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1.PLASTIC MATERIALS: In general, plastic materials are a normal part of everyday life. They also play important roles in sectors such packaging, telecommunications, transport, construction, medicine, agriculture and information technology. Plastics consist of long chains of molecules, mostly made of the element “carbon”. These chains of macromolecules are called polymers, which is another name for plastics. Polymers are composed of smaller molecules called monomers. 1.1 THE ORIGIN OF PLASTICS: Plastics can be divided into two types, according to their origin: –Natural plastics are obtained directly from vegetable or animal sources. For example, latex and cellulose are produced by plants, and casein is a protein that is found in milk. –Synthetic plastics are made with compounds that come from petroleum, natural gas and carbon. Most plastics that we use today are synthetic. 1.2 THE TRANSFORMATION OF PLASTICS: The industrial production of plastic from raw materials is called polymerisation. There are two basic steps in this process: -During the manufacturing process, fillers may be added to reduce the cost of production and enhance certain properties of the raw materials. Some typical fillers include fibreglass, paper, silica, mineral powder and sawdust. -Chemical additives can also be used, such as plasticizers which increase the flexibility and resistance of the final product. Pigments may also be added to give the plastic a certain colour. 1.3 PROPERTIES OF PLASTICS: Depending on their composition, certain plastics may be more rigid, more flexible or more elastic. In general, plastics are: -Physically resistant to stretching, bending, twisting and compression. -Good electrical, thermal and acoustic insulators. –Ductile because they can be pulled to make threads. –Malleable because they can be pressed into thin sheets. –Light with a typical density of 0.9 to 1.3 grams per cubic centimetre (g/cc). –Impermeable (to gas and liquids) –Recyclable in many ways, such as: -Chemical recycling, which breaks plastic down into its chemical components. -Mechanical recycling, which breaks plastic into small pieces that can be melted and made into tiny pellets. -Energy recovery, which burns plastic to produce heat, electricity or energy for other industrial processes.

Non-biodegradable plastic is made from petroleum products. Most of the plastics that we use today are non-biodegradable.

Biodegradable plastic is becoming more common. Some biodegradable plastics are broken down by bacteria and other biological agents. One example is biopol, which is used to make bottles and mouldings. It can be broken down by microorganisms in soil.


2.1 CLASSIFICATION BY INTERNAL STRUCTURE: Plastic materials can be divided into three groups, according to their internal structure:

Thermoplastics are composed of polymer chains that are weakly-connected to each other.

When thermoplastics are heated, they soften and can be moulded into different shapes.

Thermosetting plastics are composed of polymer chains that are strongly-connected.

Thermosetting plastics can be heated and moulded, and they maintain that shape after they cool down. However, these materials can be only heated and shaped once. The process cannot be repeated.

Elastomers are composed of polymer chains that are laterally connected. They can be folded or rolled into a ball, like string.

When new apply force to elastomers, they stretch because the polymer chains are very elastic. The production of elastomers includes a chemical process called vulcanisation, in which sulphur is added to rubber at 160ºC. This gives elastomers more strength, resistance and durability. However, it doesn’t change their natural elasticity.

2.2 INDUSTRIAL PLASTICS: Many plastics are used for industrial purposes. These are classified into groups.





Polyethylene terephthalate

Impermeable transparent and light

Packaging for food, drinks, products for personal hygiene, cosmetics and cleaning products

High-density polyethylene

Rigid and resistant

Buckets, bottles

Polyvinyl chloride

Wide range of hardness and impermeable

Low-density polyethylene

Soft, light and transparent


Flexible, chemical resistant and superficial hardness



Transparent and can be coloured

Expanded (Styrofoam)

Spongy and soft


Transparent and impact-resistant


Non-stick, smooth and slippery and heat-resistant


Transparent and flexible


Highly resistant and flexible

Production of textiles tennis racket strings









Polyester resins (UP)



Raw material



Natural rubber


Resistant and inert

Thermal and electrical insulation, shoe soles, waterproof suits, tyres, steering wheels, bumpers, paving, pipes, hoses, sponges, gloves, mattresses.

Synthetuc rubber

Petroleum products

Resistant to chemical agents


Synthetic rubber

Enhances the properties of synthetic rubber, making it harder, more resistant and impermeable

Diving suits, joints, pipes, hoses, straps, gloves, adhesives.