PRESENTATION:

METHODS & PROCEDURE:

Creating The Plastic

For the study, a standard bioplastic formulation from Orenia et al. 2018 was used as the negative control. The ingredients for the plastic included polyvinyl alcohol powder (PVA) (P0154), water, glycerin (103116001), soya oil (6015), and glacial acetic acid (A0006) (see Figure 1). Many of these ingredients are highly dangerous, therefore they were handled with extreme caution (according to their respective Material Safety Data Sheets) (see Figure 1). When handling the chemicals, PPE—including protective goggles, nitrile gloves, and a lab coat—was worn throughout the procedure. Additionally, the chemicals were kept in a LabAire DynamicFlo Fume Hood at all times during the procedure, and when they weren’t being used, they were stored in safe, secure environments.

The first step of the plastic-making process requires dissolving the PVA powder in water (Silverson). 11.71 g of PVA powder was diluted in 89.29 g of cold (~4 °C) distilled water to create an 11% PVA solution. This solution was heated to 80 °C on a Flinn Scientific stir plate (AP9805) and then left to cool to room temperature (Orenia et al. 2018). The plastic was made by boiling 300 mL of water and adding the 11% PVA solution, glycerin, soya oil, and glacial acetic acid, in that order. A few drops of orange extract were added at the end to mask the pungent smell of the glacial acetic acid (Orenia et al., 2018). After mixing these ingredients together over a stir plate, they were poured onto an aluminum baking sheet lined with aluminum foil and left to cure for two days (Orenia et al., 2018). This method of curing is called solvent-casting, which results in a thin plastic sheet (do Val Siqueira et al., 2021). For the experimental arm of the experiment, the core ingredients stayed the same, and 100 grams of powderized orange peels (B07L47VZ1Z) were added to the mixture. Oranges were chosen as the organic component for the bioplastic due to their high concentrations of pectin, which is a polysaccharide that has been proven to increase the strength of plastic polymers (Mohnen, 2008; Bátori et al., 2017).

Another batch of negative and experimental plastics were created using the same ingredients, but this batch was cured differently. Instead of pouring out the liquid plastic onto a foil-lined baking sheet, they were poured into a mold to form the plastic into cylinders. This mold was created by drilling 2.85 mm-holes into an acrylic block (see Figures 2 and 3). The drill holes were then cleaned out using a nylon pipe cleaner, and the liquid plastic was poured into each hole. The goal of the acrylic mold was to get the liquid plastic to harden into tiny rods.

Tensile Strength Test

NOTE: This section consists of the proposed methods for the Tensile Strength Test. Due to time constraints, this test was unable to be conducted.

The acrylic mold was left in open air for 48 hours, after which the plastic rods were extracted from their cylindrical molds by gently pushing a thin dowel through the holes to force the plastic rods out. For tensile strength tests, objects are secured into a machine called a tensile tester, which slowly pulls the object apart and measures the force required to break it apart (Mielle, 2021). The lab in which this experiment was conducted does not have a tensile tester, therefore a make-shift tensile tester was devised by fixing a 20 kg load cell (B07BGS58TL) and Arduino circuit board (A000067) to a drill press.

Following their extraction from the mold, the negative control plastic rods were clamped into the tensile tester and pulled apart. The Arduino circuit board measured the force required to break the plastic. This process was repeated until a total of nine experimental replicates had been tested. The same procedure was followed for the experimental plastic rods. For the tensile strength test, the positive control consisted of 3-D printer filament made out of PVC plastic. Research shows that PVA plastic can be used as an effective substitute for PVC printer filament. (Bhagia et al., 2021).

The analysis process involved filming and watching all of the tensile strength trials, and then comparing the amount of force it took to break each plastic rod apart. The average amount of force was taken for each arm of the experiment. The more force required to break the plastic, the higher its tensile strength.

The present study hypothesizes that the orange peels in the experimental plastic formula will increase the tensile strength of the resultic plastic. Therefore, for the tensile strength test, if the experimental plastic is able to withstand more tensile force than the negative control plastic, the hypothesis will be supported.

Chemical Resistance Test

The purpose of this test was to determine how well each plastic can maintain their original form after being exposed to various chemicals. Chemical resistance tests are crucial for determining the viability of plastics in the market, especially biodegradable plastics, as they are generally more sensitive to moisture than synthetic plastics (Al-Hassan, Norziah, 2012).

The positive control plastic for this test consisted of strips of Ziploc bags, which have similar properties to the negative and experimental plastics made in this study. This is because plastic bags, like Ziplocs, are made from a type of plastic called linear low-density polyethylene (Reusch, 2013), which has similar properties to polyvinyl alcohol (El-Kader, Elabassy 2020). Nine strips of each plastic were submerged in three solvents—water, pure acetone (Flinn Scientific | A0009 | MSDS), and 10% ammonia (Flinn Scientific | A0038 | MSDS)—for two hours. As with the plastic ingredients, all chemicals were handled while exercising proper caution; PPE was worn at all times, and the chemicals were kept in the fume hood. When not in use, they were stored according to their MSDS. These chemicals were chosen because previous research has indicated that plastic, when exposed to these three chemicals, face varying degrees of deformation (Yang et al., 2021; Lohmann et al., 1991; Orenia et al., 2018). After two hours had elapsed, all the plastic samples were removed from the chemical solutions and laid out on individual petri dishes for inspection. Photos were taken of every plastic strip (81 total: three types of plastic; nine experimental replicates for each type; three chemicals).

Chemical Resistance Test Analysis

The photos were uploaded to a Google spreadsheet and analyzed. Quantitative and qualitative observations were recorded, and every strip of plastic was scored on a scale of 1-5 (1 being completely insoluble and 5 being soluble). The scores were averaged for each arm of the experiment, and the plastic with the highest average score was declared the most chemically resistant.

The chemical resistance scale was modeled after Orenia et al.’s three-point scale (2018). This scale is based around a series of qualitative observations, such as number of holes in the plastic, level of deformation, etc. Orenia et al. provides no key for converting these qualitative observations to quantitative results, so the present study will create its own key: A score of 5 correlates to no visible change in the plastic; 4 means there was a visible change, no matter how small; 3 signifies a defined weakening of the plastic (holes/tears, shriveling, etc.); 2 indicates a drastic change in the plastic’s form, making it unusable; 1 means the plastic is nearly or completely dissolved.

As with the tensile strength test, this study hypothesizes that the experimental plastic will have a higher chemical resistance. If the chemical resistance analysis shows that the experimental plastic maintains its form more than the negative control plastic when subjected to the chemicals, the hypothesis will be supported.

Biodegradability Test

Generally, the criterion for biodegradable plastic is that over 90% of it must be converted into carbon-dioxide within 180 days (Flury and Narayan, 2021). Due to time constraints, the present study could not gather data throughout the full 180-day period. However, researchers from Orenia et al. buried their plastic for just four weeks and still saw statistically significant results (2018). This data is further corroborated by Ruggero et al., which concluded that 30 days is enough time to see significant decomposition of bioplastics when buried (2019). Therefore, for this experiment, strips of each plastic were buried in compost in a plastic bin, 25.5 x 15.5 x 16.5 cm in dimension. In the biodegradability test from Azahari et al., researchers concluded that a burial depth of 10 cm was sufficient for allowing biodegradation to occur (2011). Thus, in the present study, the compost was filled up to 12.5 cm deep in the bucket, and the plastic pieces were buried 2.5 cm above the bin, making the burial depth 10 cm. A lid was placed over the plastic bins to ensure they were airtight, and they were left inside for a period of four weeks. The compost bins were undisturbed except for being watered with 237 mL (1 cup) of water every five days. This was to ensure that the compost was kept above 50% humidity, which has been concluded to be most effective in facilitating the biodegradation process (Richard, 2000). The inside temperature of the bins was kept between 20 and 30 °C, as done by Thakore et al. (2001). The water was drained through two 1 cm-holes that had been drilled in the bottom of the bins prior to filling them (Azahari et al., 2011). After the four-week period, all of the samples were dug up and lightly washed of any compost. They were then placed on individual petri dishes and photographed.

Biodegradability Test Analysis

The photos were uploaded to a Google Spreadsheet, and quantitative and qualitative observations were recorded. This process is called visual analysis, and is an effective way of measuring biodegradability (Ruggero et al., 2019). Every strip of plastic was scored on a scale of 1-5 (1 being not decomposed and 5 being completely decomposed). The scores were averaged for each arm of the experiment, and the plastic with the highest average score was declared the most biodegradable.

The biodegradability scale was inspired by Orenia et al. 2018. Like the chemical resistance scale, there is no key that can convert qualitative observations to quantitative data. One quantitative way to assess biodegradability is through weighing the plastic samples and calculating the mass lost. However, due to limited time and resources, the present study will use the qualitative 1-5 scale. Ruggero et al. determined the main visual characteristics of biodegradability to be particle size, consistency, thickness, discoloring, and erosion (2019). Therefore, the plastics in the present study will be observed on these criteria, and their level of biodegradation will be assessed using the same scale as the Chemical Resistance Test, except in the reverse order (i.e. 5 correlates to high degradation and 1 implies low degradation).

In this experiment, the Biodegradability Test is the only one in which the experimental arm is hypothesized to outperform both the negative control and the positive control. For this test, a more advanced level of degradation correlates to a higher score, therefore the experimental plastic is hypothesized to degrade more than both of the controls.

RESULTS AND DISCUSSION:

Chemical Resistance Test

The Chemical Resistance Test involved nine experimental replicates of each plastic type being submerged in three different solvents: water, acetone, and 10% ammonia. Figure 1 shows the general trends that emerged from this test. The chemical resistance score for each plastic was calculated through a number of factors including: change in appearance (holes, tears, and rough edges), change in structural integrity (i.e. plastic shape deforms), and change in mass. The scoring system is a scale from 1-5, with 1 correlating to poor chemical resistance (extreme degradation), and 5 correlating to high chemical resistance (no degradation). Commercially, it is advantageous for plastics to have high chemical resistance to withstand degradation from various solvents with which they may come into contact.

Figure 1 shows the overarching trends that emerged from each condition of the chemical resistance test. The data in Figure 1 was gathered from 81 chemical resistance test data points (three types of plastic, nine experimental replicates for each chemical), which are not all included in this section, but can be accessed through the following link titled “Supplemental Chemical Resistance Test Data”.

Figure 2 provides quantitative support for why each plastic got its respective score. Before the Chemical Resistance Test, each plastic strip was weighed and its mass recorded. After the 2.5-hr chemical exposure, the plastic strips were dried and weighed again, and new masses were recorded. All plastic strips were tracked so the change in mass could be calculated for each strip. A large decrease in mass correlates to a worse chemical resistance score, as it means the plastic’s network of polymers broke down and dissolved into the solvent. Moreover, all starting and ending masses were put through a two-tailed paired t-test in order to evaluate the significance of the data.

The percent decrease in mass for each plastic strip was calculated by subtracting the final mass from the starting mass, and dividing the difference by the starting mass. This was done for all nine experimental replicates across each condition, which were averaged and summarized in Figure 3. (Due to a mistake in the testing process, the positive control plastics in the water condition were treated as a singular cohort, and thus, no standard deviation can be calculated for that condition.) A higher percent decrease means the plastic experienced more degradation, which correlates to a lower chemical resistance score. To restate this paper’s hypothesis, the author believed that the addition of powderized orange peels would increase the chemical resistance of the bioplastic. In other words, the author hypothesized that the experimental plastic would receive higher chemical resistance scores across all three conditions compared to the negative control plastic.

Water

The positive control plastic (Ziploc bags) faced no degradation when placed in water; There was negligible change in mass—a 2.30% decrease—before and after the chemical exposure, nor were there any visual cues that the plastic was damaged in any way, therefore it received a chemical resistance score of 5. The two-tailed paired t-test confirmed that water had little effect on the mass of the positive control plastic (p>0.5). This was expected by the author, for commercially available synthetic plastics are designed to be robust and resistant to chemicals. It’s important to note that, while the positive control for this test is not technically the same formulation of plastic as the negative and experimental plastics, it still serves as an effective positive control, as it gives an example of how a standard, commercial synthetic plastic (linear low-density polyethylene plastic) fares in comparison to a biodegradable plastic. The negative control plastic (PVA formulation without orange peels), too, fared well to water exposure. Aside from a few tiny holes in some of the samples, the negative control was largely unharmed by the water. This qualitative observation is supported by the minimal change in mass before and after the chemical test. As shown by Figures 5 and 6, respectively, the negative control plastic experienced an average mass decrease of 0.04 g, or a 2.37% decrease (p<0.01). Overall, the negative control plastic received a score of 4; though it hardly lost mass, it didn’t receive a perfect score because of the small holes that formed in the plastic and its loss of structural integrity (i.e. being easier to tear). Despite the author’s hypothesis that orange peels would increase chemical resistance to water, the experimental plastic actually performed worse than the negative control plastic. Figure 3 shows that the experimental plastic decreased by an average of 57.60% in mass, with the average starting mass at 1.90 g and the average ending mass at 0.80 g. Using a two tailed paired t-test, the average final mass was determined to be significantly different from the starting mass (p<.01). On top of the mass change, the plastic became very susceptible to tearing, with several holes appearing in many of the replicates (as visible in Figure 1). The author attributes this result to the fact that orange peel powder, being completely organic, is water-soluble, which causes it to break down when exposed to water for extended periods of time. In fact, the orange peel provider describes its powder as “fast dissolving” (B07L47VZ1Z). This left the experimental plastic with a chemical resistance score of 1.5. In order to determine the validity of the results, a two-tailed independent t-test was conducted to compare the average percent change in mass when exposed to water between the negative and experimental plastics. The t-test found the results to be statistically significant (p<0.01), showing that there indeed is appreciable difference between the negative and experimental mass changes.

Acetone

When exposed to acetone, the positive control plastic was unaffected. There was negligible change in mass (0.28% 5.65%, p=1) before and after the test, and the structure of the plastic was unchanged, giving the positive control a score of 5. Though acetone is known to degrade certain plastics, the chemical resistance test showed that the positive control is unaffected by it. The negative control condition, on the other hand, experienced an extremely large decrease in mass. Figure 2 shows that the average starting mass of the negative control plastic was 1.22 g, whereas the average ending mass was just 0.15 g (p<0.01). This translates to an 87.51% decrease in mass. Visually, the acetone had striking effects on the plastic as well. All nine experimental replicates became shriveled after exposure, with their edges curling up considerably. What’s more, the acetone made the plastic extremely brittle, taking away all of its elasticity. The combination of these effects left the negative control plastic with a score of 1, meaning it dissolved nearly or entirely in the chemical and was rendered unusable after exposure. The experimental plastic experienced slight degradation after the acetone treatment, with an 11.10% decrease in mass before and after the chemical test (p<0.01). The average starting and ending masses of the experimental plastic, however, are within the same margin of error, meaning that the mass decrease may be even less drastic than Figures 5 and 6 suggest. Interestingly, after exposure to acetone, the experimental plastic lost much of its characteristic bright orange tint. This fade in color was the only change in appearance that the experimental plastic experienced after the acetone. Because of its very slight change in mass, the experimental plastic received a score of 4.5. Interestingly, even though the present study and Orenia et al. used the same plastic formulation, Orenia et al. saw no effect from the acetone on the negative control plastic (2018). It’s unknown why there is a discrepancy between studies, and the present study replicated Orenia et al.’s plastic formulation entirely. Despite these differing results, the acetone test from this paper supports the author’s hypothesis that the orange peels strengthened the biodegradable plastic formulation, as the experimental plastic performed far better than the negative control. The two-tailed independent t-test showed statistical significance (p<0.01) between the negative and experimental plastics in the acetone condition.

10% Ammonia

As with the previous conditions, the positive control plastic received a score of 5 for the 10% ammonia test. There were no visible or structural changes in the plastic, nor was there any significant change in mass. In fact, the positive control plastic experienced a 3.65% increase in mass after the ammonia treatment. The researcher attributes this seemingly impossible result to human error; It’s likely that one or multiple positive control strips were not dried completely before calculating their final mass. Any excess liquid on the plastic after chemical exposure would result in a higher-than-accurate mass. What’s more, even though there was such a minimal difference between the plastic’s starting and ending masses, the p-value showed that there was a significant difference (p<0.05). It’s likely that this is also a product of human error. Regardless, the standard deviation for the positive control is roughly 9%, putting it within a range of expected values. Given all of this, the takeaway from this condition was that the positive control plastic overall experienced a negligible percent decrease in mass. The negative control plastic was also hardly affected by the ammonia test, decreasing in mass by an average of 3.98% (p<0.01). Unlike the water, the ammonia left no holes in the negative control plastic, nor did it make the plastic brittle, as the acetone did. In addition, the plastic retained its elasticity, which it lost after the water and acetone tests. The main visual change the ammonia had on the negative control was shriveling the plastic, causing small ripples to form along its surface. This is apparent in the negative control photo in Figure 1. All of these results considered, the negative control plastic received a score of 3.5, equating to moderate degradation. As with the acetone test, these results differ from Orenia et al., which found the negative control plastic to be significantly degraded by 10% ammonia. As for the experimental plastic, Figure 2 shows the stark difference between the starting and ending masses for the ammonia test. The average starting mass for the experimental plastic was 1.92 g, whereas the average ending mass was just 0.75 g (p<0.01). This is a 60.59% decrease in mass—roughly the same percent decrease that the experimental plastic experienced in water. The results for the water and ammonia may be similar due to the fact that the 10% ammonia is predominantly water. The visual changes mirrored the water condition as well; the plastic became very soggy and lost much of its structural integrity. What’s more, similar to the acetone, the ammonia took away the plastic’s orange tint. One comparison between the experimental plastic and the negative control plastic is that, while the experimental plastic lost more mass after the ammonia test, none of the replicates had any holes in them, while the negative control plastic did. This finding suggests the structure of the orange peel plastic was more stable, despite its more severe degradation. Overall, the author gave the experimental plastic a score of 2.75, meaning the plastic would be essentially unusable after the chemical treatment. Like the previous conditions, a two-tailed independent t-test showed the difference between the negative and experimental plastics in the 10% ammonia condition to be statistically significant (p<0.01).

Biodegradability Test

Prior to testing the plastic, the author hypothesized that the addition of powderized orange peels would increase biodegradability, allowing organic plastics to compete with synthetic plastics. In other words, a high biodegradability score for the experimental plastic and a low biodegradability score for the negative control plastic would prove the author’s hypothesis. For the Biodegradability Test, nine experimental replicates from each arm of the experiment were buried in 11 L plastic storage bins filled with organic compost for 60 days. The plastics were buried at a depth of 10 cm, and watered with a cup of water every five days. On the final day, all plastic samples were exhumed and scored on a qualitative scale of 1-5 (1 being not decomposed at all and 5 being completely decomposed). Note that this scale differs from the Chemical Resistance Test scale. For the chemical resistance scale, a score of 1 correlates to heavy degradation, and a 5 correlates to no degradation. For the biodegradability scale, however, a score of 1 correlates to no degradation, while a 5 correlates to heavy degradation. This is because biodegradability is a measurement on an object’s ability to degrade over time due to natural causes (Ratner et al., 2013, p. 613), whereas chemical resistance is a measurement of an object’s ability to resist chemical degradation over time (Wypych, 2020). Despite these differences, a higher score in both tests is desirable, as the ideal commercial biodegradable plastic would be resistant to chemicals, but able to biodegrade quickly. When exhumed, all the plastic strips were covered in compost, and the plastic’s fragility made it difficult to clean them thoroughly. Because of this, a before/after mass calculation was not feasible, as there was no way to remove the soil stuck to each strip without damaging them.

Figure 4 shows the trends that emerged for each type of plastic during the Biodegradability Test. The trends displayed in Figure 4 were gathered from 27 data points (three branches of plastic, nine experimental replicates), which are not all included in this section. To view the full biodegradability test, see “Supplemental Biodegradability Test Data.”

Being made from standard Ziploc bags, the positive control plastic is not marketed as biodegradable. This was supported by the Biodegradability Test, for none of the positive control strips experienced any degradation—no holes appeared in the plastic after 60 days, and the plastic retained its original shape and structural integrity. The positive control plastic, therefore, received a score of 1.

The negative control plastic also received a poor biodegradability score. Individually, the scores for each experimental replicate ranged from 1 to 4, with the average score being 1.75. Several of the negative control samples had small holes in them by the end of the 60 days; with some also experiencing slight degradation along their edges. In Figure 4, the representative photo of the negative control shows that the top left corner of the plastic sample is missing. What’s more, there are several holes in the plastic. Overall, though, the degradation was minimal for the negative control.

The experimental plastic experienced significant biodegradation, receiving an average score of 4. Six of the nine experimental replicates either had large holes in them, or were heavily degraded at the edges. All of the experimental plastic samples completely lost their structural integrity, becoming flimsy and weak after being buried. The photo in Figure 4 illustrates this observation, as the edges and corners of the plastic samples are jagged and falling apart, or missing entirely. Moreover, there are numerous holes in the middle of the plastic strip.

The Biodegradability Test has shown that the orange peel plastic (experimental arm)—with a score of 4—outperforms both the negative control and positive control plastic—with scores of 1.75 and 1, respectively—supporting the hypothesis laid out by this paper. This is because the negative and positive controls are made entirely of synthetic materials, while the experimental plastic had an organic element in it—the powderized orange peels.

Conclusion

Both the chemical resistance and biodegradability tests show that the positive control served its intended purpose; it remained unchanged after each chemical, and didn’t biodegrade while it was buried. The negative control plastic performed as expected in the biodegradability test, with slight degradation but not nearly enough to be considered biodegradable. Conversely, the experimental plastic experienced significant biodegradation. These findings support the author’s hypothesis that the addition of powderized orange peels would aid the biodegradation process. Overall, the biodegradability test proved to be an effective measure of a plastic’s ability to decompose, as each type of plastic showed a distinct phase in the biodegradation process. This is consistent with the results from Ruggero et al., which found that the majority of the biodegradation process occurred within 30-60 days (2019).

There is conflicting evidence to support the author’s hypothesis as it pertains to the chemical resistance test. The experimental plastic far outperformed the negative control in the acetone condition, yet performed significantly worse in the water and ammonia conditions. On top of this, while Orenia et al. found that 10% ammonia degraded the negative control and acetone had no effect, the present study found the reverse to be true. Because of these conflicting results, no declarative statement can be made regarding orange peels’ effect on chemical resistance of plastic. However, the author proposes that more research must be done in this field to address this knowledge gap. Specifically, future research should aim to figure out which chemicals bioplastics are more resistant to, and why this is the case. Additionally, the author suggests more data be collected in regard to testing the tensile strength of bioplastics compared to synthetic plastics, as the present study was unable to complete this branch of the experiment. Once there is sufficient data relating to this topic, future researchers can further optimize bioplastic formulations with the objective of producing a bioplastic that can outperform synthetic plastics. A commercial switch from synthetic plastics to biodegradable plastics would have substantial positive effects on our environment, including reduction of global municipal solid waste, detoxification of composts, and depollution of our oceans. The long-term goal of this field is to transition holistically from synthetic materials to biomaterials, paving the way for a more organic, sustainable future for the planet.

SUPPLEMENTAL INFO AND FIGURES:

Full Procedure: