How to make Homemade Plastic with Milk and Vinegar

What is Plastic

Plastic is durable, washable material, that’s why it’s frequently used for making toys. Plastic can consist of synthetic or semi-synthetic organic compounds. Those compounds are malleable and can be molded into solid objects. There is another term for that - plasticity. That’s the property of the material that can be formed or modified into a new, permanent shape. You probably heard that our brain is plastic or has plasticity - that’s because it can change based on our experiences.

Plastic is usually synthetic and most commonly made from petrochemicals. But there are other materials for making plastic that is renewable and we can get them from corn, cotton, milk and many other plants.

Plastic is widely used due to the versatility it possesses. Low cost, ease of manufacture and imperviousness to water are just some of the characteristics that make plastic so popular. Today, we find plastic used in things that range from paperclips to space stations that orbit the earth.

The first fully synthetic plastic was Bakelite, invented in 1907 by Leo Baekeland, who named it after himself. The word "plastic" is much older than that: it comes from the Greek plastikos, meaning something that can be moulded.

The downside of plastic is that its widespread use in the early 20th century created a huge amount of trash due to the slow decomposition of the plastic large molecules. So today there is a lot of effort put in solving that problem, mainly through recycling.

But there are other ways to get plastic, for example from milk! Plastic made from milk was patented in 1899 under the name Galalith, and in the first decades of the 20th century it was everywhere: buttons, buckles, jewellery, fountain pens and knitting needles were all made from it, right up until cheaper oil-based plastics pushed it aside.

Plastic from Milk and Vinegar Explanation

Milk is a colloid (a mixture in which one substance of microscopically dispersed insoluble particles is suspended throughout another substance). Milk is mostly water, and floating in that water are fat, a sugar called lactose, vitamins, and minerals such as calcium. Two types of proteins are present in milk: around 80% of the protein is casein and the rest is whey protein.

Casein is already a polymer: every protein is a long chain of smaller units joined together. In fresh milk those chains are folded up into tiny bundles called micelles, and each micelle carries a slight negative charge. Because like charges push each other away, the micelles keep their distance and stay evenly spread out through the milk. That is why milk is a smooth white liquid and not a lumpy one.

Adding vinegar changes the balance. The acid neutralises that negative charge, and the moment the micelles stop repelling each other, nothing keeps them apart. They unfold, tangle together and clump into a solid - exactly what we call curdling. Drain off the watery part and the tangled mass left behind is our plastic.

These clumped chains do not dissolve in water and can be molded in different shapes, in other words, they form organic plastic (bioplastic). Plastic made from casein is biodegradable and comes from a renewable source, but today it costs more to produce, so its usage is not that widespread. (Worth knowing: the casein plastic once sold as Galalith was hardened with formaldehyde, so despite starting life as milk, the real industrial version was never something you would want to eat.)

Environmental impact of plastic and bioplastic

As already mentioned, most of today's plastic is made from fossil fuels. On the other hand, organic plastic, or bioplastic, is mostly made from starch, cellulose, sugar, wood, and biomass. Since all of those are renewable resources, it makes it a more sustainable production activity than conventional plastic that is made from non-renewable fossil fuels.

But is the bioplastic better for the environment is still a highly debatable topic. We know today that bioplastic does significantly reduce emissions of greenhouse gases and saves non-renewable energy consumption. But with that said, it also has some negative effects on our environment:

• Eutrophication - when water becomes overly enriched with nutrients and minerals and that results in excessive growth of algae. This process often results in oxygen depletion of the water) and
• Acidification - reduction of the waters pH value due to the more production of carbon dioxide (CO2). This can have a major negative impact on many water lifeforms.

In any case, we should strive to use plastic responsibly. Don’t create more trash, repurpose or recycle stuff. And now on to the experiment!

Materials needed for Homemade Plastic

• Milk (300 mL or more, with higher fat content)
• Vinegar (2 spoons)
• Kettle
• Colander
• Spoon
• Bowl to mix it
• Paper towel
• Molds

Instructions for Milk and Vinegar Plastic

You can check the video at the start of the article for how to make a homemade plastic, or continue reading instructions below.

1. Heat the milk on the stove or in the microwave to at least 70℃ (158℉ ). We had the most success with fresh milk with 3.2% milk fat.
2. Pour the hot milk into the bowl and add 2 spoons of vinegar to it. Mix vigorously for a minute or two, you should see clumps forming.
3. Drain the mixture so you are working only with the solid part
4. Use the paper towels (4-5) to drain that mass of any leftover water. Knead that mass with your hands and shape it into the ball
5. Use the mold to make desired shapes or just shape it freestyle and leave it to dry 48h
6. After that time, your sculpture got hardened and it’s done! Now you can decorate it as you wish markers or art colors

If you liked this activity, you should also check out how to make Homemade Playdough, and for more similar activities you can try and make your own rocket or try using chemistry creating some sweet treats with homemade sugar crystals. Or if you’re more into organic magic, be sure to check how to make a potato battery.

What will you develop and learn?

• Chemistry principles
• Fine motor skills
• Creativity
• Working memory

Frequently Asked Questions