1. Chapter 9: The World of Polymers and Plastics
Why is plastic so important?
What happens to recycled
plastics and polymers?
Are there downsides to recycling?

2. Polymers
(American Plastics Council.)
(Shopping for Polymers)
(Plastics Resource.)

3. What do you think of when you hear the word “plastic”?
rayon
nylon
Lycra
polyurethane
Teflon
Styrofoam
Saran

4. Plastics are polymers. What is a polymer?
The most simple definition of a polymer is something made of many units.
Polymers are large molecules made up of long chains of atoms covalently bonded together.
Monomers (from mono meaning “one” and meros meaning “unit”) are small molecules used to synthesize the polymeric chain, like a strand of paper clips.
9.1

5. The polymers (poly means “many”) can be formed from the same type of monomer or from a combination of monomers:
A representation of a monomer
A representation of a polymer made of one monomer
A representation of a polymer made of two different monomers
9.1

6. Polymers are referred to as macromolecules because they involve thousands of atoms, and their molecular masses can reach over a million.
9.1

7. Annual U.S. production of plastics from
1935 to 1997

8. Wallace Carothers, inventor of Nylon (1930 at DuPont).

9. Sources of Plastics Crude oil: End uses of one barrel of crude oil:
47% gasoline
20% diesel and home heating oil
10% lubricants, waxes, dry cleaning
7% boiler oil
3% asphalt and road oil
1.5% chemical products
1.5% plastics

11. Polymers have been with us since the beginning of time.
Natural polymers include such things as tar and shellac, tortoise shell and horns, as well as tree saps that produce amber and latex.
These polymers were processed with heat and pressure into useful articles like hair ornaments and jewelry.
Natural polymers began to be chemically modified during the 1800s to produce many materials. The most famous of these were vulcanized rubber, gun cotton, and celluloid.
The first semi-synthetic polymer produced was Bakelite in 1909 and was soon followed by the first synthetic fiber, rayon, which was developed in 1911.
9.1

12. The polymers (poly means “many”) can be formed from the same type of monomer or from a combination of monomers:
A representation of a monomer.
A representation of a polymer made of one monomer.
A representation of a polymer made of two different monomers.
9.1

13. Many common classes of polymers are composed of hydrocarbons.
These polymers are specifically made of small units bonded into long chains. Carbon makes up the backbone of the molecule and hydrogen atoms are bonded along the backbone. Below is a diagram of polyethylene, the simplest polymer structure.
Other examples of polymers that contain only carbon and hydrogen include polypropylene, polybutylene, and polystyrene.
9.1

14. There are over 60,000 synthetic polymers today
There are over 60,000 synthetic polymers today. Here are the most common; we will call them the “Big Six”:
9.2

15. How do we make sense of these representations?
What makes one polymer different from another?
9.2

16. One way to differentiate between polymers is to look at their functional groups - distinctive arrangements of atoms that impart characteristic chemical properties to the molecules that contain them.
9.2

17. Additional ethylene molecules join, and the chain grows:
In addition polymers, the monomers simply add to the growing polymer chain in such a way that the product contains all the atoms of the starting material.
ethylene
monomer
addition product
Additional ethylene molecules join, and the chain grows:
No other products are formed, and no atoms are eliminated.
9.3

18. The overall process can be represented as:
If one of the H atoms on ethylene is replaced with a Cl atom,
The result is the formation of polyvinyl chloride (PVC)
9.3

19. You may realize there is more than one way for the PVC monomers to join together:
9.3

20. styrene monomer
The polystyrene foam used for Styrofoam cups is made by the same addition process
9.3

21. Formation of Polyethylene: Mechanism
A free-radical process, initiated by a catalyst
9.4

22. Stretching or “necking” a plastic bag
(b) Represents the molecular rearrangement as PE is stretched
9.4

23. Branching alters the physical properties of PE
Branched
chain
Straight chain
Low density PE – soft, stretchy, not too strong
High density PE-greater rigidity, strength, higher mp
9.4

24. Condensation Polymers
Formation of PET
Examples
Natural: starch, wool, silk, proteins
Synthetic: nylon, kevlar, and ABS
9.5

26. Composition of municipal solid waste:
100 billion pounds of plastic is produced in the U.S. each year- much of this ends up in landfills.
9.7

27. Paper or Plastic? Observations for 1000 bags:
- plastic = 17 lbs ; 1219 cubic inches, most are non-biodegradable, processing involves a great amount of toxic chemicals, some are recyclable.
- paper = 122 lbs ; 8085 cubic inches, large volume of solid waste, processing involves deforestation, recyclable.
Will it be paper or plastic?

28. Fig. 9.11

29. Note the date on the newspaper!

30. Disposing of Plastics Four major strategies: 1. incineration
2. biodegradation
3. recycling
4. source reduction

31. Disposing of Plastics Incineration:
- Chief products are : water, carbon dioxide, and energy.
- Drawbacks: PVC releases HCl gas. Others release metals used in pigments such as lead and cadmium.
- If carefully monitored and controlled, incineration can reduce plastic waste, generate energy, and have little negative impact on the environment.

32. Disposing of Plastics Biodegradation:
- Bacteria and fungi have special enzymes that break down naturally occurring polymers. Synthetic plastics are more durable than natural polymers and bacteria do not find them appetizing.
- Most synthetic plastics are nonbiodegradable. Thus, scientists are attempting to engineer biodegradability into synthetic ploymers.
- One strategy has been to incorporate starch into plastic formulations.

33. Disposing of Plastics
Procter and Gamble launched a program to evaluate the biodegradation of filers used in disposable diapers.
- Although some progress has been made in this area, the EPA cautions of the uncertainties regarding performance of the degradation process and the environmental impact of the byproducts of degradable nature.
- Part of the problem is that in landfills the bacterial and fungal action is slowed down by the anaerobic conditions created under the soil.

34. Disposing of Plastics Recycling:
- 20% of the soft drink bottles are being melted and reused.
- Only 1% of all the plastics are recycled compared to 30% of aluminum.
- polyethylene grocery bags are now being recycled by many companies. Recycling centers pay about 8 cents per pound of PET and is sold back at 38 cents per pound. This is half the cost of virgin PET at 67 cents per pound!

35. Clothes made from PET.

36. Disposing of Plastics
- More than 200 million pounds of polystyrene (Styrofoam) were recycled in 1989.
- The goal of the National Polystyrene Recycling Company is to recycle 25% of the Styrofoam products in 1995 (this is equivalent to a quarter billion pounds of polystyrene).
- Here are some considerations for recycling to be economically self-sustaining:
1. supply, 2. collection, 3. coding, 4. sorting, processing (many plastics are constructed of different polymers), and 6. marketing.

37. Disposing of Plastics Source Reduction:
- This is the simplest and most direct - simply decrease the quantity of plastics produced and consumed.
- Now. will it be paper or plastic?

39. Plastics are polymers. What is a polymer?
Polymers are large molecules made up of long chains of atoms covalently bonded together.
Monomers (from mono meaning “one” and meros meaning “unit”) are the small molecules used to synthesize the polymeric chain, like a strand of paper clips.
9.1

40. Polymers have been with us since the beginning of time.
Natural polymers include such things as cellulose, starch, tar and shellac, tortoise shell and horns, as well as tree saps that produce amber and latex.
These polymers were processed with heat and pressure into useful articles like hair ornaments and jewelry.
Natural polymers began to be chemically modified during the 1800s to produce many materials. The most famous of these were vulcanized rubber, gun cotton, and celluloid.
The first semi-synthetic polymer produced was Bakelite in 1909 and was soon followed by the first synthetic fiber, rayon, which was developed in 1911.
9.1

41. Recycling Ever heard of aluminum dross?
Example of closed loop recycling
Ever heard of aluminum dross?
9.8

42. Aluminum dross is a by-product of the primary and secondary aluminum industries
Recycling
White dross Black dross Salt cake
None are on the EPAs Hazardous Materials List
Scrap + white dross
Al skimming tool
So in the U.S. it has been co-disposed along side of municipal solid waste for many years. Two Billion Tons are buried each year.
9.8

43. Recycling: Al Aluminum dross 9.8 “Mount Rumke” before
“Mount Rumke” after dross exposure to water
9.8

44. Recycling: Al Aluminum dross The chemistry behind the troubles
2 Al H2O → Al(OH) H2 + heat
AlN H2O → Al(OH)3 + NH3
Fe2O3 (or sometimes Fe3O4) + Al → Al2O3 + molten iron (Fe) + A LOT OF HEAT
9.8