Week 8

This week was very exciting for our team. After 7 long weeks of planning, adjusting and experimenting with the bioplastic material, it was finally time to put it through an ultimate tensile strength test. With help from Mr. Steve Pagano, Mr. Brian Wisner and Mr. Satish Rajaram, our team was able to observe our first tensile test in the Mechanical Engineering and Mechanics laboratory, as well as record the data and graphs displayed on the MARK-10 machines.

Figure 8.b: Preparing the test sample

Figure 8.a: Load weight displayed on MARK-10 screen

Figure 8.c: Slippage is evident through the lines seen on the

Setting up the machine seemed difficult initially, as the software and computer were slow. However, after several minutes of changing settings, we were finally able to place our sample in between the two grips. One of the biggest problems we faced was the slipping of our samples through the grips. When the sample would slip through, even just a little bit, the load value (expressed in Newtons) would be greatly affected. Thus, Mr. Wisner and Mr. Rajaram advised us to find a material to attach our samples to that would prevent them from slipping.

Figure 8.d: Brian and Satish in action

Even though we were not able to test all our samples and our collected data was quite different from what we expected, we were still able to make some good quantitative and qualitative observations. It seems that the less glycerol we mix into the plastic, the more brittle it becomes. The samples with the most amount of glycerol just kept stretching as far as the MARK-10 machine could go, while the ones with less glycerol would snap within seconds.

Figure 8.e: Stress-strain curve seen through the tensile test software

Week 7

During Week 7's lab we tried both methods that we came up with during Week 6. First we tried laser cutting the shape into the sheet of plastic. The result wasn't bad, the shape was quite accurate which was good. However, the edges of the samples ended up being very irregular because of the effects of the laser on the plastic. Later on we tried our second method: cutting the shape with an x-acto knife. This method turned out to be the most ideal one, since the samples cut had the desired shape and their edges were regular and clean.

Figure 7.a: Laser Cutting our New Mold

To follow our new method, we needed to come up with a way to make a regular, flat sheet of each batch of our plastic. To achieve this, we made a new mold with three pieces of acrylic: a simple rectangle that acts as a base, a frame that the plastic will be poured into, and a second smaller rectangle that takes up some of the frame's inner area in order to reduce the volume of plastic that would go to waste after cutting the samples.

Figure 7.c: Plastic in the New Mold

Figure 7.b: Cooking Batch of Plastic

Week 6

Our samples made after the change in the mold during Week 5 were still flawed. During Week 6's lab we went to the lab where we will test our samples planning on testing the samples made during Week 4, which were the closest to the expected shape. However, once we got there, the tensile machine wasn't working properly so we couldn't go through with our testing. We spoke to Brian and agreed on making all of our batches and then testing them all the same day.

Figure 6.b: Tensile Machine

Figure 6.a: Brian setting the machine up

Our next approach for making the plastic will be to pour it into a bigger rectangular mold and then cut the shape of the samples into the dried sheet of plastic with an x-acto knife. This way, warping and flashing won't be a problem.

Background

Majority of our project's techniques and processes come from Green Plastics, by E.S. Stevens. This book was generously lent to us by Dr. Richard Cairncross, of Drexel's Biological and Chemical Engineering department.

The emergence of bioplastics came about due to the fact that regular plastics would use non-renewable sources, or fossil fuel, in their production, such as crude oil. This kind of process would produce a large amount of waste, as well as a huge negative impact on our environment. Bioplastics were created to ensure that we can use plastic to continue to make our lives' easier, without causing so much harm to the environment around us.

Bioplastics are created from renewable biomass sources, such as vegetable oil, starch, vegetable fat, and a lot more other materials. These kinds of "green plastics" can be used in a variety of materials, such as packaging, cutlery, electronics casing, etc. Engineers, as well as ourselves, hope to increase the production of these bioplastics to lessen the damage inflicted by regular plastic production on the world.

Frequently Asked Questions

What do we use to make the plastic?
The ingredients used to make our bioplastic are easy to find products. Our recipe includes water, glycerol and gelatin.
How long does it take to make the plastic?
The preparation of the plastic is relatively quick. Cooking it takes from 10 to 15 minutes, and pouring it in the mold takes about a minute or two. Once the plastic is in the mold, it takes about 5 days for it to dry.
What is the difference between bioplastic and normal plastic?
Bioplastics are made with materials that are easier to break down when they are tossed out than the materials used to make normal plastics. This is because bioplastics use materials that are more natural than plastics.

Week 5

When we looked at the sample made during Week 4's lab we realized that it was flawed. It shrunk to about half its thickness and it had a lot of flashing. The samples also had a lot of bubbles that would affect the breaking point while testing it. These flaws would highly affect our tensile testing, so during Week 5's lab we spoke to Professor Speidel and Mr. Pagano about what changes we could make to our mold in order to get rid of the imperfections. Two more pieces of acrylic were laser cut. They are both the same size as our mold, but they don't have the shape of the sample cut into them. Once we made the new batch of plastic, we put one of the acrylic rectangles underneath the mold, poured the plastic in, put one of the negatives of the original mold (acrylic pieces in the shape of the sample) in each plastic sample and then put the other acrylic rectangle on top of everything. We pressed them together using duct-tape and heavy books. The whole setting is shown in the pictures below. In order to get rid of some of the bubbles formed, we put the mold on an ac unit that constantly vibrates for the first few minutes of the drying process.

Figure 5.a: Mold Arrangement

Figure 5.b: Mold Arrangement