Introduction: Make Potato Plastic!
**Note: If you like this Instructable and are looking for something a little more challenging that will yield better results then check out my new potato plastic instructables here https://www.instructables.com/id/Starch_Plastic_20_Pressure_Cooker_Hacking/**
Also if you have questions and want some expert answers try heading to this website http://green-plastics.net and just post your question on the Q&A board, they will be able to help out with your question in a more timely manner!
Have you ever wondered if there is a more environmentally friendly way to make plastic with OUT using foreign oil? Currently, it is estimated that the worldwide production of petroleum based plastic is around 100 million tons annually, and that seven million barrels of petroleum are required PER DAY to produce that plastic ( info source ). What if we could take that number and cut it down to zero! This is all possible with the eco-friendly plastic of the future, and you can make some right now- OUT OF A POTATO! When I first discovered that you could do this, I used corn starch, water, and corn oil to make the plastic; I then made a science fair project out of it, won second place at my school, and won honorable mention (3-6 place) at the 2003 Regional Science Fair. The plastic I made for the science fair worked, but it dried out and became brittle in about a week. A few years later, I discovered an article describing a way to enhance it's plasticity by altering the chemical composition of the starch.
For this instructable, I will describe how to make plastic from scratch, by extracting starch from a potato, and processing it into a resin with household items. If you don't feel like taking the time to extract the starch from a potato, you can just use corn starch instead. This is a project for all you environmentalists, tree hungers, global warming believers (I am not one by the way), and especially you Al Gore.
Lets have some fun and make potato plastic!
Step 1: Gather Materials
Most of the materials you will need will be in your house or can be bought at most supermarkets and home improvement stores.
2 White skinned potatoes OR potato starch OR corn starch
100% Vegetable Liquid Glycerin
Tools / Supplies:
Non stick pan
Spatula or Spoonula
Stove Top or Hot Plate
Knife or guillotine
Step 2: Optional: Extract the Starch!
Now that you have a potato, you might be wondering just how we will be making plastic out of this? The answer: extract the starch. How will we do this? BLENDER! Since potatoes are about 95% starch (besides the water), making a potato into a powdered starch form, is relatively easy.
A note to younger viewers: be sure to ask your parents if it is alright to use a peeler, knife and blender, and always use caution when working with exposed blades.
1) Get a potato, and wash it.
2) Use a peeler to take all the skin off.
3) Cut the naked potato up into cubes your blender can handle.
4) Add about 1 cup of water and the cubes to the blender, and turn it on high for a minute or two.
5) Use a coffee filter to strain off the cloudy water.
6) If you plan on making the plastic right away, drying the mixture is not completely necessary, but if you plan on storing it for a while, spread it out on wax paper in a sunny area for it to dry (it could get moldy otherwise).
Heres a suggestion by legionlabs to purify the starch extracted from the potato, by removing unwanted cellulose:
"Given only potatoes, you might be able to increase the purity of the starch for your process by removing cellulose using this reagent, which can be made from commonly available materials:
You can reuse the reagent by precipitating the cellulose out by acidifying the mixture, filtering out the cellulose, and making the reagent basic again."
If you do not wish to make the starch from scratch, you can order pre-made higher quality starch online, or buy it at your local grocery store. Corn starch and tapioca starch also work well to make plastic with. On to step 3...
Step 3: Mix It Up !
1) Measure out 60 ml (4 tablespoons) of cold water and pour it into the beaker or container your heating the mixture in.
2) Measure out 10 grams (or about 1 tablespoon) of starch ( the potato / corn starch you made or bought) and add that to the water.
3) Add 5 ml or about 1 teaspoon of acid (vinegar) to the mixture.
4) Add 5 ml or about 1 teaspoon of glycerin to the mixture, more glycerin will make it softer and more flexible, less will make it harder and stiffer but more brittle.
5) If a colored plastic is desired, add in the food coloring now. About 5 drops is good enough.
6) Turn the burner on low and constantly stir the mixture. When it starts to thicken up turn the heat up to medium and stir even more. When it starts to boil, keep boiling it for 5 minutes. You want it to be very clear and sticky (not like toothpaste though, think flubber)
7) You should now have a "gooey" substance that you can pour into a mold, or you can pour it onto a sheet of aluminum foil/silicone heat pad to dry.
8) Depending on humidity, it should take about 1 day to dry in a sunny place. You can dry it faster by putting it in an oven set to 150 F for 1-2 hours.
Step 4: Use It !
-Plates and dinnerware
-And whatever else you can imagine...
a video showing a piece of colored plastic that is very flexible and strong (the tear in it is from drying)
Step 5: The Science Behind It.
Now that you have made green plastic to your hearts content, you might be wondering just HOW its possible to make plastic from a potato? To find out we must look into what starch is made out of at a molecular level, and how plastics are formed. I will use some help from our good friend Wikipedia to define some of the terms we will be talking about.
First, lets look at how regular petroleum based plastics are formed. According to Wikipedia plastics are:
polymers: long chains of atoms bonded to one another. Common thermoplastics range from 20,000 to 500,000 in molecular weight, while thermosets are assumed to have infinite molecular weight. These chains are made up of many repeating molecular units, known as "repeat units", derived from "monomers"; each polymer chain will have several 1000's of repeat units. The vast majority of plastics are composed of polymers of carbon and hydrogen alone or with oxygen, nitrogen, chlorine or sulfur in the backbone. The backbone is that part of the chain on the main "path" linking a large number of repeat units together.
If you want a really good visual explanation of polymers go here to polymer planet.
So now that we understand polymers and how regular plastics are formed, lets look at how this happens with starch.
Starch is mixture of two polymers called Amylose and Amylopectin, in a ratio of about 1:4 ( 4 being the Amylopectin). Amylose is a linear polymer of glucose linked with mainly a(1 --> 4) bonds. It can be made of several thousands of glucose units , where as Amylopectin is a highly branched polymer of glucose.
What does all this mean? Well to get something that resembles plastic, we need to have LONG STRAIGHT chains of polymers. Since starch has both straight and branched polymers, we need to remove or alter the amylopectin, so we are left with long straight chains. Since going through and picking out all the individual amylopectin molecules with an electron microscope is not an option, we had to alter the starch. We used vinegar (acetic acid) to break down the amylopectin into straight but short molecules of dextrin ( commercially dextrin is produced from amylopectin by Hydrochloric acid hydrolysis: the amylopectin is roasted in vessels jacketed in hot oil - the oil is heated to 450C - at the same time HCl is added to the amylopectin - the acid plus the heat causes the molecular structure of the starch to change/polymerize ).
So now we are left with amylose and dextrin to which we added glycerin. Why did we do this? Well, not all normal plastics are soft and flexible. To achieve this property something called a plasticiser is added to the plastic resin. From wikipedia, Plasticisers for plastics are additive, most commonly phthalates, that give hard plastics like PVC the desired flexibility and durability. They are often based on esters of polycarboxylic acids with linear or branched aliphatic alcohols of moderate chain length. Plasticisers work by embedding themselves between the chains of polymers, spacing them apart (increasing of the "free volume"), and thus significantly lowering the glass transition temperature for the plastic and making it softer. For plastics such as PVC, the more plasticiser added, the lower its cold flex temperature will be. This means that it will be more flexible, though its strength and hardness will decrease as a result of it.
Imagine that you have a bunch of cooked spaghetti noodles laid out lengthwise. When the water in the spaghetti dries out they begin to stick to each other. If you were to grab a large handful of it and bend it, the spaghetti would most likely break. However, if we added some olive oil or butter to the spaghetti, it would be more flexible and not break. The butter or oil is getting in between the individual spaghetti strings and lubricating them.
This same concept applies to our plastic. The glycerin gets in between the amylose and dextrin molecules and keeps them from sticking together. Without the glycerin in our plastic, it would crack and shatter if we bent it, or put stress on it, but since we added glycerin- a plasticiser to it, the starch plastic is flexible.
Now that you understand how to make potato plastic, and the science behind it, go forth and spread the good news to all, so they can enjoy it themselves, and save our planets resources at the same time.