Plastics

Casein Formaldehyde (CF)

General information

Description

The starting material of casein plastics is milk. Addition of formaldehyde (approx. 4%) causes the milk protein casein to cross-link into a thermoharder. Casein formaldehyde (CSF) feels hard and cold and produces a clear sound when tapped upon. CF can readily absorb dyes and is therefore often coloured. It can be made translucent and opaque. Nowadays production is limited but it is still used for specific applications such as buttons.

History

The first patents date back to 1885 but CSF became commercially available only after 1905 as imitation of natural materials. Production declined after the 1950s.

Production, Application, Appearance

Casein is used mainly for jewellery, buttons, brushes, and handles (for example umbrellas). In the early 20th century it served as an imitation of natural materials such as ivory, tortoiseshell and horn. Nowadays it is mostly used for buttons.

Properties

Material properties

Thermoset
Density: ?? g/cm3
Melting point: 80-85°C (softens)
Glass transition temperature: not applicable

Identification properties

Cell structure (foam): not applicable
Smell: no particular smell but can produce a rancid odour.
Touch: feels hard and cold
Sound: produces a fairly clear sound
UV-radiation (when clear): not applicable
Polarizing filters (for clear CE): produces prismatic colours - reversing the effect of the filters

Degradation

Process

Photo-oxidation (degradation by light), atmospheric degradation, soiling (electrostatic).

Details

Is not considered a sensitive plastic.

Symptoms

Craquelure, yellowing, surface becomes matte, loss of mechanical properties resulting in tears and fractures, deformation (warping).

Susceptibility

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

CF objects contain a small amount of water as a 'plasticiser'. Nevertheless, CF is sensitive to water (vapour and liquid), absorbs water easily and consequently swells. CF also reacts to RH fluctuations. It is resistant to various solvents but strong alkaline solutions cause degradation of the polymer. CF is best kept at a relatively high, constant humidity (RH 60% ±5%). At a low RH CF will desiccate, shrink and become brittle.

Preventive conservation

Recommendations

UV-RADIATION: keep below 75 µW/lm UV filter for daylight and fluorescent light - reduce intensity
LIGHT: 1 just noticeable 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: 60% RH fluctuations: keep constant - setpoint ±5%