Plastics

Extruded polystyrene (PS, XPS extruded)

General information

Description

Extruded Polystyrene (XPS) is only produced as foam. It is commonly white, light pink, yellow, or blue cloloured. It has a compact, closed cell structure with small cells. It is hard, tough, and light-weight. XPS foam can make a squeaky sound when rubbing over its surface (rubbing over a window works well too). XPS foam is highly susceptible for acetone.

History

XPS foam is commercially available since 1944.

Production, Application, Appearance

XPS is often produced as boards in white, light pink, yellow, or blue. Owing to its light weight it has good buoyancy. It also has good insulation properties and is used for boats and disposables (cups etc.)

Properties

Material properties

Thermoplastic
Density: foam = 0.028-0.045 g/cm3
Melting point: 275°C
Glass transition temperature: 85-102°C

Identification properties

Cell structure (foam): closed - spherical
Smell: no characteristic smell
Touch: no characteristic touch
Sound: foam = squeaky
UV-radiation (when clear): not applicable
Polarizing filters (for clear PS): not applicable

Degradation

Process

Photo-oxidation.

Details

XPS is not considered a problem plastic.

Symptoms

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

Susceptibility

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

EPS is highly susceptible for polar and non-polar solvents, especially acetone; also for plasticizers that can be emitted by other plastics.

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%
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Handle with care. XPS is not elastic and indentations are irreversible