[Chemistry Class Notes] on Properties of Plastics Pdf for Exam

Plastic is a polymer just like synthetic fibers which can be molded into desired shape and size when soft and can be hardened to produce durable articles. The term ‘Plastic’ was derived from the word ‘Plastikos’ which means ‘to mould’ in Greek, and it is used to refer to a wide range of semi-synthetic or synthetic organic polymers. Different types of plastics are known to possess different physical and chemical properties. Many articles like chairs, tables, buckets, toys, balls, etc are made of plastic material.

Properties of Plastics

• They are light in weight and are chemically stable.

• Easily moulded into different shapes and sizes.

• Good insulation and low thermal conductivity.

• Good impact resistance and they do not rust.

• Good transparency and wear resistance.

• Poor dimensional stability and can be easily deformed.

• Low processing cost.

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Different Types of Plastic

Plastics are of Two Types. They are

• Thermoplastics

• Thermosetting Plastic

Thermoplastics

The term ‘thermoplastic’ refers to plastics that do not undergo any chemical changes when subjected to high temperatures. These plastics do not undergo any changes in their chemical structures and chemical compositions when subjected to heat and can be changed into a soft state and remolded multiple times. Examples: Polystyrene, Teflon, Acrylic, Nylon, etc.

Thermosetting Plastics

They are also known as thermosets, and are plastics that can be molded only once and do not change shape on applying heat. These plastics can only be molded once and they cannot be softened on further heating. These plastics undergo degradation and become damaged when exposed to a large amount of heat. Examples: Vulcanized rubber, Bakelite, Polyurethane, Epoxy resin, Vinyl ester resin, etc.

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Polyethylene

It is one of the most commonly used thermoplastics in the world. The primary application of polyethylene (polythene) is in packaging. It is often used to make plastic bags, bottles, plastic films, containers, etc.

Polyethylene Properties

• They exhibit strong creep when placed under a persistent force.

• The mechanical strength of polyethylene is comparatively lower than other plastics.

• They are very good insulators of electric current.

• The rigidity and the hardness of the polymer are relatively low.

• They exhibit strong creep when placed under continuous force.

Structure of Polyethylene

Polyethylene is made by the reaction of multiple ethylene molecules in the presence of a catalyst to break the double bond and connect the carbon atoms into a chain.

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Types of Polyethylene

Polyethylene can be classified into different types based on the plastic density and the degree of branching in its structure.  Different types of polyethylene exhibit different mechanical properties and melting point of plastic.

• High-density polyethylene (HDPE)

• High-density cross-linked polyethylene (HDXLPE)

• Medium-density polyethylene (MDPE)

• Cross-linked polyethylene (XLPE)

• Low-density polyethylene (LDPE)

Uses of Polyethylene

• It is used in packaging products.

• It is used for cable jacketing because it is a good insulator of electric current.

• LDPE is also used in pipes, fittings, garbage bags, food packaging, etc.

• HDPE is also used in ropes, fishing and agricultural nets, and industrial fabrics.

Recycling of Plastic

• It is hard to overstate the importance of plastic recycling. They become mixed with other chemicals or materials if they are not recycled at the appropriate time, making recycling more difficult and causing pollution.

• They are non-biodegradable and are not degraded by microbial action.

• To circumvent this, biopolymers or biodegradable polymers must be used.