Some Common Plastics

What Is Plastic?

All plastics are polymers that are long chain-like molecules. These molecules are made up of many units called monomers repeating about thousands of times.

• However, different types of plastics have different types of properties.
• Some melt on heating, whereas some don’t.
• Some are transparent, whereas some are opaque.
• Some are rigid, whereas some are flexible.

Plastics Are Classified As:

1.Thermoplastics

Heating makes them soft and cooling makes them hard. This can be done many times without letting the plastic change its chemical properties. They can even be liquefied on heating. Thus, they can be molded into any shape again and again.

Examples Of Thermoplastics

Liquid crystalline polymers, polypropylene, polyesters, polysulfones, polyurethanes, polyethylene, polyvinyl chloride, ketones, polystyrene, and polyphenylene sulfide.

2. Thermosetting Plastics

They are initially soft or in a liquid state but become hard when heated. The plastic gets cured by increasing the cross-linking between the polymers. This can be done through the chemical reactions caused by heating. Two ways to increase the rate of curing are: to use a catalyst or to increase the pressure.

Examples Of Thermosetting Plastics

Melamine, bakelite, fiberglass, vulcanized rubber, silicone resin, duroplast, and cyanate esters.

Some Positive Points

• They have good electrical and thermal insulating properties. Thus, they are useful in making handles for the utensils.
• They do not corrode, rust, are resistant to chemicals, and are insoluble in water.
• Many plastics can be melted, molded again, cost low, and are odorless.
• They are thermoplastics that can be recycled.
• They are too versatile, durable, can be used on a wide range, and can be shaped with less heat.
• They can be combined with adhesives and aluminum foil.
• Rates to recycle plastic are less than that of paper.
• For the economy, their contribution has been high.
• Useful for transportation of items, furniture, and automotive design.
• Plastic has a good shock absorption capacity and lasts long.
• Safety tools like helmets, mouth gears, etc. are made easily with plastic.
• Used to store food and blood for a long time as fish, flesh, and blood cannot be wrapped up in paper.

Some Negative Points

• They are not stronger than metals. They may get deformed under pressure.
• They generally have low density.
• Cannot be used at high temperatures. Many types of plastics result in chemical reactions with the stuff inside when heated. This increases the risk of having cancer when that stuff is consumed.
• Most of the plastics are non-degradable and take over 20 to 500 years to decompose according to the structure.
• They clog waterways.
• Plastic is flammable.
• Plastic items become a hurdle for the rainwater to reach the ground. This affects the plants and grasses nearby as they don’t get enough water from the soil.
• Plastic items are thrown anywhere randomly. Thus, the animals eat them, get hurt, or get stuck in the marine litter.
• Toxic gases are released by the creation and recycling of plastic.

Some Common Plastics

1. Bakelite

It is also called polyoxybenzylmethylenglycolanhydride and its monomer is Dimethyl phenol. Its chemical formula is (C₆H₆O·CH₂O)n. When condensation reaction of phenol occurs with formaldehyde, Bakelite is formed. It can be quickly molded, but after setting it, it cannot be re-melted. It breaks easily if dropped and isn’t flexible. It is a thermosetting phenol-formaldehyde resin and is quite hard and brittle. It is resistant to temperature and fire. Much lightweight stuff or packaging cannot be made by it.

Uses of Bakelite

• It is used for making the handles of kitchen utensils, mineral wool bonding, office supplies, automobile insulators, mining foams, and electrical switches.
• Old heavy telephone instruments, radios, letter openers and tumbler switches were made up of Bakelite.
• The jewelry boxes, billiard balls, clocks, poker chips, sports equipment, fashion accessories, building materials, abrasives, oil filtration, buttons, toys, and kitchenware contain Bakelite.

Image depicting the structure of Bakelite

2. Nylon

It is a synthetic polymer. Amide is its monomer and is made of amide (-CONH₂) groups. Nylon fibers are made up of petroleum that helps us to melt and process them into various forms. It is composed of interlacing threads. Nylon fibers are elastic, stronger, tough, abrasion-resistant, chemical resistant, long-lasting, easy to wash, and temperature resilient. Nylon 66, Nylon 6, Nylon 510, and Nylon 1,6 are some types of Nylons.

Uses of Nylon

• The toothbrush bristles, sewing threads, tights, umbrellas, sportswear, ropes, fishing nets, reinforcing cords, ties, and undergarments, tapestry, and surgical sutures are made up of Nylon.
• Nylon increases the strength of the wool when blended with it.
• In the textile industry, it is used for making carpets, draperies, clothes, products that are resistant to fire, and elastic hosiery such as stockings.
• Military uses of Nylon include parachutes, mosquito netting, fuel pump diaphragms, shoelaces, flak jackets, hammocks, and tires for vehicles.
• For making machine parts, it can act like plastic.

Image depicting the Nylon(6,6) structure

3. ABS plastic

It is a terpolymer(or a copolymer) where ‘ABS’ stands for Acrylonitrile, Butadiene, and Styrene. Its chemical formula is (C₈H₈·C₄H₆·C₃H₃N)_n.

• Rigidity, fatigue resistance, hardness, and chemical resistance are provided to ABS plastic by Acrylonitrile. Formula for Acrylonitrile is (C₃H₃N).
• Butadiene is responsible for providing ductility and toughness when the temperature is low. This challenges its rigidity and heat resistance. The formula for Butadiene is (C₄H₆).
• The impenetrable surface, shine, rigidity, easy processing, and hardness are provided by styrene. Formula for styrene is (C₈H₈).

Uses of ABS plastic

• LEGO toys, power-tool housing, for 3D printing, steering wheel covers, computer keyboard, dashboards, door liners and handles, music instruments, compressors, gardening tools, nebulizers, and pillar trim.
• For household appliances, it is useful for refrigerator lines, food processors, vacuum cleaners, shavers, pipes and fittings, wall socket face-guard, briefcases, suitcases, and control panels.

Image depicting the formula for Acrylontrile, Butadiene, and Styrene

4. Polyvinyl Chloride

It is thermoplastic and Vinyl Chloride is its polymer. The formula of PVC is (C₂H₃Cl)_n. It acts like plastic as well as fiber. It is stiff, heavy, and transparent. It has thermal stability and high melt viscosity. Thus, it cannot be processed on its own and has to be combined with some polymer. Its low stability has introduced some issues in its processing. However, its improved composition has made it suitable for various applications.

Uses of Polyvinyl Chloride

• Useful for making water pipes, vinyl flooring tiles, boots, toys, shower curtains, siding and windows, garden hose, drainage pipes, raincoats, and electric wire insulation.
• In the medical field, it is used for making blood-collection bags, blister and clamshell packaging, medical tubing, and IV bags.
• Plasticizers added in PVC make it a rubber-like soft material useful to make soft slippers.

Image depicting the structure of PVC

Conclusion

Plastic can be found almost everywhere in various forms. As we see, it is irreplaceable for many applications. It turned into a threat to the environment due to its improper disposal by humans. If it is properly disposed of, instead of throwing it anyhow, it will prove to be a boon during as well as after its usage.

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