• Meyer, Anne S.
• Thomsen, Thore Bach
• Hunt, Cameron J.

Abstract

This work examines the significance of the degree of polyethylene terephthalate (PET) crystallinity (X_C) and glass transition temperature (T_g) on enzymatic degradation of PET at elevated temperatures using two engineered, thermostable PET degrading enzymes: LCC_ICCG, a variant of the leaf-branch compost cutinase, and DuraPETase, evolved from the <i>Ideonella sakaiensis</i> PETase. X_C was systematically varied by thermal annealing of PET disks (Ø 6 mm, thickness 1 mm). X_C affected the enzymatic product release rate that essentially ceased at XC 22-27% for the LCC_ICCG and at X_C ∼17% for the DuraPETase. Scanning Electron Microscopy revealed that enzymatic treatment produced cavities on the PET surface when X_C was &gt;10% but resulted in a smooth surface on amorphous PET (XC ∼10%). The T_g of amorphous PET disks decreased from 74°C to 61°C during 24 h pre-soaking in water at 65°C, while X_C remained unchanged. Enzymatic reaction on pre-soaked disks at 65°C, i.e. above the T_g, did not affect the enzymatic product release rate, but delayed the initiation of enzymatic attack despite the lower T_g compared to enzymatic reaction on un-soaked samples. The data suggest that extended soaking of PET at 65°C induces an increase in the rigid amorphous fraction (X_RAF) that impedes the enzymatic attack. These findings improve the understanding of enzymatic PET degradation and have implications for development of efficient enzymatic PET upcycling processes.

Topics

• surface
• amorphous
• scanning electron microscopy
• glass
• glass
• glass transition temperature
• annealing
• crystallinity