Introduction: Starch Plastic 2.0- Pressure Cooker Hacking
Heres a video of me doing some strength tests of thick and film-like pieces of my awesome plastic
Step 1: The Pressure Is On
The starch we will be using: Hylon VII, has a 70% amylose content. The problem is that as the percent of amylose in starch increases, so does the gelatinization temperature. What does that mean? Wikipedia kindly says that "Starch gelatinization is a process that breaks down the intermolecular bonds of starch molecules in the presence of water and temperature and allows the hydrogen bonding sites (the hydroxyl hydrogen and oxygen) to engage more water. Penetration of water increases randomness in the general structure and decreases the number and size of crystalline regions. Crystalline regions do not allow water entry. Heat causes such regions to be diffused, so that the chains begin to separate into an amorphous form." The bad news is that the temperature difference that is needed is rather large. The exact requirements are: "HYLON VII requires higher cooking temperatures than conventional corn starch to adequately gelatinize. Super atmospheric cooking temperatures are required, typically 310-340oF (154-171oC) depending on the solids level of the formulation being used." Hmmmm how can we increase the boiling point of water to 154 Celsius? The answer: increase the atmospheric pressure. With those handy math skills that you learned at one point, you might be able to do the calculations to find out what pressure is needed. But why waste your time when I am going to tell you that it is pretty close to 52 psi and 55-60 psi just to make sure we get it to fully gelatinize. So if you have access to a high pressure autoclave then your in business, if not your going to have to do it the dangerous way. Be cool my babies, we're on to step 3.
Step 2: Make the Pressure Vessle
Step 3: Mix Up a Plastic Batch!
The starch we will be using was a free sample from National Starch Food Innovation called Hylon VI. I usually experimented with a 25:25:1 ratio of water to starch to glycerin by weight, with adjusting the amount of glycerin more yielding a more ductile plastic and less yielding a stiffer harder plastic. Then pour that into a Pyrex beaker and put that into the pressure cooker. Fill the pressure cooker with water till it reaches the bottom of the beaker (about 1/2 inch of water). Then fit your modified top on and start cranking up the heat while observing all the safety rules. When your temperature or pressure gauge reads 320F or 55psi respectively turn off the heat and release the steam out of the valve. When all the steam i gone remove the lid with hot pan holders and pour your hot gel resin into the mold of your choice. Let it cool and harden for several hours them remove and enjoy!
*Note I am still going to be revising this instructable as I do more experiments so keep checking back for more data.