Not as tough as Tungsten Carbide. • Uses nickel and molybdenum as a binder. • Most often used as cutting tools. • Silicon carbide • Low friction coefficient while still retaining its strength at elevated temperatures.

48. Nitrides • Silicon Nitride • Used in high temperature applications since it possesses a high resistance to thermal shock and creep. • Definition • Creep is the permanent elongation of a component under a static load over a long period of time. Cubic Boron Nitride It is the second hardest known substance. Synthetically made in a manner similar to synthetic diamonds. It is not found in nature. It is often used in cutting tools and abrasive wheels.

49. Nitrides • Titanium Nitride (TiN) • Is gold in color and is very widely used as a coating for cutting tools. Drill bits, end mills, etc.

50. Sialon and Cermets • Sialon • It is a combination of Silicon, Aluminum, Oxygen, and Nitrogen. • It is more thermal-shock resistant and has a higher strength than Silicon Nitride. • It sees use as a machine cutting tool. • Cermets • It is a combination of Ceramics phase bonded with a Metallic phase. • They marry the high temperature oxidation resistance of ceramics with the ductility, toughness, and thermal-shock of metals. • Introduced in the 1960’s. • Often used in machining tools.