Method for measuring content of bound rubber in silicon / SiO2 rubber compound based on low-field nuclear magnetic resonance technology

Abstract

The invention discloses a method for determining the content of bound rubber in a silicone rubber / SiO2 rubber compound based on a low-field nuclear magnetic resonance technology. The method comprises the following steps: simultaneously capturing a fast relaxation signal of a bound rubber layer and slow relaxation signals of other components in the silicone rubber / SiO2 rubber compound through a set MSE-CPMG sequence and test parameters; the adopted three-component model formula has a good fitting effect on a transverse relaxation curve of the silicone rubber / SiO2 rubber compound, and the fitting degree is higher than 99%; compared with a chemical solution method, the method has the advantages that toxic solvents are not needed, the test period is shortened from 2-3 days to 5-10 minutes, and the method is a rapid, efficient, safe and environment-friendly automatic nondestructive test method.

Description

Technical Field

[0001] The invention relates to the technical field of silicone rubber analysis, and in particular to a method for determining the content of binding rubber in a silicone rubber / SiO2 mixed rubber based on a low-field nuclear magnetic resonance technique. Background Art

[0002] As an extremely important organic silicon product in the industrial field, silicone rubber shines in many fields such as aerospace, electrical instruments, automobile manufacturing, medical equipment and daily life due to its excellent low temperature resistance, thermal stability, ozone resistance, radiation resistance, chemical resistance and tissue cell compatibility. However, the main chain of silicone rubber molecules is composed of flexible Si-O-Si bonds, resulting in its poor mechanical properties. To make up for this defect, fillers are often added in practical applications to enhance its mechanical properties. Nano-silica (white carbon black) is the best among silicone rubber reinforcing fillers, which can significantly improve the tensile modulus, tensile strength and compressive strength of silicone rubber.

[0003] The rubber compound formed by mixing white carbon black with silicone rubber (linear polysiloxane with high molar mass) will be transformed into a polymer elastomer with a network structure after vulcanization treatment, which is the silicone rubber we are familiar with. Regarding the reinforcement mechanism of white carbon black, the academic community generally believes that the key lies in the physical and chemical interactions between white carbon black and silicone rubber molecular chains. These interactions promote the formation of a bonding layer at the interface, and the bonding layers in the system are interconnected to build an interpenetrating network structure. It can be seen that the reinforcing effect of white carbon black on silicone rubber is closely related to the content of bonding rubber in the rubber compound. By measuring the content of bonding rubber, the reinforcing effect of white carbon black can be effectively evaluated.

[0004] The traditional method for determining the binding adhesive is the chemical solvent method, which usually uses toluene as a solvent to dissolve the mixed rubber. After ultrasonic treatment, the undissolved part is extracted or filtered out, dried and weighed, and finally the binding adhesive content is calculated. The principle and operation method of the chemical solvent method are simple, but it is destructive to the sample, the dissolution process is time-consuming, the solvent is toxic, and there are many uncertainties introduced by manual operation. Therefore, the development of a fast, non-destructive, and safe binding adhesive content testing technology is an urgent problem to be solved in the silicone rubber field. Summary of the invention

[0005] The purpose of the present invention is to provide a method for determining the content of binding glue in silicone rubber / SiO2 mixed rubber based on low-field nuclear magnetic resonance technology in order to solve the above problems. Low-field nuclear magnetic resonance technology is a characterization method developed based on the principle of magnetic resonance, combined with static magnets, signal detection, pulse sequence and inversion calculation. The magnetic field strength of the low-field nuclear magnetic resonance device is lower than 1 Tesla (T), and the transverse relaxation curve of hydrogen protons can be obtained, thereby reflecting the mobility of hydrogen-containing segments in polymers and the chemical environment in which they are located. It has the advantages of high efficiency, non-destructiveness, and in-situ, and is an effective means for characterizing the microstructure and dynamic behavior of polymer materials. To use low-field nuclear magnetic technology for testing the content of binding glue in mixed rubber, there are two precautions. One is to set appropriate sequence pulses and test parameters to capture the relaxation signals of various components with different relaxation speeds in the mixed rubber system; the other is to use a reasonable model formula to ensure the validity and reliability of the inversion calculation results. The present invention has the characteristics of fast, non-destructive, efficient, automated, environmentally friendly, safe and non-toxic.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0007] A method for determining the content of binding rubber in a silicone rubber / SiO2 mixed rubber based on low-field nuclear magnetic resonance technology comprises the following steps:

[0008] Step 1, performing a low-field nuclear magnetic resonance test on the silicone rubber / SiO2 mixed rubber to obtain a transverse relaxation curve of the sample;

[0009] Step 2, using the model formula to fit the curve, to obtain the relative strengths of the bonding layer (A1), the transition layer (A2) and the main body (A3) in the mixed rubber;

[0010] Step 3, calculating the ratio of the relative strength (A1) of the bonding adhesive layer to the total strength (A1+A2+A3), which is the content of the bonding adhesive layer.

[0011] A further solution is that in step 1, a VTMR-20-010V-I low-field nuclear magnetic resonance analyzer of Suzhou Newmai is used, and the magnetic field strength is 0.5 T. The mixed rubber sample is cut into small pieces and directly loaded into the bottom of the sample tube. The loading height is equal to the height of the magnetic field uniformity zone of the instrument. The inner diameter of the sample tube of the VTMR-20-010V-I instrument is 8 mm, the total length of the tube is 200 mm, and the height of the magnetic field uniformity zone is 20 mm. The test temperature is set to be above the glass transition temperature of the silicone rubber (110±5)°C, and the temperature is kept constant for 10 minutes after the sample is injected before starting the test.

[0012] A further solution is that in step 1, an MSE-CPMG sequence pulse is used, which is a combination sequence of MSE and CPMG. A series of 90° pulses are applied in the MSE sequence to create echoes to regroup spin dephasing caused by magnetic field inhomogeneity. The MSE sequence can not only effectively compensate for magnetic field inhomogeneity, but also infer the amount of signal loss caused by dead time based on the change in echo signal intensity collected at different time points, and is suitable for capturing the fast relaxation signal of the rigid bonding layer segment in the compound rubber. After applying a 90° pulse, the CPMG sequence is followed by a series of 180° pulses with equal time intervals, and an echo signal is generated after each 180° pulse, and the peak points of each signal constitute the relaxation curve of the sample. This sequence can effectively avoid the interference of magnetic field inhomogeneity on the long relaxation signal, and has a high test efficiency, and is suitable for capturing the long relaxation signals of the flexible transition layer segment and the main body segment in the compound rubber. In actual tests, it was also confirmed that the MSE-CPMG sequence pulse can simultaneously capture the relaxation signals of various components with different relaxation rates in the mixed rubber system.

[0013] A further solution is that in step 1, the test parameters include sampling frequency, waiting time, number of scans, echo time and number of echoes, as well as the demarcation time point of MSE and CPMG sequences (the time point when the MSE sequence ends and the CPMG sequence starts). The sampling frequency is 250kHz, the waiting time is 4000ms, the number of scans is 8 or 16 times, the echo time is 0.1ms, and the number of echoes is set according to the integrity of the relaxation process to ensure that the complete relaxation part accounts for more than 1 / 3 of the relaxation curve, and is set to 10000 for the initial debugging. The demarcation time point of MSE and CPMG is 0.2ms.

[0014] A further solution is that in step 2, the hydrogen-containing segments in the silica-filled mixed rubber system can be divided into three parts, namely, the bonding rubber layer in contact with the silica phase, the bulk region, and the transition layer between the bonding rubber and the bulk. In the three-component model formula, A1, A2, and A3 represent the relative strengths of the bonding rubber layer, the transition layer, and the bulk region, respectively; T 2,1 , T 2,2 and T 2,3 represents the transverse relaxation time of each component; A(t) represents the relaxation signal intensity at time t. The chain segment movement of the bonding layer is restricted by the interaction with silica, showing rigidity and a fast relaxation process; while the hydrogen-containing chain segments in the transition layer and the bulk region are not restricted by chemical reactions, showing flexibility and a relatively slow relaxation process. Therefore, in the model formula, the index of the bonding layer is set to 2, and the index of the chain segments in the transition layer and the bulk region is set to 1; the details are as follows:

[0015]

[0016] A further solution is that in step 3, the formula for calculating the content of the binding glue is as follows: The calculation basis is that the nuclear magnetic resonance signal comes from the hydrogen protons in the chain segment, so the relaxation signal intensity A1, A2 and A3 is positively correlated with the hydrogen content in each component. For a long polymer chain composed of repeating structural units, the relative content of its hydrogen protons can represent the relative content of the corresponding hydrogen-containing chain segment. Therefore, the relative intensity ratio of the rigid relaxation signal in the mixed rubber is the content of the binding glue layer (C BR ).

[0017]

[0018] The beneficial effects of the present invention are:

[0019] (1) The MSE-CPMG sequence and test parameters set in the present invention can simultaneously capture the fast relaxation signal of the bonding layer and the slow relaxation signal of the remaining components in the silicone rubber / SiO2 mixed rubber;

[0020] (2) The three-component model formula used in the present invention has a good fitting effect on the transverse relaxation curve of silicone rubber / SiO2 mixed rubber, and the fitting degree is higher than 99%;

[0021] (3) The present invention successfully applies low-field nuclear magnetic resonance technology to the determination of the content of binding rubber in silicone rubber / SiO2 mixed rubber. Compared with the chemical solution method, this method does not require the use of toxic solvents, and the test cycle is shortened from 2 to 3 days to 5 to 10 minutes. It is a rapid, efficient, safe, and environmentally friendly automated non-destructive testing method. This method can achieve rapid, non-destructive, and automated identification of the SiO2 enhancement effect, and has a positive role in promoting the structural research and performance prediction of SiO2-enhanced silicone rubber systems in basic research and production applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 It is a schematic structural diagram of the white carbon black filled compound rubber system of the present invention.

[0024] Figure 2 The relaxation curves of the mixed rubbers filled with different contents of SiO2 in the present invention are shown in FIG.

[0025] Figure 3 The figure is a comparison of the content of binding rubber in the silicone rubber / SiO2 mixed rubber obtained by the low-field nuclear magnetic resonance method of the present invention and the chemical solution method. DETAILED DESCRIPTION

[0026] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0027] Example 1

[0028] Determination of the content of binding rubber in SiO2 reinforced silicone rubber compound by gas phase method

[0029] Experimental materials: gas phase SiO2 (HT, provided by the Institute of Physical and Chemical Technology, Chinese Academy of Sciences); phenyl silicone rubber (PDMMPS poly (dimethylsiloxy-methylphenylsiloxane), viscosity average molecular weight 580000 g / mol, provided by Shandong University). HT20, HT40, and HT60 are mixed rubbers obtained by mixing SiO2 and phenyl silicone rubber, and the SiO2 filling amounts are 20wt.%, 40wt.%, and 60wt.%, respectively.

[0030] Experimental instrument: Suzhou Newmai VTMR-20-010V-I, magnetic field strength is 0.5T, sample temperature control range is room temperature ~ 200℃.

[0031] The waiting time is 4000ms, and the echo time and number of echoes are set according to the completeness of the relaxation process to ensure that the complete relaxation part occupies more than 1 / 3 of the relaxation curve. It is set to 10000 for the initial debugging.

[0032] Test conditions: sampling frequency is 5000kHz, echo time is 0.06ms, number of echoes is 12000, waiting time is set to 4000ms, number of scans is 8 times, and the boundary time point between MSE and CPMG is 0.2ms.

[0033] (1) Sample loading: Cut the mixed rubber HT20, HT40, HT60 and unfilled SiO2 silicone rubber into pieces smaller than 8mm in size and load them into four dry and clean sample tubes. The inner and outer diameters of the sample tubes are 8mm and 10mm respectively, and the tube length is 200mm. Note that the sample loading height is 20mm, and the sample to be tested shall not be attached to the tube wall above this height.

[0034] (2) Test: Place the loaded sample tube into the instrument and start the test after keeping it at 35°C for 15 min. Use the MSE-CPMG pulse sequence to test the transverse relaxation time relaxation spectrum of the sample.

[0035] The transverse relaxation time and relaxation spectra of the mixed rubber HT20, HT40, HT60 and silicone rubber are shown in Figure 2 It can be seen that the addition of SiO2 accelerates the relaxation behavior of the sample as a whole, and the more SiO2 content, the faster the relaxation rate. The overall relaxation signal is the coupling of the fast relaxation of the rigid segment and the slow relaxation of the flexible segment. The relaxation curve of the silicone rubber confirms that the CPMG pulse sequence can successfully capture the slow relaxation behavior of the flexible segment. In the enlarged image, it can be intuitively seen that the MSE sequence successfully captured the fast relaxation signal of the rigid segment of the bonded glue layer in the SiO2 filling system.

[0036] (3) Fitting and inversion: The three-component model formula is input into the data analysis software of the low-field nuclear magnetic resonance analyzer. The software automatically uses the iterative method to fit and invert the test curve, thereby obtaining the relative intensities of the transverse relaxation signals (A1, A2 and A3) of the bonding layer, transition layer and main body of each sample.

[0037] (4) Calculation of the content of the binding glue: Since the relative intensity of the relaxation signal is positively correlated with the number of corresponding hydrogen-containing segments, the percentage ratio of A1 to (A1+A2+A3) is calculated, which is the content of the binding glue. Figure 3 It can be seen that the binding glue content obtained by low-field NMR method increases with the increase of silica filler content.

[0038] For comparison, the binding glue content of HT20, HT40 and HT60 was obtained by chemical solvent method. From the numerical point of view, the binding glue content obtained by low-field nuclear magnetic resonance method is slightly higher than that by chemical solvent method. This difference comes from the different testing principles of the two. However, in terms of the trend of change, the binding glue content obtained by chemical solvent method is also positively correlated with the silica filler content. This conclusion confirms the reliability of low-field nuclear magnetic resonance method for testing binding glue content.

[0039] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further explain various possible combinations. In addition, the various different embodiments of the present invention can also be combined arbitrarily, as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for determining the content of binding rubber in silicone rubber / SiO2 mixed rubber based on low-field nuclear magnetic resonance technology, characterized in that: The following steps are involved: Step 1, performing a low-field nuclear magnetic resonance test on the silicone rubber / SiO2 mixed rubber to obtain a transverse relaxation curve of the sample; Step 2, using the model formula to fit the curve, to obtain the relative strengths of the bonding layer (A1), the transition layer (A2) and the main body (A3) in the mixed rubber; Step 3, calculating the ratio of the relative strength (A1) of the bonding adhesive layer to the total strength (A1+A2+A3), which is the content of the bonding adhesive layer.

2. A method for determining the content of binder in silicone rubber / SiO2 mixed rubber based on low-field nuclear magnetic resonance technology as claimed in claim 1, characterized in that: In step 1, the test temperature is set to be (110±5)° C. above the glass transition temperature of the silicone rubber, and the temperature is kept constant for 10 minutes after the sample is injected before starting the test.

3. The method for determining the content of binder in silicone rubber / SiO2 mixed rubber based on low-field nuclear magnetic resonance technology as claimed in claim 1, characterized in that: In the step 1, an MSE-CPMG sequence pulse is used.

4. The method for determining the content of binder in silicone rubber / SiO2 mixed rubber based on low-field nuclear magnetic resonance technology as claimed in claim 1, characterized in that: In step 1, the test parameters include sampling frequency, waiting time, number of scans, echo time and number of echoes, and the demarcation time point of MSE and CPMG sequences.

5. The method for determining the content of binder in silicone rubber / SiO2 mixed rubber based on low-field nuclear magnetic resonance technology as claimed in claim 1, characterized in that: In step 1, the sampling frequency is 250kHz, the waiting time is 4000ms, the number of scans is 8 or 16 times, the echo time is 0.1ms, the number of echoes is set according to the integrity of the relaxation process to ensure that the complete relaxation part occupies more than 1 / 3 of the relaxation curve, and the initial debugging is set to 10000; the demarcation time point of MSE and CPMG is 0.2ms.

6. The method for determining the content of binder in silicone rubber / SiO2 mixed rubber based on low-field nuclear magnetic resonance technology according to claim 1, characterized in that: In step 2, the model formula adopts a three-component model, and the hydrogen-containing segments in the silica-filled mixed rubber system are divided into three parts, namely, the bonding rubber layer in contact with the silica phase, the bulk region, and the transition layer between the bonding rubber and the bulk; in the three-component model formula, A1, A2, and A3 represent the relative strengths of the bonding rubber layer, the transition layer, and the bulk region, respectively; T 2,1 , T 2,2 and T 2,3 represents the transverse relaxation time of each component; A(t) represents the relaxation signal intensity at time t; in the model formula, the index of the bonding layer is set to 2, and the index of the transition layer and the bulk region segment is set to 1; the details are as follows:

7. The method for determining the content of binder in silicone rubber / SiO2 mixed rubber based on low-field nuclear magnetic resonance technology as claimed in claim 1, characterized in that: In step 3, the formula for calculating the binding rubber content is as follows: the relaxation signal intensities A1, A2 and A3 are positively correlated with the hydrogen content in each component. For a polymer long chain composed of repeating structural units, the relative content of its hydrogen protons represents the relative content of the corresponding hydrogen-containing chain segment. The relative intensity ratio of the rigid relaxation signal in the mixed rubber is the content of the binding rubber layer;

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