Plastics

Polyethylene terephthalate (PET)

General information

Description

PET is a plastic best known from plastic bottles. It has a low permeability for gasses which ensures that soft drinks retain their sparkle. It is a thermoplastic, available from clear transparent to coloured opaque. PET is produced as film, sheet, industrial product and 3D-printing material. The price of PET is in the midrange. It is the fourth most produced plastic after PE, PP, and PVC. This is mainly due to the production of the synthetic polyester fibre.

History

PET was discovered in 1941 and soon after the production of polyester (textile) fibres followed. In 1952 the first polyester film became commercially available. From 1977 onwards bottles have been produced in a stretch blow moulding process.

Production, Application, Appearance

PET is often used as a (textile) fibre under the name 'polyester'. It is also well-known as (soft drink) bottles and it is used as a support for photographic and motion picture films and magnetic tapes.

Properties

Material properties

Thermoplastic
Density: Rigid = 1.3-1.4 g/cm3
Melting point: 245-265°C
Glass transition temperature: calc = 76-88°C; exp = 60-85°C; 60-76°C (amorphous)

Identification properties

Cell structure (foam): not applicable
Smell: no characteristic smell
Touch: no characteristic feeling
Sound: Rigid = quite high; Film = no characteristic sound
UV-radiation (when clear): fluoresces blue clearly
Polarizing filters (for clear EVA): film produces iridescence (rainbow colours like oil on water); rigid produces a colour pattern

Degradation

Process

Photo-oxidation.

Details

PET is not considered a problem plastic.

Symptoms

Discolouration, loss of mechanical properties resulting ultimately in small fractures.

Susceptibility

UV-radiation: Low
Light: Low
Oxygen/Ozone: Low
Temp: Low
RH: Medium (fluctuations)

Preventive conservation

Recommendations

UV-RADIATION: avoid extremes
LIGHT: 1 slight change in approx. 300 Mlx.h Avoid high light dose
OXYGEN / OZONE: ambient conditions
TEMP: common indoor conditions 10-30°C
RH: common indoor conditions 30-70% RH fluctuations: setpoint ±5% when allowing seasonal fluctations between 35-65%