Method for determining content of bound rubber in unvulcanized rubber

Abstract

The invention relates to the technical field of rubber detection, and particularly discloses a method for measuring the content of bound rubber in unvulcanized rubber, which is used for solving the problem of inconvenience in measurement in the prior art. Comprising the following steps: step 1, a sample preparation stage: cutting unvulcanized rubber into predetermined cuboid rubber strips for later use; 2, a sample pretreatment stage: putting the adhesive tape into a quartz sample tube, and keeping the constant temperature in a dry thermostat until the magnetic field test temperature of a low-field nuclear magnetic resonance analyzer is 32 DEG C; step 3, setting parameters; and step 4, a sample testing stage: putting the quartz sample tube filled with the sample into a magnetic field of a low-field nuclear magnetic resonance analyzer, and carrying out cyclic accumulation sampling. The method for determining the content of the bound rubber in the unvulcanized rubber by adopting a low-field nuclear magnetic resonance (LF-NMR) technology is provided for the first time, and the blank of determination of the content of the bound rubber in the technical field of rubber detection is filled.

Description

Technical Field

[0001] The invention relates to the technical field of rubber detection, in particular to a method for determining the content of bound rubber in unvulcanized rubber. Background Art

[0002] Bound rubber usually refers to the part of rubber that is insoluble in good solvents such as benzene (or toluene) when reinforcing agent (carbon black, white carbon black) is mixed with raw rubber. The formation of bound rubber is mainly through two aspects: one is that the rubber molecular chain adsorbed on the surface of carbon black combines with the surface group of carbon black, or the rubber is mixed and a large number of rubber free radicals or ions are generated during the processing process and combine with carbon black to produce chemical adsorption; the other is the physical adsorption of rubber macromolecule chains on the surface of carbon black ions, and the force of these physical adsorptions is greater than the dissolving power of good solvents. Bound rubber is actually the rubber adsorbed on the surface of filler (that is, the rubber in the interface layer between filler and rubber).

[0003] In recent years, people have found that the reinforcing effect of fillers such as carbon black and white carbon black on elastomers is closely related to the content of binder rubber in the rubber mix. As the mass of binder rubber increases, the modulus, wear resistance and hysteresis of the vulcanized rubber are improved, so binder rubber is used as a yardstick to measure the reinforcing ability of carbon black.

[0004] The traditional method of testing the binding rubber is a chemical method, which mainly involves cutting the unvulcanized rubber into small particles, encapsulating them in a stainless steel mesh or filter paper that is permeable to linear macromolecules but not to gel, soaking them in toluene for at least 72 hours, taking them out and drying them, and calculating the mass of gel in the rubber as a percentage of the total rubber mass or filler mass in the sample. Patent WO2018048157A1 uses time-domain NMR technology as one of the means to characterize the reinforcing effect of silica-filled rubber polymers. The sc-lc-co mode is used at 40°C to obtain the time decay signal of the rubber polymer, and the binding rubber content is calculated by double exponential fitting. The error of the fitting algorithm in testing the binding rubber content is large, and the accuracy of the results cannot be ensured.

[0005] Regarding the method of determining the bound rubber content in unvulcanized rubber by chemical method, this method consumes a large amount of toxic reagents, has a long detection cycle, and the test results are easily affected by the solvent dissolution temperature and have high requirements for ambient temperature. As the dissolution temperature increases, the bound rubber content decreases, so the repeatability is relatively poor. Due to objective factors such as the poor stability and non-environmental nature of the chemical method itself, there are currently few testing institutions that conduct systematic analysis and research on the bound rubber content in unvulcanized rubber, and there are also few corresponding standard methods and data documents.

[0006] Based on this, a method for determining the bound rubber content in unvulcanized rubber is now provided, which can eliminate the drawbacks of the existing device. Summary of the invention

[0007] The purpose of the present invention is to provide a method for determining the content of bound rubber in unvulcanized rubber, which solves the problem of inconvenient measurement in the prior art.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A method for determining the content of bound rubber in unvulcanized rubber comprises the following steps:

[0010] Step 1: Sample preparation stage: Cut the unvulcanized rubber into predetermined rectangular rubber strips for later use;

[0011] Step 2: Sample pretreatment stage: Place the rubber strip into a quartz sample tube and keep it in a dry thermostat at a constant temperature of 32°C, which is the magnetic field test temperature of the low-field nuclear magnetic resonance analyzer;

[0012] Step 3: Parameter setting:

[0013] Step 4: Sample testing stage: Place the quartz sample tube containing the sample into the magnetic field of the low-field nuclear magnetic resonance analyzer for cyclic cumulative sampling;

[0014] Step 5: Data analysis stage: export the original data, use the Abragamian & three-component fitting formula to inversely calculate the relaxation time, the signal amount of each component, and calculate the bound glue content.

[0015] On the basis of the above technical solution, the present invention also provides the following optional technical solution:

[0016] In an optional solution: cut the unvulcanized rubber into rectangular rubber strips with a length of 4 mm, a width of 4 mm, and a height of 10 mm for later use.

[0017] In an optional scheme: In step three: the parameter setting is specifically: call the HahnEcho sequence, set the parameters: magnetic probe diameter 13mm, main frequency 21MHz, sampling frequency 5000KHz, RF delay 0.003ms, analog gain 20dB, 90 degree pulse width 3.0us, 180 degree pulse width 5.0us, waiting time 2000ms, number of echoes 40, echo time 0.03ms-50ms.

[0018] In an optional solution: the calculation in step 5 is specifically as follows:

[0019] Where: w i —Binding glue content, %;

[0020] A i —The signal amplitude of different relaxation components, dimensionless.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] According to the requirements of rubber processing, formula design, etc. for rubber performance, the present invention proposes for the first time a method for determining the bound rubber content in unvulcanized rubber using low-field nuclear magnetic resonance (LF-NMR) technology, filling the gap in the determination of bound rubber content in the field of rubber detection technology. It helps rubber industry technicians to quickly obtain bound rubber content test data. Conventional chemical methods use a large amount of organic reagents, are time-consuming, and are easily interfered by environmental factors. This method is simple and fast, such as no need to use toxic reagents, non-destructive testing of samples, and a short detection cycle. Utilizing the principle of the difference in spin-spin transverse relaxation time T2 of different components inside the elastomeric material, the HahnEcho sequence is used to achieve quantitative analysis of bound rubber; a new method for characterizing the reinforcing properties of carbon black is provided, providing more options for the research of rubber products. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the filler-rubber network structure of the present invention.

[0024] Figure 2 It is a schematic diagram of the testing principle of the bonding glue content of the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] like Figure 1-2 As shown, an embodiment of the present invention provides a method for determining the content of bound rubber in unvulcanized rubber, comprising:

[0028] The following steps are involved:

[0029] Step 1: Sample preparation stage: Cut the unvulcanized rubber into predetermined rectangular rubber strips, and cut the unvulcanized rubber into rectangular rubber strips with a length of 4 mm, a width of 4 mm, and a height of 10 mm for use;

[0030] Step 2: Sample pretreatment stage: Place the rubber strip into a quartz sample tube and keep it in a dry thermostat at a constant temperature of 32°C, which is the magnetic field test temperature of the low-field nuclear magnetic resonance analyzer;

[0031] Step 3: Parameter setting. In step 3: parameter setting is as follows: call the HahnEcho sequence, set the parameters: magnetic probe diameter 13mm, main frequency 21MHz, sampling frequency 5000KHz, RF delay 0.003ms, analog gain 20dB, 90 degree pulse width 3.0us, 180 degree pulse width 5.0us, waiting time 2000ms, number of echoes 40, echo time 0.03ms-50ms;

[0032] Step 4: Sample testing stage: Place the quartz sample tube containing the sample into the magnetic field of the low-field nuclear magnetic resonance analyzer for cyclic cumulative sampling;

[0033] Step 5: Data analysis stage: export the original data, use the Abragamian & three-component fitting formula to inversely calculate the relaxation time, the signal amount of each component, and calculate the bound glue content.

[0034] The calculation in step 5 is specifically as follows:

[0035] Where: w i —Binding glue content, %;

[0036] A i —The signal amplitude of different relaxation components, dimensionless.

[0037] Embodiment 1

[0038] The compound rubber formula consists of the following components by mass fraction: 100 parts of natural rubber, 50 parts of three N series carbon blacks (N134, N330, N660), 3 parts of stearic acid, 5 parts of zinc oxide, 0.66 parts of DM, and 0.27 parts of sulfur. After weighing the ingredients according to the formula, the mixing process is carried out in accordance with national standards.

[0039] This experiment needs to determine the content of bound rubber in three N series carbon black filled rubber compounds. The specific steps are as follows:

[0040] (1) Sample preparation: Cut the unvulcanized rubber that has been stored for a certain period of time into a rectangular rubber strip with a length of 4 mm, a width of 4 mm, and a length of 10 mm, and put it into a quartz sample tube with a height of 200 mm and a diameter of 8 mm. Set the temperature of the dry-wet thermostat to 32°C and put it into the quartz sample tube to maintain the constant temperature for 5 minutes;

[0041] (2) Sample test: call the HahnEcho sequence and set the parameters: magnetic probe diameter 13mm, main frequency 21MHz, sampling frequency 5000KHz, RF delay 0.003ms, analog gain 20dB, 90 degree pulse width 3.0us, 180 degree pulse width 5.0us, waiting time 2000ms, number of echoes 40, echo time 0.03ms-50ms. Place the quartz sample tube in the magnetic field of the device for cyclic cumulative sampling;

[0042] (3) Data analysis: Export the original data, use the Abragamian & three-component fitting formula to inversely calculate the relaxation time and the signal amount of each component, and calculate the bound glue content according to the following formula

[0043] Where: w i —Binding glue content, %;

[0044] A i —The amplitude of the signal of different relaxation components, dimensionless;

[0045] Example 1 Data: Table 1 Different carbon black variables-bound rubber content

[0046] method N134-Rubber Compound N330-Rubber Compound N660-Rubber Compound The present invention, % 8.81 7.64 5.98 Chemical method, % 29.63 27.22 15.77

[0047] The experimental results in Table 1 above show that when measuring the N series carbon black compound rubber samples, the relaxation time is the shortest in the area with the lowest migration rate, which is due to a layer of rubber tightly bound to the carbon black surface. The signal intensity percentage of the shortest relaxation is the bound rubber content. This result can more truly reflect the bonding between carbon black and rubber than the chemical method, and at the same time proves that with the decrease of the specific surface area of ​​carbon black, the bound rubber content shows a downward trend.

[0048] Embodiment 2

[0049] The compounding formula is composed of the following components by mass fraction: 100 parts each of N types of rubber (natural rubber 20#, solution polymerized styrene butadiene rubber 5251, emulsion polymerized styrene butadiene rubber 1723, emulsion polymerized styrene butadiene rubber 1502, butadiene rubber BR9000, butyl rubber 301, chlorobutyl rubber 1301), 70 parts of N375, 1 part of stearic acid, 3 parts of zinc oxide, and 37 parts of environmentally friendly aromatic oil. After weighing the ingredients according to the formula, the mixing process is carried out in accordance with national standards.

[0050] This experiment needs to determine the content of bound rubber in the mixed rubber of N different rubber types. The specific steps are as follows:

[0051] (1) Sample preparation: Cut the unvulcanized rubber that has been stored for a certain period of time into a rectangular rubber strip with a length of 4 mm, a width of 4 mm, and a length of 10 mm, and put it into a quartz sample tube with a height of 200 mm and a diameter of 8 mm. Set the temperature of the dry-wet thermostat to 32°C and put it into the quartz sample tube to maintain the constant temperature for 5 minutes;

[0052] (2) Sample test: call the HahnEcho sequence and set the parameters: magnetic probe diameter 13mm, main frequency 21MHz, sampling frequency 5000KHz, RF delay 0.003ms, analog gain 20dB, 90 degree pulse width 3.0us, 180 degree pulse width 5.0us, waiting time 2000ms, number of echoes 40, echo time 0.03ms-50ms. Place the quartz sample tube in the magnetic field of the device for cyclic cumulative sampling;

[0053] (3) Data analysis: The original data were exported, and the relaxation time and the signal quantity of each component were inverted and calculated using the Abragamian & three-component fitting formula, and the bound glue content was calculated according to the following formula;

[0054] Where: w i —Binding glue content, %;

[0055] A i —The amplitude of the signal of different relaxation components, dimensionless;

[0056] Example 2 Data: Table 2 Different rubber variables - combined rubber content;

[0057]

[0058] The experimental results in Table 2 above show that when measuring mixed rubber samples of N different rubber types, the area with the lowest migration rate has the shortest relaxation time. This is because a layer of rubber is tightly bound to the surface of carbon black, and the signal intensity percentage of the shortest relaxation is the bound rubber content. This result can more truly reflect the bonding between carbon black and rubber than the chemical method.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining the content of bound rubber in unvulcanized rubber, characterized in that: The following steps are involved: Step 1: Sample preparation stage: Cut the unvulcanized rubber into predetermined rectangular rubber strips for later use; Step 2: Sample pretreatment stage: Place the rubber strip into a quartz sample tube and keep it in a dry thermostat at a constant temperature of 32°C, which is the magnetic field test temperature of the low-field nuclear magnetic resonance analyzer; Step 3: Parameter setting: Step 4: Sample testing stage: Place the quartz sample tube containing the sample into the magnetic field of the low-field nuclear magnetic resonance analyzer for cyclic cumulative sampling; Step 5: Data analysis stage: export the original data, use the Abragamian & three-component fitting formula to inversely calculate the relaxation time, the signal amount of each component, and calculate the bound glue content.

2. The method for determining the content of bound rubber in unvulcanized rubber according to claim 1, characterized in that: Cut the unvulcanized rubber into rectangular strips with a length of 4mm, a width of 4mm and a height of 10mm and set aside.

3. The method for determining the content of bound rubber in unvulcanized rubber according to claim 1, characterized in that: In step three: the parameter settings are as follows: call the HahnEcho sequence, set the parameters: magnetic probe diameter 13mm, main frequency 21MHz, sampling frequency 5000KHz, RF delay 0.003ms, analog gain 20dB, 90 degree pulse width 3.0us, 180 degree pulse width 5.0us, waiting time 2000ms, number of echoes 40, echo time 0.03ms-50ms.

4. The method for determining the content of bound rubber in unvulcanized rubber according to claim 1, characterized in that: The calculation in step 5 is specifically as follows: Where: w i —Binding glue content, %; A i —The signal amplitude of different relaxation components, dimensionless.

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