Analysis method for measuring content of 1, 4-cyclohexanedimethanol in copolyester chip

Abstract

The invention belongs to the technical field of polyester analysis, and discloses an analysis method for determining the content of 1, 4-cyclohexanedimethanol in a copolyester chip. Comprising the steps of transesterification, chromatographic column separation, component qualification, establishment of a standard working curve and determination of adding standard recovery. According to the present invention, the CHDM in the copolyester chip can be rapidly quantified by using the gas chromatography after the working curve is established, such that the operation is simple and convenient, and the method has characteristics of high accuracy and good precision.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyester analysis, and particularly relates to an analytical method for determining the content of 1,4-cyclohexanedimethanol in copolyester chips by a gas chromatograph. Background Technique

[0002] 1,4-Cyclohexanedimethanol (CHDM) is a new type of organic chemical raw material and is an intermediate for the synthesis of saturated polyesters and unsaturated polyesters in coatings, inks, adhesives, insulating materials and some special applications; it is used to manufacture polyester fibers, polyester electrical appliances, unsaturated polyester resins, polyester glazes, polyurethane foams, and is used in the production of lubricants and hydraulic fluids.

[0003] 1,4-Cyclohexanedimethanol is the raw material of the new copolyester PETG, and the full name of this copolyester is polyethylene terephthalate / 1,4-cyclohexanedimethanol ester. It is a linear homopolymer polyester formed by the polycondensation of three monomers, namely purified terephthalic acid (PTA), ethylene glycol (EG) and 1,4-cyclohexanedimethanol (CHDM), and is a non-crystalline copolyester.

[0004] In the process of synthesizing and researching PETG copolymers, different CHDM addition amounts have effects on the thermal properties and crystallization properties of PETG. There have been literatures using superconducting pulse Fourier transform nuclear magnetic resonance spectrometers to qualitatively and quantitatively analyze polyesters. The existing method for analyzing the structure of PETG uses nuclear magnetic resonance (1H-NMR), and then the relative mass percentage content of CHDM in the polymer can be calculated. However, nuclear magnetic resonance instruments are expensive and are limited in industrial production applications.

[0005] Gas chromatography is a separation and analysis technology that has developed rapidly in the past 70-odd years and is mainly used for the analysis of low molecular weight and volatile organic compounds. After the instrument operating conditions are determined, a certain amount of sample is injected into the chromatographic column. After a certain time, the components in the sample are separated in the column. After passing through the detector, a definite chromatogram is recorded. Qualitative analysis can be carried out from the position of each component peak in the chromatogram, and quantitative analysis can be carried out from the peak height and peak area of each chromatographic peak.

[0006] For high molecular materials such as copolyesters, when using gas chromatography for analysis, first, it is necessary to consider how to degrade the sample into small molecules, then process the degraded sample into a liquid that can be injected into the chromatographic column, select a suitable chromatographic column, and then carry out qualitative and quantitative analysis after separation.

[0007] In summary, when analyzing the content of the third monomer in high molecular materials such as polyesters, NMR instruments are expensive and have high maintenance costs, and their applications are limited. To quickly and accurately determine the monomer content in copolyester products, it is very necessary to study an analytical method with simple implementation and strong operability. Summary of the Invention

[0008] In order to overcome the deficiencies of the prior art, the present invention provides an analytical method for determining the content of 1,4 - cyclohexanedimethanol in copolyester chips. This method is easy to operate, with high accuracy and small error in the analysis results.

[0009] The above object of the present invention is achieved by the following technical solutions: An analytical method for determining the content of 1,4 - cyclohexanedimethanol in copolyester chips, the steps include:

[0010] 1. Take no less than three products with different CHDM contents, and carry out transesterification reactions under the conditions of high temperature and the presence of methanol respectively. The samples degrade and each monomer is liberated.

[0011] 2. Separate the filtrate after the transesterification reaction in step 1 by a chromatographic column.

[0012] 3. Qualitatively identify each component separated in step 2 accurately.

[0013] 4. Select a suitable quantification method, establish a standard working curve, and quantify the CHDM after qualitative identification.

[0014] 5. Determine the spiked recovery rate by the method of adding an external standard substance.

[0015] Further, step 1 is specifically as follows: Weigh about 1 g of the test sample, accurate to 0.1 mg, and add it to the reaction tube; accurately add 25.00 mL of the transesterification solution, and tighten the reaction tube with a wrench; place the reaction tube in a heating device and react at 210 °C for 2 h (when the sample is crushed to less than 1 mm, sampling oil bath heating can also shorten the reaction time to 60 min). Take out the reaction tube, cool it to room temperature with tap water, and filter the upper clear liquid into a triangular flask.

[0016] Further, step 2 is specifically as follows: Pipette 0.8 μL of the filtrate and test it with a gas chromatograph.

[0017] Further, step 3 is specifically as follows: Calculate the content of CHDM in the copolyester sample according to the calibration curve determined from the prepared calibration solution.

[0018] Further, the transesterification solution is: Weigh (0.06 ± 0.0002) g (accurate to 0.1 mg) of zinc acetate and (16 ± 0.0002) g (accurate to 0.1 mg) of triethylene glycol in a 50 mL small beaker, shake well and transfer to a 2000 mL volumetric flask, and make up to the mark with methanol.

[0019] Further, the chromatographic column and instrument operating conditions used in the gas chromatograph are as follows: the chromatographic column is DB-WAX (30m×0.32mm×0.25um); the carrier gas is hydrogen, the carrier gas flow rate is 40 mL / min, the combustion gas flow rate is 400 mL / min, and the auxiliary gas flow rate is 30 mL / min; the column temperature is 180 °C; the injection port temperature is 250 °C; the detector temperature is 250 °C.

[0020] Further, the preparation of the calibration solution: Accurately weigh 1,4-cyclohexanedimethanol (CHDM), triethylene glycol, and ethylene glycol (EG) solutions in three 50 mL conical flasks and mix them evenly to obtain a series of calibration solutions, where the ratio of CHDM:triethylene glycol:EG is 0.5:1:8.5, 1:2:7, and 2:4:4.

[0021] Further, the drawing of the calibration curve: Respectively pipette 0.8 μL of the calibration solution in Claim 4 for gas chromatographic testing. Each sample is measured in parallel three times. Using the concentration ratio of CHDM and the internal standard in the calibration solution as the ordinate and the ratio of the peak area of CHDM to the peak area of the internal standard as the abscissa, draw the calibration curve, and simultaneously calculate the relative correction factor f. The applicable range of the standard curve can be reasonably adjusted according to the actual content of CHDM; the content of CHDM in the copolyester sample is calculated using Equation (1).

[0022]

[0023] In the formula:

[0024] w—the content of CHDM in the sample, % (mass fraction);

[0025] A 1 —the peak area of CHDM;

[0026] f—the relative mass correction factor of CHDM to the internal standard;

[0027] A ST —the peak area of the internal standard;

[0028] m s —the mass of the internal standard, g;

[0029] m—the mass of the sample, g.

[0030] The beneficial effects of the present invention compared with the prior art are as follows: The present invention uses a common gas chromatograph with an FID detector in a laboratory to establish an analytical method for determining CHDM in copolyester chips. The successful development of this method can play a very good guiding role in the process adjustment of polyester new material production devices, and also provide technical support for the quality improvement and post-processing performance of end products. After establishing a working curve by gas chromatography, the present invention can quickly quantify CHDM in copolyester chips, with simple and convenient operation, high accuracy and good precision of the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0032] Figure 1 It is a typical gas chromatogram for copolyester determination.

[0033] Figure 2 It is a calibration curve for determining the CHDM content on copolyester. SPECIFIC EMBODIMENTS

[0034] The present invention will be described in detail below through specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0035] Example 1

[0036] The reagents and materials used in the present invention are as follows:

[0037] Methanol, of superior grade purity; ethylene glycol, of superior grade purity; triethylene glycol, of chromatographic grade purity; 1,4-cyclohexanedimethanol (CHDM), of chromatographic grade purity; zinc acetate, of analytical grade purity.

[0038] High-purity air: The hydrocarbon impurity content calculated as methane is ≤2.0 μL / L.

[0039] High-purity hydrogen: The purity is 99.99%, and the hydrocarbon impurity content calculated as methane is ≤0.5 μL / L.

[0040] High-purity nitrogen: The purity is 99.99%, and the hydrocarbon impurity content calculated as methane is ≤0.5 μL / L.

[0041] (1) Weigh about 0.06 g (accurate to 0.1 mg) of zinc acetate and 16 g (accurate to 0.1 mg) of triethylene glycol in a 50 mL small beaker. After shaking well, transfer them to a 2000 mL volumetric flask and make up to the mark with methanol. This is the transesterification solution.

[0042] (2) Weigh accurately 1,4 - cyclohexanedimethanol (CHDM), triethylene glycol, and ethylene glycol (EG) solution respectively, mix them evenly (accurate to 0.1 mg), and use it as the mass calibration solution. According to the set experimental conditions, aspirate 0.8 μL of the mass calibration solution for chromatographic analysis, and repeat the determination three times. Calculate the mass correction factor of CHDM relative to the internal standard triethylene glycol according to the peak area in the chromatogram and the mass of each component in the calibration solution. Among them, the concentration of the component to be measured in the calibration solution should be similar to the content of the component to be measured in the sample.

[0043] (3) Select copolyester chip samples, weigh 1 g of the sample (accurate to 0.1 mg), put it into a reaction tube, accurately add 25 mL of the transesterification solution, tighten the reaction tube with a wrench, add it to the heating device, react at 210 °C for 2 h, then take it out, cool it to room temperature with tap water, filter it into a triangular flask, and aspirate 0.8 μL of the filtrate for gas chromatography test.

[0044] Six parallel samples were measured, and the standard deviation was 0.20%.

[0045] Table 1 Test results of copolyester chips (n = 6)

[0046]

[0047] Example 2

[0048] According to Example 1, select samples at different time periods during process adjustment, weigh 1 g of the sample (accurate to 0.1 mg), put it into a reaction tube, accurately add 25 mL of the transesterification solution, tighten the reaction tube with a wrench, add it to the heating device, react at 210 °C for 2 h, then take it out, cool it to room temperature with tap water, filter it into a triangular flask, and aspirate 0.8 μL of the filtrate for gas chromatography test.

[0049] Six parallel samples were measured, and the standard deviation was 0.38%.

[0050] Table 2 Test results of copolyester chips (n = 6)

[0051]

[0052] Example 3

[0053] According to Example 1, select the esterified product during the production process of the copolyester process, weigh 1 g of the sample (accurate to 0.1 mg), put it into a reaction tube, accurately add 25 mL of the transesterification solution, tighten the reaction tube with a wrench, add it to the heating device, react at 210 °C for 2 h, then take it out, cool it to room temperature with tap water, filter it into a triangular flask, and aspirate 0.8 μL of the filtrate for gas chromatography test.

[0054] Six parallel samples were measured, and the standard deviation was 1.09%.

[0055] Test results of esterified products during the production process of copolyester (n = 6) in Table 3

[0056]

[0057] Example 4

[0058] Weigh 1 g of the sample (accurate to 0.1 mg) according to Example 1, Example 2, and Example 3 respectively, and then add different masses of CHDM for determination respectively.

[0059] Determine the spiked recovery rate by parallel determination three times.

[0060] Test results of copolyester chips in Table 4 (n = 3)

[0061]

[0062] The above-described embodiments are only the preferred embodiments of the present invention, rather than all the feasible embodiments of the present invention. Any obvious changes made by those of ordinary skill in the art without departing from the principle and spirit of the present invention should be considered to be included within the protection scope of the claims of the present invention.

Claims

1. An analytical method for determining the content of 1,4 - cyclohexanedimethanol in copolyester chips, characterized in that the steps include: S1. Take no less than three products with different CHDM contents, and carry out transesterification reactions under the conditions of high temperature and the presence of methanol. The samples degrade and each monomer is freed. S2. Perform chromatographic column separation on the filtrate after the transesterification reaction in step S1. S3. Qualitatively identify each component separated in step S2. S4. Select a suitable quantification method, establish a standard working curve, and quantify the qualitatively identified CHDM. S5. Determine the spike recovery rate by the method of adding an external standard substance.

2. The analytical method for determining the content of 1,4 - cyclohexanedimethanol in copolyester chips according to claim 1, characterized in that the specific step S1 is: Weigh about 1 g of the test sample accurately to 0.1 mg, add it to the reaction tube; accurately add 25.00 mL of the transesterification solution, and tighten the reaction tube with a wrench; place the reaction tube in a heating device and react at 210 °C for 2 h; take out the reaction tube, cool it to room temperature with tap water, and filter the upper clear liquid into a triangular flask.

3. The analytical method for determining the content of 1,4 - cyclohexanedimethanol in copolyester chips according to claim 1, characterized in that the specific step S2 is to pipette 0.8 μL of the filtrate and test it with a gas chromatograph.

4. The analytical method for determining the content of 1,4 - cyclohexanedimethanol in copolyester chips according to claim 1, characterized in that the specific step S3 is to calculate the content of CHDM in the copolyester sample according to the calibration curve determined from the prepared calibration solution.

5. The analytical method for determining the content of 1,4 - cyclohexanedimethanol in copolyester chips according to claim 2, characterized in that the transesterification solution is: Weigh 0.06 ± 0.0002 g of zinc acetate and 16 ± 0.0002 g of triethylene glycol in a 50 - mL small beaker, shake well and transfer to a 2000 - mL volumetric flask, and make up to the mark with methanol.

6. The analytical method for determining the content of 1,4 - cyclohexanedimethanol in copolyester chips according to claim 3, characterized in that the chromatographic column and instrument operating conditions used in the gas chromatograph are: The chromatographic column is DB - WAX, with a specification of 30 m × 0.32 mm × 0.25 μm; the carrier gas is hydrogen, the carrier gas flow rate is 40 mL / min, the combustion gas flow rate is 400 mL / min, and the auxiliary gas flow rate is 30 mL / min; the column temperature is 180 °C; the injection port temperature is 250 °C; the detector temperature is 250 °C.

7. The analytical method for determining the content of 1,4 - cyclohexanedimethanol in copolyester chips according to claim 4, characterized in that the preparation of the calibration solution: Weigh accurate masses of 1,4 - cyclohexanedimethanol, triethylene glycol, and ethylene glycol solution in three 50 - mL conical flasks and mix them evenly to obtain a series of calibration solutions, where CHDM:triethylene glycol:EG is 0.5:1:8.5, 1:2:7, 2:4:

4.

8. The analytical method for determining the content of 1,4 - cyclohexanedimethanol in copolyester chips according to claim 7, characterized in that, the calibration curve is drawn as follows: 0.8 μL of the calibration solution is respectively taken for gas chromatography test, and each sample is determined in parallel three times. With the concentration ratio of CHDM and the internal standard in the calibration solution as the ordinate and the ratio of the peak area of CHDM to the peak area of the internal standard as the abscissa, the calibration curve is drawn, and the relative correction factor f is calculated at the same time. The applicable range of the standard curve can be reasonably adjusted according to the actual content of CHDM; the content of CHDM in the copolyester sample is calculated by formula (1); wherein: w—the content of CHDM in the sample, %(mass fraction); A 1 — peak area of CHDM; f—the relative mass correction factor of CHDM to the internal standard; A ST — Peak area of the internal standard substance; m s — Mass of the internal standard substance, g; m—the mass of the sample, g.

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