Tuneable bioplastics

Plastics pose a problem for the planet – from the fossil fuels used to produce them to the harmful chemicals released during their slow degradation. But plastic is so ubiquitous that giving it up presents a complex challenge.

Plastic has become such an integral part of life in the Western world that it’s often easy to forget that the material was only invented in the 19th century. This is just as well, as many of the durable plastics in single-use products, such as bottled water and six-pack rings, can take up to 450 years to degrade. Today, we could probably find remnants of the first plastics ever manufactured still laying in landfill or floating in our oceans.

The longevity of plastics wouldn’t be as acute a problem if it weren’t for the scale of their use. Polymers are remarkably versatile materials, boasting wide-ranging characteristics from durability and stiffness to tensile strength and flexibility, depending on the specific polymer used. This versatility means plastics feature everywhere from structural reinforcement to disposable packaging.

In March 2019, the Ellen MacArthur Foundation published its New Plastics Economy report, which noted that 8 million tonnes of plastic packaging is produced every year by 30 global brands. Almost 50% of this packaging was produced by Coca Cola, totalling three million tonnes. Much of this packaging will be single use, so the majority of the eight million tonnes produced this year will be plastic pollution next year.

The problem goes much further than just a build-up of waste plastic cluttering the land and sea. Because plastic is a man-made material, it is generally difficult to break down naturally. For most naturally occurring materials, decomposition occurs because bacteria consume the larger material and break it down into smaller, useful compounds.

Breaking the chain

Unless they are recycled or incinerated, plastic products that are discarded end up in one of two places. They are either disposed of with general waste and destined to reside in landfill, or are thrown away as litter, which can then wind up in the oceans. According to figures published in Science in 2015, anywhere between 4.8 and 12.7 million tonnes of plastic finds its way to sea every year.

“For the tonnes of plastic that are washed away into the ocean, ultraviolet radiation from the sun is the main factor influencing degradation,” explains Dr Ashlee Jahnke, director of research at renewable polymer producer Teysha Technologies (pictured). “The decomposition process of plastic involves the long, complex polymer chains of the material being separated into smaller chains through a process known as chain scission, whereby the linkages holding the atoms of the material together break.”

Although it can take more than 450 years for plastic to fully degrade, the process of chain scission happens at a much faster rate, with the first chains breaking in under one year.

In our oceans, this poses two fundamental problems. The first is that the smaller the polymer debris is, the easier it is for organisms to ingest. The second problem posed by plastic degradation in our waters is that of the chemicals produced during chain scission.

For the plastics that stay on land and are buried in landfill, the process of degradation is similar. As many pieces of plastic waste in landfill will not be exposed to sunlight or UV radiation in the same way as sea plastics, the factor affecting degradation is heat.

“As a dumping ground for waste, landfills contain a mix of many types of solid waste, most of which does not have the same trouble degrading that plastics do,” Dr Jahnke continues. “As these products deteriorate, the chemical reactions that occur lead to an elevated temperature, which can contribute to polymer breakdown. However, the same problem of potentially toxic chemical leakage persists, which can easily enter soil and make its way back into our food chain over time.”

Nature finds a way

Plastics and plastic pollution are among the top problems facing the planet and life as we know it today. As such, researchers around the world have been vehemently searching for a solution, which led to the development of bioplastics and biodegradable plastics.

Dr Jahnke says: “Often confused, bioplastics are based on naturally occurring components, either entirely or in part, whereas biodegradable plastics are any plastic that can be completely broken down naturally to accepted industry standards. Generally, all biodegradable plastics are bioplastics, and that is why naturally occurring microorganisms can consume them, unlike fossil-fuel derived plastics.

“Theoretically, developing biodegradable plastics means that it’s easy to solve the plastics problem. We simply need to move away from unsustainable plastics and adjust manufacturing processes to use naturally occurring, safely biodegradable polymers instead. Of course, this is not the pragmatic approach.”

The reason why plastic in its current form has proven so popular is its versatility. It can be soft, flexible and malleable where the application needs it, or it can be developed in a way that makes it highly durable and rigid. Biodegradable plastics have so far lacked this versatility, limiting the scope of their application.

“But now, we’re on the precipice of change in the industry,” Dr Jahnke says. “Following years of research, Teysha Technologies has achieved a landmark breakthrough in creating a viable substitute for existing petroleum-based polycarbonates.

“The breakthrough is more of a platform than a single polymer system, providing inherent versatility in the properties that can be achieved. It can be thought of as a plug-and-play system where various modified natural-product monomers and various co-monomers can be used. In addition to co-monomers, various additives can be used to modify the properties of the final polymer produced. This versatility allows for the formation of a variety of materials that can vary greatly in their thermal and mechanical properties.”

Because the platform facilitates the use of various components, everything from strength and toughness to thermal stability and even the degradation rate of the material can be controlled.

“This is the pragmatic solution for consumers, material scientists and design engineers alike,” Dr Jahnke states. “Not only does it accommodate for the existing lifestyle of the end user, but it also allows materials scientists to create something that serves as a desired, drop-in replacement for petroleum-based plastics.

“Traditional plastics might pose a problem for the planet, but tuneable plastics could offer a viable solution that lets us sustain life as we know it.”

Author
Engineering Materials

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