Industrial chemistry - Polymers

Question 1

Polymers

Answer 1

Polymers are formed by the chemical bonding of a very large number of relatively small molecules referred to as monomers.

Question 2

Main 2 types of polymers and their examples

Answer 2

Natural - Natural rubber, blood and enzymes

Synthetic - P.V.C, Bakelite, Nylon, Teflon

Question 3

Classification of polymers according mechanical properties and their definitions

Answer 3

Elastomers and Plastromers

If a certain polymer regains their original shape when the mechanical force applied is removed, such a polymer is called an elastomer.

Plastromers are made to maintain their shape permanently.

Question 4

Classification of polymers according to the action of heat

Answer 4

Thermoplastic and thermosetting

Thermoplastic polymers are thermally stable and their shape can be removed using heat.
The forces of attraction between chains are weak. e.g: PVC, PP, PS

Thermosetting polymers can never be removed to change shape through heated once their original shape and texture is determined. e.g: Bakelite, urea formaldehyde

Question 5

Polyethylene (PE) monomer

Answer 5

Ethylene n(CH2=CH2)

Question 6

Polyvinylchloride (PVC) monomer

Answer 6

Vinyl chloride n(CH2=CHCl)

Question 7

Polytetrafluoro ethylene (PTFE) monomer

Answer 7

Tetrafluoro ethylene (TFE) n(CF2=CF2)

Question 8

Polystyrene (PS) monomer

Answer 8

Styrene n(C6H5CH=CH2)

Question 9

Polymerization

Answer 9

Production of polymers from monomers

Question 10

According the reaction in polymerization, 2 types of polymers

Answer 10

Addition polymers

Condensation polymers

Question 11

Addition polymer

Answer 11

If a polymer is formed by the bonding of monomers by an addition reaction, such a polymer is known as an addition polymer

The molar mass of the monomer is equal to the molar mass of the repeating unit

Question 12

Condensation polymers

Answer 12

During the formation of condensation polymers, a condensation reaction occurs.

In addition to the polymer, small molecules of low mass are produced.

A number of water molecules equal to the number of ester bonds formed are released. If the volume of the water produced can be measured correctly, the number of ester bonds formed could be calculated.

Question 13

Types of condensation polymers and their examples

Answer 13

1. Long chain- Poly-amide, Polyester, Terylene

2. 3-dimensional - Bakelite-phenol formaldehyde, Urea formaldehyde

Question 14

According to the nature of the structure , polymers can be classified as (characteristics)

Answer 14

Linear - less stable, single chained and can be packed easily. High in density and has high melting points.

Branched - Cannot be packed very closely. Very low density and melting point. Less elastic.

Network - Presence of cross bonds. Less elastic and fragile. Can be very closely packed. Very high density and melting point.

Question 15

Semicrystalline polymers

Answer 15

Polymers having certain amount of crystalline regions
e.g: Polythene

Light does not penetrate well through membranes of semi crystalline polymers. Crystalline regions in them scatter light and reduce transparency. Light does not scatter through semicrystalline layers. Therefore they are transparent.

Question 16

HDPE and LDPE

Answer 16

High density polythene - Linear polythene molecules pack closely with each other and have more high density areas

Low density polythene - Their density is low and have more amorphous regions.

Question 17

E,g: for artificial rubber

Answer 17

Nitryl rubber

Question 18

Plastics

Answer 18

Polymers with limited elastic properties
e.g: PVC, PET, PP and PE

When stretched beyond the elastic limit its shape changes irreversibly.

Question 19

Types of plastics

Answer 19

Thermosetting - Have a molecular structure arranged as a network e.g: Phenol-formaldehyde (bakelite)

Thermoplastics - Composed of linear polymers or branched polymers. Can be softened by heating e.g: PVC, PE and PS

Question 20

Natural rubber

Answer 20

Obtained by coagulating latex of rubber tree (Hevea braziliensis)
Contains 60-65% water and 30-35% rubber.

In rubber latex rubber occurs as a colloidal solution in which very small rubber particles are dispersed. Simple sugars and salts are also dissolved in this colloidal solution.

There is a lipid and protein layer around a rubber particle. Inner to it lie rubber molecules. Since –COO- groups associate the outer layers of a rubber partical its outer surface is negatively charged.

Question 21

Coagulation of latex

Answer 21

In addition of acids H+ ions neutralize the –COO- groups and the surface of the particles become electrically neutral. Then the particles combine together and settle down as a mass. This is known as ‘coagulation of latex’.

Question 22

Microbial activity and preventing coagulation of rubber

Answer 22

Since the rubber latex contains salts, sugar, amino acids etc. It is a suitable medium for microbial action.

coagulation can be prevented by basifying the latex by adding an ammonia solution. Ammonia prevents the medium becomes acidic and stabilizes the negative charges around the rubber particles. Under these basic conditions the microbial action is suppressed.

Question 23

Reason for the elasticity of natural rubber

Answer 23

Existence of cis-polyisoprene chains

Question 24

Vulcanisation of rubber

Answer 24

Changing the elastic property of rubber as required industrially and strengthening it, it is heated with 1-3% sulphur.

Question 25

Ebonite

Answer 25

Ebonite is obtained when rubber is heated with 25-35% sulphur by weight. Ebonite doesn’t show elastic properties. This is due to the fact that activity associated with the double bonds in rubber molecules form large number of crosslinks with sulphur atoms.

Question 26

Additives

Answer 26

The substances used to improve the qualities of the end product and reduce its production cost in the production of polymers are referred to as additives.

e.g: carbon black, ZnO and CaCO3

Question 27

Plastics definition

Answer 27

Polymers with limited elastic properties

Question 28

Terylene is formed by

Answer 28

Ethylene glycole and terephthalic acid

Question 29

Urea-formaldehyde production

Answer 29

nontransparent thermosetting resin or polymer. It is produced from urea and formaldehyde

Question 30

Terylene characteristics and uses

Answer 30

Thermoplastic polymer
Used as a substitute for natural fibres such as cotton and wool
Used in the production of textiles, photographic films and audio tapes

Question 31

Bakelite uses

Answer 31

Used to produce certain parts of electrical equipments such as switch and plug.
Insulating wires