Introduction: Bioplastics: Casein Plastic and Starch-Based Plastic
Today, plastic is a term referring to the fossil based polymer that begun production on industrial scale in the 1940s. Nowadays, the products are used in applications ranging from cutlery to electronic devices and much more. In the year 2012, the total production of plastic reached 288 million tons, of which 40% is used for packaging and short term use. In 2016, 268 tons are estimated to float around the world's oceans.
This can be done more sustainably, with bioplastics! In this instructable, we will explain how to make two kinds of bioplastics: casein plastic and starch-based plastic, each with different properties to fit your product needs.
This instructable was made as part of a course called Technology for Concept Design (TfCD), TUDelft.
Step 1: What Is Casein Plastic?
Let's start with Casein Plastic.
What is casein?:
Milk contains many molecules of a phosphoprotein called casein. In cow's milk, 82% of milk protein is casein, and 18% is whey protein. The suspended caseins in milk form structures called micelles. Apart from casein molecules, casein micelles contain water and salts, which are mostly calcium and phosphorous. When the micellar structure is disturbed by heating the milk and by adding an acid (in our case white vinegar) or alkali to milk which lowers the pH level to pH 4.6, then the casein micelles come apart and the the casein molecules reorganize into a long chain and precipitate into the polymer casein. This is the formed gelatinous curd in our solution[2, 3, 4].
During the first part of the 20th century, plastic was commonly being made from milk. This so called casein plastic were sold under trade names Galalith and Erinoid, and were manufactured into products like plastic jewelry, mirrors or combs.
Step 2: Tools & Materials (Casein Plastic)
- One cup of milk
- 4 teaspoons of white vinegar
- A cooking pot
- A strainer
- Kitchen towels
- A stove
- Optional: Molds, cookie cutter, food colouring, paint
Step 3: Step 1: (Casein Plastic)
Heat up the milk on the stove until it is hot. (Do not make it boil!) Then turn off the heat, and put the pot elsewhere.
Step 4: Step 2: (Casein Plastic)
While the milk is still hot, add the white vinegar, and stir for 2 minutes.
Step 5: Step 3: (Casein Plastic)
Pour the milk through the strainer into the sink, collecting the created white blobs, called curds.
Step 6: Step 4: (Casein Plastic)
While kneading the curds together, dip them dry with the kitchen towels. Do not completely dry them; you should still be able to knead them.
Step 7: Step 5: (Casein Plastic)
Knead the curds into a shape of your choice.
Step 8: Step 6: (Casein Plastic)
Dry the shapes for at least two days until they are hard and dry. Congratulations, you made casein plastic!
What you get is a stiff and hard material with a matte white finish.
Step 9: What Is Starch-Based Plastic?
Let's continue with Starch-Based Plastic!
What is starch-based plastic:
One type of bioplastic is PLA (polylactic acid). PLA does come from a starch source, like industry-graded corn or potato, but is is created through a process that is done at an industrial manufacturing plant. PLA is composed of a long chain of lactic acid molecules which are made by fermenting starches and sugars, whereas starch is composed of a long chain of glucose molecules, called polysaccharides.
In this instructable, we are making a starch-based plastic rather than PLA. The potato starch contains two polymers in its glucose molecules: a linear molecule amylose and a branched molecule amylopectin. Water is used as a solvent to disperse the starch. Heating the water helps the molecules to become denatured. The acetic acid in vinegar breaks down the amylopectin into shorter molecules called dextrins. What is left are the dextrin molecules and the long, linear amylose molecules. The amylose is what gives the material strength, whereas the branched amylopectin molecules would have given the material lower mechanical properties. The added glycerol acts as a plasticiser. It prevents the polymer chains from lining up in a crystalline structure, which would make the plastic become more brittle and inflexible, and helps the polymers to slide of each other easily. What is left is a flexible material. [8, 9, 10, 11]
The use of starch in the manufacturing of bioplastics already began in the 70s.
Step 10: Tools & Materials (Starch-Based Plastic)
- 1 tablespoon of Starch (Maizena or potato starch)
- 5 tablespoons of cold water
- One teaspoon of glycerine (glycerol) (100%)
- One teaspoon of white vinegar
- Measuring tools (tablespoon and teaspoon)
- Spatula or other tool for mixing
- Cooking pot
- Mould or surface for spreading (Aluminium foil or silicone)
Step 11: Step 1: (Starch-Based Plastic)
Measure 1 tablespoon of starch in a pot
Step 12: Step 2: (Starch-Based Plastic)
Add the cold water. Mix to solve the starch completely.
Step 13: Step 3: (Starch-Based Plastic)
Add the glycerine and vinegar and stir again.
Step 14: Step 4: (Starch-Based Plastic)
Heat the mix on medium temperature and stir all the time.
Step 15: Step 5: (Starch-Based Plastic)
When heated, the mixture will transform from watery liquid to a thicker liquid. Keep mixing until you have a uniform, sticky mix. Then take if off from the heat.
Step 16: Step 6: (Starch-Based Plastic)
Pour out in a mould or one a flat surface, for example aluminium foil or silicon cutting board.
Step 17: Step 7: (Starch-Based Plastic)
Let dry in room temperature. Time to dry depends on the size and thickness of the moulded piece but will be about 2 - 4 days. Congratulations, you made starch-based plastic!
What you get is a flexible and semitransparent material.
Step 18: References
- Milkfacts (n.d.). Milk Protein. Retrieved on 18 December 2016 via http://www.milkfacts.info/Milk%20Composition/Protein.htm
- Science buddies (2016). Turn Milk into Plastic!. Retrieved on 18 December 2016 via http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p101.shtml#background
- ANSC 438 (2010). Milk Composition - Proteins. Retrieved on 18 December 2016 via http://ansci.illinois.edu/static/ansc438/Milkcompsynth/milkcomp_protein.html
- IdahoMilkProducts (2011). What is a Casein Micelle?. Retrieved on 18 December 2016 via http://idahomilkproducts.com/content/what-casein-micelle
- ScienceBob (n.d.). Make Plastic Milk. Retrieved on 18 December 2016 via https://sciencebob.com/make-plastic-milk/
- Green Plastics (2013). The basics of making corn starch bioplastic. Retrieved on 18 December 2016 via http://green-plastics.net/posts/76/qaa-help-with-cornstarch-pla-plastic-project/
- Green Plastics (2011). Q&A: I want to make corn plastic utensils. Retrieved on 18 December 2016 via http://green-plastics.net/posts/77/qaa-i-want-to-make-corn-plastic-utensils/
- RSC - Advancing the Chemical Sciences (n.d.). Making a plastic from potato starch - extracting starch; index 3.1.7. Retrieved on 18 December 2016 via http://www.rsc.org/education/teachers/Resources/inspirational/resources/3.1.7.pdf
- Green Plastics (2011). Q&A: Why water and vinegar? Retrieved on 18 December 2016 via http://green-plastics.net/posts/69/qaa-why-water-and-vinegar/
- Field, S. Q. (2016). Starch and Modified Starch. Retrieved on 18 December 2016 via http://sci-toys.com/ingredients/starch.html
- Ezenwanne, J. N. & Ezeoha, S. L. (2013) Production of Biodegradable Plastic Packaging Film from Cassava Starch. IOSRJEN Vol. 3, Issue 10, 2013, Department of Agricultural and Bioresources Engineering, University of Nigeria, Nsukka. Retrieved on 18 December 2016 via http://www.iosrjen.org/Papers/vol3_issue10%20(part-5)/C031051420.pdf
- Averous, L. & Vilpoux, O. (n.d.) Starch-based plastics. Retrieved on 18 December 2016 via https://biodeg.net/fichiers/Starch-based_Plastics.pdf