JP6657664B2 - Chemical state measurement method - Google Patents

Description

The present invention relates to a chemical state measuring method capable of obtaining information on sulfur in a crosslinked portion with high accuracy in a polymer composite material containing sulfur.

Conventionally, as a method of analyzing a sulfur cross-linked structure in a vulcanized rubber cross-linked using a sulfur-containing compound such as a sulfur vulcanizing agent, the cross-linking is selectively cut with a reagent such as LiAlH ₄ or propane 2-thiol. Based on the degree of swelling before and after, a monosulfide bond (RS ₁ -R) and a disulfide bond (RS ₂ -R) in the vulcanized rubber are obtained using the Flory-Rehner formula (for example, see Non-Patent Document 1). ) And a method for calculating the crosslink density [mol / cm ³ ] of polysulfide bonds (R—S _n —R (n ≧ 3)).

Hideo Nakauchi, 4 others, "Journal of the Rubber Association of Japan", 1987, Vol. 60, No. 5, p. 267-272

If the sulfur cross-linked structure in sulfur-containing polymer composite materials such as vulcanized rubber cross-linked using sulfur-containing compounds can be controlled, the performance required for sulfur-containing polymer composite materials such as mechanical properties will be improved. It is thought that precise control is possible, and the analysis of the sulfur crosslinked structure in the sulfur-containing polymer composite material is very important in controlling the required performance.

As described above, a technique for analyzing a sulfur crosslinked structure in a vulcanized rubber has been conventionally known. However, in the conventional method, a monosulfide bond (RS ₁ -R) and a disulfide bond (RS Only three types of crosslink densities of R—S ₂ —R) and polysulfide bonds (R—S _n —R (n ≧ 3)) could be calculated. And further, polysulfide bond _{(R-S n -R (n} ≧ 3)) often may not be used for preferentially cleave propane 2-thiol strong odor and therefore, monosulfide bonds (R-S ₁ -R), and calculates the two kinds of the crosslinking density of the polysulfide bond containing a disulfide bond _{(R-S n -R (n} ≧ 2)), it was often the case of analyzing a sulfur bridge structure. However, in these methods, polysulfide bond details _{(R-S n -R (n} = 2,3,4,5,6,7,8)) is not known, the required performance by controlling the sulfur bridge structure It was not enough to control. Thus, there is room for improvement in the method of analyzing the sulfur crosslinked structure in more detail.

Against this background, the present inventors measured the crosslink density by fitting the X-ray absorption spectrum of a sulfur-containing polymer composite material by a reverse Monte Carlo method in Japanese Patent Application Nos. 2015-130060 and 2015-138963. Suggested how to. However, this method has room for improvement in the following points.

Usually, zinc oxide (ZnO) is blended in the sulfur-containing polymer composite material in order to promote a crosslinking reaction. However, as shown in FIG. 1, the X-ray absorption spectrum of the sulfur-containing polymer composite material is as follows. The profile changes depending on the presence or absence of ZnO. This is considered to be due to sulfur oxide (zinc sulfate: ZnSO ₄ ) generated by the reaction between zinc oxide and sulfur. In addition, since sulfur oxides are generated even when the sulfur-containing polymer composite is deteriorated, it is considered that the X-ray absorption spectrum of the sulfur-containing polymer composite is also affected by sulfur oxides other than zinc sulfate. .

As described above, the X-ray absorption spectrum of the sulfur-containing polymer composite material includes not only the sulfur in the crosslinked portion but also information on the sulfur in the sulfur oxide. For this reason, it is difficult to accurately obtain information on the sulfur in the crosslinked portion even if it is used for analysis as it is.

An object of the present invention is to solve the above problems and to provide a chemical state measuring method capable of obtaining information on sulfur in a crosslinked portion with high accuracy.

The present invention relates to a measuring step of irradiating a sulfur-containing polymer composite material with high-intensity X-rays and measuring an X-ray absorption spectrum while changing the energy of the X-rays. And a removing step for removing oxide components.

In the removing step, at least the sulfur oxide and the X-ray absorption spectrum of a standard sample of a plurality of compounds having different numbers of sulfur linkages other than the sulfur oxide are used to obtain the X-ray absorption spectrum of the sulfur-containing polymer composite material. By XAES region waveform separation, the sulfur oxide ratio in the X-ray absorption spectrum of the sulfur-containing polymer composite material is calculated, and the EXAFS vibration of the sulfur-containing polymer composite material is calculated based on the obtained sulfur oxide ratio. It is preferable to remove the sulfur oxide component from the X-ray absorption spectrum of the sulfur-containing polymer composite material by subtracting the EXAFS vibration of the sulfur oxide from.

In the measurement step, it is preferable to measure the X-ray absorption spectrum of sulfur near the sulfur K-shell absorption edge by setting the energy range for scanning using X-rays to 2300 to 4000 eV.

In the measurement step, the X-rays preferably have a photon number of 10 ⁷ (photons / s) or more and a luminance of 10 ¹⁰ (photons / s / mrad ² / mm ² /0.1% bw) or more.

ADVANTAGE OF THE INVENTION According to this invention, by removing the component of a sulfur oxide from the X-ray absorption spectrum of a sulfur-containing polymer composite material, it becomes possible to obtain the information on the sulfur in the crosslinked portion with high accuracy.

It is a graph which shows the X-ray absorption spectrum of sulfur crosslinked rubber containing ZnO, and the X-ray absorption spectrum of sulfur crosslinked rubber without ZnO. It is a graph which shows the X-ray absorption spectrum of sulfur crosslinked rubber, and the result of having performed fitting using the X-ray absorption spectrum of the standard sample. It is a graph which shows the X-ray absorption spectrum of a sulfur crosslinked rubber. FIG. 4 is a graph showing EXAFS vibration extracted from the spectrum of FIG. 3 (broken line portion in FIG. 3). Is a graph showing the X-ray absorption spectra of ZnSO _4. 6 is a graph showing EXAFS vibration extracted from the spectrum of FIG. 5 (broken line portion in FIG. 5) multiplied by a coefficient α. It is a graph which shows what removed the component of the sulfur oxide from the EXAFS vibration of the sulfur crosslinked rubber. It is a graph which shows the radial distribution function (Example) which removed the sulfur oxide, and the radial distribution function which is not removed (comparative example).

The present invention relates to a measuring step of irradiating a sulfur-containing polymer composite material with high-intensity X-rays and measuring an X-ray absorption spectrum while changing the energy of the X-rays. And a removing step of removing oxide components.

In the present invention, by performing the measurement step and the removal step in this order, an X-ray absorption spectrum from which the sulfur oxide component has been removed can be obtained. By analyzing this X-ray absorption spectrum, information on sulfur in the crosslinked portion can be obtained with high accuracy. By analyzing the obtained information, it is expected that the number and amount of sulfur bridging between the polymers can be accurately obtained.

In the measurement step in the present invention, a sulfur-containing polymer composite material (hereinafter, also simply referred to as a “sample”) is irradiated with high-intensity X-rays, and an X-ray absorption spectrum is measured while changing the energy of the X-rays. In the above measurement step, an X-ray absorption fine structure (X-ray absorption fine structure: X-ray absorption fine structure near the absorption edge) method may be used as a method for measuring the X-ray absorption spectrum, for example.

As a method for measuring the crosslink density of a sulfur-containing polymer composite material such as a rubber material using a sulfur-containing compound such as a sulfur vulcanizing agent, the XAFS method near the sulfur K shell absorption edge is useful.
The XAFS method is a method of irradiating X-rays and measuring the amount of X-ray absorption at a target atom. The XAFS method utilizes the fact that the X-ray energy that can be absorbed differs depending on the chemical state (bond), and the detailed chemical state (bonding) is used. ) Can be checked. However, in the sulfur-containing polymer composite material, there are sulfur bridges having different sulfur bond lengths such as a monosulfide bond, a disulfide bond, and a polysulfide bond, and these have similar peak energies detected in the spectrum. When zinc oxide is added, zinc sulfide is also generated, and its spectrum is observed. As described above, since the chemical state of sulfur in the sulfur-containing polymer composite material is complicated, the obtained XAFS spectrum tends to be a broad spectrum as compared with a polymer material containing no sulfur component. Therefore, more accurate measurement is required for the analysis of the sulfur-containing polymer composite material. Therefore, in order to perform more accurate measurement in the XAFS method, high-brightness X-rays can be used.

In the analysis by the XAFS method, an XANES (X-ray Absorption Near Edge Structure) region in which a peak from the absorption edge (energy at which absorption rises) to about 50 eV appears, and a slower vibration component having a higher energy than the XANES region There is an analysis in an EXAFS (Extended X-ray Absorption Fine Structure) region, which is a region where appears. In the XANES region, when the sample is irradiated with X-rays near the absorption edge of the target atom, the electrons at the inner core level transition to an excited state, and therefore, what kind of atom is bonded to the target atom ( Chemical state). On the other hand, in the EXAFS region, core electrons leave the binding of atomic nuclei and jump out as photoelectrons. At this time, since the photoelectrons are represented as waves, if there are other atoms nearby, the waves interfere and return. Therefore, information such as the number of atoms around the central atom, the type of atom, and the distance between atoms can be obtained. In the present invention, it is preferable to use a spectrum in the EXAFS region near the sulfur K-shell absorption edge obtained by the XAFS method (hereinafter, also referred to as “EXAFS vibration”) as the X-ray absorption spectrum to be used in the removal step described later. .

The sulfur-containing polymer composite material subjected to the method of the present invention is not particularly limited as long as it is crosslinked using a sulfur-containing compound such as a sulfur vulcanizing agent and has a sulfur crosslinked structure. And a sulfur-crosslinked rubber obtained by crosslinking a rubber composition containing a sulfur-containing compound such as a sulfur vulcanizing agent, a rubber component, and other compounding materials.

Examples of the sulfur-containing compound include sulfur vulcanizing agents such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

Examples of the rubber component include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), and halogen. And diene rubbers such as butyl rubber (X-IIR) and styrene isoprene butadiene rubber (SIBR). Further, the rubber component may include one or more modifying groups such as a hydroxyl group and an amino group. Further, various elastomers can be used as the rubber component.

Further, as the rubber component, a composite material in which the rubber component and one or more resins are composited can be used. The resin is not particularly limited, and includes, for example, those widely used in the field of rubber industry, for example, petroleum resins such as C5 aliphatic petroleum resin and cyclopentadiene petroleum resin.

Fillers such as carbon black and silica, silane coupling agents, zinc oxide, stearic acid, antioxidants, waxes, oils, vulcanizing agents other than sulfur, vulcanization accelerators, etc. A conventionally known compound in the rubber field may be appropriately compounded. Such a rubber material (rubber composition) can be produced using a known kneading method, vulcanization method, or the like. Examples of such a rubber material include vulcanized rubber materials for tires (vulcanized rubber compositions for tires).

As a specific method of irradiating high-intensity X-rays and measuring the X-ray absorption spectrum while changing the energy of the X-rays, the following transmission method, fluorescence method, electron yield method, and the like are widely used.

(Transmission method)
This is a method for detecting the X-ray intensity transmitted through the sample. A photodiode array detector or the like is used for the transmitted light intensity measurement.

(Fluorescence method)
This is a method of detecting fluorescent X-rays generated when a sample is irradiated with X-rays. The detector includes a Lytle detector, a semiconductor detector, and the like. In the case of the transmission method, when the X-ray absorption measurement of an element having a small content in a sample is performed, the signal is small and the background becomes high due to the X-ray absorption of the element having a large content, so that the S / B ratio is poor. It becomes a spectrum. On the other hand, in the fluorescence method (particularly when an energy dispersive detector or the like is used), it is possible to measure only the fluorescent X-ray from the target element, so that the effect of the element having a large content is small. Therefore, it is effective when performing an X-ray absorption spectrum measurement of an element having a small content. Further, since the fluorescent X-ray has a high penetrating power (the interaction with the substance is small), the fluorescent X-ray generated inside the sample can be detected. Therefore, this method is the best method for obtaining bulk information after the transmission method.

(Electron yield method)
This is a method of detecting a current flowing when a sample is irradiated with X-rays. Therefore, the sample needs to be a conductive material. Another feature is that the surface is sensitive (information about several nm on the surface of the sample). When a sample is irradiated with X-rays, electrons escape from the element, but the electrons have a strong interaction with the substance, so that the mean free path in the substance is short.

As described above, the transmission method is a basic measurement method of XAFS, and is a method of measuring the amount of X-ray absorption by detecting the intensity of incident light and the intensity of X-rays transmitted through the sample. In addition, if the concentration of the target compound is not less than a certain level (for example, several wt% or more), it is difficult to measure. The electron yield method is a surface-sensitive method, and information about several tens of nanometers on the surface of a sample can be obtained. On the other hand, the fluorescence method has a feature that information can be obtained from a portion somewhat deeper than the surface as compared with the electron yield method, and a feature that it can be measured even when the concentration of the target compound is low. In the present invention, a fluorescence method is preferably used.
Thus, the fluorescence method will be described more specifically below.

The fluorescence method is a method of monitoring fluorescent X-rays generated when a sample is irradiated with X-rays, and uses the fact that there is a proportional relationship between the amount of absorbed X-rays and the intensity of the fluorescent X-rays. This is a method of indirectly obtaining the amount of X-ray absorption from the intensity. In the case of performing the fluorescence method, a method using an ionization chamber and a semiconductor detector such as an SDD (silicon drift detector) or an SSD (silicon strip detector) are often used. The ionization chamber can measure relatively easily, but it is difficult to classify the energy, and the background may be raised because X-rays scattered from the sample or fluorescent X-rays other than the target element enter. It is necessary to install a solar slit or a filter between the sensor and the detector. In the case of using SDD or SSD, since it is sensitive and energy can be separated, only fluorescent X-rays from the target element can be extracted, and measurement can be performed with a good S / B ratio.

It is preferable that the number of photons of the X-ray used in the above measurement step is 10 ⁷ photons / s or more. This enables highly accurate measurement. The number of photons of the X-ray is more preferably at least 10 ⁹ photons / s. Although the upper limit of the number of photons of the X-ray is not particularly limited, it is preferable to use an X-ray intensity that is equal to or less than the radiation damage.

It is preferable that the X-ray used in the above measurement step has a luminance of 10 ¹⁰ photons / s / mrad ² / mm ² /0.1% bw or more.
The XAFS method requires a continuous X-ray generator as a light source to scan with X-ray energy, and measures the X-ray absorption spectrum with a high S / N ratio and S / B ratio to analyze a detailed chemical state. There is a need to. X-rays emitted from a synchrotron have a luminance of 10 ¹⁰ photons / s / mrad ² / mm ² /0.1% bw or more and are a continuous X-ray source, so they are optimal for XAFS measurement. . Here, bw indicates the band width of X-rays emitted from the synchrotron. The luminance of the X-ray is more preferably 10 ¹¹ photons / s / mrad ² / mm ² /0.1% bw or more. The upper limit of the luminance of the X-ray is not particularly limited, but it is preferable to use an X-ray intensity that is equal to or lower than the radiation damage.

The energy range for scanning using X-rays in the measurement step is preferably in the range of 2300 to 4000 eV. By scanning the above range, the X-ray absorption spectrum of sulfur near the sulfur K shell absorption edge can be measured, and information on the chemical state of sulfur in the sample can be obtained. The above energy range is more preferably 2350-3500 eV.

In the removing step in the present invention, a sulfur oxide component is removed from the X-ray absorption spectrum of the sulfur-containing polymer composite material. Hereinafter, an example of the removing method will be described.

First, using the X-ray absorption spectrum of the standard sample, the XANES region of the X-ray absorption spectrum of the sulfur-containing polymer composite material is waveform-separated to obtain the sulfur oxide in the X-ray absorption spectrum of the sulfur-containing polymer composite material. Calculate the ratio.

As the standard sample, at least a sulfur oxide and a plurality of compounds having different numbers of sulfur linkages other than the sulfur oxide (hereinafter, also referred to as “sulfur sample”) are used. The sulfur oxide is to be removed in this step, and the sulfur sample corresponds to the sulfur in the crosslinked portion.

The sulfur oxides, for example, addition to the above-mentioned zinc sulfate _{(ZnSO 4), R-SO} 4 (R is a hydrocarbon group) can also be used a compound having a structure represented by. If crosslinking moiety such sulfur-containing polymer composite material is oxidized, it is preferable to use a compound having a structure represented by R-SO _4.

Examples of the sulfur sample include a compound having a mono bond (C-S-C), a compound having a di-bond (C-S-S-C), and a poly bond (C- _Sn- C, n≥3). Can be used.

Hereinafter, the case where the following compound is used as a standard sample and a sulfur crosslinked rubber is used as a sulfur-containing polymer composite material will be described. The standard sample is not limited to the following compounds, and other compounds can be used as long as the sulfur moiety is similar. The method of preparing the sulfur crosslinked rubber and the content of the compounding are the same as in the examples described later.
(Standard sample)
Compound having a mono bond: poly (3-hexyl thiophen)
A compound having a di bond: poly (ethylene glycol) with disulide linkage
Compound having poly bond: sulfur
・ Sulfur oxide: ZnSO ₄

The measurement conditions and analysis conditions of the X-ray absorption spectrum are as follows. Note that the semiconductor detector such as the SDD used this time was counted down in the case of high-measurement measurement. The counting correction method is disclosed in the literature “Masayoshi Ito, Hajime Yada, synchrotron radiation July 2008 Vol.21 No.4” and the like.
(Used equipment)
XAFS: XAFS measurement device of B branch of SPring-8 BL27SU (measurement conditions)
Luminance: 1 × 10 ¹⁶ photos / s / mrad ² / mm ² /0.1% bw
Number of photons: 5 × 10 ¹⁰ photons / s
Spectrometer: Crystal spectrometer Detector: SDD (Silicon drift detector)
Measurement method: Fluorescence energy range: 2360-3500 eV
(XAFS analysis)
XAFS analysis integrated software REX2000 manufactured by Rigaku Corporation

FIG. 2 is a graph showing the X-ray absorption spectrum of the sulfur crosslinked rubber and the result of fitting using the X-ray absorption spectrum of the standard sample. Each spectrum is normalized such that the peak intensity around 2470 eV, which is the highest intensity, is 1. Based on this result, the XANES region of the X-ray absorption spectrum of the sulfur crosslinked rubber is subjected to waveform separation, whereby the ratio (coefficient α) of sulfur oxide in the X-ray absorption spectrum of the sulfur crosslinked rubber can be calculated.

Next, the sulfur oxide component is removed from the X-ray absorption spectrum of the sulfur-containing polymer composite material by subtracting the EXAFS vibration of the sulfur oxide from the EXAFS vibration of the sulfur-containing polymer composite material based on the calculated coefficient α. I do.

FIG. 3 is a graph showing an X-ray absorption spectrum of the sulfur crosslinked rubber, and FIG. 4 is a graph showing EXAFS vibration extracted from the spectrum of FIG. 3 (broken line portion in FIG. 3). FIG. 5 is a graph showing the X-ray absorption spectrum of ZnSO ₄ , and FIG. 6 is a graph showing the EXAFS vibration extracted from the spectrum of FIG. 5 (broken line portion in FIG. 5) multiplied by a coefficient α. is there. Then, by subtracting the component of the sulfur oxide, that is, the EXAFS vibration of ZnSO ₄ multiplied by the coefficient α (FIG. 6) from the EXAFS vibration of the sulfur crosslinked rubber (FIG. 4), as shown in FIG. The EXAFS vibration of the sulfur crosslinked rubber excluding the component of ZnSO ₄ is obtained.

By the above procedure, the components of the sulfur oxide can be removed from the X-ray absorption spectrum of the sulfur crosslinked rubber. By performing various analyzes based on the spectrum after the removal, the state of sulfur in the crosslinked portion can be accurately analyzed.

The present invention will be specifically described based on examples, but the present invention is not limited to these.

(Preparation of sample)
In accordance with the following composition, materials other than sulfur and the vulcanization accelerator are charged into a 1.7 L Banbury mixer manufactured by Kobe Steel Co., Ltd. so that the filling ratio becomes 58%, and the temperature reaches 140 ° C. at 80 rpm. It was kneaded (step 1). To the kneaded product obtained in Step 1, sulfur and a vulcanization accelerator were added in the following proportions, and the mixture was vulcanized at 160 ° C. for 20 minutes to obtain a rubber sample (sulfur crosslinked rubber) (Step 2).

The compounding is 50 parts by mass of natural rubber, 50 parts by mass of butadiene rubber, 60 parts by mass of carbon black, 5 parts by mass of oil, 2 parts by mass of antioxidant, 2.5 parts by mass of wax, 3 parts by mass of zinc oxide, 2 parts by mass of stearic acid. Parts, 1.2 parts by mass of powdered sulfur, and 1 part by mass of a vulcanization accelerator. The materials used are as follows.
Natural rubber: TSR20
Butadiene rubber: BR150B manufactured by Ube Industries, Ltd.
Carbon black: Show Black N351 manufactured by Cabot Japan
Oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Antiaging agent: Nocrack 6C (N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd.
Zinc oxide: Ginrei R manufactured by Toho Zinc Co., Ltd.
Stearic acid: Camellia powder sulfur manufactured by NOF Corporation (containing 5% oil): 5% oil-treated powder sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. (soluble sulfur containing 5% by mass of oil)
Vulcanization accelerator: Noxeller CZ (N-cyclohexyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

(Example)
The obtained rubber sample and the standard sample were measured by the XAFS method near the sulfur K shell absorption edge to obtain an XAFS spectrum. The used standard sample, measurement conditions and analysis conditions of the XAFS method are the same as those in the above-described embodiment.

From the obtained XAFS spectrum, a component of sulfur oxide (zinc sulfate: ZnSO ₄ ) was removed by the same procedure as in the above-described embodiment. The EXAFS vibration was converted to a radial distribution function by Fourier transform. FIG. 8 shows the results. FIG. 8 also shows a spectrum before removal as a comparative example.

As shown in FIG. 8, the spectrum of the example had a profile different from that of the spectrum of the comparative example, and it was confirmed that the sulfur oxide component was removed.

Claims (3)

A measuring step of irradiating the sulfur-containing polymer composite material with high-intensity X-rays and measuring an X-ray absorption spectrum while changing the energy of the X-rays;
A removal step of removing a component of the sulfur oxides from the X-ray absorption spectrum of the sulfur-containing polymer composite seen including,
At least the XANES region of the X-ray absorption spectrum of the sulfur-containing polymer composite material is waveform-separated using the X-ray absorption spectra of a standard sample of a sulfur oxide and a plurality of compounds having a different number of sulfur linkages other than the sulfur oxide. By calculating the sulfur oxide ratio in the X-ray absorption spectrum of the sulfur-containing polymer composite material,
By subtracting the EXAFS vibration of the sulfur oxide from the EXAFS vibration of the sulfur-containing polymer composite based on the obtained ratio of the sulfur oxide, the sulfur oxide component can be obtained from the X-ray absorption spectrum of the sulfur-containing polymer composite. Chemical state measurement method to be removed . The energy range of scanning with the X-ray by a 2300～4000EV, chemical state measuring method according to claim 1 Symbol mounting to measure the X-ray absorption spectra of sulfur in the vicinity of the sulfur K-shell absorption edge. The chemical state measurement according to claim 1 or 2 , wherein the X-ray has a photon number of 10 ⁷ (photons / s) or more and a luminance of 10 ¹⁰ (photons / s / mrad ² / mm ² /0.1% bw) or more. Method.

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