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Managing Editor  | June 2017

Biodegradable plastic developed from sugar and carbon dioxide


Researchers at the Centre for Sustainable Chemical Technologies (CSCT) at the University of Bath (U.K.) have developed a process for creating biodegradable polycarbonate plastic from sugars and carbon dioxide at low pressure and at room temperature, according to a report from the university website.

 

sugar_2_500

Researchers have developed plastic through sugar and carbon dioxide.
(University of Bath)

 

Polycarbonates are widely used across the plastics industry from drink bottles to lenses to coatings for phones, CDs and DVDs, but concerns have been raised over the use of BPA (bisphenol A), which was just named a substance of very high concern by the EU, or highly toxic phosgene in the manufacturing process.

 

To avoid using toxic materials, Bath scientists turned to a sugar found in DNA, thymidine, as the building block for the new polycarbonate because it is already present in the body and therefore biocompatible. The scientists used CO­2 to turn the sugar into a plastic precursor.

 

“The resulting plastic has similar physical properties to those derived from petrochemicals, being strong, transparent and scratch-resistant,” the article explained. “The crucial difference is that they can be degraded back into carbon dioxide and sugar using the enzymes found in soil bacteria.”

 

The hope is that BPA-free plastic can replace polycarbonates used in food packaging or in medical implants.

 

Three research papers have been published on the subject. Two papers were published in Polymer Chemistry and the third was in Macromolecules.

 

Read the first at http://pubs.rsc.org/en/Content/ArticleLanding/2017/PY/C7PY00118E#!divAbstract. The second was at http://pubs.acs.org/doi/abs/10.1021/acs.macromol.6b01492 and the third at http://pubs.rsc.org/-/content/articlehtml/2017/py/c7py00236j.

 

The abstract of an article published in February read:

 

“The development of biodegradable polymers from renewable resources is vital in addressing the dependence of plastics on petroleum-based feedstocks and growing ocean and landfill waste. Herein, both CO2 and natural sugar diols are utilised as abundant, safe and renewable building blocks for the synthesis of degradable and biocompatible aliphatic polycarbonates.

 

“Despite a strong potential for advanced polymer properties, inspired by Nature's supramolecular base-pairing, polycarbonates from the sugar components of DNA, 2′-deoxyribonucleosides have been limited by the inability of phosgene derivatives to form the cyclic carbonate monomers that would allow for controlled ring-opening polymerisation. CO2 insertion at 1 atm pressure into methylated thymidine 2′-deoxyribonucleoside, facilitated by organic base 1,8-diazabicyclo-[5.4.0]-undec-7-ene, affected an intramolecular SN2-like displacement of a tosyl leaving group to yield the cyclic carbonate by stereochemical inversion.

 

“Organocatalytic ring-opening polymerisation proceeded rapidly in solution resulting in high monomer conversions of 93% and number-average molecular weights, substantially greater and more controlled than via polycondensation routes. The thermodynamic parameters of the polymerisation (ΔHp = −12.3 ± 0.4 kJ mol−1 and ΔSp = −29 ± 1.1 J mol−1 K−1) were determined from the equilibrium monomer conversions over a temperature range of 0 to 80 °C and pseudo-first order kinetics demonstrated.

 

“The amorphous thymidine-based polycarbonates exhibited high glass transition temperatures of 156 °C and were found to be highly degradable to the constituent diol under basic aqueous conditions. Static water contact angle measurements and cell studies with MG-63 cell line indicated slightly hydrophilic and biocompatible materials, promising for tissue-engineering applications.

 

“The novel, CO2-driven approach to cyclic carbonate synthesis represents a means of expanding the scope of sugar-based monomers for tailored material properties derived from natural products.”

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