Researchers from the University of Birmingham, U.K., and Duke University, U.S., have created a new family of renewably-sourced degradable polymers offering similar qualities as common plastics.
Using sugar-based isoidide and isomannide as building blocks, the scientists made two new polymers, one that is stretchable like rubber and another which is tough but ductile, like most commercial plastics. These two sugar alcohols differ only in their stereochemistry, or three-dimensional structure, yet this resulted in their very different physical properties.
The isoidide-based polymer showed a stiffness and malleability similar to common plastics, and a strength that is similar to high grade engineering plastics such as PA 6. The isomannide-based material had similar strength and toughness but also showed high elasticity, recovering its shape after deformation.
Both materials retained their mechanical properties following pulverisation and thermal processing, which is the usual method for mechanically recycling plastics.
As Duke University professor Dr Matthew Becker noted: “Our findings really demonstrate how stereochemistry can be used as a central theme to design sustainable materials with what truly are unprecedented mechanical properties.”
Computational modelling simulated how the polymer chains pack and interact to produce such different polymer properties. By creating copolymers containing both isoidide and isomannide units, the researchers discovered they could control the mechanical properties and degradation rates independently of one another. As a result, the degradability of the polymers can be independently tuned for a specific use without significantly altering the properties of the material.
This study shows what is possible with sustainable plastics, Professor Andrew Dove, who led the research team from Birmingham. More work is needed to reduce costs and study the potential environmental impact of these materials, he said but ‘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’.
The scientists also noted that the two polymers could be blended without any complex compatibilisation requirements - probably because the materials are chemically so similar - and yielded macroscopically homogeneous films. This offers a distinct advantage in recycling, which often has to deal with mixed feeds, according to Dr Josh Worch, from Birmingham’s School of Chemistry, and a co-author in the research.
Dr Connor Stubbs, also from Birmingham’s School of Chemistry, added: “Petrol based plastics have had decades of research, so catching up with them is a huge challenge. We can look to the unique structures and shapes that biology have to offer to create far better plastics with the same expanse of properties that current commercial plastics can offer.”
A joint patent application has been filed by University of Birmingham Enterprise and Duke University. The researchers are now looking for industrial partners who are interested in licensing the technology.