Milk, it's good for us in more ways than one!

There are thousands of plastics that are made all the time, from every day items like egg cartons to spacecraft. Understanding plastic chemistry can help us understand how to fabricate and use plastic wisely. Once we're familiar with the varieties of plastics, we can recycle many of them and use them again. That's good for the environment.

Plastics are polymers. What is a polymer? The simplest definition of a polymer is something made of many units. Think of a polymer as a chain. To make the chain, many links or "mers" are hooked or polymerized together. Polymerization can be demonstrated by linking strips of construction paper together to make paper garlands or hooking together hundreds of paper clips to form chains. Most plastics are man-made from oil and natural gas, but some plastics are found in nature.

Man-made plastics:

Polyethylene - It's the plastic used to make many containers, among other things. Small tubes of polyethylene are heated, inserted into molds, and blown up like balloons to make containers for soft drinks, fruit juices, water, and milk.

Vinyl - Exterior siding made of polyvinyl chloride (PVC) is better known as vinyl. Easy to clean, waterproof, and resistant to corrosion, vinyl is also used in car interiors and in the pipes that carry sewage away from buildings.


Water-resistant paints and varnishes derive from a family of synthetic polymers called acrylics.


Polystyrene foam can be made into cartons to protect eggs or into packing "peanuts" to cushion fragile objects for shipping. It insulates, so folks put drinks in foam cups and coolers to keep the warm ones warm and the cold ones cold.

Natural Plastics:


The insect Laccifer lacca - or just plain "lac" - lives on trees in India and Southeast Asia. It secretes a resin, also called lac, a polymer from which people make lacquer and shellac. They use these varnishes to coat ships, houses, furniture, fruit, pills, and candy.


Silkworms, which are actually caterpillars, are raised on silk farms and fed mulberry leaves. People in China discovered more than 4,500 years ago that they could unravel silk, a polymer, from the worms' cocoons and weave it into soft fabrics.

Animal Horns

Antelope, buffalo, sheep, cattle, and rhinoceroses all have horns. Unlike a deer's antlers, made of bone, horns are made of the polymer keratin. Parts of you are made of keratin too: It's the primary ingredient in our hair and fingernails.


South American Indians slash the bark of trees in the rain forest to obtain a milky white fluid called latex. They discovered that it could form a solid that was elastic; you could stretch it and it would snap back to its original shape. If you rubbed it on penciled words, the writing would disappear, so Europeans called it rubber.


Cow's milk is loaded with the polymer casein, a protein. Without this polymer, cheese would come unglued. Glue would come unglued too, since casein from milk provides its sticking power.



Procedure to make plastic from milk

What You Need

  • 1 cup skim milk
  • a jar
  • Small saucepan
  • Dropper
  • Spoon
  • White vinegar


What to Do

Pour the milk into a jar. Place the jar in a saucepan filled with water. Warm up the milk. Add vinegar dropwise, and continue heating, and stirring frequently. You will need approximately 10 mL of vinegar. Do not let the milk boil. You will see tiny lumps (curds) forming. Continue adding the vinegar until the milk turns to a clear liquid (whey). The curds should form a glob at the bottom of the liquid. Slowly pour off the liquid from the jar into the sink.

The curds will form a yellowish glob at the bottom of a clear liquid. The glob is actually fat, minerals, and the protein casein. Pour out the liquid, remove the rubbery yellow glob from the jar, wash the glob with water, and knead it until it attains the consistency of dough.

Mold the plastic into any shape you wish. If you wish to make a pendant for a necklace, use a nail to poke a hole in the plastic and let it dry overnight. Once it is sufficiently dried, use metallic gel pens to decorate it in your own design.

What Happens

The casein from the milk hardens into plastic that can be painted with acrylic paints.

Why It Works

The combination of heat and acetic acid precipitates the casein, an ingredient used to make plastic, from the milk.

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BCIT Chemistry Department