Recyclable bioplastics cooled down, cooked up in labs
“The textbooks and journals said it couldn’t be done.”
But Colorado State University chemists have done it: They’ve made a completely recyclable, biodegradable polymer, paving a potential new road to truly sustainable, petroleum-free plastics. Recyclable, in the purest sense of the word.
Their starting feedstock was a biorenewable monomer that textbooks and journal papers had declared non-polymerizable, or could not be bonded into large molecules – polymers – typically required for use as a material.
Plastics are the most common type of manmade polymer, which is the chemical term for a long chain of repeating small molecules, or monomers. Plastics like polyethylene and polystyrene are king among synthetic polymers, and have come under fire for piling up in landfills. 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,” Chen said. “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.”
here are several biodegradable plastics on the market today, chief among them a starch-based material made from polylactic acid, or PLA. Compostable cups, cutlery and packaging in dining halls are made from PLA. They’re biodegradable, yes, but they’re not truly recyclable – once made, they can’t be completely reconstituted into their original monomeric states without forming other, unwanted byproducts.
And what about those little numbers on the bottoms of plastic containers? Doesn’t that mean “recyclable”? Sort of. Soda bottles, computer keyboards and millions of other plastics can be repurposed to extend their product lifecycle. But in the true, chemical sense of “recyclability” – biomolecules that can be synthesized into a useful material, and then completely converted back to the same molecules simply by heating the bulk material – is unheard of. Until now.
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.
“In my 15 years at CSU, I would probably call this my group’s most exciting piece of work,” Chen said. “This work creates a class of truly sustainable biopolymers, as they are both biorenewable and recyclable, based on a bioderived monomer previously declared non-polymerizable.”