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Synthetic Fibres and Plastics

Plastics

Have you noticed how everything nowadays is derived from plastics? The plates we use, our cell phones, etc. Everything is plastic! Why is plastic so popular? What are the various types of plastics? Let us study in-depth about it below.

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What are Plastics?

Any synthetic or semi-synthetic polymers are ‘plastics’. Plastics used for industrial work come from petrochemicals. Plastic refers to its ability to deform without breaking. The polymer used in making a plastics are usually a combination of additives, colorants, plasticizers, stabilizers, fillers, and reinforcements. These additives affect the chemical composition, properties, and mechanical properties of plastics and affect its cost.

The two types of plastics are Thermoplastics and thermosetting polymers.

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Thermoplastics and Thermosetting Polymers

Thermoplastics can be remoulded over and over again after heating. Some of these polymers are amorphous and some carry a partially crystalline structure. Thermosetting polymers are those polymers that solidify into a permanent shape. These polymers too are amorphous and have infinite molecular weight.

Physical Properties of Plastics

  • Properties of plastics vary depending on the chemical composition, arrangements and the processing method of its subunits.
  • Plastics come from polymers, hence all plastics are polymers, but not all polymers are plastic.
  • Plastics may be amorphous solids, crystalline solids, or semicrystalline solids (crystallites) or any other form of solids.
  • They are poor conductors of heat and electricity. The plastics that act as insulators mostly have a high dielectric strength.
  • Plastics have a slow rate of degradation and tend to be durable.

Can you think of more such properties?

Composition and Structure of Plastics

Plastics are mostly carbon-based atoms. Silicones are an exception since they based on the silicon atom. The carbon atom is capable of linking to other atoms with up to four chemical bonds. In plastics, the carbon atoms also link to hydrogen, oxygen, nitrogen, chlorine, or sulfur. When the linking of these atoms results in long chains, like pearls on a string of pearls, the polymer is termed as ‘Thermoplastic’. Thermoplastics are meltable. All thermoplastics have repeating units,i.e. the smallest identical section of the chain.  About vast majority of plastics are 92% thermoplastics.

To make unit cells a group of atoms is used called ‘Monomers’.Upon the combination of monomers, we get polymers or plastics. All the monomers contain double bonds between carbon atoms such that the carbon atoms can subsequently react to form polymers.

The plastic behavior of polymers is influenced by their arrangement of molecules on a large scale. In other words, polymers are either amorphous or crystalline. The arrangement of molecules in the amorphous state is random and are intertwined. In crystalline state, the arrangement of molecules is in a closely identifiable manner. On the other hand, semicrystalline materials exhibit crystalline regions, called crystallites, within an amorphous matrix.

The chemical structure of the plastics can change, with the use of copolymers, and the chemical binding of different elements and compounds and on the other hand, the use of crystallizability can change the processing, aesthetic, and performance properties of plastics. Alteration of plastics can also happen by adding additives.

Solved Examples For You

Q. Telephone instruments, plastic toys, ballpoint pens, plastic bowls are examples of :

a. Thermoplastics

b. Thermosetting plastics

c. Polyester

d. None of the above

Sol: a. Thermoplastics

Telephone instruments, plastic toys, ballpoint pens, plastic bowls are thermoplastics and so can be recycled.
Cooker handles carry bags, plastic covering on an electric wire, plastic chains etc are thermosetting plastics and so cannot be recycled.

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