JP2014238287A - Chemical state measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chemical state measurement method capable of accurately measuring a chemical state of rubber material, specifically variation (degradation state of rubber material) of a chemical state caused from a surface, such as degradation.SOLUTION: In the chemical state measurement method, an X ray is radiated to a sample formed by applying a free surface removal treatment to a new rubber material or a degraded rubber material while the energy is varied, the degradation state of the sample after the degradation is analyzed by comparing spectra acquired through measurement of X-ray absorbed amount with each other, and the degradation ratio between the polymer degradation level and the sulfur degradation level is determined. The chemical state of the rubber material is measured by employing a surface analysis method using an X ray.

Description

The present invention relates to a chemical state measurement method capable of accurately examining the chemical state of a rubber material.

X-ray absorption near the absorption edge of a specific element of interest using X-ray photoelectron spectroscopy (XPS method) or high-intensity X-ray as a method for examining the chemical state of rubber materials containing rubber components such as diene rubber A method using X-rays such as a method of measuring a spectrum (such as NEXAFS method) is known (see Patent Document 1).

The XPS method and the NEXAFS method are surface-sensitive measurement methods having a detection depth of from the surface to several tens of nanometers. For example, in order to examine the chemical state of a polymer, the XPA method uses a NEXAFS method such as a spectrum near the carbon 1s orbit. Then, a measurement focusing on the spectrum near the carbon K shell absorption edge is performed.

However, it is desired to provide an evaluation method that can measure the chemical state of the rubber material more accurately than conventional evaluation methods.

JP 2012-141278 A

An object of the present invention is to solve the above-mentioned problems and to provide a chemical state measurement method capable of accurately measuring a chemical state of a rubber material, in particular, a change in a chemical state generated from the surface such as deterioration (deterioration state of the rubber material). To do.

The present invention relates to a chemical state measurement method for measuring a chemical state of a rubber material by applying a surface analysis method using X-rays after performing a free sulfur removal treatment on the rubber material.

The free sulfur removal treatment preferably reduces the free sulfur content in the rubber material to 0.2% by mass or less.

It is preferable that the chemical state measurement method is a method for examining a change in the chemical state of the rubber material and measuring a deterioration state of the rubber material.

It is preferable that the said free sulfur removal process is what removes the free sulfur in the said rubber material using a solvent. Here, the solvent is preferably an organic solvent.

It is preferable that the said free sulfur removal process removes the free sulfur in the said rubber material using a solvent extraction method.

According to the present invention, the rubber material is a chemical state measurement method for measuring the chemical state of a rubber material by applying a surface analysis method using X-rays after performing free sulfur removal treatment on the rubber material. The exact chemical state of can be measured. Therefore, it is possible to accurately measure changes in the chemical state caused by the surface such as deterioration, and to evaluate the deterioration state of the rubber material.

XAFS spectrum near the sulfur K-shell absorption edge. XAFS spectrum near sulfur K shell absorption edge (before and after free sulfur removal treatment). The graph which showed the NEXAFS measurement result of the K-shell absorption edge of the carbon atom of the new blend rubber of natural rubber and butadiene rubber and the sample subjected to ozone degradation for 7 hours (before standardization). The graph which showed the NEXAFS measurement result of the K-shell absorption edge of the carbon atom of the new blend rubber of natural rubber and butadiene rubber and the sample subjected to ozone degradation for 7 hours (after normalization). The graph which showed the XAFS measurement result of the K-shell absorption edge of the sulfur atom of the sample which implemented the new blend rubber of natural rubber and butadiene rubber, and thermal oxygen degradation for one week (before standardization). The graph which showed the XAFS measurement result of the K-shell absorption edge of the sulfur atom of the sample which implemented the new blended rubber of natural rubber and butadiene rubber and thermal oxygen deterioration for one week (after normalization). The graph which showed the measurement result of the X-ray photoelectron spectrum in S2p (2p orbit of sulfur) of the polymeric material of the sample which implemented the new blend rubber of natural rubber and butadiene rubber, and thermal oxygen deterioration for one week. The graph which showed the measurement result of the X-ray photoelectron spectrum in S1s (1s orbit of sulfur) of the polymer material of the sample which implemented the new blend rubber of natural rubber and butadiene rubber, and thermal oxygen deterioration for one week.

The chemical state measuring method of the present invention is a method for measuring the chemical state of a rubber material by applying a surface analysis method using X-rays after performing a free sulfur removal treatment on the rubber material.

Known degradation factors for sulfur-crosslinked rubber materials such as vulcanized rubber include degradation of polymer molecular chains due to ultraviolet rays, oxygen, ozone, heat, etc., and degradation of sulfur cross-links. For this purpose, it is important to know how the polymer molecular chain and the sulfur cross-linked structure change due to which factors.

In this regard, a method has been proposed in which a sample is measured using the NEXAFS method, and the amount of oxygen, ozone, or the like combined with the rubber material is determined from the entire area of the X-ray absorption spectrum near the oxygen K-shell absorption edge. It cannot be determined whether it is bonded to a polymer portion or a sulfur cross-linking portion. In addition, a method for obtaining the sulfur bridge deterioration by calculating the ratio of the peak of the oxide bonded to the sulfur bridge to the total area of the S1s orbital spectrum obtained by the XPS method is conceivable. In this method, the deterioration of the sulfur cross-linking portion is required, and the cutting amount of the cross-linking portion directly related to the deterioration cannot be measured.

In contrast, sulfur-crosslinked rubber materials (polymer materials) are irradiated with X-rays and the X-ray absorption is measured while changing the energy of the X-rays. By using the deterioration analysis method for determining the deterioration ratio of the polymer deterioration and the sulfur crosslinking deterioration from the deterioration state, the respective deterioration ratios can be determined. For example, the degree of deterioration of a polymer is obtained from the X-ray absorption spectrum near the carbon K-shell absorption edge, and the degree of sulfur bridge deterioration is obtained from the change in the amount of S—S bonds in the X-ray absorption spectrum near the sulfur K-shell absorption edge. Thus, it is possible to provide an analysis method capable of measuring the degree of deterioration of each of the polymer and the sulfur cross-linking and determining which deterioration is progressing more.

Here, regarding the sulfur crosslinking deterioration of the analysis method, by obtaining an X-ray absorption spectrum using the XAFS method in the vicinity of the sulfur K-shell absorption edge, a peak attributed to the S—S bond is obtained as shown in FIG. The detected S—S bond is cleaved due to deterioration and the peak is reduced, so that the degree of sulfur cross-linking deterioration can be measured by the reduction rate. However, when rubber is vulcanized, there is a case where all of the sulfur does not react and remains in the rubber material. In this case, since the S—S bond of the sulfur cross-linked portion is not detected with high accuracy, the degree of deterioration of the sulfur cross-linking is reduced. It cannot be determined accurately.

In the present invention, before performing surface analysis such as NEXAFS method, XAFS method, and XPS method, a free sulfur removal treatment using a solvent or the like is performed in advance to remove free sulfur that does not form a sulfur bridge in a rubber material. Since the S—S bond of the sulfur cross-linked portion can be detected with high accuracy and not only the polymer portion but also the sulfur cross-linked portion can be accurately measured, the accurate chemical state of the rubber material can be measured. Therefore, an accurate chemical state can be measured using a NEXAFS spectrum, an XAFS spectrum, an XPS spectrum, and the like, and a deterioration state (degradation degree) can also be accurately measured by comparing spectra before and after deterioration.

Specifically, FIG. 2 shows an XAFS spectrum near the sulfur K-shell absorption edge for the rubber material before and after the free sulfur removal treatment. As shown, the spectrum after the free sulfur removal treatment is as follows. The S—S bond peak is smaller than the spectrum before the removal treatment. This is because free sulfur contained in the rubber material is removed before being subjected to the XAFS method, so that the S—S bond content of the free sulfur is reduced, and the S—S bond of the sulfur cross-linked portion is accurately detected. It is considered possible.

In the present invention, the rubber material is first subjected to a free sulfur removal treatment.
The rubber material used in the present invention is not particularly limited, and a conventionally known rubber composition can be used, and examples thereof include a rubber composition containing a rubber component and other compounding materials.

As rubber components, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), halogenated Examples thereof include diene rubbers such as butyl rubber (X-IIR) and styrene isoprene butadiene rubber (SIBR). The rubber component may contain one or more modifying groups such as hydroxyl groups and amino groups.

Furthermore, as the rubber component, a composite material in which the rubber component and one or more kinds of resins are combined can also be used. The resin is not particularly limited, and examples thereof include those widely used in the rubber industry field, and examples thereof include petroleum resins such as C5 aliphatic petroleum resins and cyclopentadiene petroleum resins.

Rubber materials include conventionally known rubbers such as fillers such as carbon black and silica, silane coupling agents, zinc oxide, stearic acid, anti-aging agents, waxes, oils, vulcanizing agents, vulcanization accelerators, and crosslinking agents. You may mix | blend the compound of a field | area suitably. Such a rubber material (rubber composition) can be produced using a known kneading method or the like. Examples of such rubber materials include tire rubber materials (tire rubber compositions).

As a free sulfur (sulfur that does not form sulfur crosslinks in the rubber material), any treatment method capable of removing free sulfur from the rubber material can be applied, and examples thereof include a method using a solvent. Examples of the free sulfur removal treatment using a solvent include a method in which a rubber material is wetted (impregnated) in a solvent under a predetermined condition such as room temperature and a heating state, and solvent extraction is performed using an extraction device such as a Soxhlet extractor. Examples include extraction methods (solvent extraction methods). Among these, extraction methods such as Soxhlet extraction are preferable, and Soxhlet extraction is particularly preferable because free sulfur can be efficiently removed.

As the Soxhlet extraction, an extraction operation by a Soxhlet extraction method according to JISK6229 can be performed. For example, an extraction flask provided at the bottom of a Soxhlet extractor is filled with a solvent (solvent), and a predetermined amount of rubber prepared as a test piece of an appropriate size in a paper or sintered glass container provided in the middle part. This can be done by putting the material and connecting a cooling tube at the top.

The extraction time such as Soxhlet extraction is not particularly limited as long as it can remove free sulfur and does not change the chemical state of the rubber, and may be appropriately set according to the constituent components of the rubber material applied to the present invention. For example, the extraction time for Soxhlet extraction is preferably 10 to 36 hours. If it is less than 10 hours, free sulfur may not be sufficiently removed, and if it exceeds 36 hours, rubber molecules that have deteriorated and become shorter may be removed. In addition, for example, the amount of free sulfur when using acetone soxhlet extraction is about 10% of the amount of sulfur compounded in the rubber material, and the deteriorated rubber material tends to have a smaller amount of free sulfur than the new one. It is in.

In the free sulfur removal treatment (wetting, extraction, etc.) using a solvent, an organic solvent is suitable as a usable solvent. Examples of the organic solvent include monohydric alcohols such as methanol, ethanol, propanol and butanol; polyhydric alcohols such as ethylene glycol, propylene glycol and butylene glycol; ketones such as acetone and methyl ethyl ketone; esters such as methyl acetate and ethyl acetate. Linear and cyclic ethers such as tetrahydrofuran and diethyl ether; polyethers such as polyethylene glycol; halogenated hydrocarbons such as dichloromethane, chloroform and carbon tetrachloride; hydrocarbons such as hexane, cyclohexane and petroleum ether; Aromatic hydrocarbons such as benzene and toluene; In addition, these can be used individually or in combination of 2 or more types.

In the free sulfur removal treatment in the present invention, the content of free sulfur in the rubber material is preferably reduced to 0.2% by mass or less, more preferably 0.1% by mass or less, and S- In order to measure the S bond with high accuracy, it is desirable to remove it.

In the present invention, a surface analysis method using X-rays is applied to the obtained sample (rubber material subjected to the removal treatment) after the rubber material is previously subjected to the free sulfur removal treatment. Such surface analysis methods include NEXAFS (Near Edge X-ray Absorption Fine Structure: X-ray absorption fine structure near the absorption edge) method, XAFS (X-FS), because the chemical state of the rubber material surface can be accurately measured. The ray absorption fine structure (X-ray absorption fine structure in the vicinity of absorption edge) method is preferable. By applying the surface analysis method to a sample from which free sulfur has been removed, an accurate chemical state can be examined. It is also possible to apply to each sample before and after deterioration, and to accurately check the deterioration state (deterioration degree) by comparing the peak intensity and area before and after deterioration.

For example, X-rays are irradiated while changing energy to samples prepared by free sulfur removal treatment on new and deteriorated rubber materials, and each spectrum obtained by measuring X-ray absorption is compared. Thus, the deterioration state of the sample after deterioration is analyzed, and the deterioration ratio of the polymer deterioration degree and the sulfur deterioration degree is determined. Specifically, by measuring the X-ray absorption spectrum near the absorption edge of a specific element, etc., by measuring a sample from which free sulfur has been removed, the degree of degradation of the polymer and the degree of sulfur crosslinking can be accurately measured. Analyze well, and determine the deterioration rate of polymer and sulfur cross-linking from the degree of deterioration obtained.

For example, the degradation state of the polymer portion is analyzed from the peak area of the X-ray absorption spectrum of the K-shell absorption edge of carbon atoms obtained by NEXAFS measurement, and the X-ray absorption of the K-shell absorption edge of sulfur atoms obtained by XAFS measurement The deterioration state of the sulfur cross-linked portion is analyzed from the peak area of the spectrum, and the deterioration rate of the polymer and the sulfur cross-link can be determined from the obtained degree of deterioration. The X-ray energy used differs between the vicinity of the carbon K-shell absorption edge and the vicinity of the sulfur K-shell absorption edge. Therefore, in general, a necessary energy range of continuous X-rays radiated from the synchrotron is cut out by a spectrometer and used for measurement. However, different spectrometers are used depending on the energy used.

The NEXAFS and XAFS methods require a continuous X-ray generator for the light source to scan with X-ray energy, and X-ray absorption with a high S / N ratio and S / B ratio is required to analyze detailed chemical states. It is necessary to measure the spectrum. Therefore, the X-ray emitted from the synchrotron has a brightness of at least 10 ¹⁰ (photons / s / mrad ² / mm ² /0.1% bw) and is a continuous X-ray source. And optimal for XAFS measurements. Note that bw represents the band width of X-rays emitted from the synchrotron.

The X-ray luminance (photons / s / mrad ² / mm ² /0.1% bw) is preferably 10 ¹⁰ or more, more preferably 10 ¹¹ or more. Although an upper limit is not specifically limited, It is preferable to use the X-ray intensity below the extent that there is no radiation damage.

Further, the number of photons (photons / s) of the X-ray is preferably 10 ⁷ or more, more preferably 10 ⁹ or more. Although an upper limit is not specifically limited, It is preferable to use the X-ray intensity below the extent that there is no radiation damage.

The energy range scanned using the X-ray is preferably 5000 eV or less, more preferably 4000 eV or less, and still more preferably 3500 eV or less. When it exceeds 5000 eV, there is a possibility that the degradation state analysis in the target polymer composite material cannot be performed. The lower limit is not particularly limited.

The measurement can be performed by, for example, a method in which photoelectrons are emitted by irradiating a sample placed in an ultra-high vacuum with X-rays, electrons flow from the ground to compensate for it, and the sample current is measured. Therefore, although it is sensitive to the surface, the conditions of the sample that can be measured include the fact that it does not emit gas in a vacuum and that it is electrically conductive. There has been little research on rubber samples that are likely to be removed and that are insulators.

In this regard, NEXAFS and XAFS are seeing excitation to unoccupied orbitals, and are greatly affected by the elements bound to the elements to be investigated. Therefore, it is possible to separate individual bonding states and to separate degradation factors. It can be used for analysis of polymer degradation.

The following three methods are typically used as NEXAFS and XAFS measurement methods. In the examples of the present invention, the NEXAFS method was performed using the electron yield method and the XAFS method was performed using the fluorescence method. However, the present invention is not limited to this, and various detection methods may be used. May be.

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

(Fluorescence method)
This is a method for detecting fluorescent X-rays generated when a sample is irradiated with X-rays. Examples of the detector include a Lytle detector and a semiconductor detector. In the case of the transmission method, when X-ray absorption measurement of an element having a small content in a sample is performed, the background is increased due to the X-ray absorption of an element having a small content and a large content, so that the S / B ratio is poor. It becomes a spectrum. On the other hand, in the fluorescence method (especially when an energy dispersive detector or the like is used), it is possible to measure only the fluorescent X-rays from the target element, so that the influence of the element having a large content is small. Therefore, it is effective when measuring an X-ray absorption spectrum of an element having a small content. In addition, since fluorescent X-rays have strong penetrating power (low interaction with substances), it is possible to detect fluorescent X-rays generated inside the sample. Therefore, this method is the most suitable method for obtaining bulk information after the transmission method.

(Electron yield method)
This is a method for detecting a current flowing when a sample is irradiated with X-rays. Therefore, the sample needs to be a conductive material. Since the polymer material is an insulator, until now, the X-ray absorption measurement of the polymer material has mostly used a sample with a sample placed on a substrate by vapor deposition or spin coating, but in the present invention, By processing (cutting) the rubber material to 100 μm or less, preferably 10 μm or less, more preferably 1 μm or less, and even more preferably 500 nm or less with a microtome, measurement with a high S / B ratio and S / N ratio can be realized.

Another characteristic of the electron yield method is that it is surface sensitive (information on the surface of the sample about several nm). When the sample is irradiated with X-rays, electrons escape from the element, but electrons have a strong interaction with the substance, so that the mean free path in the substance is short.

For example, it is possible to analyze the degree of polymer degradation (%) and the degree of sulfur cross-linking degradation (%) by measuring and analyzing the X-ray absorption spectrum of a sample prepared by subjecting a rubber material to a free sulfur removal treatment. This will be described below.

As a technique for obtaining the polymer degradation state in the sulfur-crosslinked rubber material by the NEXAFS method, for example, the necessary range of the K-shell absorption edge of the carbon atom is scanned in the X-ray energy range of 260 to 400 eV. The normalization constants α and β are calculated by the following (Equation 1-1) based on the X-ray absorption spectrum obtained by the above, and the K-shell absorption edge of the carbon atom corrected using the normalization constants α and β is calculated. There is a method of separating the waveform of the X-ray absorption spectrum and obtaining the degree of polymer degradation (%) by the following (Equation 1-2) using the obtained peak area attributed to the π ^* transition near 285 eV.
(Formula 1-1)
[Total area of X-ray absorption spectrum of measurement range in sample before deterioration] × α = 1
[Total area of X-ray absorption spectrum in the measurement range of the sample after deterioration] × β = 1
(Formula 1-2)
[1-[(Peak area of π ^* after degradation) × β] / [(Peak area of π ^* before degradation) × α]] × 100 = Polymer degradation degree (%)

Thereby, the deterioration degree (%) of the polymer (polymer part) after deterioration can be obtained, and the polymer partial deterioration rate can be analyzed. Here, in the method for obtaining the degree of polymer degradation, it is preferable that the energy of the X-ray is in the range of 260 to 350 eV. In the method for obtaining the degree of deterioration, the background is drawn by evaluating from the slope before the absorption edge before performing the operation of (Equation 1-1).

In the method for determining the degree of polymer degradation, the total area of the X-ray absorption spectrum in (Equation 1-1) is obtained by integrating the spectrum within the measurement range, and the energy range can be changed depending on the measurement conditions and the like. .

Regarding the method for determining the degree of polymer degradation, samples prepared by subjecting a new blend rubber of NR and BR and a degraded product subjected to ozone degradation for 7 hours (both sulfur cross-linked) to free sulfur removal treatment were used. A specific example will be described.

FIG. 3 shows the NEXAFS measurement results of the K-shell absorption edge of carbon atoms for these samples that have been subjected to the removal treatment. As shown in FIG. 3, in the deteriorated sample, the peak of π ^* near 285 eV is smaller than that of the new product, but it is difficult to measure the absolute value by the NEXAFS method. The reason is that subtle changes such as the distance of the sample from the light source affect the magnitude of the X-ray absorption spectrum. For the above reasons, the NEXAFS measurement result of the K-shell absorption edge of carbon atoms cannot be simply compared between samples.

Therefore, in order to compare the measured X-ray absorption spectra between samples, normalization was performed as follows (the X-ray absorption spectra of each sample were corrected so that they could be directly compared). Since the X-ray absorption amount of the carbon shell does not change before and after deterioration, the above (Equation 1-1) is used to normalize the peak area of the K-shell absorption edge of the carbon atom to 1. That is, first, normalization constants α and β are calculated based on (Formula 1-1) for the X-ray absorption spectrum before normalization, and then the spectrum obtained by multiplying the X-ray absorption spectrum before normalization by α and β is obtained. By correcting (normalizing), π ^* peaks between samples can be directly compared.

FIG. 4 shows the spectrum (NEXAFS) of the K-shell absorption edge of the carbon atom after normalization obtained as described above. The degree of polymer degradation is determined from the normalized spectrum using the above (Equation 1-2). The degree of polymer degradation is the rate of decrease in the peak of π ^* from before degradation to after degradation, and indicates the degradation rate (%) of the polymer chain in the sample.

In the above method for determining the degree of polymer deterioration, the degree of polymer deterioration can be determined in the same manner even if the peak intensity is used instead of the peak area in (Equation 1-2).

In the above description, ozone-degraded products are described. However, oxygen-degraded products and degraded products degraded by both ozone and oxygen can be analyzed by the same method, and the degree of degradation of the polymer chain can be obtained.

The aforementioned polymer degradation state can be analyzed using, for example, the BL12 beam line of the Saga Kyushu Synchrotron Light Research Center.

Furthermore, as a technique for obtaining the deterioration state of sulfur crosslinking in a rubber material crosslinked with XAFS, for example, the required range of the K-shell absorption edge of the sulfur atom in the X-ray energy range of 2460 to 3200 eV is used. Based on the X-ray absorption spectrum obtained by scanning, the normalization constants γ and δ are calculated by the following (Equation 1-3), and the K-shell absorption of sulfur atoms corrected using the normalization constants γ and δ. An X-ray absorption spectrum at the end is waveform-separated, and the obtained peak area attributed to the S—S bond in the vicinity of 2472 eV is used to obtain a sulfur crosslinking deterioration degree (%) by the following (Equation 1-4). It is done.
(Formula 1-3)
[Total area of X-ray absorption spectrum in measurement range in sample before deterioration] × γ = 1
[Total area of X-ray absorption spectrum in the measurement range of the sample after deterioration] × δ = 1
(Formula 1-4)
[1-[(Peak area of S—S bond after deterioration) × δ] / [(Peak area of S—S bond before deterioration) × γ]] × 100 = Degree of sulfur crosslinking deterioration (%)

Thereby, the deterioration degree (%) of the sulfur bridge | crosslinking part after deterioration is obtained, and the deterioration rate of sulfur bridge | crosslinking can be analyzed. Here, in the method for determining the degree of sulfur cross-linking deterioration, it is preferable that the energy of the X-ray is in the range of 2460 to 2500 eV. In the method for obtaining the degree of deterioration, the background is obtained by evaluating from the slope before the absorption edge before performing the operation of (Equation 1-3).

In the method for determining the degree of sulfur crosslinking deterioration, the total area of the X-ray absorption spectrum in (Equation 1-3) is obtained by integrating the spectrum within the measurement range, and the energy range can be changed depending on the measurement conditions and the like. .

Regarding the method for determining the degree of sulfur cross-linking degradation, a new sample of blended rubber of NR and BR and a sample made by applying free sulfur removal treatment to each of the deteriorated products subjected to thermal oxygen deterioration for one week (both sulfur cross-linking) are used. A specific example will be described.

FIG. 5 shows the XAFS measurement results of the K-shell absorption edge of sulfur atoms for these samples that have been subjected to the removal treatment. As shown in FIG. 5, in the deteriorated sample, the peak corresponding to the S—S bond (sulfur-sulfur bond) near 2472 eV is decreased, and the peak corresponding to SOx (sulfur oxide) is increased. This indicates that the S—S bond is cleaved and oxygen is bonded to the portion, but the XAFS method is difficult to measure the absolute value. The reason is that subtle changes such as the distance of the sample from the light source affect the magnitude of the X-ray absorption spectrum. For the above reasons, the XAFS measurement result of the K-shell absorption edge of sulfur atoms cannot be simply compared between samples.

Therefore, in order to compare the measured X-ray absorption spectra between samples, normalization was performed as follows (the X-ray absorption spectra of each sample were corrected so that they could be directly compared). Since the amount of X-ray absorption of the sulfur shell does not change before and after deterioration, the above (Equation 1-3) is used to normalize the peak area of the K-shell absorption edge of sulfur atoms to 1. That is, first, normalization constants γ and δ are calculated based on (Formula 1-3) for the X-ray absorption spectrum before normalization, and then the spectrum obtained by multiplying the X-ray absorption spectrum before normalization by γ and δ is obtained. By correcting (normalizing), the S—S bond peak between samples can be directly compared.

The spectrum (XAFS) of the K-shell absorption edge of the sulfur atom after normalization thus obtained is shown in FIG. The degree of sulfur cross-linking degradation is determined from the normalized spectrum using the above (Equation 1-4). The degree of sulfur cross-linking deterioration is the rate of decrease of the peak of S—S bonds from before deterioration to after deterioration, and indicates the deterioration rate (%) of sulfur cross-linking in the sample.

In the method for obtaining the degree of sulfur cross-linking deterioration, the degree of sulfur cross-linking deterioration can be obtained in the same manner even if the peak intensity is used in place of the peak area in (Equation 1-4).

In the above description, oxygen-degraded products are described. However, ozone-degraded products and degraded products degraded by both ozone and oxygen can be analyzed by the same method, and the degree of deterioration of sulfur crosslinking can be obtained.

The deterioration state of the above-mentioned sulfur bridge can be analyzed using, for example, the B branch of BL27SU of SPring-8.

In addition, XPS (X-ray photoelectron spectroscopy) is also effective as a surface analysis method in the present invention, and an accurate chemical state can be examined by applying the XPS method to a sample from which free sulfur has been removed. It is also possible to apply to each sample before and after deterioration, and to accurately check the deterioration state (deterioration degree) by comparing the peak intensity and area before and after deterioration.

Specifically, it is possible to determine the degradation state of the polymer and the degradation state of the sulfur bridge by a degradation analysis method that irradiates a sulfur-crosslinked rubber material with X-rays of constant energy and measures the excited and emitted photoelectrons. it can. Further, by obtaining the deterioration state of the polymer and the deterioration state of the sulfur bridge, the respective deterioration ratios can be analyzed.

For example, each spectrum obtained by irradiating a new and deteriorated rubber material with X-rays of constant energy to samples prepared by removing free sulfur and measuring excited and emitted photoelectrons. By comparing, the deterioration state of the sample after deterioration is analyzed, and the deterioration ratio of the polymer deterioration degree and the sulfur deterioration degree is determined. Specifically, using a method that measures the X-ray photoelectron spectrum of a specific orbit, etc., by measuring the sample from which free sulfur has been removed, the degree of deterioration of the polymer and the degree of deterioration of the sulfur cross-link are analyzed accurately. The deterioration rate of the polymer and sulfur cross-linking is determined from the obtained degree of deterioration.

For example, the degradation state of the polymer portion is analyzed from the peak area of the spectrum near the carbon 1s orbit obtained by XPS measurement, and the degradation state of the sulfur bridge portion is analyzed from the peak area of the spectrum corresponding to the sulfur S2p and S1s orbitals. And the deterioration rate of a polymer and sulfur bridge | crosslinking can be determined from each obtained deterioration degree.

Here, as a technique for irradiating a sulfur-crosslinked rubber material with constant energy X-rays and measuring excited and emitted photoelectrons, X-ray photoelectron spectroscopy (XPS) and the like can be specifically mentioned. In addition, it can be measured using an XPS method using a normal Al Kα ₁ line (1486.6 eV), a hard X-ray photoelectron spectroscopy (HAX-PES: Hard X-ray Photoluminescence Spectroscopy) and the like.

As a technique for measuring the degradation state of sulfur crosslinking by the XPS method, for example, X-rays in which photoelectrons excited and emitted by irradiating X-rays with a constant energy are dispersed and the photoelectron intensity corresponding to sulfur S2p is measured. There is a method (Method 1) in which a photoelectron spectrum is waveform-separated and a sulfur crosslinking deterioration degree (%) is obtained by the following (Formula 2-1) using a peak area attributed to the obtained sulfur oxide.
(Formula 2-1)
(Peak area attributed to sulfur oxide of S2p) / (Total peak area related to S2p) × 100 = Deterioration degree of sulfur crosslinking (%)
Thereby, the deterioration degree (%) of the sulfur bridge | crosslinking part after deterioration is obtained, and a deterioration rate can be analyzed.

In Method 1, the total peak area related to S2p in (Equation 2-1) above is obtained by integrating the spectrum within the measurement range, and the energy range can be changed depending on the measurement conditions and the like.

In the above method 1, the energy range of the constant energy X-ray used is preferably 150 to 200 eV, more preferably 155 to 180 eV, in that the area of the peak related to S2p (sulfur 2p orbit) can be measured. It is.

Using Method 1 above, an example using a sample prepared by subjecting a new blend rubber of NR and BR and a deteriorated product (both sulfur cross-linked) subjected to thermal oxygen deterioration for one week to free sulfur removal treatment. This will be specifically described.

FIG. 7 shows the measurement result of the X-ray photoelectron spectrum in S2p (sulfur 2p orbit) for these samples after the removal treatment. As shown in FIG. 7, in the deteriorated sample, the peak corresponding to the S—S bond decreases and the peak corresponding to the sulfur oxide (SOx) increases. Therefore, the X-ray photoelectron spectrum at S2p of the deteriorated product is waveform-separated into S—S bond and SOx peaks, and the peak area attributed to SOx and the total peak area related to S2p are expressed by the above (formula 2-1). The degree of sulfur cross-linking degradation (%) is required.

Here, since the S2p orbital is spin orbital splitting, two peaks appear for one assignment, and the peak of sulfur oxide (SOx) is considered to be overlapped with a plurality of peaks having different valences. Considering in principle, as shown in FIG. 7, it is possible to largely separate the peak attributed to SS and the peak attributed to SOx.

In the above method 1, the sulfur cross-linking degradation degree can be obtained in the same manner even when the peak intensity is used instead of the peak area in (Equation 2-1).

Moreover, as a technique for measuring the degradation state of sulfur crosslinking by the HAX-PES method, for example, photoelectrons excited and emitted by irradiating X-rays with a constant energy are dispersed, and the photoelectron intensity corresponding to the sulfur S1s is obtained. There is a method (Method 2) for separating the waveform of the measured X-ray photoelectron spectrum and obtaining the degree of sulfur cross-linking degradation (%) by the following (Formula 2-2) using the peak area attributed to the obtained sulfur oxide. It is done.
(Formula 2-2)
(Peak area attributed to sulfur oxide of S1s) / (total peak area related to S1s) × 100 = sulfur cross-linking deterioration degree (%)
Thereby, the deterioration degree (%) of the sulfur bridge | crosslinking part after deterioration is obtained, and a deterioration rate can be analyzed.

In particular, by using the HAX-PES method, there is an advantage that an S1s orbit that cannot be measured by a normal XPS method can be measured. That is, in the normal XPS method, the spectrum of the S2p orbit is measured. However, since the energy of the X-ray used is low, the detection depth is from the surface to several nm, whereas in the HAX-PES method, Since the S1s trajectory can be measured and the energy of X-rays used is high, the detection depth is from the surface to several tens of nm. Therefore, since a sulfur compound bloom occurs on the extreme surface of the rubber material, there is a concern that the XPS method for measuring the extreme surface may affect the measurement result. However, the HAX-PES method has a deep detection depth and the influence of bloom. It is thought not to receive. Therefore, according to the HAX-PES method, it is possible to analyze the deterioration of sulfur crosslinking particularly in the bulk (inside) of the rubber material.

Even when the spectrum of the S2p orbit is measured by the normal XPS method, it is also possible to obtain a measurement result in which the influence of bloom is reduced by measuring after removing the extreme surface by argon ion etching or the like. .

In Method 2, the total peak area of sulfur corresponding to S1s in (Equation 2-2) above is obtained by integrating the spectrum within the measurement range, and the energy range can be changed depending on the measurement conditions and the like.

In the method 2, the X-ray energy range of constant energy used is preferably 4 to 10 kev from the viewpoint that the area of the peak related to sulfur S1s (sulfur 1s orbit) can be measured.

Regarding method 2 above, an example using a sample prepared by subjecting a new blend rubber of NR and BR and a deteriorated product subjected to thermal oxygen deterioration for one week (both sulfur cross-linked) to free sulfur removal treatment was used. This will be specifically described.

FIG. 8 shows the measurement results of the X-ray photoelectron spectrum in S1s (sulfur 1s orbit) for these samples after the removal treatment. As shown in FIG. 8, in the deteriorated sample, the peak corresponding to the S—S bond decreases and the peak corresponding to the sulfur oxide (SOx) increases. Therefore, the X-ray photoelectron spectrum in S1s of the deteriorated product is waveform-separated into S—S bond and SOx peaks, and the peak area attributed to SOx and the total peak area related to sulfur are represented by the above (formula 2-2). The degree of sulfur cross-linking degradation (%) is required.

Here, although the peak of sulfur oxide (SOx) is considered to be a plurality of peaks having different valences, in principle, as shown in FIG. It is possible to separate into peaks attributed to SOx.

In the above method 2, the degree of sulfur cross-linking degradation can be obtained in the same manner even when the peak intensity is used instead of the peak area in (Equation 2-2).

In addition, in the above methods 1 and 2, oxygen-degraded products are described, but ozone-degraded products and degraded products degraded by both ozone and oxygen can be analyzed by the same method, and the degree of deterioration of sulfur crosslinking can be obtained. Is possible.

The deterioration state of the above-mentioned sulfur bridge can be analyzed using, for example, a normal XPS apparatus such as AXIS Ultra manufactured by Kratos, or a HAX-PES apparatus attached to the SPring-8 BL46XU beam line.

Furthermore, in the above degradation analysis method, for example, the contribution ratio of polymer degradation and sulfur cross-linking degradation can be calculated by the following (Equation 3).
(Formula 3)
[Polymer degradation degree (%)] / [Sulfur crosslinking degradation degree (%)] = Contribution rate of polymer degradation and sulfur crosslinking degradation

In other words, the degree of polymer degradation (%) and the degree of sulfur crosslinking degradation (%), which indicate the degree of degradation of each polymer and sulfur crosslinking, using the method for obtaining the degree of polymer degradation or the method for obtaining the degree of sulfur crosslinking degradation as described above. By determining the ratio (ratio), it is possible to determine which deterioration is progressing more. Specifically, in the above (Equation 3), when the contribution rate of polymer degradation and sulfur cross-linking degradation> 1, the progress of polymer degradation is larger, and the contribution rate of polymer degradation and sulfur cross-linking degradation <1. In this case, it can be judged that the progress of sulfur cross-linking degradation is larger. For this reason, by adopting the above-described degradation analysis method for the rubber material subjected to the free sulfur removal treatment, a more effective countermeasure against degradation can be established than before.

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

<Examples and Comparative Examples>
(Rubber material)
In accordance with the following blending contents, materials other than sulfur and vulcanization accelerator were charged into a 1.7 L Banbury mixer manufactured by Kobe Steel Co., Ltd. so that the filling rate was 58%, and until reaching 140 ° C. at 80 rpm. Kneaded (Step 1). Sulfur and a vulcanization accelerator were added to the kneaded material obtained in step 1 in the following composition, and vulcanized at 160 ° C. for 20 minutes to obtain a rubber material (step 2).

(Combination)
Natural rubber 50 parts by mass, butadiene rubber 50 parts by mass, carbon black 60 parts by mass, oil 5 parts by mass, anti-aging agent 2 parts by mass, wax 2.5 parts by mass, zinc oxide 3 parts by mass, stearic acid 2 parts by mass, powder 1.2 parts by mass of sulfur and 1 part by mass of vulcanization accelerator.
The materials used are as follows. The deteriorated rubber material is deteriorated under the following conditions.
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.
Anti-aging agent: NOCRACK 6C (N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Wax: Ozoace 0355 manufactured by Nippon Seiwa Co., Ltd.
Zinc oxide: Silver candy R made by Toho Zinc Co., Ltd.
Stearic acid: Koji powder sulfur manufactured by NOF Corporation (containing 5% oil): 5% oil-treated powder sulfur manufactured by Tsurumi Chemical Co., Ltd. (soluble sulfur containing 5% by mass of oil)
Vulcanization accelerator: Noxeller CZ (N-cyclohexyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.
(Deterioration conditions)
Ozone degradation: 40 ° C, 50 pphm (24 hours)
Oxygen degradation: 80 ° C in air (168 hours)

After the pretreatment described in Tables 1 and 2 was performed on the produced rubber material (new article, deteriorated article), NEXAFS measurement was performed in the vicinity of the carbon K-shell absorption edge for each sample after treatment to obtain a NEXAFS spectrum. Further, XAFS measurement was performed in the vicinity of the sulfur K-shell absorption edge to obtain an XAFS spectrum, and further XPS measurement was performed to obtain an XPS spectrum.

<NEXAFS measurement>
Using NEXAFS, the degree of polymer degradation (%) was measured by performing the following analysis for each sample before and after degradation.
(Device used)
NEXAFS: NEXAFS measurement system (measurement conditions) attached to the BL12 beam line at Saga Prefectural Kyushu Synchrotron Light Research Center
Luminance: 5 × 10 ¹² photons / s / mrad ² / mm ² /0.1% bw
Number of photons: 2 × 10 ⁹ photons / s
Spectrometer: Grating spectrometer Measuring method: Electron yield method

(Polymer degradation analysis)
The X-ray energy was scanned in the range of 260 to 400 eV to obtain an X-ray absorption spectrum of the K-shell absorption edge of the carbon atom. Normalization constants α and β were calculated from (Equation 1-1) based on the range of 260 to 350 eV, which is a necessary range in this spectrum, and the spectrum was normalized (corrected) using these constants. The normalized spectrum was separated into waveforms, and the degree of polymer degradation (%) was determined from (Equation 1-2) based on the peak area attributed to the π ^* transition near 285 eV.

<XAFS measurement>
Using XAFS, the degree of sulfur cross-linking deterioration (%) was measured for each sample before and after deterioration by carrying out the following analysis.
(Device used)
XAFS: SPring-8 BL27SU B-branch XAFS measurement system (measurement conditions)
Luminance: 1 × 10 ¹⁶ photons / 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 method

(Sulfur crosslinking degradation analysis 1)
The X-ray energy was scanned in the range of 2460 to 3200 eV to obtain an X-ray absorption spectrum of the K-shell absorption edge of the sulfur atom. Normalization constants γ and δ were calculated from (Equation 1-3) based on the range of 2460 to 2500 eV, which is a necessary range in this spectrum, and the spectrum was normalized (corrected) using these constants. The normalized spectrum was subjected to waveform separation, and the sulfur bridge deterioration degree (%) was determined from (Equation 1-4) based on the peak area attributed to the SS bond near 2472 eV.

<XPS measurement>
Using XPS, the degree of sulfur cross-linking deterioration (%) was measured for each sample after deterioration by carrying out the analysis of Method 1 below.
(Device used)
XPS: AXIS Ultra manufactured by Kratos
(Measurement condition)
Measurement light source: Al (monochromator)
Irradiation X-ray energy: 1486 eV
Measurement output: 20 kV x 10 mA
Measuring element and orbit: S2p
Binding energy: 163.6 eV (S2p1 / 2), 162.5 eV (S2p3 / 2)

(Sulfur crosslinking degradation analysis 2 (Method 1))
The photoelectrons excited and emitted by irradiating the above-mentioned X-rays having a constant energy were dispersed to obtain an X-ray photoelectron spectrum in which the photoelectron intensity corresponding to the sulfur S2p was measured. In the range of 160 to 175 eV of this spectrum, waveforms are separated into peaks corresponding to S—S bonds near 164 eV and SOx near 168 eV, respectively, and the peak area attributed to the obtained sulfur oxide and the range of 160 to 175 eV The degree of sulfur crosslinking deterioration (%) was determined from (Equation 2-1) using the total peak area of sulfur.

(Contribution analysis of polymer degradation and sulfur crosslinking degradation)
Applying the polymer degradation degree obtained in the above-mentioned polymer degradation degree analysis and the sulfur crosslinking degradation degree obtained in 1 or 2 to (Equation 3), polymer degradation and sulfur crosslinking The contribution rate of deterioration was calculated.

The results obtained in the above-described polymer degradation analysis and sulfur crosslinking degradation analysis 1 are shown in Table 1, and the results obtained in the above-described polymer degradation analysis and sulfur crosslinking degradation analysis 2 are shown in Table 2, respectively.

After removing free sulfur in the rubber material in advance, surface analysis using NEXAFS, XAFS, XPS, etc. makes it possible to accurately measure not only polymer degradation but also sulfur cross-linking degradation. The effectiveness of the evaluation method was proved.

Claims (6)

A chemical state measurement method for measuring the chemical state of a rubber material by applying a surface analysis method using X-rays after subjecting the rubber material to a free sulfur removal treatment. 2. The chemical state measuring method according to claim 1, wherein the free sulfur removal treatment reduces the free sulfur content in the rubber material to 0.2% by mass or less. The chemical state measuring method according to claim 1 or 2, wherein a change in the chemical state of the rubber material is examined to measure a deterioration state of the rubber material. The chemical state measuring method according to any one of claims 1 to 3, wherein the free sulfur removal treatment removes free sulfur in the rubber material using a solvent. The chemical state measuring method according to claim 4, wherein the solvent is an organic solvent. The chemical state measurement method according to any one of claims 1 to 5, wherein the free sulfur removal treatment removes free sulfur in the rubber material using a solvent extraction method.

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