Starch Plastic 2.0- Pressure Cooker Hacking

So you have done or were interested in my first instructable on potato plastic and now your looking for something that will yield better results and a little more danger, well here it is. First and foremost I strongly recommend that you approach this project only if you are willing to accept some safety rules, and I will go over those in another step. The basic premise behind making a starch based plastic is to get a starch crammed full of polymers and nothing else, as impurities would detract from the strength properties we want. To do this we are going to have to enter into the realm of modified food starches. For this instructable we will be using a starch that has been modified to have an amylose content of 70% as opposed to the normal 20% found in most starches. The product is called Hylon VII from National Starch Food Innovation. The reason we want a high amylose content is because amylose is "is a planar polymer of glucose linked mainly by hydrogen bonds. It can be made of several thousand glucose units. It is one of the two components of starch, the other being amylopectin". So basically it makes really long polymer chains (good), and if you don't fully understand this go check out my first instructable on Potato Plastic. There is a catch 22 however that puts us in quite a pickle metaphorically speaking, go to step 1 to discover this conundrum.

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

In this step we will be modifying an ordinary pressure cooker to cook at 4 times it's normal pressure. As you would imagine this is extremely dangerous and you HAVE to abide by some safety rules. See the video below as to why you don't want an exploding pressure cooker.

First off this is possible to accomplish without being injured if done properly, however I assume no responsibility for you're mistakes and lapses in judgment. A safety full face shield must be worn at all times, ear protection must be worn at all times, and protective long clothing must be worn at all times. Finally I can only recommend this project if you are willing to construct some kind of enclosing structure to contain the pressure cooker or if you can do this outside and be several yards away from it with a barrier between you and it at all times.Moving on, now it is time to modify the valves on the pressure cooker. Since all pressure cookers are different and you most likely will not have the same one as me I can only give you steps that you must do to modify it. I would recommend that you get the smallest one you can find with the thickest walls, as it will be less prone to exploding. First you need to remove the safety blowout valve and replace that with either a pressure or temperature gauge that fits the threads of that hole. Next you can either keep the weighted release valve and manually use a 2X4 pressing on top of it to keep the steam in like I did or you can install a resetting pressure release valve with one of those pull tabs that release the pressure, the latter I recommend more but I did it the first way for simplicity sake. After you have done that you need to get a portable electric hotplate/burner to heat your pressure cooker. And thats it you're ready to make some high quality plastic.

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.