Know Your Plastics
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| Top left: Vintage tortoise shell jewellry. Top right: Tortoise shell telephone. Bottom right: Modern-day plastic. |
In this article, the focus
is to paint a simplified picture of plastics – what they are, their structure, arrangement
and uses.
A brief history and
introduction…
World War I ushered
in grave hardships that made previously common materials like wood, metal and glass
a luxury. In that period, it became apparent that processing petroleum into raw
materials was a lot easier than processing coal. The first attempt at man-made
plastic was the “Parkesine” by Alexander Parkes. Debuted at the 1862 Great International
Exhibition in London, this organic material was gotten from cellulose and is
now known as celluloid.
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| Left: Victorian brooch made from Parkesine. Right: Dial telephone made from Bakelite. |
Uses of plastic…
Plastics are the most
versatile, manufactured material of our modern world. We see it everywhere in a
million and one things around us;
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Toys
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Roofs
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Paint
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Clothes and shoes
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Water pipes
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Adhesives
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Insulation (thermal and electrical)
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Replacements for body parts
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Soundproofing
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Electrical cables
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Automobiles (Body parts of cars and boats)
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Packaging for products e.t.c.
Talking About the General
Features/Characteristics/Attributes…
The name “plastic” connotes “flexibility” but, this does not mean weak; certain plastics are unbelievably strong and long-lasting. Whether the plastic is hard or soft, in prosthetic limbs or adhesives, they all share very many attributes that include:
1. Plastics are plastic. Plastic is flexible and easily moulded into different shapes, sizes and colours. For example, while some plastics are bottles and drums, others will end up as car parts (fender and dashboard) and even as foam (Styrofoam).
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| Pictoral description of .plastic polymer design. |
2. Plastics are primarily synthetic materials that are chemically-designed under artificial conditions. Meaning, even though the plastics may appear similar to natural resins from trees and plants, plastics cannot exist randomly in the natural environment. Plastics, generally, are a composition of numerous, large, heavy molecules of long-chain carbon atoms that have spaces filled with hydrogen, oxygen, chlorine, nitrogen, fluorine or sulphur. These molecules are known as polymers (poly and monomers) which mean “many monomers”. For example, the combination of two hydrogen atoms and one carbon atom creates the ethene monomer. The continuous replication of this monomer creates polyethylene known as polythene.
3. The molecular weight of plastic is very high because each molecule within has thousands of atoms bound together. E.g. nylon can have 38 or more atoms.
4. Plastics are light-weight. Compared to aluminium, copper or stone used in the production of space station frames and bulletproof vests, their density is smaller even though the plastics have varying degrees of strength.
5. Plastics are insulators. A closer look at the handles of pots and pans, thermos cups, coolers and, the inner lining of winter jackets and thermal underwear will reveal heat-resistant plastics. The wiring, cords and outlets of your electrical appliances and fittings are all electrically insulating plastic.
6. Plastic polymers are easily modified into an unlimited array of applications with the help of additives. Polymer properties are such that they can appear like cotton or silk fibres in one application; marble or aluminium in another then, foam insulation or flexible films in another application.
7.
Plastics are waterproof.
8.
Plastics are relatively inexpensive.
Classes/Types/Groups of
Plastic…
The word plastic is
often used in the singular like it is a single, individual material, but did
you know that there are so many types of plastics? If you are like me and
believed “plastic is plastic! Put a lot, it is hard, but a little, it is soft.
The End,” Boy, you (and I both!) are so off! Plastics are so many and so
differing that their similarities determine their grouping. For instance,
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Some plastics are gotten from natural plants and
animals (e.g. cellulose), while others are synthetically manufactured in
complex chemical processes (e.g. nylon).
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Plastics are also grouped according to the expected
life of products. Appliances, furniture, automobiles and construction materials
should last an average of three years so, are labelled durable products.
Non-durables have product lives of less than three years, for example, utensils,
toys, disposables, sport and recreation equipment, packaging.
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Plastics can be grouped according to the
structure of the monomers in their polymers, for example, polyethenes,
polyesters, polyurethanes etc.
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Based on processing (whether previously-moulded
plastic softens or not when heated after moulding), plastics are in two broad
groups - thermoplastics and thermosets. For example, when heated, celluloid,
thermoplastic can be remoulded while materials like Bakelite and polyphenol
formaldehyde decompose.
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For the all-important recycling process,
plastics are arranged into groups that will minimise contamination during
processing. The grouping is according to the type of polymers that produce the
plastic alongside physical and chemical properties. This group has seven
sub-sets and, if you have ever looked on the side of any packaging and seen the
recycling symbols “1 – 6” and “null” or "1 to 7", then you have handled a sub-set of this
group.
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| Seven Plastic Types in Recycling. |
Over the next few
weeks, I will simplify the seven different types of plastics as they relate to
the world of recycling.
Stay tuned! Stay Green!
REFERENCES
https://plastics.americanchemistry.com/Lifecycle-of-a-Plastic-Product/
https://www.explainthatstuff.com/plastics.html
https://plastics.americanchemistry.com/How-Plastics-Are-Made/
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