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CN-121978244-A - Method for measuring formyl end group content in polyacetal resin molecular chain

CN121978244ACN 121978244 ACN121978244 ACN 121978244ACN-121978244-A

Abstract

The invention relates to the technical field of high polymer material analysis and test, in particular to a method for measuring the content of formyl end groups in a polyacetal resin molecular chain, which comprises the steps of carrying out digestion reaction on a polyacetal resin sample through a hydrochloric acid and methanol system to quantitatively convert the formyl end groups in the molecular chain into methyl formate, adopting a staged temperature control distillation procedure to realize effective separation of the methyl formate and a complex matrix through precisely controlling the distillation temperature, collecting distillate for gas chromatographic analysis, calculating the concentration of the methyl formate by combining an external standard method, and finally deducing the content of the formyl end groups based on sample mass, distillate mass and methyl formate concentration data. The invention effectively solves the technical problem of incomplete separation of the target object caused by azeotropic interference of the complex digestion matrix and inaccurate distillation temperature control, establishes a set of detection method with good system, accuracy and reproducibility, and provides a reliable analysis means for polyacetal resin quality control.

Inventors

  • ZHAO MING
  • QIU JUNLIN
  • ZHANG YONGCHENG
  • XU JIANWEI
  • XU ZHIFEI

Assignees

  • 内蒙古汇能耀宁科技发展有限公司

Dates

Publication Date
20260505
Application Date
20260224

Claims (10)

  1. 1. A method for measuring the content of formyl end groups in a polyacetal resin molecular chain is characterized by comprising the following steps: Step 1, collecting a polyacetal resin sample, and obtaining sample quality data by weighing; Step 2, weighing a polyacetal resin sample by using the sample mass data in the step 1, and reacting with a mixed solution of hydrochloric acid and methanol under a heating condition to convert a formyl terminal group into methyl formate to generate a digestion solution containing methyl formate; Step 3, distilling and separating the digestion solution obtained in the step 2, controlling the distillation temperature to evaporate methyl formate, collecting distillate containing methyl formate, and recording distillate quality data; Step 4, carrying out gas chromatographic analysis on the distillate obtained in the step 3 to obtain methyl formate peak area data, and calculating methyl formate concentration data by an external standard method; And 5, substituting the sample mass data in the step 1, the distillate mass data in the step 3 and the methyl formate concentration data in the step 4 into a calculation formula to obtain a formyl end group content result.
  2. 2. The method for measuring the formyl end group content in the polyacetal resin molecular chain according to claim 1, wherein the digestion reaction in the step 2 is carried out under a heating reflux condition, the capacity of a round-bottom flask is 100 ml to 250 ml, the length of a condensing tube is 30 cm to 40 cm, the volume ratio of hydrochloric acid to methanol is 1:5 to 1:10, the concentration of hydrochloric acid is 36% to 38%, methanol is anhydrous methanol, the purity is not lower than 99.8%, the reaction temperature is controlled to 40 ℃ to 50 ℃, the precision is +/-0.1 ℃ by a digital thermometer, the reaction time is maintained to 30 minutes to 60 minutes, the time is controlled by a timer, the error is not more than +/-1 second, the digestion reaction is carried out under a stirring condition, and the stirring speed is 200 rpm to 300 rpm.
  3. 3. The method for measuring the formyl end group content in the molecular chain of a polyacetal resin according to claim 2, wherein the distillation temperature program in the step 3 is divided into two stages, wherein the first stage controls the heating power to make the system slightly boiling, the power is set to 100 to 150 watts, the distillation thermometer measuring range is 0 to 100 ℃, the graduation value is 0.1 ℃ and the reading is not more than 41 ℃ for 10 minutes to 15 minutes, the second stage increases the heating power to 200 to 250 watts, the distillation rate is controlled to 1 to 2% of the total liquid per minute, the total liquid volume is 50 ml to 100ml, and the heating is immediately stopped when the distillation thermometer shows an increase to 61 ℃.
  4. 4. The method for measuring the formyl end group content in the polyacetal resin molecular chain according to claim 3, wherein the distillation separation in the step 3 is carried out under the cooling condition of an ice water bath, the size of the ice water bath container is 20 cm x 15 cm x 10 cm, the ratio of the crushed ice to the water mixture is 1:1, the condensation temperature is maintained at 0 ℃ to 5 ℃, the accuracy of temperature monitoring is +/-0.5 ℃ through a thermocouple, the material of the receiving bottle is borosilicate glass, the capacity is 50 ml to 100 ml, and the ratio of the volume of the ice water bath to the capacity of the receiving bottle is 3:1.
  5. 5. The method according to claim 4, wherein the gas chromatography in step 4 is performed by using a flame ionization detector, the hydrogen flow rate is 30 ml/min, the air flow rate is 300 ml/min, the tail blowing flow rate is 25 ml/min, the chromatographic column is a polar capillary column, the stationary phase is polyethylene glycol, the column length is 30m, the inner diameter is 0.25 mm, the film thickness is 0.25 μm, the column temperature is maintained at an initial temperature of 40 ℃ for 2 minutes, the temperature is then raised to 100 ℃ at a rate of 5 ℃/min for 5 minutes, the carrier gas is high-purity nitrogen, the purity is not lower than 99.999%, the flow rate is controlled at 1.0 ml/min, the sample inlet temperature is 200 ℃, the sample injection amount is 1 microliter, and the split ratio is 10:1.
  6. 6. The method for measuring the content of the formyl end groups in the polyacetal resin molecular chain according to claim 5, wherein the external standard method in the step 4 is carried out by preparing a methyl formate standard solution series, wherein the standard solution series comprises 5 concentration gradients ranging from 10 ppm to 100 ppm and interval of 20 ppm, the standard solution is prepared with methanol as a solvent, the precision of preparation is +/-0.05 milliliter, the sample injection volume is 1 microliter, the removal precision is +/-0.1 microliter, the linear calibration curve is drawn by a least square method, the number of data points is not less than 5, and the fitting goodness-of-fit coefficient is not less than 0.995.
  7. 7. The method for measuring the content of formyl end groups in the molecular chain of a polyacetal resin according to claim 6, wherein in the calculation of the content of formyl end groups in the step 5, the molar ratio of formyl end groups to methyl formate is 1:1, the molecular weight of formyl end groups is 29 g/mol, and the molecular weight of methyl formate is 60 g/mol, and the calculation is performed by the formula of formyl end group content= (methyl formate mass X29)/(sample mass X60) ×10≡6, wherein the methyl formate mass is obtained by multiplying the net weight of the distillate in the step 3 by the concentration data in the step 4, and the sample mass is introduced from the step 1.
  8. 8. The method for measuring the formyl terminal group content in the polyacetal resin molecular chain according to claim 7, wherein the control accuracy of the duration of the first-stage distillation in the step 3 is + -0.5 min, the setting value is 10min to 15 min, the termination of the second-stage distillation is achieved by temperature monitoring, the measurement error is not more than + -0.5 ℃, and the heating power is reduced to zero within 1 second after the termination signal is triggered.
  9. 9. The method for measuring the formyl terminal group content in the polyacetal resin molecular chain according to claim 8, wherein the cooling in the ice water bath in the step 3 is carried out under the circulating condition, the flow is 5 liters/min to 10 liters/min, the fluctuation range of water temperature monitoring is controlled within + -1 ℃, and the vertical distance between the receiving bottle placing position and the outlet of the condensing tube is 5cm to 10 cm.
  10. 10. The method for measuring the formyl terminal group content in the polyacetal resin molecular chain according to claim 9, wherein steps 1 to 5 are carried out under ventilation conditions, the wind speed is 0.5 m/s to 1.0 m/s, the relative humidity is less than 30%, the weighing accuracy is 0.1 mg, the sample mass data is recorded to four decimal places, and all glassware is previously treated at 105 ℃ for 1 hour, and the temperature fluctuation is + -2 ℃.

Description

Method for measuring formyl end group content in polyacetal resin molecular chain Technical Field The invention relates to the technical field of high polymer material analysis and test, in particular to a method for measuring the content of formyl end groups in polyacetal resin molecular chains. Background As an engineering plastic polymerized by formaldehyde monomer, the molecular chain of the polyacetal resin is composed of repeated methylene oxygen units, and the formyl end group at the tail end of the molecular chain is formyl group which is usually generated by incomplete reaction or side reaction of the monomer in the polymerization process, and the formyl end group content directly influences the thermal stability and the processing performance of the resin, so that the technology for measuring the formyl end group content, such as an analysis method based on infrared spectrum or nuclear magnetic resonance, can quantitatively evaluate the distribution level of the end group in the molecular chain, and in the scene of controlling the quality of the polyacetal resin, the measurement provides key data for monitoring the polymerization reaction progress and the resin purity, thereby supporting the optimization of the production process and maintaining the consistency of the product performance. The technology for measuring the content of the formyl end groups in the polyacetal resin molecular chain has the following technical pain, and particularly comprises incomplete separation and low quantitative accuracy of target substances caused by azeotropic interference and inaccurate distillation temperature control in a complex digestion matrix. In the process of quality control of polyacetal resin, the mixture produced after digestion reaction comprises excessive hydrochloric acid, methanol, polymer fragments and byproducts, and the components are easy to form azeotrope, for example, in the stage of distillation separation, methyl formate and methanol or water may generate azeotropic phenomenon, so that high boiling point impurities are mixed in the distillate, thereby interfering with the specificity of gas chromatographic analysis. Meanwhile, lack of standardized temperature control programs, such as non-uniform distillation end point temperature settings, can cause insufficient recovery of low boiling point target materials or introduction of non-target components, ultimately affecting reliability of formyl end group content calculation. Disclosure of Invention Aiming at the defects of the prior art, the invention provides a method for measuring the content of formyl end groups in polyacetal resin molecular chains, which solves the technical problems of incomplete separation of target objects and low quantitative accuracy caused by azeotropic interference of complex digestion matrixes and inaccurate distillation temperature control. In order to solve the technical problems, the specific technical scheme of the invention is as follows: the invention provides a method for measuring the content of formyl end groups in a polyacetal resin molecular chain, which comprises the following steps: Step 1, collecting a polyacetal resin sample, and obtaining sample quality data by weighing; Step 2, weighing a polyacetal resin sample by using the sample mass data in the step 1, and reacting with a mixed solution of hydrochloric acid and methanol under a heating condition to convert a formyl terminal group into methyl formate to generate a digestion solution containing methyl formate; Step 3, distilling and separating the digestion solution obtained in the step 2, controlling the distillation temperature to evaporate methyl formate, collecting distillate containing methyl formate, and recording distillate quality data; Step 4, carrying out gas chromatographic analysis on the distillate obtained in the step 3 to obtain methyl formate peak area data, and calculating methyl formate concentration data by an external standard method; And 5, substituting the sample mass data in the step 1, the distillate mass data in the step 3 and the methyl formate concentration data in the step 4 into a calculation formula to obtain a formyl end group content result. Further, the digestion reaction in the step 2 is carried out under the condition of heating reflux, the capacity of a round bottom flask is 100 ml to 250 ml, the length of a condensing tube is 30 cm to 40 cm, the volume ratio of hydrochloric acid to methanol is 1:5 to 1:10, the concentration of the hydrochloric acid is 36% to 38%, the methanol is anhydrous methanol, the purity is not lower than 99.8%, the reaction temperature is controlled to be 40 ℃ to 50 ℃, the precision is +/-0.1 ℃ through a digital thermometer, the reaction time is maintained to be 30 minutes to 60 minutes, the time is controlled through a timer, the error is not more than +/-1 second, the digestion reaction is carried out under the condition of stirring, and the stirring speed is 200 rpm to 300 rpm. Furt