Scientists Use Stereochemistry to Create a Sustainable Plastic Alternative

The sugar-based polymers could possibly replace petrochemical-sourced plastics.

Germany, Empty plastic bottles recycling
Westend61 / Getty Images

A joint United Kingdom-U.S. research team may have found a sweet solution to plastic pollution. 

The scientists from the University of Birmingham and Duke University say they have developed a workaround to one of the problems with most sustainable plastics. These alternatives to petrochemical plastics tend to be brittle and generally have a small range of properties.

“To change properties, chemists have to fundamentally alter the chemical composition of the plastic, i.e. redesign it,” study co-author Josh Worch of Birmingham’s School of Chemistry tells Treehugger in an email. 

But Worch and his team think they have found a more flexible alternative using sugar alcohols, which they announced in a recent paper published in the Journal of the American Chemical Society. 

“Our work shows that you can change a material from plastic to elastic by simply using differently shaped molecules obtained from the same sugar source,” Worch says. “The ability to access these really different properties from materials with the same chemical composition is unprecedented.” 

Sugar High 

Sugar alcohols are good building blocks for plastics in part because they exhibit a trait called stereochemistry. This means they can form chemical bonds that have different three-dimensional orientations but the same chemical composition, or the same number of different component atoms. This is actually something that sets sugars apart from oil-based materials, which do not have this trait. 

In the case of the new research, scientists made polymers from isoidide and isomannide, two compounds made from sugar alcohol, a University of Birmingham press release explains. These compounds have the same composition, but different three-dimensional orientations and this was enough to make polymers with very different properties. The isoidide-based polymer was both stiff and malleable like common plastics while the isomannide-based polymer was elastic and flexible like rubber. 

“Our findings really demonstrate how stereochemistry can [be] used as a central theme to design sustainable materials with what truly are unprecedented mechanical properties,” study co-author and Duke University professor Matthew Becker said in the press release. 

example of isoidide and isomannide

Connor J. Stubbs et al

A Tale of Two Polymers 

Each of the two polymers has unique characteristics that could potentially make them useful in the real world. The isoidide-based polymer is ductile like High Density Poly Ethylene (HDPE), which is used for milk cartons and packaging, among other things. This means it can stretch very far before breaking. However, it also has the strength of nylon, which is used in fishing gear for example. 

The isomannide-based polymer acts more like rubber. That is, it gets stronger the farther it’s stretched, but it can then return to its original length. This makes it similar to elastic bands, tires, or the material used to make sneakers. 

“Theoretically, they could potentially be used in any of these applications, but would need more rigorous mechanical testing before [their] suitability could be confirmed,” Worch tells Treehugger. 

Because the two polymers have such a similar chemical composition, they could also be easily blended to create plastic alternatives with improved or just different characteristics, the press release points out.

However, for a plastic alternative to be truly sustainable, it isn’t enough for it to be useful. It also has to be reusable and, if it does end up in the environment, pose less of a threat than plastics derived from fossil fuels. 

When it comes to recycling, the two polymers can be recycled similarly to HDPE or Polyethylene terephthalate (PET). Their similar chemical structures help with this too. 

“The ability to blend these polymers together to create useful materials, offers a distinct advantage in recycling, which often has to deal with mixed feeds,” Worch says in the press release. 

Biodegradable vs. Degradable 

However, only nine percent of all the plastic waste ever produced has been recycled, according to the UN Environment Programme. A further 12% has been incinerated while an alarming 79% has lingered in dumps, landfills, or the natural environment. The alarming thing about plastic waste is that it can persist for centuries, breaking down only into smaller particles, or microplastics, that work their way up the food web from smaller to larger animals until they end up on our dinner plates.

The claim made for nature-based or sustainable plastics is that they would disappear more quickly, but what does this really mean? A 2019 study submerged a shopping bag billed as biodegradable in the marine environment for three years and found that afterward, it could still haul a full load of groceries. 

Part of the problem lies with the term “biodegradable” itself, study co-author Connor Stubbs of Birmingham’s School of Chemistry explains to Treehugger in an email. 

“Biodegradability is a commonly misconstrued concept, even in chemistry and plastics research!” Stubbs says. “If a material is biodegradable then it must eventually break down into biomass, carbon dioxide, and water through the action of microorganisms, bacteria, and fungi. If left long enough, some current plastics could eventually reach a point near this but it might take hundreds or thousands of years and probably happen only after fragmenting into microplastics (hence our current state of affairs!).” 

The study authors think degradable is a more accurate term, and that is the word they used to describe their sugar-based polymers. 

Determining how degradable a given plastic alternative is truly adds another layer of difficulty. How quickly it breaks down can depend on whether it ends up in the ocean or the soil, what temperature its surroundings are, and what type of microorganisms it encounters. 

“It is perhaps the single greatest challenge in plastics research to design a robust and universal standard/protocol for measuring how plastics degrade within a reasonable time span,” Stubbs says.

The study authors assessed the degradability of their polymers by conducting experiments on their plastics in alkaline waters, combining this with data on other plastics that degrade in the environment and using mathematical models to estimate how well the sugary polymers would break down in seawater. 

“Our polymers were estimated to degrade an order of magnitude quicker than some of the leading sustainable (degradable) plastics, but models will always struggle to capture all factors that can impact degradability,” Stubbs says. 

The research team is now working on testing how well the polymers will degrade in the environment without the aid of modeling, but this could take months or years to determine. They also want to expand the range of environments the plastics might degrade in.

“We have spent time on this project examining and modelling these degradable materials in aqueous environments (i.e. the ocean), but a future improvement would be to ensure that the materials can be degraded on land, possibly via composting,” Stubbs says. “More broadly, we have had some promising work in creating plastics that can degrade via sunlight (photodegradable plastics) and long-term we would like to incorporate this technology into other plastics.”

Next Steps?

In addition to assessing and improving their degradability, there are many other ways the researchers hope to improve these sugar-based polymers before they can actually begin to replace petrochemical plastics. 

For one thing, the researchers hope to improve the polymers’ recyclability and extend their lifespan. Currently, they begin to work slightly less well after being recycled twice.

In terms of producing the polymers, to begin with, the researchers have two main goals:

  1. Creating a greener, less energy-intensive system using reusable chemicals.
  2. Scaling up from synthesizing tens of grams to kilograms. 

“Ultimately translating this to a commercial scale (100’s of kilograms, tons, and beyond) would require industry collaborations, but we’re very open to seeking out partnerships,” Worch tells Treehugger. 

The University of Birmingham Enterprise and Duke University have already filed a joint patent for their polymers, the press release said. 

“This study really shows what is possible with sustainable plastics,” co-author and University of Birmingham research-team leader Professor Andrew Dove said in the press release. “While we need to do more work to reduce costs and study the potential environmental impact of these materials, in the long term it is possible that these sorts of materials could replace petrochemically-sourced plastics that don’t readily degrade in the environment.” 

View Article Sources
  1. Stubbs, Connor J., et al. "Sugar-Based Polymers with Stereochemistry-Dependent Degradability and Mechanical Properties." Journal of the American Chemical Society, vol. 144, no. 3, 2022, pp. 1243-1250., doi:10.1021/jacs.1c10278

  2. "Our Planet is Drowning in Plastic Pollution—It's Time for Change!" United Nations Environment Programme.

  3. Smith, Madeleine, et al. "Microplastics in Seafood and the Implications for Human Health." Current Environmental Health Reports, vol. 5, no. 3, 2018, pp. 375-386., doi:10.1007/s40572-018-0206-z

  4. Napper, Imogen E., and Richard C. Thompson. "Environmental Deterioration of Biodegradable, Oxo-Biodegradable, Compostable, and Conventional Plastic Carrier Bags in the Sea, Soil, and Open-Air Over a 3-Year Period." Environmental Science & Technology, vol. 53, no. 9, 2019, pp. 4775-4783., doi:10.1021/acs.est.8b06984