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© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
Polymer (Plastics)Polymer (Plastics)고분자재료고분자재료
Associate Professor Su-Jin Kim
School of Mechanical EngineeringGyeongsang National University
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
Contents1. Plastics (Polymers, 고분자재료 )• Thermoplastics (열가소성수지 )• Thermoses (열경화성수지 )• Rubbers (고무 )
2. Physical Properties
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
Automotive Plastics andComposites UseExterior• doors• hoods• fenders• bumper covers Interior• instrument panels, door trim, seats, consolesEngine• valve covers, intake manifolds, fluid containers
Automotive fender
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
Recreational Plastics andComposites UseSnow Equipment• skis, snow boards, snow mobiles, etc.Water Sports Equipment• water skis, water crafts, snorkel equipment, fishing gear• diving equipment and clothesLand Sports Equipment• shoes, roller blades, skate boards, tennis, golf, etc.
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
Commercial Plastics Usage
Packaging• Wrapping, bags, bottles, foams, shrink wrap.Textiles• Clothing, carpets, fabrics, diapers, netting for sportsFurniture, 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
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
Medical Plastics and CompositesUseContainers• Bottles, bagsDrug delivery• IV bags, syringes• tubing and tools for surgery• Implants, artificial skins
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
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
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
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-[C2H4]n-/Polymer
Polymerization
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
Chemical Structure of PolymerMonomer Polymer
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
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 polymer’s viscosity.
Ex) Polyethylene -[C2H4]n- plastic
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
Covalent (primary) bonding
• Occurs when two nonmetal atoms are in close proximity.• Both atoms share outer electron shells.• Strong Bond
Carbon 2C + hydrogen 4H
C
-
-
--
H
-
H
-
H
-
H
-
Ethene C2H4
C
- -
- -
- -
H
H
C
- -
- -
- -
H
H
C
- -
- -
- -
H
H
Polyethylene -[C2H4]n-
C
-
-
--
C
- -
- -
- -
H
H
C
- -
- -
- -
H
H
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
Van der Waals (secondary) bonding
• Due to the Interaction between molecules called intermolecular force. It is much weaker than covalent bonding.
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
Covalent bonding
Van der Waals bonding
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
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
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PlasticsPlasticsMaterial ScienceMaterial Science
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)
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PlasticsPlasticsMaterial ScienceMaterial Science
Thermoplastics•little crosslinking, ductile•soften with heatingex) polyethylene, polypropylene, polycarbonate, polystyrene
Thermosets•large crosslinking (10~50%), hard and brittle•do not soften with heatingex) rubber, epoxies, polyester resin, phenolic resin
Thermoplastics vs. Thermosets
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PlasticsPlasticsMaterial ScienceMaterial Science
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.
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
Thermoplastics
PET Polyethylene terephthalate Water, sports drink, ketchup bottle; butter jarHDPE High density polyethylene Milk, water, juice bottle; yogurt tub; retail bagPVC Polyvinyl chlorideWrap; meat, cheese and grocery are wrapped in PVCLDPE Low-density polyethylenebread and frozen food bag and squeezable bottlePP Polypropyleneketchup bottle, yogurt tubsPS Polystyrenecup, toy, styroporOthers (PC Polycarbonate)Baby bottle, microwave ovenware, eating utensils
Recycle
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PlasticsPlasticsMaterial ScienceMaterial Science
Thermosets
• During polymerization, the shape of the part is permanently set.
• Curing is irreversible. Not recycled. • Polymerization process takes place in 2 stages:1. molecules are partially polymerized into linear chains2. cross-linking is completed under heat and pressure
• Ex) Epoxy, Polyester, Polyurethane
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PlasticsPlasticsMaterial ScienceMaterial Science
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:1. Natural rubber2. Synthetic rubbers3. Silicones4. Polyurethane
© GNU Su-Jin Kim© GNU Su-Jin Kim
PlasticsPlasticsMaterial ScienceMaterial Science
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
Elongation
Loading
Unloading
Loa
d
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PlasticsPlasticsMaterial ScienceMaterial Science
Polymer Additives(첨가제 )
Improve mechanical properties, processability, durability, etc.
• Fillers (충진제 )– Added to improve tensile strength & abrasion
resistance, toughness & decrease cost– ex: carbon black, silica gel, wood flour, glass,
limestone, etc.• Plasticizers (가소제 )
– Added to reduce the glass transition temperature Tg
– commonly added to PVC - otherwise it is brittle
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PlasticsPlasticsMaterial ScienceMaterial Science 22
Polymer Additives
• Stabilizers (안정화제 )– Antioxidants– UV protectants
• Lubricants (윤활제 )– Added to allow easier processing – “slides” through dies easier – ex: Na stearate
• Colorants (색소제 )– Dyes or pigments
• Flame Retardants (방염제 )– Cl/F & B
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PlasticsPlasticsMaterial ScienceMaterial Science 23
Stress-strain curve (응력 -변형율 )
Strain >10 possible (metals < 0.1)
brittle polymer
plastic
elastomer
Str
ess
10
% o
f met
al
Network linked
Amorphous chain
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PlasticsPlasticsMaterial ScienceMaterial Science 24
↑Temperature ↓Elastic modulus, ↓ Tensile strength ↑Ductility
Sensitive to Temperature
00 0.1 0.2 0.3
4°C
20°C
40°C
60°Cto 1.3
Str
ess
Strain
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PlasticsPlasticsMaterial ScienceMaterial Science
Viscoelastic (점탄성 )
Stress relaxation(응력이완 )strain to ε0 and hold stress decrease with time.
Relaxation modulus(이완계수 ) Er(t) = σ(t)/ ε0
time
stra
in,
stre
ss
Strain ε0
Stress σ(t)
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PlasticsPlasticsMaterial ScienceMaterial Science
Glass-transition(유리천이 ) temperature• Relaxation modulus drop large at Glass-transition
temperature, Tg.
glassy(rigid, brittle)
Tg Tm
rubbery
E G
elastic solid(탄성고체 )
viscous liquid(점성유체 )
dy
dv
Viscoelastic(점탄성체 )
leathery viscous
mC
Log
Rel
axat
ion
mod
ulus
Er
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PlasticsPlasticsMaterial ScienceMaterial Science 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.
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PlasticsPlasticsMaterial ScienceMaterial Science
Injection molding (사출성형 )
Hopper
Barrel
Mold
• Plastics are melted in a heated cylinder and forced into a mold by hydraulic plunger of rotating screw.
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PlasticsPlasticsMaterial ScienceMaterial Science
References
• Polymer material: LG Chemical http://www.lgchem.com• Mold: JY-Solutec, Nara, Daedong, Machine: Dongshin