Patent Application
20230028235
The present invention relates to a pretreatment method and relates to a method for pretreating a sample consisting of polyester or a polyester decomposition product before carrying out size exclusion chromatography of the sample.
Polyester having thermoplasticity (thermoplastic polyester) has both strength and flexibility and is thus used as engineering plastic for various purposes. For example, the thermoplastic polyester polyethylene terephthalate (PET) is used in films, fibers, bottles for beverages, etc., some of which are also recycled. The deterioration of the thermoplastic polyester progresses due to heat or light. It is industrially important to understand the state of this deterioration. The understanding of the state of the deterioration mentioned above can be carried out, for example, by the measurement of a molecular weight distribution.
The molecular chain scission reaction and cross-linking reaction of the thermoplastic polyester progress due to heat or light. The progression of molecular chain scission or the formation of a cross-linked structure largely influences the mechanical characteristics, such as strength, of the thermoplastic polyester and causes reduction in performance such as reduction in strength. This leads to the deterioration of the thermoplastic polyester. Thus, the progression of molecular chain scission or the formation of a cross-linked structure mentioned above can be understood by the measurement of a molecular weight distribution, and the state of the deterioration of the thermoplastic polyester can thereby be evaluated. This measurement of a molecular weight distribution employs size exclusion chromatography (see Non-Patent Literature 1).
The size exclusion chromatography is a method of separating or purifying an analysis sample by exploiting different times at which molecules pass through a column depending on their sizes. For analysis using the size exclusion chromatography, as in other chromatography techniques, a detector is placed in the discharge destination of a column, and a substance that has passed through the column is detected and output as signals (chromatogram) corresponding to the concentration of the substance in the detector.
In this kind of analysis, insoluble components are removed from an analysis sample by filtration through a filter at the stage of preparation of the analysis sample in order to prevent the clogging of a column. In the case of thermoplastic polyester, a solution of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) supplemented with approximately 1 to 10 mmol/L of a salt such as sodium trifluoroacetate is generally used as an eluent to prepare an analysis sample. In the preparation of the analysis sample, a thermoplastic polyester sample is dissolved in the eluent mentioned above, left standing at room temperature for several hours, and then filtered through a filter (pore size: e.g., 0.2 μm) for the removal of insoluble components. The measurement is carried out by using this filtrate as an analysis sample.
A deteriorated thermoplastic polyester sample rich in cross-linked structure contains insoluble components that cannot be dissolved in an eluent. These insoluble components are removed by the filtration mentioned above and are no longer contained in an analysis sample. Thus, the insoluble components mentioned above are not included in results of measuring a molecular weight distribution. However, for understanding the state of the deterioration of thermoplastic polyester, it is important to analyze (evaluate) a molecular weight in a state also including the insoluble components mentioned above.
In order to gain information on molecular weight as to components that cannot be dissolved in an eluent, it is possible to carry out size exclusion chromatography by decomposing a particular molecular structure contained in insoluble components and dissolving the resultant in an eluent in pretreatment. For this pretreatment, it is desired that molecular structures contained in repeat units of a molecular chain, such as ester bonds in polyester should not be decomposed.
As mentioned above, molecular chain scission is an index for deterioration. If a molecular chain is cleaved by decomposing a portion of molecular structures contained in repeat units of the molecular chain, whether this is due to pretreatment or due to deterioration cannot be determined. Thus, measurement results are difficult to interpret. Furthermore, it is not easy to control the degree of progression of decomposition of molecular structures in repeat units of a molecular chain. Thus, reproducibility is difficult to secure.
As is well known, thermoplastic polyester deteriorated due to light or heat is in a state containing an acid anhydride structure. Provided that this anhydrous oxide can be selectively decomposed without decomposing ester bonds, the problems mentioned above are solved. Since the anhydrous oxide is more susceptible to decomposition with a base than ester bonds, it is considered that the acid anhydride structure can be decomposed, for example, by dissolving a thermoplastic polyester sample in HFIP and adding an organic base thereto.
As a result of examining whether the pretreatment for the size exclusion chromatography of thermoplastic polyester mentioned above decomposes an acid anhydride structure without decomposing ester bonds, it has been found that ester bonds are also decomposed. When deteriorated thermoplastic polyester is used as a sample and dissolved in HFIP containing an organic base, the anhydrous oxide structure can be decomposed. In this respect, the decomposition of ester bonds is supposed to rarely proceed by properly setting the amount of the organic base added and avoiding heating for a long time.
In this context, the size exclusion chromatography is carried out, as mentioned above, by dissolving a sample in HFIP containing a proper amount of an organic base, heating the solution for a proper time so that an acid anhydride structure is decomposed, then removing the solvent from this solution to obtain a solid sample, and dissolving the obtained solid in an eluent. As a result of analyzing the obtained solid to be dissolved in this eluent for the state of ester bonds, it has been confirmed that ester bonds not supposed to be decomposed by the pretreatment using the organic base mentioned above were decomposed. Thus, a problem of the pretreatment merely using an organic base as mentioned above is the decomposition of ester bonds.
Embodiments of the present invention have been made in order to solve the problems as mentioned above. An object of embodiments of the present invention is to suppress the decomposition of ester bonds in the pretreatment of a sample consisting of polyester or a polyester decomposition product for carrying out size exclusion chromatography.
The pretreatment method according to embodiments of the present invention is a method for pretreating a sample consisting of polyester or a polyester decomposition product before carrying out size exclusion chromatography of the sample, comprising: a first step of dissolving the sample in 1,1,1,3,3,3-hexafluoro-2-propanol to prepare a first solution; a second step of adding an organic base to the first solution to prepare a second solution; a third step of heating the second solution to obtain a substance in which an anhydrous oxide structure in the sample has been decomposed; a fourth step of, following the third step, adding an organic solvent that has a higher boiling point than that of 1,1,1,3,3,3-hexafluoro-2-propanol and is compatible with 1,1,1,3,3,3-hexafluoro-2-propanol to the second solution to prepare a third solution; and a fifth step of removing the solvent from the third solution to obtain a solid sample consisting of the substance.
As described above, according to embodiments of the present invention, the decomposition of ester bonds can be suppressed in the pretreatment of a sample consisting of polyester or a polyester decomposition product for carrying out size exclusion chromatography, because an organic solvent that has a higher boiling point than that of 1,1,1,3,3,3-hexafluoro-2-propanol and is compatible with 1,1,1,3,3,3-hexafluoro-2-propanol is added.
Hereinafter, a pretreatment method according to an embodiment of the present invention will be described with reference to
First, in first step Sol, the sample is dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) to prepare a first solution.
Next, in second step S102, an organic base is added to the first solution to prepare a second solution. The concentration of the organic base in the second solution is larger than 0.05 [mmol/L] and less than 0.4 [mmol/L]. Any of amines such as ethylamine, diethylamine, triethylamine, n-propylamine, i-propylamine (isopropylamine), n-butylamine, s-butylamine, t-butylamine, dimethylethylamine, and pyridine can be used as the organic base.
Next, in third step S103, the second solution is heated to obtain a substance in which an anhydrous oxide structure in the sample has been decomposed. This substance is dissolved in the second solution at this stage.
Subsequently, in fourth step S104, an organic solvent that has a higher boiling point than that of HFIP and is compatible (miscible) with HFIP is added to the second solution to prepare a third solution. The ratio of amount V [mL] of the organic solvent to amount “a” [ml] of HFIP in the third solution is V/a≥1. The organic solvent containing any of an ester bond, an ether bond, ketone, an aromatic ring, and a hydroxy group can be used.
Then, in fifth step S105, the solvent is removed from the third solution to obtain a solid sample consisting of the substance in which an anhydrous oxide structure in the sample has been decomposed. The solvent can be vaporized by heating and thereby removed, for example. However, when the boiling point of the organic solvent is higher than 50° C., the solvent is removed from the third solution through treatment in a range that does not allow the solution temperature to become 50° C. by concentration under reduced pressure, to obtain a solid sample.
The solid sample is thus obtained, and for subsequent size exclusion chromatography, the obtained solid sample is dissolved in a solvent (eluent) for size exclusion chromatography (sixth step).
Here, the deterioration of thermoplastic polyester will be described. As the deterioration of thermoplastic polyester progresses due to heat (heating) or light (light reception), its molecular chain scission reaction and cross-linking reaction progress, causing reduction in performance such as deterioration in strength. The course of reaction leading to molecular chain scission includes a pathway leading to molecular chain scission by only light, such as “Norrish II” reaction.
A molecular structure represented by the chemical structural formula (1) given below is converted to a molecular structure represented by the chemical structural formula (2) through photooxidation reaction and then converted to a molecular structure represented by the chemical structural formula (3) through ambient oxygen to form an acid anhydride structure which is a molecular structure weak in water. Then, the pathway leads to molecular chain scission as represented by the chemical structural formula (4) through hydrolysis.
In the course of reaction to form a cross-linked structure, a molecular structure represented by the chemical structural formula (5) given below is converted to a molecular structure represented by the chemical structural formula (7) through the withdrawal of a hydrogen radical by radical R. as represented by the chemical structural formula (6), and two molecular structures of the chemical structural formula (7) form a cross-linked structure through radicals to yield a molecular structure represented by the chemical structural formula (8). Such a course of reaction increases the number of cross-linked structures so that the thermoplastic polyester is insolubilized.
For example, when the thermoplastic polyester polyethylene terephthalate (PET) is deteriorated, as shown in
Hereinafter, embodiments of the present invention will be described in more detail with reference to experimental results. First, the addition of an organic solvent that had a higher boiling point than that of HFIP and was compatible (miscible) with HFIP was tested. In this test, solid samples were prepared by a pretreatment method under varying conditions, and the solid sample prepared under each condition was analyzed for the state of ester bonds and the state of an acid anhydride structure.
The state of ester bonds was evaluated as a decrease in the number of ester bonds by analyzing (quantifying) an increase in the number of hydroxy group ends formed through the decomposition of ester bonds in the solid sample by nuclear magnetic resonance (NMR) measurement. More specifically, 1H NMR (300 MHz) was measured using the nuclear magnetic resonance device Oxford from Varian Medical Systems, Inc.
A sample was dissolved in a solvent of deuterated chloroform [containing 0.03% (v/v)Me4Si] CDCl3 and 1,1,1,3,3,3-hexafluoro-2-propanol-2d (HFIP-2d) mixed at a volume ratio of 1:1.
Measurement was carried out under a temperature condition of 50° C. For the measurement, the Me4Si peak of deuterated chloroform [containing 0.03% (v/v)Me4Si] CDCl3 was defined as 0 ppm.
Concentration COH of hydroxy group ends was determined for repeat units from the intensity ratio between the peak of a proton on an aromatic ring (88.10 ppm) and the peak of a proton on a methylene group at hydroxy group ends (δ4.05 ppm) resulting from the decomposition of ester bonds.
The state of an acid anhydride structure was analyzed (quantified) as the presence or absence of a residual acid anhydride structure in a solid sample by infrared spectroscopy (FT-IR). More specifically, measurement was performed by reflection ATR with a single-reflection diamond ATR plate using the FT-IR analysis device Frontier Gold manufactured by PerkinElmer, Inc. The residual acid anhydride structure was confirmed from A1785/A1016 wherein the absorbance of 1785 cm−1 (light absorption by the acid anhydride structure) was normalized with the absorbance of 1016 cm−1 (light absorption by an aromatic ring).
ΔA1785/A1016=(A1785/A1016 when a deteriorated sample is pretreated)−(A1785/A1016 of an undeteriorated sample).
Light-deteriorated PET (approximately 10 mg) was used as deteriorated thermoplastic polyester.
Any of the following organic bases were used.
Isopropylamine (boiling point: 34° C.)
Diethylamine (boiling point: 56° C.)
n-Butylamine (boiling point: 78° C.)
Triethylamine (boiling point: 89° C.)
Pyridine (boiling point: 115° C.)
In addition to HFIP (boiling point: 59° C.), hexane (boiling point: 69° C.), ethyl acetate (boiling point: 77° C.), tetrahydrofuran (boiling point: 66° C.), diisopropyl ether (boiling point: 69° C.), toluene (boiling point: 110° C.), 2-butanone (boiling point: 79° C.), dioxane (boiling point: 101° C.), xylene (boiling point: 144° C.), propyl acetate (boiling point: 97° C.), butyl acetate (boiling point: 126° C.), and isopropyl acetate (boiling point: 89° C.) were used as organic solvents.
In test 1, light-deteriorated PET (10 mg) was dissolved in HFIP (2 mL) (first solution). To this solution, the organic base mentioned above was added at C mmol/L (second solution), followed by warming at 50° C. for 1 h. A small aliquot of this solution (second solution) was collected and subjected to NMR measurement, and “ΔCCH2OH before solvent removal” was calculated. Then, the solvent was removed to obtain a solid sample. The obtained solid sample was subjected to NMR measurement, and “ΔCCH2OH after solvent removal” was calculated. The calculation results are shown in Table 1 below.
As shown in Table 1, there was neither an increase in the number of hydroxy group ends nor the decomposition of ester bonds before removal of the solvent in all the cases. On the other hand, the number of hydroxy group ends was increased after removal of the solvent, demonstrating that the decomposition of ester bonds progressed during the course of removal of the solvent.
In test 2, light-deteriorated PET (10 mg) was dissolved in HFIP (2 mL) (first solution). To this solution, the organic base mentioned above was added at C mmol/L (second solution), followed by warming at 50° C. for 1 h. To this solution (second solution), v mL of ethyl acetate was added as organic solvent, and the mixture was thoroughly stirred (third solution). Then, the obtained solution was concentrated under reduced pressure at 30° C. for the removal of the organic solvent to obtain a solid sample. The obtained solid sample was subjected to NMR measurement, and “ΔCCH2OH after solvent removal” was calculated. Also, the obtained solid sample was subjected to Fr-IR measurement, and “ΔA1785/A1016” was calculated. The results of each calculation are shown in Table 2 below.
As shown in Table 2, for the combination of triethylamine and ethyl acetate, the number of hydroxy group ends was increased after removal of the solvent, revealing that the decomposition of ester bonds progressed. This is presumably because, since the boiling point of the organic base exceeded the boiling point of the organic solvent, the concentration of the solvent facilitated elevating the base concentration.
In contrast to these results, for isopropylamine which had a lower boiling point than that of ethyl acetate, the number of hydroxy group ends was increased when the amount of the base added was 0.40 mmol/L or more, demonstrating the progression of decomposition of ester bonds. On the other hand, for isopropylamine, the number of hydroxy group ends was not increased when the amount of the base added was in the range of 0.10 to 0.30 mmol/L, demonstrating that the decomposition of ester bonds did not progress.
In the case of adding 0.05 mmol/L of isopropylamine, ΔA1785/A1016>0 held, demonstrating that when the amount of the organic base added is small, the decomposition of an acid anhydride structure is not completed. When the amount of ethyl acetate added was 1 mL, the number of hydroxy groups was increased, demonstrating the decomposition of ester bonds. It is considered that if the amount of the organic solvent added is small, a portion of PET resin remains dissolved so that ester bonds have been decomposed.
From these results, it was found necessary to add an organic solvent that has a higher boiling point than that of HFIP and does not dissolve thermoplastic polyester. It was also found that the concentration of the organic base added is suitably 0.05<c<0.4. When the amount of HFIP is defined as “a” mL, it is evidently desired that amount V mL of the organic solvent added should satisfy the relationship of “V/a≥1”.
In test 3, light-deteriorated PET (10 mg) was dissolved in HFIP (2 mL) (first solution). To this solution, dimethylamine was added at 0.25 mmol/L (second solution), followed by warming at 50° C. for 1 h. To this solution (second solution), 2 mL of an organic solvent was added, and the mixture was thoroughly stirred (third solution). Then, the obtained solution was concentrated under reduced pressure at TC for the removal of the organic solvent to obtain a solid sample. The obtained solid sample was subjected to NMR measurement, and “ΔCCH2OH after solvent removal” was calculated. The calculation results are shown in Table 3 below.
In the case of using hexane as an organic solvent, hexane was not miscible with HFIP so that the number of hydroxy group ends was increased after removal of the solvent, revealing that the decomposition of ester bonds progressed. These results demonstrated that it is necessary to use an organic solvent that contains a molecular structure such as an ester bond, an ether bond, an aromatic ring, or ketone and is sufficiently miscible with HFIP.
In the case of using isopropylamine having a low boiling point, the decomposition of ester bonds did not occur, irrespective of concentration temperature. In the case of using n-butylamine having a boiling point higher than 50° C., it was confirmed that the decomposition of ester bonds progressed under a concentration temperature condition of 60° C. or higher. These results demonstrated that even in a precipitated state of PET resin at the time of concentration, the decomposition of ester bonds progresses upon contact with a base at a high temperature. As for a base, such as pyridine, which has a high boiling point, the decomposition of ester bonds does not occur as long as concentration under reduced pressure is performed at 50° C.
From these results, it was found necessary to use an organic solvent that can be mixed with HFIP. In the case of using an organic base having a boiling point higher than 50° C., it was also found necessary to remove the solvent by concentration under reduced pressure at 50° C. or lower.
Hereinafter, results of carrying out the pretreatment method of embodiments of the present invention and carrying out measurement by size exclusion chromatography will be described. In this experiment, light-deteriorated PET (10 mg) was dissolved in HFIP (2 mL) (first solution). Isopropylamine was added thereto as an organic base at 0.25 mmol/L (second solution), followed by warming at 50° C. for 1 h. Then, 2 mL of ethyl acetate was added, and the mixture was thoroughly stirred (third solution). Then, the solvent was removed by concentration under reduced pressure at 30° C. to obtain a solid sample. The obtained solid sample was measured by size exclusion chromatography.
For measurement, the SEC device ACQUITY APC from Waters Corp. was used. Also, APC-XT, 186006995, 186006998, 186007003, and 18600754 were used as columns.
Six types of commercially available polymethyl methacrylate (PMMA) standard samples having a peak top molecular weight of 102500, 56900, 24400, 10900, 8350, or 4250 were used to carry out measurement. A triple calibration curve was prepared.
The solid sample obtained by pretreatment was dissolved at 1 mg/l mL in an eluent of HFIP containing 10 mmol/L of sodium trifluoroacetate. A sample bottle of the obtained solution was capped and left standing overnight. The sample was added to a vial for measurement, filtered through a PTFE syringe filter having a pore size of 0.2 μm, and subjected to measurement.
Eluent: HFIP containing 10 mmol/L of sodium trifluoroacetate
Column temperature: 40° C.
Flow rate: 0.25 mL/min
Sample concentration: 1 mg/mL
Injection volume: 0.2 μL/run
Detector: RI detector (40° C.)
The measurement results are shown in
As described above, according to embodiments of the present invention, the decomposition of ester bonds can be suppressed in the pretreatment of a sample consisting of polyester or a polyester decomposition product for carrying out size exclusion chromatography, because an organic solvent that has a higher boiling point than that of 1,1,1,3,3,3-hexafluoro-2-propanol and is compatible with 1,1,1,3,3,3-hexafluoro-2-propanol is added.
The present invention is not limited by the embodiments described above. It is obvious that those ordinarily skilled in the art are capable of carrying out many modifications and combinations without departing from the technical brief of the present invention.
This patent application is a national phase filing under section 371 of PCT application no. PCT/JP2019/047222, filed on Dec. 3, 2019, which application is hereby incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/047222 | 12/3/2019 | WO |
