Qingjun Jia,Zixuan Zhang,Lankai Su,Shu Bai,Di Cai,Changjing Chen,Linling Yu,Yan Sun
Enzymatic degradation of poly(ethylene terephthalate) (PET) into its corresponding monomers provides an attractive route for green plastic recycling and environmental remediation applications. However, the binding of PET hydrolases toward the PET surface is a rate-limiting step in PET degradation. Hence, we selected three anchor peptides and four linker peptides to fuse the previously engineered leaf-branch compost cutinase for facilitating enzyme binding and improving degradation of real post-consumer PET wastes of Coca Cola and C′eastbon PET bottles, with using the amorphous PET as a control. The systematical characterization of the seven cutinases revealed that the anchor peptide with moderate hydrophobicity plus chaperone activity and the flexible linker peptide with small hydrophobicity but long length were more suitable for each domain to serve its own role, affording the facilitated PET binding affinities and enhanced PET degradation performance. Thus, the optimal fusion cutinase possessed up to 3.3 times higher catalytic efficiency ( k cat / K m ) and 76 % increased long-term degradation performance than the parental cutinase, respectively. Further, complete degradation of C′eastbon PET wastes and 77 % degradation of Coca Cola PET wastes were achieved by the optimal cutinase of 33.3 nmol·g −1 PET in 96 h, proving its superiority against the real post-consumer PET wastes.
Chemical recycling is a promising way to achieve the closed-loop recycling for polyethylene terephthalate (PET). During this process, the post-consumer PET is depolymerized into bis(2-hydroxyethyl) terephthalate (BHET) through glycolysis and BHET can be polymerized again to produce recycled PET (rPET). However, since the applications of rPET is greatly limited to the color, recycling of PET fibers is challenged by the residual of colored impurities. In this study, a modified recrystallization process using ethyl acetate (EA) as the solvent was employed for the removal of colored impurities from the BHET. The process showed a decoloring rate of over 97.5% for the model colored impurities, performing better than the reported physical adsorption processes . Since almost no disperse dye was precipitated during the nucleation and crystal growth process due to the high solubility in EA, only a small amount of colored impurities adsorbed on the surface of crystals, leading to an excellent decolorization performance and post-consumer EA could be easily recycled through evaporation followed by condensation. Besides the model colored BHET, raw BHET obtained from the depolymerization of dark PET fibers was also purified by this modified recrystallization. By applying a composite purification strategy combining EA-based recrystallization and activated carbon adsorption, the whiteness (L*) of BHET greatly increased from around 65 to over 95 (L*=100 for pure white) and the whiteness of rPET produced from purified BHET (L*=86.21) was greatly improved compared with that from raw BHET (L*=44.01), showing the possibility of achieving the closed-loop recycling of dark PET fibers.
危险品化学品经营许可证（带存储）