HIDROCARBON GROUPS. Polymer = many mers POLYMER MICROSTRUCTURE.

HIDROCARBON GROUPS

• Polymer = many mers

C C C C C CHHHHHH

HHHHHH

Polyethylene (PE)

mer

ClCl Cl

C C C C C CHHH

HHHHHH

Polyvinyl chloride (PVC)

mer

Polypropylene (PP)

CH3

C C C C C CHHH

HHHHHH

CH3 CH3

mer

POLYMER MICROSTRUCTURE

POLYMER MATERIALS

POLYMER MATERIALS

Branched Cross-Linked NetworkLinear

secondarybonding

• Covalent chain configurations and strength:

Direction of increasing strength

MOLECULAR STRUCTUREHomopolymers

MOLECULAR STRUCTURECopolymers

MOLECULAR STRUCTURECopolymers

• Molecular weight, Mw: Mass of a mole of chains.

smaller Mw larger Mw

• Tensile strength (TS): --often increases with Mw. --Why? Longer chains are entangled (anchored) better.

• % Crystallinity: % of material that is crystalline. --TS and E often increase with % crystallinity. --Annealing causes crystalline regions to grow. % crystallinity increases.

crystalline region

amorphous region

MOLECULAR WEIGHT & CRYSTALLINITY

CRYSTALLINITY

POLYMER CRYSTALS

6

• Compare to responses of other polymers: --brittle response (aligned, cross linked & networked case) --plastic response (semi-crystalline case)

TENSILE RESPONSE: ELASTOMER CASE

initial: amorphous chains are kinked, heavily cross-linked.

final: chains are straight,

still cross-linked

0

20

40

60

0 2 4 6

(MPa)

8

x

x

x

elastomer

plastic failure

brittle failure

Deformation is reversible!

• Decreasing T... --increases E --increases TS --decreases %EL

20

40

60

80

00 0.1 0.2 0.3

4°C

20°C

40°C

60°Cto 1.3

(MPa)

Data for the semicrystalline polymer: PMMA (Plexiglas)

T AND STRAIN RATE: THERMOPLASTICS

• Stress relaxation test:

Er(t)

(t)o

--strain to and hold.--observe decrease in stress with time.

• Relaxation modulus:

• Data: Large drop in Er

for T > Tg.(amorphouspolystyrene)

TIME DEPENDENT DEFORMATION

time

strain

tensile test

o

t( )

VULCANIZATION

0

unload/reload

0

brittle failure

plastic failure

20

40

60

2 4 6

(MPa)

x

x

semi- crystalline

case

amorphous regions elongate

crystalline regions align

crystalline regions

slide

8

onset of necking

aligned, cross- linked case

networked case

Initial

Near Failure

near failure

TENSILE RESPONSE: BRITTLE & PLASTIC

CRYSTALLIZATION, MELTING AND GLASS TRANSITION PHENOMENA IN POLYMERS

Dependence of polymer properties as well as melting and glass transition temperatures on molecular weight

POLYMER TYPES

FORMING TECHNIQUES FOR PLASTICS

FORMING TECHNIQUES FOR PLASTICS