Probing Supercritical CO2 to Improve the Susceptibility of Semicrystalline Polyethylene Terephthalate to Enzymatic Hydrolysis

• Published in: ACS sustainable chemistry & engineering 2024-05, Vol.12 (20), p.7713-7723
• Main Authors: Gurrala, Lakshmiprasad, Anowar, Rafi, Morais, Ana Rita C.
• Format: Article
• Language: English
• Subjects: carbon dioxide; crystal structure; cutinase; enzymatic hydrolysis; green chemistry; Humicola insolens; hydrophobicity; molecular weight; particle size; polyethylene terephthalates; surface area
• ISSN: 2168-0485; 2168-0485
• DOI: 10.1021/acssuschemeng.3c08286

Enzymatic hydrolysis of semicrystalline poly­(ethylene terephthalate) (PET) is hindered by the hydrophobic nature and crystallinity of the substrate, and it highly depends on the available interfacial area between substrate and aqueous phase. While most studies leverage particle size reduction to increase interfacial area, this study investigates the use of supercritical CO2 (scCO2) to increase internal surface area in PET, and its impact on the enzymatic hydrolysis yields. Our work shows that scCO2 pretreatment of semicrystalline PET resulted in up to 2-fold higher terephthalic acid (TPA) yield relative to the untreated counterpart using Humicola insolens cutinase (HiC) enzyme. There is a positive correlation between the total pore surface area in the scCO2-pretreated PET samples and the final TPA yield. In addition, preliminary kinetic studies revealed faster initial production of TPA for scCO2-treated PET relative to untreated PET. ScCO2-treated PET samples showed no significant changes in the crystalline content and thermal properties. However, NMR data indicated that scCO2-treated PET has a slightly higher apparent number-average molecular weight (M n) relative to that of untreated PET. Overall, scCO2 pretreatment led to increased semicrystalline PET susceptibility to HiC enzyme action, resulting in increased TPA yields.