Plastics

Polylactic Acid (PLA)

General information

Description

Polylactic acid (PLA) is a bioplastic. It is made of renewable biomass. Contrary to plastics derived from fossil sources, it is a green material. Consequently, its price is somewhat higher than average. Under appropriate conditions (industrial compost facilities) it is biodegradable. However, under normal conditions PLA is relatively stable. It is by nature quite a hard plastic which can be transparent and can be coloured. When transparent it may fluoresce slightly, not at all or at best vaguely yellow/greenish under UV.

History

Already in 1946 the first patent was registered, but commercial production started only at the beginning of the 21st century. Owing to the interest in bioplastics production is increased hugely since and the number of applications and production methods is growing.

Production, Application, Appearance

PLA is used as film, for bottles, degradable medical implants, food packaging and as 3D printing material.

Properties

Material properties

Thermoplastic
Density: Rigid = 1.21-1.29 g/cm3
Melting point: 164-178°C
Glass transition temperature: 55-75°C

Identification properties

Cell structure (foam): not applicable
Smell: no characteristic smell
Touch: no characteristic feeling
Sound: Rigid = no characteristic sound; Film = hard rustling sound
UV-radiation (when clear): fluoresces slightly or at best vaguely yellowish/greenish
Polarising filters: it does not give an effect or shows neutralises the effect (gives a blue and yellow hue)

Degradation

Process

Photo-oxidation, soiling (electrostatic).

Details

PLA is not considered a problem plastic. However, it is compostable and may show problems with time.

Symptoms

Yellowing, surface becomes matte, loss of mechanical properties resulting fractures and tears.

Susceptibility

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

Preventive conservation

Recommendations

UV-RADIATION: keep below 75 µW/lm UV filter for daylight and fluorescent light - reduce intensity
LIGHT: 1 slight change in approx. 30 Mlx.h Moderate light dose - control intensity and exposure time
OXYGEN / OZONE: ambient conditions
TEMP: common indoor conditions 10-30°C
RH: common museum conditions 40-60% RH fluctuations: setpoint ±10% or ±5% when allowing seasonal fluctations between 35-65%