Method for detecting content of insoluble sulfur in insoluble sulfur masterbatch

Abstract

The invention relates to a method for detecting the content of insoluble sulfur in insoluble sulfur masterbatch, which comprises the following steps: S1, pretreatment of a masterbatch sample to be detected: sampling from a plurality of different parts of the masterbatch to be detected, accurately weighing, and placing in a sealed crucible to prepare a test sample; s2, testing the test sample by using a differential scanning calorimeter (DSC) to obtain a DSC curve, analyzing the DSC curve, and calculating to obtain a melting peak area; and S3, inputting the melting peak area into a preset insoluble sulfur content calculation model, and calculating to obtain the insoluble sulfur content of the masterbatch particle sample to be detected. The method has the advantages that the detection efficiency is high, the period is short, tedious steps such as solvent extraction and filtration are not needed, compared with a traditional solvent extraction method, the efficiency is improved, real-time quality monitoring on a production line can be achieved, and unqualified masterbatch particles are prevented from flowing into subsequent procedures.

Description

Technical Field

[0001] This invention relates to a method for detecting the insoluble sulfur content in insoluble sulfur masterbatch, belonging to the field of quality testing and control of vulcanizing agents in the rubber industry. Background Technology

[0002] Insoluble sulfur (IS) is a key vulcanizing agent in the rubber industry. To improve its dispersibility, it is usually prepared into masterbatch granules. The insoluble sulfur content in the masterbatch granules directly determines the vulcanization effect and product performance of the rubber, so its content needs to be accurately detected. The existing methods in the industry for detecting the insoluble sulfur content in insoluble sulfur masterbatch granules are mainly solvent extraction methods (such as toluene and carbon disulfide extraction of soluble sulfur), and the content is calculated by weighing the remaining insoluble sulfur (refer to the relevant description in the paper "Detection of Insoluble Sulfur Content"). In addition, some methods rely on complex chemical titration (such as titration after converting sulfur to thiosulfate according to ISO 8332:2011), which requires multiple pretreatment steps.

[0003] Defects and shortcomings of existing technology: 1. Cumbersome and time-consuming operation: Solvent extraction requires multiple steps such as sample dissolution, filtration, washing, drying, and weighing, and a single test takes more than 4 hours, which cannot meet the needs of real-time quality control in production. 2. Significant organic solvent pollution: The extraction process relies on toxic solvents such as toluene and carbon disulfide, which are volatile and harmful to the health of operators. At the same time, it generates waste liquid that pollutes the environment, which is inconsistent with the concept of green production. 3. High detection error: Solvent extraction is prone to errors due to incomplete extraction of soluble sulfur from the mother liquor particles and loss of insoluble sulfur during washing. Chemical titration is affected by the determination of the titration endpoint and fluctuations in reagent concentration, with error rates generally exceeding 10%. 4. Inability to simultaneously reflect thermal stability: Existing methods can only detect the content of insoluble sulfur and cannot simultaneously assess the thermal stability of insoluble sulfur in masterbatch, while thermal stability directly affects the safety of subsequent rubber processing. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention, based on the thermal analysis principle of differential scanning calorimetry (DSC), establishes a mathematical model of "melting peak area of ​​insoluble sulfur content" to achieve rapid detection of insoluble sulfur content in insoluble sulfur masterbatch particles. This invention provides a method for detecting the insoluble sulfur content in insoluble sulfur masterbatch particles. The technical solution of this invention is as follows: A method for detecting the insoluble sulfur content in insoluble sulfur masterbatch particles includes the following steps: S1. Pretreatment of the masterbatch sample to be tested: Samples are taken from multiple different parts of the masterbatch to be tested, weighed accurately, and placed in a sealed crucible to obtain the test sample. S2. The test sample is tested using a differential scanning calorimeter (DSC) to obtain a DSC curve. The DSC curve is then analyzed to calculate the melting peak area. S3. Input the melting peak area into the preset insoluble sulfur content calculation model to calculate the insoluble sulfur content of the masterbatch sample to be tested; The insoluble sulfur content calculation model is a mathematical fitting model established using standard samples, relating the melting peak area to the insoluble sulfur content.

[0005] The standard samples were prepared by the following method: insoluble sulfur powder with a purity of ≥99% was divided into several portions and subjected to constant temperature heat treatment at 105℃ for different durations to obtain a series of standard samples with different insoluble sulfur contents.

[0006] The specific preparation steps for the standard sample are as follows: a. Divide insoluble sulfur powder with a purity of ≥99% into 9 equal portions, each with a mass of 5.0g; b. Nine samples were placed in an environment of 105℃ and subjected to constant temperature heat treatment for 0 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, and 40 min respectively to obtain nine standard samples with gradient insoluble sulfur content, numbered 0# to 8# respectively; 2.0 g of sulfur powder was taken as a blank control, numbered 9#.

[0007] The specific steps of step S1 are as follows: at least three different parts are randomly selected from the masterbatch particles to be tested, and 8-10 mg of each part is taken and weighed. The samples are placed in an aluminum sealed crucible, compacted and sealed to obtain test samples of each part.

[0008] The specific steps of step S2 are as follows: the prepared test sample is placed in a differential scanning calorimeter and heated from 25°C to 125°C at a heating rate of 2~5°C / min under a nitrogen atmosphere, and the DSC curve is recorded; then the DSC curve is baseline corrected and the integral area X of the melting peak is calculated.

[0009] The specific steps of step S3 are as follows: inputting the melt peak area X obtained in step S2 into a preset Logistic model or Boltzmann model to calculate the insoluble sulfur content of a single test sample; taking the average value of the calculation results of several test samples obtained from different parts of the same masterbatch as the final insoluble sulfur content of the batch of masterbatch.

[0010] It also includes step S5, which is a thermal stability assessment step, specifically: based on the peak characteristics of the DSC curve obtained in step S2, the thermal stability of the insoluble sulfur is assessed simultaneously. If the DSC curve shows a single melting peak around 100-110℃, it is determined that the thermal stability is good; if the DSC curve shows a double peak or a broadened peak, it is determined that the thermal stability is reduced.

[0011] The expression for the Logistic model is: Y = A2 + (A1 − A2) / (1 + (X / X0)p), where Y is the insoluble sulfur content, X is the melting peak area, and A1, A2, X0, and p are fitting parameters.

[0012] The expression for the Boltzmann model is: Y = A2 + (A1 − A2) / (1 + exp((X − X0) / dx)); where Y is the insoluble sulfur content, X is the melting peak area, and A1, A2, X0, and dx are fitting parameters.

[0013] The advantages of this invention are: (1) High detection efficiency and short cycle: No need for cumbersome steps such as solvent extraction and filtration. The entire process of sample pretreatment + DSC test + content calculation only takes 30 minutes. Compared with the traditional solvent extraction method, the efficiency is improved, and real-time quality monitoring on the production line can be realized to avoid unqualified masterbatch particles from flowing into subsequent processes.

[0014] (2) No toxic organic solvents such as toluene and carbon disulfide are used throughout the process. Only thermal analysis technology is used, and no waste liquid or waste gas is generated. This protects the health of operators and reduces the environmental protection costs of enterprises, which is in line with the green production trend of the rubber industry.

[0015] (3) The fit of the established Logistic and Boltzmann models is higher than 0.974, and the local non-uniformity error is avoided by taking average values ​​from multiple sites, thus ensuring the reliability of the content data.

[0016] (4) Traditional methods can only detect content, while this invention can simultaneously determine the thermal stability of insoluble sulfur through the peak shape (single peak / double peak) and peak temperature of the DSC curve. For example, the masterbatch prepared at 75℃ in a mixer only shows a decomposition peak at 105℃, which directly indicates its poor thermal stability. This provides a key reference for setting the subsequent rubber mixing temperature and reduces the loss of insoluble sulfur during processing. (5) The testing process relies on the automated operation of the instrument, which does not require professional chemical analysis skills. Ordinary operators can get started after simple training. Moreover, the DSC instrument used is a conventional equipment in the chemical industry, which does not require the purchase of additional special equipment, and the enterprise has low modification costs. Attached Figure Description

[0017] Figure 1 This is the DSC temperature curve of the standard sample 8# of this invention after being treated at 105°C for 40 minutes.

[0018] Figure 2This is a curve showing the fitting of the melting peak area of ​​the insoluble sulfur content in this invention.

[0019] Figure 3 This is a DSC curve of the masterbatch particles prepared by the open mill according to the present invention.

[0020] Figure 4 This is a DSC curve of the masterbatch particles prepared by the present invention using a 45°C internal mixer.

[0021] Figure 5 This is a DSC curve of the masterbatch particles prepared by the present invention using a 75°C internal mixer. Detailed Implementation

[0022] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as a result. However, these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0023] See Figures 1 to 5 This invention relates to a method for detecting the insoluble sulfur content in insoluble sulfur masterbatch particles, comprising the following steps: I. Establishing the Standard Curve (Constructing the Core Fitting Model) 1. Preparation of standard samples: Take insoluble sulfur powder with a purity ≥99% (IS90 grade), divide it into 9 equal portions, each with a mass of 5.0 g, and spread them evenly in a petri dish; place the 9 samples in an electric heating drying oven at 105℃ and treat them at a constant temperature for 0 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, and 40 min to obtain standard samples with different decomposition degrees (i.e., different insoluble sulfur contents), numbered 0#~8#; take another 2.0 g of commercially available sulfur powder (conventional) as a blank control (numbered 9#).

[0024] 2. DSC test conditions: Instrument: Differential scanning calorimeter; Crucible: Sealed aluminum crucible, sample mass controlled at 9.5~9.7mg (accurate to 0.1mg); Temperature program: Initial temperature 25℃, heating rate 3℃ / min, final temperature 125℃, nitrogen atmosphere (flow rate 50mL / min), record DSC curve and melting peak area; Blank correction: using an empty aluminum crucible as a reference, subtract the influence of baseline drift.

[0025] 3. Insoluble sulfur content calibration and model fitting: The actual insoluble sulfur content of standard samples 0#~8# was calibrated using the industry standard method (GB / T18952-2003 solvent extraction method). Using the "melting peak area (X, unit j / g)" obtained from DSC testing as the independent variable and the "actual insoluble sulfur content (Y, unit %)" as the dependent variable, two high-fit models were established through nonlinear fitting using Origin software: (1) Logistic model: Y=A2+(A1−A2) / (1+(X / X0)p) Where, A1=-2.37326±43.98206, A2=117.50578±52.2075, X0=4.82827±0.8797, p=2.38179±2.29605, and the adjusted R²=0.97414; (2) Boltzmann model: Y = A2 + (A1 − A2) / (1 + exp((X − X0) / dx)) Where, A1=-6124.71405±1322616.88844, A2=133.63974±179.44864, X0=-18.39932±1234.96183, dx=5.28173±26.74084, and after adjustment, R²=0.97792.

[0026] II. Detection Procedures for Insoluble Sulfur Masterbatch Samples 1. Sample pretreatment: Randomly select 5 different parts from the masterbatch particles to be tested (to avoid the influence of local unevenness), take about 8.4mg of sample from each part (accurate to 0.1mg), and ensure that the sample is free of bubbles and impurities; put the sample into a clean aluminum crucible, compact and seal it (to prevent the sample from escaping during the heating process).

[0027] 2. DSC test: Using the same instruments and test conditions as "Standard curve establishment" (heating rate 3℃ / min, 25℃~125℃, nitrogen atmosphere), record the DSC curve of the sample; use the instrument's built-in software or Origin software to perform baseline correction on the DSC curve and calculate the integral area of ​​the melting peak (i.e., X value).

[0028] 3. Content Calculation: Substitute the measured melting peak area X into the Logistic model or Boltzmann model mentioned above to calculate the insoluble sulfur content of a single sample; take the average content of the five samples as the final insoluble sulfur content of the batch of masterbatch (if the deviation of a single sample from the average value exceeds 5%, it is necessary to resample and test).

[0029] 4. Simultaneous assessment of thermal stability: If the DSC curve shows only one melting peak (such as when the masterbatch granules are prepared on a two-roll mill at around 115℃), it indicates that the insoluble sulfur has good thermal stability; if two peaks appear (low-temperature melting peak + high-temperature decomposition peak) or the peak shape is broadened, it indicates that the insoluble sulfur has partially decomposed and has poor thermal stability, and it is necessary to indicate the temperature control for subsequent processing.

[0030] Example 1: Detection of insoluble sulfur masterbatch particles prepared by open mill 1. Sample source: Natural rubber-based insoluble sulfur masterbatch (formulation: NR 20 phr, dispersant 1 phr, naphthenic oil 4 phr, insoluble sulfur 75 phr) prepared using an open mill (front / back roll temperature 50℃). 2. Sample pretreatment: Take 8.4 mg of sample from each of the five parts of the masterbatch: edge, center, surface, subsurface, and inner layer, number them 01~05, and seal them in an aluminum crucible; 3. DSC test: Using Netzsch DSC214, the temperature was initially increased to 25℃ at a rate of 3℃ / min and terminated at 125℃ with a nitrogen flow rate of 50mL / min. The DSC curves of each sample were recorded. 4. Data Processing: Melting peak areas calculated using Origin: 01 (3.69 J / g), 02 (4.27 J / g), 03 (4.55 J / g), 04 (4.63 J / g), 05 (3.90 J / g); Contents calculated using the Logistic model: 39.09%, 50.61%, 56.98%, 54.58%, 42.85%; Results: The average insoluble sulfur content was 48.82%, RSD = 15.64%, and the DSC curve showed only a single peak near 115℃, indicating good thermal stability.

[0031] Example 2: Detection of insoluble sulfur masterbatch particles prepared by internal mixer at 45℃ 1. Sample source: Masterbatch prepared by internal mixer at an initial temperature of 45℃ (formulation same as in Example 1); 2. Testing steps: Same as in Example 1, with 5 samples numbered 11-15; 3. Data Processing: Melting peak areas: 11 (3.97 J / g), 12 (4.22 J / g), 13 (4.05 J / g), 14 (3.88 J / g), 15 (4.34 J / g); Substituting into the Boltzmann model, the calculated content is: 45.68%, 49.47%, 47.22%, 43.51%, and 51.89%; Results: The average content was 47.55%, RSD was 6.85%, and the DSC curve showed a double peak at 105℃ and 115℃, indicating moderate thermal stability.

[0032] Example 3: Detection of insoluble sulfur masterbatch particles prepared by a 75℃ internal mixer 1. Sample source: Masterbatch prepared by internal mixer at a starting temperature of 75℃ (formulation same as in Example 1); 2. Testing steps: Same as in Example 1, with 5 samples numbered 31-35; 3. Data Processing: Melting peak areas: 31 (3.08 J / g), 32 (3.27 J / g), 33 (3.33 J / g), 34 (3.00 J / g), 35 (3.11 J / g); Substituting into the Logistic model, the calculated content is: 27.15%, 30.61%, 31.72%, 25.51%, and 27.68%. Results: The average content was 28.53%, RSD = 8.98%, and the DSC curve showed only a decomposition peak at 105℃, indicating poor thermal stability and suggesting that the temperature should be lowered in subsequent processing.

[0033] like Figure 1 As shown, its curve characteristics include two absorption peaks (low temperature peak at 104.9℃ and high temperature peak at 120.9℃). like Figure 2 As shown, the horizontal axis represents the melting peak area (j / g), and the vertical axis represents the insoluble sulfur content (%). Curve characteristics: The two curves are the fitting results of Logistic (R² = 0.97792) and Boltzmann (R² = 0.97414) respectively, and the data points are evenly distributed on both sides of the curves. Explanation: This proves that the model has a high degree of fit and can accurately estimate the content through the peak area (corresponding to the core achievement of "model fitting" in the technical solution).

[0034] The low-temperature peak is the melting peak of insoluble sulfur, and the high-temperature peak is the decomposition peak, which confirms the thermal decomposition characteristics of insoluble sulfur and provides a theoretical basis for model establishment (corresponding to the decomposition law of "standard sample preparation" in the technical solution).

[0035] like Figures 3 to 5 As shown, Figure 3 Single peak (115℃) Figure 4 Double peaks (105℃ / 115℃) Figure 5 The single peak (105℃) directly reflects the differences in thermal stability of different masterbatch particles, realizing the simultaneous "content detection + thermal stability assessment" (corresponding to the "simultaneous thermal stability assessment" function in the technical solution).

[0036] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for detecting the insoluble sulfur content in insoluble sulfur masterbatch particles, characterized in that, Includes the following steps: S1. Pretreatment of the masterbatch sample to be tested: Samples are taken from multiple different parts of the masterbatch to be tested, weighed accurately, and placed in a sealed crucible to obtain the test sample. S2. The test sample is tested using a differential scanning calorimeter (DSC) to obtain a DSC curve. The DSC curve is then analyzed to calculate the melting peak area. S3. Input the melting peak area into the preset insoluble sulfur content calculation model to calculate the insoluble sulfur content of the masterbatch sample to be tested; The insoluble sulfur content calculation model is a mathematical fitting model established using standard samples, relating the melting peak area to the insoluble sulfur content.

2. The method for detecting the insoluble sulfur content in insoluble sulfur masterbatch particles according to claim 1, characterized in that, The standard samples were prepared by the following method: insoluble sulfur powder with a purity of ≥99% was divided into several portions and subjected to constant temperature heat treatment at 105℃ for different durations to obtain a series of standard samples with different insoluble sulfur contents.

3. The method for detecting the insoluble sulfur content in insoluble sulfur masterbatch particles according to claim 2, characterized in that, The specific preparation steps for the standard sample are as follows: a. Divide insoluble sulfur powder with a purity of ≥99% into 9 equal portions, each with a mass of 5.0g; b. Nine samples were placed in an environment of 105℃ and subjected to constant temperature heat treatment for 0 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, and 40 min respectively to obtain nine standard samples with gradient insoluble sulfur content, numbered 0# to 8# respectively; 2.0 g of sulfur powder was taken as a blank control, numbered 9#.

4. The method for detecting the insoluble sulfur content in insoluble sulfur masterbatch particles according to claim 3, characterized in that, The specific steps of step S1 are as follows: at least three different parts are randomly selected from the masterbatch particles to be tested, and 8-10 mg of each part is taken and weighed. The samples are placed in an aluminum sealed crucible, compacted and sealed to obtain test samples of each part.

5. The method for detecting the insoluble sulfur content in insoluble sulfur masterbatch particles according to claim 4, characterized in that, The specific steps of step S2 are as follows: the prepared test sample is placed in a differential scanning calorimeter and heated from 25°C to 125°C at a heating rate of 2~5°C / min under a nitrogen atmosphere, and the DSC curve is recorded; then the DSC curve is baseline corrected and the integral area X of the melting peak is calculated.

6. The method for detecting the insoluble sulfur content in insoluble sulfur masterbatch particles according to claim 5, characterized in that, The specific steps of step S3 are as follows: inputting the melt peak area X obtained in step S2 into a preset Logistic model or Boltzmann model to calculate the insoluble sulfur content of a single test sample; taking the average value of the calculation results of several test samples obtained from different parts of the same masterbatch as the final insoluble sulfur content of the batch of masterbatch.

7. The method for detecting the insoluble sulfur content in insoluble sulfur masterbatch particles according to claim 6, characterized in that, It also includes step S5, which is a thermal stability assessment step, specifically: based on the peak characteristics of the DSC curve obtained in step S2, the thermal stability of the insoluble sulfur is assessed simultaneously. If the DSC curve shows a single melting peak around 100-110℃, it is determined that the thermal stability is good; if the DSC curve shows a double peak or a broadened peak, it is determined that the thermal stability is reduced.

8. The method for detecting the insoluble sulfur content in insoluble sulfur masterbatch particles according to claim 6, characterized in that, The expression for the Logistic model is: Y = A2 + (A1 − A2) / (1 + (X / X0)p), where Y is the insoluble sulfur content, X is the melting peak area, and A1, A2, X0, and p are fitting parameters.

9. The method for detecting the insoluble sulfur content in insoluble sulfur masterbatch particles according to claim 4, characterized in that, The expression for the Boltzmann model is: Y = A2 + (A1 − A2) / (1 + exp((X − X0) / dx)); where Y is the insoluble sulfur content, X is the melting peak area, and A1, A2, X0, and dx are fitting parameters.

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