JP2019078670A - Method for analyzing sulfur crosslinked structure of high polymer material - Google Patents

Abstract

To evaluate the sulfur crosslinked structure of a sulfur crosslinked high polymer material such as a vulcanized rubber.SOLUTION: A sulfur crosslinked structure analysis method pertaining to an embodiment of the present invention includes: finding a relationship between a sulfur concentration and an edge jump height using a sample of a known sulfur concentration; irradiating a sulfur crosslinked high polymer material with an X-ray and acquiring the X-ray absorption spectrum of a sulfur K-shell absorption edge; fitting the obtained X-ray absorption spectrum with at least two components including a sulfur-to-sulfur component and a sulfur-to-carbon component; calculating the peak area of the sulfur-to-sulfur component and the peak area of the sulfur-to-carbon component and calculating a crosslinked sulfur chain connection length from the peak area ratio of the sulfur-to-sulfur component to the sulfur-to-carbon component; finding an edge jump height from the X-ray absorption spectrum with respect to the high polymer material, finding a sulfur concentration from the obtained edge jump height on the basis of the relationship, and calculating a sulfur crosslinked density from the obtained sulfur concentration and crosslinked sulfur chain connection length.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method of analyzing a sulfur crosslinked structure in a sulfur crosslinked polymeric material such as a vulcanized rubber.

  In order to evaluate the physical properties of a sulfur-crosslinked polymer material such as vulcanized rubber, a technique for analyzing the sulfur cross-linked structure of the polymer material is required. Conventionally, there is a swelling method as a technique for evaluating the chemical state of a sulfur-crosslinked polymer material. The swelling method is a method of swelling a crosslinked polymer material with a solvent such as toluene to evaluate the network chain density, but it is not possible to specify the crosslinked sulfur chain linkage length of the polysulfide chain. In addition, the swelling method does not look at crosslinking itself but causes errors such as entanglement between polymers. Furthermore, in the swelling method, interaction parameters between the solvent and the polymer are required, and there is also a problem that rubbers having different polymer types are difficult to compare.

  On the other hand, as a method of analyzing the sulfur crosslinking structure in a sulfur-crosslinked polymer material, Patent Documents 1 and 2 irradiate the polymer material with high-intensity X-rays and change the X-ray energy while changing the X-ray absorption spectrum A method is proposed to calculate the crosslink density by determining the three-dimensional structure of sulfur in the polymer material by the reverse Monte Carlo method.

Unexamined-Japanese-Patent No. 2016-057285 JP, 2017-020906, A

  An object of the present invention is to provide an analysis method capable of evaluating a sulfur crosslinked structure of a sulfur-crosslinked polymer material such as a vulcanized rubber.

  The method for analyzing a sulfur crosslinked structure of a polymer material according to the present invention is to increase the sulfur concentration and edge jump by irradiating a sample having a known sulfur concentration with X-rays to acquire an X-ray absorption spectrum of the sulfur K shell absorption edge. X-ray was irradiated to a sulfur-crosslinked polymer material whose sulfur crosslinking density is unknown, X-ray absorption spectrum of sulfur K-shell absorption edge was obtained, X was obtained for the polymer material. The line absorption spectrum is fitted with at least two components including a sulfur-sulfur component and a sulfur-carbon component, and the peak area of the sulfur-sulfur component and the peak area of the sulfur-carbon component are calculated. The cross-linked sulfur chain linkage length is calculated from the peak area ratio of the sulfur-sulfur component and the sulfur-carbon component, and the height of the edge jump is determined from the X-ray absorption spectrum of the polymer material. Determine the sulfur concentration on the basis of the relationship from the height of the di-jump, and calculates the sulfur crosslink density from the obtained sulfur concentration and the bridging sulfur chain joining length.

  According to the present invention, it is possible to calculate the cross-linked sulfur chain link length of the sulfur cross-linked polymer material from the X-ray absorption spectrum of the sulfur K shell absorption end, and to use the cross link sulfur chain link length Can be calculated.

Figure showing an example of X-ray absorption spectrum of sulfur K shell absorption edge Figure showing an example of a sulfur cross-linked form in a polymer body Diagram showing asymmetric Gaussian function used for sulfur-sulfur component Conceptual diagram showing the relationship between the measurement sample of the X-ray measurement device and the detector Graph showing the relationship between sulfur concentration and edge jump in the first embodiment

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

The sulfur crosslinked structure analysis method according to the present embodiment includes the following steps.
Step 1: Irradiating a sample having a known sulfur concentration with X-rays to acquire an X-ray absorption spectrum of the sulfur K-shell absorption edge, thereby obtaining the relationship between the sulfur concentration and the height of edge jump (edge jump)
Step 2: Irradiating a sulfur-crosslinked polymer material of unknown sulfur crosslinking density with X-rays to obtain an X-ray absorption spectrum of the sulfur K-shell absorption edge,
Step 3: fitting the X-ray absorption spectrum obtained in Step 2 with at least two components including a sulfur-sulfur component and a sulfur-carbon component
Step 4: The peak area of the sulfur-sulfur component and the peak area of the sulfur-carbon component are calculated from the fitting result, and the crosslinked sulfur chain linkage length is determined from the peak area ratio of the sulfur-sulfur component and the sulfur-carbon component. Calculating, and
Step 5: For the polymer material whose sulfur crosslinking density is unknown, the height of the edge jump is determined from the X-ray absorption spectrum, and the sulfur concentration is determined based on the relationship of step 1 from the determined height of the edge jump Calculating a sulfur crosslinking density from the determined sulfur concentration and the crosslinked sulfur chain linkage length.

  As described above, in this embodiment, the X-ray absorption spectrum of the sulfur K shell absorption edge is peak-separated by using at least two components including the sulfur-sulfur component and the sulfur-carbon component. Determination is carried out, and from the results, the crosslinked sulfur chain connection length and the sulfur crosslinking density of the polymer material are evaluated.

  Generally, in an X-ray absorption spectrum obtained by irradiating an object with X-rays, a sharp rise specific to an element contained in the body is observed, and this rise is called an absorption edge. The fine structure near the absorption edge is called an x-ray absorption fine structure (XAFS). XAFS has an X-ray absorption near-edge structure (XANES) up to several tens of eV from the absorption edge and an X-ray broad-range fine structure (approx. 1000 eV on the higher energy side) EXAFS: consists of extended x-ray absorption fine structure). Among them, XANES is sensitive to chemical states such as electronic states, and can be applied to the analysis of chemical states such as to which atom the atom of interest is bonded. In this embodiment, analysis of the sulfur crosslinking structure is performed using an X-ray absorption spectrum in the XANES region for the sulfur K-shell absorption edge, which is the K-shell absorption edge of a sulfur atom.

  In the present embodiment, the polymer material to be measured may be a polymer such as a sulfur-crosslinked resin or rubber, and the type of the polymer is not particularly limited. Preferably, it is a vulcanized rubber, and a vulcanized rubber formed by vulcanizing a rubber composition in which various compounding agents containing a vulcanizing agent such as sulfur are mixed with a rubber polymer can be used as a measurement target.

  Here, as the rubber polymer, for example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR And diene rubbers such as halogenated butyl rubber (X-IIR) and styrene isoprene butadiene rubber (SIBR), which may be used alone or in combination of two or more.

  In the polymer material, sulfur for sulfur crosslinking is blended as a vulcanizing agent. Examples of the vulcanizing agent include sulfur such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur and highly dispersible sulfur. As one embodiment, in the above rubber composition, the compounding amount of the vulcanizing agent may be 0.1 to 10 parts by mass, or 0.5 to 8 parts by mass with respect to 100 parts by mass of the rubber polymer.

  The polymer material may also contain various additives such as a filler and a vulcanization accelerator as optional components. In one embodiment, in the case of the above rubber composition, such a compounding agent as a filler, a silane coupling agent, a softener such as oil, a plasticizer, an antiaging agent, zinc flower, stearic acid, a wax, a vulcanization accelerator For example, various compounding agents usually used in the rubber industry can be used. Examples of the filler include various inorganic fillers such as carbon black, silica, talc, clay and alumina, and carbon black and / or silica are preferable. In the case of the above rubber composition as one embodiment, the blending amount of the filler may be, for example, 10 to 200 parts by mass, or 20 to 150 parts by mass with respect to 100 parts by mass of the rubber polymer. Moreover, 0.1-7 mass parts may be sufficient as the compounding quantity of a vulcanization accelerator with respect to 100 mass parts of rubber polymers, and 0.5-5 mass parts may be sufficient. In addition, the blending amount of zinc oxide may be 0.1 to 10 parts by mass, or 0.5 to 5 parts by mass with respect to 100 parts by mass of the rubber polymer.

  The rubber composition can be prepared by kneading each component according to a conventional method using a mixer such as a Banbury mixer, and the rubber composition is heated and vulcanized according to the conventional method to obtain a vulcanized rubber. Is obtained.

  The shape of the polymer material to be measured is not particularly limited, and for example, a sheet-like material can be used. As one embodiment, as a measuring object, a rubber sheet vulcanized and formed into a sheet may be used, or alternatively, a sheet cut out from a vulcanized rubber product such as a tire may be used.

  In step 1 described above, a sample having a known sulfur concentration is used to determine the relationship between the sulfur concentration and the height of the edge jump (hereinafter referred to as the relationship W). As a known sample of the sulfur concentration, as long as the sulfur concentration is known, the same sulfur-crosslinked one as the above-mentioned polymer material as the measurement target may be used, or the one which is not crosslinked may be used. Moreover, it is not necessary to necessarily use a polymer material, and for example, a powder obtained by mixing KBr powder and sulfur powder in a mortar or the like and using a tablet molding machine may be used. The rubber composition is preferably a rubber polymer blended with a vulcanizing agent such as sulfur.

  In step 1, the relationship W is determined by irradiating a sample having a known sulfur concentration with X-rays to acquire an X-ray absorption spectrum of the sulfur K-shell absorption edge. In order to obtain the relationship W, X-ray absorption spectra may be obtained for a plurality of samples having different sulfur concentrations to obtain edge jumps, and a calibration curve indicating the relationship W between the sulfur concentration and the height of the edge jump may be obtained. it can.

  As a method of acquiring the X-ray absorption spectrum of the sulfur K shell absorption edge, a known XAFS method (in particular, the XANES method) can be used. Specifically, the sample is irradiated with X-rays, and the X-ray absorption amount (absorption intensity) is measured while changing the energy of the X-rays. The X-rays are irradiated at an energy corresponding to the K-shell absorption edge of the sulfur atom, whereby an X-ray absorption spectrum in the XANES region is obtained for the sulfur K-shell. The scanning energy range of X-rays is preferably 2400 to 3000 eV, and may be 2450 to 2500 eV, or 2460 to 2490 eV.

  In the XAFS method at the sulfur K-shell absorption edge, (1) a transmission method of detecting the intensity of X-rays transmitted through a sample using a photodiode array detector or the like, and (2) when the sample is irradiated with X-rays There are a fluorescence method that detects the fluorescent X-rays that are generated using a Lytle detector or a semiconductor detector, and (3) an electron yield method that detects the current that flows when the sample is irradiated with X-rays. May be used. Preferably, the fluorescence method is used. More specifically, the fluorescence method is a method of measuring fluorescent X-rays generated when a sample is irradiated with X-rays, and using the fact that there is a proportional relationship between the amount of X-ray absorption and the intensity of fluorescent X-rays, This is a method of indirectly determining the amount of X-ray absorption from the intensity of fluorescent X-rays.

As X-rays used when performing the XAFS method, for example, high-intensity X-rays of 10 ¹⁰ (photons / s / mrad ² / mm ² /0.1% bw) or more are preferable. The number of photons of X-rays is preferably 10 ⁷ (photons / s) or more, more preferably 10 ⁹ (photons / s) or more. Examples of such synchrotrons that emit X-rays include SPring-8 of the High Intensity Research Center for Light Science, Aichi Synchrotron Center of "Aichi Base of Knowledge", and the like.

  The height of the edge jump is not particularly limited as a method of determining the height of the edge jump from the X-ray absorption spectrum, but for example, the height of the edge jump may be read directly from the X-ray spectrum. The height of the edge jump may be determined from the step function component obtained as a result.

  When the height of the edge jump is read from the X-ray absorption spectrum, for example, the X-ray absorption amount at a specific energy value in the range of 2485 to 3000 eV may be read. In general, the amount of X-ray absorption does not change significantly in this range, so the energy value may be determined within such a range. More preferably, it is in the range of 2485 to 2500 eV, and for example, the amount of X-ray absorption at 2490 eV may be read.

  When acquiring an X-ray absorption spectrum in step 1, it is preferable to fix the position of the X-ray detector. That is, when X-ray absorption spectra are acquired for a plurality of samples having different sulfur concentrations, X-ray absorption is performed with the distance between the sample and the X-ray detector fixed and X-ray absorption spectrum of sulfur K shell absorption edge To get

  Specifically, as shown in FIG. 4, in the fluorescence method, a sample such as a polymer material is irradiated with X-rays, and the fluorescent X-rays generated thereby are detected by an X-ray detector. At that time, if the position of the X-ray detector is close, the edge jump becomes large. For example, the height of the edge jump is larger when the X-ray detector is disposed at the position indicated by the solid line than the position indicated by the two-dot chain line in FIG. Therefore, in normal measurement, the X-ray detector is placed at an optimum position in accordance with the concentration of the target atom in the sample. On the other hand, in the present embodiment, by measuring the X-ray detector fixed at the same position, the difference in the concentration of sulfur as the target atom can be represented by the height of the edge jump.

  In step 2 above, an X-ray absorption spectrum is obtained for a sulfur-crosslinked polymer material whose sulfur crosslinking density is unknown. The method of acquiring the X-ray absorption spectrum of the sulfur K-shell absorption edge in step 2 is the above-described step except that a sulfur-crosslinked polymer material whose sulfur crosslinking density is unknown (sulfur concentration is also unknown) is used as a measurement sample It is the same as 1 and the explanation is omitted.

  In step 2, the distance between the X-ray detector and the polymer material whose sulfur crosslinking density is unknown is set to the same distance as the distance between the sample and the X-ray detector when the relationship W is obtained in step 1. Preferably, the polymer material is irradiated with X-rays. Thus, in step 5 described later, the sulfur concentration can be calculated using the relationship W from the height of the edge jump.

  In the step 3, the X-ray absorption spectrum obtained in the step 2 contains a sulfur-sulfur component (hereinafter referred to as an S-S component) and a sulfur-carbon component (hereinafter referred to as an S-C component). Fit with at least two components. More preferably, fitting is performed with at least three components including an S-S component, an S-C component, and a step function component, and still more preferably, as shown in an example in FIG. The above-mentioned fitting is performed using a sulfur-zinc component (hereinafter referred to as an S-Zn component) and a multiple scattering component together with a -C component and a step function component.

  Since the X-ray absorption at the sulfur K-shell absorption edge is mainly due to the S-S component and the S-C component, the S-S component and the S-C component can be obtained by fitting an X-ray absorption spectrum using these two components. Each peak area of the component can be calculated. In one embodiment, a step function component may also be used for fitting in order to determine the height of the edge jump. More strictly, X-ray absorption at the sulfur K-shell absorption edge is affected not only by the S-S component, S-C component and step function component, but also by the S-Zn component and multiple scattering components. Each peak area can be calculated with higher accuracy by fitting the X-ray absorption spectrum with five components including two components.

  Here, the S-S component is an X-ray absorbing component based on an S-S bond, and the S-C component is an X-ray absorbing component based on an S-C bond. The sulfur cross-linked structure in the polymer material is a structure in which carbon (C) of the polymer chain is linked via sulfur (S) as shown in FIG. It is an S bond, and the bond between the carbon atom of the polymer chain and the sulfur atom of the bridging moiety is an S-C bond.

  The S-Zn component is an X-ray absorbing component based on the S-Zn bond. As described above, zinc flower (ZnO) may be compounded into the rubber composition, in which case the zinc flower reacts to contain zinc sulfide (ZnS) in the vulcanized rubber. Absorption is considered. Therefore, when the polymeric material such as vulcanized rubber does not contain zinc, it is not necessary to consider this component. Therefore, in the case of a polymer material not containing zinc, the above-mentioned fitting may be performed using the S-S component, the S-C component, the step function component and the multiple scattering component as one embodiment.

  Multiple scattering components are x-ray absorption components based on multiple scattering by photoelectrons in the XANES region. Since photoelectrons in the XANES region have low kinetic energy, they have a long mean free path and are scattered many times by surrounding atoms (multiple scattering), so the X-ray absorption by this is taken into consideration.

  The step function component is an x-ray absorption component based on the transition of electrons to the continuous band. The XANES domain is an excitation from an inner shell orbit (K shell) to an unoccupied orbit. As the excitation energy (incident X-ray energy) increases, electrons move out of the nuclear restraint and become excited to a continuous band of higher energy than the unoccupied orbital. In this way, X-ray absorption due to the transition of electrons to the gradually increasing continuous band is considered.

  As a function used when fitting an X-ray absorption spectrum, various functions can be used as long as they can represent each of the components described above.

  In one embodiment, as shown in FIG. 1, it is preferable to use a Gaussian function for the S-C component, the S-Zn component, and the multiple scattering component. Since the X-ray absorption by these components generally exhibits a normal distribution, it can be expressed using a Gaussian function. As the Gaussian function, for example, one represented by the following formula (1) can be used.

In formula (1), a is peak height (peak intensity), b is X-ray energy at peak top (eV), c is half width of peak (eV), x is irradiation X-ray energy (eV) .

  In one embodiment, for the S-C component, the above fitting is performed with a as a variable, b and c as constants, and for S-Zn components and multiple scattering components, a and b as variables and c as a constant. . The X-ray energy b at the peak top of the S-C component can be set to a value obtained by measurement of a standard sample, for example, 2473 eV.

  Further, as shown in FIG. 1, it is preferable to use a sigmoid function as the step function component. As described above, since the step function component gradually increases as energy becomes higher, it can be expressed using a sigmoid function. As a sigmoid function, what is represented by following formula (2) can be used, for example.

In Formula (2), d is the height of an edge jump, e is a constant, and f shows ionization potential (eV). In one embodiment, the above fitting may be performed with d as a variable and e and f as constants. However, when the height of the edge jump is directly read from the X-ray absorption spectrum in step 5 described later, the read value may be used as a constant.

  On the other hand, the S-S component can also be expressed using a Gaussian function having a symmetrical distribution like the S-C component, but the fluctuation of the S-S bond length due to the thermal vibration of the crosslinked sulfur chain is taken into consideration It is preferable to use an asymmetric Gaussian function having an asymmetrical distribution. That is, thermal vibration of the crosslinked sulfur chain causes molecular motion of the S-S bond to change the bond length, and the longer the S-S bond length, the higher the peak height and the narrower the half width. In consideration of the fluctuation of the S-S bond length, as the S-S component, as shown in FIG. 3, an asymmetric Gaussian function having an asymmetric distribution by using a plurality of Gaussian functions is used. It is preferable to use those having different peak heights and half widths as the plurality of Gaussian functions. More specifically, as the asymmetric Gaussian function, a reference Gaussian function and a plurality of Gaussian functions in which peak tops are equally shifted to the high energy side of the reference Gaussian function and peak heights equally decrease are synthesized It is preferable to use one.

In one embodiment, the asymmetric Gaussian function used for the S-S component can be represented by the addition of a plurality of Gaussian functions represented by the above equation (1). Specifically, as shown in FIG. 3, the reference Gaussian function (C ₁ function) represented by the above equation (1) is determined, and the peak tops are equally shifted to the high energy side of the C ₁ function and the peak height is A plurality of Gaussian functions (C _m functions: C ₁ , C ₂ ,..., Where m is an integer greater than or equal to 1) in which the errors decrease equally. In the C ₁ function, the above a, b and c are constant, and for the C _m function (m = 2 to 2) after the C ₁ function, the difference between the peak top shift width and the peak height is determined. Define _m C _m functions. At that time, the product of the half width and peak height C _m function is constant. By combining the _m C _m functions, an asymmetric Gaussian function is obtained. In the obtained asymmetric Gaussian function, it is preferable to perform the above-described fitting, with the X-ray energy (eV) at the peak top as a constant and the peak height as a variable. Therefore, when creating an asymmetric Gaussian function, the variable or shift width of the C ₁ function, etc., so that the X-ray energy at the peak top when combining the multiple Gaussian functions matches the value of the constant The difference reduction value, the product of the above, etc. may be determined. The X-ray energy at the peak top of the S-S component can be set to a value obtained by measurement on a standard sample, for example, 2472 eV.

  The method for fitting (also referred to as curve fitting) to the X-ray absorption spectrum using each of the above components is not particularly limited, and a general method can be used. For example, fitting may be performed so that the sum of squared residuals of the X-ray absorption spectrum (measurement spectrum) approaches 0 as a function obtained by adding the function of each component (preferably five components). Thereby, X-ray absorption spectrum can be peak-separated into each component. That is, since the curve after the fitting process is obtained for each component, the peak area of each component can be calculated from the curve after the fitting process of each component. FIG. 1 shows the curves of the five components after the fitting process and the composite curves of these five components (approximated curves by fitting), and it can be seen that they are in good agreement with the measured spectrum.

  In Step 4 above, the peak area of the S-S component and the peak area of the S-C component are calculated from the S-S component and the S-C component fitting curves obtained in Step 3, respectively, and the ratio of the two ( By calculating the peak area ratio, the cross-linked sulfur chain linkage length of the polymer object to be measured is calculated. The peak area is the area of a portion surrounded by each fitting curve in the measurement range.

Here, the crosslinked sulfur chain connection length of the polymer material will be described. As described above, the sulfur crosslinked structure in the polymer material is a structure in which carbon (C) of the polymer chain is linked via sulfur (S) (see FIG. 2), and represented by _"C-S n -C" as n, n = 1 to the monosulfide structure (C-S-C), n = 2 of the disulfide structure _{(C-S 2 -C),} n = 3~ There are eight ways to the polysulfide structure (C-S ₈ -C) of eight (ie, an integer of n = 1 to 8). The number of linked sulfurs is the bridged sulfur chain linkage length. In general, in a sulfur-crosslinked polymer material, since the sulfur bridged structure is a mixture of some with different linkage number n, the average is the cross-linked sulfur chain linkage length of the polymer material. Each sulfur bridged structure has S-C bonds at both ends (that is, the number of S-C bonds is two in all), and the number of S-S bonds increases one by one as the number n of linkages increases. If the ratio of the amount of S-S bonds to the amount of S-C bonds present in the polymer material is known, it is possible to evaluate the cross-linked sulfur chain linkage length.

  In this embodiment, since the peak area of the S-S component corresponding to the S-S bond amount and the peak area of the S-C component corresponding to the S-C bond amount are obtained as described above, S-S The crosslinked sulfur chain linkage length can be calculated by calculating the peak area ratio of the component and the S-C component.

  For example, the ratio R = C / (C + S) of the both is calculated from the peak area S of the S-S component and the peak area C of the S-C component, and the crosslinked sulfur chain linkage length L is calculated from the following formula (3) You may

Here, in the sulfur-crosslinked polymer material, the S-C ratio which is the ratio of the number of S-S bonds and the number of S-C bonds is
"S-C ratio" = "S-C number of bonds" / ("S-C number of bonds" + "number of S-S bonds")
I assume. The sulfur cross-linking structure in the polymer material is such that the number of S-C bonds is always two, provided that both S-S bonds and S-C bonds are used for the cross-linking,
"S-C ratio" = 2 / (2+ "number of SS bonds"),
“Number of SS bonds” = (2−2 × “S-C ratio”) / “S-C ratio”. Since the bridging sulfur chain linking length L, which is the linking number of sulfur, is a value obtained by adding 1 to the number of SS bonds,
Cross-linked sulfur chain linkage length L = {(2-2 × "S-C ratio") / "S-C ratio"} + 1
It becomes. Since the S-C ratio is equal to the ratio R of the peak area S to the peak area C, the above equation (3) is obtained.

  In addition, as bridge | bridging sulfur chain connection length calculated at the process 4, ratio of the peak area S of the S-S component with respect to the peak area C of a S-C component instead of L of Formula (3) (S / C ) May be calculated. The larger the ratio S / C, the larger the number of sulfur linkages in the cross-linked portion, so the ratio S / C can be used as an index representing the cross-linked sulfur chain linkage length. The cross-linked sulfur chain linkage length calculated in step 4 may indicate the relative linking number of sulfur in the cross-linked portion in this manner, for example, the peak area of the sum of the S-S component and the S-C component (S + C The peak area ratio (S / (S + C)) of the S—S component to

  In the step 5, the sulfur crosslinking density is calculated from the height of the edge jump and the crosslinked sulfur chain linkage length calculated in the step 4.

  As a method of determining the height of the edge jump, the height of the edge jump may be read from the X-ray absorption spectrum obtained in the step 2. Alternatively, when fitting is performed using the step function component in the step 3. The height of the edge jump in the step function component after the fitting of H may be used. The details of the method of reading the height of the edge jump from the X-ray absorption spectrum are the same as step 1 above.

  In general, the shape of the spectrum obtained by the XAFS method is a step jump (i.e., an edge jump) of the signal intensity which is sharp from the baseline on the energy side lower than the absorption edge toward the high energy side. Is known to be proportional to the concentration of the measurement target atom (Watanabe, S., “Adsorption behavior of ions to monolayers at gas-liquid interface using XAFS,” Surface Science, Vol. 25, No. 3, 139-145, 2004). Therefore, the height of the edge jump of the step function component is proportional to the number of sulfur atoms (sulfur concentration) included in the X-ray irradiation range.

In this embodiment, the sulfur concentration of the polymer material is determined based on the relationship W obtained in the step 1 from the height d of the edge jump of the polymer material whose sulfur crosslinking density is unknown in the step 5 Ask P. Then, from the determined sulfur concentration P and the crosslinked sulfur chain linkage length L obtained in step 4, the sulfur crosslinking density D _c can be calculated by D _c = P / L. The sulfur crosslinking density D _c can be determined as the number of crosslinks (eg, per mL) or the number of moles of crosslink (eg, mol / mL) per unit volume (eg, per mL) of the polymer material, and has a unit It can be calculated as a value.

  As described above, according to this embodiment, the peak area ratio of these components can be obtained by peak separation of the X-ray absorption spectrum of the sulfur K-shell absorption edge using the S-S component and the S-C component. As it can be determined, the cross-linked sulfur chain linkage length can be determined using the peak area ratio. The larger the cross-linked sulfur chain linkage length is, the more it means that it has a sulfur cross-linked form with more thermally unstable S-S bonds, so by evaluating the cross-linked sulfur chain linkage length, Heat resistance can be evaluated. Therefore, it can be used, for example, for evaluating the heat resistance of a vulcanized rubber product such as a pneumatic tire.

  Further, according to the present embodiment, since the sulfur crosslinking density can be calculated from the crosslinked sulfur chain linkage length and the edge jump, the crosslinking density can be evaluated together with the crosslinking form, and more detailed information on the sulfur crosslinking structure You can get Moreover, according to the present embodiment, the sulfur concentration in the polymer material to be analyzed can be determined based on the relationship W between the sulfur concentration and the edge jump determined using a sample having a known sulfur concentration, The crosslink density can be calculated as the number of crosslinks per unit volume. Thus, since the crosslink density is calculated as a value having a unit, the absolute evaluation of the crosslink density is possible, and comparison can be made even if the measurement date etc. changes for various polymer materials.

  Note that each step such as the above fitting, calculation of peak area, calculation of cross-linked sulfur chain linkage length, calculation of sulfur cross-link density, derivation of relationship W between sulfur concentration and edge jump height, etc. may be performed using a computer By performing each step, an analysis device comprising a computer in which a program for executing each of these steps is read can analyze the sulfur cross-linking structure of the polymer material. In addition, a fitting unit that performs the above fitting, a peak area calculation unit that calculates the peak area, a crosslink length calculation unit that calculates the crosslink sulfur chain linkage length, a crosslink density calculation unit that calculates the sulfur crosslink density, and the above relationship W A sulfur bridge structural analysis device comprising an input unit for acquiring information of X-ray absorption spectrum of sulfur K shell absorption edge and an output unit for outputting calculation results together with a derivation unit for deriving a general-purpose computer as a basic hardware It may be realized by using it as

Hereinafter, although the example of the present invention is shown, the present invention is not limited to these examples.
[First embodiment]
Using a Banbury mixer, according to the composition (parts by mass) shown in Table 1 below, the compounding agents were added to the rubber polymer and kneaded to prepare an unvulcanized rubber composition.

The details of each component in Table 1 are as follows.
SBR: "JSR 1502" manufactured by JSR Corporation
・ Zinc flower: "Zinc flower type 1" manufactured by Mitsui Mining & Smelting Co., Ltd.
・ Stearic acid: Kao Corporation "Lunack S-20"
・ Sulfur: Powdered sulfur 150 mesh for rubber manufactured by Hosoi Chemical Industry Co., Ltd.
・ Vulcanization accelerator: "Noxceler CZ" manufactured by Ouchi Shinko Chemical Co.

The obtained unvulcanized rubber composition was press-processed (160 ° C., 30 minutes) with a mold to prepare a vulcanized rubber sheet (rubber sheets 1 to 3) having a thickness of 1.0 mm. The XANES measurement at the sulfur K-shell absorption end was performed with the obtained rubber sheets 1 to 3 as the measurement target, to obtain an X-ray absorption spectrum. The XANES measurement was performed under the following measurement conditions at the Aichi Synchrotron Light Center of "the base of Aichi". In the measurement, the distance between the X-ray detector and the measurement object was constant for all the measurement objects.
・ X-ray intensity: 2.0 × 10 ¹² photons / s / mrad ² / mm ² /0.1% bw
Number of photons of X-ray: ~ 3.0 × 10 ¹⁰ photons / s
Spectrometer: Crystal spectrometer • X-ray detector: Silicon drift detector • Measurement method: Fluorescence • X-ray energy range: 2400-2500 eV

  The obtained X-ray absorption spectrum was fitted with five components of an S-S component, an S-C component, an S-Zn component, a multiple scattering component, and a step function component to calculate a peak area of each component. At this time, the Gaussian function of equation (1) was used for the S-C component, the S-Zn component and the multiple scattering component. In the equation (1), for the S-C component, a (peak height) is a variable, b (energy at peak top) is 2473 eV, c (half width of peak) is 1.8 eV, S is For the -Zn component, a and b are variables, c is 1.8 eV, and for multiple scattering components, a and b are variables and c is 4 eV. Moreover, the sigmoid function of Formula (2) was used about the step function component. The parameters in equation (2) were set such that d (height of edge jump) was a variable, e (constant) = 0.7, f (ionization potential) = 2476 eV.

In addition, an asymmetric Gaussian function was used for the S-S component. The asymmetric Gaussian function is represented by the addition of a plurality of Gaussian functions of equation (1). Specifically, using equation (1), at regular intervals to a 2, b a defines a C ₁ functions as a 2471.1EV, also in order from the C ₁ function, peak top to a high energy side (0.015EV) The 100 C _m functions (m = 1 to 100) are defined, which shift to and reduce the peak height equally (0.003). At that time, the _Cm function was defined such that the product of the peak height and the half width had a constant value (2.8). By summing these 100 C _m function to obtain an asymmetric Gaussian function of S-S component. The energy (eV) of the peak top of the asymmetric Gaussian function was set to 2472 eV, and the peak height was used as a variable.

  The residual sum of squares of the measured spectrum approaches 0 as a function combining the five components of the S-S component, the S-C component, the S-Zn component, the multiple scattering component, and the step function component defined in this way As a result, fitting was performed to calculate the peak area of each component. And bridged sulfur chain connection length L was computed by the above-mentioned formula (3).

In addition, the sulfur concentration P is calculated from the height d of the edge jump using the calibration curve 1 shown in FIG. 5 and the sulfur crosslinking density D _c (this / mL) from the sulfur concentration P and the crosslinked sulfur chain linkage length L = P / L was calculated. The results are shown in Table 1.

  Here, the calibration curve 1 was calculated | required as follows prior to preparation of the said rubber sheets 1-3.

100 parts by mass of SBR (JSR Ltd. "JSR 1502") was mixed with the parts by mass (phr) of sulfur shown in Table 2 below ("The powdered sulfur 150 mesh for rubber" manufactured by Hosoi Chemical Industry Co., Ltd.) Thereafter, low temperature pressing was performed at 100 ° C. to obtain an unvulcanized rubber sheet having a thickness of 1.0 mm. For the obtained unvulcanized rubber sheet, the sulfur concentration P, that is, the number of sulfur atoms per unit volume (number / mL) was calculated from the compounding composition. Further, the unvulcanized rubber sheet was irradiated with X-rays to obtain an X-ray absorption spectrum of the sulfur K-shell absorption end. The measurement conditions of the X-ray absorption spectrum are the same as those of the rubber sheets 1 to 3 described above. From the obtained X-ray absorption spectrum, the same fitting as the rubber sheets 1 to 3 was performed, and the edge jump height d of each unvulcanized rubber sheet was determined from the step function component obtained as a result. From the edge jump height d thus determined and the sulfur concentration P, a calibration curve 1 (d = 5 × 10 ⁻²² P + 0.0081) showing the relationship W between the two was obtained.

  The heat resistance was evaluated using the rubber sheets 1 to 3 obtained above. Heat resistance is a tensile test according to JIS K6251 for each of the rubber sheets 1 to 3 prepared by aging each of the rubber sheets 1 to 3 for 1 week at 100 ° C. using a gear oven Heat resistance was evaluated by the retention of the elongation at break of the aged sample to the elongation at break of the unaged sample.

  Moreover, the tension test (dumbbell shape 3 form) according to JISK6251 was done using each rubber sheet 1-3, and M100 (100% tensile stress) was measured.

The results are as shown in Table 1. The smaller the blending amount of sulfur, the shorter the linking sulfur chain length is, and the higher the retention of breaking elongation before and after aging is, and the heat resistance is excellent. As the vulcanized rubber has a sulfur crosslinked form with less thermally unstable S-S bonds as the crosslinked sulfur chain linkage length decreases, from the results in Table 1, using the crosslinked sulfur chain linkage length of the vulcanized rubber It turns out that heat resistance can be evaluated. Further, as shown in Table 1, as the blending amount of sulfur was smaller, the sulfur crosslinking density D _c was smaller and the 100% tensile stress was also smaller.

Claims (4)

The relationship between the sulfur concentration and the height of the edge jump is determined by irradiating a sample with a known sulfur concentration with X-rays to acquire the X-ray absorption spectrum of the sulfur K-shell absorption edge,
Irradiating a sulfur-crosslinked polymer material of unknown sulfur crosslinking density with X-rays to acquire an X-ray absorption spectrum of the sulfur K-shell absorption edge,
Fitting the X-ray absorption spectrum obtained for the polymeric material with at least two components including a sulfur-sulfur component and a sulfur-carbon component;
The peak area of the sulfur-sulfur component and the peak area of the sulfur-carbon component are calculated, and the crosslinked sulfur chain linkage length is calculated from the peak area ratio of the sulfur-sulfur component and the sulfur-carbon component,
For the polymer material, the height of the edge jump is determined from the X-ray absorption spectrum, the sulfur concentration is determined from the height of the determined edge based on the relationship, and the determined sulfur concentration and the crosslinked sulfur chain linkage length Calculate the sulfur crosslinking density,
Method of analyzing sulfur cross-linking structure of polymer material   The distance between the X-ray detector and the polymer material whose sulfur crosslinking density is unknown is the same distance as the distance between the sample and the X-ray detector when the relationship is determined using a sample whose sulfur concentration is known The sulfur crosslinked structure analysis method according to claim 1, wherein the polymer material is irradiated with X-rays after being set.   From the peak area S of the sulfur-sulfur component and the peak area C of the sulfur-carbon component, the bridging sulfur chain linkage length L = {(2-2 × R) / R} +1 (where, R = C / ( The sulfur bridged structure analysis method according to claim 1 or 2, wherein the sulfur bridged density is calculated from the sulfur concentration determined from the bridged sulfur chain linkage length L and the height of the edge jump, which is C + S).   The fitting is performed with at least three components including the sulfur-sulfur component, the sulfur-carbon component, and the step function component, and the sulfur concentration is determined based on the relationship from the height of the edge jump of the step function component The sulfur bridged structure analysis method according to any one of claims 1 to 3, wherein the sulfur bridged density is calculated from the sulfur concentration and the bridged sulfur chain linkage length.