Decoding Biodegradable Plastics: Insights into Soil and Seawater Degradation

The surge in global plastic production has reached unprecedented levels, with approximately 460 million tonnes generated in 2019 alone – a weight equivalent to nearly a thousand Burj Khalifas, the tallest building on Earth. This prolific production has led to a parallel increase in plastic waste, with alarming predictions from the UN indicating that by 2040, approximately 30 million tonnes of plastic waste will have infiltrated marine ecosystems worldwide. The pervasive nature of plastic pollution is evident, with microplastics detected in urban air, remote Antarctic regions, American food sources, and even the depths of the ocean floor.

Recognizing the urgent need for alternative materials, the quest for biodegradable plastics has intensified. While currently representing a small fraction of the total plastics market, these eco-friendly materials are gaining traction, with approximately 1.14 million tons produced in 2022. However, their widespread adoption faces challenges due to an incomplete understanding of their degradation mechanisms across various environments.

In a recent study published in Polymer Testing [DOI: https://10.1016/j.polymertesting.2024.108338], Korean researchers investigate the performance of three classes of biodegradable plastics – polycaprolactone (PCL), poly(butylene succinate) (PBS), and poly(butylene adipate-co-terephthalate) (PBAT) – in soil and seawater conditions. These polymers were synthesized in laboratory-scale systems and fabricated into films of various sizes and shapes tailored to each experiment.

The researchers conducted soil degradation experiments by burying the polymer films in horticultural topsoil and fertilized soil for six months. Regular assessments revealed that while PCL and PBS exhibited minimal changes in horticultural soil, PCL experienced significant degradation in fertilized soil, with visible holes forming on its surface within three months. PBS showed surface cracking and later weight loss, while PBAT remained relatively unchanged in both soil environments. Interestingly, the molecular weight of the biodegradable plastics showed no significant decrease after six months, regardless of soil type, highlighting the need for further research into degradation mechanisms.

Seawater degradation tests focused on PCL, which displayed the fastest decomposition rate in soil. Samples were submerged in warm seawater within coarse and fine fishing nets, with regular assessments over a year revealing accelerated decomposition in coarse nets due to increased aeration and seawater circulation. Vibro species dominated microbial populations on the samples, indicating the influence of environmental factors on degradation.

Real-world marine tests conducted off the coast of South Korea demonstrated faster decomposition rates for PCL films submerged in coastal seas compared to controlled aquarium conditions. PBAT exhibited the slowest degradation, attributed to differences in chemical structure. Notably, 3D-printed fishing jars made from PCL maintained mechanical properties for several months, suggesting potential applications in the fishery industry to mitigate ghost fishing.

Reference:

Junhyeok Lee, Semin Kim, Sung Bae Park, Mira Shin, Soyoun Kim, Min-Sun Kim, Giyoung Shin, Taewook Kang, Hyo Jeong Kim, Dongyeop X. Oh, Jeyoung Park. “Mimicking real-field degradation of biodegradable plastics in soil and marine environments: From product utility to end-of-life analysis,” Polymer Testing 131 (2024) 108338. DOI: https://10.1016/j.polymertesting.2024.108338