1. Chemistry of Some Polymeric Materials Synthetic Polymers & Plastics
Chapter Thirteen
Chemistry of Some Polymeric Materials Or
Synthetic Polymers & Plastics

2. Timeline

3. Definition Plastic is broadly defined as
Any inherently formless material that can be molded or modeled under heat or pressure

4. In the beginning… Greek word plastikos First natural plastics
Tortoise shell
Tree resins
Shellac
Insect secretion

5. Observations About Plastics
Some plastics are clear, others translucent
Some plastics are stiff, others are flexible
Some plastics stretch, others don’t
Some plastics melt, others don’t
Some plastics smell, particularly when hot
Some glues dry, others harden without drying
Most burn and generate toxic gases upon combustion
Involved in virtually all common fires

6. What Are Polymers?
Molecules are larger than most, and chemists call them macromolecules.
Some polymers soften when exposed to heat but then return to their original condition when cooled.
Thermoplastics
Other polymers solidify or set irreversibly when heated.
Thermosetting polymers

7. What Are Polymers?
Polymers are often classified according to the ways they are used.
Plastics are polymers that can be shaped.
Some are used as threads or yarns called fiber.
Fibers are usually woven or knitted to produce textiles.
Elastomers are a type of polymer characterized by molecules that can elongate when strained and reversibly assume the original shape when the tension is released.

8. Polymers
Chemists often place the prefix poly- before the name of the substances used to produce specific polymers.

9. Plastic Comparison to other organic molecules
Polymers: enormous chain or tree like molecules

10. Plastic Structure
The polymer chain layout determines a lot of material properties:
Amorphous:
Crystalline:

11. Plastic structure Amorphous Crystalline random mess of polymers
neatly oriented polymers
Demonstration: Compare Clear Plexiglas to Translucent Polyethylene

12. Amorphous vs. Crystalline
Amorphous (a-morphous = without shape) - The polymer chains are in random arrangement. Molecular structure is incapable of forming regular order (crystallizing) with molecules or portions of molecules regularly stacked in crystal-like fashion. Molecular arrangement is randomly twisted, kinked and coiled.
Crystalline - The polymer chains form a regular pattern. Molecular structure forms regular order (crystals) with molecules or portions of molecules regularly stacked in crystal-like fashion. Molecular arrangement is arranged in an ordered fashion.
By understanding what area specific materials fall into, you can develop a broad understanding of their properties in the virgin state. However, by modifying some materials with fillers and other chemical additives, you may see these properties created overlap into other categories.

13. Glass phase (hard plastic)
Glass-rubber-liquid
Amorphous plastics have a complex thermal profile with 3 typical states:
Glass phase (hard plastic)
Temperature 3 9 6 7 8 4 5
Leathery phase
Log(stiffness) Pa
Rubber phase (elastomer)
Liquid

14. Thermoplastics
Polymers which melt and solidify without chemical change are called thermoplastics.
They support hot-forming methods such as injection-molding

15. Thermoset plastics
Polymers which irreversibly change when heated are called thermosets.
Most often, the change involves cross-linking which strengthens the polymer (setting).
Thermosets will not melt, and have good heat resistance.
They are often made from multi-part compounds and formed before setting (e.g. epoxy resin).
Setting accelerates with heat, or for some polymers with UV light.

16. Polymerization Plastics employ covalent bonds
Individual monomer molecules are joined
This polymerization forms giant molecules
Some molecules are linear chains
Some are branched tree-like structures
Some are networked together completely
Demonstration: Make Poly(methyl methacrylate)
Demonstration: Make Nylon

17. Polymerization
A unique type of chemical reaction involving the union of certain substances called monomers
Only a select number of compounds can be induced to polymerize.
Chains that compose macromolecules can also be folded, coiled, stacked, looped, or intertwined into definite three-dimensional shapes.

18. Polymer chemistry
Polymers are chain molecules. They are built up from simple units called monomers.
E.g. polyethylene is built from ethylene units: which are assembled into long chains:

19. Cross-linking Generally, amorphous polymers are weak.
Cross-linking adds strength: vulcanized rubber is polyisoprene with sulphur cross-links:

20. Branched polymers Polymer chains can branch:
Or the fibers may aligned parallel, as in fibers and some plastic sheets.

21. Copolymers
Polymers often have two different monomers along the chain – they are called copolymers.
With three different units, we get a terpolymer. This gives us an enormous design space…

22. Autopolymerization
Some monomers are capable of undergoing spontaneous polymerization.
While inert compounds may be selected to dilute liquids that are prone to autopolymerization, the common practice used is to add an inhibitor.
To warn fire fighters, the NFPA recommends the insertion of a “P” in the bottom quadrant of the NFPA diamond posted in the storage area.

23. Polymer Decomposition and Combustion
Most products from natural and synthetic polymers are combustible when exposed to an ignition source.
Polymeric products often melt and thermally decompose into the monomers from which they were made or a mixture of simpler substances.
The surfaces of some polymeric products tend to char as they burn.

24. Polymer Decomposition and Combustion
Burning polymeric products releases considerable heat.
Burning polymeric products can evolve voluminous amounts of smoke, carbon monoxide, and other hazardous gases, vapors, and fumes.

25. Polymer Decomposition and Combustion
The generation of flammable vapors, a result of thermal decomposition, at a location isolated from the source of heat gives rise to flashover, the phenomenon responsible in part for the spread of fire from one room into an adjacent room.
Most common polymers evolve nearly twice as much heat when they burn as an equivalent amount of wood.

26. Polymer Decomposition and Combustion
Carbon monoxide is the most prevalent gas at a fire.
Other gases include hydrogen chloride, ammonia, hydrogen cyanide, sulfur dioxide, and nitrogen dioxide.
More smoke is typically produced in fires involving polymers—usually heavy, thick, noxious smoke

27. Vegetable and Animal Fibers
Cotton and linen are examples of vegetable fibers.
Wool and silk are examples of animal fibers.
If all natural, burning does not produce toxic gases
Both can be chemically altered to produce synthetic fibers.

28. Cellulose and Cellulosic Derivatives
When the natural binding agent lignin is removed from wood, the principle substance that remains is a polymer called cellulose.
Primary structural component of the cell walls in plants
Cellulose is the raw material of the paper, wood, cotton textiles, etc.
All natural cellulose does not produce toxic gases when it burns
Cellulose plastics industries—synthetic adaption

29. Parkes Invents Celluloid
The first man-made plastic was unveiled by Alexander Parkes at the 1862 Great International Exhibition in London.
Parkesine- organic material derived from cellulose that could be molded in heat and retain its shaped when cooled
Buttons
Combs
Pens

30. Wool and Silk Common animal fabrics
Composed of proteins, which are biological substances whose molecules possess recurring amino groups
Ignition temperature >1058°F

31. Glues are Plastics White Glue (Water-Soluble Plastic)
Model Cement (Solvent-Soluble Plastic)
Heat Melting Glue (Glue Gun Glue)
UV-Hardening Acrylic Glues (Acrylates)
Superglues (Cyanoacrylates)
Mix-Hardening Glues (Epoxies)
Demonstration: Let White Glue Dry
Demonstration: Let Model Cement Dry
Demonstration: Apply Glue from a Glue Gun
Demonstration: Harden Acrylic Glue with UV Lamp
Demonstration: Superglue Metals together
Demonstration: Epoxy Surfaces together

32. Bakelite Dr. Leo Baekeland Patented in 1909 Thermoset resin
First totally synthetic plastic (1907)
Didn’t throw away his foul glassware
Patented in 1909
Thermoset resin
Replaced rubber for insulation in electrics

33. Bakelite

34. Bakelite
Phenol-formaldehyde resins which he called Bakelite.

35. Vinyl Polymers
A synthetic polymer made from one or more vinyl compounds
Used in the production of textiles, including carpets, curtains, and upholstery fabrics

36. Polyethylene
Probably most common plastic – food bags, packing material, children’s toys
Simple formula:
Not quite amorphous!
Melting point 130 C

37. Polyethylene High density or HDPE Low Density or LDPE
Thermosetting
Products like toys
Both can be recycled.
Releases more heat per unit mass than any other commercially popular polymer when it burns

38. Polypropylene Used to manufacture silky fibers to rigid containers
Recyclable polymer
Does not ignite easily

39. Poly(vinyl chloride) or PVC
Flammable gas subject to autopolymerization
Recognized as a human carcinogen
Used in building construction materials
PVC is recyclable

40. Applications of PVC

41. Poly(vinyl chloride) or PVC
Hydrogen chloride is produced when PVC burns.
During incomplete combustion, dioxins are produced which cause a variety of illnesses.

42. Polyacrylonitrile Very volatile, toxic, and flammable liquid
Acrylonitrile is the monomer from which polyacrylonitrile is made.
Acrylic fibers are those fibers composed of at least 85% by mass of acrylonitrile units.
Orlon and Acrilan are popular trade names.

43. Poly(methyl methacrylate)
Several polyvinyl polymers are produced from the esters of acrylic acid and methacrylic acid.
Very volatile and flammable liquid
Used in the production of Plexiglas and Lucite

44. Polyurethane
A substance produced by the condensation of a glycol and an organic diisocyante
Polyurethane foam results when the frothy mixture solidifies.
Used as insulation, sound-deadening boards, and wall panels
Flexible foams are used in carpet padding and bedding, furniture, and automobile seat cushioning.

45. Polyurethane
It is essential to check for total fire extinguishment within the foam to prevent reigniting.
Products in today's market have been formulated with fire retardants or treated with additives to reduce their ease of combustion.
Note: fire retardants are toxic to the human body & can be absorbed through the skin

46. Heat- and Fire-Resistant Polymers
Poly(tetrafluoroethylene) or Teflon
Used to produce virtually non-destructible tubing, gaskets, and valves
Heat resistance is extraordinary.
Extraordinarily unreactive with hot corrosive acids
Teflon coated cooking utensils—teflon leaches into food & is toxic

47. Teflon Teflon Polytetrafluoroethylene (PTFE)
Dupont Chemical Department
First used for artillery shell covers

48. Heat- and Fire-Resistant Polymers
Nomex
Heat-resistant fabric used in the fire service
Carbonizes and thickens when exposed to intense heat

49. Kevlar
Kevlar is flameproof and can be drawn into fibers having a strength five times stronger than steel.

50. Natural and Synthetic Rubber
Rubber has two main properties:
Deformation under strain and elastic recovery after vulcanization
Vulcanization
Produced by heating natural rubber with elemental sulfur
Vulcanization permits the casting of rubber into shapes.

51. Natural Rubber Natural rubber: mainly polyisopropene
Tends to be sticky when hot, brittle when warm
Does not reform when stretched

52. Natural Rubber Natural rubber: mainly polyisopropene
Charles Goodyear, 1839
Oven cleaning
Natural rubber: mainly polyisopropene
Tends to be sticky when hot, brittle when warm
Does not reform when stretched

53. Ebonite bracelet from 1880
1851: Hard Rubber— 20-30% Sulfur

54. Natural and Synthetic Rubber
The amount of sulfur used determines how soft and elastic the product will be.
Natural rubber accounts for 35% of the demand.
Chemists have synthesized elastomers having the properties similar to those of natural rubber.
Styrene Butadiene Rubber or SBR
Raw material used to produce tire treads
Neoprene rubber is chemically resistant to petroleum products and ozone.

55. Ebonite bracelet from 1880
1851: Hard Rubber— 20-30% Sulfur

56. Responding to Incidents
As they burn, rubber products produce sulfur dioxide, carbon monoxide, and water vapor.
Smoke is extraordinarily dense.
Neoprene, when it burns, also produces hydrogen chloride.