Sweeeeeet….sustainable plastics can now be made from sugar

Plastics are an inanimate monster if there ever was one. Despite desperate efforts to reverse inevitable doom for our planet, they keep invading landfills and oceans, and can even be a breeding ground for antibiotic-resistant superbugs.

The plastics of the future may be the sustainable substitute we need before the Earth literally turns into an enormous ball of trash. It has already been proven that they can be recycled into things as unexpected as vanilla flavoring, and now, in an inverse move, polymers made from sugars were used to create new sustainable plastics that are biodegradable and recyclable. These can even improve on the properties of regular plastic — so they are less likely to break or fall apart.

The sweet discovery was made by a research team from Duke University and the University of Birmingham in the U.K., including Birmingham researcher Connor Stubbs, who coauthored a study recently published in Journal of the American Chemical Society. Plastics are made of polymers. They stay together because of polymer chains that are bonded together from smaller units known as monomers. It doesn’t matter whether you use petrochemicals or sugar.

“Our monomers were made starting from isomannide or isoidide, which are both renewable sugar-based products,” Stubbs told SYFY WIRE. "We then made the polymers from these monomers using a technique designed to create different polymers conveniently.”

Stubbs and his colleagues used that technique, known as “click polymerization,” because it is a convenient way to create polymers so that they would be able to find out the differences between different types of bioplastics created from sugar monomers. The monomers they were made of determined their properties. Types of click polymerizations can vary, but they are all extremely efficient. They can occur at room temperature and produce long polymer chains with no by-products. This can work wonders for energy costs and the environment.

Petrochemical plastics are made under harsh conditions that burn excessive energy (if you needed one more reason to not want them around). Both isomannide and isoidide were produced using a method that only needed one step, and have shown that they can be superior to the plastics clogging up the environment, so there really is no excuse to still be using petrochemicals. They can challenge materials as tough as Nylon-6. In both, hydrogen bonds form between polymer chains and create order throughout, boosting the plastic’s strength.

“Many other common plastics or polymers, such as polyethylene, do not have the chemical structure to facilitate hydrogen bonding and are thus comparatively weaker,” said Stubbs. “Our polymer is structurally more complex than Nylon-6, although it is still very easy to make.”

What makes Nylon-6 stand out among petrochemical plastics is that it is a polyamide. The monomers in this polymer are held together with amide bonds, which make it easier to form secondary hydrogen bonds. It really doesn’t matter that this is a less complex material than sugar-based bioplastics. What makes the bioplastics even cooler is that isomannide and isoidide give them stereochemistry, the 3D structure of atoms and molecules in the material that affects chemical reactions. The urethane bonds in them can also give hydrogen bonds an assist.

In the polymers used for the new bioplastics, stereochemistry and urethane bonds join forces and are in charge of the formation of hydrogen bonds. This can work within the same polymer chain and even between separate polymer chains. Isomannide-based polymers showed especially high elasticity because stereochemistry determines the type of hydrogen bonds that form. Hydrogen bonds can break and re-form in different polymer chains when the isomannide-based plastic is stretched. Isoidide-based plastics are less stretchy but have super strength.

“Isomannide and isoiodide are isomers which means they have the same chemical formula (C₆H₁₀O₄) but only the 3D orientation of their bonds is different,” Stubbs said. “This means that they can easily be co-incorporated into polymers together.”

So you can actually put both isoidide and isomannide monomers together in a polymer depending on whether you want more stretch or toughness. That makes them even sweeter.