© gnu su-jin kim plastics material science polymer (plastics) 고분자재료 associate professor...

PlasticsPlasticsMaterial ScienceMaterial Science

Polymer (Plastics)Polymer (Plastics)고분자재료고분자재료

Associate Professor Su-Jin Kim

School of Mechanical EngineeringGyeongsang National University

Contents1. Plastics (Polymers, 고분자재료 )• Thermoplastics (열가소성수지 )• Thermoses (열경화성수지 )• Rubbers (고무 )

2. Physical Properties

Automotive Plastics andComposites UseExterior• doors• hoods• fenders• bumper covers Interior• instrument panels, door trim, seats, consolesEngine• valve covers, intake manifolds, fluid containers

Automotive fender

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.

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

Medical Plastics and CompositesUseContainers• Bottles, bagsDrug delivery• IV bags, syringes• tubing and tools for surgery• Implants, artificial skins

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

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

Chemical Structure of PolymerMonomer Polymer

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

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 -[C2H4]n-

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

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

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)

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

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.

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

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

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

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

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

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

Stress-strain curve (응력 -변형율 )

Strain >10 possible (metals < 0.1)

brittle polymer

plastic

elastomer

Network linked

Amorphous chain

↑Temperature ↓Elastic modulus, ↓ Tensile strength ↑Ductility

Sensitive to Temperature

00 0.1 0.2 0.3

60°Cto 1.3

Strain

Viscoelastic (점탄성 )

Stress relaxation(응력이완 )strain to ε0 and hold stress decrease with time.

Relaxation modulus(이완계수 ) Er(t) = σ(t)/ ε0

Strain ε0

Stress σ(t)

Glass-transition(유리천이 ) temperature• Relaxation modulus drop large at Glass-transition

temperature, Tg.

glassy(rigid, brittle)

rubbery

elastic solid(탄성고체 )

viscous liquid(점성유체 )

Viscoelastic(점탄성체 )

leathery viscous

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.

Injection molding (사출성형 )

Hopper

Barrel

• Plastics are melted in a heated cylinder and forced into a mold by hydraulic plunger of rotating screw.

References

• Polymer material: LG Chemical http://www.lgchem.com• Mold: JY-Solutec, Nara, Daedong, Machine: Dongshin

© gnu su-jin kim plastics material science polymer (plastics) 고분자재료 associate professor...

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