Deep Eutectic Solvent as an Additive to Improve Enzymatic Hydrolysis of Polyethylene Terephthalate (PET)

Enzymatic hydrolysis of polyethylene terephthalate (PET) for surface modification of polyester fibers has attracted considerable research attention in recent years. However, the high crystallinity of polyester fibers, combined with limited enzyme activity and stability, challenges the surface modification study of enzymes. Deep eutectic solvents (DES) can create a favorable environment for proteins and are a new generation of biodegradable solvents. Few studies have been conducted on the use of DES to enhance enzymatic degradation. Therefore, we attempted to hydrolyze PET with DES-activated enzymes to increase the hydrolysis yield and thus improve PET modification. Using betaine and choline chloride as hydrogen bond acceptors and polyols as hydrogen bond donors, we investigated the effects of DES type, molar ratio, and concentration on enzymatic hydrolysis. Humicola insolens cutinase (HiC) was used as the biocatalyst for PET fabric hydrolysis, the role of DES as an additive in improving the yield of enzymatically hydrolyzed PET fabric was investigated. The results showed that under the conditions of an enzyme concentration of 6.5% v/v (volume of enzyme on the total volume), a temperature of 60 °C, and a reaction time of 72 h, the low concentration (20% v/v) of DES (betaine: sorbitol; 1:2 molar ratio) increased the hydrolysis yield by more than 1.5 times. Enzymatic hydrolysis in DES aqueous solution (betaine: sorbitol; 1:2 molar ratio) and DES single-component aqueous solution (betaine, sorbitol without synthesis of DES) indicated that the increase in hydrolysis yield was mainly due to the formation of hydrogen bonds between betaine and sorbitol, rather than the superposition of individual components. Further analysis revealed that HiC exhibited high relative enzyme activity and stability at low DES concentrations. Additionally, CD spectroscopy and fluorescence spectroscopy analyses demonstrated the effective preservation of HiC structure by DES. Our work provides insights into the development of efficient and sustainable methods to enhance HiC hydrolysis of PET fabric, unlocking new opportunities and potential for the comprehensive utilization of DES in the bio-modification of PET fabric.

Graphic Abstract