关键词: 废弃聚酯, 密实化, 醇解, 酯交换, 再生DMT

Abstract: Polyester fiber, with excellent elasticity, wrinkle resistance and shape conformal property, is widely used in textile clothing, industrial packaging and other fields. As the amount of polyester fiber increases, the accumulation of waste polyester textiles also rises year by year, resulting in serious environmental pollution and resource waste problems. Waste polyester is depolymerized by chemical solvents to monomer as an effective raw material for the synthesis of high value-added recycled polyester materials, which is an effective way to achieve high-value recycling of the waste polyester textiles. Among the chemical methods, the glycolysis method not only has the advantages of mild reaction conditions and simple process, but also the ester exchange reaction between the alcoholysis product BHET and methanol can produce regenerated DMT comparable to primary petroleum-based materials, which is the most promising process route for the industrial preparation of the high-quality regenerated polyester materials. The densification methods of waste polyester textiles are a key factor affecting the efficiency and cost of the reaction during polyester alcoholysis and transesterification. However, most of the current glycolysis methods focus on the development of new and efficient depolymerization catalysts, and little research has been reported on the effect of different densification retreatment processes of raw materials on the alcoholysis products and the downstream regenerated DMT thereof.
In order to find the most suitable dense raw material for industrial decomposing poly waste polyester textile and preparation of regenerated DMT, the foaming, melt materials and melt extrusion materials derived from waste polyester textiles were prepared by the three densification methods of strong friction stirring, high temperature melting and screw heated extrusion, and depolymerized by ethylene glycol. Then, the alcoholysis products were futher transesterified by methanol to prepare the regenerative dimethyl terephthalate. The effect of different densification methods on the glycolysis and transesterification products of waste polyester textiles was investigated. The experimental results indicated that the maximum depolymerization rates of 99.2%, 99.02% and 98.2% and the yields of bis(2-hydroxyethyl) terephthalate (BHET) of 69.7%, 68.8% and 65.2%, respectively were achieved in 120 min for the foaming, melt, and melt extrusion materials under the same reaction conditions. The main components of the glycolysis products were BHET and its dimer, and the content of oligomers decreased with increase of depolymerization. Three glycolysis products were further transesterified with methanol under the same conditions to obtain DMT, and the DMT yields of 81.2%, 76.8% and 72.2% were achieved within 2.5 h for the foaming, melt, melt extrusion materials, respectively. Three transesterification products were purified by four times' methanol recrystallization and the DMT content was higher than 99%, which meets the requirements of the downstream high-performance recycled polyester products.
In order to improve the utilization rate of the reactor space, the reaction efficiency and product yield in the industrial production, it is an economical, efficient and feasible route to select the waste polyester with high specific surface area and relatively low densification as the raw material for the production of the regenerated DMT. The experimental results provide a useful reference for selecting suitable raw materials in the recycled polyester industry.

Key words: waste polyester, densification, glycolysis, methanol transesterification, regenerated DMT