9.21C - Uses and properties of polymers

Match a property to the job

A property describes how a material behaves; a use is the job it does. Explain suitability by linking the property to what the product needs. For example, an electrical cable covering must prevent current passing to a person, so the polymer needs to be an electrical insulator. It must also bend with the cable.

The reverse reasoning is useful too: knowing that a polymer is flexible and waterproof suggests uses such as bags or wrapping. No single polymer is best for every job, and different grades or additives can change a polymer's properties.

Poly(ethene) and poly(propene)

Poly(ethene) can be made into thin, flexible, waterproof films. This makes it suitable for carrier bags and food wrapping: the film bends around its contents and resists water. Tougher, more rigid grades are used for bottles and containers. Its low density keeps products light; its electrical insulation allows use around cables.

Poly(propene) is tough, has low density and can be made into fibres, making it useful for ropes and carpets. Suitable grades are relatively rigid and heat resistant, so they are also used for food containers. A thin poly(propene) hinge can bend repeatedly without snapping: this is fatigue resistance, useful for flip-top lids.

Compare properties for the particular grade, thickness and use. A rigid container and a flexible film can be made from the same polymer type.