Eco-Friendly Biodegradable Agricultural Mulch Film with Light-Triggered Pesticide Release System

Video Transcript:

What if the very thing meant to protect our food is poisoning our soil? My name is Kaylee Wang. When watching my mom garden in our backyard, I learned about the white pollution crisis: global agriculture uses over 7 million tons of plastic mulch annually, yet with less than 30% recovery, it leaves a toxic residue of microplastics in our food and water.

Current biodegradable options are often too brittle for application. I engineered a bio-composite using PCL, starch, and calcium carbonate. This is four times stronger than conventional plastic while maintaining flexibility. In addition, I created a smart system by integrating UV-triggered microcapsules for controlled nutrient release. In a 72-day trial, my microsphere composite produced greater growth than test alternatives.

This transforms agricultural waste into a sustainable tool that can boost farming efficiency without sacrificing the health of our planet.

Plastic mulch films are widely used in modern agriculture because they improve crop yield, retain soil moisture, and reduce weeds (Tiwari & Sistla, 2024). However, they also create a major environmental problem. Globally, millions of tons of plastic mulch are used each year, and much of it remains in the soil, gradually breaking down into microplastics (Huang et al., 2023). These microplastics can disrupt soil structure, harm microorganisms, and even enter the food chain, posing risks to both ecosystems and human health (Salama & Geyer, 2023).

At the same time, existing biodegradable alternatives are not ideal enough. They are often too weak, too expensive, or degrade unpredictably, limiting their real-world adoption (Salama & Geyer, 2023). This creates a critical challenge: how can we design a material that is both environmentally sustainable and industrially practical?

This project was inspired by the growing issue of “white pollution” in agriculture and the need for smarter material systems. The key question explored was: Can we create a biodegradable agricultural film that is strong, cost-effective, and capable of controlled release?

To address this, I developed a composite material combining PCL, starch, and CaCO3, integrated with light-responsive microcapsules. This approach not only targets plastic pollution but also improves the efficiency of agricultural inputs. This work could benefit farmers, ecosystems, and consumers by reducing plastic waste, lowering chemical runoff, and supporting more sustainable food production systems.

To develop this project, I first explored scientific articles and review papers on biodegradable plastics, microplastic pollution, and agricultural mulch films to understand current challenges and possible solutions. I focused on peer-reviewed sources to ensure the information was accurate and reliable, which helped guide my material design.

I then created a biodegradable film using polycaprolactone (PCL) as the main material, combined with calcium carbonate to improve strength and starch to enhance flexibility and biodegradability. These components were mixed and heated to form a uniform composite. To ensure the materials bonded well, calcium carbonate was chemically treated, and ultrasonic mixing was used to evenly distribute the particles and prevent clumping.

Next, I designed light-responsive microcapsules to enable controlled release. I prepared a water-based solution containing a model compound (methylene blue and urea) and dispersed it into an oil phase to form tiny droplets. Through a crosslinking reaction, these droplets were solidified into stable microspheres. A light-sensitive compound was included so that the microspheres could respond to UV light.

To evaluate the system, I conducted structural, mechanical, and functional tests, including microscopy, thermal analysis, and release experiments under different conditions. Finally, I carried out a 72-day plant experiment, where all environmental factors were kept constant, and only the material type was changed, allowing for a fair comparison of plant growth outcomes.

Overall, this step-by-step design from material synthesis to real-world plant testing allowed me to systematically evaluate both the performance and practical potential of the system.

This project developed a biodegradable agricultural system combining PCL-based composite films and light-responsive microcapsules, and evaluated their structural, functional, and biological performance.

1. Composite Film Characterization

SEM imaging (Fig. 1) revealed clear differences in internal structure among the materials. Pure PCL showed a porous morphology, while the PCL/CaCO3 composite exhibited a much denser structure with significantly reduced voids. The PCL/Starch film displayed partial pore filling but still contained some irregularities. In contrast, the PCL/CaCO3/Starch composite presented a smooth, compact, and nearly defect-free structure, indicating improved dispersion and compatibility.

FTIR analyses (Fig. 2) confirmed the successful incorporation of calcium carbonate (CaCO3) and starch into the PCL matrix.

Thermogravimetric analysis (Fig. 3) showed that although additional decomposition stages appeared, the overall thermal stability of PCL was maintained. This suggests that the composite remains suitable for practical applications without significant loss of thermal performance.

The tensile test (Fig. 4) further demonstrated how each additive influenced material behavior. Pure PCL exhibited high ductility with moderate strength. Adding CaCO3 increased strength but reduced elongation, while starch increased flexibility but slightly reduced strength. The combined composite achieved balanced performance, maintaining both high strength and strong ductility.

To evaluate environmental performance, a degradation study was conducted. After 60 days of burial, the composite and microsphere films showed clear fragmentation, while pure PCL remained largely intact (Fig. 5). This suggests that additives disrupt the polymer structure, allowing moisture and microbes to accelerate degradation.

2. Microcapsule Characterization and Release Behaviour

Optical microscopy and SEM (Fig. 6) confirmed the successful synthesis of uniform, spherical PVA microspheres with smooth surfaces and minimal aggregation. Particle size analysis (Fig. 7) showed a relatively narrow, consistent distribution, with an average diameter of approximately 37.56 μm, indicating good control of the fabrication process.

To evaluate release behaviour, a calibration curve for methylene blue was first established (Fig. 8), showing strong linearity and confirming the reliability of the measurement method. The release experiments (Fig. 9) revealed a clear difference between conditions with and without UV exposure. Under UV light, the microspheres released their contents rapidly, reaching a high cumulative release within 24 hours. Without UV stimulation, the release was significantly slower and lower overall. This result confirms that the system is responsive to external stimuli and capable of controlled release.

3. Plant Growth Performance

A 72-day controlled experiment (Fig. 10) was conducted to evaluate real-world performance. All plants were maintained under identical conditions, with the type of material used as the only variable. Growth was assessed using leaf number, plant height, and fresh weight (Fig. 11).

The results showed a consistent trend across all indicators. Plants treated with the microsphere system demonstrated the strongest growth, followed by those with the composite film, while pure PCL showed moderate improvement compared to the control. The control group consistently exhibited the lowest growth performance. These findings indicate that the integrated system not only improves material properties but also enhances biological outcomes in a practical setting.

This project demonstrates that combining biodegradable composite materials with stimulus-responsive delivery systems can significantly enhance both material performance and agricultural efficiency.

A key conclusion is that synergistic material design enables simultaneous optimization of multiple properties. By integrating calcium carbonate and starch, the composite overcomes the typical trade-off between strength and flexibility seen in biodegradable plastics. This highlights how microstructure and filler interactions directly determine macroscopic performance.

In addition, the successful development of UV-responsive microcapsules shows that external stimuli can be used to precisely control the timing and rate of substance release. Compared to conventional passive release systems, this approach enables more efficient use of active compounds.

These findings are important because they address two major challenges: the limited mechanical performance of biodegradable materials and the inefficient use of agricultural inputs such as fertilizers or pesticides. By improving durability and enabling controlled release, this system has the potential to reduce material waste and environmental impact while enhancing crop growth.

Overall, this work provides a promising strategy for developing smart, sustainable agricultural materials with both functional and environmental benefits.

While this study demonstrates promising results, several improvements can extend its impact. First, future experiments will replace methylene blue with real agricultural pesticides or fertilizers to better validate practical performance. Second, long-term and quantitative degradation studies (e.g., mass loss and molecular weight changes) will be conducted to assess environmental sustainability more rigorously. Additionally, the mechanism behind enhanced plant growth observed in the microsphere group requires further investigation.

Next steps include optimizing the system for scalability and field conditions, with the goal of developing a high-performance, biodegradable alternative that enables controlled release while reducing agricultural waste and environmental impact.

I would like to sincerely thank my mentor, Dr. Liu, for guiding me throughout this project. She helped me refine my research question, encouraged deeper background research, and provided valuable feedback on my design, experiments, and data analysis, which greatly improved the quality of my work.

I am also grateful to the laboratory at Nanjing University for providing access to essential facilities and equipment. Special thanks to Dr. Li for patiently teaching me how to use the instruments and offering helpful suggestions during the experimental process.

Finally, I would like to thank my parents for their continuous support. They provided the materials needed for the plant experiments, including purchasing plants and equipment, and supported me in connecting with my mentor and accessing research opportunities. Their encouragement made this project possible.

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