Hi my name is Brandon Sweeney and I’m going to show you how to make some bio plastic in your kitchen. Bioplastics are a form of plastics derived from renewable biomass sources, like vegetable oil, or corn starch, rather than conventional plastics which are made from petroleum. Now some of you may be wondering why anyone would want to make bio plastic.
Things made with conventional plastics all have one common flaw and that is they all are made using petroleum based plastics. Worldwide we produce about 100 million tons of petroleum plastic per year. To make these plastics we use about 7 million barrels of oil per day. Now imagine that number dropping to zero. With the help of bio plastics, one day that may be a reality.
So before we begin, let’s have a brief review on the chemistry of polymers. A polymer is the main building block of all plastics. Think of it as a long chain of large molecules also called monomers. An ideal plastic would have very long straight polymer chains allowing it to be strong and flexible. Starch is made of two basic components: amylose and amylopectin. Amylose is a very long and straight polymer like we want; amylopectin on the other hand is a branched and short polymer meaning it will yield brittle and weak plastic... not good. There are two things we will be doing to enhance the properties of our plastic. The first is a simple technique called acid hydrolysis. By adding a small amount of vinegar to the plastic, we can break up some of the branches of the amylopectin which otherwise would have made it brittle. Secondly we will be adding a plasticizer. The easiest to obtain from a drug store or grocery store is called glycerin. Glycerin acts like a lubricant at the molecular level, imagine a bowl of sticky pasta that you add butter to so that it doesn’t all stick together. If you want very pliable plastic for a bag for instance, you would add more glycerin, and if you wanted stiff plastic then you would add less glycerin. So now that you know how everything works, let’s go make some.
First get a pot, silicon spatula, a stove or hot plate, a tablespoon and teaspoon, water, vinegar, glycerin, and finally some starch. I've found that tapioca starch works the best, but almost any kind of starch will work, for this experiment I will be using potato starch. Before you start get either some aluminum foil or a silicone heat pad like this so you have something to spread your plastic on for it to dry. You can also make molds to inject the plastic into but for now we'll keep it simple.
Measure out 1 tablespoon of cornstarch, 4 tablespoons of cold water which I already pre-measured, 1 teaspoon of glycerin, and 1 teaspoon of vinegar, add everything to the pot. Turn the heat on to medium and begin stirring, keep heating and stirring until the mixture turns from cloudy white to clear, watch how the starch makes a transformation from liquid to a goopy like gel. This is called gelatinization. Now turn the heat up a little bit and keep stirring rapidly until it is completely clear. Quickly pour your plastic onto the cooling sheet of your preference. Depending upon the humidity in the air it should dry in about a day. When it’s dry you can do whatever you want with it.