Casein Formaldehyde (CF)
DescriptionThe 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. CSF 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.
HistoryThe 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, AppearanceCasein 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.
Density: ?? g/cm3
Melting point: 80-85°C (softens)
Glass transition temperature: not applicable
Identification propertiesCell 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
ProcessPhoto-oxidation (degradation by light), atmospheric degradation, soiling (electrostatic).
DetailsIs not considered a problem plastic.
SymptomsYellowing, craquelure, surface becomes matte, loss of mechanical properties resulting in tears and fractures, deformation (warping).
CSF objects contain a small amount of water as a 'plasticiser'. Nevertheless, CSF is sensitive to water (vapour and liquid), absorbs water easily and consequently swells. CSF also reacts to RH fluctuations. It is resistant to many solvents but strong alkaline solutions cause degradation of the polymer. CSF is best kept at a relatively high, constant humidity (RH 60±5%). At a low RH CSF will desiccate, shrink and become brittle.
RecommendationsUV-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%