Since the 1950s, humans have produced over 9 billion tons of plastic, with another 400 million tons added annually. Plastic has become popular because it is durable, cheap, and versatile, but it also poses environmental problems.
It usually takes centuries for plastics to decompose fully. Even then, they do not really disappear; they only get smaller and accumulate into an ocean of microplastics.
Biodegradable Plastic as Solution to Pollution
Biodegradable plastics have been considered as the potential solution to address these environmental challenges. Like compostable plastics, microorganisms can break down biodegradable plastics into water, carbon dioxide, and biomass, but only under the right conditions.
In reality, compostable plastic products usually fail to meet their mission. They often fail to break down during the typical composting process. In addition, they contaminate other recyclable plastics, which presents another problem for recyclers.
Most compostable plastics mainly comprise a polyester type called polylactic acid (PLA). When they end up in landfills deprived of oxygens, they can last as long as forever plastics.
A Novel Type of Biodegradable Plastic
At the University of California, San Diego, scientists have pioneered a new type of thermoplastic polyurethane (TPU), a soft commercial plastic commonly used in floor mats, footwear, cushions, and memory foam. In the paper "Biocomposite thermoplastic polyurethanes containing evolved bacterial spores as living fillers to facilitate polymer disintegration," the experts described the material as durable and truly biodegradable.
The innovative breakthrough involves embedding bacterial spores within the plastic material. When exposed to nutrients typically found in compost environments, the harmless spores activate and break down the material. They are also essentially dormant bacteria that wake up when the time is right, such as when the plastic product has reached the end of its lifetime.
In this study, the research team utilized Bacillus subtilis, a species of bacteria known for its ability to decompose polymer materials. Bacillus subtilis and TPU pellets were fed into a plastic extruder, combining and melting them at 275 degrees Fahrenheit (135 degrees Celsius) into thin plastic strips.
Compared to fungal spores, bacterial spores contain a protective protein wrapping that enables them to survive in a vegetative state without nutrients. This shield also allows the bacteria to withstand the high-temperature environment during plastic manufacturing. As a result, they can be easily embedded inside bulk plastic.
To evaluate how well the new plastic material breaks down, the researchers placed the strips in two compost environments: one teeming with microbes and the other sterile. Both setups were kept at 98.6 degrees Fahrenheit (37 degrees Celsius) with humidity between 44% and 55%. Water and nutrients in the compost activated the spores embedded in the plastic strips, resulting in 90% material degradation within five months.
According to co-senior author Jon Pokorski, their material is remarkable because it breaks down without the presence of additional microbes. Most of them will not likely end up in microbially rich composting facilities. This ability to self-degrade in a microbe-free environment makes their technology versatile.
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