Korean researchers investigate degradation of commercial materials in soil and seawater

Global plastic production is at an all-time high. In 2019, we produced 460 million tonnes of it – that’s close to the weight of a thousand Burj Khalifas (the world’s tallest building). And as plastic production has increased, so too has waste. The UN predicts that by 2040, around 30 million tonnes of plastic waste will have entered Earth’s marine ecosystems. In the past year alone, microplastics have been reported in the air above cities, in remote regions of Antarctica , in nearly all American food proteins, and on the deep ocean floor. The situation is dire, and so the hunt for alternative materials is on. Biodegradable plastics have been proposed as one such solution to the rapidly worsening problem of plastic pollution. Currently a small percentage of the total plastics market (1.14 million tons were produced in 2022), these materials look set to grow in popularity. One of the bottlenecks to their widespread adoption is an as-yet-incomplete understanding of how these plastics degrade in all environments.

In a new paper published in the latest issue of Polymer Testing [DOI: 10.1016/j.polymertesting.2024.108338], Korean scientists report on the performance of three classes of biodegrade plastics in soil and seawater conditions. Their materials of choice were polycaprolactone (PCL), poly(butylene succinate) (PBS), and poly(butylene adipate-co-terephthalate) (PBAT) which were all synthesised using lab-scale systems. The synthesized polymers were then used to fabricate films that were cut into a range of sizes and shapes suited to each test.

For soil degradation experiments, films of each polymer were placed in either horticultural topsoil mixed with water, or fertilized soil (a mixture of topsoil, vermicompost, and water). Every three weeks for six months, the samples were temporarily removed from the soil, cleaned and dried and their weight measured. To evaluate any changes in molecular weight of the polymers over time, powered samples of each polymer were added to both soils. At three-week intervals, 3g of the soil containing the powder was collected and dissolved in chloroform to extract the biodegradable plastic.

The PCL and PBS films showed little-to-no visible changes in horticultural soil. In contrast, in fertilized soil, PCL exhibited substantial degradation and weight loss, with “large, highly curved holes” forming on its surface within the first three months; PBS exhibited extensive surface cracking, and later, some weight loss, while the sample itself deformed and bent. PBAT did not show any major changes in either soil environment. In addition, the authors found that of the molecular weight of biodegradable plastics showed no significant decrease after 6 months, regardless of soil type. In terms of microbial growth, the higher nutrient content of the fertilised soil was seen to provide “a more favorable environment.”

To investigate degradability in seawater conditions, samples of PCL – which exhibited the fastest rate of decomposition in soil – were placed in either a coarse or fine fishing net before being submerged in an aquarium that was filled with warm seawater and inhabited by marine fish. Every three weeks for one year, the researchers temporarily removed each sample and dried it, weighing it to monitor any losses. They found that PCL samples submerged within coarse nets exhibited a considerably faster rate of decomposition than those submerged in fine nets. In addition, there was a greater abundance of microbes on the surface of the PCL in the coarse nets. The authors attribute this to an increased degree of aeration and circulation of seawater, facilitated by the coarse nets. Vibro species represented close to 95% of all microbes present on the samples, regardless of whether coarse or fine nets were used.

All three biodegradable plastics were subjected to a real-world marine test. Dog-bone-shaped samples of each were prepared and placed inside a coarse net and then enclosed in a larger fishing net and submerged in coastal seas off South Korea. Every two months for a period of one year, samples were temporarily retrieved from the fishing net, washed, dried and weighed. Tensile tests were also carried out after each retrieval. The researchers found that the PCL films decomposed 2 – 2.5 times faster in the marine environment than in the aquarium, and that marine samples also exhibited a wider variety of microorganisms. The PBAT sample exhibited the slowest rate of biodegradation among the tested specimens. The authors attribute this to the chemical structures of the plastics.

Finally, the authors 3D printed fishing jars – typical of those used in Cephalopod-farming – from PCL. The goal was to investigate whether biodegradable plastics might be suitable for use in the fishery industry. They write, “The mechanical properties of the samples were maintained for several months before significant weakening occurred, which can prevent ghost fishing [where marine species are killed by waste nets and plastic] supporting the potential application of biodegradable plastics as replacements for nondegradable materials in fishing gear.”


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: 10.1016/j.polymertesting.2024.108338