Abstract: Polyethylene terephthalate (PET) is widely used in textile fibers, packaging materials, industrial films and other fields because of its chemical stability, good resilience and high strength. The rapid development of polyester products in all walks of life has also worsened energy shortage and environmental pollution problems. Research on recycled polyester in recent years has contributed to sustainable development. However, oligomers contained in polyester materials can be migrated to fiber surface or deposited on the machine during the production process, affecting product performance and production efficiency. In this study, a method for determining the composition of oligomers in polyester was established, which provides a technical basis for further research on oligomers in recycled polyester. 
In this study, photo-diode array (PDA) and refractive index detector (RID) were connected in series on advanced polymer chromatography (APC) to analyze the mixture standard sample according to the principle of them, and the standard curve and linear equation of each composition oligomer were established by the external standard method. At the same time, we verified the feasibility of the method by repeating experiments. The oligomer content in recycled polyester and virgin polyester was calculated by the linear equation and compared to characterize the differences. It is found that more sensitive and accurate information can be obtained by selecting chromatography at the maximum absorption wavelength of 240 nm. According to the spectral information obtained by RID and PDA, the standard curves plotted have a good linearity within a certain range. It can be seen from the repeatability test that the method is stable and efficient, and is suitable for the detection of oligomers in PET. With the help of standard curve and linear equation, the content of each oligomer in the regenerated and virgin PET fibers was calculated, and it could be seen that the oligomer compositions in PET fibers include cyclic dimers, cyclic dimers containing a diethylene glycol, cyclic trimers…cyclic dodecamers and above. There are many oligomeric species that can be extracted by the one-step precipitation method. Cyclic trimer and cyclic tetramer are the main compositions of PET oligomers, with a relative content of about 60% and 17%, respectively. The total amount of oligomers contained in physically recycled PET is 22.64 mg/g, which is higher than that of virgin PET at 21.03 mg/g, and the total amount of oligomers in chemically recycled PET is 20.73 mg/g, which is lower than that of virgin PET. It is in accordance with the physical and chemical recovery processes. 
In this study, PDA was coupled with RID on APC to extract chromatogram information at 240 nm; the standard curve of each composition oligomer was ploted, so as to establish the quantitative detection method of oligomers in PET. The method is simple and efficient, with better stability. From the calculation results, it is clear that different recovery methods of PET affect its internal oligomer content. Therefore, for different product performance requirements, the selection of suitable PET recovery methods is crucial for its high quality.

Key words: oligomer, APC, PDA, RID, composition

摘要： 聚对苯二甲酸乙二醇酯（PET）材料中的低聚物会显著影响其加工性能和终端产品的品质。为探究PET中低聚物的组成，通过一步沉淀法提取PET中的低聚物，借助超高效聚合物色谱（APC）、光电二极管阵列检测器（PDA）和示差折光检测器（RID）对自制的低聚物混合标准溶液进行标定，由外标法拟合各组分的标准曲线，建立定量检测低聚物组成的方法。结果表明：在240 nm吸收波长下，可获得分离度高且重复性好的低聚物色谱图；在测定范围内，相关系数R2＞0.99，相对标准偏差RSD＜2.00%，方法的线性关系及重复性良好。对未知浓度的试样进行检测可知，PET纤维中的低聚物包括环状二聚体、含一个二甘醇的环状二聚体、环状三聚体、环状四聚体，其中以环状三聚体和环状四聚体为主；所测试样品中，物理法再生PET中低聚物总含量最多，原生PET次之，化学法再生PET中低聚物含量最少。

关键词:  , 聚对苯二甲酸乙二醇酯（PET）, 低聚物, 超高效聚合物色谱, 光电二极管阵列检测器, 示差检测器, 组成