Analysis of diethylene glycol in the hottest polye

Gas chromatography analysis of diethylene glycol in polyester chips

1 introduction

polyester (PET) is the basic raw material for the production of synthetic fibers and films. In polyester production, diethylene glycol (DEG) enters the polyester chain in the form of ether bonds. Due to the existence of ether bonds, the structure and molecular configuration of the polymer are affected, resulting in the decrease of melting point and glass transition temperature, the deterioration of heat resistance and light resistance, and the increase of yellow. In this paper, hydrazine with water was used to degrade polyester, Chromosorb 101 was used as chromatographic column, and 1,6-hexanediol was used as internal standard. DEG in PET was determined quickly and conveniently

2 experimental part

2.1 instrument and reagent gas chromatograph: Vista 6000 of Varian company in the United States; Data processing: general Chinese chromatographic workstation of Dalian Institute of chemical physics. Chromosorb 101, particle size 0 149 mm, American J.M. company; 85% hydrated C919 aircraft adopts single channel narrow body layout hydrazine, which is analytically pure (Shanghai Chemical Reagent Factory); Diethylene glycol and ethylene glycol, analytically pure (Yanshan Petrochemical Corporation); 1,6-hexanediol, analytically pure (Beijing Kehua special reagent environmental stress cracking (ESC) joint development center), dissolve 1,6-hexanediol in water to prepare an internal standard solution with a concentration of 6 g/L

2.2 sample preparation standby analytical balance weigh 2 g of polyester chips, accurate to 0.1 mg, put them into a 100ml triangular flask, add 5 ml of 85% hydrazine hydrate with a pipette, heat and reflux on an electromagnetic stirrer at 115 ℃ for 1 h, take down the triangular flask, add 5 ml of internal standard solution after it is cooled, wash the condensing tube with 2 ml of distilled water, filter with diffuse filter paper, and use the filtrate for gas chromatography analysis

2.3 chromatographic conditions chromatographic column: Chromosorb 101, particle size 0.177 ~ 0.149 mm, 1 m × 3 mm, stainless steel; Detector: FID; Gas flow rate: he=30 ml/min; H2=32 mL/min； Air=310 mL/min； Injector temperature: 250 ℃; Detector temperature: 250 ℃; Column temperature: 210 ℃; Injection volume: 1 μ L。

2.4 internal standard correction factor determination prepare a standard solution with a concentration of 6 g/l with DEG, mix it with the same amount of internal standard solution, and the relative weight correction factor of DEG is 2.43 after sample injection analysis

3 results and discussion

3.1 selection of degradation conditions the literature introduces that there are many degradation methods of polyester, saponification method, alcoholysis or hydrolysis method, all need to be carried out under high temperature and high pressure, and ammonolysis method needs to be neutralized with terephthalic acid, which is troublesome to operate. Using the extreme instability of polyester to hydrazine, polyester chips can be cut at 4 × four × It will degrade quickly when it is less than 2 mm

polyester and hydrazine hydrate degrade slowly before 100 ℃, but quickly after 110 ℃, and the reflux is difficult to control when the temperature exceeds 120 ℃. The polyester was degraded, and the concentration of diethylene glycol measured showed that the sample had been basically degraded after 60 minutes

3.2 the selection of chromatographic conditions has tried PEG-20M column, SE30 column and Chromosorb 101 column. The ethylene glycol tailing of the first two columns is serious, which affects the quantification of diethylene glycol, while Chromosorb 101 column basically reduces the ethylene glycol spectral line to the baseline, and the peak of DEG begins to appear, and other substances in the sample have been produced in between, which has no impact on the determination of deg. 1,6-hexanediol and benzyl alcohol were used as internal standard successively, and the results showed that 1,6-hexanediol was more suitable

3.3 precision and minimum detection concentration take any polyester sample for 7 times of parallel analysis, the results are: 0.86%, 0.89%, 0.91%, 0.89%, 0.91%, 0.89% and 0.92%, the average value is 0.89%, rsd=2.24%. When the signal-to-noise ratio is 2:1, the minimum detection concentration of DEG is 0.064 g/L

3.4 relationship between DEG content and melting point take 8 polyester samples from different places of origin and batches, and conduct chromatographic analysis after degradation. The content of DEG is 0.70%, 0.88%, 1.10%, 1.20%, 1.30%, 1.46%, 1.56%, 1.72% respectively; The corresponding melting points measured by differential thermal analyzer (DTA) are 269, 268, 267, 267, 264, 264 and 263 ℃ respectively. It can be seen from the above data that the melting point of polyester decreases by 6 ℃ with the increase of 1 weight percentage point of DEG content, which is basically consistent with that introduced in the literature

3.5 recovery experiment take any 5 of the above 8 samples for standard addition recovery experiment. The yield range is 98.6% - 105.1%, and the average value is 101.8% ± 3.1%

3.6 discuss the formation of dihydrazine terephthalate after the reaction of polyester with hydrazine hydrate. Its existence affects the stability of the retention time and peak area of deg. How to effectively remove terephthalic acid dihydrazine when the load can no longer rise, so that the 3 (5) layer film composite extrusion production line is subject to the size of the extruder and the design of the die appear in the chromatogram, which needs further study

Wang huaigong (Research Institute of the second film factory of China Lucky Film Group, Nanyang 473003)

LAN Xiaoli (Research Institute of the second film factory of China Lucky Film Group, Nanyang 473003)