Plastics

PLASTICS

Plastics are important class of synthetic material. Like synthetic fibres, plastics are also polymers.
Plastics are part of our every day life.
The arrangement of the monomers in plastic can be linear or cross-linked.

Depending upon the arrangement of monomer units plastics are of different types like-

Thermoplastics:

A thermoplastic (sometimes written as thermo plastic) is a type of plastic made from polymer resins that become a homogenized liquid when heated and hard when cooled.
Thermoplastics can be reheated, reshaped, and frozen repeatedly. This quality makes thermoplastics recyclable.

Polystyrene (a plastic) objects

Example:

Low density Polyethylene (LDPE):

Polyethylene is the most commonly encountered thermoplastic and is used to make polybags, grocery bags, and packaging of foods and bread.
It is a polymer of ethylene.

HDPE (High-Polyethylene)- Used for making containers for strong and corrosive household and industrial chemicals such as bleaches and acids.

PET (Polyethylene terephthalate) – Used for making containers for Microwave cooking, bottles of carbonate beverages, and other food containers.
PP (Polypropylene) - Used for making ketchup bottles, yogurt containers, medicine bottles, and automobile battery casings.

PVC(Polyvinyl chloride):

Thermosetting plastics:

Thermoset, or thermosetting plastics are synthetic materials that strengthen on being heated but cannot be successfully remoulded on reheating.

On heating the monomers get cross linked and become hard.
This is in contrast to thermoplastics, which soften when heated and hardened and strengthened after cooling.

Example:

Bakelite:

Bakelite is a poor conductor of heat and electricity. It is used for making electrical switches, handles of various utensils, etc.

Melamine:

It is a versatile material. It resists fire and can tolerate heat better than other plastics.
It is used for making floor tiles, kitchenware and fabrics which resist fire.