Unit of Chemistry Teaching Education University of Helsinki Science Education Centre LUMA Centre Finland
PLASTIC FROM MILK
FOCUS GROUP: This experiment can be done with all age groups and the theory can be fitted on the knowledge level. When making the plastic with primary school students, you could talk about networking and the networked structure of plastic in general. With them the theory doesn’t go too deep and the milk should be warmed up by the teacher. With high school students, you could talk about polymerization and how you can make a polymer from monomers. With upper secondary level students, you could talk about how casein crosslinks and forms polymers. It can be done in molecular and bond level. LENGTH: 20 - 45 minutes MOTIVATION: You want to make a present for your friend, but you don’t know what to make them. Here is a guide how to make jewelry or a refrigerator magnet from milk! OBJECTIVE: To understand everyday chemistry phenomena and to understand industrial processes on a small scale. Understanding the chemical structure of plastics. TEYWORDS: Proteins – Denaturation – Polymers – Acidity – Everyday chemistry
Finland’s first plastic factory started operating in 1921 in Tampere. This factory produced plastic from milk. The plastic was used to making buttons. Its strength was a low fire sensitivity, but the challenge with it was that it had a low moisture resistance. Eventually, the casein plastic was replaced by synthetic thermoplastics that came on the market in the 1950s and 1960s.
BACKROUND INFORMATION
Plastic has gradually become an indispensable assistant for out everyday lives. It is lightweight, inexpensive, pleasant to touch and possible to use for almost any purpose.
Plastics are mainly polymers. Polymers are long chained molecules in which the same base structure is repeated many times. One molecule may be composed of 1 000 to 100 000 smaller building blocks so called monomers. Polymers can be divided into natural polymers and synthetic polymers. Starch, keratin and DNA are examples of natural polymers. Synthetic polymers are industrially manufactured polymers such as polyethylene. Polyethylene is the most commonly used synthetic polymer in the world and is used e.g. in plastic bags.
In this experiment the casein plastic is made from proteins in milk. Proteins are polymers consisting of amino acids. The proteins in milk can be modified e.g. with heat and acids. Heat modifies, denatures, the structure of whey proteins in milk and acid causes the casein proteins to attach to each another with whey protein bridges. This creates a protein structure which, when dried, hardens into casein plastic.
Unit of Chemistry Teaching Education University of Helsinki Science Education Centre LUMA Centre Finland
Now you will learn how to make plastic at home!
Did you know: When a protein is denatured, its three-dimensional structure changes and the protein loses its biological activity. A familiar reaction of this is when you boil an egg. The heat modifies the structure of the proteins in the egg so that the initially liquid egg becomes solid.
PREMILITARY QUESTIONS FOR STUDENTS
What objects are made out of plastic?
Why are the products you mentioned made out of plastic?
Describe what kind of material is plastic.
What raw materials are used by industries when making plastic?
SUPPLIES
A saucepan or other heat resistant container/dish. A spoon A graduated measuring cylinder A thermometer A hotplate REAGENTS
Fresh nonfat milk Vinegar Food coloring Unit of Chemistry Teaching Education University of Helsinki Science Education Centre LUMA Centre Finland
INSTRUCTIONS
Measure 200 ml of milk and pour it into the saucepan.
If you want colorful plastic, add a few drops of food coloring.
Heat the milk carefully up to 50-60 °C (if the temperature rises above 60 degrees, milk will quickly burn to the bottom!).
When the milk is warm, take the saucepan out from the hotplate and add 10 ml of vinegar to the milk and stir.
WHAT CAN YOU OBSERVE?
Lift the plastic with a spoon onto a paper towel and shape it to the shape you want. You can glue a magnet to the back of your plastic to make a great refrigerator magnet.
QUESTIONS AFTER THE WORK
When does a similar type of reaction occur in milk, where lumps are formed?
Why does acid change the water solubility of casein micelles?
What happens to human proteins if the body temperature rises too high?