Casein Plastic from Milk
Observe how casein protein from milk can be transformed into a biodegradable plastic through acid precipitation and molding. This was one of the earliest forms of plastic used for buttons and decorative items.
Plastic
Heat the milk and add vinegar to precipitate casein protein. Then mold the precipitate into plastic.
The Science Behind Casein Plastic
Casein plastic is made from milk protein through acid precipitation:
- Milk contains about 3% casein protein
- Adding acid (vinegar) changes the pH, causing casein to precipitate
- The precipitated casein forms long polymer chains
- When dried, these form a hard, plastic-like material
- Casein plastic is biodegradable and was used historically before petroleum plastics
1. Heat milk to about 50°C (not boiling)
2. Add vinegar (acetic acid) to lower pH to 4.6 (casein's isoelectric point)
3. Casein precipitates out as white curds
4. Separate curds from whey (liquid)
5. Mold curds into desired shape and let dry
6. Final plastic can be polished and finished
- Used from early 1900s to 1940s for buttons, buckles, jewelry
- Tradename "Galalith" (French for "milk stone")
- Replaced by synthetic plastics after WWII
- Recently revived as a biodegradable alternative to petroleum plastics
