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Polymer (Plastics)

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Polymer (Plastics) Associate Professor Su-Jin Kim School of Mechanical Engineering Gyeongsang National University * Polymers are almost never used as ... – PowerPoint PPT presentation

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Title: Polymer (Plastics)


1
  • Polymer (Plastics)
  • ?????

Associate Professor Su-Jin Kim School of
Mechanical Engineering Gyeongsang National
University
2
Contents
  • 1. Plastics (Polymers, ?????)
  • Thermoplastics (??????)
  • Thermoses (??????)
  • Rubbers (??)
  • 2. Physical Properties

3
Automotive Plastics andComposites Use
  • Exterior
  • doors
  • hoods
  • fenders
  • bumper covers
  • Interior
  • instrument panels, door trim, seats, consoles
  • Engine
  • valve covers, intake manifolds, fluid containers

Automotive fender
4
Recreational Plastics andComposites Use
  • Snow Equipment
  • skis, snow boards, snow mobiles, etc.
  • Water Sports Equipment
  • water skis, water crafts, snorkel equipment,
    fishing gear
  • diving equipment and clothes
  • Land Sports Equipment
  • shoes, roller blades, skate boards, tennis, golf,
    etc.

5
Commercial Plastics Usage
  • Packaging
  • Wrapping, bags, bottles, foams, shrink wrap.
  • Textiles
  • Clothing, carpets, fabrics, diapers, netting for
    sports
  • Furniture, Appliances, House wares
  • Telephones and other communication equipment,
    computer housings and cabinets, luggage, seating,
    components for
  • washers, dryers, etc.
  • Musical instruments, CDs, VCRs, TVs, cases

6
Medical Plastics and CompositesUse
  • Containers
  • Bottles, bags
  • Drug delivery
  • IV bags, syringes
  • tubing and tools for surgery
  • Implants, artificial skins

7
Solid Materials
Metals
Plastics
Ceramic
Thermoplastics
Thermosetts
Elestomers
Plastic means to form or mold (from plastikos in
Greek) Polymer Poly (many) mer (structural
unit) Plastic Polymer
8
Chemical Structure of Polymer
  • A monomer is the basic building block of a
    polymer.
  • Polymers are long-chain molecules.
  • Monomers linked in repeating units by
    polymerization reaction.

Ethylene /Monomer
Polyethylene-C2H4n- /Polymer
Polymerization
9
Chemical Structure of Polymer
Monomer
Polymer
10
Degree of Polymerization
  • 1. Molecular weight
  • - M n M0 , n degree of polymerization
  • 2. Degree of polymerization, n
  • - the higher the n, the longer the chain and the
    higher polymers viscosity.
  • Ex) Polyethylene -C2H4n-

plastic
11
Covalent (primary) bonding
  • Occurs when two nonmetal atoms are in close
    proximity.
  • Both atoms share outer electron shells.
  • Strong Bond

Carbon 2C hydrogen 4H
Ethene C2H4
Polyethylene -C2H4n-
12
Van der Waals (secondary) bonding
  • Due to the Interaction between molecules called
    intermolecular force. It is much weaker than
    covalent bonding.

Covalent bonding
Van der Waals bonding
13
Structure of Polymer
  • 1. Linear
  • - Thermoplastic such as acrylics, nylons,
    polyethylene, polyvinyl.
  • 2. Branched
  • - polyethylene.
  • 3. Cross-linked Network
  • - Thermosets epoxis, phenolics silicones,
    rubbers, elastomers

14
Amorphous vs. Crystalline
  • Amorphous region polymer chains exist random.
    (Polyvinyl chloride, Polystyrene)
  • Crystalline region Uniform (regular) arrangement
    of molecules. It is stiffer, harder, less
    ductile. (Polyethylene, Polypropylene)

15
Thermoplastics vs. Thermosets
  • Thermoplastics
  • little crosslinking, ductile
  • soften with heating
  • ex) polyethylene, polypropylene, polycarbonate,
    polystyrene
  • Thermosets
  • large crosslinking (1050), hard and brittle
  • do not soften with heating
  • ex) rubber, epoxies, polyester resin, phenolic
    resin

16
Thermoplastics
  • Linear and branched polymers will weaken
    secondary bonds.
  • When above glass-transition temperature, polymers
    is easier to mold into shapes.
  • Small increasing in temperature drops strength
    and increase ductility.

17
Thermoplastics
Recycle
  • PET Polyethylene terephthalate
  • Water, sports drink, ketchup bottle butter jar
  • HDPE High density polyethylene
  • Milk, water, juice bottle yogurt tub retail bag
  • PVC Polyvinyl chloride
  • Wrap meat, cheese and grocery are wrapped in PVC
  • LDPE Low-density polyethylene
  • bread and frozen food bag and squeezable bottle
  • PP Polypropylene
  • ketchup bottle, yogurt tubs
  • PS Polystyrene
  • cup, toy, styropor
  • Others (PC Polycarbonate)
  • Baby bottle, microwave ovenware, eating utensils

18
Thermosets
  • During polymerization, the shape of the part is
    permanently set.
  • Curing is irreversible. Not recycled.
  • Polymerization process takes place in 2 stages
  • molecules are partially polymerized into linear
    chains
  • cross-linking is completed under heat and
    pressure
  • Ex) Epoxy, Polyester, Polyurethane

19
Elastomers (Rubbers)
  • An elastomer is capable of recovering
    substantially in shape and size after its load
    has been removed.
  • Rubber is capable of quickly recovering from
    large deformations.
  • Major types of elastomers are
  • Natural rubber
  • Synthetic rubbers
  • Silicones
  • Polyurethane

20
Elastomers (Rubbers)
  • Elastomers encounter hysteresis loss in
    stretching or compression. During the deformation
    energy is lost.
  • undergo large elastic deformations without
    rupture, soft, low elastic modulus

21
Polymer Additives(???)
  • Improve mechanical properties, processability,
    durability, etc.
  • Fillers (???)
  • Added to improve tensile strength abrasion
    resistance, toughness decrease cost
  • ex carbon black, silica gel, wood flour, glass,
    limestone, etc.
  • Plasticizers (???)
  • Added to reduce the glass transition
    temperature Tg
  • commonly added to PVC - otherwise it is brittle

22
Polymer Additives
  • Stabilizers (????)
  • Antioxidants
  • UV protectants
  • Lubricants (???)
  • Added to allow easier processing
  • slides through dies easier ex Na stearate
  • Colorants (???)
  • Dyes or pigments
  • Flame Retardants (???)
  • Cl/F B

23
Stress-strain curve (??-???)
Network linked
Stress 10 of metal
Amorphous chain
Strain gt10 possible (metals lt 0.1)
24
Sensitive to Temperature
?Temperature ? ?Elastic modulus, ? Tensile
strength ? ?Ductility
25
Viscoelastic (???)
  • Stress relaxation(????)
  • strain to e0 and hold ? stress decrease with
    time.
  • Relaxation modulus(????) Er(t) s(t)/ e0

26
Glass-transition(????) temperature
  • Relaxation modulus drop large at Glass-transition
    temperature, Tg.

glassy (rigid, brittle)
rubbery
leathery
viscous
viscous liquid (????)
elastic solid (????)
Viscoelastic (????)
Log Relaxation modulus Er
Tg
Tm
27
Drawing
Drawing (ex monofilament fish line) -
stretches the polymer prior to use - aligns
chains in the stretching direction Results of
drawing - increases the elastic modulus (E)
in the stretching direction - increases the
tensile strength (TS) in the stretching
direction - decreases ductility (EL)
Annealing after drawing - decreases alignment
- reverses effects of drawing.
28
Injection molding (????)
  • Plastics are melted in a heated cylinder and
    forced into a mold by hydraulic plunger of
    rotating screw.

29
References
  • Polymer material LG Chemical http//www.lgchem.co
    m
  • Mold JY-Solutec, Nara, Daedong, Machine Dongshin
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