Lecture on Different Plastic Materials and Thier Properties

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Lecture 7. Plastic Part Manufacture, Injection Molding

In the last 30 years, plastics have become the most dominant engineering material for most products. We take

a brief look at the most common types of plastics, and how they are processed.

All plastics are polymers; these polymers are further divided into two basic types: thermoplastics and

thermosets. Thermoplastics melt when heated – so they can be melted and re-formed again and again.

Thermosets harden when they are heated, if heated further, they will break down chemically and lose their

properties. Some thermosets have properties very similar to rubber, and are used as synthetic rubber; they are

categorized as elastomers. Here are some typical plastics and their uses:

Thermosets

General properties: more durable, harder, tough, light.

Typical uses: automobile parts, construction materials.

Examples:

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Unsaturated Polyesters: lacquers, varnishes, boat hulls, furniture

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Epoxies and Resins: glues, coating of electrical circuits, composite materials like fiberglass used in

helicopter blades, boats etc

Elastomers

General properties: these are thermosets, and have rubber-like properties.

Typical uses: medical masks, gloves, rubber-substitutes

Examples:

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Polyurethanes: mattress, cushion, insulation, toys

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Silicones: surgical gloves, oxygen masks in medical and other applications, joint seals,…

Thermoplastics

General properties: low melting point, softer, flexible.

Typical uses: bottles, food wrappers, toys, …

Examples:

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Polyethylene: packaging, electrical insulation, milk and water bottles, packaging film

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Polypropylene: carpet fibers, automotive bumpers, microwave containers, prosthetic body parts for

disabled people

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Polyvinyl chloride (PVC): sheathing for electrical cables, floor and wall coverings, siding, credit

cards, automobile instrument panels

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Polystyrene: disposable spoons, forks etc., also used to make Styrofoam™...