Method for decomposing fluorine-containing polymer

Abstract

To provide a method for decomposing a fluorine-containing polymer that is capable of decomposing the fluorine-containing polymer while suppressing impurity formation following the decomposition reaction.SOLUTION: A method for decomposing a fluorine-containing polymer comprises a decomposition step of reacting the fluorine-containing polymer in subcritical water at a temperature of 180°C or more and less than 250°C, with a concentration of 0.5 M or less of at least one basic compound selected from alkali metal hydroxides and alkaline earth metal hydroxides.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a method for decomposing a fluorine-containing polymer. [Background technology]

[0002] Since fluorine-containing polymers have high chemical stability and high thermal resistance, not only do they require high temperatures for incineration in waste disposal, but the hydrogen fluoride produced causes significant deterioration of incinerator materials. Therefore, new waste disposal methods other than incineration and landfilling are required. For example, Patent Documents 1 and 2 and Non-Patent Document 1 describe a method of decomposing fluorine-containing polymers by reacting them in subcritical water containing a basic compound such as potassium hydroxide. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-155478 [Patent Document 2] JP 2023-066742 A [Non-patent literature]

[0004] [Non-Patent Document 1] Jin Hamaura et al., Eur. Polym. J. 182 (2023), 111724 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a method for decomposing a fluorine-containing polymer, which is capable of decomposing a fluorine-containing polymer while suppressing the generation of impurities after the decomposition reaction. [Means for solving the problem]

[0006] The present disclosure (1) relates to a method for decomposing a fluorine-containing polymer, comprising a decomposition step of reacting the fluorine-containing polymer in subcritical water at a temperature of 180° C. or higher and lower than 250° C., and containing at least one basic compound selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides at a concentration of 0.5 M or lower.

[0007] The present disclosure (2) relates to the method for decomposing a fluorine-containing polymer according to the present disclosure (1), in which the temperature of the subcritical water in the decomposition step is 200° C. or higher.

[0008] The present disclosure (3) is the method for decomposing a fluorine-containing polymer according to the present disclosure (1) or (2), in which the fluorine-containing polymer is a fluorine-containing rubber.

[0009] The present disclosure (4) relates to the method for decomposing a fluorine-containing polymer according to the present disclosure (3), in which the object of decomposition in the decomposition step is a crosslinked product of a composition containing the fluororubber.

[0010] The present disclosure (5) is a method for decomposing a fluorine-containing polymer in any combination with any of the present disclosures (1) to (4), which includes a crushing step of crushing the fluorine-containing polymer into crushed particles having a maximum linear length of 3 mm or less before the decomposition step.

[0011] The present disclosure (6) is a method for decomposing a fluorine-containing polymer in any combination with any of the present disclosures (1) to (5), in which the basic compound is sodium hydroxide and / or potassium hydroxide.

[0012] The present disclosure (7) is a method for decomposing a fluorine-containing polymer in any combination with any of the present disclosures (1) to (6), which includes, after the above-mentioned decomposition step, a recovery step of adding calcium hydroxide to the aqueous solution after the decomposition step and recovering the generated calcium fluoride. Effect of the Invention

[0013] According to the present disclosure, it is possible to provide a method for decomposing a fluorine-containing polymer, which can decompose a fluorine-containing polymer while suppressing the generation of impurities after the decomposition reaction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present disclosure will now be described in detail.

[0015] The present disclosure relates to a method for decomposing a fluorine-containing polymer, comprising a decomposition step of reacting the fluorine-containing polymer in subcritical water at 180° C. or higher and lower than 250° C. and containing at least one basic compound selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides in a concentration of 0.5 M or lower. Since the method for decomposing a fluorine-containing polymer of the present disclosure has the above-mentioned configuration, it is possible to decompose the fluorine-containing polymer while suppressing the generation of impurities after the decomposition reaction.

[0016] In the present disclosure, a fluorine-containing polymer is treated in subcritical water containing a basic compound, and it is believed that the basic compound extracts hydrogen fluoride (HF) from the polymer, causing the polymer to decompose. According to this mechanism, it is believed that decomposition by the present disclosure is difficult for polymers that do not contain hydrogen atoms, such as polytetrafluoroethylene (PTFE). Therefore, it is preferable that polymers that do not contain hydrogen atoms are excluded from the application of the present disclosure.

[0017] In addition, in the present disclosure, as described above, it is considered that decomposition occurs by abstracting HF from the polymer, and although fluorine atoms are removed from the polymer, the polymer is not completely decomposed to carbon dioxide. However, since it is possible to remove fluorine atoms from the polymer, in the present disclosure, even decomposition that is not completely decomposed to carbon dioxide is treated as decomposition of the polymer.

[0018] Subcritical water is pressurized water in a liquid state at a temperature range above 100°C but lower than the critical temperature of 374°C. Subcritical water has different physical properties from water below 100°C. In particular, subcritical water in the range of 200°C to 300°C has a significantly reduced dielectric constant, exhibiting lipid solubility almost equivalent to that of methanol or acetone at room temperature, and has a low dielectric constant of 10 at room temperature. -14The ion product in mol / L is 10 -11 The concentration of hydrogen ions and hydroxide ions is on the order of mol / L, and is 30 times higher than that of water at room temperature. Therefore, it is known that subcritical water, particularly at 200°C to 300°C, exhibits a different reactivity from water at room temperature. In the decomposition method of the present disclosure, the temperature of the subcritical water in the decomposition step is less than 250°C, preferably 245°C or less, more preferably 240°C or less, and even more preferably 235°C or less, and is 180°C or more, preferably 200°C or more, more preferably 205°C or more, even more preferably 210°C or more, even more preferably 215°C or more, particularly preferably 220°C or more, and even more preferably 225°C or more.

[0019] The water used for preparing the subcritical water is not particularly limited, and any water may be used, such as tap water, ion-exchanged water, distilled water, well water, etc., but ion-exchanged water and distilled water are preferred from the viewpoint of suppressing side reactions caused by the influence of coexisting salts, etc. The amount of water used may be enough to fully immerse the fluorine-containing polymer to be treated, but care must be taken if the amount of water introduced into the sealed container for pressurization is extremely small, as the water will all turn into steam after heating and will not become subcritical water.

[0020] In the decomposition method of the present disclosure, at least one basic compound selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides is used. As already mentioned, the basic compound is used to cause a reaction of abstracting HF from the fluorine-containing polymer.

[0021] Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, etc., and among these, sodium hydroxide and / or potassium hydroxide are preferred. Here, potassium hydroxide is known to have a higher activity and higher basicity than sodium hydroxide in a concentrated solution, and is expected to have high activity in the HF abstraction reaction. In fact, in the present disclosure, it has been confirmed that when potassium hydroxide is used to decompose a fluorine-containing polymer, the activity is higher than when sodium hydroxide is used. From this viewpoint, potassium hydroxide is the most preferred.

[0022] Examples of the alkaline earth metal hydroxide include calcium hydroxide and barium hydroxide.

[0023] The concentration of the basic compound in the subcritical water is 0.5 M or less, preferably 0.45 M or less, more preferably 0.40 M or less, and even more preferably 0.35 M or less, and is preferably 0.01 M or more, more preferably 0.05 M or more, even more preferably 0.10 M or more, and even more preferably 0.15 M or more. As is well known to those skilled in the art, the unit "M" means mol / L.

[0024] The pH of the subcritical water is preferably 12 or higher, more preferably 12.7 or higher, and even more preferably 13 or higher, and is preferably 13.7 or lower, more preferably 13.6 or lower, and even more preferably 13.5 or lower.

[0025] Next, a method of reacting a fluorine-containing polymer in subcritical water containing a basic compound will be described. Water, a basic compound, and the fluorine-containing polymer to be treated are added to a pressure vessel having a size corresponding to the amount of the fluorine-containing polymer to be treated, and the inside of the pressure vessel is pressurized and sealed. To pressurize the inside of the pressure vessel, a gas may be enclosed. Examples of such gas include air, argon, and nitrogen. The degree of pressurization may be about 0.5 MPa, but is not particularly limited.

[0026] The pressure vessel that has undergone the above process is heated to initiate the decomposition reaction. The heating temperature is less than 250°C, but is preferably 245°C or less, more preferably 240°C or less, and even more preferably 235°C or less, and is 180°C or more, preferably 200°C or more, more preferably 205°C or more, even more preferably 210°C or more, even more preferably 215°C or more, particularly preferably 220°C or more, and even more preferably 225°C or more. When the pressure vessel itself is equipped with a heating means, the heating means may be used for heating, and when the pressure vessel itself is not equipped with a heating means, the entire pressure vessel may be heated in an autoclave or oven. The reaction time may be about 6 hours to 24 hours.

[0027] In the aqueous solution after the decomposition reaction, the fluorine atoms contained in the fluorine-containing polymer are contained as fluoride ions. The decomposition method of the present disclosure preferably includes, after the decomposition step, a recovery step of adding calcium hydroxide to the aqueous solution after the decomposition and recovering the calcium fluoride produced. The fluoride ions contained in the aqueous solution after the decomposition can be converted into calcium fluoride, which is a raw material for all fluorine compounds, by reacting with calcium ions generated from the added calcium hydroxide. The decomposition method of the present disclosure includes the recovery step, thereby making it possible to effectively utilize resources. Furthermore, as described above, the decomposition method of the fluorine-containing polymer of the present disclosure can suppress the generation of impurities after the decomposition reaction, and therefore can reduce impurities when recovering calcium fluoride.

[0028] In addition to fluoride ions, the aqueous solution after the decomposition reaction contains polymer decomposition products after HF extraction. As mentioned above, these decomposition products are considered to be elemental carbon with double bonds, and are often black in color. Since they are solid, they can be easily separated, and since the fluorine atoms have been removed by the above-mentioned recovery process, they can be easily disposed of by incineration.

[0029] The decomposition method of the present disclosure preferably includes a pulverization step of pulverizing the fluorine-containing polymer into pulverized particles having a maximum linear length of 3 mm or less before the decomposition step. By including the pulverization step in the decomposition method of the present disclosure, the fluorine-containing polymer can be easily decomposed.

[0030] The grinding method is not particularly limited, but examples thereof include freeze grinding, disk milling, hammer milling, stone mill type grinding machine, jet milling, and the like.

[0031] The grinding temperature is preferably −200° C. or higher, and preferably 90° C. or lower, more preferably 40° C. or lower, and further preferably 0° C. or lower.

[0032] The maximum linear length of the ground particles of the fluorine-containing polymer is preferably 3 mm or less, more preferably 2 mm or less, even more preferably 1 mm or less, and even more preferably 500 μm or less. Also, it is preferably 10 μm or more, more preferably 30 μm or more, and even more preferably 100 μm or more. When the average particle size of the ground particles of the fluorine-containing polymer is within the above range, the fluorine-containing polymer is more easily decomposed.

[0033] The maximum linear length was determined by observing 100 or more secondary particles using SEM images, measuring the major axis of each secondary particle, and determining the largest major axis among the secondary particles as the maximum linear length.

[0034] The transmittance of the aqueous solution after the decomposition reaction can be measured using an Agilent Cary 7000 UMS. At this time, the average value of %T from 380 to 780 nm was taken as the transmittance. The higher the transmittance value, the lighter the color of the solution and the fewer impurities there are.

[0035] The transmittance of the aqueous solution after the decomposition reaction is preferably 40% T or more, more preferably 50% T or more, and even more preferably 70% T or more. There is no particular upper limit and it may be 100% T, but it is usually about 90% T. When the transmittance of the aqueous solution after the decomposition reaction is within the above range, calcium hydroxide can be added to the aqueous solution after the decomposition step, and the amount of impurities contained in the generated calcium fluoride can be reduced.

[0036] The fluorine-containing polymer to be decomposed in the present disclosure is a polymer containing a fluorine atom in the molecule, and if the molecule contains even one fluorine atom, it is the decomposition target of the present disclosure. Fluorine-containing polymers are evaluated for their high chemical resistance, heat resistance, weather resistance, and other properties, and are used in all fields including industry and medicine. On the other hand, these polymers are not easily decomposed due to their high chemical stability and high durability against heat. The present disclosure provides a method for chemically decomposing these polymers. As such a fluorine-containing polymer, it is preferable that the polymer has a hydrogen atom in the molecule. In addition, the fluorine-containing polymer may be a fluororesin or a fluororubber, and may be a homopolymer or a copolymer.

[0037] Examples of the fluororesin include polytetrafluoroethylene [PTFE], tetrafluoroethylene [TFE] / perfluoro(alkyl vinyl ether) [PAVE] copolymer [PFA], TFE / hexafluoropropylene [HFP] copolymer [FEP], ethylene [Et] / TFE copolymer [ETFE], Et / TFE / HFP copolymer [EFEP], polychlorotrifluoroethylene [PCTFE], chlorotrifluoroethylene [CTFE] / TFE copolymer, CTFE / TFE / PAVE copolymer, Et / CTFE copolymer, polyvinyl fluoride [PVF], polyvinylidene fluoride [PVdF], vinylidene fluoride [VdF] / TFE copolymer, VdF / HFP copolymer, VdF / TFE / HFP copolymer, VdF / HFP / (meth)acrylic acid copolymer, VdF / CTFE copolymer, VdF / pentafluoropropylene copolymer, VdF / PAVE / TFE copolymer, and TFE / perfluoroalkyl allyl ether copolymer. The above perfluoroalkyl allyl ether is CF 2 =CFCF 2 -O-Rf 4 (Rf 4 is a monomer represented by a perfluoroalkyl group having 1 to 5 carbon atoms.

[0038] The fluororesin may be a partially fluorinated polymer or a perfluoropolymer, with the partially fluorinated polymer being preferred.

[0039] As the fluororesin, at least one selected from the group consisting of ETFE, EFEP, Et / CTFE copolymer, PVF, PVdF, VdF / TFE copolymer, VdF / HFP copolymer, VdF / TFE / HFP copolymer, VdF / HFP / (meth)acrylic acid copolymer, VdF / CTFE copolymer, VdF / pentafluoropropylene copolymer, and VdF / PAVE / TFE copolymer is preferred, and VdF / HFP copolymer and VdF / TFE / HFP copolymer are more preferred.

[0040] The number of carbon atoms in the perfluoroalkyl group in the above PAVE is preferably 1 to 10, and more preferably 1 to 5. Examples of the perfluoroalkyl group include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group, and perfluoro(propyl vinyl ether) [PPVE] in which the perfluoroalkyl group is a perfluoropropyl group is preferred.

[0041] The fluororubber may be a partially fluorinated rubber or a perfluororubber, with the partially fluorinated rubber being preferred.

[0042] Examples of the partially fluorinated rubber include vinylidene fluoride (VdF)-based fluororubber, tetrafluoroethylene (TFE) / propylene (Pr)-based fluororubber, tetrafluoroethylene (TFE) / propylene / vinylidene fluoride (VdF)-based fluororubber, ethylene / hexafluoropropylene (HFP)-based fluororubber, ethylene / hexafluoropropylene (HFP) / vinylidene fluoride (VdF)-based fluororubber, ethylene / hexafluoropropylene (HFP) / tetrafluoroethylene (TFE)-based fluororubber, etc. Among these, at least one selected from the group consisting of vinylidene fluoride-based fluororubber and tetrafluoroethylene / propylene-based fluororubber is preferred.

[0043] The vinylidene fluoride-based fluororubber is preferably a copolymer consisting of 45 to 85 mol % of vinylidene fluoride and 55 to 15 mol % of at least one other monomer copolymerizable with vinylidene fluoride, and more preferably a copolymer consisting of 50 to 80 mol % of vinylidene fluoride and 50 to 20 mol % of at least one other monomer copolymerizable with vinylidene fluoride.

[0044] In this specification, the content of each monomer constituting the fluoropolymer can be calculated by an appropriate combination of NMR, FT-IR, elemental analysis and X-ray fluorescence analysis depending on the type of monomer.

[0045] Examples of at least one other monomer copolymerizable with the vinylidene fluoride include tetrafluoroethylene (TFE), hexafluoropropylene (HFP), fluoroalkyl vinyl ether, trifluoroethylene, trifluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, hexafluoroisobutene, vinyl fluoride, perfluoroalkyl allyl ether, and a compound represented by the general formula (6): CH 2 =CFRf 61 (In the formula, Rf 61 is a straight-chain or branched fluoroalkyl group having 1 to 12 carbon atoms), a fluoromonomer represented by the general formula (7): CH 2 =CH-(CF 2 ) n -X 2 (In the formula, X 2 is H or F, and n is an integer of 3 to 10.) and monomers such as monomers that provide crosslinking sites; and non-fluorinated monomers such as ethylene, propylene, and alkyl vinyl ethers. These can be used alone or in any combination. Among these, it is preferable to use at least one selected from the group consisting of TFE, HFP, and fluoroalkyl vinyl ethers. Fluoroalkyl vinyl ethers include: General formula (8):CF 2 =CF-ORf 81 (In the formula, Rf 81 represents a perfluoroalkyl group having 1 to 8 carbon atoms; General formula (9):CF 2 =CFOCF 2 ORf 91 (In the formula, Rf 91is a linear or branched perfluoroalkyl group having 1 to 6 carbon atoms, a cyclic perfluoroalkyl group having 5 to 6 carbon atoms, or a linear or branched perfluorooxyalkyl group having 2 to 6 carbon atoms and containing 1 to 3 oxygen atoms), and General formula (10):CF 2 =CFO(CF 2 CF(Y 10 )O) m (CF 2 ) n F (In the formula, Y 10 represents a fluorine atom or a trifluoromethyl group. m is an integer of 1 to 4. n is an integer of 1 to 4.) is preferred, and a fluoromonomer represented by general formula (8) is more preferred. The perfluoroalkyl allyl ethers include General formula (11): CF 2 =CF-CF 2 ORf 111 (In the formula, Rf 111 represents a perfluoroalkyl group having 1 to 5 carbon atoms.

[0046] Specific examples of vinylidene fluoride-based fluororubbers include VdF / HFP-based rubber, VdF / HFP / TFE-based rubber, VdF / fluoromonomer-based rubber represented by general formula (6), VdF / fluoromonomer-based rubber represented by general formula (6) / TFE-based rubber, VdF / perfluoro(methyl vinyl ether) [PMVE]-based rubber, VdF / PMVE / TFE-based rubber, VdF / PMVE / TFE / HFP-based rubber, etc. Examples of VdF / fluoromonomer-based rubber represented by general formula (6) include VdF / CH 2 =CFCF 3 The VdF / fluoromonomer / TFE rubber represented by the general formula (6) is preferably VdF / TFE / CH 2 =CFCF 3 Rubbers of this type are preferred.

[0047] Above VdF / CH2 =CFCF 3 The rubber is made of VdF40 to 99.5 mol% and CH 2 =CFCF 3 It is preferable that the copolymer is composed of 0.5 to 60 mol % of VdF, 50 to 85 mol % of CH 2 =CFCF 3 It is more preferable that the copolymer is composed of 20 to 50 mol %.

[0048] The above-mentioned tetrafluoroethylene / propylene-based fluororubber is preferably a copolymer consisting of 45 to 70 mol % of tetrafluoroethylene, 55 to 30 mol % of propylene, and 0 to 5 mol % of a fluoromonomer that provides a crosslinking site.

[0049] The monomer that provides a crosslinking site is a monomer (cure site monomer) having a crosslinkable group that provides a crosslinking site to the fluoropolymer for forming a crosslink with a crosslinking agent.

[0050] Examples of monomers that provide crosslinking sites include: General formula (12):CX 3 2 =CX 3 -R f 121 CHR 121 X 4 (In the formula, X 3 is a hydrogen atom, a fluorine atom or CH 3 , R f 121 represents a fluoroalkylene group, a perfluoroalkylene group, a fluoro(poly)oxyalkylene group or a perfluoro(poly)oxyalkylene group; R 121 is a hydrogen atom or CH 3 , X 4 is an iodine atom or a bromine atom), General formula (13):CX 3 2 =CX 3 -R f 131 X 4 (In the formula, X 3is a hydrogen atom, a fluorine atom or CH 3 , R f 131 represents a fluoroalkylene group, a perfluoroalkylene group, a fluoropolyoxyalkylene group or a perfluoropolyoxyalkylene group; X 4 is an iodine atom or a bromine atom), General formula (14):CF 2 =CFO(CF 2 CF(CF 3 )O) m (CF 2 ) n -X 5 (In the formula, m is an integer of 0 to 5, n is an integer of 1 to 3, X 5 is a cyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CH 2 I) a fluoromonomer represented by the formula: General formula (15):CH 2 =CFCF 2 O(CF(CF 3 )CF 2 O) m (CF(CF 3 )) n -X 6 (In the formula, m is an integer of 0 to 5, n is an integer of 1 to 3, X 6 is a cyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CH 2 OH), and General formula (16):CR 162 R 163 =CR 164 -Z-CR 165 =CR 166 R 167 (In the formula, R 162 , R 163 , R 164 , R 165 , R 166 and R 167are the same or different and each is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. Z is a linear or branched alkylene group having 1 to 18 carbon atoms, which may have an oxygen atom, a cycloalkylene group having 3 to 18 carbon atoms, an at least partially fluorinated alkylene group or oxyalkylene group having 1 to 10 carbon atoms, or -(Q) p -CF 2 O-(CF 2 CF 2 O) m (CF 2 O) n -CF 2 -(Q) p - (wherein Q is an alkylene group or an oxyalkylene group, p is 0 or 1, and m / n is 0.2 to 5), and is a (per)fluoropolyoxyalkylene group having a molecular weight of 500 to 10,000.

[0051] X 3 is preferably a fluorine atom. f 121 and R f 131 R is preferably a perfluoroalkylene group having 1 to 5 carbon atoms. 121 is preferably a hydrogen atom. 5 is a cyano group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CH 2 It is preferably I. 6 is a cyano group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CH 2 It is preferably OH.

[0052] The monomer that provides the crosslinking site is CF 2 =CFOCF 2 CF(CF 3 )OCF 2 CF 2 C.N., C.F. 2 =CFOCF 2 CF(CF 3 )OCF 2 CF2 COOH, CF 2 =CFOCF 2 CF(CF 3 )OCF 2 CF 2 CH 2 I, C.F. 2 =CFOCF 2 CF 2 CH 2 I, C.H. 2 =CFCF 2 OCF(CF 3 )CF 2 OCF(CF 3 )CN, CH 2 =CFCF 2 OCF(CF 3 )CF 2 OCF(CF 3 )COOH, CH 2 =CFCF 2 OCF(CF 3 )CF 2 OCF(CF 3 )CH 2 OH, CH 2 =CHCF 2 CF 2 I, C.H. 2 =CH(CF 2 ) 2 CH=CH 2 , C.H. 2 =CH(CF 2 ) 6 CH=CH 2 , and CF 2 =CFO(CF 2 ) 5 CN, and CF 2 =CFOCF 2 CF(CF 3 )OCF 2 CF 2 CN and CF 2 =CFOCF 2 CF 2 CH 2 It is more preferable that the compound is at least one selected from the group consisting of I.

[0053] The fluororubber has a glass transition temperature of preferably −70° C. or higher, more preferably −60° C. or higher, and even more preferably −50° C. or higher, from the viewpoint of excellent compression set characteristics at high temperatures. Also, from the viewpoint of good cold resistance, the glass transition temperature is preferably 5° C. or lower, more preferably 0° C. or lower, and even more preferably −3° C. or lower.

[0054] The glass transition temperature can be determined by obtaining a DSC curve using a differential scanning calorimeter (DSC822e, manufactured by Mettler Toledo) by heating 10 mg of a sample at a rate of 10°C / min, and by determining the temperature that indicates the midpoint between the two intersection points of an extension of the baseline before and after the second-order transition of the DSC curve and a tangent to the inflection point of the DSC curve.

[0055] The above fluororubber has a Mooney viscosity of ML at 170°C, which is excellent in heat resistance. (1+20) is preferably 30 or more, more preferably 40 or more, and even more preferably 50 or more. In terms of good processability, it is preferably 150 or less, more preferably 120 or less, and even more preferably 110 or less.

[0056] The above fluororubber has a Mooney viscosity of ML at 140°C, which is excellent in heat resistance. (1+20) is preferably 30 or more, more preferably 40 or more, and even more preferably 50 or more. In terms of good processability, it is preferably 180 or less, more preferably 150 or less, and even more preferably 110 or less.

[0057] The above fluororubber has a Mooney viscosity of ML at 100°C, which is excellent in heat resistance. (1+10) is preferably 10 or more, more preferably 20 or more, and even more preferably 30 or more. From the viewpoint of good processability, it is preferably 120 or less, more preferably 100 or less, and even more preferably 80 or less.

[0058] The Mooney viscosity can be measured using a Mooney viscometer MV2000E manufactured by ALPHA TECHNOLOGIES at 170° C., 140° C. or 100° C. in accordance with JIS K6300.

[0059] In the decomposition method of the present disclosure, the decomposition target of the decomposition step may be a crosslinked product of a composition containing the fluororubber. The composition preferably contains the fluororubber and a crosslinking agent.

[0060] Examples of the crosslinking agent include crosslinking agents used in peroxide crosslinking, polyol crosslinking, polyamine crosslinking, triazine crosslinking, oxazole crosslinking, imidazole crosslinking, and thiazole crosslinking. When the fluororubber is a fluororubber having a cyano group (-CN group), the crosslinking agent is preferably at least one selected from the group consisting of an oxazole crosslinking agent, an imidazole crosslinking agent, and a thiazole crosslinking agent.

[0061] The crosslinking agent used in peroxide crosslinking may be any organic peroxide that can easily generate peroxy radicals in the presence of heat or an oxidation-reduction system, and specifically, for example, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane can be used. In general, the type and amount of organic peroxide used are selected taking into consideration the amount of active -OO-, decomposition temperature, etc.

[0062] In addition, the crosslinking aid that can be used in this case may be any compound that has a reactive activity with peroxy radicals and polymer radicals, such as -CH=CH 2 , -CH 2 CH=CH 2 , -CF=CF 2 , -C(CF 3 )=CF 2 , -C(CH 3 )=CF 2 , -CF = CF(CF 3 ), -CF=CF(CH 3 ), -C(C 6 H 5 )=CF 2 , -CF = CF(C6 H 5 ), -CH=CF 2 , -CF=CHF, -C(CF 3 )=CHF, -CF=CH(CF 3 ), -CH=CF(CF 3 ) and other polyfunctional compounds having functional groups (see "C 6 H 5 " represents a phenyl group). Specific examples include triallyl cyanurate, triallyl isocyanurate (TAIC), triacryl formal, triallyl trimellitate, N,N'-n-phenylene bismaleimide, dipropargyl terephthalate, diallyl phthalate, tetraallyl terephthalate amide, triallyl phosphate, bismaleimide, fluorinated triallyl isocyanurate (1,3,5-tris(2,3,3-trifluoro-2-propenyl)-1,3,5-triazine 2,4,6-trione), tris(diallylamine)-S-triazine, triallyl phosphite, N,N-diallylacrylamide, 1,6-divinyldodecafluorohexane, and the like.

[0063] In addition, the crosslinking aid used together with the peroxide crosslinking agent is represented by the general formula (48): [ka] (Wherein, six R 31 each independently represents H, a halogen atom, or an optionally halogenated group having 1 to 5 carbon atoms which may have an ether bond inserted therein; Z 31 can also include a compound represented by a linear or branched alkylene group, cycloalkylene group, or (per)fluoropolyoxyalkylene group having 1 to 18 carbon atoms, which optionally contains a heteroatom and is optionally halogenated.

[0064] The compound represented by the general formula (48) includes the compound represented by the general formula (49): [ka] (In the formula, j is an integer of 2 to 10, preferably an integer of 4 to 8, and four R 32 each independently represents H, F, or an alkyl group or a (per)fluoroalkyl group having 1 to 5 carbon atoms), a compound represented by general formula (50): [ka] (In the formula, Y 31 are each independently F, Cl or H; Y 32 each independently represents F, Cl, H, or OR 33 (where R 33 is a branched or straight chain alkyl group, which may be partially, substantially or completely fluorinated or chlorinated; Z 33 is a divalent group having 2 to 10 carbon atoms, optionally fluorinated, which may have an ether bond inserted therein, preferably Z 33 m is an integer from 3 to 5; -(CF 2 ) m - group, and the compound represented by the general formula (50) is preferably F 2 C=CF-O-(CF 2 ) 5 -O-CF=CF 2 A compound represented by the general formula (51): [ka] (In the formula, Y 31 , Y 32 and Z 33 is as above, and R 34 are each independently H, F, or an alkyl group or a (per)fluoroalkyl group having 1 to 5 carbon atoms.

[0065] The crosslinking aid used together with the above crosslinking agent or peroxide crosslinking agent is a crosslinking aid represented by the general formula (52): [ka] (In the formula, R 35 ~R 37are each independently a hydrogen atom, a fluorine atom, an alkyl group, a fluorinated alkyl group, or a substituted or unsubstituted aryl group; R 35 ~R 37 At least one of R is a fluorine atom or a group containing a fluorine atom. m is an integer of 1 to 5. When m is 2 or more, m R 35 ~R 37 may be the same or different. The hydrogen atom of the benzene ring may be substituted. When m is 1, it is preferable that the compound has two or more of the structure.

[0066] The compound having the structure represented by general formula (52) includes the compound having the structure represented by general formula (53): [ka]

[0067] (In the formula, R 35 ~R 37 is as defined above, p is an integer of 0 to 2, and n is an integer of 2 to 6.), a compound represented by the general formula (54): [ka] (In the formula, R 35 ~R 37 As stated above. R 38 is a single bond, -SO 2 -, -O-, -S-, -CO-, a heteroatom-containing group, a substituted or unsubstituted alkylene group, a substituted or unsubstituted cycloalkylene group, or a substituted or unsubstituted arylene group. m is an integer of 1 to 5. These groups may be partially or completely fluorinated.

[0068] The heteroatom-containing group is not particularly limited as long as it is a divalent group containing a heteroatom. Examples of the heteroatom include an oxygen atom, a nitrogen atom, a sulfur atom, a boron atom, and a phosphorus atom.

[0069] Examples of crosslinking agents used in polyol crosslinking include polyhydric alcohol compounds such as bisphenol A and bisphenol AF.

[0070] Examples of crosslinking agents used in polyamine crosslinking include polyamine compounds such as hexamethylenediamine carbamate, N,N'-dicinnamylidene-1,6-hexanediamine, and 4,4'-bis(aminocyclohexyl)methane carbamate.

[0071] Examples of the crosslinking agent used for the oxazole crosslinking, imidazole crosslinking, and thiazole crosslinking include those represented by the general formula (55):

[0072] [ka] (In the formula, R 41 -SO 2 -, -O-, -CO-, an alkylene group having 1 to 6 carbon atoms, a perfluoroalkylene group having 1 to 10 carbon atoms or a single bond, or

[0073] [ka]

[0074] R 42 and R 43 One is -NH 2 and the other is -NHR 44 , -NH 2 , -OH or -SH, R 44 is a hydrogen atom, a fluorine atom or a monovalent organic group, preferably R 42 Ga-NH 2 And R 43 Ga-NHR 44 Examples of the crosslinking agent include a bisdiaminophenyl crosslinking agent, a bisaminophenol crosslinking agent, and a bisaminothiophenol crosslinking agent, which are represented by the formula:

[0075] Preferred specific examples of the alkylene group having 1 to 6 carbon atoms include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, and a hexylene group. Examples of the perfluoroalkylene group having 1 to 10 carbon atoms include [ka] etc.

[0076] These compounds are known as examples of bisdiaminophenyl compounds in JP-B-2-59177, JP-A-8-120146 and the like.

[0077] The crosslinking agent used for the oxazole crosslinking, imidazole crosslinking, and thiazole crosslinking also includes a crosslinking agent represented by the general formula (56): [ka] (In the formula, R 41 As mentioned above, R 45 are each independently any of the following groups: [ka] ), a bisamidrazone-based crosslinking agent represented by the general formula (57): [ka] (In the formula, Rf 41 is a perfluoroalkylene group having 1 to 10 carbon atoms), an amidrazone crosslinking agent represented by the general formula (58): [ka] (wherein n is an integer of 1 to 10), a bisamidoxime-based crosslinking agent represented by the general formula (59): HN=CR 45 R 46 (In the formula, R 45 H, NH 2 , and N.H.R. 47 R 46 Ph,SO 2H, N.R. 48 R 49 , 2-pyridine, and CH 2 CONH 2 R 47 Ph, NH 2 R is selected from the group consisting of 48 H, NHPh, CH 2 CONH 2 , a linear alkyl group having 1 to 8 carbon atoms, and a branched alkyl group having 1 to 8 carbon atoms; and R 49 Ph, COOC(CH 3 ) 3 , N.H. 2 , C.H. 2 COOH, CSNH 2 , CNHNH 3 + Cl - , p-phenylCN, [ka] and COPh).

[0078] These bisaminophenol-based crosslinking agents, bisaminothiophenol-based crosslinking agents, bisdiaminophenyl-based crosslinking agents, etc. have traditionally been used in crosslinking systems in which the cyano group is the crosslinking point, but they also react with carboxyl groups and alkoxycarbonyl groups to form oxazole rings, thiazole rings, and imidazole rings, thereby giving crosslinked products.

[0079] The crosslinking agent may also be a compound represented by the general formula (60): X 41 -(CH 2 ) n -R 50 -(CH 2 ) m -X 41 (In the formula, X 41 each independently represents an alkyne group, a nitrile group, or Y 41 P N 3 (Y 41 SO, SO 2 , C 6 H 4or CO, and p is 0 or 1; n and m are independently integers of 1 to 4; R 50 teeth, i) a fluoroalkylene group having 3 to 10 carbon atoms, ii) a fluoroalkoxysilane group having 3 to 10 carbon atoms, iii) a substituted arylene group, iv) oligomers containing copolymerized units of vinylidene fluoride and perfluoro(methyl vinyl ether); v) Oligomers containing copolymerized units of vinylidene fluoride and hexafluoropropylene; vi) oligomers containing copolymerized units of tetrafluoroethylene and perfluoro(methyl vinyl ether); and vii) a crosslinking agent selected from the group consisting of oligomers containing copolymerized units of tetrafluoroethylene and hydrocarbon olefin. This crosslinking agent is preferably used together with a fluororubber having a nitrile group, an azide group, a sulfonyl azide group, a carbonyl azide group, or an alkyne group. For example, the nitrile group of the fluororubber reacts with the azide group of the crosslinking agent to form a tetrazole ring, giving a crosslinked product.

[0080] Particularly preferred crosslinking agents include compounds having a plurality of 3-amino-4-hydroxyphenyl groups or 3-amino-4-mercaptophenyl groups, or compounds represented by the general formula (61):

[0081] [ka]

[0082] (In the formula, R 41 , R 42 and R 43As described above, specific examples of the compounds include 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (general name: bis(aminophenol) AF), 2,2-bis(3-amino-4-mercaptophenyl)hexafluoropropane, tetraaminobenzene, bis-3,4-diaminophenylmethane, bis-3,4-diaminophenyl ether, 2,2-bis(3,4-diaminophenyl)hexafluoropropane, 2,2-bis[3-amino-4-(N-phenylamino)phenyl] [3-amino-4-(N-methylamino)phenyl]hexafluoropropane, 2,2-bis[3-amino-4-(N-ethylamino)phenyl]hexafluoropropane, 2,2-bis[3-amino-4-(N-propylamino)phenyl]hexafluoropropane, 2,2-bis[3-amino-4-(N-perfluorophenylamino)phenyl]hexafluoropropane, 2,2-bis[3-amino-4-(N-benzylamino)phenyl]hexafluoropropane, and the like.

[0083] Among these, the crosslinking agent is preferably 2,2-bis[3-amino-4-(N-phenylamino)phenyl]hexafluoropropane in terms of heat resistance, steam resistance, amine resistance, and good crosslinking properties.

[0084] The content of the crosslinking agent is preferably 0.01 to 10 parts by mass, and more preferably 0.05 to 5 parts by mass, based on 100 parts by mass of the fluororubber.

[0085] The composition may contain conventional fillers.

[0086] Examples of the above-mentioned general fillers include imide-based fillers having an imide structure, such as polyimide, polyamideimide, and polyetherimide; organic fillers made of engineering plastics, such as polyarylate, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyetherketone, and polyoxybenzoate; metal oxide fillers, such as aluminum oxide, silicon oxide, and yttrium oxide; metal carbides, such as silicon carbide and aluminum carbide; metal nitride fillers, such as silicon nitride and aluminum nitride; and inorganic fillers, such as aluminum fluoride, carbon fluoride, and carbon black.

[0087] Among these, aluminum oxide, yttrium oxide, silicon oxide, polyimide, carbon fluoride, silicon carbide, silicon nitride, aluminum nitride, and carbon black are preferable.

[0088] The inorganic fillers and organic fillers may be used alone or in combination of two or more kinds.

[0089] The amount of the general filler to be mixed is preferably 0.5 to 100 parts by mass, and more preferably 5 to 50 parts by mass, based on 100 parts by mass of the fluororubber.

[0090] In particular, in fields where high purity and non-staining properties are not required, ordinary additives which are blended into fluoropolymer compositions, such as fillers, processing aids, plasticizers, colorants, etc., may be blended as necessary, and one or more types of commonly used crosslinking agents or crosslinking assistants different from the above-mentioned ones may also be blended.

[0091] The composition can be produced by kneading the fluororubber, the crosslinking agent, and, if necessary, the crosslinking accelerator and a filler.

[0092] The above kneading can be carried out using a general polymer processing machine, for example, an open roll, a Banbury mixer, a kneader, an internal mixer, or the like.

[0093] The crosslinked body can be produced by molding the composition and crosslinking the resulting molded article, or by simultaneously carrying out molding and crosslinking.

[0094] The molding method is not particularly limited, and examples thereof include compression molding, extrusion molding, transfer molding, and injection molding.

[0095] The crosslinking conditions are preferably determined depending on the type of crosslinking agent used, etc., and, for example, crosslinking is preferably performed for 1 minute to 24 hours at a temperature of 140 to 300° C. In addition, crosslinking can be performed under normal pressure, increased pressure, reduced pressure, or in air.

[0096] The crosslinking method is not particularly limited, and may be steam crosslinking, pressure molding, or a conventional method in which a crosslinking reaction is initiated by heating, or may be a radiation crosslinking method at room temperature and pressure.

[0097] Although only the initial crosslinking treatment (called primary crosslinking) may be performed, a post-treatment called secondary crosslinking may be performed after the primary crosslinking.

[0098] When primary crosslinking and secondary crosslinking are performed, the primary crosslinking is preferably performed for 5 to 120 minutes at 150 to 250° C., and more preferably for 5 to 60 minutes at 170 to 210° C. As the crosslinking means, a known crosslinking means may be used, and examples thereof include press crosslinking.

[0099] The secondary crosslinking is preferably carried out at 180 to 320° C. for 2 to 24 hours, more preferably at 280 to 310° C. for 5 to 20 hours. STEP crosslinking may also be used. As the crosslinking means, a known crosslinking means may be used, for example, oven crosslinking.

[0100] Although the embodiments have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims. EXAMPLES

[0101] Next, the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0102] The values ​​in the examples were measured by the following methods.

[0103] (1) Color of the solution after the decomposition reaction The transmittance of the solution after the decomposition reaction was measured using an Agilent Cary 7000 UMS, and the average value of %T from 380 to 780 nm was taken as the transmittance. The higher the transmittance value, the lighter the color of the solution and the fewer impurities there were.

[0104] (Production of crosslinked body of fluororubber composition) The materials were mixed in the compositions shown in Table 1 and kneaded with an open roll to obtain fluororubber compositions 1 to 3. The obtained fluororubber composition 1 was pressed at 160°C for 10 minutes and then further subjected to heat treatment in an oven at 180°C for 4 hours to obtain crosslinked body 1. The fluororubber composition 2 was pressed at 170°C for 15 minutes and then further subjected to heat treatment in an oven at 230°C for 24 hours to obtain crosslinked body 2. The materials shown in Table 1 are as follows. Fluororubber 1: VdF / HFP=78 / 22 (mol%), Mooney viscosity (ML 1+10 (100℃) = 70 Fluororubber 2: VdF / HFP=78 / 22 (mol%), Mooney viscosity (ML 1+10 (100℃))=57 Carbon black: Trade name "Thermax N990", manufactured by Cancarb Crosslinking agent 1: Perhexa 25B (2,5-dimethyl-2,5-di(t-butylperoxy)hexane, manufactured by NOF Corporation) Crosslinker 2: Bisphenol AF Crosslinking aid: TAIC (triallyl isocyanurate, manufactured by Nippon Kasei Co., Ltd.) Crosslinking accelerator: 8-benzyl-1,8-diazabicyclo[5.4.0]-7-undecenium chloride (DBU-B) Acid acceptor 1: Calcium hydroxide (product name "CALDIC#2000", manufactured by Kawamo Co., Ltd.) Acid acceptor 2: Magnesium oxide (product name "Kyowa Mag" TM 150" (manufactured by Kyowa Chemical Industry Co., Ltd.)

[0105] (Freeze-grind the sample) The freeze-grinding was carried out using a "JFC-5000" manufactured by Japan Analytical Industry Co., Ltd. 10 mg of the sample and a stainless steel ball with a diameter of 250 mm were added to a 75 mL sample container, and the sample was cooled with liquid nitrogen for 10 minutes, and then pulverized at 50 Hz and a pulverizing temperature of -196°C for 10 minutes. This process was repeated twice to obtain a powdered sample with a maximum linear length of 200 μm. Fluorine rubber 1, crosslinked bodies 1 and 2 were pulverized using this procedure and used in the following examples and comparative examples.

[0106] Example 1 30 mg of crosslinked product 1 and 10 mL of 0.1 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 230°C for 6 hours. The pressure during the reaction was 3.4 MPa. After the reaction was completed, the contents were cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0107] Example 2 The reaction was carried out in the same manner as in Example 1, except that a 0.2 M aqueous potassium hydroxide solution was used instead of a 0.1 M aqueous potassium hydroxide solution, and the pressure during the reaction was changed from 3.4 MPa to 3.5 MPa. The results are shown in Table 2. Furthermore, the aqueous solution after the reaction was centrifuged to remove the solids, and a stoichiometric amount of calcium hydroxide was added to the aqueous phase, which was then washed with hydrochloric acid to obtain calcium fluoride.

[0108] Example 3 30 mg of crosslinked product 1 and 10 mL of 0.1 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 200°C for 18 hours. The pressure during the reaction was 2.3 MPa. After the reaction was completed, the contents were cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0109] Example 4 The reaction was carried out in the same manner as in Example 1, except that in Example 3, a 0.3 M aqueous potassium hydroxide solution was used instead of a 0.1 M aqueous potassium hydroxide solution, and the reaction time was changed from 18 hours to 6 hours. The results are shown in Table 2.

[0110] Example 5 30 mg of fluororubber 1 and 10 mL of 0.1 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 230°C for 6 hours. The pressure during the reaction was 3.4 MPa. After the reaction was completed, the contents were cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0111] Example 6 30 mg of crosslinked product 2 and 10 mL of 0.2 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 200°C for 18 hours. The pressure during the reaction was 2.2 MPa. After the reaction was completed, the contents were cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0112] Example 7 30 mg of fluororubber 1 and 10 mL of 0.2 M sodium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 200°C for 18 hours. The pressure during the reaction was 2.3 MPa. After the reaction was completed, the contents were cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0113] Example 8 30 mg of fluororubber 1 and 10 mL of 0.2 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 200°C for 18 hours. The pressure during the reaction was 2.2 MPa. After the reaction was completed, the contents were cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0114] Comparative Example 1 30 mg of crosslinked product 1 and 10 mL of 0.3 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 250°C for 6 hours. The pressure during the reaction was 5.7 MPa. After the reaction was completed, the contents were cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0115] Comparative Example 2 30 mg of fluororubber 1 and 10 mL of 0.5 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 250°C for 6 hours. The pressure during the reaction was 4.4 MPa. After the reaction was completed, the contents were cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0116] Comparative Example 3 30 mg of crosslinked product 1 and 10 mL of 1.0 M potassium hydroxide aqueous solution were placed in a hot water reactor, pressurized to 0.5 MPa with argon gas, and reacted at 250°C for 6 hours. The pressure during the reaction was 4.2 MPa. After the reaction was completed, the contents were cooled to room temperature, and the fluoride ions generated in the aqueous phase were quantified by ion chromatography to confirm the yield of fluoride ions. The results are shown in Table 2.

[0117] [Table 1]

[0118] [Table 2]

Claims

1. A method for decomposing a fluorine-containing polymer, comprising a decomposition step of reacting a fluorine-containing polymer in subcritical water at a temperature of 180° C. or higher and lower than 250° C. and containing at least one basic compound selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides in a concentration of 0.5 M or lower.

2. 2. The method for decomposing a fluorine-containing polymer according to claim 1, wherein the temperature of the subcritical water in the decomposition step is 200° C. or higher.

3. 3. The method for decomposing a fluorine-containing polymer according to claim 1, wherein the fluorine-containing polymer is a fluorine-containing rubber.

4. 4. The method for decomposing a fluorine-containing polymer according to claim 3, wherein the object of decomposition in the decomposition step is a crosslinked product of the composition containing the fluororubber.

5. 3. The method for decomposing a fluorine-containing polymer according to claim 1, further comprising, prior to the decomposition step, a pulverization step of pulverizing the fluorine-containing polymer into pulverized particles having a maximum linear length of 3 mm or less.

6. 3. The method for decomposing a fluorine-containing polymer according to claim 1, wherein the basic compound is sodium hydroxide and / or potassium hydroxide.

7. 3. The method for decomposing a fluorine-containing polymer according to claim 1, further comprising, after the decomposition step, a recovery step of adding calcium hydroxide to the aqueous solution obtained after the decomposition step and recovering the calcium fluoride produced.

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