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.
<p>This is brilliant. can you please send me a copy of your research paper? Badly need it. Thank you :)</p>
Hi! :) Your work is really great and knowlegeable!! I'm an incoming Grade 10 this school year in the phillipines.Your study could really help us in our science investigatory project.Can i ask u something, instead of using potato, can we use cassava instead?? And, what chemicals can we use to make its tensile strenght stronger?? Are we also going to use chemicals to make it colorless and for it to become hard? Thankiie soo much!! I would really appreciate it if your gonna answer my question for my research study... Thank you againn!!<br><br>Reply ASAP once u receive this, thank u!!
<p>Hi.I am an environmental artist currently making work about conservation and the environment.I would love to make something out of biodegradable plastic that is not petroleum based.Could you send me a copy of your research paper.</p>
<p>Iam here again. Please send me a copy of your research paper. I madly need it. i only have 4 days to prepare for this project defense. I beg you. Here's my email: micahmerilles@rocketmail.com Please please!!!!</p>
<p>Hi. Is it possible to use TARO, as a substitute for potato? Answer please. Thanks. :)</p>
<p>i am making plastics with Hemp and Kenaf in America.</p><p>Feel free to contact me 213 572 7351 hempmayor@gmail.com.</p><p>I will not be back here to answer questions so get with me if you like</p>
hi i am really interested in work can <br>you please send me a copy of your research paper . I see that you you <br>are very knowledgeable with this and i need this for my science project. <br>please! please! i beg you. thanks<br><br>here's my email dilrajdeep1994@gmail.com
Hi, I'm doing a research project, where I'm reinforcing these plastics with natural fibers, and entering a contest with it. However, I'm having great results with reinforcement, but without it (what you are doing here), my plastics are not drying, and are still gooey after a month. I have dried the other plastics by pressing them between two glass plates, because I need a smooth surface as I am testing them with a tensile tester. I have followed your recipe perfectly in terms of materials, but could you give me some more specific temperatures in Farenheit, of what you consider "low" and "high" temperature? I think that this may be the problem. Thanks, I would really appreciate an expedient response. (alisonlyang@gmail.com)
Hello there. I am currently doing a project on bioplastics. But i face a problem as the strength of the plastic is not that strong. I have tried a few methods to strengthen it. But this way of using natural fibres is something new and i would love to try it out. Can you please send me a copy of your research paper. Please please please. My email is dilrajdeep1994@gmail.com. thank you
<p>hello.I really like your ideas with this investigative project.. If you don't mind, may I ask you to please send me a copy of your research study for me to use as my guide because I will be conducting a research study with regards to bioplastic using squash starch and jute to plasticize it. I will greatly thank you for that. I will recognize your paper as my reference in my study. Thank you so much. This is my email add (rodniewicas@yahoo.com/ rdwicas@gmail.com)</p>
Hey Lupe,<br>I really like the idea of your project. I really want to make that as our project too; however, we don't have tensile tester in our school. My plan originally is to make a plastic bag ( which I don't know how to accomplish) Next I will test the strength of the plastic bag in carrying things. I don't know how to logically do the testing in testing the strength. Can we do that without the tensile tester? I mean is testing the tensile the same with testing the ultimate strenth the plastic can handle? What can you suggest as the best step that we could take? and about the fiber thing that you add to your plastics.. what are they for? What are fibers? As I understand it they can help strengthen the plastic. Would the existence of the fiber somehow affect the biodegradability of the plastics? Cause you see, aside from the strength of the plastics, * durability* , *practicability* we also aim to test its biodegradability by burying it in soil and observing it. Do you think it can really be decomposed. I have read in the net a certain study claiming that after two weeks, she had seen her plastics decompose by fifty percent. I don't what that fifty percent mean. Could that really possibly happen? I would really appreciate if you can answer all my questions and offer my advice. I really want to succeed on this project. What makes this project hard for me is the fact that it's a group project. (whew...)
From my understanding, vegetable oils will work just fine. Plasticizers do affect the durability of plastics, but if you use the plasticizer as a control it should not be an issue if you are doing a comparative study. <br> <br>Natural fibers are the individual strands that make up cotton clothing (the filaments on the threads that tear off your shirts) or that make up different types of strings. In nature, they make up plants stalks, etc. When amylose &amp; amylopectin fuse, natural fibers will strengthen that bond. As you see in my study, the thickest, most tangled fiber did the best job of reinforcing the plastic. <br> <br>I worked at a plastics company for this project, so I had access to a tensile tester. Get in touch with a nearby company or university, no doubt they will have a tester that you can use. They are easy to operate. As for the fibers, I also used a grinder at the company lab to grind my fibers down, but you can try a coffee grinder... not sure if it'll work though. <br> <br>Addressing the testing if you cannot find a tensile tester-- I think that you could make bags by coating two glass plates and then connecting the bottoms of the plates? Experiment with this. I did not try making plastic bags, it is probably more difficult. You could always try a less exact method of measuring strength/durability by placing small weights inside the bags and seeing how many the bag can hold. Definitely less exact and the chance of scientific error will increase, but make do with what you have. <br> <br>I have sent you the paper, let me know if you have other questions. I encourage you to seek out local plastic companies or contact professors universities. Most labs have tensile testers. Good luck.
<p>hi i am really interested in work can <br>you please send me a copy of your research paper . I see that you you <br>are very knowledgeable with this and i need this for my science project. <br> please! please! i beg you. thanks</p><p>here's my email besslightyear@gmail.com</p>
<p>hi i am really interested in work can you please send me a copy of your research paper . I see that you you are very knowledgeable with this and i need this for my science project. please! please! i beg you. thanks</p><p>here's my email besslightyear@gmail.com</p>
hello, please also send me the research paper at tawinligahon@yahoo.com or toweeligahon@gmail.com......... <br>please, please, please!
hello can you send me research paper at silverhaseo@gmail.com or mr.mime95@yahoo.com plsss
hi lupefiasco <br>i dont know how i could use or extract the fibers for my potato plastic <br>it seems to have worked for you so could you tell me? <br>thanks
What are glass plates? How do your glass plates look like? How do you think can I combine the bottom of the two glass plates? What's the shape of your glass plates?
Didn't see the biodegradability question, sorry. I have no experience with soil biodegradability. Look at my paper and you will see that I used hydrodegradation by placing plstics in water... didn't work incredibly well. Just try it, who knows what will happen. That's the fun of science! 50% would mean that when they massed the plastic after being buried in soil, the plastic was half of its original mass. Try it out with your plastics and let me know how it goes.
helo, lupefiasco, wat kind of natural fibers tat u add on ?my plastic is too soft and tear off when juz&nbsp;touching it...I wan to test my plastic on tensile test too, but it is too soft and cannot be tested by machine... do u hv the same problem as i had ?
Hi there, <br /> You may be adding too much plasticizer, or you may just need to spread the plastic thicker. Experiment with types of plasticizer, because that will dictate those kinds of properties. I use cotton, jute, and hemp fibers in my study, and hemp performed the highest in resisting water degradation as well as in strength tests. I will share my methods with you here, feel free to ask if you have more questions. <br /> <br /> &quot;Phase I of the experiment involved the creation of samples for testing. A slurry of <b>2 tablespoons of starch</b> and <b>8 teaspoons of water</b> was created. If applicable, <b>6g of fiber</b> was added and mixed into the slurry until it became relatively homogenized. Then <b>1 teaspoon each of glycerin and vinegar</b> were added to the slurry. The slurry was heated at low on an electric stove, then when it began to steam, turned up to high and allowed to boil. Then the slurry was poured and spread onto two glass plates with non-stick surfaces. The plates were then pressed together to create a flat layer of plastic. This process was repeated for each fiber, and for the control plastic without fiber. After the plastic had partially solidified, one glass plate was removed and the plastic allowed to air dry until completely solidified.&quot; <p>&quot;<font face="Times New Roman" size="3">The results of the tensile testing supported the hypothesis that the hemp fiber reinforced plastic would demonstrate the greatest tensile strength. The reinforced plastic had an average tensile stress at break of 2138.63 psi. A Kruskal-Wallis test, which compares the differences among medians, conducted on the tensile strengths of hemp, jute, and cotton, and non-reinforced (control) plastics showed that the differences are statistically significant (k=10.3846, p.= 0.016).&nbsp; As shown in Figure 5, the hemp-reinforced plastic was significantly stronger than the other plastics. The fiber-reinforced plastics were also significantly stronger than the non-reinforced control. As shown in Figure 6, though the hemp plastic failed quickly under tensile stress, it was a brittle failure, and the plastic held a large load.&quot;<br /> <br /> So since&nbsp;the plastics suffered brittle failure, the problem was the plasticizer, and&nbsp;I suspect that you are having the same problems. Following these methods you should be able to create plastics that stay together and are strong. </font></p>
&nbsp;Awesome! Finally a comment posted above the average elementary school&nbsp;intelligence&nbsp;level. Lupe if you publish a paper on this when your done would you mind sending me a copy?&nbsp;
&nbsp;Hey there, I've actually been long done with this project. I did well with it at state competitions in 2009, but I changed my focus to the biological aspect of plasticizers this year. I do have a copy of the paper, where would you like it sent?
hello lupefiasco!!, I am very much interested in your work. if you would not mind ,can you send me a copy of your research paper?? at rean_jean@yahoo.com . btw i am a highschool student from the phils.your efforts will surely be recognized. Thank you so much ... :DD
Hi! I hope you will still be around to see this, but do you think you could also send me your paper? I'm a conbio student and would love to work on this! luckyprincessmelody@yahoo.com Thank you so much if you are able to send it! Melody
&nbsp;Brandon121233@gmail.com &nbsp; &nbsp; &nbsp;thanks, I'll let you know what I think about it, its always good to see other peoples ideas on the same topic&nbsp;
what are fibers? What's in them that makes the plastic stronger? Where can we find them? Are those in the grocery? How does it looks like? What else can we use as fibers?
Can I just simply use vegetable oil as plasticizer since glycerine isn't available in our place?
thx 4 yor info....i hope u dont mind if i hv questions to ask u...haha...anyway, thx 4 for yor guide and tips....i'll try my best... ;)
&nbsp;Sure thing, let me know. I can't promise I can tell you everything, I haven't worked on this topic for a while, so it's a little hazy. I hope to pick it up again this year though!
Hi, lupe....one more question....how long time does the (gel looks plastic)plastic takes to solidify as a real plastic (dry and hard plastic )&nbsp;after u put the plastic on the flat plate ?
Less than 24 hours for me.
anyway, can I have a copy of you research paper if possible and if it's okay. ( mildredmongcupa@gmail.com)
I have never really taken accurate measurements with a thermometer, just because its easier for me to just look at it and know its done. The starch changes dramatically in appearance when its done, from a gooey paste to a bubbly and very clear gel thats very sticky (look at the video to see what I mean). Sorry I can't help you more with that
<p>can you mix this with other starches </p>
<p>What if we don't have 100% Vegetable Liquid Glycerin, will it still work?And where can you buy it?</p>
<p>Wondering if this could hold water if I made a bowl out of it and if there are any properties at all that would leach that may be harmful.. Thanks!</p>
<p>Hi, may i asked if how did you test the degrade capability of the bioplastic? I BADLY need this for OUR INVESTIGATORY PROJECT. can you please send me your research work in my email besslightyear@gmail.com Your work is highly appreciated and praise in my project.thanks :)</p>
<p>I notice you have red potatoes depicted above. It's my understanding that something like a russet potato will work better for for producing starch.</p><p>I also have some doubts about how &quot;green&quot; the production of this plastic is. Energy is used in the harvesting and transport of the potatoes. It's used in the production and transpoert of the glycerin. It's used in the production of the plastic itself. To get the maximum &quot;green&quot;, the potatoes would need to be locally grown. You'd also maybe want to use some sort of solar cooker instead of fossil fuels in the process process.</p><p>That being said, I do realize what you've got is more of a &quot;proof of concept&quot;, rather than a full blown production process.</p>
the waste cellulose could be fermented into alcohol to use as fuel or turned into plastic its self cellulose acetate. Some potatoes could also be used to make alcohol for fuel instead of just make the plastic
<p>Further thoughts.</p><p>What kind of scale do you see this being used on? We use a LOT of plastic these days. This stuff is supposed to be biodegradeable, so that implies it being used for disposable items. What sort of items? Does it make sense to expend resources to make something that is disposable?</p><p>How are these potato plants being grown? In rows? Potato towers grow more potatoes in a smaller space, but don't lend themselves to mechanized farming (yet). How are they being fertilized? Petrochemical fertilizers would tend to defeat the purpose of making &quot;green&quot; plastic from potaotes. But using organic methods, especially to manufacture any useful amount of plastic in a cost effect way, would present its own set of problems.</p><p>What about the water used in extracting the starch? For large scale production, thats a lot of water. Once it's been ised, now it's &quot;polluted&quot;, albeit with a fairly harmless substsnce. Can it be used to water the potato fields?</p><p>What about whatever is left of the potato after the starch os extracted? Can ot be composted? Used for animal feed? What is the ratio of potatoes needed pounds of plastic produced?</p><p>What about using potatoes for food, vs making plastic? What is that going to do to the price/availability of potatoes in general?</p><p>Rather than being disposed of, could the plastic be recycled? Could a version be created that could be used as the raw material for 3D printer output? That might have some interesting possibilities.</p><p>There is also the spectre of Monsanto becoming involved in the whole process. GMO potatoes optimized (and patented) for plastics production. Gives me the shivers just thinking about it.</p>
can you make the plastic out of old potatoes? <br>thx
potatoes that are unfit for consumption can still be made into starch or alcohol for fuel
Hey Brandon! I hope you're doing well.<br> <br> I just thought I'd mention that we're constantly posting answers to specific questions that people have about making bioplastic at home on the website,<br> <br> <a href="http://green-plastics.net">http://green-plastics.net</a><br> <br> We've had recent questions about everything from how to make home-made bioplastic waterproof, to explaining the chemistry behind why the vinegar helps improve the bioplastic that you are making.<br> <br> It would be great if you&nbsp; could let people know about our Q&amp;A board in your instructable!<br> <br> <br>
done, you get the headline spot boss! Thanks for helping with the questions.
<p>can we use vegetable oil in stead of glycerin?</p>
Thank you so much!
And is there any type of catalyst that can be used for speeding up the hardening process? Like epoxy/polyester hardener?
So the reason why this takes a long time to &quot;cure&quot; is because the starch polymer molecules are complexed with water in a gel matrix. The process by which the gel hardens is called densification; essentially the water diffuses out of the gel and evaporates. The remaining starch molecules pack closely together and contract due to the surface tension of the remaining water. The only way I can think of making this happen faster is to remove the water from the gel more rapidly. This can be accomplished by reducing the ambient air pressure in a vacuum, or something like freeze drying the starch gel. As for a catalyst, that term is generally used to indicate that a substance can speed up a chemical reaction, like cross linking an epoxy resin. In this case, there's no chemical reaction occurring between the water and starch, the water simply needs to be removed from the gel plastic. I will keep on brainstorming this idea, and I'll let you know if I come up with anything. <br><br>Hope this helps- Brandon
Just out of curiosity, how is this in molds? Can i pour the mixture in to a mold and expect that it will sett and be a little rubber like depending on the glycerin amount? And just hypothetically... could i make a dildo out of this? Just curious... :3

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