Enabling Internal PET Accessibility: A Pre-Amorphization-Enabled Positive Feedback Loop for Accelerated PET Biodegradation

The biodegradation of polyethylene terephthalate (PET) is typically confined to the polymer surface owing to its high crystallinity, which impedes enzymatic penetration into the fiber interior. To address this bottleneck, this study developed a structural destabilization strategy using eco-friendly plasticizers─epoxidized soybean oil (ESO), tri-n-butyl citrate (TBC), and acetyl tributyl citrate (ATBC)─to induce preamorphization of PET. This mild pretreatment substantially reduced PET crystallinity, with TBC exhibiting the most pronounced effect, lowering it to 14.6% and, for the first time, enabling enzymatic accessibility within the PET matrix. Following degradation by the whole-cell biocatalyst Comamonas testosteroni F6, the degradation efficiency of preamorphized PET was significantly enhanced. Weight loss in TBC-treated fibers increased from 4.9% in untreated controls to 16.9%, representing a 3.5-fold enhancement. This enhancement stems from a synergistic, self-reinforcing positive feedback loop: expanded amorphous regions and chemically activated ester bonds in alkaline media promote rapid initial hydrolysis; accelerated release of soluble monomers further stimulates microbial growth and enzyme production, thereby sustaining depolymerization. This cycle is evidenced by severe surface erosion, a marked increase in crystallinity after degradation, and accelerated terephthalic acid (TA) release. Crucially, over 93% of the plasticizer can be recovered, underscoring the economic and environmental sustainability of the process. This study establishes a green and efficient integrated pretreatment-biocatalytic system, offering a novel pathway to advance the circular economy model for PET waste.