Turn Milk Into Plastic


Turn Milk Into Plastic

Turning milk into plastic is a fascinating exploration of the intersection of chemistry and everyday materials. This project not only provides a hands-on learning experience, but also opens the door to further experimentation and discovery. While most modern plastics come from petrochemicals, milk contains the protein casein, which forms a natural polymer. The project is easy and fun and only requires familiar everyday materials.

Background Information

History of Casein Plastic

White Milk Plastic Buttons
Pre-1953 Royal Australian Royal Air Force buttons made of milk plastic or Galalith. (Tyranny Sue, CC Attribution-Share Alike 3.0 Unported)

People have been using the milk protein casein for making plastic for over a century. Casein plastic, known as Galalith, was first produced in the late 19th and early 20th centuries. Galalith was popular for making buttons, jewelry, fountain pens, and even knitting needles. Its production peaked before the widespread use of synthetic plastics derived from petroleum.

Commercial Casein Plastic vs. Homemade Casein Plastic

Commercial casein plastic production involves a more controlled and precise process, often incorporating formaldehyde or other toxic additives to enhance the material’s properties, such as durability and flexibility. In contrast, the homemade method is simpler and non-toxic, produces a less refined product. Homemade plastic from milk is ideal for educational purposes and small craft projects.

Materials Needed

The only ingredients you need are milk and vinegar. For best results, use a measuring cup and measuring spoons.

  • 1 cup of milk (any type, though whole milk works best)
  • 4 teaspoons of white vinegar (other types work, but impart color)
  • A stove, hot plate, or microwave oven
  • A small saucepan (for the stove or hot plate) or a bowl (for the microwave)
  • A measuring cup and measuring spoons
  • A spoon
  • Paper towels or a cheesecloth or old piece of t-shirt
  • Molds or cookie cutters (optional for shaping)
  • Food coloring, glitter, or acrylic paints (optional for decorating)

Procedure

  1. Heat the Milk: Pour the milk into the saucepan and heat it over medium heat until it is hot but not boiling. Stir occasionally to prevent a skin from forming on the surface. Alternatively, heat the milk in a bowl in the microwave so that it is hot, but not boiling. The time depends on the appliance power, but it’s around 90 seconds.
  2. Add Vinegar: Remove the milk from the heat and add the vinegar to the hot milk. Stir the mixture for a few minutes. If you like, add glitter or food coloring. Notice the milk beginning to curdle as the casein proteins separate from the liquid.
  3. Strain the Curds: Pour the mixture through a paper towel or cloth to separate the solid curds from the liquid whey. Press out as much liquid as possible from the curds.
  4. Shape the Plastic: While the curds are still pliable, mold them into the desired shapes using your hands, candy molds, or cookie cutters. Kneading the curds before molding or cutting them yields the smoothest finish.
  5. Drying: Place the shaped plastic on a paper towel and let it dry for at least 48 hours. The plastic hardens as it dries.
  6. Decorate: Once the plastic is completely dry, decorate it with acrylic paints or other craft materials. For a shiny finish, sand any rough edges and coat the plastic with craft sealant.

Safety Information

  • Heat Safety: Be cautious when heating the milk. Use a stove or hot plate with adult supervision if necessary.
  • Handling: The curds may be slightly acidic due to the vinegar, so wash your hands after handling them.
  • Ventilation: Ensure the area is well-ventilated or else the odor of vinegar and curdled milk will linger.
  • Disposal: Don’t discard unused casein down the drain, as it clogs pipes. Instead, throw away any leftover material.

The Chemistry Behind the Process

Milk contains a protein called casein, which coagulates when exposed to an acidic substance like vinegar (diluted acetic acid). The low pH disrupts the micelles in milk that consist of calcium phosphate and casein, making the protein accessible. In the presence of heat, the casein molecules unfold and reorganize into long chains, forming a polymer. This polymer network traps the liquid whey, which you separate out, leaving behind a solid mass of casein plastic. The process of adding vinegar essential curdles the milk. This is a form of denaturation and precipitation, common in many biochemical processes.

You can use pretty much any mammal milk (cow, sheep, goat, camel, etc.) for this project. However, human milk only contains low levels of casein, so it is not a great choice.

Turning the Project Into an Experiment

To transform this project into an experiment, consider the following variables:

  • Type of Milk: Test different types of milk (whole, skim, soy, almond) and see how they affect the quantity and quality of the plastic produced.
  • Amount of Vinegar: Vary the amount of vinegar added to the milk and observe the effects on the curdling process and the final product.
  • Other Acids: Test the effectiveness of other common safe household acids, such as lemon juice, carbonated soda, or citric acid.
  • Heating Temperature: Experiment with different temperatures for heating the milk to see how it impacts the separation of curds and whey.
  • Drying Time: Compare the properties of the plastic with different drying times (24, 48, 72 hours).

Record your observations for each variable, noting changes in texture, strength, flexibility, and appearance of the plastic. This systematic approach aids in understand the factors influencing the production and properties of casein plastic.

How to Turn Plant-Based Milk Into Plastic

While it is a spoiler alert if you’re testing types of milk for an experiment, here is what you need to know if you’re using a plant-based milk for this project. Plant-based milks contain proteins, but these proteins differ significantly from the casein found in animal milk. The chance of getting plastic from plant milks depends on the type and structure of these proteins.

Soy Milk

Soy milk contains proteins, such as glycinin and beta-conglycinin. These proteins denature and form a gel-like substance following exposure to heat and acidic conditions, similar to the process with casein in cow’s milk. However, the resulting material has different properties from casein plastic. Basically, the procedure produces tofu. Of all the plant-based milks, soy milk has the best chance of forming a plastic.

Almond Milk

Almond milk contains fewer proteins compared to soy milk and cow’s milk. The primary protein in almond milk is amandin. Although it coagulates, the amount of protein is generally too low to form a substantial polymer network similar to casein plastic. If you want plastic from almond milk, you’ll need a lot more milk than just one cup of it.

Other Plant-Based Milks

Other plant-based milks, such as oat, rice, and coconut milk, have varying protein contents and structures. Generally, these milks have lower protein concentrations than animal milk. As with almond milk, you need a lot more milk to get a decent amount of plastic. But, the basic process remains the same. Heat the milk, add vinegar, and strain the solids.

References

  • PanouillĂ©, M.; Durand, D.; et al. (2005). “Aggregation and gelation of micellar casein particles”. Journal of Colloid and Interface Science. 287 (1): 85–93. doi:10.1016/j.jcis.2005.02.008
  • Robinson, R. (2012). Robinson: Modern Dairy Technology: Volume 1 Advances in Milk Processing. Springer Science & Business Media. ISBN 9781461520573.
  • Trimborn, Christel (August 2004). “Jewelry Stone Make of Milk“. GZ Art+Design.