Enzymatic depolymerization of highly crystalline polyethylene terephthalate enabled in moist-solid reaction mixtures.

Area of Science:

• Biotechnology
• Polymer Science
• Environmental Science

Background:

• Global plastic pollution is a significant environmental issue, with less than 9% of plastic being recycled.
• Current thermomechanical recycling of polyethylene terephthalate (PET) results in lower-quality materials.
• Enzymatic recycling of PET is hindered by the need for energy-intensive pretreatment to overcome enzyme inactivity towards crystalline PET.

Purpose of the Study:

• To develop an efficient enzymatic method for direct depolymerization of polyethylene terephthalate (PET).
• To enhance enzyme activity and efficiency for PET recycling without pretreatment.
• To improve the selectivity of enzymatic PET hydrolysis.

Main Methods:

• Utilized the cutinase from *Humicola insolens* in moist-solid reaction mixtures.
• Applied the enzyme directly to amorphous and crystalline PET without prior melt-amorphization.
• Analyzed hydrolysis products to determine selectivity.

Main Results:

• The enzyme directly depolymerized both amorphous and crystalline PET regions effectively.
• Achieved a 13-fold higher space-time yield and a 15-fold higher enzyme efficiency compared to previous studies.
• Demonstrated a 26-fold selectivity for terephthalic acid over other hydrolysis products.

Conclusions:

• Enzymatic depolymerization of PET is feasible and highly efficient in moist-solid conditions.
• This novel approach bypasses the energy-intensive pretreatment step, making PET recycling more sustainable.
• The enhanced enzyme performance and selectivity offer a promising solution for tackling plastic pollution.