Thursday, 19 February 2015

9.4 Synthetic Polymers and Their Uses

■ Polymer

Long-chained molecules with a high relative molecular mass.

Made up of many smaller units called monomers, which are joined through a process called polymerisation.

Thus, the monomer is the repetitive unit of a long polymer chain.

Types of polymer:
Natural polymer
Synthetic polymer

The animation below shows the classification of polymers.

Natural polymers
■ Natural polymers

Made up of carbon, hydrogen, nitrogen and oxygen.

Occur naturally in living things.

Examples: natural rubber, cellulose, fat, protein and carbohydrates.
■ Natural polymers and its monomer.

Natural polymer and it monomer Structure of polymer
Natural rubber
2-methyl-1, 3-butadiene, also called isopropene, joined together to form a long chain
amino acid molecules
glucose molecule

The animation below shows the polymerisation of isopropene into polyisoprena(rubber).
■ This video contains information about natural polymer.

Synthetic polymer
■ Synthetic polymers

A polymer that is manufactured in industry from chemical substances through the polymerisation process.

Examples: plastic, synthetic fibres and elastomer
■ Types of polymerisation

Addition polymerisation

Condensation polymerisation
■ Addition polymerisation

Monomers with C=C bonding, join together to make a long chain without losing any simple molecules from it.

Examples: polythene, PVC perspex and other plastics

The animation below shows the addition polymerisation of synthetic polymer with their monomers.
■ Condensation polymerisation

The elimination of small molecules like water, methanol, ammonia or hydrogen during polymerisation process.

Examples: terylene and nylon 66.

The animation below shows the condensation polymerisation of synthetic polymer with their monomers.
Uses of synthetic polymers
■ Plastics

Light, strong and do not react with any chemical substances like acid and alkalis.

Can be made into many shapes and sizes.

Good insulators of heat and electricity.

The following table shows the plastic types, structure and uses.
Name Structure of monomer Structures of polymer Uses Properties
Polythene (polyethylene)
Plastic bags, containers and cups Light and cannot tear easily
Polyvinyl chloride (PVC)
Raincoat, pipes, wires insulators Heat and electricity resistant
(Polytetrafluoroethene or PTFE)
Non-stick pots and pans Hard, can withstand high temperatures and corrosives chemicals
Plastics, bottles,. Strong and light
Packaging materials, toys Heat and electrics insulators, light and strong
Perspex (Polymethyl 2-methyle propene)
Aeroplane window panes, lenses, car lamp covers. Light, strong, translucent, stable towards sunlight
■ Synthetic Fibre

Nylon and terylene are synthetic fibres which undergo the condensation polymerisation process.

These fibres resemble natural fibres but more resistant to stress and chemicals, and more long-lasting.

The following table shows the synthetic fibre, structure and uses.
Name and structures of monomer → polymer Uses
Nylon – polyamide polymer resulting from condensation of a diamine monomer and a dicarboxylic acid monomer
To make umbrellas, socks, carpets, nylon string and rope, toothbrush, comb and so on.
Terylene – polyester polymer produced by the condensation of a diol with a carboxylic acid as the monomers.
To make fishing nets, clothes.
■ Synthetic Rubber

Synthetic rubber is an elastomer or polymer which regains its size original shape after being pulled or pressed.

The following table shows the synthetic rubber, structure and uses.
Name and structures of monomer → polymer Uses
To make rubber gloves and to insulate electric wires
Styrene-butadiene or SBR
To make tyres, soles of shoes and mechanical belts

Effects of disposing items made from synthetic polymers on the environment
■ Synthetic polymers cause environmental pollution:

Most polymers are not biodegradable.
Polymers cannot be decomposed biologically or naturally by bacteria or fungus as in the case of other garbage.
The disposal of polymers has resulted in environmental pollution because they remain in the environment forever.

Careless disposing of synthetic polymers.
Plastic containers and bottles strewn around become good breeding places for mosquitoes which cause dengue fever, or malaria.

Burning of synthetic polymers.
The open burning of plastics creates poisonous and acidic gases like carbon monoxide, hydrogen chloride and hydrogen cyanide.
Burning of plastics can also produce carbon dioxide, too much of this gas in the atmosphere leads to the “green house effect”.
■ This problem can be overcome by the following ways:

Recycling polymer
Plastics can be decomposed by heating them without oxygen at 700°C. This process is called pyrolysis. The products of this process are then recycled into new products.

Replacement of polymer with others material.
Example: Use paper bag instead of plastic bag.

Polymer can be reused and made into decorative items.

Inventing biodegradable polymer.
Such polymers should be mixed with substances that decompose by bacteria or light.

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1 comment:

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