Breakthrough Engineered Enzyme Boosts Recycling of PET Bottles and Blended Fibers at Moderate Temperatures

A team led by Professor Akihiko Nakamura from the Research Institute of Green Science and Technology at Shizuoka University—working with Kirin Holdings Co., Ltd., the Institute for Molecular Science, and Osaka University—has engineered a novel PET hydrolase named PET2-21M. This enzyme exhibits significantly enhanced performance for depolymerizing bottle-grade polyethylene terephthalate (PET), one of the world’s most widely used plastics, at relatively low energy input.

Overcoming Traditional Recycling Limitations

Conventional mechanical recycling of PET often results in degraded material quality and is particularly ineffective for blended textiles such as PET/cotton and PET/polyurethane (PU). Chemical recycling offers high-purity outputs but usually requires harsh conditions and hazardous reagents. In contrast, enzymatic recycling provides a more sustainable solution, operating under milder, aqueous conditions and recovering original monomers for circular reuse.

Engineering the PET2 Enzyme Family

The researchers improved the natural PET2 enzyme by combining random and targeted mutagenesis, adding beneficial mutations and structural modifications inspired by HotPETase. The resulting variant, PET2-14M-6Hot, demonstrated strong activity against challenging blended fibers. Further optimization produced PET2-21M, which achieved 28.6 times higher efficiency than the original PET2 in initial tests.

High Efficiency at Moderate Temperatures

In scaled-up 300 mL reactor experiments, PET2-21M degraded 95% of commercial bottle-grade PET powder (20 g/L) within 24 hours at 60 °C—while the widely studied benchmark enzyme LCC-ICCG required 72 °C for similar performance. Even when the enzyme loading was cut in half, PET2-21M maintained about 50% degradation efficiency, nearly double that of LCC-ICCG under the same conditions.

For textile waste recycling, PET2-14M-6Hot outperformed LCC-ICCG in degrading PET fibers, PET/cotton (65/35 wt%) blends, and PET/PU (85/15 wt%) textiles, showing particularly strong activity at lower temperatures where PU blends are difficult to process.

Scalable Production

Both PET2-21M and PET2-14M-6Hot were successfully produced at large scale using Komagataella phaffii yeast, reaching high expression yields without glycosylation-related issues, demonstrating their readiness for potential industrial application.

Impact and Future Outlook

These engineered enzymes pave the way for energy-efficient, cost-effective, and sustainable PET recycling at industrial scale, particularly for previously challenging textile blends. Future research aims to further improve efficiency at even lower reaction temperatures and expand applicability to more complex polymer wastes, accelerating the shift toward a circular plastics economy.

Source: ACS Sustainable Chemistry & Engineering (DOI: 10.1021/acssuschemeng.5c01602)