Can Biodegradable Materials Replace Plastic as Protective Food Packaging?

This project follows the Scientific Method. Review the steps before you begin.

Making the Hydrogels

1. You will prepare hydrogels with three different gelatin-to-starch ratios. The ingredients for each recipe and their amounts are provided in Table 1. The amounts are calculated for a glass container with a length of 9 inches (about 23 cm) and a width of 7 inches (about 18 cm). If you use a different container, you will have to adjust your amounts. You want to make a hydrogel that is approximately 5 mm thick.
   
   
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   Ingredients	Recipe 1: 0% starch	Recipe 2: 10% starch	Recipe 3: 20% starch
   Distilled water	150 mL	150 mL	150 mL
   Gelatin powder	15 g	15 g	15 g
   Cornstarch	0 g	15 g	30 g

   Table 1. Hydrogel recipes.
2. Use tape and a marker to label the three pots and the three heat-resistant containers. Label one pot and one container "0% starch." Repeat with "10% starch" and "20% starch."
3. Prepare your hydrogels. You can prepare them all at the same time or one after the other. For each hydrogel, follow these steps:
   1. Measure 150 mL of distilled water.
   2. Weigh 15 g of gelatin powder into a small bowl.
   3. Weigh the amount of cornstarch you need for your hydrogel (given in Table 1) into another small bowl.
   4. Pour a small amount of the measured distilled water into the bowl with the cornstarch. Use a fork to mix the cornstarch with the water, making sure all the cornstarch is dissolved. This will prevent the cornstarch from forming clumps in the hydrogel later.
   5. Pour the remaining water into the appropriately labeled pot. Place the lid on the pot and bring the water to a boil.
   6. Once the water is boiling, add the 15 g gelatin and the dissolved cornstarch to the water. Use a whisk to mix until everything is dissolved.
   7. Carefully pour the hot mixture into the appropriately labeled heat-resistant container. Note: If there are lots of air bubbles on the surface of the gel, take a spoon or fork and skim them to the sides of the container.
4. Put all three containers into the refrigerator to let the hydrogels solidify. Make sure to put the containers on a flat surface. It takes at least one hour for the hydrogel to solidify. You can check whether the hydrogel has solidified by carefully poking the gel with your finger.
5. Once the hydrogels are solid, take them out of the refrigerator. With a sharp knife, cut around the edges of the glass containers to separate the gels from the containers. Then carefully peel the gel out of each container.
6. Wrap each hydrogel in a piece of cling wrap and label it with the appropriate starch percentage. Note: The gels should not be stored longer than 3 days in the cling wrap.
7. Repeat steps 2–6 two more times. When you are done, you will have three hydrogel sheets for each starch percentage. You will do each of your tests with all three sheets. Repeating an experiment multiple times is good practice in science and helps to ensure that you can trust your results.

Testing the Hydrogels

1. Qualitative description. Before you start cutting your hydrogels, look at each of them closely and make notes about how they look, feel, etc. Record your observations in a data table like Table 2.
   
   
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   Hydrogel	Qualitative description of the hydrogel
   Recipe 1: 0% cornstarch
   Recipe 2: 10% cornstarch
   Recipe 3: 20% cornstarch

   Table 2. Data table to record the qualitative features of the different hydrogels.
2. Coefficient of restitution (COR). In this test, you will investigate how well your hydrogel can absorb the impact of a collision, which is an important property for protective packaging materials. To measure the COR, make a data table like Table 3 in your lab notebook and follow steps a–h to test all of your hydrogels.
   1. From each of your three gels with 0% cornstarch, cut a 6 cm x 6 cm piece with a sharp knife. Make sure your gel piece is free of defects such as tears, large bubbles, or ridges.
   2. Measure the thickness of your gel pieces with a ruler. Record your measurements in millimeters in your data table. All gels should have the same thickness.
   3. Lay one of the gel pieces flat on a table or a plate. Next to it, place a ruler upright, with the zero mark at the bottom, as shown in Figure 3. You can set the ruler against an object to make it stand up, but the ruler should be straight and not lean in any direction.
      
      
      Image Credit: Svenja Lohner, Science Buddies / Science Buddies
      Figure 3. Experimental setup for the COR measurements.
   4. Set up a camera facing the ruler. Put the camera in slow-motion video mode. In your camera frame, you should be able to see the gel at the bottom and the 25 cm mark on the ruler at the top, as shown in Figure 3.
   5. Start the slow-motion video. Then take the glass marble and hold it at the 25 cm (or 10 inch) mark of the ruler , as shown in Figure 3. Line up the bottom of the marble with the 25 cm mark. (You will do this for every trial.) Let the marble drop directly onto the gel piece.
   6. Stop the camera and view the video. Your drop height (H) is 25 cm (or 10 inches). In the video, find the highest point that the bottom of the marble reaches on its first bounce, after it touches the gel for the first time. Read the ruler at that point and record the bounce height (h) in centimeters in your data table.
   7. Repeat steps e and f with the remaining two gel pieces with the same cornstarch percentage.
   8. Repeat steps a–g with the 10% cornstarch and 20% cornstarch hydrogels.

3. Food packaging test (egg). In this test, you will investigate how well your hydrogel can protect fragile products—in this case, an egg—from impact damage. To measure how well your hydrogel protects fragile foods, make a data table like Table 4 in your lab notebook and follow steps a–g to test all of your hydrogels.
   1. From each of your three gels without cornstarch, cut a 17 cm x 6 cm piece with a sharp knife. Make sure your gel pieces are free of defects such as tears, large bubbles, or ridges.
   2. Wrap an egg in one of the hydrogel strips, as shown in Figure 4. Use one piece of tape to hold the hydrogel strip together. While wrapping the egg with the hydrogel, observe how stiff or flexible the gel is. How easy is it to roll the hydrogel? Does it break or crack when you wrap it around the egg? Record your observations in your data table.
      Image Credit: Svenja Lohner, Science Buddies / Science Buddies
      Figure 4. Eggs wrapped in two different hydrogel sheets.
   3. With one hand, hold the ruler upright on a table or other flat surface, as shown in Figure 5. The surface should be relatively hard, like wood, marble, or stone. With the other hand, hold the wrapped egg next to the ruler so that its bottom lines up with the 38 cm (or 15 inch) mark. Hold the egg so the taped, double-layered hydrogel part is on the top, and the single-layered hydrogel part is at the bottom. Let the egg drop onto the hard surface. Carefully unwrap the egg and check whether it cracked upon impact. Record your result in the data table.
      Image Credit: Svenja Lohner, Science Buddies / Science Buddies
      Figure 5. Experimental setup for the food packaging test.
   4. Repeat steps b and c with the remaining two gel pieces with the same cornstarch percentage. Use a new egg for each trial.
   5. Repeat steps a–d with the 10% cornstarch and 20% cornstarch hydrogels.

Trial	Did the gel break during egg wrapping?		Did the egg break upon impact?
Hydrogel recipe 1: 0% cornstarch
1	yes	no	yes	no
2	yes	no	yes	no
3	yes	no	yes	no
Total	__ yes	__ no	__ yes	__ no
Hydrogel recipe 2: 10% cornstarch
1	yes	no	yes	no
2	yes	no	yes	no
3	yes	no	yes	no
Total	__ yes	__ no	__ yes	__ no
Hydrogel recipe 3: 20% cornstarch
1	yes	no	yes	no
2	yes	no	yes	no
3	yes	no	yes	no
Total	__ yes	__ no	__ yes	__ no

Table 4. Data table to record your results from the food packaging test.

Analyzing Your Data

1. Coefficient of restitution
   1. For each hydrogel recipe and each trial, use the drop height H (25 cm) and your measured bounce height h of the marble in your data table 2 to calculate the coefficient of restitution. To do so, first divide the bounce height h by the drop height H (h/H) and then use a calculator to calculate the square root of h/H. Record the results in your data table.
   2. For each hydrogel, use the data from all three trials to calculate the average COR. To do so, add together the calculated CORs of all three trials, then divide the result by three. Record the results in your data table.
   3. Make a bar graph of your data. Put the cornstarch percentage on the x-axis (the horizontal axis) and the average COR on the y-axis (the vertical axis).
2. Food packaging test
   1. Review your data table 4. For each question, count the total number of "yes" and "no" answers for each hydrogel. Record the results in your data table.
   2. Make a bar graph that shows how often the hydrogel broke while wrapping the egg. This data represents how stiff or flexible your hydrogel is.
      1. Put the cornstarch percentage on the x-axis and the number of "yes" answers for this question on the y-axis.
      2. Using a different color, add a second data series to the graph that shows the number of "no" answers for this question.
   3. Make a bar graph that shows how often your egg broke for each hydrogel. This data represents how well the hydrogel protects fragile food from impact.
      1. Put the cornstarch percentage on the x-axis and the number of "yes" answers for this question on the y-axis.
      2. Using a different color, add a second data series to the graph that shows the number of "no" answers for this question.
3. Look at your data tables, graphs, and observations to draw a conclusion from your results about which hydrogel recipe makes the best food packaging material. Take the following questions into consideration.
   1. How did the different cornstarch percentages affect the hydrogel properties?
   2. What similarities or differences do you see between the different hydrogel sheets?
   3. How is the COR different for the different hydrogels? What does this mean for their suitability as a packaging material?
   4. Which hydrogel performed best in protecting the egg from impact? Did you expect your results?
   5. Is there a possibility that other factors could have affected your test results? If yes, which ones?
4. Based on your results, do you think hydrogels like the gelatin/starch hydrogel are a good food packaging alternative to protect food from damage? Think about other factors that might be important for food packaging materials.
5. Do you think the hydrogel you made in this project is more or less sustainable than conventional plastic packaging? Use the 12 principles of green chemistry to answer this question.