Global plastic production, use and disposal currently contributes more than 850 million tonnes of CO2 to the atmosphere; about 2% of the total emitted due to human activity. To reduce their environmental impact, bio-derived and biodegradable polymers such as PHAs may play a major role in the future plastics system. However, rather than letting them biodegrade, the value of the material could be captured through developing an efficient chemical recycling process which this work aimed to do. Principles of green chemistry were applied to identify safe, environmentally friendly solvents and catalysts, with which PHA was depolymerised, thus enabling the recycling of the carbon back into virgin quality plastic and preventing it’s release to the environment.
Image Credit: University of Birmingham, RePHASE
Image Credit: University of Birmingham, RePHASE
Image Credit: University of Birmingham, RePHASE
What are the key innovative aspects of the project and the story behind it?
The particular type of PHA investigated, poly(3-hydroxy butyrate) (P3HB) is bio-derived, biodegradable, and has the potential to replace conventional, fossil-derived plastic in a range of applications. Rather than relying on it’s biodegradability, we should aim to capture the value of the material when a product has reached the end of it’s useful life through adopting effective waste management strategies. However, it’s recycling has very rarely been investigated within the academic literature.
Using principles of green chemistry and engineering, a low temperature hydrolysis process was developed to depolymerise the plastic at a range of conditions. Modification of the polymer surface using methanol reduced it’s hydrophobicity. This significantly reduced mass transfer limitations of water and hence reduced the reaction time for complete depolymerisation from 4 h to 1.5 h. By varying the reaction time and temperature, the reaction kinetics were also investigated which allowed key parameters such as the activation energy to be calculated. These values are vital when modelling the reaction process and designing an industrial scale system. This work therefore demonstrated the proof-of-concept of a lab-scale chemical depolymerisation process for, what could be, the next generation bioplastic.
https://www.birmingham.ac.uk/research/plastics/spotlights/recycling-pha-for-second-life
https://www.birmingham.ac.uk/staff/profiles/chemical-engineering/keith-matt
