SYNTHETIC POLYMERS NATURALLY OCCURRING POLYMERS This group consists of naturally occurring polymers and chemical modifications of these polymers. Cellulose, starch, lignin, chitin, and various polysaccharides are included in this group. These materials and their derivatives offer a wide range of properties and applications. Natural polymers tend to be readily biodegradable, although the rate of degradation is generally inversely proportional to the extent of chemical modification. –
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Naturally occuring polymers exist in plants or animals Natural polymers are made up of carbon, hydrogen, nitrogen and oxygen Examples of naturally occuring polymers are (a) Protein : in muscles, skin, silk, hair, wool and fur (b) Carbohydrates : in starch and cellulose (c) Natural rubber : in latex Proteins is formed by the polymerisation or monomers known as amino acids polymerisation
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amino acids
protein
(monomers)
(polymer)
Carbohydrates such as starch and cellulose consist of monomers known as glucose joined together chemically. polymerisation
glucose (monomers) – –
carbohydrates (polymer)
Natural rubber found in latex consists of monomers known as isoprene ( 2 – methylbuta – 1, 3 – diene ) joined together chemically. Natural rubber comprises the molecules of the monomer 2-methyl-1,3-butadiene, also called isopropene, joined together to form a long chain.
SYNTHETIC POLYMERS •
Synthetic polymer is a polymer that is manufactured in industry from chemical substances through the polymerisation process. Through research, scientists are now able to copy the structure of natural polymers to produce synthetic polymers.
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Plastics, synthetic fibres and elastomers are examples of synthetic polymers.
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The raw materials for the manufacture of synthetic polymers are distillates of petroleum.
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However, most of them can be classified in at least three main categories: thermoplastics, fibres and elastomers. Thermoplastics
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is a polymer which, when subjected to heat, becomes soft so they can be moulded into various shapes.
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the properties of plastics are : light, strong, inert to chemicalssuch as acids and alkali and are insulators of electricity and heat.
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examples of plastics are polyethylene (PE), polyvinylchloride (PVC), polypropylene (PP), polystyrene, Perspex and Bakelite. Synthetic fibres
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are long chained polymers that withstand stretching.
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examples of synthetic fibres are nylon and Terylene.
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Nylon is used to make ropes, fishing lines, stocking, clothing and parachutes.
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Terylene is used to make clothing, sleeping bags and fishing nets. Clothes made from Terylene do not crease easily.
Elastomer –
is a polymer that can regain its original shape after being stretched or pressed.
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both natural rubber and synthetic rubber are examples of elastomer.
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examples of synthetic rubbers are neoprene and styrene – butadiene rubber ( SBR )
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SBR is used to make car tyres.
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The two types of polymerisation are:
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polymerisation by addition . polymerisation by condensation .
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Polymerisation by addition involves monomers with >C = C< bonding, where the monomers join together to make a long chain without losing any simple molecules from it. Examples of polymers produced through this process are polythene, PVC perspex and other plastics.
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Polymerisation by condensation involves the elimination of small molecules like water, methanol, ammonia or hydrogen chloride during the process. Examples of products of this process are terylene and nylon-66.
SYNTHETIC POLYMER & THEIR USES IN DAILY LIFE Synthetic Polymer Neoprene Polyvinyl chloride or PVC (polychloroethene) Polyamide (nylon) Polypropene Teflon (polytetrafluoroethene or PTFE) Polyester Polyethylene terephthalate (PET, PETE) Polythene (polyethylene) Perspex (polymethyl2-methyl propene) Polystyrene – • • • • •
Uses Shoe soles, hoses, radiator hoses, wetsuits Raincoat, pipes, to insulate electric wires Parachutes, carpet, ropes, form-fitting skiwear, hosiery Plastics, bottles, plastic tables and chairs To make non-stick pots and pans Filters, conveyor belts, sleeping bag insulation Soft drink bottles, peanut butter jars, salad dressing bottles Plastic bags, containers and cups Aeroplane window panes, lenses, car lamp covers Styrofoam® cups, grocery store meat trays, cafeteria trays
Synthetic polymers have been used widely to replace natural materials such as metals, wood, cotton, animal skin and natural rubber because of the following advantages : Strong and light Cheap Able to resist corrosion Inert to chemical reactions Easily moulded or shaped and becoloured
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Can be made to have special properties
THE EFFECT OF THE USES OF SYNTHESIS POLYMERS TO OUR ENVIRONMENT The use of synthetic polymers, however results in environmental problems Most polymers are not biodegradable. Polymers cannot be decomposed biologically or naturally by bacteria or fungi as in the case of other garbage. Thus, the disposal of polymers has resulted in environmental pollution because they remain in the environment forever. Discarded plastic items may cause blockage of drainage systems and rivers thus causing flash floods. Plastic containers and bottles strewn around become good breeding places for mosquitoes which cause dengue fever, or malaria. Small plastic items that are thrown into the rivers, lakes and seas are somethings swallowed by aquatic animals. These animals may die from choking. The open burning of plastics gives rise to poisonous and acidic gases like carbon monoxide, hydrogen chloride and hydrogen cyanide. These are harmful to the environment as they cause acid rain. Burning of plastics can also produce carbon dioxide, too much of this gas in the atmosphere leads to the `green house effect'. The main source of raw materials for the making of synthetic polymers is petroleum. Petroleum is a non – renewable resource. This problem can be overcome by the following ways: Recycling polymers: 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. Inventing biodegradable polymers: Such polymers should be mixed with substances that can be decomposed by bacteria (to become biodegradable) or light (to become photodegradable) .
