Polymers are large organic molecules formed by chemical union of many small and simple molecules called monomers. There are two main types of polymerization - addition polymerization and condensation polymerization. Plastics can be thermoplastics or thermosetting plastics depending on whether they can be remelted or reshaped after solidifying. Common plastics include polyethylene, PVC, nylon, bakelite. Rubber is a natural polymer of isoprene that is obtained from latex. It undergoes vulcanization by adding sulfur to improve its properties. Polymers find wide applications in medicine, packaging and other industries due to properties like light weight and resistance to corrosion.

1. Unit V
Polymers and Rubber

2. Polymers
Union of many simple organic molecules to form a
giant molecule with large molecular mass in the
order of 15000 to 20000 with or without elimination
of simple molecules like H2O, NH3etc.
eg. Ethylene Polyethylene
Monomer Polymer
(Single unit) (Many units)

3. Types of polymerization
polymer
Addition
polymerization Condensation
Polymerization

4. Addition polymerization
Addition of simple molecules to form a giant
molecule
n(CH2=CH2)  ( -CH2-CH2-)n
Ethylene Polyethylene

5. Condensation Polymerization
These types of polymers are formed by
reaction between small molecules with
elimination of molecules like H2O,NH3 , etc.
Eg. Formation of Phenol-formaldehyde resin. It is formed by the
reaction between phenol and formaldehyde.
OH
C 6H5 OH + HCHO - (-C 6H4 –CH2 -) n
Phenol Formaldehyde Phenol-formaldehyde
(Bakelite)

6. Types of Plastics
Thermoplastics
They are the resins which soften on heating and set on
cooling. Therefore, they can be remoulded any number
of times and used.
Eg: Polythene, PVC
and
Thermosetting plastics
They are the resins which set on heating and
cannot be resoftened. Hence, their scrap cannot
be reused.
Eg: Phenol-formaldehyde resin (Bakelite)

7. Distinction between thermoplastics and thermoset plastics
Thermoplastics Thermoset plastics
They soften on heating and set on
cooling every time
They hardened on heating
The polymer chains are held together
by weak force called vander Waal’s
force of attraction.
The polymers chains are linked by
strong chemical bonds.
(Covalent bonds)
They are soluble in organic solvents. They are insoluble in organic solvents.
They expand very much on heating. Their expansion is only marginal due to
heat.
They are formed by addition
polymerization
They are formed by condensation
polymerization
They are processed by injection
moulding.
They are processed by compression
moulding.
Scarp can be reused. Scarp cannot be reused.
Polythene, PVC, Nylon Bakelite, Plaskon

8. Mechanical properties of Plastics
1. Creep or Cold flow: Plastics undergo deformation when a load is
applied continuously.
2. Strength to weight
ratio
Plastics have good strength when compared to their
lightweight. Therefore, they replace lightweight
metals like magnesium, aluminium in many fields
3. Impact strength: Plastics have better impact strength when
compared to glass. Hence, they are replacing
glasses in many places.
4. Tear resistance Plastics have poor tearing resistance
5. Thermal stability: Plastics either degrade or soften at high
temperatures
6. Hardness: Thermosetting plastics are hard in nature when
compared to thermoplastics.
7. Softening
temperature
The temperature below which a polymer is hard
and above which it is soft is known as glass
transition temperature (Tg).

9. Advantages of plastics over other traditional materials
(like wood and Metals)
1. Plastics are available in attractive colours.
2. They do not undergo corrosion
3. They are not affected by insects
4. They are light in weight
5. They are cheap.
6. They can be moulded into any shape easily
7. They are chemically inert.
8. They have good abrasion resistance

10. Specific uses of some plastics
Bakelite (Phenol-
formaldehyde):
TV cabinets, excellent adhesive.,
housing laminates, telephone
components, electrical goods,
P.V.C (Polyvinyl
chloride):
table clothes, rain coats, toys, tool
handles, radio components, pipes,
hoses, helmets, refrigerator components,
cycle and automobile parts
Nylon (Nylon 6:6): Ropes , gears and bearings, household
articles, as fibre in textile industry.
Urea-formaldehyde
(Beetle ware):
making radio cabinets, switches, buttons,
cups, plates cation exchanger in water
treatment,

11. SPECIFIC USES OF PLASTICS

12. Polymers in Medicine and Surgery
Polymer Applications
Polyurethane Heart valves, blood filters, artificial
hearts, vascular tubes, etc.
Polyvinyl chloride
(PVC)
Disposable syringes, etc.
Polypropylene Heart valves, blood filters, etc.
Polyethylene Disposable syringes, etc.

13. Medical application of polymers

15. RUBBER

16. Rubber
Rubber is a natural elastic polymer of
isoprene. It is obtained from the milk
of rubber called ‘Latex’. The structure
of natural rubber is as follows.
-(-CH2-C=CH-CH2-)n-
|
CH3

17. Preparation of Natural Rubber from
Latex
• Latex is rubber milk containing about 30 to 45% of rubber.
• The rubber milk is diluted with water and allowed to stand
for sometime.
• To the clear liquid from the top is treated with acetic acid or
formic acid to precipitate rubber.
• The precipitated rubber is collected and passed through
rollers to get sheets of rubber.
• Rubber sheets are finally dried by smoking. This rubber is
called ‘Smoked rubber’.
• During the coagulation of rubber milk with acetic or formic
acid, retardant like sodium bisulphite (NaHSO3) is added to
prevent oxidation of rubber. This is called ‘Creep rubber’.

20. Defects of natural rubber
• It becomes soft and sticky during summer.
• It becomes brittle during winter.
• It swells up in oils.
• It flows plastically due to prolonged stress.
• Chemicals easily affect rubber.

21. Compounding of rubber
Reinforcing agents or
Hardeners
They are compounded with natural rubber to get soft
spongy rubber.
Example: vegetable oils, Stearic acid and paraffin oil.
Softeners They are compounded with natural rubber to get soft
spongy rubber.
Example: vegetable oils, Stearic acid and paraffin oil.
Anti-Oxidants They are added to prevent aerial oxidation of rubber.
Example: Beta-naphthol.
Vulcanization Vulcanization is compounding of rubber with sulphur. By
vulcanization, we get rubber of different hardness.
Colouring matter Zinc oxide – White ,Lead chromate – Yellow
Chromium oxide – Green,Carbon black – Black
Accelarators They are added to speed up the vulcanization reaction of
rubber.Example: Lime-magnesia, White lead, etc.
. Fillers Fillers are added to i) reduce the cost, ii) increase the bulk
and i) introduce new characters.
Example: Textile wastes, Asbestos, Mica, Gypsum, Talc, etc.

22. Tyres

23. Thank you