Composites are materials that are made from two components, one of which is a matrix and the other a binder (often called the resin). The matrix is some sort of fiber, while the binder is typically some sort of epoxy resin. Fiberglass composite is made with fiberglass for the matrix and fiberglass resin as the binder.
The benefit of composites is that the combination of matrix and resin can create substances that have most of the good physical properties of both substances, and few or none of the poor physical properties. It is also common for composites to have additional good properties that neither of the original materials had. For instance, fiberglass resin by itself tends to be weak and brittle and fiberglass is extremely flexible and easily pulled apart. Together though, they create a strong, rigid, slightly flexible substance that is also fairly hard.
When making composites, you generally entirely soak the matrix in resin, then remove as much resin as possible. This minimizes the negative properties of the resin, while still effectively binding the matrix (the ratio of matrix to resin is sometimes used as a measure of quality of a composite). In industry this is often done using vacuum bags. (The composite is put into a large plastic bag, then the air and excess resin is vacuumed out.) In a post apocalyptic setting it will probably not be feasible to use a vacuum bag, even if you do happen to have the proper equipment. Instead, a tight fitting mold would work (one with two parts that compresses the material between the parts).
As an experiment, I am going to try using casein glue (see the previous post) with cotton or some other fiber that is commonly used in fabrics (I have to see what my wife has that she does not need). Since casein seems to bind well with cellulose (it was originally used as wood glue), cotton or some other natural fiber would probably be ideal. I think I actually have some scrap cotton around, so I'll use that for the first test.
Another common type of composite is wood laminates. (Look at the edge of a piece of plywood. Notice that it is made from several layers of wood glued together? This is a wood laminate. Plywood has several layers that alternate the grain direction, to make the sheet strong in all directions, instead of just directions that do not follow the grain.) In theory, casein would be a suitable glue for this as well, though probably not as good as the thermal epoxies commonly used now.
Monday, February 28, 2011
Plastics, glues, and paints
In a few more weeks, I will have a chance to test the forge. In the mean time, let's discuss plastics.
In a post apocalyptic world, it is likely that you will eventually discover something you need that would not be suitable made from metal, or something that would be extremely difficult to make from metal. Plastics are ideal for a lot of products and are generally easier to mold or cast. The problem here is that most modern plastics are made from crude oil products, which will not only be extremely difficult to obtain in a post apocalyptic world, but which also require chemicals which are dangerous and will be equally difficult to obtain. Thankfully, you will likely have at least limited access to ingredients to make plastics that were used as far back as ancient Egypt.
Milk contains a protein (or actually a class of proteins) called casein. This protein can be extracted by making the milk acidic. Generally the easiest way to do this is to add vinegar. My research has yielded many different formulas for this. The one I tested was 2 teaspoons of vinegar for every cup of milk. This was the lowest vinegar to milk ratio. The recipe with the highest ratio recommended 12 teaspoons per cup of milk. The 2 teaspoons to 1 cup of milk worked relatively well for me and in a post apocalyptic setting, I would go with the smallest amount that works well, to conserve resources.
The recipe I used said to warm the milk to simmering, then add the vinegar (2 teaspoons per cup of milk) and remove it from the heat. I did this on an electric stove, though if electricity was not available, you would be doing this over a fire. The protein separated from the milk very quickly (note that you should stir the milk as it heats and as the vinegar is acting). Once the milk had separated entirely into clear whey and lumpy, white curds, I strained out the liquid. This can be done with whatever is available (I used a plastic coffee filter; a paper one would probably have worked better). The instructions then said to add 1 more teaspoon per cup of milk (original volume, not the new volume) and to let it sit for an hour or two (it said to do this in a jar). The curds were supposed to separate further from the remaining water and the added vinegar, but it did not happen the way it was supposed to. Now I'll get back to this in a moment.
It turns out that casein can also be used to make glue (and paint). The previous instructions are actually the first part of making glue, except that you do not add any vinegar after filtering (I am not even sure that adding the extra vinegar after filtering is useful for making plastic; it could probably be skipped without any problems). Once it is filtered, you add some baking soda to neutralize the vinegar. This allows the casein to dissolve in water once again and the result is a sticky mess. I do not recall the exact amounts, but you can add 1/4 of a teaspoon per cup of milk (original volume again, not the new volume) at a time, mix it well, then give it 5 minutes for the reaction to finish. If it is not a sticky, gluey consistency after 5 minutes, do it again. Once you have the right consistency, you can add water to dilute it if needed (there should not be any curds or lumps). This can also be used as paint, by adding more water until you have the consistency you want for paint (food coloring or other pigments can be added for color). Casein glue was originally used as a wood glue, so this stuff has some construction applications (though I would not trust it to hold a lot of weight, without extensive testing).
Ok, back to the plastic. Even after a lot of kneading (as recommended in the instructions), I was unable to get the curds to stick together well enough for molding or casting (it is possible I gave up too soon). So, knowing about the glue recipe, I decided to try something else. I added around 1/8 of a teaspoon of baking soda to the mixture. This allowed some of the casein to dissolve, but not all of it. At first, the result was a sticky, rubbery, fluffy substance. The reaction between the vinegar and the baking soda produced a lot of CO2 bubbles, which made the casein mixture fluffy and airy. Of course, this is not good for a plastic as it will dramatically weaken it. So, I waited for the reaction to finish. This took around 5 minutes. After that, I kneaded the bubbles out of the mixture. It was no longer sticky, but it was still quite rubbery. At this point it was perfect for molding or casting. So, I rolled it into a ball, then flattened it between two pieces of wax paper. It is now between 1/8-1/4 of an inch thick, with a diameter of around 3 inches (this was from 1 cup of milk). It is currently setting. For flat pieces, you should put some weight on it while it cures, to avoid curling or warping. In the morning I will check it and maybe post the results (though, it may not be finished curing).
Some extra notes:
In a post apocalyptic world, it is likely that you will eventually discover something you need that would not be suitable made from metal, or something that would be extremely difficult to make from metal. Plastics are ideal for a lot of products and are generally easier to mold or cast. The problem here is that most modern plastics are made from crude oil products, which will not only be extremely difficult to obtain in a post apocalyptic world, but which also require chemicals which are dangerous and will be equally difficult to obtain. Thankfully, you will likely have at least limited access to ingredients to make plastics that were used as far back as ancient Egypt.
Milk contains a protein (or actually a class of proteins) called casein. This protein can be extracted by making the milk acidic. Generally the easiest way to do this is to add vinegar. My research has yielded many different formulas for this. The one I tested was 2 teaspoons of vinegar for every cup of milk. This was the lowest vinegar to milk ratio. The recipe with the highest ratio recommended 12 teaspoons per cup of milk. The 2 teaspoons to 1 cup of milk worked relatively well for me and in a post apocalyptic setting, I would go with the smallest amount that works well, to conserve resources.
The recipe I used said to warm the milk to simmering, then add the vinegar (2 teaspoons per cup of milk) and remove it from the heat. I did this on an electric stove, though if electricity was not available, you would be doing this over a fire. The protein separated from the milk very quickly (note that you should stir the milk as it heats and as the vinegar is acting). Once the milk had separated entirely into clear whey and lumpy, white curds, I strained out the liquid. This can be done with whatever is available (I used a plastic coffee filter; a paper one would probably have worked better). The instructions then said to add 1 more teaspoon per cup of milk (original volume, not the new volume) and to let it sit for an hour or two (it said to do this in a jar). The curds were supposed to separate further from the remaining water and the added vinegar, but it did not happen the way it was supposed to. Now I'll get back to this in a moment.
It turns out that casein can also be used to make glue (and paint). The previous instructions are actually the first part of making glue, except that you do not add any vinegar after filtering (I am not even sure that adding the extra vinegar after filtering is useful for making plastic; it could probably be skipped without any problems). Once it is filtered, you add some baking soda to neutralize the vinegar. This allows the casein to dissolve in water once again and the result is a sticky mess. I do not recall the exact amounts, but you can add 1/4 of a teaspoon per cup of milk (original volume again, not the new volume) at a time, mix it well, then give it 5 minutes for the reaction to finish. If it is not a sticky, gluey consistency after 5 minutes, do it again. Once you have the right consistency, you can add water to dilute it if needed (there should not be any curds or lumps). This can also be used as paint, by adding more water until you have the consistency you want for paint (food coloring or other pigments can be added for color). Casein glue was originally used as a wood glue, so this stuff has some construction applications (though I would not trust it to hold a lot of weight, without extensive testing).
Ok, back to the plastic. Even after a lot of kneading (as recommended in the instructions), I was unable to get the curds to stick together well enough for molding or casting (it is possible I gave up too soon). So, knowing about the glue recipe, I decided to try something else. I added around 1/8 of a teaspoon of baking soda to the mixture. This allowed some of the casein to dissolve, but not all of it. At first, the result was a sticky, rubbery, fluffy substance. The reaction between the vinegar and the baking soda produced a lot of CO2 bubbles, which made the casein mixture fluffy and airy. Of course, this is not good for a plastic as it will dramatically weaken it. So, I waited for the reaction to finish. This took around 5 minutes. After that, I kneaded the bubbles out of the mixture. It was no longer sticky, but it was still quite rubbery. At this point it was perfect for molding or casting. So, I rolled it into a ball, then flattened it between two pieces of wax paper. It is now between 1/8-1/4 of an inch thick, with a diameter of around 3 inches (this was from 1 cup of milk). It is currently setting. For flat pieces, you should put some weight on it while it cures, to avoid curling or warping. In the morning I will check it and maybe post the results (though, it may not be finished curing).
Some extra notes:
- This plastic is not very strong without a little bit of extra processing. Thick pieces should be fine, but thin pieces like the one I am making will probably be easy to bend until they break. If you happen to have access to formaldehyde, soaking the plastic in a 5% solution will strengthen it. This can take a long time however. One source said that plastic 25mm thick can take over a year of soaking to be entirely strengthened. Also, this process tends to cause warping. I can think of a few other ways of strengthening this plastic.
- Adding some kind of fiber should improve the strength. Cotton would probably work, fiberglass might work as well. If you want to make actual composites, you should probably use a thick mixture of the casein glue on cloth made from the chosen fiber. More on this in the next post. Also, this is supposed to be water proof once it is totally dried and is porous enough to paint.
- Casein is a food protein and as such will eventually spoil if left wet. Refrigerating it will extend its usable life. These products should last around a week or so refrigerated. Generally, it is probably best to only make them as they are needed.
- Even after it is dried, casein plastics will decompose if left wet for long periods of time. This is not generally enough to be a problem in daily use and is actually a good thing. Unlike petroleum plastics, Casein plastics are biodegradable.
- As this plastic can warp when drying, it has been common to cast a piece in a large chunk, then grind it to the desired dimensions. Historically, casein plastics used to make buttons were cast into long rods, cured using the above formaldehyde solution, then sliced and drilled to make the buttons (with additional grinding for more complex patterns). I will probably end up grinding the piece I am making into something, though I have not decided what yet. In theory, you could use a CNC milling machine to mill this plastic into useful objects (though, this would not be that useful in a post-apocalyptic world).
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