1. CHAPTER 14: POLYMER STRUCTURES
ISSUES TO ADDRESS...
• What are the basic microstructural features?
• How are polymer properties effected by
molecular weight?
• How do polymeric crystals accommodate the
polymer chain?
What are the tensile properties of polymers and how are they affected by basic microstructural features?
• How does the elevated temperature mechanical
response of polymers compare to ceramics and metals?

2. Chapter 14 – Polymers What is a polymer? Poly mer many repeat unit C H
Polyethylene (PE) Cl C H
Polyvinyl chloride (PVC) H
Polypropylene (PP) C
CH3
Adapted from Fig. 14.2, Callister 7e.

3. Ancient Polymer History
Originally natural polymers were used
Wood – Rubber
Cotton – Wool
Leather – Silk
Oldest known uses
Rubber balls used by Incas
Noah used pitch (a natural polymer) for the ark

4. Polymer Composition Most polymers are hydrocarbons
– i.e. made up of H and C
Saturated hydrocarbons
Each carbon bonded to four other atoms
CnH2n+2

6. Chemistry of Polymers Note: polyethylene is just a long HC
Adapted from Fig. 14.1, Callister 7e.
Polymer- can have various lengths depending on number of repeat units
Note: polyethylene is just a long HC
- paraffin is short polyethylene

7. Bulk or Commodity Polymers
Relatively few polymers responsible for virtually all polymers sold – these are the bulk or commodity polymers

10. MOLECULAR WEIGHT • Molecular weight, Mi: Mass of a mole of chains.
Lower M
higher M
Simple for small molecules
All the same size
Number of grams/mole
Polymers – distribution of chain sizes
Mw is more sensitive to higher molecular weights
Adapted from Fig. 14.4, Callister 7e.

11. Molecular Weight Calculation
Example: average mass of a class

12. Degree of Polymerization, n
n = number of repeat units per chain
ni = 6

13. Polymers – Molecular Shape
Conformation – Molecular orientation can be changed by rotation around the bonds
note: no bond breaking needed
Adapted from Fig. 14.5, Callister 7e.

14. End to End Distance, r
Adapted from Fig. 14.6, Callister 7e.

15. Molecular Structures • Covalent chain configurations and strength:B
ranched
Cross-Linked
Network
Linear
secondary
bonding
Direction of increasing strength
Adapted from Fig. 14.7, Callister 7e.

16. Tacticity Tacticity – stereoregularity of chain
isotactic – all R groups on same side of chain
syndiotactic – R groups alternate sides
atactic – R groups random

17. Copolymers two or more monomers polymerized together
Adapted from Fig. 14.9, Callister 7e.
two or more monomers polymerized together
random – A and B randomly vary in chain
alternating – A and B alternate in polymer chain
block – large blocks of A alternate with large blocks of B
graft – chains of B grafted on to A backbone
A – B –
random
alternating
block
graft

18. Polymer Crystallinity
Adapted from Fig , Callister 7e.
Ex: polyethylene unit cell
Crystals must contain the polymer chains in some way
Chain folded structure
Adapted from Fig , Callister 7e.
10 nm

19. Polymer Crystallinity
Polymers are rarely 100% crystalline
Too difficult to get all those chains aligned
crystalline
region
• % Crystallinity: % of material that is crystalline.
-- TS and E often increase
with % crystallinity.
-- Annealing causes
crystalline regions
to grow. % crystallinity
increases.
amorphous
region
Adapted from Fig , Callister 6e.
(Fig is from H.W. Hayden, W.G. Moffatt,
and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, John Wiley and Sons, Inc., 1965.)

20. Mechanical Properties
i.e. stress-strain behavior of polymers
brittle polymer
FS of polymer ca. 10% that of metals
plastic
elastomer
elastic modulus – less than metal
Adapted from Fig. 15.1, Callister 7e.
Strains – deformations > 1000% possible (for metals, maximum strain ca. 10% or less)

21. Thermoplastics vs. Thermosets
-- little crosslinking
-- ductile
-- soften w/heating
-- polyethylene
polypropylene
polycarbonate
polystyrene
• Thermosets:
-- large crosslinking
(10 to 50% of mers)
-- hard and brittle
-- do NOT soften w/heating
-- vulcanized rubber, epoxies,
polyester resin, phenolic resin

22. Processing of Plastics
Thermoplastic –
can be reversibly cooled & reheated, i.e. recycled
heat till soft, shape as desired, then cool
ex: polyethylene, polypropylene, polystyrene, etc.
Thermoset
when heated forms a network
degrades (not melts) when heated
mold the prepolymer then allow further reaction
ex: urethane, epoxy
Can be brittle or flexible & linear, branching, etc.

23. T and Strain Rate: Thermoplastics
(MPa)
• Decreasing T...
-- increases E
-- increases TS
-- decreases %EL
• Increasing
strain rate...
-- same effects
as decreasing T. 20 4 6 8
Data for the
4°C
semicrystalline
polymer: PMMA
20°C
(Plexiglas)
40°C
to 1.3
60°C e
0.1
0.2
0.3
Adapted from Fig. 15.3, Callister 7e. (Fig 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.)

24. Melting vs. Glass Transition Temp.
What factors affect Tm and Tg?
Both Tm and Tg increase with increasing chain stiffness
Chain stiffness increased by
Bulky sidegroups
Polar groups or sidegroups
Double bonds or aromatic chain groups
Regularity – effects Tm only
Adapted from Fig , Callister 7e.

25. Polymer Additives
Improve mechanical properties, processability, durability, etc.
Fillers
Added to improve tensile strength & abrasion resistance, toughness & decrease cost
ex: carbon black, silica gel, wood flour, glass, limestone, talc, etc.
Plasticizers
Added to reduce the glass transition
temperature Tg
commonly added to PVC - otherwise it is brittle
Polymers are almost never used as a pure material
Migration of plasticizers can be a problem

26. Polymer Additives Stabilizers Antioxidants UV protectants Lubricants
Added to allow easier processing
“slides” through dies easier – ex: Na stearate
Colorants
Dyes or pigments
Flame Retardants
Cl/F & B

27. Polymer Types: Elastomers
Elastomers – rubber
Crosslinked materials
Natural rubber
Synthetic rubber and thermoplastic elastomers
SBR- styrene-butadiene rubber
styrene
butadiene
– Silicone rubber

28. Polymer Types: Fibers Fibers - length/diameter >100
Textiles are main use
Must have high tensile strength
Usually highly crystalline & highly polar
Formed by spinning OR
the fibers are drawn
leads to highly aligned chains- fibrillar structure

29. .357 Magnum, 22 Layers of Kevlar

30. Polymer Types Coatings – thin film on surface – i.e. paint, varnish
To protect item
Improve appearance
Electrical insulation
Adhesives – produce bond between two adherands
Usually bonded by:
Secondary bonds
Mechanical bonding
Films – blown film extrusion
Foams – gas bubbles in plastic

31. Advanced Polymers Ultrahigh molecular weight polyethylene (UHMWPE)
Molecular weight ca. 4 x 106 g/mol
Excellent properties for variety of applications
bullet-proof vest, golf ball covers, hip joints, etc.
UHMWPE
Adapted from chapter-opening photograph, Chapter 22, Callister 7e.

32. •SWNTs are unique:•Polymers of pure carbon•High aspect ratio (>1000:1)•Unique electron configuration•SWNTs have extraordinary properties•Strength (~100x steel)•Electrical conductivity (~Copper)•Thermal conductivity (~3x Diamond)•Accessible surface area (theoretical limit)•Thermal stability (~500 °C air, ~1400 °C anaerobic)•SWNTs can be customized via organic chemistry•Modification of properties•Compatibilization with other materials~nm~1 nm nm ––10,000 nm10,000 nmA polymerA new backbone polymerThe The most inherently conductive organic moleculemoleculeThe The most thermally conductive materimaterialalThe The strongest, stiffest, toughest molecule bemolecule there will ever beThe emitterThe best field emitterThe The ultimate engineering polymerengineering polymerA

33. Poly (p-phenylene-2,6-benzobisoxazole) (PBO) Zylon has 5
Poly (p-phenylene-2,6-benzobisoxazole) (PBO) Zylon has 5.8 GPa of tensile strength,[3] which is 1.6 times that of Kevlar. Like Kevlar, Zylon is used in a number of applications that require very high strength with excellent thermal stability. Tennis racquets, table tennis blades, various medical applications,

34. Plastics & Environment
To replace all the plastic bags being used in the European Union with paper/year, need to cut down an additional 2.2 million trees. This is the same as chopping down 110 Km2 of forest / forest! According to CDA area of Islamabad minus the hills is sq km! So a forest as big as Islalmabad will be chopped down every year to make paper bags!
1 year’s supply (EU) = 220 million

35. Estimation done by Pacebutler Corporation says that $15,000 worth precious metals can be extracted by recycling 1 ton of discarded cell phones.
Only little more than 12% of the E-Waste is getting recycled. Read more at

37. RETHINK!
saves
520 bag/year
1/week

38. Recycling Economics Gap = Opportunity!
Sales Contributions = $236 billion annually in the US (EPA)
21.2% = Rs. 271 million (US $4.5 million) annually in Lahore!
Gap = Opportunity!

39. 25 minutes! OR
6 hours!

40. 2000 lbs!
1 ton +
1 year! + + +
2 months!
1.8 lbs!

41. Summary • General drawbacks to polymers:
-- E, sy, Kc, Tapplication are generally small.
-- Deformation is often T and time dependent.
-- Result: polymers benefit from composite reinforcement.
• Thermoplastics (PE, PS, PP, PC):
-- Smaller E, sy, Tapplication
-- Larger Kc
-- Easier to form and recycle
• Elastomers (rubber):
-- Large reversible strains!
• Thermosets (epoxies, polyesters):
-- Larger E, sy, Tapplication
-- Smaller Kc
• Plastics & Environment
-- Practice 4 R’s; Reduce, Reuse, Recycle, Rethink!
Table 15.3 Callister 7e:
Good overview
of applications
and trade names
of polymers.