1. CHAPTER 10
Polymeric Materials 1

2. Polymeric material is a material that contains many chemically bonded parts or units that themselves are bonded together to form a solid
Plastics are large and varied group of a synthetic polymer which can be moulded into the desired shapes under pressure with or without the application of heat
Plastics - Advantages
Wide range of properties
low cost
Minimum finishing
Minimum lubrication
Dimensional stability
Good insulation
Light weight
Noise Reduction
Corrosion resistant 2

3. 2 Types of Plastics

4. Thermoplastics
A plastic martial that requires heat to make it formable, and after cooling, remains its shape. Thermoplastic can be reheated and remolded by the application of heat and pressure. Typical thermoplastics are Polyethylene, polyvinyl chloride (PVC), polypropylene and polyesters
thermoplastic pens
thermoplastics objects
thermoplastic resin.

5. Thermosetting plastics
Usually formed into a permanent shape by heat and pressure during which time a chemical reaction takes place that bonds the atoms together to form a rigid solid.
Some thermosetting reactions take place at room temperature without the use of heat and pressure.
Thermosetting plastic cannot be remelted after they are set or cured and upon heating to a high temperature, they degrade or decompose. CAN NOT BE RECYCLED .
Typical thermosetting plastics are phenolics, unsaturated polyesters and epoxies.
The linear chains are crosslinked - strongly chemically bonded. This prevents a thermosetting plastic object from being melted and reformed

6. Polymerization reactions
Polymerization reactions- a chemical reaction in which many small molecules are covalently bonded together to form very long molecular chains.
Monomers- a simple molecular compound that can be covalently bonded together to form long molecular chains (polymers). For example ethylene.
Polymer - is the long chain molecule formed from the monomer units, example polyethylene.

7. Polyethylene (polymer) Ethylene (monomer)
General reaction for the chain polymerization of ethylene monomer into polyethylene may be written as H
Mer
Polyethylene (polymer)
Ethylene (monomer)
Mer: a repeating unit in a chain polymer molecule.
n is the Degree of polymerization (DP) : is equal to the number of subunits or mers in the polymer molecular chain
The average DP for the polyethylene ranges from about 3500 to 25,000 corresponding to average molecular masses ranging from about 100,000 to 700,000 g/mol.

8. Sample Problem
Example. If a particular type of polyethylene has a molecular mass of 150,000 g/mol, what is its degree of polymerization (DP)?
Solution : the repeating unit or mer for polyethylene is –[CH2–CH2]–. This mer has a mass of 4atoms x 1g =4g for the hydrogen atoms plus a mass of 2 atoms x 12g=24 g for the carbon atoms, making a total of 28 g for each polyethylene mer. H
Mer
Polyethylene (polymer)
Ethylene (monomer)

9. Sample Problem on Degree of Polymerization
Problem1. A high molecular weight polyethylene has an average molecular weight of 410,000 g/mol. What is its average degree of polymerization?
Problem2. If a type of polyethylene has an average degree of polymerization of 10,000, what is its average molecular weight?

10. Chain Polymerization - Steps
Initiation:
A Radical is needed.
Example H2O2
Free radical is an atom/molecule that has
a free electron that can covalently bond
to a free electron of another atom/molecule
One of free radicals react with ethylene molecule to form new longer chain free radical.
In General 10

11. Chain Polymerization – Steps (cont..)
Propagation: Process of extending polymer chain by addition of monomers.
Energy of system is lowered by polymerization.
Termination:
By addition of termination free radical
Combining of two chains
Impurities.
R CH2 CH2 + CH2 CH R CH2 CH2 CH2 CH2
R(CH2 CH2)m + R’(CH2 CH2)n R(CH2 CH2)m R (CH2 CH2)n R’
Coupling of two chains 11

12. Average Molecular Weight
Average molecular weight determined by special physical and chemical techniques.
= average molecular weight of
thermoplastics.
Mi = Mean molecular weight of each
molecular range selected.
fi = Weight fraction of the material having
molecular weights of a selected molecular
weight range.
= 19,550 g/mol 12

13. Example Problem (pp 476)
Calculate the average molecular weight for a
thermoplastic material that has the mean molecular
weight fraction for the molecular weight ranges
listed in the following table :
= 19,550 g/mol

14. Structure of Noncrystalline Linear Polymers
Zig-Zag configuration in ethylene due to 109 degree angle between carbon covalent bonds.
Chains are randomly entangled.
Entanglement increases tensile strength.
Branching decreases tensile strength. 14

15. Homopolymer and Copolymers
Homopolymers: Polymer chain is made up of single repeating units.
Example: AAAAAAAA
Copolymers: Polymer chains made up of two or more repeating units.
Random copolymers: Different monomers randomly arranged in chains. Eg:- ABBABABBAAAAABA
Alternating copolymers: Definite ordered alterations of monomers. Eg:- ABABABABABAB
Block copolymers: Different monomers arranged in long blocks. Eg:- AAAAA…….BBBBBBBB……
Graft copolymers: One type of monomer grafted to long chain of another. Eg: AAAAAAAAAAAAAAAAAAA B B 15

16. Sample Problems
Example 3 - A copolymer consists of 15 wt% polyvinyl acetate (PVA) and 85 wt% polyvinyl chloride (PVC). Determine the mole fraction of each component.
Molecular weight of the PVA mer and PVC mer can be calculated from;
Structural formulas for the mers of polyvinyl chloride (PVC)
Structural formulas for the mers of Polyvinyl acetate (PVA)
Example 4:- Determine the mole fractions of vinyl chloride and vinyl acetate in a copolymer having a molecular weight of 10,520 g/mol and a degree of polymerization of 160.
Example 5:- If a vinyl chloride - vinyl acetate copolymer has a ratio of 10:1 vinyl chloride to vinyl acetate mers and a molecular weight of 16,000 g/mol, what is its degree of polymerization ?

17. Industrial Polymerization
Raw Materials:
Natural gas, Petroleum and coal
Granules, pellets, powders or liquids.
Polymerization
Bulk polymerization :
Monomer and activator
mixed in a reactor and
heated and cooled as desired
Solution polymerization: Monomer
dissolved in non-reactive solvent
and catalyst.
Suspension polymerization: monomer
and catalyst suspended in water.
Emulsion polymerization: Monomer
and catalyst suspended in water along with emulsifier. 17

18. Solution polymerization of ethylene, using Ziegler-Natta catalysts18

19. General Purpose Thermoplastics
Polyethylene, polyvinyl chloride (PVC) polypropylene and polyesters account for most plastic materials sold. 19

20. Polyethylene Clear to whitish translucent thermoplastic. Types
High density
Low Density
Linear low density 20

21. Polyethylene Toughness at room and low temperatures
Properties
Toughness at room and low temperatures
Sufficient strength for many product applications
Good flexibility and over wide range of temperatures
Excellent corrosion resistance
Excellent insulating properties
Low water-vapor transmission
Odorless, tasteless
Applications: containers, insulation, chemical tubing, bottles, housewares, blow molded bottles .water pond liners etc. 21 21

22. Polyvinyl Chloride and Copolymers
PVC is amorphous, does not recrystallize.
Chlorine atoms produce large dipole moments and also hinder electrostatic repulsion.
PVC homopolymer has high strength (7.5 to 9 KSI) and is brittle,good electrical properties, high solvent resistance, high chemical resistance.
Compounding of PVC: Modifies and improves properties.
Plasticizers: Impart flexibility. Eg – Phthalate.
Heat Stabilizers: Prevent thermal degradation. Eg – lead and tin compounds.
Lubricants: Aid in melt flow of PVC. Eg – Waxes and fatty esters.
Fillers: Lower the cost. Eg – Calcium Carbonate.
Pigments : Give color. 22

23. Polyvinyl Chloride (PVC)

24. Polypropylene H H C C Methyl group substitute every other carbon
H CH3
Methyl group substitute every other carbon
atom in carbon polymer chain.
High melting ( C) and heat deflection
temperature.
Low density, good chemical resistance, moisture resistance and heat resistance.
Good surface hardness and dimensional stability.
Applications: Housewares, appliances, packaging,
laboratory ware, bottles, etc. n 24

25. Polystyrene Phenyl ring present on every other H H carbon atom.
Very inflexible, rigid, clear and brittle.
Low processing cost and good dimensional
stability.
Poor weatherability and easily attacked
by chemicals.
H H
C C H
Applications: Automobile interior parts, dials and knobs of appliances and housewares. n 25

26. Polystyrene

27. Fluoroplastics F F Exceptionally resistant to chemicals. Melting C C
Monomers have one or more atoms of fluorine.
Polytetrafluoroethylene(PTFE):
Applications: Chemically resistant pipe, parts, molded electrical components, nonstick coating etc.
F F
C C
F F
Exceptionally resistant to
chemicals.
Useful mechanical properties
at a wide temperature range.
High impact strength but low
tensile strength.
Good wear and creep resistance.
Melting
Point
3270C n 27

28. Polychlorotrifluroethylene (PCTFE)
F F
C C
F Cl
Melting
Point
2180C
Chlorine atom substitutes
for every fourth fluorine atom.
lower melting point than PTFE
Can be extruded and mold
easily.
Applications: Gaskets, chemical processing equipments, seals and electric components. n 28

29. Engineering Thermoplastics
Low density, low tensile strength.
High insulation, good corrosion resistance. 29

30. Polycarbonate High strength, toughness and dimensional stability.
Very high impact strength.
high heat deflection
temperature.
Resistance to corrosion.
Applications: Precision parts, cams, gears, helmets, power tool housings and computer terminals. 30

31. Phenyl Oxide Based Resins
Produced by oxidative coupling of phenolic monomers.
Applications: Electric connectors, TV tuners, small
machine housing, dashboards and grills.
High rigidity, strength, chemical resistance, dimensional stability and heat deflection temperature.
Wide temperature range, low creep
High modulus. 31

32. Acetals 2 Types H Homopolymers Copolymers Polyoxymethylene C O
Strongest (68.9 Mpa) and stiffest (2820 Mpa) thermoplastics.
Homopolymer is harder and rigid than copolymer.
Low wear and friction but flammable.
Applications: Fuel systems, seat belts, window handles of automobiles, couplings, impellers, gears and housing.
2 Types
Homopolymers
Copolymers H
C O
Polyoxymethylene
mp: 1750C
Excellent long term load carrying capacity
and dimensional stability. n 32

33. Thermoplastic Polyesters
Phenylene ring provides rigidity.
Good strength and resistant to most chemicals.
Good insulator: independent of temperature and humidity.
Applications: Switches, relays, TV tuner components, circuit boards, impellers, housing and handles. 33

34. Thermosetting Plastics
High thermal and dimensional stability, rigidity, resistance to creep, light weight. 34

35. Epoxy Resins O Epoxide CH2 C group H
Good adhesion, chemical resistance and mechanical properties.
High molecular mobility, low shrinkage during hardening.
Applications: Protective and decorative coating, drum lining, high voltage insulators and laminates. O
CH C H
Epoxide
group 35

36. Unsaturated Polyesters
Have reactive double
Carbon-Carbon covalent
bonds.
Low viscosity and can be reinforced with low viscosity materials.
Open mold lay up or spray up techniques are used to process many small parts.
Compression molding is used for big parts.
Applications: Automobile panels and body parts, boat hulls, pipes, tanks etc. 36