IE 21 - TFU DIMAANO, JOYCE ANNE PATAG, CELINE PEREIRA, NOREEN ANNE SUANSING, ANNE BERNADETTE

1. P L M R O Y E S IE 21 - TFU DIMAANO, JOYCE ANNE PATAG, CELINE PEREIRA, NOREEN ANNE SUANSING, ANNE BERNADETTE

2. POLYMERS: THEY’RE EVERYWHERE! STYROFOAM CUPS (POLYSTYRENE) PAINT (ACRYLICS) “MOLECULES” (POLYETHYLENE) DOLLHOUSE EXTERIOR (POLYVINYL CHLORIDE)

3. POLYMERS Made up of macromolecules, have high molar masses and are composed of a large number of repeating units

4. POLYMERS (GENERAL PROPERTIES) lightweight low strength and stiffness corrosion resistance high electrical resistance low thermal conductivity good resistance to chemicals high coefficient of expansion good optical properties (opaque, transparent, colors) high formability low cost (compared to metals) low energy content not as dimensionally stable as metals

5. polymerization >> Chemical reaction by which monomers are linked to form larger molecules • >> Two types: • A. Condensation • B. Addition

6. condensation polymerization • >> Reaction by products such as water • are condensed out • >> Also called step-reaction • polymerization because polymer • molecules grows step by step

7. addition polymerization >> Also known as chain-reaction polymerization >> Bonding takes place without reaction by- products >> Called chain reaction because of the high rate at which long molecules form simultaneously

8. some definitions >> monomers – used in the synthesis of the large molecule >> Molecular Weight  higher molecular weight, greater chain length >> degree of polymerization  Ratio of molecular weight of polymer to the molecular weight of monomer

9. bonding >> Monomers are linked by covalent bonds (primary bonds), forming a polymer chain >> Polymer chains are held together by secondary bonds, such as van der Waals bonds, hydrogen bonds, and ionic bonds. >> The longer the polymer chain, the greater is the energy needed to overcome the secondary bond strength

10. Linear polymers >> Chain like polymers are called linear polymers because of their linear structure. A linear polymer may contain some branched and cross-linked chains. As result of branching and cross-linking, the polymer’s properties can change.

11. branching >> Side-branched chains are attached to the main chain during the synthesis of the polymer >> Branching interferes with the relative movement of the molecule chains. Resistance to deformation and stress- cracking are affected.

12. cross-linking >> Have adjacent chains linked by covalent bonds >> Polymers with cross-linked chain structures are called thermosetting plastics (thermosets) >> Cross linking influence hardness, strength, brittleness, and better dimensional stability, vulcanization of rubber

13. networks Are highly cross-linked

14. MECHANICAL PROPERTIES OF POLYMERS >> deformation is very dependent on time >> deformation is dependent on temperature  as temperature increases, the weak van der waals forces are further diminished, and slip occurs more easily between adjacent chains

15. MECHANICAL PROPERTIES OF POLYMERS >> with the application of stress: when two atoms within a chain are held by strong covalent bonds, displacement of the atoms relative to each other occurs instantaneously on the application of stress >> stress is removed: atoms immediately return to their original positions

16. MECHANICAL PROPERTIES OF POLYMERS >> tensile properties are highly dependent on temperature. rigid polymers: elongation increases with an increase in temperature rubbers: elongation increases with a decrease in temperature

17. STRESS - STRAIN DIAGRAMS Soft and weak Hard and brittle Hard and strong Soft and tough Hard and tough Ideal elastomer

18. MECHANICAL PROPERTIES OF POLYMERS >> creep: dependent on temperature  below tg, increase in temperature: creep rate increases, elongation increases  At tg, increase in temperature: gives much greater elongation than in lower temperatures  above tg, increase in temperature: great increase in elongation, creep rate decreases

19. POLYMERS (TYPES) THERMOPLASTICS THERMOSETS ELASTOMERS ADDITIVES BIODEGRADABLE PLASTICS

20. thermoplastics >> most commonly used polymer >> high molecular weight polymers whose chains associate through weak van der waals forces >> can go through melting or freezing cycles repeatedly >> can be softened repeatedly by the application of heat >> they melt to a liquid and freezes to a brittle, glassy state when cooled sufficiently

21. Effect of temperature

22. Effect of rate of deformation >> can undergo large uniform deformations in tension before they fracture >> allows thermoforming into complex shapes, such as bottles of soft drinks

23. orientation >> When thermoplastics are deformed (e.g. stretching) long chain molecules tend to align in the general direction of elongation. This strengthens the polymer in this direction but weakens in the traverse direction. >> Anisotropic – the specimen becomes stronger and stiffer in the elongated direction than in its traverse direction

24. crazing • >> When subject to tensile stresses or bending the • polymer develops localized, wedged- shaped, narrow • regions of high of highly deformed material. • >> Appears like cracks. • >> Spongy material with 50% voids • >> When further tensile strength is applied, the voids • causes the polymer to fracture • >> Typically observed in transparent glassy polymers • >> Enhanced by: •  Environment: the presence of solvents, • lubricants or water vapor •  Residual stress •  Radiation

25. Stress whitening • >> when subject to tensile stresses (e.g. • bending) the plastic becomes lighter in color • due to the voids formed. • >> Material becomes less translucent or more • opaque • Example: White line formed when a plastic • folder is bent

26. Water absorption • >> Water acts as a plasticizing agent-- • makes the polymer more plastic • >> Lubricates the chains in the amorphous • region • >> Lowers the glass-transition temperature, • yield stress and elastic modulus • >> Also changes the dimensions of the • polymer especially in a humid environment

27. Thermal and electrical properties • >> Low electrical conductivity •  Used for insulators and • packaging material for • electronic components •  Doping – to increase the • electrical conductivity • by introducing • impurities e.g. metal • powder • Increases with water absorption • >> Low specific gravity • >> High coefficient of thermal expansion

28. Creep and stress relaxation • >> Susceptible to creep and stress • relaxation at room temperature

29. thermoplastics acetals polyesters acrylics polyethylenes abs polyimides cellulosics polypropylenes fluorocarbons polystyrenes polyamides polysulfones polycarbonates Polyvinyl chloride

30. ACETALS >> [ ACETIC AND ALCOHOL ] >> COMMON TRADE NAME: DELRIN >> VERY GOOD STRENGTH AND STIFFNESS >> ARE CREEP RESISTANT >> GOOD FATIGUE ENDURANCE >> HIGH CRYSTALLINITY AND HIGH MELTING POINT MAKE IT SUITABLE FOR REPLACING SOME METALS >> HAVE GOOD RESISTANCE TO ABRASION, MOISTURE, HEAT AND CHEMICALS >> GOOD ELECTRICAL PROPERTIES >> HAVE LOW FRICTION >> SLIGHT WATER ABSORPTION >> PROVEN RESISTANT TO PESTICIDAL CHEMICALS

31. DESIGN CONSIDERATIONS -- acetals >> affected by prolonged exposure to UV light (not good for outdoor use) >> cannot be used for applications involving high stress or power frequencies at temperatures above 70oc >> difficult to join to self and other materials

32. ACETALS ( APPLICATIONS ) • IMPELLORS AND OTHER PARTS FOR WATER PUMPS, WASHING MACHINES, AND EXTRACTOR FANS • HINGES AND WINDOW CATCHES • SHOWER HEADS • INSTRUMENT PANELS AND HOUSINGS FOR AUTOMOBILES (A) (C)

33. thermoplastics acetals polyesters acrylics polyethylenes abs polyimides cellulosics polypropylenes fluorocarbons polystyrenes polyamides polysulfones polycarbonates Polyvinyl chloride

34. ACRYLICS >> POLYMETHYL METHACRYLATE (PMMA) >> COMMON TRADE NAME: PLEXIGLAS AND LUCRITE >> HAVE MODERATE STRENGTH >> GOOD OPTICAL PROPERTIES; HAVE HIGHEST OPTICAL CLARITY, TRANSMITTING OVER 90% LIGHT >> TRANSPARENT, BUT CAN BE MADE OPAQUE >> AVAILABLE IN A WIDE RANGE OF COLORS >> GENERALLY RESISTANT TO CHEMICALS >> GOOD ELECTRICAL AND WEATHER RESISTANCE >> HIGH TENSILE AND DIALECTRIC STRENGTHS >> GOOD LOW TEMPERATURE CHARACTERISTICS

35. DESIGN CONSIDERATIONS -- acrylics >> poor fatigue resistance >> low scratch resistance compared to glass >> higher cost than rigid transparent pvc and polystyrene >> low continuous use temperature (approx. 50oc)

36. ACRYLICS ( APPLICATIONS ) • FIBER OPTICS • AUTOMOTIVE REAR LIGHT LENSES • SIGNS • LIGHTING FITTINGS • MOTORCYCLE WINDSCREENS • WINDSHIELDS (A) (F) (E) (C)

37. thermoplastics acetals polyesters acrylics polyethylenes abs polyimides cellulosics polypropylenes fluorocarbons polystyrenes polyamides polysulfones polycarbonates Polyvinyl chloride

38. ABS >> ACRONYM MEANS ACRYLONITRILE-BUTADIENE- STYRENE >> ARE DIMENSIONALLY STABLE AND RIGID >> HAVE HIGH IMPACT VALUE ALONG WITH HIGH STRENGTH (RESISTS IMPACT BY FLYING STONES) >> ARE FLAMMABLE >> HAVE LOW WEIGHT >> HAVE GOOD HEAT, WEATHER, ABRASION, ELECTRICAL AND CHEMICAL RESISTANCE >> GOOD STRENGTH AND TOUGHNESS EVEN AT SUB- ZERO TEMPERATURES >> RESISTS ATTACK BY ACIDS

39. ABS ( APPLICATIONS ) • PIPES • PROTECTIVE HELMETS • INSTRUMENTS AND APPLIANCE HOUSINGS • REFRIGERATOR PARTS • BATTERY CASES • WATER PUMPS • TELEPHONE CASINGS • LUGGAGE CASES (G) (B) (H)

40. thermoplastics acetals polyesters acrylics polyethylenes abs polyimides cellulosics polypropylenes fluorocarbons polystyrenes polyamides polysulfones polycarbonates Polyvinyl chloride

41. CELLULOSICS >> MADE FROM NATURALLY OCCURRING MATERIALS, SUCH AS COTTON >> HAVE VERY GOOD OPTICAL PROPERTIES >> GOOD RESISTANCE TO OUTDOOR WEATHERING >> ARE RIGID, STRONG AND TOUGH >> HAVE HIGH WATER ABSORPTION RATES >> ARE AFFECTED BY HEAT AND CHEMICALS

42. DESIGN CONSIDERATIONS – cellulosics >> optical properties are inferior to acrylics >> high electrical dissipation (power) factor >> tendency to creep under load >> staining can occur on contact with some other plastics >> all types will burn slowly, though self- extinguishing grades are available >> permeable to water vapor and gases in various degrees

43. CELLULOSICS ( APPLICATIONS ) • KNOBS • SAFETY GOGGLES • STEERING WHEELS • LIGHT FIXTURES • FRAMES FOR EYEGLASSES • BILLIARD BALLS (C) (F) (E) (B)

44. thermoplastics acetals polyesters acrylics polyethylenes abs polyimides cellulosics polypropylenes fluorocarbons polystyrenes polyamides polysulfones polycarbonates Polyvinyl chloride

45. FLUOROCARBONS >> COMMON TRADE NAME: TEFLON >> HAVE LOW FRICTION >> HAVE NON-ADHESIVE PROPERTIES >> HAVE GOOD RESISTANCE TO TEMPERATURE, CHEMICALS, WEATHER AND ELECTRICITY >> DO NOT DEGRADE IN UV LIGHT AND ARE NOT ATTACKED BY FUNGI OR BACTERIA >> SELF-EXTINGUISHING >> STABLE AT HIGH TEMPERATURES (UP TO 260OC CONTINUOUS EXPOSURE)

46. DESIGN CONSIDERATIONS – fluorocarbons >> expensive >> stiffer at low temperatures, but not brittle >> not good for high loading and elevated temperatures >> toxic products upon decomposition >> have very high thermal expansion – difficult to machine

47. FLUOROCARBONS ( APPLICATIONS ) • NONSTICK COATINGS FOR COOKWARE • ELECTRICAL INSULATION FOR HIGH-TEMPERATURE WIRE AND CABLE • GASKETS • ANTI-ADHESIVE AND ANTI-ICING COATINGS (A) (C)

48. thermoplastics acetals polyesters acrylics polyethylenes abs polyimides cellulosics polypropylenes fluorocarbons polystyrenes polyamides polysulfones polycarbonates Polyvinyl chloride

49. POLYAMIDES >> [ FROM POLY, AMINE, AND CARBOXYL ACID ] >> COMMON TRADE NAME: KEVLAR >> TWO MAIN TYPES: A. NYLON B. ARAMIDS

50. POLYAMIDES  NYLONS >> HAVE GOOD STRENGTH AND TOUGHNESS >> FLEXIBLE >> RESISTANT TO ABRASION >> SELF-LUBRICATING >> LOW COEFFICIENT OF FRICTION >> RESISTANT TO MOST CHEMICALS >> ARE HYGROSCOPIC (ABSORB WATER), BUT RESULTS IN THE REDUCTION OF MECHANICAL PROPERTIES AND INCREASES PART DIMENSIONS >> HAVE GOOD RESISTANCE MOST COMMON SOLVENTS >> DETERIORATES WHEN EXPOSED TO UV LIGHT