Plastic is one of those materials that is used for everything from dishes to toys. Have you ever wondered about how it all gets made? We have an activity here that allows you to make your own plastic. This is a wonderful exhibit area that changes every day and has lots more activities. We also, for your reading pleasure, have gone on to extend the activity to discuss how plastic gets made and add a little more science behind, Plastic Milk.
1 cup whole milk
What to do:
Pour the milk into the saucepan.
Add 2 teaspoons of vinegar.
Heat, stirring frequently until the milk boils. The milk will form tiny lumps (curds) in a clear liquid (whey).
Slowly pour off the liquid.
Spoon the curds into the jar.
Add 1 teaspoon of vinegar to the curds and let stand for two hours.
The curds will form a yellowish glob at the bottom of the jar.
Pour off the liquid.
Mold the plastic into any shape you wish.
Place on wax paper and let harden and dry overnight.
What’s the Science:
The yellowish glob is made of fat, minerals and the protein casein. The combination of heat and vinegar (acetic acid) helps to pull out or precipitate the protein casein from the milk. Plastic is now synthesized from petroleum products but before this way of making plastic, it was common to make natural plastics from plants and animal fat. In fact, this plastic is environmentally friendly because it will eventually decompose, unlike plastics made from petroleum products.
How can you get plastic from cows?
Stop snickering! It’s true you can get plastic from animals and even plants! You can make plastic from animal fat/protein and what better source of fat and protein to use than milk! You might be thinking to yourself right now… there is fat and protein in my milk? So let’s take a little detour on the milk train and explore: WHAT IS IN YOUR MILK?
What is in my milk? Milk is made up of fat, protein, minerals, water and carbohydrates. The exact composition of milk according to Cornell University is 87.7% water, 4.9% lactose (carbohydrate), 3.4% fat, 3.3% protein, and 0.7% minerals (referred to as ash). Visit the site and learn all about the different components of milk. You’d be surprised how much information there is about this common liquid. The important components of milk for making plastic are the fats, minerals and protein.
By heating the milk above the boiling temperature of water (212°Fahrenheit or 100°Celsius) it causes the fat to come together or coagulate. There are two main proteins found in milk, casein and whey. The casein protein contains phosphorus and coagulates because the acetic acid (vinegar) causes the pH of the milk to drop below 4.6. The whey proteins found in the liquid of the milk do not coagulate at this pH because they do not contain phosphorus.
A Bit about the History of Casein
Believe it or not, the protein casein is still used to make plastics today that are used for items like fountain pens. It was first introduced at the Paris Universal Exhibition of 1900 and was named Galalith. It was mostly used for small items like jewelry, buttons and buckles due to its tendency to splinter and break. In fact, there are many people who collect the jewelry, buttons and buckles made from Casein. Many artists like Jacob Bengel and Auguste Bonaz designed many artistic pieces like hair combs and jewelry. If you ever make it out to Leominster, Massachusetts you could pay a visit to the National Plastic’s Center Museum and views exhibits about the history, uses and recycling of plastics.
How is Plastic Made?
Plastics are made from petroleum and there is a lot of technical information about how plastics are made but below is a very brief and condensed 7-step overview of how petroleum is turned into plastics.
Petroleum is drilled and transported to a refinery.
Crude oil and natural gas are refined into several petroleum products two of which can be ethane and propane.
Ethane and propane are then further refined into ethylene and propylene using high-temperature furnaces.
A catalyst is combine with the ethylene and propylene and this results in a powdered polymer.
This powdered polymer is then melted and extruded.
It is then cooled and cut into tiny plastic pellets.
These pellets are shipped to manufacturers of plastic products.
Imagination Station just opened a learning world called Energy Factory in May of 2010. The exhibits within this area focus on the process of refining oil and solar energy. There is one exhibit that shows the cost per barrel of oil for common household products. In order to calculate the cost per barrel for a household product just divide 128 by the number of ounces in a product then multiply by 42 and then multiply by the price of the product (128 / # of oz. x 42 x price of product = cost/barrel). For example, we have calculated the cost per barrel for some common household items below:
$1,839.60 for a 6.4 oz. tube of Crest toothpaste
$1,443.81 for a 13 oz. jar of Vaseline
$3,218.88 for a 12 oz. bottle of Pepto Bismol
$752.10 for a 100 oz. or 2.95L bottle of Tide detergent
Plastics Made from Renewable Resources
There are some ways to make plastics from renewable resources such as plants. Chemists at Pacific Northwest National Laboratory in Richland, Washington have been studying how to use glucose as a source of fuel, plastics and other petroleum products. Below is an excerpt from the article in Scientific American that discusses the processes and work that this group has been doing.
Chemist Conrad Zhang and colleagues at PNNL tested a variety of metal catalysts—compounds that speed chemical reactions—in their search for an efficient method of transforming glucose and other natural sugars into hydroxymethylfurfural (HMF), a molecule that can easily be manipulated into a variety of chemicals and plastics.
“Because glucose can be derived directly from cellulose and starch, it is nature’s most abundant carbohydrate building block,” Zhang says. “HMF from renewable carbohydrates, such as fructose and glucose, is a versatile platform chemical from which hundreds of other chemicals can be produced (Biello, 2007).”
This work is very exciting and other companies such as Novomer Inc. are also working on creating plastics from renewable resources. If you would like to learn more about this subject take a look at Making Plastics Out of Pollution another article from Scientific American.
We hope that our extended explanation of the science behind our Plastic Milk activity has answered all of your questions. However, if we haven’t just come on in and stop by the Science Studio, we’d love to talk more about it!