关键词: 废弃聚酯, 解聚, 氨基改性活性碳纤维, 四氧化三铁

Abstract: "Polyethylene terephthalate (PET) possesses excellent crease resistance and shape retention, making it widely used in textile clothing industrial packaging and other fields. However, with the increase in polyester production, the accumulation of waste polyester textiles has also increased annually, leading to serious environmental pollution and resource waste problems. Waste polyester is depolymerized into monomer by chemical solvent, and then used as effective raw materials for synthesizing high-value-added recycled polyester materials, which is an effective way to achieve high-value recycling of waste polyester textiles. At present, there are four main chemical recycling methods for waste polyester, namely methanolysis, hydrolysis, glycolysis and ammonolysis. Among them, glycolysis has attracted great attention due to its mild reaction conditions and the use of low-volatility solvents. To solve the problems of low monomer conversion rates and difficult catalyst recovery in the glycolysis reaction system of waste polyester, this thesis aims to prepare efficient depolymerization catalysts as the research objective, using commercial activated carbon fibers (ACFs) as the substrate material. By first co-depositing polydopamine (PDA) and polyethyleneimine (PEI) on the surface of the activated carbon fibers, on the one hand, abundant amino groups were introduced onto the surface through the deposition, which synergistically catalyzed with metal ions, significantly enhancing the catalyst’s performance in depolymerizing waste PET. On the other hand, the amino-modified ACFs not only roughened the originally smooth fiber surface but also facilitated the complexation of amino groups with iron, which was beneficial for the loading of iron-based catalysts. The paper successfully co-deposited PDA and PEI onto ACF substrates through steps such as ultrasonic dispersion and oscillating water bath. Subsequently, Fe3O4 was loaded on the ACFs via an impregnation-reduction method, resulting in the preparation of an highly efficient heterogeneous catalyst (Fe3O4@ACFs-PDA/PEI) for depolymerizing waste polyester. The prepared catalyst was characterized by SEM, TEM, EDS, XRD, XPS and the alcoholysis products were analyzed by 1H NMR, FTIR, DSC and TGA. The depolymerization performance of Fe3O4@ACFs-PDA/PEI for waste PET was also investigated. The results showed that Fe3O4@ACFs-PDA/PEI exhibits excellent depolymerization performance for waste PET, converting it into bis(2-hydroxyethyl) terephthalate (BHET) monomers. Under optimized reaction conditions—2 g of waste PET,, reaction temperature of 200 ℃, reaction time of 120 min, Fe3O4@ACFs-PDA/PEI mass loading of 5% and ethylene glycol volume of 40 mL—the PET conversion rate reached 100%, with a BHET yield of 87.04%. Moreover, after seven reuse cycles, the PET conversion rate and BHET yield remained above 90% and 75%, respectively, demonstrating the catalyst’s excellent reusability. This thesis provides a new idea for the efficient depolymerization and recycling of waste PET."

Key words: waste polyester, depolymerization, amino-modified activated carbon fibers, Fe3O4