Process for producing low molecular weight polytetrafluoroethylene

Abstract

The present invention provides a method for the preparation of a high molecular weight polytetrafluoroethylene comprising the steps of: 1 -OR 2 wherein R1 and R2 are C1 to C 10 A linear or branched aliphatic group of C4 to C 10 an alicyclic or heterocyclic group of C5 to C 10 R is independently selected from aromatic or heteroaromatic groups 1 and R 2 is a C4-C alkyl group which may optionally contain heteroatoms 10 and (per)fluorinated olefins; and, optionally, aromatic hydrocarbons substituted with one or more linear or branched alkyl or alkoxy groups and / or halogen atoms; and a) a first step of mixing the mixture with at least one additive selected from the group consisting of (per)fluorinated vinyl ethers; (per)fluorinated olefins; and, optionally, aromatic hydrocarbons substituted with one or more linear or branched alkyl or alkoxy groups and / or halogen atoms; and b) a second step of irradiating the mixture thus obtained with ionizing radiation, the second step being carried out substantially in the absence of oxygen.

Description

Technical Field

[0001] This application claims priority based on European Patent Application No. 19219405.8 filed on December 23, 2019, and all the contents of this application are incorporated herein by reference for all purposes.

[0002] The present invention relates to a method for producing low molecular weight polytetrafluoroethylene (PTFE). More specifically, the present invention relates to a method for producing low molecular weight PTFE in which the production of perfluorocarboxylic acids (PFCA) having 4 to C 14 and their salts, particularly perfluorooctanoic acid (PFOA) and its salts, is restricted and further suppressed.

Background Art

[0003] Low molecular weight polytetrafluoroethylene, also called PTFE wax or PTFE micropowder, has a molecular weight of several thousand to several hundred thousand grams per mole, which is much smaller than the molecular weight of high molecular weight PTFE, also called regular PTFE, which is on the order of 10 6 ~10 7 grams per mole.

[0004] In addition to retaining the functions of regular PTFE, low molecular weight PTFE has high dispersibility. This means that it can be used as an additive particularly in rubber and plastics.

[0005] Low molecular weight PTFE is generally produced by irradiating fragments of regular PTFE to cause a decomposition reaction. Known production methods employ irradiation in the presence of oxygen, which is particularly effective in rapidly increasing the decomposition rate of PTFE and consequently rapidly decreasing its melt viscosity.

[0006] However, oxygen produces a certain amount of short-chain perfluorocarboxylic acids (PFCA), particularly C4 to C 14involved in the production of those within the range, which are currently major environmental concerns. Among these, perfluorooctanoic acid (PFOA) is particularly known for its high bioaccumulation potential.

[0007] Therefore, efforts have been made to date to provide a method for producing low molecular weight PTFE with a low potential for generating perfluorocarboxylic acids having 4 to 14 carbon atoms, and as a result, to provide PTFE micropowder that does not contain or substantially does not contain such PFCA.

[0008] Irradiation is carried out substantially in the absence of oxygen, but a method has been developed that is carried out in the presence of a specific additive that can decompose PTFE and thus can reduce the molecular weight of PTFE at a sufficient rate. For example, U.S. Patent Application Publication No. 2019 / 0023818 discloses a method for producing low molecular weight PTFE in which the additive is selected from hydrocarbons, chlorinated hydrocarbons, alcohols, and carboxylic acids.

[0009] C4~C 14 There is an increasing demand for alternative additives that can limit and even suppress the production of perfluorocarboxylic acids having 4 to carbon atoms, particularly perfluorooctanoic acid.

Summary of the Invention

Means for Solving the Problems

[0010] The present invention provides a) high molecular weight polytetrafluoroethylene (PTFE) with an ether having the formula R 1 -O-R 2 (wherein R 1 and R 2 are independently selected from linear or branched aliphatic groups having 1 to 10 carbon atoms, alicyclic or heterocyclic groups having 4 to 10 carbon atoms, aromatic or heteroaromatic groups having 5 to 10 carbon atoms, and R 1 and R 2which may optionally contain heteroatoms, especially oxygen atoms, and C4-C 10 may form an aliphatic cyclic structure); (per)fluorinated vinyl ether; (per)fluorinated olefin; and a first step of mixing with at least one additive selected from the group consisting of an optional substituted aromatic hydrocarbon; b) a second step of irradiating the mixture thus obtained with ionizing radiation, the second step being carried out substantially in the absence of oxygen; relates to a method for producing low molecular weight polytetrafluoroethylene (PTFE) comprising.

[0011] According to another aspect, the present invention relates to low molecular weight polytetrafluoroethylene (PTFE) obtained by the method specified above.

[0012] The applicant has surprisingly found that the process according to the invention produces only very small amounts of C4-C 14 perfluorocarboxylic acids (PFCA), especially very small amounts of perfluorooctanoic acid (PFOA).

DETAILED DESCRIPTION OF THE INVENTION

[0013] As used herein, a) a first step of mixing high molecular weight PTFE with at least one additive; and b) a second step of irradiating a mixture containing high molecular weight PTFE and at least one additive with ionizing radiation substantially in the absence of oxygen; A method for producing low molecular weight PTFE is described. The additive is an ether having the formula R 1 -O-R 2 wherein R 1 and R 2 are independently selected from linear or branched aliphatic groups of C1-C 10 , alicyclic or heterocyclic groups of C4-C 10 , aromatic or heteroaromatic groups of C5-C 10 , and R 1 and R 2 are C4-C which may optionally contain heteroatoms, especially oxygen atoms 10which may form an aliphatic cyclic structure); (per)fluorinated vinyl ether; (per)fluorinated olefin; and optionally substituted aromatic hydrocarbon; selected from the group consisting of.

[0014] Surprisingly, by using these additives, the production of C4-C 14 perfluorocarboxylic acids was found to be significantly reduced to 25 ppb or less, and further to less than 25 ppb, respectively. In particular, the production of perfluorooctanoic acid (PFOA) was reduced to less than 10 ppb.

[0015] As used herein, unless otherwise indicated, the following terms shall have the following meanings.

[0016] The adjective "aliphatic" means any straight or branched chain containing hydrogen and carbon atoms. An aliphatic group may be saturated or unsaturated and may contain one or more heteroatoms such as nitrogen, oxygen, sulfur, and chlorine in the chain, typically nitrogen, oxygen, or sulfur.

[0017] The adjective "alicyclic" means any aliphatic cyclic group consisting of one or more rings of all carbon atoms, which may be either saturated or unsaturated.

[0018] The adjective "aromatic" means any mononuclear or polynuclear cyclic group having a number of π electrons equal to 4n + 2 (where n is 0 or any positive integer).

[0019] The alicyclic and aromatic groups may be substituted with one or more straight or branched alkyl or alkoxy groups and / or halogen atoms, and / or may contain one or more heteroatoms such as nitrogen, oxygen, and sulfur in the ring. An alicyclic group containing one or more heteroatoms such as nitrogen, oxygen, and sulfur in the ring is referred to herein as a "heterocyclic group". An aromatic group containing one or more heteroatoms such as nitrogen, oxygen, and sulfur in the ring is referred to herein as a "heteroaromatic group". The heteroatoms of the heterocyclic group or heteroaromatic group are selected from the group consisting of oxygen, nitrogen, and sulfur.

[0020] The term "hydrocarbon" means an organic compound consisting of hydrogen and carbon. "Aromatic hydrocarbon" consists of one core composed of one benzene ring or a plurality of benzene rings condensed together by sharing two or more adjacent ring carbon atoms. Aromatic hydrocarbons can contain one or more heteroatoms such as nitrogen, oxygen, and sulfur within the ring.

[0021] The terms "alkyl" and derivative terms such as "alkoxy" include straight-chain and branched-chain within their scope. Examples of alkyl groups are methyl, ethyl, propyl, isopropyl, butyl, and isobutyl. Unless otherwise specifically indicated, each alkyl group may be unsubstituted or substituted with one or more substituents selected from, but not limited to, hydroxy, sulfo, C1-C6 alkoxy, and C1-C6 alkylthio, provided that the substituents are sterically compatible and the rules of chemical bonding and strain energy are satisfied.

[0022] The term "halogen" includes fluorine, chlorine, bromine, and iodine.

[0023] When ranges are indicated, the range endpoints are included.

[0024] The expression "high molecular weight PTFE" refers to PTFE having a standard specific gravity (SSG) of at least 2.130. The standard specific gravity (SSG) of high molecular weight PTFE does not exceed 2.300.

[0025] Preferably, the high molecular weight PTFE in which the first step a) is performed has a standard specific gravity (SSG) of 2.130 to 2.230. The standard specific gravity (SSG) is a value determined in accordance with ASTM D4895. The standard specific gravity is used as an indicator of the molecular weight of high molecular weight PTFE.

[0026] According to one embodiment of the present invention, the at least one additive has the formula R 1 -O-R 2is an ether (wherein R 1 and R 2 are each independently selected from linear or branched aliphatic groups having 1 to 10 carbon atoms, preferably linear or branched aliphatic groups having 3 to 6 carbon atoms, more preferably linear or branched aliphatic groups having 3 to 4 carbon atoms). Preferably, R 1 and R 2 are alkyl groups. More preferably, R 1 and R 2 are butyl groups or isopropyl groups).

[0027] R 1 and R 2 may alternatively form a C4 - 10 alicyclic structure which may optionally contain heteroatoms, particularly oxygen atoms. Particularly non - limiting examples of cyclic ethers suitable for use as additives in the method of the present invention are tetrahydrofuran and dioxane).

[0028] According to another embodiment of the present invention, said at least one additive is a (per)fluorinated vinyl ether).

[0029] In a preferred embodiment, said (per)fluorinated vinyl ether is a (per)fluoroalkyl vinyl ether (MVE) having the following formula: CF2 = CFOR f (wherein R f is selected from the group consisting of C1 - C6 (per)fluoroalkyl, C5 - C6 cyclic (per)fluoroalkyl, and C2 - C6 (per)fluorooxyalkyl). Preferably, R f is - CF3, - CF2CF3, or - CF2CF2CF3).

[0030] In another preferred embodiment, said (per)fluorinated vinyl ether is a (per)fluoro - alkylmethyleneoxy - vinyl ether (MOVE) having the following formula: CF2 = CFOCF2OR f (wherein R fis selected from the group consisting of C1-C6 (per)fluoroalkyl; C5-C6 cyclic (per)fluoroalkyl; and C2-C6 (per)fluorooxyalkyl. Preferably, R f is -CF2CF3 (MOVE1), -CF2CF2OCF3 (MOVE2), or -CF3 (MOVE3).

[0031] According to a further embodiment of the present invention, the at least one additive is a (per)fluorinated olefin, preferably a (per)fluorinated vinyl derivative having the following formula: CF2=CFR f (wherein R f is selected from the group consisting of C1-C6 (per)fluoroalkyl, C5-C6 cyclic (per)fluoroalkyl, and C2-C6 (per)fluorooxyalkyl).

[0032] Also, according to an embodiment of the present invention, the at least one additive is a substituted aromatic hydrocarbon. Preferably, the substituted aromatic hydrocarbon has 6 to 18 carbon atoms, preferably 6 to 12 carbon atoms, more preferably 6 carbon atoms.

[0033] Preferably, the aromatic hydrocarbon is substituted with one or more linear or branched alkyl groups and / or linear or branched alkoxy groups and / or halogen atoms. More preferably, the aromatic hydrocarbon is substituted with one or more linear or branched alkyl or alkoxy groups having 1 to 8 carbon atoms, preferably 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms. When the aromatic hydrocarbon has two or more substituents, they may be in the ortho, meta, or para positions relative to each other. Preferably, the at least one additive is an aromatic hydrocarbon having one substituent or an aromatic hydrocarbon having two substituents.

[0034] Preferably, the at least one additive is a substituted C6 aromatic hydrocarbon. Preferably, the C6 aromatic hydrocarbon is substituted with a C1 alkyl group and / or an alkoxy group. Preferably, the C6 aromatic hydrocarbon is toluene or 1,3-dimethoxybenzene.

[0035] Preferably, the at least one additive selected from among the compounds identified above is present in an amount of 0.001 wt% to 10 wt%, 0.01 wt% to 10 wt%, 0.1 wt% to 10 wt%, 0.001 wt% to 5 wt%, 0.01 wt% to 5 wt%, 0.1 wt% to 5 wt%, 0.001 wt% to 4 wt%, 0.01 wt% to 4 wt%, 0.1 wt% to 4 wt%, 0.001 wt% to 2 wt%, 0.01 wt% to 2 wt%, 0.1 wt% to 2 wt% based on the total weight of the high molecular weight PTFE.

[0036] As already stated above, the second step b) of irradiating the mixture comprising high molecular weight PTFE and at least one additive is carried out substantially in the absence of oxygen. The expression "substantially in the absence of oxygen" means that the second step b) is carried out in an atmosphere containing less than 5.0% by volume, preferably less than 3.0% by volume, more preferably less than 1.0% by volume, more preferably less than 0.1% by volume, even more preferably less than 0.01% by volume of oxygen.

[0037] Preferably, the first step a) of mixing the high molecular weight PTFE with at least one additive is also carried out substantially in the absence of oxygen, where the expression "substantially in the absence of oxygen" has the same meaning as above.

[0038] According to different embodiments, the second step b) is carried out in the presence of an inert gas and / or in the presence of an oxygen adsorbent. In one embodiment, the inert gas and / or the oxygen adsorbent are mixed with the high molecular weight PTFE and the at least one additive during the first step a). In another embodiment, the inert gas and / or the oxygen adsorbent are added to the mixture obtained from the first a), i.e., the mixture obtained before irradiating the mixture according to the second step b).

[0039] Preferably, the inert gas is selected from nitrogen, helium, argon, etc. Preferably, the inert gas is nitrogen.

[0040] The oxygen adsorbent may be any adsorbent capable of adsorbing oxygen. For example, the oxygen adsorbent is selected from inorganic oxygen adsorbents such as iron-based, zinc-based, or hydrosulfite-based adsorbents, and organic oxygen adsorbents such as ascorbic acid-based, polyhydric alcohol-based, or activated carbon-based oxygen adsorbents. The oxygen adsorbent may be either a water-dependent type that requires water to react with oxygen or a self-reactive type that does not require water. The oxygen adsorbent is preferably of the self-reactive type. Preferably, the oxygen adsorbent is an iron-based self-reactive oxygen adsorbent.

[0041] Preferably, the ionizing radiation is selected from electron beams, ultraviolet rays, gamma rays, X-rays, neutron beams, and high-energy ions. Electron beams and gamma rays are preferred.

[0042] Preferably, the ionizing radiation has an exposure dose of 1 to 2500 kGy, 1 to 1000 kGy, 1 to 750 kGy, 10 to 2500 kGy, 10 to 1000 kGy, 10 to 750 kGy, 100 to 2500 kGy, 100 to 1000 kGy, 100 to 750 kGy.

[0043] The irradiation temperature may be any temperature from 5°C to the melting point of PTFE, preferably 5°C to 320°C, more preferably 5°C to 300°C, and still more preferably 5°C to 260°C.

[0044] The method according to the present invention optionally includes a third step c) of heating the low molecular weight PTFE obtained from the second step b). Preferably, the heating is carried out at 50°C to 300°C, 70°C to 300°C, 90°C to 300°C, 100°C to 300°C, 50°C to 230°C, 70°C to 230°C, 90°C to 230°C, 100°C to 230°C, 50°C to 200°C, 70°C to 200°C, 90°C to 200°C, 100°C to 200°C, 50°C to 130°C, 70°C to 130°C, 90°C to 130°C, 100°C to 130°C.

[0045] Another object of the present invention is the low molecular weight PTFE obtained by the above method. The expression "low molecular weight PTFE" refers to PTFE having a melt flow index of at least 0.1 g / 10 min, determined in accordance with ASTM D1238 by applying a load of 10 Kg at 372°C.

[0046] Preferably, the low molecular weight PTFE has a melt flow index of at least 0.2 g / 10 min, more preferably at least 0.3 g / 10 min, still more preferably at least 0.5 g / 10 min, and still more preferably at least 1.0 g / 10 min, determined in accordance with ASTM D1238 by applying a load of 10 Kg at 372°C. The melt flow index is used as an indicator of the molecular weight of the low molecular weight PTFE.

[0047] The applicant has found that the low molecular weight PTFE according to the present invention does not contain a carboxyl group at the chain end.

[0048] The low molecular weight PTFE preferably has a melting point of 324°C to 337°C, more preferably 330°C to 337°C, still more preferably 333°C to 337°C, determined according to the method described in the following experimental section.

[0049] Preferably, the low molecular weight PTFE of the present invention is C4 - C 14Perfluorocarboxylic acids (PFCA) and their salts are each included in a mass of 25 ppb or less, more preferably each 20 ppb or less, still more preferably each 15 ppb or less, still more preferably each 10 ppb or less, and most preferably each 5 ppb or less.

[0050] Preferably, the low molecular weight PTFE of the present invention contains perfluorooctanoic acid (PFOA) and its salts in a mass of 25 ppb or less, more preferably 20 ppb or less, still more preferably 15 ppb or less, still more preferably 10 ppb or less, still more preferably 5 ppb or less, most preferably 2 ppm or less, and further less than 2 ppb.

[0051] Preferably, the low molecular weight PTFE is in the form of a powder. Preferably, the specific surface area of the powder is 0.5 - 20 m 2 / g. Preferably, the average particle size of the powder is 0.5 - 200 μm, more preferably 0.5 - 20 μm, still more preferably 0.5 - 10 μm, and still more preferably 0.5 - 5 μm.

[0052] The present invention will be described in more detail in the following experimental section by way of non - limiting examples.

Examples

[0053] Experimental section Materials PTFE Algoflon® F5FT is a high molecular weight PTFE and is commercially available from Solvay Specialty Polymers Italy.

[0054] Dibutyl ether, diphenyl ether, toluene, and 1,3 - dimethoxybenzene were purchased from Sigma - Aldrich.

[0055] Diisopropyl ether was purchased from Merck.

[0056] MOVE1 is a perfluorinated vinyl ether of the formula CF2=CFOCF2OCF2CF3 and is commercially available from Solvay Specialty Polymers Italy.

[0057] Ethanol was purchased from Carlo Erba Reagents.

[0058] FreshUS® is an oxygen scavenger commercially available from FreshUS PAC.

[0059] Method Determination of the amount of perfluoro-n-octanoic acid (PFOA) and its salts [Method A] The amount of perfluoro-n-octanoic acid and its salts was determined using a liquid chromatograph-mass spectrometer (Agilent Technologies Infinity 1290 II and Triple Quad6495). The measurement powder (1 g) was extracted with methanol (3 ml) at 50 °C for 16 h. The resulting liquid phase was analyzed by multiple reaction monitoring (MRM). A gradient of aqueous formic acid (10 mmol / L, phase A) and formic acid in acetonitrile (10 mmol / L, phase B) was used as the mobile phase. The separation column (Acquity UPLC BEH C18 1.7 μm) was used at a column temperature of 50 °C and an injection volume of 5 μl. As the ionization method, negative mode electrospray ionization (ESI) was used. The ratio of the molecular weight of the precursor ion to the molecular weight of the product ion was measured to be 413 / 369. The amount of perfluoro-n-octanoic acid and its salts was calculated by the internal standard method (perfluoro-n-[1,2,3,4- 13 C4]octanoic acid as the internal standard). Perfluoro-n- 13 C8]octanoic acid was used as the surrogate recovery standard. The detection limit of this measurement was 2 ppb.

[0060] C4~C 14 Determination of the amount of perfluorocarboxylic acids (PFCA) and their salts [Method B] C4~C 14Perfluorocarboxylic acids and their salts were detected using a liquid chromatograph-mass spectrometer (Agilent Technologies Infinity1290 and Triple Quad6460). The measurement powder (0.35 g) was mixed with acetone (3.5 g), and the mixture was sonicated for 15 minutes and stirred for 45 minutes. The resulting liquid phase was distilled off, redissolved in methanol, and measured by MRM. The measurement conditions were based on the measurement conditions for perfluoro-n-octanoic acid. The ratio of the molecular weight of the precursor ion to the molecular weight of the product ion was 213 / 169 for perfluorobutanoic acid (C4), 263 / 219 for perfluoropentanoic acid (C5), 313 / 169 for perfluorohexanoic acid (C6), 319 / 169 for perfluoroheptanoic acid (C7), 369 / 169 for perfluorooctanoic acid (C8), 419 / 219 for perfluorononanoic acid (C9), 469 / 269 for perfluorodecanoic acid (C 10 ), 519 / 269 for perfluoroundecanoic acid (C 11 ), 613 / 569 for perfluorododecanoic acid (C 12 ), 663 / 619 for perfluorotridecanoic acid (C 13 ), and 713 / 669 for perfluorotetradecanoic acid (C 14 ). The amounts of each perfluorocarboxylic acid were calculated by the external standard method. Perfluoro-n- 13 C4]butanoic acid, perfluoro-n-[1,2,3,4,6- 13 C5]hexanoic acid, perfluoro-n- 13 C8]octanoic acid, perfluoro-n- 13 C9]nonanoic acid, and perfluoro-n-[1,2,3,4,5,6- 13 C6]decanoic acid were used as SRS (surrogate recovery standards). The detection limit for this measurement for each perfluorocarboxylic acid was 25 ppb.

[0061] DSC DSC analysis was performed on a Mettler Toledo DSC1 Star apparatus according to ASTM D3418. A sample of approximately 10 mg of dried low molecular weight PTFE was heated from 220 °C to 370 °C at a rate of 10 °C / min. The melting temperature (T m ) mentioned below is the endothermic peak observed during the first heating cycle.

[0062] Measurement of Melt Flow Index (MFI) The Melt Flow Index (MFI) was measured according to the ASTM D1238 standard method by applying a load of 10 Kg at 372 °C.

[0063] Synthesis Examples Example 1 (E1) PTFE Algoflon® F5FT (100 g) was placed in a multilayer barrier bag for food preservation (FoodSaver®), degassed by 3 cycles of vacuum / N2, and then dibutyl ether (4 g) was added under nitrogen. Subsequently, the bag was heat-sealed under an inert gas and irradiated with 200 kGy of radiation at room temperature. Then, the obtained powder was taken out and treated at 80 °C under vacuum to remove volatile by-products. The melting temperature (T m ) and Melt Flow Index (MFI) of the obtained low molecular weight PTFE powder were determined.

[0064] Example 2 (E2) The same procedure as in Example 1 was applied, but diisopropyl ether (4 g) was added to PTFE Algoflon® F5FT (100 g) instead of dibutyl ether. The melting temperature (T m ) and Melt Flow Index (MFI) of the obtained low molecular weight PTFE powder were determined.

[0065] Example 3 (E3) The same procedure as in Example 1 was applied, but toluene (4 g) was added to PTFE Algoflon® F5FT (100 g) instead of dibutyl ether. The melting temperature (T m) and the melt flow index (MFI) were determined.

[0066] Example 4 (E4) The same procedure as in Example 1 was applied, but 1,3-dimethoxybenzene (4 g) was added to PTFE Algoflon® F5FT (100 g) instead of dibutyl ether. The melting temperature (T m ) and the melt flow index (MFI) of the obtained low molecular weight PTFE powder were determined.

[0067] Example 5 (E5) The same procedure as in Example 1 was applied, but MOVE1 (4 g) was added to PTFE Algoflon® F5FT (100 g) instead of dibutyl ether. The melting temperature (T m ) and the melt flow index (MFI) of the obtained low molecular weight PTFE powder were determined.

[0068] Comparative Example 6 (CE6) The same procedure as in Example 1 was applied, but ethanol (4 g) was added to PTFE Algoflon® F5FT (100 g) instead of dibutyl ether. The melting temperature (T m ) and the melt flow index (MFI) of the obtained low molecular weight PTFE powder were determined.

[0069] Example 7 (E7) The same procedure as in Example 1 was applied, and dibutyl ether (4 g) and FreshUS® oxygen adsorbent were added to PTFE Algoflon® F5FT (100 g). The melting temperature (T m ) and the melt flow index (MFI) of the obtained low molecular weight PTFE powder were determined.

[0070] Example 8 (E8) The same procedure as in Example 1 was applied, and dibutyl ether (2 g) and FreshUS® oxygen adsorbent were added to PTFE Algoflon® F5FT (100 g). The melting temperature (T m) and the melt flow index (MFI) were determined.

[0071] Example 9 (E9) Following the same procedure as in Example 1, dibutyl ether (0.5 g) and FreshUS® oxygen scavenger were added to PTFE Algoflon® F5FT (100 g). The melting temperature (T m ) and the melt flow index (MFI) of the resulting low molecular weight PTFE powder were determined.

[0072] Example 10 (E10) Following the same procedure as in Example 1, dibutyl ether (4 g) and FreshUS® oxygen scavenger were added to PTFE Algoflon® F5FT (100 g). Instead of irradiating with 200 kGy, the bag was irradiated with 150 kGy of radiation at room temperature. The melting temperature (T m ) and the melt flow index (MFI) of the resulting low molecular weight PTFE powder were determined.

[0073] Example 11 (E11) Following the same procedure as in Example 1, dibutyl ether (4 g) and FreshUS® oxygen scavenger were added to PTFE Algoflon® F5FT (100 g). Instead of irradiating with 200 kGy, the bag was irradiated with 300 kGy of radiation at room temperature. The melting temperature (T m ) and the melt flow index (MFI) of the resulting low molecular weight PTFE powder were determined.

[0074] Example 12 (E12) The same procedure as in Example 1 was applied, but instead of dibutyl ether, toluene (4 g) and FreshUS® oxygen scavenger were added to PTFE Algoflon® F5FT (100 g). The melting temperature (T m ) and the melt flow index (MFI) of the resulting low molecular weight PTFE powder were determined.

[0075] Example 13 (E13) The same procedure as in Example 1 was applied, but toluene (2 g) and FreshUS® oxygen adsorbent were added to PTFE Algoflon® F5FT (100 g) instead of dibutyl ether. The melting temperature (T m ) and melt flow index (MFI) of the obtained low molecular weight PTFE powder were determined.

[0076] Example 14 (E14) The same procedure as in Example 1 was applied, but toluene (0.5 g) and FreshUS® oxygen adsorbent were added to PTFE Algoflon® F5FT (100 g) instead of dibutyl ether. The melting temperature (T m ) and melt flow index (MFI) of the obtained low molecular weight PTFE powder were determined.

[0077] Example 15 (E15) The same procedure as in Example 1 was applied, but toluene (4 g) and FreshUS® oxygen adsorbent were added to PTFE Algoflon® F5FT (100 g) instead of dibutyl ether. The bag was irradiated with radiation at 150 kGy instead of 200 kGy at room temperature. The melting temperature (T m ) and melt flow index (MFI) of the obtained low molecular weight PTFE powder were determined.

[0078] Example 16 (E16) The same procedure as in Example 1 was applied, but diphenyl ether (4 g) and FreshUS® oxygen adsorbent were added to PTFE Algoflon® F5FT (100 g) instead of dibutyl ether. The melting temperature (T m ) and melt flow index (MFI) of the obtained low molecular weight PTFE powder were determined.

[0079] Example 17 (E17) The same procedure as in Example 1 was applied, but diphenyl ether (2 g) and FreshUS (registered trademark) oxygen adsorbent were added to PTFE Algoflon (registered trademark) F5FT (100 g) instead of dibutyl ether. The melting temperature (T m ) and melt flow index (MFI) of the resulting low molecular weight PTFE powder were determined.

[0080] Results Table 1 reports the mass (ppb) of C4 - C perfluorocarboxylic acids in the samples according to Examples 1 - 5, 7 - 17 (E1 - E5, E7 - E17) and the sample according to Comparative Example 6 (CE6), determined according to Method B above. 14

[0081] Table 2 reports the mass (ppb) of perfluorooctanoic acid in the samples according to Examples 1 - 5, 7 - 17 (E1 - E5, E7 - E17) and the sample according to Comparative Example 6 (CE6), determined according to Method A above.

[0082] Table 3 reports the melting point (T m ) and melt flow index (MFI) of the samples according to Examples 1 - 5, 7 - 17 (E1 - E5, E7 - E17) and the sample according to Comparative Example 6 (CE6).

[0083]

Table 1

[0084]

Table 2

[0085]

Table 3

Claims

1. a) mixing high molecular weight polytetrafluoroethylene (PTFE) with an ether having the formula R １ -O-R ２ (wherein R １ and R ２ are independently selected from straight-chain or branched aliphatic groups of C １ to C １０ , alicyclic or heterocyclic groups of C ４ to C １０ , aromatic or heteroaromatic groups of C ５ to C １０ , and R １ and R ２ may optionally form an aliphatic cyclic structure of C ４ to C １０ which may contain heteroatoms); (per)fluorinated vinyl ether; (per)fluorinated olefin; and optionally, an aromatic hydrocarbon substituted with one or more straight-chain or branched alkyl or alkoxy groups and / or halogen atoms; in a first step of mixing with at least one additive selected from the group consisting of; and b) a second step of irradiating the mixture thus obtained with ionizing radiation, the second step being carried out substantially in the absence of oxygen; A process for producing low molecular weight polytetrafluoroethylene (PTFE) comprising.

2. The method according to claim 1, wherein the low molecular weight PTFE has a melt flow index of at least 0.1 g / 10 min as determined in accordance with ASTM D1238 by applying a load of 10 kg at 372 °C.

3. The method according to claim 1 or 2, wherein the high molecular weight polytetrafluoroethylene (PTFE) has a standard specific gravity of at least 2.130 as determined in accordance with ASTM D4895.

4. The at least one additive has the formula R １ -O-R ２ (wherein R １ and R ２ are C ３ ~C ６ and is an ether independently selected from among linear or branched aliphatic groups of C), the method according to any one of claims 1 to 3.

5. R １ and R ２ are a butyl group or an isopropyl group, the method according to claim 4.

6. The at least one additive is a (per)fluoroalkyl vinyl ether (MVE) having the following formula: CF ２ =CFOR ｆ (wherein R ｆ is selected from the group consisting of C １ ~C ６ (per)fluoroalkyl, C ５ ~C ６ cyclic (per)fluoroalkyl, and C ２ ~C ６ (per)fluorooxyalkyl).

7. The at least one additive is a (per)fluoro-alkylmethyleneoxy-vinyl ether (MOVE) having the following formula: CF ２ =CFOCF ２ OR ｆ (wherein R ｆ is selected from the group consisting of C １ ~C ６ (per)fluoroalkyl, C ５ ~C ６ cyclic (per)fluoroalkyl, and C ２ ~C ６ (per)fluorooxyalkyl).

8. R ｆ is, -CF ２ CF ３ (MOVE1), -CF ２ CF ２ OCF ３(MOVE2), or -CF ３ The method according to claim 7, which is (MOVE3).

9. The method according to any one of claims 1 to 3, wherein the at least one additive is a (per)fluorinated vinyl derivative having the following formula: CF ２ = CFR ｆ (In the formula, R ｆ is C １ to C ６ (per)fluoroalkyl; C ５ to C ６ cyclic (per)fluoroalkyl, and C ２ to C ６ selected from the group consisting of (per)fluorooxyalkyl).

10. The method according to any one of claims 1 to 3, wherein the at least one additive is an aromatic hydrocarbon substituted with one or more linear or branched alkyl or alkoxy groups and / or halogen atoms.

11. The method according to claim 10, wherein the at least one additive is an aromatic hydrocarbon substituted with one or two groups selected from linear or branched alkyl or alkoxy groups and / or halogen atoms.

12. The method according to claim 10 or 11, wherein the at least one additive is a substituted C ６ aromatic hydrocarbon.

13. The method according to any one of claims 1 to 12, wherein the at least one additive is 0.001% to 10% by weight based on the total weight of the high molecular weight PTFE.

14. The method according to any one of claims 1 to 13, wherein the second step b) is carried out in the presence of an inert gas and / or an oxygen adsorbent.

15. The method according to any one of claims 1 to 14, wherein the ionizing radiation is selected from an electron beam, ultraviolet rays, gamma rays, X-rays, neutron rays, and high-energy ions.

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