Recyclable bioplastics cooled down, cooked up in chem lab

Recyclable bioplastics cooled down, cooked up in chem lab

4:59 AM, 8th December 2015
Recyclable bioplastics cooled down, cooked up in chem lab
Compostable cutlery and other products made from the biomaterial PLA are biodegradable, but not fully recyclable. Researchers have reported a breakthrough in recyclable polymers, which can be transformed back into their original molecular states using heat, which leads to truly recyclable plastics.

FORT COLLINS, US: Colorado State University chemists have developed a completely recyclable, biodegradable polymer, paving a potential new road to truly sustainable, petroleum-free plastics.

This polymer can be transformed back into their original molecular states using heat.

The innovation is from the lab of Eugene Chen, prof of chemistry and recent recipient of the Presidential Green Chemistry Challenge award.

This research is published in the journal Nature Chemistry.

Chen and Miao Hong, postdoctoral fellow describes synthesizing polyester that, when simply reheated for an hour, converts back to its original molecular state, ready for reuse.

Their starting feedstock was a biorenewable monomer that textbooks and journal papers had declared non-polymerizable, or could not be bonded into large molecules.

Chen’s lab is focused on making renewable and degradable plastics and other polymers to replace conventional petroleum-based materials.

“More than 200 pounds of synthetic polymers are consumed per person each year – plastics probably the most in terms of production volume. And most of these polymers are not biorenewable,” said Chen. “The big drive now is to produce biorenewable and biodegradable polymers or plastics. That is, however, only one part of the solution, as biodegradable polymers are not necessarily recyclable, in terms of feedstock recycling.”

The researchers’ starting monomer is a mouthful for being such a small molecule: Gamma-butyrolactone, or GBL. It is a colourless liquid and common chemical reagent, derived from a top-12 biomass compound best suited to replace petrochemicals, according to the Department of Energy.

Textbooks and scientific literature had described these small molecules as too happy and thermally stable in their monomeric chemical states to polymerize.

“Don’t even bother with this monomer,” Chen summarized the conventional wisdom. “You cannot make a polymer out of it because the measured reaction thermodynamics told you so. We suspected that some of the previous reports were probably incorrect.”

Not only did they make a polymer, Chen and Hong figured out how to get the polymers to take different shapes, such as linear or cyclic, based on the catalysts and conditions they selected. For their experiments, they used both metal-based and metal-free catalysts to synthesize the polymer, called poly(GBL), which is chemically equivalent to a commercial biomaterial called poly(4-hydroxybutyrate), or P4HB.

Precise reaction conditions

They employed specifically designed reaction conditions, including low temperature, to make the polymer and heat between 220-300 degrees Celsius to convert the polymer back into the original monomer, demonstrating the thermal recyclability of the polymer.

P4HB is derived from bacteria, which is a more expensive, complex process than how most plastics are made. By starting with the readily available GBL and ending up with a replacement material for P4HB, Chen’s discovery has promising market potential, and a provisional patent has been filed with the help of CSU Ventures.

© Colorado State University News



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