JP6849580B2 - Method of estimating the life of polymer materials - Google Patents

Description

The present invention relates to a method for estimating the life of a polymer material, and more particularly to a method for estimating the life of a polymer material made of polyester due to a decrease in strength.

Conventionally, polyesters such as thermoplastic polyesters have both flexibility and toughness, and are therefore widely used as packaging materials, fibers for clothing, and the like. Polyester is also widely used as a main material for products used for a long period of time in an outdoor environment, such as solar panel films and anticorrosion coatings.

In particular, when a product containing polyester as a main material is used in an outdoor environment, it is known that the strength decreases due to deterioration due to ultraviolet rays and water. Therefore, in practice, by grasping the life until the strength of the polyester material falls below the value of the durable strength, maintenance efficiency can be improved and the life is considered to be a standard for evaluation even in the development of new materials. Be done.

Conventionally, the life of a polyester material due to a decrease in strength has been measured by placing a sample outdoors, collecting the sample as the test period elapses, and performing a tensile test on the recovered sample. In the case of polyester materials, it cannot be evaluated as a value indicating a decrease in strength until a relatively long period of time has passed from the start of use. Therefore, the conventional method for measuring the life of a polyester material requires a long test period.

The strength of many polyester materials does not decrease for a while after the start of use in an outdoor environment, and the strength decreases after a certain period of time elapses and the molecular weight decreases due to ultraviolet rays, water, or the like. In particular, in the evaluation by the tensile test, it is difficult to grasp the progress of deterioration until the strength of the material actually decreases, and it is necessary to continue the test until the strength decreases.

Further, especially in recent years, the development of highly weather-resistant materials containing additives such as ultraviolet absorbers and light stabilizers has been progressing, and it takes several years to more than ten years to evaluate the life of these materials. are doing. Reducing the period required for this life evaluation is an important issue for improving the efficiency of product development and performance evaluation.

Therefore, conventionally, instead of directly measuring the change in the strength of the sample with time, a method of estimating the life by evaluating the change in the average molecular weight and the change in the molecular structure of the polymer associated with the deterioration leading to the decrease in strength has been used. It is being studied (see Non-Patent Document 1).

In such a method of estimating the life based on the change in molecular weight, the molecular weight of polyester is measured by Gel Permeation Chromatography (GPC), but the reproducibility of the measurement is low and it is easy to apply to the measurement of the change over time of the material. is not it.

More specifically, in the measurement of the molecular weight of polyester by GPC, HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) to which sodium trifluoroacetate was added as a solvent at about 5 to 10 mmol / L. Is used. Further, in the measurement of this molecular weight, it is common to use a polymethyl methacrylate (PMMA) resin as a standard sample and use an RI (differential refractometer) detector.

However, the measurement of the molecular weight under such conditions is easily affected by a small amount of water contained in the solvent, and the value of the molecular weight obtained for each measurement is deviated. Therefore, it is difficult to estimate the lifetime by collating the newly acquired measurement result of the molecular weight with the measurement result of the previously acquired molecular weight.

For example, suppose a sample is collected every few months in a long-term outdoor exposure test, and the molecular weight data of the collected sample is sequentially reflected in the life estimation. In such a case, when a new sample is collected, it is not appropriate to collate only the new sample with the data already acquired by GPC measurement and reflect it in the life estimation.

When performing GPC measurement, it is necessary to perform GPC measurement on all the samples used for life estimation at once, including the samples that have already been measured. Therefore, the solvent is not added during the measurement, and all the samples are continuously measured.

As described above, in the conventional GPC measurement, all the samples whose lifespan is to be estimated must be evaluated by a series of measurements, which is troublesome and requires a large amount of HFIP, which is an expensive solvent. It also leads to an increase in running costs. Therefore, it is desirable to use a polyester life estimation method that does not rely on GPC measurement.

As an alternative method to the conventional GPC measurement, a method of evaluating an increase in functional groups caused by decomposition of a polymer by infrared spectroscopy (IR) measurement is known. The IR measurement is characterized in that it is easy to integrate the data acquired in the past and the newly acquired data, and the running cost of the measurement is low.

In the conventional IR measurement, the measurement is performed focusing on the fact that the ester bond is decomposed and the COOH group and the OH group are increased due to the progress of deterioration of the polyester in the outdoor environment. For example, changes in the peak of the expansion and contraction vibration of C = O of the COOH group and the peak of the expansion and contraction vibration of the OH bond of the COOH group and the OH group are generally attracting attention (see Non-Patent Document 2).

However, the peak corresponding to the structural change such as COOH group and OH group used for evaluating the deterioration of polyester in the conventional IR measurement cannot be said to be a peak with excellent quantification, and the measurement result shows the life of polyester. It was difficult to make an estimate.

More specifically, when evaluating the increase in COOH groups by IR measurement, it is sufficient to evaluate the increase in absorption in the vicinity of ^{1690 cm-1} due to the expansion and contraction vibration of C = O of the COOH groups. ^{However, the absorption around 1690 cm -1} due to the expansion and contraction vibration of C = O of the COOH group ^{overlaps with the large absorption around 1715 cm -1} due to the expansion and contraction vibration of C = O in the ester bond of the repeating structure of polyester, and it is difficult to detect. is there.

Therefore, it is necessary to pretreat the sample by converting the carboxyl group into acid fluoride (C (= O) F) using sulfur tetrafluoride gas. Since converting a COOH group into an acid fluoride by pretreatment of the samples with sulfur tetrafluoride gas, absorption by the stretching vibration of C = O separates the large absorption near 1715 cm ^-1, 1841Cm around ^-1 (See Non-Patent Document 2).

Since sulfur tetrafluoride gas is not easy to handle, special experimental equipment is required, and it becomes difficult to perform IR measurement. Therefore, it is desired to estimate the life of the polyester by using a peak that can be measured without the need for pretreatment work using sulfur tetrafluoride gas or the like.

For example, the peak of the stretching vibration of the OH bond of COOH groups and OH groups, respectively 3450-3500Cm ^-1, detected around 3250-3300Cm ^-1, it is possible to perform an IR measurement without performing pre-treatment of the sample ( See Non-Patent Document 2).

However, these peaks have weak intensity, and peak shift occurs depending on whether the hydrogen atom of the OH bond is hydrogen-bonded or not, and further, it is also a peak derived from an additive such as an ultraviolet absorber or a light stabilizer. It cannot be said that the peak has excellent quantitativeness because of overlapping. Therefore, it is difficult to estimate the life by evaluating the progress of the deterioration reaction of the polyester material from the increase in absorbance near ^{3450-3500 cm -1} and 3250-3300 cm ^-1.

W. Wang, A. Taniguchi, M Fukuhara, TOkada, J. et al. Apple. Polym. Sci. , 67,705-714 (1998) T. Grossetete et al. , Polymer, 41, 3541-3554 (2000). A. Rivaton, Polymer Degradation and Stability, 41, 1993, 283-296. A. M. Ilarduya and S. M. Guerra, Macromol. Chem. Physics, 215, 2138-2160 (2014).

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a more reliable and efficient method for estimating the life of polyester.

In order to solve the above-mentioned problems, the method for estimating the life of a polymer material according to the present invention includes a first step of obtaining a first absorbance related to a crosslinked structure of an aromatic ring of a polymer material made of polyester by infrared spectroscopic measurement. A second step of performing an exposure treatment of exposing the polymer material to the outdoors for a predetermined test period, and a third step of obtaining a second absorbance relating to the crosslinked structure of the aromatic ring by the infrared spectroscopic measurement after the exposure treatment. It is characterized by comprising a step and a fourth step of estimating the life of the polymer material based on the first absorbance and the second absorbance.

In the method for estimating the life of a polymer material according to the present invention, in the first step, the absorption of the CC bond in which the aromatic ring is crosslinked is measured as the first absorbance, and the CH bond of the aromatic ring is further measured. The absorption was measured as the third absorbance, and in the third step, the absorption of the CC bond crosslinked by the aromatic ring was measured as the second absorbance, and the absorption of the CH bond of the aromatic ring was further measured as the fourth absorbance. measured as absorbance, in the fourth step, the ratio of the first absorbance to the third absorbance to estimate the life of the polymeric material on the basis of the ratio of the second absorbance to the fourth absorbance.

Further, in the method for estimating the life of a polymer material according to the present invention, the time of absorption of the crosslinked structure of the aromatic ring when the mechanical strength of the polymer material decreases from the initial value to a predetermined threshold value a. The change b is b = 0.2 × (1-0.01 × a) + 1.2 × 10 ^-5 × Mn (0) (Mn (0) is an initial value of the number average molecular weight of the polymer material). The fourth step further comprises the time-dependent change b in the approximate curve obtained from the relationship between the time-dependent change from the first absorbance to the second absorbance and the test period. The corresponding time may be estimated as the lifetime of the polymeric material.

Further, in the method for estimating the life of a polymer material according to the present invention, during the test period in which the exposure treatment is carried out, the change over time from the first absorbance to the second absorbance is set to a value smaller than the change over time b. It may be the period until it is reached.

Further, in the method for estimating the life of a polymer material according to the present invention, the initial value of the number average molecular weight of the polymer material is 1,1,1,3,3,3-hexafluoro for the undegraded polymer material. The terminal group may be quantified and determined by dissolving it in a mixed solution of -2-isopropanol and deuterated chloroform, adding an amine, and measuring by proton nuclear magnetic resonance.

According to the present invention, since the absorbance related to the crosslinked structure of the aromatic ring generated by the crosslinking reaction progressing in the deterioration process of the polyester is obtained by infrared spectroscopic measurement and used for quantitative evaluation, the polyester is more reliable and efficient. Life can be estimated.

FIG. 1 is a diagram for explaining a change with time b of absorbance used for estimating the life of the polyester according to the embodiment of the present invention. FIG. 2 is a flowchart illustrating a method for estimating the life of polyester according to the embodiment of the present invention. FIG. 3A is a diagram illustrating a change over time in the absorbance of polyester according to the embodiment of the present invention. FIG. 3B is a diagram illustrating the estimated life of the polyester according to the embodiment of the present invention. _{FIG. 4A is a diagram illustrating the relationship between ΔA 3465} (t) and the test period t according to the embodiment of the present invention. _{FIG. 4B is a diagram illustrating the relationship between ΔA 3260} (t) and the test period t according to the embodiment of the present invention. FIG. 5 is a diagram showing experimental results for samples P-1 and P-2. FIG. 6 is a diagram showing experimental results for samples P-3 and P-4.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 1 to 6. The components that are common to each figure are designated by the same reference numerals.

[Outline of Invention]
In the method for estimating the life of a polyester by reducing the strength of the polyester according to the present invention, a sample pretreatment operation is performed by conducting an outdoor exposure test of the polyester material in a relatively short period of time and evaluating the formation of a crosslinked structure of an aromatic ring by IR measurement. Estimate the life without performing.

In the deterioration of polyester due to ultraviolet rays, the molecular chain cleavage reaction in the ester bond is generally focused on, but it has been reported that the cross-linking reaction in the aromatic ring also proceeds (see Non-Patent Document 3).

The inventors analyzed the polyesters subjected to the outdoor exposure test to identify the type of deterioration reaction that was underway. It was confirmed that two main molecular chain cleavage reactions in the ester bond, i) a photooxidation reaction at the methylene group at the α-position of the ester bond and ii) a Norrish II reaction in the ester bond, proceeded.

As an example, the reaction formulas of the deterioration reactions of i) and ii) above with polyethylene terephthalate are shown.

In addition, the inventors analyzed the polyester subjected to the outdoor exposure test and confirmed that the cross-linking reaction was also proceeding, although it was not as remarkable as the molecular chain breaking reaction. The following is an example of a cross-linking reaction that is considered to occur with polyethylene terephthalate.

In general, it is known that the progress of the molecular chain breaking reaction has a great influence on the decrease in the strength of a polymer material such as polyester, and the molecular chain breaking proceeds predominantly in the molecular chain breaking reaction and the cross-linking reaction. .. To date, there have been no reports evaluating the relationship between the progress of the cross-linking reaction and the decrease in strength of polymer materials such as polyester, but in the present specification, the inventors have focused on the progress of the cross-linking reaction and made polyester. The method of estimating the lifespan due to the decrease in strength of the

[Embodiment]
As described above, in the present invention, the life of the polyester is estimated by paying attention to the cross-linking reaction due to the decrease in the strength of the polyester. Therefore, in the present embodiment, the absorbance indicating the absorption of the CC bond crosslinked by the aromatic ring of the polyester material, which is the target of estimation of the life, and the absorbance indicating the absorption of the CH bond of the aromatic ring are measured by IR, and the fragrance is measured. The evaluation is made by the ratio of the absorbance of the CH bond of the aromatic ring to the absorbance of the CC bond in which the ring is crosslinked. Further, the progress of the cross-linking reaction due to the decrease in the strength of the polyester is determined from the change over time in the test time t with respect to the obtained absorbance ratio.

More specifically, IR measurement is performed, and the absorbance A _x (t) having a ^{wave number x = 1625 cm -1} based on the expansion and contraction vibration of the CC bond of the biphenyl structure in which the aromatic ring is crosslinked is measured at the test time t. An increase in absorbance A _x (t) with wavenumber x = 1625 cm ^-1 indicates an increase in crosslinked structure.

Further, the absorbance A _y (t) of the ^{wave number y = 1015 cm -1} based on the in-plane angular vibration of the CH bond of the aromatic ring at the test time t is measured by IR. The absorbance at wave number y = 1015 cm ^-1 is almost unchanged before and after deterioration of the polyester material. Therefore, the peak intensity of 1625 cm ^-1 is evaluated based on this peak intensity.

Specifically, the following formula (1) is used to determine the temporal change ΔA _x (t) of the _{absorbance A x} (t) indicating the progress of the cross-linking reaction of the aromatic ring in the polyester material.

ΔA _x (t) = {A _x (t) / A _y (t) -A _x (0) / A _y (0)} ... (1)
In the above equation (1), x and y indicate predetermined wave numbers different from each other, and as described above, x = 1625 and y = 1015 are used in the present embodiment, but the present invention is not limited to this.

Next, in the present embodiment, the change with time of absorbance when the mechanical strength of the polyester material whose life is estimated becomes a% of the initial value ΔA _x value b (time of absorbance with respect to the crosslinked structure of the aromatic ring). Change b) is determined. The time at which ΔA _x = b is a value indicating the life of the polyester material.

More specifically, the value b is determined based on the following equation (2).
b = 0.2 × (1-0.01 × a) + 1.2 × 10 ^-5 × Mn (0) ・ ・ ・ (2)
In the above formula (2), Mn represents a number average molecular weight. Mn (0) may be determined by quantifying the amount of terminal groups of the undegraded sample using a nuclear magnetic resonance apparatus (NMR).

Here, the derivation process of the above equation (2) will be described.

As described above, the change with time of absorbance in the polyester sample whose tensile strength is less than a% of the initial value ΔA _x (t) = {A _x (t) / A _y (t) −A _x (0) / A _y (0)} has a value b.

On the other hand, the inventors measured the IR measurement of the deteriorated sample of the polyester material, and found that the change with time ΔA _x of the absorbance increased at a constant rate with the lapse of the test period, and ΔA _x = k ₁ × t (k ₁ is It was confirmed that it can be approximated by (constant). It is considered that this is because the cross-linking reaction, which is a factor of increasing the _{change with time ΔA x of the absorbance, proceeds at a constant rate during the test period.}

Further, the mechanical strength σ (t) of the polyester material does not decrease for a while from the start of the test period, but the strength decreases after the _{test time t c has elapsed.} From this, the mechanical strength σ (t) is approximated by the following equation (3).
σ (t) = σ (0) −k ₂ × (t−t _c ) ・ ・ ・ (3)
In the above equation (3), k ₂ indicates a constant.

From the above equation (3), a% become test time t _a mechanical value the initial value of the strength sigma (0) is, by solving the following equation (4), further represented by the formula (5).
σ (t _a ) = a ÷ 100 × σ (0) = σ (0) −k ₂ × (t _a −t _c ) ・ ・ ・ (4)
_{t a = (1-a ÷} 100) ÷ k 2 × σ (0) + t c ··· (5)

Substituting the above equation (5) into ΔA _x = k ₁ × t, the value b is expressed by the equation (6).
_{b = ΔA x (t a)} = k 1 × {(1-a ÷ 100) ÷ k 2 × σ (0) + t c}
= K ₁ x (1-a ÷ 100) ÷ k ₂ x σ (0) + ΔA _x (t _c ) ・ ・ ・ (6)

In the above equation (6), k ₁ , k ₂ , and σ (0) are constants, and _{when replaced with k 3} , the following equation (7) is obtained.
b = k ₃ × (1-a ÷ 100) + ΔA _x (t _c ) ・ ・ ・ (7)

Furthermore, it was confirmed that the change with time ΔA _x (t _c ) of the absorbance can be approximated by the following equation (8) using Mn (0) and the constant k _4.
ΔA _x (t _c ) = k ₄ x Mn (0) ・ ・ ・ (8)

Substituting the above equation (8) into the equation (7) gives the following equation (9).
_{b = ΔA x (t a)} = k 3 × (1-a ÷ 100) + k 4 × Mn (0) ··· (9)

Using the above equation (9), the horizontal axis (1-a ÷ 100), the vertical axis plotting the measurement data indicating a .DELTA.A _x (t _a) in the following Table 1. Furthermore, an approximate expression for each number average molecular weight was obtained from the measurement data.

FIG. 1 is a diagram showing a plot of the measurement data in Table 1 and an approximate expression for each number average molecular weight.
In FIG. 1, "triangular" points indicate measurement data of a polyester material having a number average molecular weight (Mn) of 15,000, and "diamond" points indicate measurement data of a polyester material having a number average molecular weight (Mn) of 20000. The points shown and indicated by "squares" indicate the measurement data in the polyester material having a number average molecular weight (Mn) of 40,000.

_{Further, k 3} = 0.20 and k ₄ = 1.2 × 10 ^-5 are obtained from the average of the approximate curve equations for each number average molecular weight shown in FIG. 1, and b = 0.2 × (1-0). It was confirmed that a good approximation can be made with 0.01 × a) + 1.2 × 10 ^{-5 × Mn (0).}

Next, the method of estimating the life due to the decrease in the strength of the polyester according to the present embodiment will be described with reference to the flowchart of FIG.
First, as a premise, the life of the polyester material is defined as the maximum stress of the tensile test is less than a% of the initial value. The value of a (threshold value) may be determined according to the use of the material.

_{Next, the initial value A λ} (0) of the absorbance of vibration at ^{the wave number λ cm -1} of the polyester at the test time t is measured by IR (step S1). Note that λ is a preset wave number, and x = 1625 and y = 1015 are used in this embodiment. The peak intensity at a predetermined wave number λ = x is evaluated using the above-mentioned equation (1), where the measured value obtained by the IR measurement is A _{λ (t).}

Next, an outdoor exposure test of the polyester material is carried out (step S2). More specifically, an _{outdoor exposure test is performed until ΔA x} (t) = c (c <b), and the sample is collected for an arbitrary test period T. For the value c, c ≧ (b × 0.1) may be used.

The outdoor exposure test will be conducted for a period of at least one year to reflect the effects of seasonal fluctuations. Further, in order to improve the accuracy of life estimation, the sample is collected a plurality of times over the test period T.

Next, IR measurement is performed on the recovered polyester material sample, and the change with time ΔA _x of the absorbance is obtained using the above formula (1) (step S3).

Next, the estimated life of the polyester material is calculated from an approximate expression of the change in absorbance over time (step S4). FIG. 3A is a diagram showing the relationship between the _{change with time ΔA x of absorbance and the test period t.} Note that FIG. 3A shows an example of x = 1625.

Based on each point shown in FIG. 3A, the change with time of absorbance _{is approximated by ΔA x} = kt to calculate the constant k. The time during which the change in absorbance with time becomes a value b (ΔA _x = b), that is, the estimated lifetime t is calculated by t = b / k.

FIG. 3B is a diagram illustrating an estimated lifetime calculated by approximating the change in absorbance with time shown in FIG. 3A. _{As shown in FIG. 3B, the time t corresponding to ΔA x} = b in the approximate curve of the change over time of the absorbance is the value of the estimated life due to the decrease in strength of the polyester material to be estimated.

[Example]
Next, the above-mentioned method of estimating the life due to the decrease in the strength of the polyester will be described in detail by the following examples.
(Measuring method)
Fourier Transform Infrared Spectroscopy (FT-IR) measurement:
It was measured by the reflection ATR method using a single reflection diamond ATR (Attenuated Total Reflection) plate using an FT-IR analyzer (Fournier Gold (registered trademark)) manufactured by PerkinElmer.

NMR measurement:
^{A 1} H-NMR (proton nuclear magnetic resonance) (300 MHz) spectrum was measured using a Varian nuclear magnetic resonance apparatus Oxford. The chemical shift δ was expressed in ppm, and the peak of _{Me 4 Si was 0 ppm.} The sample was dissolved in 1,1,1,3,3,3-hexafluoro-2-isopropanol (HFIP) -d2 (0.75 g) and then deuterated chloroform (CDCl3, Me ₄ Si 0.03). % (V / v) content) (0.68 g) and isopropylamine (1.5 mg) were sequentially added and measured at 50 ° C.

The number average molecular weight (Mn) was calculated using the following equations (10) and (11) based on the measurement results by NMR measurement.
Mn = (composition formula amount) x {1 / ((molecular chain terminal group amount [mol%]) x 1/2)} x 100 ... (10)
(Molecular chain terminal group amount [mol%]) = (Aromatic carboxylic acid amount [mol%]) + (Hydroxy group amount [mol%]) ... (11)

(Tensile test)
A tensile test was carried out in an environment of 23 ± 2 ° C. and 50% RH using an Autograph AG-X manufactured by Shimadzu Corporation. Using JIS K6251 No. 6 test piece, measure the maximum stress and breaking elongation at a chuck distance of 50 mm, a marked line distance of 20 mm, and a tensile speed of 5 mm / min. The standard deviation was calculated.

(Comparison example)
First, a comparative example using two types of thermoplastic polyester samples will be described. Sample P-1 is a PET (polyethylene terephthalate) film, and is a sample to which an antioxidant, a light stabilizer, or the like is not added. Sample P-2 is also a PET film, but Sample P-2 is a sample to which an antioxidant, a light stabilizer, or the like is added. An outdoor exposure test of samples P-1 and P-2 was carried out, IR measurement was performed according to the elapse of the test period, and the period of the outdoor exposure test required for life estimation was evaluated.

Generally, in the deterioration of polyester, OH groups and COOH groups increase as it progresses. Of these peaks, the peaks that can be measured without pretreatment are the absorption of ^{3465 cm -1} due to the expansion and contraction vibration of the OH bond of the OH group and ^{3260 cm -1 due to the expansion and contraction vibration of the OH bond of the COOH group.} , 3465 cm ^-1 and 3260 cm ^-1 were evaluated.

In order to estimate the life, it is necessary to express the following equations (12) and (13) as a function of time t.
ΔA ₃₄₆₅ (t) = {A ₃₄₆₅ (t) / A ₁₀₁₅ (t) -A ₃₄₆₅ (0) / A ₁₀₁₅ (0)} ・ ・ ・ (12)
ΔA ₃₂₆₀ (t) = {A ₃₂₆₀ (t) / A ₁₀₁₅ (t) −A ₃₂₆₀ (0) / A ₁₀₁₅ (0)} ・ ・ ・ (13)

FIG. 4A is _{a diagram showing the relationship between ΔA 3465} (t) and the test period t. FIG. 4B is _{a diagram showing the relationship between ΔA 3260} (t) and the test period t.
In FIGS. 4A and 4B, the points indicated by “X” indicate the values of sample P-1, and the points indicated by “circles” indicate the values of sample P-2.

As shown in FIGS. 4A and 4B, _{the values of ΔA 3465} (t) and ΔA ₃₂₆₀ (t) both increased with the lapse of the test period t. As mentioned above, the absorption of 3465 cm ^-1 and 3260 cm ^-1 has a weak strength, a peak shift occurs when the hydrogen atom of the OH bond is hydrogen-bonded and when it is not, and the ultraviolet absorber. It was thought that the quantification was not excellent because it overlapped with the peak derived from additives such as and light stabilizers. However, even at 3465 cm ^-1 and 3260 cm ^-1 , an increasing tendency was confirmed with the passage of the test period t.

However, the rate of increase in the values of ΔA ₃₄₆₅ (t) and ΔA ₃₂₆₀ ^{(t) at 3465 cm -1} and 3260 cm ^-1 is large in the early stage of deterioration, and the sample P-1 is exposed to the outdoors for 3 months and the sample P-2 is exposed to the outdoors. The slope of the graph changed after about 6 months.

To _{approximate ΔA 3465} (t) and ΔA ₃₂₆₀ (t) as a function of time t, _{the data for ΔA 3465} (t) and ΔA ₃₂₆₀ (t) are obtained at multiple points over the initial degradation period and further. , It suffices to obtain a plurality of points in the subsequent test period. The initial period of deterioration means that the sample P-1 is exposed to the outdoors within 3 months and the sample P-2 is exposed to the outdoors within 6 months.

In addition, for sample P-1, _{data of ΔA 3465} (t) and ΔA ₃₂₆₀ (t) up to 12 months of outdoor exposure were acquired, and for sample P-2, ΔA ₃₄₆₅ (t) and ΔA ₃₂₆₀ (t) up to 18 months were acquired. Need to get the data of.

Here, Sample P-1 and Sample P-2 subjected to the outdoor exposure test were evaluated by a tensile test. The tensile strength of sample P-1 and sample P-2 decreased to less than 90% of the initial value after 12 months for sample P-1 and after 24 months for sample P-2.

Therefore, _{when estimating the lifetime by expressing ΔA 3465} (t) or ΔA ₃₂₆₀ (t) as a function of time t, the outdoor exposure test is carried out until the tensile strength of the samples P-1 and P-2 actually decreases. It was found that an outdoor exposure test period similar to that of the above was required, and the test period could not be shortened very much.

As a factor of the change in the slope of the graph at the boundary of 3 months of outdoor exposure for sample P-1 and 6 months of outdoor exposure for sample P-2, the inventors of the present invention have an ether bond as shown in the following chemical formula. It was considered that the photolysis reaction had an effect. The ether structure is a structure produced as a by-product during the production of polyester, and is contained in an amount of several mol% with respect to all repeating units of the molecule (see Non-Patent Document 4).

The ether structure as described above is a molecular structure that is slightly by-produced during the production of polyester. For this reason, the photodecomposition reaction of the ether structure has not been generally paid attention to, and there has been no report so far that the progress of this decomposition reaction causes a change in the IR spectrum of polyester. However, when the ether structure is decomposed, COOH groups and OH groups increase, so the inventors thought that the progress of this deterioration reaction also affected the increase of ^{3465 cm -1} and 3260 cm ^-1.

Therefore, the inventors compared the result of IR measurement of the deteriorated sample with the amount of decomposition of the ether bond evaluated by NMR measurement. According to this comparison result, _{the period in which the amount of increase in ΔA 3465} (t) and ΔA ₃₂₆₀ (t) was large in the IR measurement, that is, the period in which the slope of the graph became large, and the amount of decomposition of the ether bond in the NMR measurement were large. It turned out that the period was in good agreement.

In addition, the inventors quantitatively evaluated the amount of decomposition of the ether bond by NMR measurement, and found that the reaction rate of photodecomposition of the ether bond was the ether structure per unit volume of the material surface in the test period t from the start of outdoor exposure. Assuming that the amount is C (t) [mol%], it was confirmed that dC (t) / dt = -kC (t) (k indicates the reaction rate constant) can be approximated.

Since the value of C is large immediately after the start of outdoor exposure, the amount of decomposition of the ether structure per unit time is also large. On the other hand, when the amount of ether structure C decreases with the lapse of the test period t, the amount of decomposition of the ether structure per unit time decreases. From this, it is considered that the photodecomposition reaction of the ether structure had an effect on the large increase in ΔA 3465 (t) and ΔA _{3260 (t) in the early stage of deterioration.}

Next, for the cross-linking reaction, which is not generally paid attention to in relation to the deterioration of the polyester material in the outdoor environment and there is no quantitative example, the progress of the reaction is evaluated by IR measurement, and from the data. We considered estimating the life of the polyester material.

The main deterioration reaction that occurs in polyesters subjected to outdoor exposure tests is, as is generally known, a molecular chain cleavage reaction, but the inventors have clarified by experiments that a cross-linking reaction in an aromatic ring also occurs. It was confirmed that the absorbance of 1625 cm ^{-1 increased as the reaction proceeded.}

FIG. 5 is _{a diagram showing the relationship between ΔA 1625} (t) and the test period t. In FIG. 5, the horizontal axis is the test period t, and the vertical axis is ΔA ₁₆₂₅ (t). Further, the points indicated by "X" are the values of the sample P-1, and the points indicated by "circles" are the values of the sample P-2.

Further, as shown in FIG. 5, for samples P-1, with _{ΔA 1625 (t) = 0.0139 ×} t, for samples P-2, well _{ΔA 1625 (t) = 0.0057 ×} t approximation I found that I could do it.

As a result, if the horizontal axis is plotted as the test period t and the vertical axis is ΔA ₁₆₂₅ (t), it _{can be approximated by ΔA 1625} (t) = kt (k is a constant). It was found that a period shorter than the life was sufficient.

(Experimental example)
Next, an experimental example using the thermoplastic polyester samples P-3 and P-4 will be described. Sample P-3 and Sample P-4 are PET films to which an antioxidant, a light stabilizer, and the like are added, and both are samples having higher weather resistance than Sample P-1 and Sample P-2.

As the life of the PET film of the sample P-3 and the sample P-4, it is defined that the strength of the tensile test is less than a% = 70% of the initial value, and this life corresponds to ΔA ₁₆₂₅ (t) = b. Then. Further, in this experimental example, in order to determine the value b, the amount of terminal groups of the undegraded sample was quantified by NMR to obtain the number average molecular weight (Mn). The number average molecular weight (Mn) of sample P-3 was 25,000, and the number average molecular weight (Mn) of sample P-4 was 30,000.

Substituting the number average molecular weight (Mn) obtained for each sample into the above equation (2),
b = 0.2 × (1-0.01 × a) + 1.2 × 10 ^-5 × Mn (0) ・ ・ ・ (2)
= 0.2 x (1-0.01 x 70) + 1.2 x 10 ^-5 x Mn (0) ... (2)'
For sample P-3, b = 0.36 was calculated, and for sample P-4, b = 0.42 was calculated.

Next, an outdoor exposure test was conducted. The outdoor exposure test was based on the above formula (ΔA _x (t) = c (c <b)), and _{the value of ΔA 1625} for sample P-3 was c = 0.04, and that for sample P-4 was ΔA _1625. It was carried out until the value of c = 0.05 (note that c ≧ (b × 0.1) may be used). In addition, the outdoor exposure test was conducted for a period of at least one year to reflect the effects of seasonal fluctuations. In addition, in order to improve the accuracy of life estimation, the sample was collected once every six months and IR measurement was performed.

FIG. 6 is a diagram showing the relationship between _{ΔA 1625 and the test period t.} In FIG. 6, the horizontal axis represents the test period t, the vertical axis represents ΔA ₁₆₂₅ , the “black square” point is the value of sample P-3, and the “white square” point is the value of sample P-4. Shown.

Further, as shown in FIG. 6, in the sample P-3, ΔA ₁₆₂₅ (t) = 0.047> 0.04 in the test period t = 18 months. Therefore, for sample P-3, an approximate expression, ΔA ₁₆₂₅ (t) = 0.0025 × t, was obtained using the data up to 18 months.

On the other hand, for sample P-4, ΔA ₁₆₂₅ (t) = 0.073> 0.05 in the test period t = 18 months. _{For sample P-4, an approximate expression of ΔA 1625} (t) = 0.004 × t was obtained using the data up to 18 months.

From the above approximation formula, the life of the sample P-3 was calculated to be t = b / k = 0.36 / 0.0025 = 144 months. The life of sample P-4 was calculated to be t = b / k = 0.42 / 0.004 = 105 months.

Further, when the outdoor exposure test was continued and the life when the actual tensile strength decreased from the initial value to 70% was evaluated, it was 144 months for the sample P-3 and 102 months for the sample P-4. It was found that the estimated life value of was highly accurate. In addition, the value of b calculated using the formula (2) (b = 0.2 × (1-0.01 × a) + 1.2 × 10 ^-5 × Mn (0)) was also valid. It could be confirmed.

The period required for estimating the life was 18 months for both samples P-3 and P-4, which was 1/8 of the period actually required for the tensile strength to decrease. The life of sample P-4 could be estimated in a relatively short period of 3/17.

As described above, in the polyester life estimation method according to the present embodiment, the absorbance of the polyester related to the crosslinked structure of the aromatic ring generated by the crosslinking reaction progressing in the deterioration process of the polyester is used for quantitative evaluation. Therefore, the correlation between the absorbance and the material strength can be obtained from the results of the outdoor exposure test for a shorter period of time, and a more reliable and efficient life estimation can be performed.

Further, since the polyester life estimation method according to the present embodiment does not use peaks related to COOH groups and OH groups due to the progress of the molecular chain cleavage reaction, which has been attracting attention in the past, pretreatment with sulfur tetrafluoride or the like is used. IR measurement can be performed without any work.

In the embodiment described, when the life estimation target is polyester, the formula (2) (b = 0.2 × (1-0.01 × a) + 1.2 × 10 ^-5 × Mn ( Although 0)) was used, the life can be estimated in the same manner by using the formula (2) in the case of the copolymerized polyester. In that case, different values may be used for the constants k ₃ and k _4.

Claims (4)

The first step of obtaining the first absorbance related to the crosslinked structure of the aromatic ring of the polymer material made of polyester by infrared spectroscopy, and
A second step of performing an exposure treatment in which the polymer material is exposed to the outdoors for a predetermined test period, and
After the exposure treatment, the third step of obtaining the second absorbance related to the crosslinked structure of the aromatic ring by the infrared spectroscopic measurement, and
The fourth step of estimating the life of the polymer material based on the first absorbance and the second absorbance, and
Equipped with a,
In the first step, the absorption of the CC bond crosslinked with the aromatic ring is measured as the first absorbance, and the absorption of the CH bond of the aromatic ring is measured as the third absorbance.
In the third step, the absorption of the CC bond crosslinked with the aromatic ring is measured as the second absorbance, and the absorption of the CH bond of the aromatic ring is measured as the fourth absorbance.
Wherein in the fourth step, high, wherein the the ratio of the first absorbance to third absorbance, you estimate the lifetime of the said polymer material based on a ratio of the second absorbance to fourth absorbance Method for estimating the lifetime of molecular materials. In the method for estimating the life of a polymer material according to claim 1,
The change b of the absorbance with respect to the crosslinked structure of the aromatic ring when the mechanical strength of the polymer material decreases from the initial value to a predetermined threshold value a is b = 0.2 × (1-0. A fifth step of determining using 01 × a) + 1.2 × 10 ^-5 × Mn (0) (Mn (0) is an initial value of the number average molecular weight of the polymer material) is further provided.
In the fourth step, the time corresponding to the time-dependent change b on the approximate curve obtained from the relationship between the time-dependent change from the first absorbance to the second absorbance and the test period is estimated as the lifetime of the polymer material. A method for estimating the life of a polymer material, which is characterized by the above. In the method for estimating the life of a polymer material according to claim 2,
The test period in which the exposure treatment is carried out is a period until the time-dependent change from the first absorbance to the second absorbance reaches a set value smaller than the time-dependent change b. Life estimation method. In the method for estimating the life of a polymer material according to claim 2,
The initial value of the number average molecular weight of the polymer material is determined by dissolving the undegraded polymer material in a mixed solution of 1,1,1,3,3,3-hexafluoro-2-isopropanol and deuterated chloroform. A method for estimating the life of a polymer material, which comprises quantifying and obtaining terminal groups by adding amine and measuring by proton nuclear magnetic resonance.

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