Seminar 1 Plastics

7/27/2019 Seminar 1 Plastics

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Major factors affecting the properties of Plastics

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Molecular View point

Intra molecular bonding (primary bonding)

Inter molecular bonding (Secondary bonding)

Functional Groups

Bi functional

Tri functionalTetra functional

Microstructure View Point

Crystalline / Amorphous

Molecular WeightMolecular Weight distribution

Shape/Steric effects

Thermal effects



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Polymer’s Structures

Bond ing – monomers are linked together by covalent bonds, forming a

polymer chain (primary bonds). The polymer chains are held together by

secondary bonds. The strength of polymers comes in part from thelength of polymer chains. The longer the chain, the stronger the polymer.

More energy is needed to overcome the secondary bonds.

Linear polymers

A sequential structure resulting in

thermoplastics like nylon, acrylic,

polyethylene(HDPE). A linear

polymer may contain some

branched and cross-linked chains

resulting in change in properties.

Branched polymers

Side branch chains are attached to themain chain which interferes with the

relative movement of the molecular chains.

This results in an increase in strength,

deformation resistance and stress cracking

resistance. Lower density than linear chain

polymers. Polyethylene(LDPE,LLDPE)



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Polymer’s Structures

Cross-linked polymers

Three dimensional structure, adjacent chains are linked

by covalent bonds. Polymers with cross-linked chains

are called thermosetting plastics (thermosets), epoxy

Phinolics and Silicones.

Cross-linking is responsible for providing hardness,strength, brittleness and better dimensional stability.

A three dimensional network of three or morecovalent bonds. Thermoplastic polymers that have

been already formed could be cross-linked to

obtain higher strength. Polymers are exposed to

high-energy radiation.

Network polymers



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Class i f icat ion o f po lymers

Thermoplastics

As the temperature is raised above the melting point, the secondary bonds

weaken, making it easier to form the plastic into any desired shape. When

polymer is cooled, it returns to its original strength and hardness. The process

is revers ible . Polymers that show this behavior are known as thermoplastics.

Thermosetting Plastics (thermosets)

Thermosetting plastics are cured into permanent shape. Cannot be re-melted to

the flowable state that existed before curing, continued heating for a long time

leads to degradation or decomposition. This cu r ing (cross -l inked) react ion is ir revers ible . Thermosets generally have better mechanical, thermal and

chemical properties. They also have better electrical resistance and dimensional

stability than do thermoplastics.

There are two major classifications of polymers



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Mechanical Propert ies o f Variou s Plast ics

Steel: 350 to 1900 MPa Brass: 200 to 850 MPa

Aluminum: 100 to 550 MPa



What decides the properties of

a polymer?• Stronger attractive forces between chains =

stronger, less flexible polymer.

• Chains able to slide past each other = flexible

polymer .• In poly(ethene) attractive forces are weak

instantaneous dipole - induced dipole, - it will be

flexible

• Nylon has strong hydrogen bonds, - It makes a

strong fibre

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Thermoplastics (80%)

• No cross links between chains.

• Weak attractive forces between chains

broken by warming .• Change shape - can be remoulded.

• Weak forces reform in new shape when

cold.10/23/2013

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Thermosets

• Extensive cross-linking formed by

covalent bonds.

• Bonds prevent chains moving relative toeach other.

• When heated the molecule disintegrate

before secondary bonds break10/23/2013

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The structure of po lymers



Crystalline polymers• Areas in polymer where

chains packed in regular

way.

• Both amorphous andcrystalline areas in same

polymer.

• Crystalline - regular chain

structure - no bulky sidegroups.

• More crystalline polymer -

stronger and less flexible.10/23/2013

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Crystalline/Amorphous

• Crystalline• Sharp Melting point

• Usually opaque

• High shrinkage

• High chemical

resistance

• High fatigue and wear

resistance

• High strength

• High density

• PVC,PS,PC,Acrilic

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• Amorphous• Broad softening range

• Usually transparent

• Low shrinkage

• High Chemical

resistance

• Low fatigue and wear

resistance

• Low strength

• Low density

• PE,Polyamide(nylon),

Teflon



Longer chains make stronger

polymers.• Critical length needed

before strength increases.

• Hydrocarbon polymers

average of 100 repeatingunits necessary but only 40

for nylons.

• Tensile strength measures

the forces needed to snap apolymer.

• More tangles + more

touching!!!10/23/2013

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Shape/Steric Effects

• Bulky pendent groups hinder

rotations/flexibility

• Expected to raise Tg (PVC with PE)

• Bulky groups make more amorphous

• Bulky group in back bone increase

strength, impact toughness and Tg

(aramids(kevlar,Nomex),LCP(Xydar,vec

tra)

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Time Temp Dependence

• Plastic deformation of polymers involves

chain uncoiling and chain sliding

• Increasing temperature increases relative

space between chains and makes

uncoiling easier.

• Slowing the strain rate means there is

more time for chain reconfiguration.

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17

T and Strain Rate: Thermoplastics

• Decreasing T ...-- increases E

-- increases TS

-- decreases %EL

• Increasing strain rate...

-- same effects

as decreasing T .

Adapted from Fig. 15.3, Callister 7e. (Fig. 15.3 is from T.S. Carswell and

J.K. Nason, 'Effect of Environmental Conditions on the Mechanical

Properties of Organic Plastics", Symposium on Plastics, American Society

for Testing and Materials, Philadelphia, PA, 1944.)

20

4 0

6 0

8 0

0

0 0.1 0.2 0.3

4°C

20°C

40°C

60°Cto 1.3

s (MPa)

e

Data for the

semicrystalline

polymer: PMMA

(Plexiglas)

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Effects of Strain Rate and

Temperaturestress

strain

Increasing temp

Increasing

strain rate

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Melting vs. Glass Transition

Temp.What factors affect T

m

and T g

?

• Both T m and T g increase with

increasing chain stiffness

• Chain stiffness increased by

1. Bulky sidegroups

2. Polar groups or sidegroups

3. Double bonds or aromatic

chain groups

• Regularity – effects T m only

19

Adapted from Fig. 15.18,

Callister 7e.

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Tg and Tm

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Effect of Temperature:

Glass Transition

Temperature

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App l ications of Thermop last ics

Design requirement: strength

Applications: Valves, gears, cams, pistons, fan blades, …

Plastics: nylon, acetal (delrin), polycarbonate, phenolic

Design requirement: wear resistance

Applications: bearings, gears, bushings, wheels, ….

Plastics: nylon, acetal (delrin), polyurethane, phenolic, polymide



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Appl icat ions o f Thermoplast ics

Design requirement: functional and decorative

Applications: knobs, handles, cases, moldings, pipe fittings, …

Plastics: ABS, acrylic, polyethylene, phenolic, polypropylene, polystyrene

Design requirement: hollow shapes and housings

Applications: pumps, helmets, power tools, cases, …

Plastics: ABS, polyethylene, phenolic, polypropylene, polystyrene, polycarbonate

Design requirement: functional and transparent

Applications: lens, goggles, signs, food processing equipment, …

Plastics: acrylic, polycarbonate, polystyrene, polysulfone



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Popu lar Plast ics

Polyethylene (LDPE (low density) and HDPE (high density)

Properties: good chemical and electrical properties, strength

depends on composition

Applications: bottles, garbage cans, housewares, bumpers, toys, luggage

ABS

Properties: dimensionally stable, good strength, impact and toughness

properties, good resistance to abrasion and chemicals

Applications: automotive components, helmets, tool handles, appliances,

boat hulls, luggage, decorative panels

Acetal (Delrin)

Properties: good strength, good stiffness, good resistance to heat,

moisture, abrasion and chemicals

Applications: mechanical components; gears, bearings, valves, rollers,

bushings, housings



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Popular Plast ic s

Polycarbonates

Properties: very versatile and has dimensional stability, good

mechanical and electrical properties, high resistance to impact and

chemicals

Applications: optical lenses, food processing equipments, electrical

components and insulators, medical equipments, windshields, signs,

machine components

Nylons

Properties: good mechanical and abrasion resistance property, self-

lubricating, resistant to most chemicals but it absorbs water, increase indimension is undesirable

Applications: mechanical components; gears, bearings, rollers, bushings,

fasteners, guides, zippers, surgical equipments,



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App l icat ions o f Thermosett ing Plast ics

EpoxiesProperties: good dimensional stability, excellent mechanical and

electrical properties, good resistance to heat and chemicals

Applications: electrical components requiring strength, tools and dies, fiber

reinforced epoxies are used in structural components, tanks, pressure

vessels, rocket motor casing

Phenolics

Properties: good dimensional stability, rigid, high resistance to

heat, water, electricity, and chemicals

Applications: laminated panels, handles, knobs, electrical components;

connectors, insulators



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App l icat ions o f Thermosett ing Plast ics

Polyesters (thermosetting, reinforced with glass fibers)Properties: good mechanical, electrical, and chemical properties,

good resistance to heat and chemicals

Applications: boats, luggage, swimming pools, automotive bodies, chairs

Silicones

Properties: excellent electrical properties over a wide rang of

temperature and humidity, good heat and chemical properties

Applications: electrical components requiring strength at high temp.,

waterproof materials, heat seals



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Plastics

Website: www.ge.com/plastics

Stress vs. Straincurve

Structural and mechanical Appl Li ht d t h i l & d ti



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ABS

Acetal (Delrin)Acrylic

Cellulosics

Fluoroplastics

Nylon

Phenylene Oxide

Polycarbonate

Polyester Polyethylene

Polyimide

Polyenylene sulfide

Polypropylene

Polystyrene

PolysulfonePolyurethane

Polyvinyl chloride

Phenolic

Polyester

Polyurethane

T h e r m o p

l a s t i c s

T h e r m o s e t s

Structural and mechanical Appl.

Gears, cams, pistons, rollers, fan

blades, rotors, pump impellers,

washing machine agitators

X

X

X

X

Handles, knobs, steering wheel,

tool handles, pipe fittings, camera

cases, eyeglass frames

X

X X

X

X

Light duty mechanical & decorative

X

X

X

Parts for wear applications Optical and transparent parts



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ABS


Cellulosics

Fluoroplastics

Nylon

Phenylene Oxide

Polycarbonate


Polyimide

Polyenylene sulfide

Polypropylene

Polystyrene


Polyvinyl chloride

Phenolic

Polyester

Polyurethane

T h e r m o p

l a s t i c s

T h e r m o s e t s

Parts for wear applications

Gears, bearings, bushings,

tracks, wheels, ware strips

X

X

X

X X

X

X

X

X

Lenses, safety glasses,

signs, refrigerator shelves,

windshields

X

X

X

X X

Optical and transparent parts

Small housing & hollow shapes Large housing & hollow shapes



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ABS


Cellulosics

Fluoroplastics

Nylon

Phenylene Oxide

Polycarbonate


Polyimide

Polyenylene sulfide

Polypropylene

Polystyrene


Polyvinyl chloride

Phenolic

Polyester

Polyurethane

T h e r m o p

l a s t i c s

T h e r m o s e t s

Small housing & hollow shapes

Phone and flashlight cases,

helmets, housings for power

tools, pumps, small appliances

X

X

X

X

X

X

X

X

X X

Boat hulls, large appliance

housings, tanks, tubs,

ducts, refrigerator liners

Large housing & hollow shapes

X

X

X X

X

X

X

X X

Small Large Parts for Optical andLightStructural &



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ABS


Cellulosics

Fluoroplastics

Nylon

Phenylene Oxide

Polycarbonate


Polyimide

Polyenylene sulfide

Polypropylene

Polystyrene


Polyvinyl chloride

Phenolic

Polyester

Polyurethane

T h e r m o p

l a s t i c s

T h e r m o s e t s

Small

housing

& hollow

shapes

X

X

X

X

X

X

X

X

X

X

Large

housing

& hollow

shapes

X

X

X

X

X

X

X

X

X

Parts for

wear

applications

X

X

X

X

X

X

X

X

X

X

X

X

X X

Optical and

transparent

parts

Light

duty

mech &

deco

Structural &

Mechanical

X X

X

X

X

X

X

X

X

X

X

X

Plastic

Documents

Seminar 1 Plastics