Transforming Industrial Food Waste into Biodegradable Food Packaging Films

Vesa Barileva

Age 15 | Oakville, Ontario

Canada-Wide Science Fair Trip Award, Silver Merit

With the ever-increasing amount of wasted food and global demand for packaging films, creating sustainable solutions that replace petroleum-based packaging while incorporating food waste reduces the impact of both problems. This research investigates whether food packaging films produced from industrial food waste, such as shrimp shells, can display comparable or even superior properties to those of traditional petroleum-based films. There is an extensive amount of scientific research on the processing of food waste into industrial compounds for manufacturing, so instead, this research focused more on the film fabrication using the waste. Solvent-casted films were fabricated with varying numbers of layers and solvent wt%, use of plasma treatment, and use of plasticizer. Property tests were performed on the films produced and on commercial films to determine the optimal film fabrication and composition. One of the more complex film types demonstrated superior properties when compared to commercial packaging representing a sustainable alternative.

INTRODUCTION

The world population is 7.8 billion as of April 2020 (Current World Population, 2020) and humans use packaging in their daily life. The global consumer packaging demand is valued at more than US$500B and is one of the fastest-growing markets (Dape, 2014). Every year, 1/3 of the food produced worldwide is lost or wasted (Kamal 2017) contributing to major negative impacts on the environment (e.g. large amounts of methane being released during the rotting/degrading process of wasted food) and on the economy (losses of over $1T). With an increasing population, large amounts of food waste, and demand for packaging, the development of sustainable solutions is of paramount importance. Food packaging films are widely utilized and must provide high strength and sufficient barrier properties against oxygen, water vapor, oil, and microorganisms. Currently, these films are largely based on fossil-fuels thus making them extremely unsustainable. Numerous bio-based materials such as cellulose nanocrystals (CNCs), Poly-lactic acid (PLA), and Chitosan (CS) have excellent film properties. There are three general processing routes for these materials (biological, chemical, and physical). Physical methods are time-consuming. Chemical treatments generally use large volumes of harmful chemicals. Lately, biological methods are being explored increasingly as a more safe, eco-friendly, and economical alternative (Biobased Industrial Alternative, 2000).

The purpose of this research is to utilize industrial food waste to produce biodegradable food packaging films that have comparable or even superior properties to those of traditional fossil fuel-based food packaging. This involved exploring various materials and fabrication methods in order to identify the optimal film composition. The hydrophobicity, tensile strength, and antimicrobial properties were tested in order to make meaningful comparisons between different films.

In descending order of performance, it is hypothesized that the films will be ordered as follows: plasma-treated PCC films, plasma-treated PCC films + soybean oil plasticizer, untreated PCC films, commercial translucent films (chocolate, cereal, cracker), PLA-only monolayer film - PCC = Multilayer film of PLA/CNC/CS. PCC films with a low concentration of CNC/CS will perform better than those with a high concentration and com- mercial films will have the worst antimicrobial properties. Plasma treatment will improve adhesion between film layers and multilayer films will perform better than the PLA-only monolayer film. All packaging films produced in this project are hypothesized to be biodegradable considering that the materials which remain in the films are known to be biodegradable (Is PLA, 2020) (Knorr et al, 1968) (Nanocrystalline cellulose, 2020).

METHODS

Solution preparation and solvent casting method
Concentration definitions: [H] = high concentration = 1 wt%, [L] = low concentration = 0.1 wt%. [H] and [L] solutions for each film component were prepared by combining the solvents and solutes - PLA (3g) in chloroform (200mL), CS (2.1g) in acetic acid diluted to 2% (200mL), and CNC (2g) in deionized water (200mL) into separate beakers.

Pour the solution of the first film layer into the desired number of petri dishes and allow to evaporate for about a week. Repeat for each film layer using the solutions in the order specified. A preliminary experiment was carried out to see if PLA and CS high concentration 1wt% [H] or low concentration [L] 0.1wt% resulted in better film properties. Here are four-layer films fabricated with solvent casting method: {PLA [L], CS [L], CNC [L], CS [L]}, {PLA [H], CS [H], CNC [H], CS [H]}, {PLA [H], CS [L], CNC [H], CS [L]}.

Fabrication of different films
A 1:1 mixture of CNC and CS solutions was created (CNC/CS) and each film type was fabricated twice using [H] and [L] CNC/CS mixtures. All films were 2-layer (PLA and CNC/CS). For the untreated films, the layers were solvent casted. For the untreated films with plasticizer, 10 wt% soybean oil was added to PLA and CNC/CS and then the layers were solvent casted. Plasma-treated films were fabricated by solvent casting layers but plasma-treated PLA layer before adding CNC/CS. For the PLA-only films, one layer of PLA [H] was solvent casted.

Property testing
Property tests (tensile strength, antimicrobial properties, water contact angle) were performed on all films. For the tensile strength testing, the Instron 3366 Tensile Testing Instrument was set-up. The Bluehill LE software was opened where a testing method was constructed with the desired properties (the dimensions of the specimens found using a caliper). Each specimen was placed in the instrument until broken. For the antimicrobial testing, each film was hole-punched three times. Three large agar-filled petri dishes were obtained and one was traced on paper. Ten small circles were marked within the traced circle and five isolated colonies of Escherichia coli bamB/tolC mutant bacteria were collected using an inoculation loop, suspended in saline solution and vortexed. A sterile inoculation loop was dipped into the inoculation tube. Antibiotic disks (one colistin and one vancomycin) and one sample of each film type were placed on marked circles for each dish. The dishes were incubated for 24 hours and zone sizes were measured. For the water contact angle testing, as the droplet is being placed onto the film surface, the program automatically starts analyzing the contact angle on both sides (left angle, right angle, and mean angle).

Figure 1: An example of what the tensile strength data look like for each film type. In this case, this is data for the PLA [H] + CNC:CS [H] film.

RESULTS

A results table was displayed which included all measured values for each tensile strength property. A stress-strain curve was pre- sented on a line graph for all samples (three samples for each film type as repeated trials).

DISCUSSION

The combined mean is calculated from the number of items (n) and mean of each set (m) and was used to improve accuracy of reported data. For the 4-layer films made from the original solu- tions, the high wt% films were extremely brittle, cracked, and folded once the second layer (CNC/CS) was added. Thus, I can infer that incorporating only high wt% materials in packaging films may result in poorer characteristics. The reasoning behind testing these film compositions was that a comparison between a monolayer of all the materials combined together and the other films seemed intriguing. However, the PLA/chloroform does not mix with the CS/acetic acid or the CNC/water because the acetic acid concentration is low enough to not repel the CNC too much. Additionally, when the preliminary experiment was performed it was found that the higher PLA concentration and the lower CNC/CS concentration were the best combination. The plasticizer worsened all film properties since they were very oily, cracked easily, and folded once the second layer was added (specifically the CNC/CS layer). The original intent of the addition was to improve the flexibility of the films. Plasma-treated films had higher tensile strength (on average) than the non-treated films because they had better adhesion between layers. Additionally, the Kirby-Bauer Disk Diffusion test results demonstrated no zone of clearance in any of the film specimens, in other words, they looked the same as the negative control. This could imply that the films do not have any antimicrobial properties, that it cannot be detected through an assay that relies on the activity being diffusible through an agar medium, or that the solvent concentrations were too low to be detectable. As expected, the positive control (colistin 25 micrograms la- belled CT25) showed a large dark clearance zone (2cm width in all the three dishes). Meaning that the bacteria could not grow within that zone because the antibiotic colistin diffused from the disk into the agar medium and was present at high enough concentrations to prevent growth. In contrast, the negative control (vancomycin at 5 micrograms, labelled VA5) showed no clearance zone (See Figure 3). The antibiotic vancomycin still diffuses from the disk into the medium but is ineffective against the strain of E. coli used therefore it could grow even with the antibiotic present. The film types in descending order of largest water contact angle based on combined mean calculations are as follows: commercial films (81.7°), PLA [H] only (79.125°), non-treated films (75.45°), plasma-treated films (74.5°). Meaning that all the film surfaces had good wettability with water, commercial films were the least hydrophilic, and plasma-treated films increased the hydrophilicity (packaging films should not be hydrophilic which means “water loving”). The high wt% 4-layer films made from the original solutions were extremely brittle, cracked, and folded once the second layer (CNC/CS) was added incorporating only high wt% materials in packaging films may result in poorer characteristics. In conclusion, the film results showed that the optimal film fabrication method and composition was PLA [H] + 1:1 CNC/CS [L] + Plasma. While other film types had better individual properties (quantitatively), this film exhibited better properties overall (See Figure 2). It also had the most identical appearance to commercial films (qualitatively) which consumers and companies are familiar with (See Figure 4).

Figure 2. The display film fabricated using the optimal film fab- rication method.

Figure 3: A summary of the data for each test across all of the different films. Antimicrobial susceptibility test results are not presented since there was no zone of inhibition for any of the films.

Figure 4: A summary of the data for the antimicrobial testing (Kirby-Bauer Disk Diffusion). Colistin showed a large dark clearance zone (2cm width in all the three dishes). Vancomy- cin showed no clearance zone in any of the dishes.

APPLICATION AND FUTURE DEVELOPMENTS

Humankind is demonstrating an immense increase in the demand for packaging alternatives as the unintended consequences of plastics and substantial amounts of food waste become more visible. Thus, companies will have a remarkable improvement in public image if biodegradable packaging from food waste are utilized. People are currently questioning whether buffets should remain open post the COVID-19 pandemic due to witnesses of people touching food with their bare hands at buffets even during a health crisis (Martyn 2020). Many buffet companies are even declaring bankruptcy (Tiffany 2019). There have been suggestions that stores and restaurants could offer pre-packaged food in place of buffets. This will result in an even larger demand for food packaging. To date, no packaging films with superior properties to commercial films using the materials and fabrication process used in this project have been developed.

The future improvements include attempting to produce the solute materials from industrial food waste through eco-friendly processes (PLA = soybean curd residue + solid state polycondensation, CNC = rice straw + ball milling, CS = shrimp waste + fer- mentation). Additionally, though chloroform entirely evaporates in the film fabrication process, it would still be interesting to explore more sustainable alternatives. Constructing films with more uniform thickness by using spin coating or doctor blading (cheaper method) and utilizing an even more accurate water contact angle measurement would increase accuracy in conclusions of the data. It would be interesting to test the biodegradability, surface printability of the films (scratch test and tape test) and the film’s effectiveness in keeping food fresh (barrier properties) to further characterize the films for use in food packaging.

CONCLUSION

The hypothesis was supported both qualitatively and quantitatively to a certain extent because although. I hypothesized that the PCC films only with plasma-treatment would perform the best and it was supported by the results but the order I had put the other films was rejected. The films produced in this research may represent an interesting alternative to petroleum-based films. Biodegradable food packaging films from food waste provide a packaging alternative that does not rely on petroleum and incorporates materials that would typically just be disposed of.

ACKNOWLEDGEMENTS

This project would not have been possible without all the support I received at various stages. I thank Dr. Jose M. Moran-Mirabal, Taylor Stimpston, Tori Marko, and Heera Marway of McMas ter University for providing me with the necessary equipment, guidance, and lab space to conduct my whole project. Next, I want to thank my brother, Nart, for giving me additional advice and motivation when I really needed it. Last but not least, I would like to thank my parents for going out of their way to support me.

REFERENCES

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ABOUT THE AUTHOR

Vesa Barileva

Vesa is a Grade 10 student from Oakville, Ontario. With a love for learning and a drive to create, Vesa is actively involved in STEM, social and environmental justice, journalism, and business to broaden her worldview. To date, she has completed three science fair projects where she has won numerous awards and was going to compete at the Canada-Wide Science Fair this year but could not as a result of the pandemic. Her project was about fabricating packaging films from food waste as both packaging and wasted food impact us all. She is very thankful that CSFJ has provided a way for her to share her project to a bigger audience. During her free time, Vesa enjoys writing, reading, dancing to music, and spending time outdoors.