1. Characterization, applications
CHAPTER 15
Characterization, applications
and processing of Polymers

2. Mechanical Characteristics of Polymers v.sensitive to
TEMPERATURE
STRAIN RATE
ENVIRONMENT
(presence of water, O2, solvents)
Stress at which fracture occurs
Modulus of Elasticity =
Tensile modulus = modulus
For polymers: 7 MPa- 4GPa
Metals: GPa

3. Three typical types of stress strain curves are found for polymers
Polymers can experience elongations
up to 1000%
Metals typically 100% maximum.

4. Typical values

5. Effect of Temperature
PMMA
Tensile modulus
Elongation
Strength

6. Effect of Molecular weight Constant
FACTORS INFLUENCING MECHANICAL PROPERTIES OF POLYMERS
Extensive chain entanglement or significant molecular bonding
= increase in modulus and strength
Effect of Molecular weight
Constant
TS = TS – A Mn
Tensile strength at infinite molecular weight
TS increases with increase in molecular weight, WHY????
Increasing chain entanglement

7. DEGREE OF CRYSTALLINITY
Important since affects extent of intermolecular secondary bonding
Tensile modulus increases with increase in degree of crystallinity
As crystallinity increases polymer more brittle

8. CRYSTALLIZATION
Occurs by nucleation and growth of ordered and aligned chain
folded layers from random and tangled molecules in the melt.

9. Tm - occurs in crystalline polymers
MELTING POINT Tm and GLASS TRANSITION TEMPERATURE Tg
Tm - occurs in crystalline polymers
Tg - occurs in amorphous and semi-crystalline polymers

10. From ordered to disordered state.
MELTING POINT
From ordered to disordered state.
Requires rotation and movement of ordered molecules
CHAIN STIFFNESS
Controlled by ease of rotation about chemical bonds along he chain
Double bond chains and aromatic groups  reduces chain flexibility
 increases Tm
Size and type of side group  affect chain rotational freedom and flexibility
Tm increases with increase in Molecular weight (chain length).
Why is there a range of Tm rather than a single temperature???

11. e.g. Polypropylene (Tm = 175 oC), Polyethylene(Tm = 115 oC)
Polyethylene MER
Polypropylene MER H H H H
- C – C -
- C – C - H H H
- C - H H H
Larger side group
Tg affected in similar way to Tm

12. Tg = Tm(in K)

14. Repeatable and reversible
THERMOPLASTIC AND THERMOSETTING POLYMERS
Classification according to mechanical response at elevated temperatures
THEMOPLASTIC
THEMOSET
Repeatable and reversible
processes
Heating = harden polymer
 cross-linking
Secondary bonding decreases with increased
Temp. due to increased molecular motion
10-50% of mers x-linked
MOST LINEAR & SLIGHTLY BRANCHED
POLYMERS
X-lined and network polymers
e.g. Epoxy

15. If plastic is x-linked and used above Tg = good elastomer
POLYMER TYPES
PLASTICS- ELASTOMERS (RUBBERS)- FIBERS, COATINGS, ADHESIVE,
FOAMS, FILMS.
If plastic is x-linked and used above Tg = good elastomer
PLASTICS
Majority of polymers
e.g. Polyethylene, Polypropylene, PVC, Polystyrene, fluorocarbons, epoxies,
polyesters.
Brittle and flexible, linear , branched, thermoplastic, thermosetting etc.
Fluorocarbons = low coeff. Of friction, extremely resistant o chemical attack
 Used as coating in cookware.
Optical applications = PMMA, polystyrene