Types of plastics

Plastics

. types of plastics

. differentiate between thermoplastics and thermosetting plastics

The dictionary meaning of plastic is 'capable of being easily formed or moulded'.

There are a number of synthetic materials available under the name of plastics.

Plastics have their origin in the chemical synthesis of materials from different sources like

-agriculture

-agriculture and petroleum

-petroleum and coal

-petroleum and mineral

-minerals

Of these, coal and petroleum are mostly used in making plastics

Plastics are divided into three major categories

-thermoplastic

-thermo-setting plastics

-elastomers

Thermoplastics

These are formed into shape by the application of heat and pressure. They soften when heated, and become solid agian when cooled. There is no chemical change in the moulding operation.

Thermoplastics are

-nylon

-polythene

-polypropylene

-polystyrene

-poly vinyl chloride

-acrylic resin

-cellulose

Nylon(polymide)

It is strong, tough and of light weight. It has a good abrasion resistance, and resistance to chemicals, fuels and oils.

It is used for making light engineering components such as gears, bushes, bearings, machine slides, rollers, brush bristles etc.

Polythene

There are two types

-low density polythene

-high density polythene

Polythene is cheap. It has high resistance to water, oils and chemicals. It can also withstand sizable temparature changes.

Low density polythene is used for making bags, sacks for package, dust bins, toys and house wares etc.

High density polythene is used for large moulded containers, bottles, milk crates, pipes and better quality House-wares.

Polypropylene

It is the lightest among plastics. It is tough and has high resistance to heat and chemicals.

It is used for making automobile accelerator pedals,suitcases, hospital equipment, ropes and twines etc.

Polystyrene

It is the cheapest, had good resistance to water, oils and alkalis. But it disolves in solvents.

It is used for making thin-walled containers for dairy products  and food stuffs. It is also used for fridge liners, spools, cassettes and cartridges for taps and photographic films. It is also used  in vaccum cleaners

Poly vinyl chloride

It possesses good physical strength, and has good resistance to water and chemicals. It is a good electrical insulator.

PVC may be flexible or rigid.

Rigid PVC is used for pipes and fittings, wall cladding, electrical conduits, gramaphone records, bottles for edible oils etc.

Flexible PVC is used for cable and wire insulation, floor and wall covering, tents and hose-pipes etc.

Acrylic resin

It is popularly known as perspex. It possesses exceptional stability in outdoor weather, resulting wide use in sings and displays and light fittings. At room temparature, it is rigid. It is transparent surface, gloss, chemical resistance and moldability.

There are used for making toys, cutlery handles, electrical parts, knobs, electrical insulating taps etc.

Cellulose nitrate, well known by the trade name of 'celluloid' is available in a variety of colours. It is still popularly used for spectacle frames, fabric coatings etc.

Thermo setting plastics

These are some plastics that undergo chemical changes during processing to become permanently insoluble and infusible.

There are

-phenolics

-aminos

-epoxy

-polyster resins

Phenolics

There are based on phenol-formaldehyde resins and are often called as Bakelite.

Bakelite is available mostly in brown and black colours. It is a good electrical insulator. Bakelite shows good resistance to water, acide and most solvents. It is rigid, and has  low thermal conductivity.

It is used for saucepans and kettle handles, terminal blocks, electrical insulator. Bakelite shows good resistance to water, acid and most solvents. It is rigid, and has  low thermal conductivity.

It is used for saucepans and kettle handles, terminal blocks, electrical swith -gears, cooker control knobs, voltage regular covers etc.

Aminos

Aminos are the products of a combination of urea or melamine with formaldehyde to form urea formaldehyde and melamine formaldehyde.

Aminos are available in an unlimited range of colours. They have good resistance to oil, grease, solvents and heat. They have good strength, and are hard, rigid and durable. They are free from odour and taste.

Urea formaldehyde is widely used in domestic electrical fittings like switch -covers, plug tops, bottle tops for scent etc.

Epoxy

Epoxy adhesive are used as casings for pipe fittings, electrical and other equipments.

They are also used as low pressure laminates such as printed circuit boards, boat bodies etc.

Polyster resins

Polyster resins are used with fibre  glass for making glassfibre reinforced plastics.

Elastomers

These are materials that can be stretched repeatedly to atleast twice their original length, which will return with force to their approximate original length when the immediate stress is released.

Elastomers are made with modified thermoplastics and rubber, natural and synthetic.

Elastomers are used for gaskets, moulds, foam mattresses and insulations.