Method for evaluating the degree of oxidation of a specimen

Abstract

To provide a method for evaluating the degree of oxidation of an oxidized polymer material.SOLUTION: When a standard piece made of a non-oxidized polymer material is measured by a chemiluminescence method while being heated in an oxygen-containing atmosphere to obtain a first integrated emission amount A, and a specimen made of the oxidized polymer material is measured by the chemiluminescence method while being heated in an oxygen-containing atmosphere to obtain a second integrated emission amount B, the degree of oxidation of the specimen is evaluated on the basis of an emission change rate R=(A-B) / A.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for assessing the degree of oxidation of a test piece. [Background technology]

[0002] Polymer materials such as resins are used in a variety of products as raw materials because they are lightweight yet have a certain degree of mechanical strength. Meanwhile, against the backdrop of social issues such as the destruction of the marine environment by microplastics, there is a social demand for the reuse and recycling of products made from polymer materials in order to reduce the amount of plastic waste. Generally, in the recycling of waste products made from polymer materials, recycled products are manufactured using a blend of ground waste products and virgin materials as the main raw material.

[0003] Polymeric materials contained in waste products, etc., are generally subject to oxidative degradation. On the other hand, recycled products may be required to have properties such as weather resistance and heat resistance depending on their intended use. Therefore, it is necessary to understand in advance the degree of oxidation of the pulverized waste products, etc., that serve as raw materials for recycled products, so that the recycled products meet the required properties, such as weather resistance. Methods using Raman spectroscopy (Patent Document 1) and microwave irradiation (Patent Document 2) have been proposed for evaluating the degree of degradation of polymeric materials. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-273334 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-148627 Summary of the Invention [Problem to be solved by the invention]

[0005] The evaluation methods in Patent Documents 1 and 2 simply evaluate the degree of degradation of polymeric materials, but are not methods for evaluating the degree of oxidation of oxidized polymeric materials. In other words, at this stage, no specific methods for evaluating the degree of oxidation of oxidized polymeric materials are known.

[0006] Therefore, an object of the present invention is to provide a method for evaluating the degree of oxidation of an oxidized polymeric material. [Means for solving the problem]

[0007] As a result of extensive research, the inventors of the present application have discovered that the degree of oxidation of a test piece made of an oxidized polymeric material can be evaluated by measuring the integrated amount of light emitted by a test piece made of an oxidized polymeric material using a chemiluminescence method while heating the test piece in an oxygen-containing atmosphere, and comparing this integrated amount of light emitted with the integrated amount of light emitted by measuring a standard piece made of the same unoxidized polymeric material under similar conditions, and have completed the present invention.

[0008] That is, the present invention provides a first evaluation method, Provided is a method for evaluating the degree of oxidation of a test piece based on the rate of change in the amount of light emitted, R=(AB) / A, where A is a first integrated amount of light emitted when a standard piece made of an unoxidized polymeric material is measured by a chemiluminescence method while being heated in an oxygen-containing atmosphere, and B is a second integrated amount of light emitted when a test piece made of an oxidized polymeric material is measured by a chemiluminescence method while being heated in an oxygen-containing atmosphere. [Effects of the Invention]

[0009] According to the present invention, a method for evaluating the degree of oxidation of an oxidized polymeric material can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] 10 is a graph showing the change over time in the luminescence intensity of standard piece Y. [Figure 2] 10 is a graph showing the correlation between the amount of oxygen and the integrated amount of light emitted in standard pieces X and Y. DETAILED DESCRIPTION OF THE INVENTION

[0011] The evaluation method according to this embodiment of the present invention is a method for evaluating the degree of oxidation of a test piece based on the rate of change in the amount of light emitted, R=(AB) / A, where A is the first integrated amount of light emitted when a standard piece made of an unoxidized polymeric material is measured by chemiluminescence while being heated in an oxygen-containing atmosphere, and B is the second integrated amount of light emitted when a test piece made of the oxidized polymeric material is measured by chemiluminescence while being heated in an oxygen-containing atmosphere.

[0012] Specifically, the evaluation method of this embodiment is carried out as follows.

[0013] First, a standard piece made of an unoxidized polymeric material is prepared. Here, the standard piece made of an unoxidized polymeric material refers to a sample in the least oxidized and degraded state available to the evaluator attempting to evaluate the degree of oxidation of the test piece described below. Specifically, it is a raw material pellet or an unused product manufactured using the raw material pellet. Next, the weight Wa1 of the standard piece made of the unoxidized polymeric material is measured. The standard piece made of the unoxidized polymeric material is then heated in an oxygen-containing atmosphere and measured using a chemiluminescence method to obtain a first integrated luminescence amount A. Finally, the weight Wa2 of the standard piece after the measurement is measured. During this measurement, oxidative degradation of the standard piece occurs, and luminescence occurs. After the luminescence intensity peaks, the luminescence gradually decreases and ends. The time integral of the luminescence intensity from the start of the measurement to the end of the luminescence is defined as the first integrated luminescence amount A', and A' / Wa1 is defined as the first integrated luminescence amount A. This first integrated luminescence amount A' corresponds to the total amount of unoxidized polymeric material in the standard piece. In order to terminate the luminescence during the measurement within a certain measurement time, it is preferable that the weight (Wa1) of the standard piece before the measurement be as small as possible. Specifically, the weight of the standard piece before the measurement is preferably 50 mg or less, more preferably 10 mg or less or 2 mg or less. The heating temperature during the measurement is 180°C or higher. The heating temperature during the measurement is preferably 350°C or higher, more preferably 500°C or higher at which the standard piece is almost completely oxidized and decomposed. The atmosphere during the measurement may be any atmosphere containing oxygen, preferably pure oxygen or air. The atmosphere during the measurement may also be an atmosphere filled with a mixed gas such as oxygen and an inert gas. The measurement may be performed in a closed system such as a sealed cell or an open system. When the measurement is performed in a closed system such as a sealed cell, the amount of oxygen in the closed system must be sufficient to prevent depletion due to reaction with the standard piece. When the measurement is performed in an open system, it is preferable to set the flow rate of the atmospheric gas to 50 ml / min or less to suppress evaporation of decomposition products derived from the standard piece.

[0014] A test piece made of the oxidized polymer material is also prepared. The test piece made of the oxidized polymer material is made of the same polymer material as the standard specimen made of the unoxidized polymer material, but is a sample in a more oxidized and deteriorated state. Next, the weight Wb1 of the test piece made of the oxidized polymer material is measured. The test piece made of the oxidized polymer material is then heated in an oxygen-containing atmosphere and measured using a chemiluminescence method to obtain a second integrated luminescence amount B. During this measurement, the test piece undergoes oxidative degradation, resulting in luminescence. After the luminescence intensity peaks, the luminescence gradually fades and then ceases. Finally, the weight Wb2 of the test piece after the measurement is completed is measured. The time integral of the luminescence intensity from the start of this measurement to the end of the luminescence is defined as the second integrated luminescence amount B', and B' / Wb1 is defined as the second integrated luminescence amount B. This second integrated luminescence amount B' corresponds to the total amount of unoxidized portions of the polymer material of the test piece. This second integrated luminescence amount B' corresponds to the total amount of unoxidized portions of the polymer material of the test piece. Because the test piece has less unoxidized portions than the standard piece, the second integrated luminescence amount B is smaller than the first integrated luminescence amount A. As with the standard piece, the weight Wb1 of the test piece before the measurement is preferably as small as possible. Specifically, the weight of the test piece is preferably 50 mg or less, more preferably 10 mg or less or 2 mg or less. The heating temperature in the measurement is 180°C or higher. The heating temperature in the measurement is preferably 350°C or higher, more preferably 500°C or higher, at which point the standard piece is almost completely oxidized and decomposed. The atmosphere during the measurement may be any atmosphere containing oxygen, preferably pure oxygen or air. The atmosphere during the measurement may also be an atmosphere filled with a mixed gas such as oxygen and an inert gas. The measurement may be performed in a sealed system such as a sealed cell, or in an open system. When the measurement is performed in a sealed system such as a sealed cell, the amount of oxygen in the sealed system must be sufficient to prevent it from being depleted by reaction with the standard piece. When the above measurement is carried out in an open system, it is desirable to keep the flow rate of the ambient gas at 50 ml / min or less in order to suppress the evaporation of decomposition products derived from the standard specimen.

[0015] Finally, the rate of change in the amount of light emitted (R = (AB) / A) is calculated based on the first accumulated amount of light emitted (A) and the second accumulated amount of light emitted (B) obtained in the above measurement, and the degree of oxidation of the test piece can be evaluated as a numerical value based on this rate of change in the amount of light emitted (R).

[0016] Note that, instead of the first integrated amount of luminescence A, the corrected first integrated amount of luminescence Acol=A' / (Wa1-Wa2) may be used to calculate the rate of change R in the amount of luminescence. Furthermore, instead of the first integrated amount of luminescence A, the corrected first integrated amount of luminescence Acol'=A' / Wa2 may be used to calculate the rate of change R in the amount of luminescence. Additionally, if the area of ​​the standard piece before measurement is Was1 and the area of ​​the standard piece after measurement is Was2, then instead of the first integrated amount of luminescence A, any of the first integrated amount of luminescence A=A' / Was1, the corrected first integrated amount of luminescence Acols=A' / (Was1-Was2), or the corrected first integrated amount of luminescence Acol'=A' / Was2 may be used to calculate the rate of change R in the amount of luminescence. From the viewpoint of determining the degree of oxidation more accurately, it is preferable to use the corrected first integrated amount of light emission Acol=A' / (Wa1-Wa2) instead of the first integrated amount of light emission A to calculate the rate of change R in the amount of light emission.

[0017] Similarly, instead of the second integrated amount of light emission B, the corrected second integrated amount of light emission Bcol=B' / (Wb1-Wb2) may be used to calculate the rate of change R in the amount of light emission. Furthermore, instead of the second integrated amount of light emission B, the corrected second integrated amount of light emission Bcol'=B' / Wb2 may be used to calculate the rate of change R in the amount of light emission. Additionally, if the area of ​​the test piece before measurement is Wbs1 and the area of ​​the test piece after measurement is Wbs2, then instead of the second integrated amount of light emission B, any of the second integrated amount of light emission B=B' / Wbs1, the corrected second integrated amount of light emission Bcols=B' / (Wbs1-Wbs2), or the corrected second integrated amount of light emission Bcol'=B' / Wbs2 may be used to calculate the rate of change R in the amount of light emission. From the viewpoint of determining the degree of oxidation more accurately, it is desirable to use the corrected second integrated amount of light emission Bcol=B' / (Wb1-Wb2) instead of the second integrated amount of light emission B to calculate the rate of change R in the amount of light emission.

[0018] In the above measurement, the time integral values ​​of the luminescence intensity from the start of measurement for the standard piece and test piece to the end of luminescence were defined as the first integrated luminescence yield A' and the second integrated luminescence yield B', but the present invention is not limited to this, and the time integral values ​​of the luminescence intensity from the start of measurement for the standard piece and test piece to the point at which the luminescence intensity reaches its peak may also be defined as the first integrated luminescence yield A' and the second integrated luminescence yield B'.

[0019] In the above evaluation, the degree of oxidation of the test piece was evaluated based on the calculated rate of change in luminescence intensity R = (AB) / A, but the present invention is not limited to this. Specifically, the above measurement may be performed on a standard piece with a sufficient amount of oxygen in multiple atmospheres with gradually increasing amounts of oxygen to obtain a calibration curve showing the correlation between the amount of oxygen and the integrated luminescence intensity, and the difference AB between the first integrated luminescence intensity A and the second integrated luminescence intensity B obtained in the above measurements for the standard piece and the test piece may be introduced into the correlation equation for the calibration curve to calculate the amount of oxygen and the oxygen ratio in the unoxidized portion of the test piece, thereby evaluating the degree of oxidation of the test piece.

[0020] Furthermore, prior to the above-mentioned chemiluminescence measurement of the test piece, the test piece may be pretreated by heating it in an inert gas atmosphere such as nitrogen gas until luminescence ceases. The heating in this pretreatment is preferably performed at a temperature of 300°C or less, at which the polymeric material of the test piece does not thermally decompose, and more preferably at 200°C or less. The heating in this pretreatment may be performed at a constant temperature or at an elevated temperature, and may be the same as or different from the heating temperature used in the above-mentioned measurement. In addition, this pretreatment may be performed as a batch process separate from the above-mentioned measurement, or may be performed continuously with the above-mentioned measurement accompanied by gas replacement. Pretreating the test piece in this manner is preferable because it melts the test piece and reshapes it. Furthermore, peroxides generated due to oxidative degradation of the polymeric material emit light upon thermal decomposition. However, in the above-mentioned measurement to evaluate the degree of oxidation of the test piece, it is necessary to capture only the luminescence due to the oxidation of the unoxidized polymeric material itself contained in the test piece. Therefore, luminescence due to peroxides contained in the test piece prior to the above-mentioned measurement may result in measurement errors. Therefore, it is preferable to remove peroxides generated due to oxidative degradation of the polymer material by the above-mentioned pretreatment in advance. Note that even for standard pieces made of unoxidized polymer material, it is preferable to carry out the above-mentioned pretreatment because the shape of the standard piece needs to be adjusted and peroxides generated during the manufacturing process of the standard piece may cause errors in the measurement.

[0021] Polymeric materials applicable to the evaluation method of this embodiment include plastics, oils and fats, resins, rubber, fibers, paints, etc. Specific examples include engineering plastics such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, epoxy resin, urethane resin, unsaturated polyester resin, urea resin, polyester resin, polyamide resin, and polyimide, as well as polyurethane, epoxy resin, acrylic resin, silicone resin, fluororesin, BR, SBR, EPDM, butyl rubber, natural rubber, isoprene rubber, rosin, glycerin, polyethylene oxide, starch, and cellulose. The evaluation method of this embodiment is not limited to the above examples and can be applied to polymeric materials in general.

[0022] Next, an example of the evaluation method of this embodiment will be described in more detail.

[0023] (Obtaining a calibration curve) A polypropylene (PP) sheet measuring 10 mm x 10 mm x 300 μm was used as the standard piece X. A sheet of the same material and size as the standard piece X, to which HALS (0.1 wt%) and UVA (0.1%) were added, was used as the standard piece Y. Next, the standard piece X or standard piece Y was placed in a φ20 mm aluminum cell, and the aluminum cell was then placed in a sealed cell (internal volume: 6.69 cm). 3 ) The sealed cell was openable and had a glass window on the top and a gas port for replacing the atmosphere inside the sealed cell. Gases with adjusted oxygen concentrations of 0%, 40%, 60%, 80%, and 100% were then flowed into the sealed cell, replacing the inside of the cell with the gas adjusted to each oxygen concentration, and the sealed cell was then sealed. Air (oxygen concentration: 21%) was also flowed into the sealed cell, replacing the inside of the cell with air, and the sealed cell was then sealed. When the sealed cell was filled with gas with an oxygen concentration of 100%, the amount of oxygen inside the sealed cell was 0.299 mmol / L.

[0024] Thereafter, the sample chamber of a chemiluminescence analyzer (manufactured by Tohoku Electronics Industry Co., Ltd.) was heated to 200°C, and while the sample chamber was maintained at 200°C, the sealed cell containing standard piece X or standard piece Y was placed in it, and chemiluminescence measurement was started.

[0025] The measurement results for Standard Specimen Y are shown in Figure 1. These results show that the time for the luminescence to rise and the time for the luminescence intensity to peak differ depending on the oxygen concentration, but that the luminescence ceases 45 minutes after the start of measurement at all oxygen concentrations. This is thought to be because all of the oxygen in the sealed cell has reacted with Standard Specimen Y 45 minutes after the start of measurement.

[0026] Figure 2 shows the correlation between the amount of oxygen O in the sealed cell before the start of measurement and the increase I in the integrated luminescence intensity at each oxygen concentration of 21%, 40%, 60%, 80%, and 100% compared to the integrated luminescence intensity at an oxygen concentration of 0%. This shows that there is a high correlation between both standard piece X with no additive and standard piece Y with additive. As mentioned above, it is estimated that all of the oxygen in the sealed cell before the start of measurement has reacted with standard pieces X and Y, so the calibration curve (I=2408*10) showing the correlation in Figure 2 6 *O), the amount of oxygen O involved in the luminescence can be estimated from the actual measured value of the integrated luminescence amount.

[0027] (Evaluation of the degree of oxidation of the test piece) First, a standard piece A made of an unoxidized polymer material was prepared. Specifically, standard piece A was prepared by placing the above-mentioned standard piece X in a DSC cell (φ5 mm × 2 mm) and heating it for 10 minutes at 150°C in a nitrogen atmosphere with a nitrogen inflow rate of 50 ml / min to remove peroxides that would cause errors in the measurement.

[0028] Next, test piece B made of the oxidized polymer material was prepared. Specifically, test piece B was prepared by placing the above-mentioned standard piece X in a DSC cell (φ5 mm × 2 mm) and heat-treating it in an oxygen atmosphere at 180°C with an oxygen inflow rate of 50 ml / min for the heating time h shown in Table 2, and then heat-treating it for 10 minutes at 150°C in a nitrogen atmosphere with a nitrogen inflow rate of 50 ml / min to remove peroxides that would cause errors in the actual measurement.

[0029] Before conducting this test, the weight Wa1 of the standard piece A was measured. Next, the standard piece A was heated at 200°C in an oxygen-containing atmosphere and the integrated luminescence yield A' was measured over 30 minutes using a chemiluminescence method, and the first integrated luminescence yield A = A' / Wa1 was calculated. The measurement results are shown in Table 1.

[0030] [Table 1]

[0031] Before conducting this test, the weight Wb1 of test piece B was measured. Next, test piece B was heated at 200 ° C in an oxygen-containing atmosphere and the cumulative luminescence yield B' was measured over 30 minutes using a chemiluminescence method, and the second cumulative luminescence yield B = B' / Wb1 was calculated. Furthermore, the rate of change in luminescence yield R = (AB) / A was calculated from the obtained first cumulative luminescence yield A and second cumulative luminescence yield B, and the degree of oxidation of test piece B was evaluated based on this rate of change in luminescence yield R. Furthermore, the difference AB between the obtained first cumulative luminescence yield A and second cumulative luminescence yield B was converted to the amount of oxygen O [mmol] involved in the luminescence corresponding to the difference using the previously obtained calibration curve, and the oxygen ratio Or [mmol%] to the mass [mmol] of test piece B was calculated. The results are shown in Table 2.

[0032] [Table 2]

[0033] From Table 2, it was found that the degree of oxidation of test piece B with different heating times h can be evaluated as specific numerical values ​​such as the rate of change in luminescence intensity R and the oxygen ratio Or. In particular, from Table 2, it was found that it can be evaluated that the degree of oxidation of test piece B increases as the rate of change in luminescence intensity R and the oxygen ratio Or increase.

Claims

[Claim 1] A method for evaluating the degree of oxidation of a test piece based on the rate of change in the amount of light emitted, R = (A - B) / A, where A is a first integrated amount of light emitted when a standard piece made of an unoxidized polymeric material is measured by a chemiluminescence method while being heated in an oxygen-containing atmosphere, and B is a second integrated amount of light emitted when a test piece made of an oxidized polymeric material is measured by the chemiluminescence method while being heated in an oxygen-containing atmosphere.

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