Moist-Solid Biocatalysis Enables Processive Depolymerization of Crystalline PET

Area of Science:

• Biocatalysis
• Polymer Science
• Sustainable Chemistry

Background:

• Enzymatic depolymerization of polyethylene terephthalate (PET) is hindered by its crystalline structure, necessitating energy-intensive pretreatment.
• Current methods often struggle with highly crystalline PET, limiting efficient plastic recycling.

Purpose of the Study:

• To investigate mechanoenzymatic depolymerization of highly crystalline PET using moist-solid conditions.
• To explore the mechanism of enzyme action and processivity in a limited water environment.
• To demonstrate a scalable and environmentally friendly PET recycling strategy.

Main Methods:

• Utilized the commercial cutinase HiC in mechanoenzymatic reactions under moist-solid conditions.
• Assessed depolymerization rates and yields for both high crystallinity and amorphous PET.
• Analyzed reaction products over time to understand cleavage patterns and enzyme processivity.

Main Results:

• Achieved nearly complete depolymerization of highly crystalline PET (42.5% crystallinity) without prior amorphization.
• Observed comparable reaction rates and yields for both crystalline and amorphous PET.
• Demonstrated processive cleavage of PET chains, a novel behavior for this enzyme in moist-solid conditions.
• Confirmed the feasibility of scaling up the moist-solid depolymerization process.

Conclusions:

• Moist-solid biocatalysis enables efficient depolymerization of crystalline PET, overcoming previous limitations.
• Limited water availability in moist solids promotes enzyme processivity, enhancing cleavage efficiency.
• This approach offers a sustainable, scalable, and economically attractive method for PET recycling.