Observations and results
Were you able to see the curds when the hot milk and vinegar were mixed together, and could you scoop out the curds to make casein plastic?
After you add the hot milk to the vinegar, small, white chunks—or curds—should become visible in the mixture. This is because adding an acid (such as vinegar) to the milk changes the latter's pH (acidity) and makes the casein molecules unfold and reorganize into a long chain, thereby curdling the milk. You should be able to use a spoon to separate the curds from most of the liquid. Additional drying of the curds with the paper towels should make the curds ready to knead into a ball and use as casein plastic, which can be molded and decorated.
More to explore
Polymer Basics from Polymer Science Learning Center, Department of Polymer Science, the University of Southern Mississippi
Casein from Plastics Historical Society
Welcome to the Caseino: A virtual museum devoted to casein plastics from John Morgan
Turn Milk into Plastic! from Science Buddies
This activity brought to you in partnership with Science Buddies