Polyurethane Cascade Depolymerization by a Combination of Thermal Pretreatment and Enzymatic Hydrolysis

Area of Science:

• Biotechnology
• Polymer Science
• Sustainable Chemistry

Background:

• Polyurethanes (PURs) present recycling challenges due to their complex chemical structures.
• Enzymatic depolymerization is a sustainable strategy for managing PUR waste.
• Developing efficient biotechnological routes for PUR deconstruction is crucial.

Purpose of the Study:

• To investigate a cascade depolymerization approach for polyether-polyester-PURs.
• To combine low-temperature thermal pretreatment with tandem enzymatic hydrolysis.
• To enhance the yield of constituent monomers from PUR waste.

Main Methods:

• A two-step process involving thermal pretreatment (180°C, 4h) followed by enzymatic hydrolysis.
• Utilized cutinase HiC and metagenomic urethanase SP2 in a one-pot cascade reaction.
• Employed docking studies to understand enzyme specificity and optimize degradation.

Main Results:

• Thermal pretreatment improved PUR film susceptibility to enzymatic degradation, achieving >8% weight loss.
• The cascade approach with HiC and SP2 significantly increased the yield of 4,4'-methylenedianiline (MDA).
• HiC demonstrated specificity for ester bonds, and engineered variants accelerated degradation.

Conclusions:

• A combined thermal-enzymatic strategy effectively deconstructs polyether-polyester-PURs.
• This cascade approach enhances monomer recovery and offers a pathway for improved PUR recycling.
• The findings provide a foundation for designing industrial-scale enzymatic depolymerization processes.