METHOD OF COAGULATING AN AMORPHOUS FLUOROPOLYMER USING MODIFIED

INORGANIC NANOPARTICLES

TECHNICAL FIELD

[0001] A process for coagulating an amorphous fluoropolymer latex in the presence of modified inorganic nanoparticles is described.

BACKGROUND

[0002] Fluoroelastomers, especially perfluorinated elastomers, are used in a wide variety of applications in which severe environments are encountered, specifically end uses where exposure to high temperatures and aggressive chemicals occur. For example, these polymers are often used as seals for aircraft engines, in semiconductor manufacturing equipment, in oil-well drilling devices, and in sealing elements for industrial equipment used at high temperatures.

[0003] Inorganic particles have been added to fluoropolymer compositions as fillers and/or to improve the final properties of the fluoropolymer article.

[0004] There are many papers which disclose adding inorganic particles and even inorganic

nanoparticles as fillers to fluoropolymer dispersions prior to coagulation. One advantage is that a more uniform blend of the filler can be achieved. For example, Malvasi et al. (U.S. Pat. No. 7,691,936) discloses adding organic or inorganic fillers into a polytetrafluoroethylene or modified

polytetrafluoroethylene dispersion and then coagulating. This process is said to produce good homogeneity and optimal distribution of the fillers in fluoropolymer fine powders. Malvasi et al. discloses coagulation occurring with the usual known methods of the prior art for the fluoropolymer dispersion, without the need of plant modification. These fillers appear to be unmodified.

[0005] Ogden et al. (U.S. Pat. No. 4,038,244) on the other hand discloses modifying the filler with a hydrophobizing agent such as a fluorocarbon derivative, to keep them hydrophobic until coagulation of the polymer occurs, ensuring that the filler is evenly dispersed in the coagulated polymer.

[0006] The traditional methods of coagulating fluoropolymer dispersions include: physical and chemical methods. In physical methods the dispersion may be subject to strong (high) shearing using a stirring device thereby coagulating the particles, (typically by rotor stator having shear rates in excess of 1000 (1/s)). Another method of physical coagulation is the freeze-thaw method. The dispersion is cooled sufficiently to freeze it, which destabilizes the dispersion so that on thawing, the coagulate separates from the liquid. Generally, this technique is not preferred for scale-up due to the scaleability and intensive energy requirements. In chemical coagulation, an electrolyte or inorganic salt is added to the dispersion so that the stability of the dispersion is decreased thereby causing coagulation. [0007] Among these methods, it is preferable to use the chemical coagulation method wherein an electrolyte or inorganic salt is added to the polymer dispersion. Examples of electrolytes used to chemically coagulate fluoropolymer primary particles include HC1, H ₂ SO ₄ , HNO ₃ , H ₃ PO ₄ , Na ₂ S0 ₄ , and MgCl ₂ , A1 ₂ (S0 ₄ )3, and ammonium carbonate. Among these compounds, it is preferable to use compounds which can volatize during the process of drying the coagulate. Examples of inorganic salts used to chemically coagulate fluoropolymer primary particles include alkali metal salts, alkaline earth metal salts, and ammonium salts, of nitric acid, hydrohalic acid, phosphoric acid, sulfuric acid, molybdate, monobasic or dibasic sodium phosphate, ammonium bromide, potassium chloride, calcium chloride, copper chloride and calcium nitrate. These electrolytes and inorganic salts may be used independently or in combinations of two or more.

SUMMARY

[0008] There is a desire to reduce process steps, cost, and/or metal ion content during the coagulation of a amorphous fluoropolymer latex. The process should not cause detrimental effects on the final polymer and may perhaps offer improved properties of the final polymer.

[0009] In one aspect, a method of coagulating a fluoropolymer latex is described comprising: providing an amorphous fluoropolymer latex; providing modified inorganic nanoparticles; and contacting the amorphous fluoropolymer with a sufficient amount of modified inorganic nanoparticles to coagulate the amorphous fluoropolymer latex

[0010] In one embodiment, the method is substantially free of a traditional coagulating agent.

[0011] In another aspect, a fluoropolymer composite is described by providing an amorphous fluoropolymer latex; providing modified inorganic nanoparticles; and contacting the amorphous fluoropolymer with a sufficient amount of modified inorganic nanoparticles to coagulate the amorphous fluoropolymer latex.

[0012] The above summary is not intended to describe each embodiment. The details of one or more embodiments of the invention are also set forth in the description below. Other features, objects, and advantages will be apparent from the description and from the claims.

DETAILED DESCRIPTION

[0013] As used herein, the term

"a", "an", and "the" are used interchangeably and mean one or more;

"and/or" is used to indicate one or both stated cases may occur, for example A and/or B includes, (A and B) and (A or B); "latex" as used herein refers to a dispersion of polymer particles in an aqueous continuous phase; and

"organic" has the common meaning in the art, for example, organic compounds are carbon- containing compounds with some exceptions/exclusions including: binary compounds such as carbides, carbon oxides, carbon disulfide; ternary compounds such as metallic cyanides, phosgene, carbonyl sulfide; and metallic carbonates, such as calcium carbonate.

[0014] Also herein, recitation of ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0015] Also herein, recitation of "at least one" includes all numbers of one and greater (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

[0016] The present disclosure relates to the use of modified inorganic nanoparticles in the coagulation of an amorphous fluoropolymer latex. The coagulated fluoropolymer latex, herein referred to as a fluoropolymer composite, may then be subsequently cured to form fluoroelastomer articles.

[0017] By using modified inorganic nanoparticles to coagulate an amorphous fluoropolymer latex, the fluoropolymer composite of the present disclosure may be substantially free of traditional coagulating agents used for coagulation of a fluoropolymer lattices. Substantially free of traditional coagulating agents as used herein, means that less than 0.1, 0.05, 0.01, or even 0.001% by weight of a traditional coagulating agent is present relative to the amorphous fluoropolymer. Such traditional coagulating agents are mentioned in the Background and include, for example, a water soluble salt such as calcium chloride, magnesium chloride, aluminum chloride, aluminum nitrate, or aluminum sulfate; or an acid such as nitric acid, hydrochloric acid, phosphoric acid, or sulfuric acid and combinations thereof. In some

embodiments, these traditional coagulating agents are also used in conjunction with an organic liquid such as an alcohol or acetone. These traditional coagulating agents are used as solutions (e.g., water), typically containing 0.5% to 5% by weight. The ratio of the traditional coagulating agent solution to latex typically ranges from 1 :5 to 5: 1.

[0018] The coagulating agents used in the present disclosure are modified inorganic nanoparticles. As used herein, a "modified inorganic nanoparticle" means that the surface of the inorganic nanoparticle is irreversibly associated (e.g., is covalently-bonded) with an organic compound.

[0019] The inorganic nanoparticles of the present disclosure may comprise metal oxide nanoparticles, which are subsequently modified with an organic compound. Such metal oxides include, for example, silicon dioxide (silica), zirconia, titania, ceria, alumina, iron oxide, zinc oxide, vanadia, antimony oxide, tin oxide, alumina/silica. Although the metal oxide may be essentially pure, it may contain small amounts of stabilizing ion such as ammonium and alkaline metal ions, or it may be a combination of metal oxides such as a combination of titania and zirconia.

[0020] The inorganic nanoparticles as used herein may be distinguished from materials such as fumed silica, pyrogenic silica, precipitated silica, etc. Such silica materials are known to those of skill in the art as being comprised of primary particles that are essentially irreversibly bonded together in the form of aggregates, in the absence of high-shear mixing. These silica materials have an average size greater than 100 nm (e.g., typically of at least 200 nanometers) and from which it is not possible to straightforwardly extract individual primary particles.

[0021] The inorganic nanoparticles may be in the form of a colloidal dispersion, which are purchased and then subsequently modified. Examples of useful commercially available unmodified silica nanoparticles include commercial colloidal silica sols available from Nalco Chemical Co. (Naperville, IL) under the trade designation "NALCO COLLOIDAL SILICAS". For example, such silicas include NALCO products 1040, 1042, 1050, 1060, 2327 and 2329. Examples of useful metal oxide colloidal dispersions include colloidal zirconium oxide, suitable examples of which are described in U.S. Pat. No. 5,037,579 (Matchett), and colloidal titanium oxide, useful examples of which are described in U.S. Pat. No. 6,432,526 (Arney et al.).

[0022] In the present disclosure, the surfaces of these inorganic nanoparticles are irreversibly- (e.g., covalently-)modified with an organic compound comprising a poly(alkylene oxide)-containing moiety to provide different surface properties (e.g., solubility and/or reactivity) to the inorganic nanoparticle.

[0023] The organic compounds comprising a poly(alkylene oxide)-containing moiety that may be used to modify the surface of the inorganic nanoparticle may be represented by the formula A-B, where the A group is capable of covalently-bonding to the surface of the inorganic nanoparticle particle and where B comprises a poly(alkylene oxide)-containing moiety.

[0024] The A group is selected such that it is compatible with the surface of the particular inorganic nanoparticle selected. For example, a siloxane group may be used to attach the organic moeity to silica or zirconia.

[0025] The B group is a poly(alkylene oxide)-containing moiety, such moieties are preferably short- chain oligomers having a molecular weight as low as 88, with a random or block structural distribution if at least two different moieties are included. Exemplary moieties include: ethylene glycol ether-containing groups, poly(ethylene oxide) ether-containing groups, ethylene glycol lactate-containing groups, sugar- containing groups, polyol-containing groups, crown ether-containing groups, oligo glycidyl ether- containing groups including methyl ether and hydroxyethyl ether, hydroxyl acylamide-containing groups [0026] Poly(ethylene oxide)-containing group has at least one -CH ₂ -CH ₂ -0- (repeat) unit, and may have -CH(R ¹ )-CH ₂ -0- (repeat) units, such that the poly(ethylene oxide) -containing group has a total of at least one, and preferably at least 3, -CH ₂ -CH ₂ -0- (repeat) units, and the ratio of -CH ₂ -CH ₂ -0- units to - CH(R ¹ )-CH ₂ -0- units is at least 2: 1 (preferably at least 3: 1). If the poly(ethylene oxide)-containing groups also include -CH(R ¹ )-CH ₂ -0- groups, R ¹ is a (C1-C4) alkyl group, which can be linear or branched. Thus, a small amount of propylene oxide (e.g., 0.2 mmol/gram of a nanoparticle) can be included in the poly(alkylene oxide) groups, although it is not desired. [0027] In the present disclosure, a preferred molecular weight of poly(alkylene oxide) -containing moiety is at least 170, 300, 500, or even 1000 g/mole; at most 1 million or even 10 million g/mole. It is generally preferred that they are limited in chain length such that they are less than the entanglement molecular weight of the oligomer. The term "entanglement molecular weight" as used in reference to the shielding group attached to the surface means the minimum molecular weight beyond which the polymer molecules used as the shielding group show entanglement. Methods of determining the entanglement molecular weight of a polymer are known, see for example Friedrich et al., Progress and Trends in Rheology V, Proceedings of the European Rheology Conference, 5th, Portoroz, Slovenia, Sep. 6- 1 1, 1998 (1998), 387. Editor(s): Emri, I. Publisher: Steinkopff, Darmstadt, Germany. Preferably, the molecular weight of such polymeric groups is no greater than 10,000 grams per mole (g/mole).

[0028] Exemplary organic compounds that may be used include poly(ethylene oxide) trimethoxysilane, having molecular weight from 200 to 650 which are commercially available at Gelest Co.

[0029] In one embodiment, a poly(alkylene oxide)-containing compound is reacted with an A group to from an organic compound comprising a poly(alkylene oxide) -containing moiety, which is then subsequently reacted with the inorganic nanoparticle. For example, poly(alkylene oxide)-containing compounds are available commercially in a variety of molecular weights, which may then be reacted with a silane for attachment to the inorganic nanoparticle.

[0030] Surface modification of nanoparticles is known in the art. For example, silica-based nanoparticles can be treated with monohydric alcohols (e.g., a saturated primary alcohol), polyols, or mixtures thereof under conditions such that silanol groups on the surface of the nanoparticles chemically bond with hydroxyl groups to produce surface-bonded ester groups. The surface of silica (or other metal oxide) particles can also be treated with organosilanes, e.g, alkyl chlorosilanes, trialkoxy arylsilanes, olefinic silanes, or trialkoxy alkylsilanes, or with other chemical compounds, e.g., organotitanates, which are capable of attaching to the surface of the nanoparticles by a chemical bond (covalent or ionic) or by a strong physical bond, and which are water dispersable . Silica-based (and zirconia-based) nanoparticles may be treated with a phase compatibilizing surface treatment agent. Additional surface reagents used to modify the polarity or hydrophobicity of the nanoparticle may be used as well. Representative examples of these reagents include, e.g., 3- aminopropyl trimethoxysilane available from Gelest Inc., Morrisville, PA.

[0031] Generally the inorganic nanoparticles are reacted, such that at least 2%, 5%, 10%, 20%, 25%,

50%, 75%, or even 100% of the surface of the inorganic nanoparticle is modified with the poly(alkylene oxide)-containing compound.

[0032] The modified inorganic nanoparticles used in the present disclosure are preferably substantially spherical.

[0033] The modified inorganic nanoparticles have an average diameter of the primary particle of at least 25 nm, 20 nm, 15 nm, 10 nm, 5 nm or even 3 nm; at most about 100 nm, 50 nm, 30nm, 20 nm, or even 10 nm depending on the inorganic nanoparticle used. The modified inorganic nanoparticles used in the present disclosure are typically un-aggregated. If the modified inorganic nanoparticles are an aggregation of primary particles, then the maximum cross-sectional dimension of the aggregated nanoparticle is within the range of range of about 3 nm to about 100 nm, about 3 nm to about 50 nm, about 3 nm to about 20 nm, or even about 3nm to about 1 Onm.

[0034] Generally, the amount of modified inorganic nanoparticles needed to coagulate the amorphous fluoropolymer latex is at least 3000 ppm, 5000 ppm, 7500 ppm, 8500 ppm, 10,000 ppm, 50,000 ppm, 100,000 ppm, 200,000 ppm, 500,000 ppm, or even 1,000,000 ppm versus the amorphous fluoropolymer latex.

[0035] If the amount of inorganic nanoparticles added is too small, coagulation occurs gradually and incompletely. As a result, it may not be possible to recover all of the amorphous fluoropolymer from the latex. In some embodiments, it may not be desirable to add a substantial excess of modified inorganic nanoparticles, for reasons of cost and/or the modified inorganic nanoparticles may impact the properties of the resulting fluoroelastomer.

[0036] Generally, the modified inorganic nanoparticles are added to the amorphous fluoropolymer latex dispersed in a liquid. Having the modified inorganic nanoparticles dispersed in a liquid and the amorphous fluoropolymer dispersed as a latex aids in the blending of the nanoparticles and the amorphous fluoropolymer and is advantageous because there is less dust created during mixing than in the case of dry blending.

[0037] The amorphous fluoropolymer latex may be stirred during or after the addition of the modified inorganic nanoparticles. The stirring device is not limited to a specific type and includes for example a device having stirring means such as propeller blades, turbine blades, paddle blades, shell-shaped blades, in which the stirring speed can be controlled. In the present disclosure, the stirring device does not itself cause coagulation, i.e., the stirring device does not place high shear on the amorphous fluoropolymer latex. Instead, in the present disclosure, it is the addition of the modified inorganic nanoparticles, which destabilize the amorphous fluoropolymer latex causing coagulation and the stirring device provides a means for efficiently dispersing the modified inorganic nanoparticles in the fluoropolymer latex. In one embodiment, high shear is not used to coagulate the fluoropolymer latex. To determine if high shear is placed on the latex to cause coagulation, one can run an identical experiment without the modified inorganic nanoparticles to determine if the amorphous fluoropolymer latex coagulates.

[0038] In one embodiment, the average shear applied by the stirring device is less than 300 Hertz (Hz), 500 Hz, 750 Hz, 850 Hz, or even 950 Hz as defined for a stirred tank in Handbook of Industrial Mixing- Science and Practive by Paul, E.L., et al. eds., John Wiley & Sons, 2004, page 370.

[0039] Although not wanting to be limited by theory, it is believed that the modified inorganic nanoparticles destabilize the latex by binding the surfactant or via a physical interaction between the modified inorganic nanoparticles and amorphous fluoropolymer latex particles, causing the amorphous fluoropolymer latex to destabilize and coagulate. In another proposed theory, it is believed that in the case of the inorganic nanoparticles which are covalently bonded to a poly(alkylene oxide)-containing compound, the poly(alkylene oxide)-containing moiety sticks to the amorphous fluoropolymer latex particle, causing destabilization and coagulation.

[0040] The amorphous fluoropolymer latex of the present disclosure may be a result of a suspension or an emulsion polymerization.

[0041] The amorphous fluoropolymer latex may be derived from non- fluorinated monomers, fluorinated monomers, or combinations thereof.

[0042] Non- fluorinated monomers include those known in the art and include for example, ethylene and propylene. Fluorinated monomers include those known in the art that are partially and fully fluorinated.

Exemplary fluorinated monomers include: fluorinated olefins such as tetrafluoroethylene,

chlorotrifluoroethylene, hexafluoropropylene, vinylidene fluoride, and vinyl fluoride; fluorinated ethers such as fluoroallyl ethers, fluoroalkyl vinyl ethers (such as perfluoromethyl vinyl ether, 3-methoxy perfluoropropylvinyl ether, and CF ₂ CFOCF ₂ OCF ₂ CF ₂ CF ₂ CF ₃ ), and fluoroalkoxy vinyl ethers; fluorinated alkoxides such as hexafluoropropylene oxide; fluorinated styrenes, fluorinated siloxanes; and combinations thereof.

[0043] Exemplary amorphous fluoropolymer lattices of the present disclosure may include copolymers such as, a tetrafluoroethylene- hexafluoropropylene -vinylidene fluoride copolymer, a vinylidene fluoride- hexafluoropropylene copolymer, a tetrafluoroethylene-propylene copolymer, a tetrafluoroethylene- perfluoro alkyl vinyl ether copolymer, a vinylidene fluoride-chlorotrifluoroethylene copolymer, and comboinations thereof.

[0044] Additionally, cure-site monomers as are known in the art may be added during the

polymerization, so that the amorphous fluoropolymer latex comprises iodine-, bromine-and/or nitrogen- containing cure site groups, which may be subsequently used to cross-link the amorphous fluoropolymer composite.

[0045] In one embodiment, iodine- and bromine- cure site groups may be derived from monomers of the formula: CX ₂ =CX(Z), wherein: (i) X each is independently H or F ; and (ii) Z is I, Br, R -U wherein U=I or Br and R =a perfluorinated or partially perfluorinated alkylene group optionally containing O atoms. In addition, non-fluorinated bromo-or iodo-olefins, e.g., vinyl iodide and allyl iodide, can be used.

Exemplary iodine- and bromine- cure site groups may be derived from: CH ₂ =CHI, CF ₂ =CHI, CF ₂ =CFI, CH ₂ =CHCH ₂ I, CF ₂ =CFCF ₂ I, CH ₂ =CHCF ₂ CF ₂ I, CH ₂ =CHCF ₂ CF ₂ CH ₂ CH ₂ I, CH ₂ =CH(CF ₂ ) ₄ I,

CH ₂ =CH(CF ₂ ) ₄ CH ₂ CH ₂ I, CH ₂ =CH(CF ₂ ) ₆ I, CH ₂ =CH(CF ₂ ) ₆ CH ₂ CH ₂ I, CF ₂ =CFCH ₂ CH ₂ I,

CF ₂ =CFCF ₂ CF ₂ I, CF ₂ =CFOCF ₂ CF ₂ I, CF ₂ =CFOCF ₂ CF ₂ CH ₂ CH ₂ I, CF ₂ =CFOCF ₂ CF ₂ CF ₂ I,

CF ₂ =CFOCF ₂ CF ₂ CF ₂ CH ₂ CH ₂ I, CF ₂ =CFOCF ₂ CF ₂ CH ₂ I, CF ₂ =CFOCF ₂ CF ₂ CF ₂ CH ₂ I,

CF ₂ =CFCF ₂ OCH ₂ CH ₂ I, CF ₂ =CFO(CF ₂ ) ₃ -OCF ₂ CF ₂ I, CH ₂ =CHBr, CF ₂ =CHBr, CF ₂ =CFBr, CH ₂ =CHCH ₂ Br, CF ₂ =CFCF ₂ Br, CH ₂ =CHCF ₂ CF ₂ Br, CF ₂ =CFOCF ₂ CF ₂ Br, CF ₂ =CFC1, CF ₂ =CFCF ₂ C1, and mixtures thereof.

[0046] In one embodiment, the nitrogen-containing cure site group may comprise for example, a nitrile, an amidine, an imidate, an amidoxime, or an amidrazone group.

Exemplary nitrogen-containing cure site group may be derived from: CF ₂ =CF-CF ₂ -0-RrCN,

CF ₂ =CFO(CF ₂ ) _w CN, CF ₂ =CFO[CF ₂ CF(CF ₃ )0] _g (CF ₂ ) _v OCF(CF ₃ )CN,

CF ₂ =CF[OCF ₂ CF(CF ₃ )] _k O(CF ₂ ) _u CN, and mixtures thereof, wherein w represents an integer of 2 to 12; g represents an integer of 0 to 4; k represents 1 or 2; v represents an integer of 0 to 6; u represents an integer of 1 to 6, R _f is a perfluoroalkylene or a bivalent perfluoroether group. Specific examples include perfluoro(8-cyano-5-methyl-3,6-dioxa-l-octene), CF ₂ =CFO(CF ₂ ) ₅ CN, and CF ₂ =CFO(CF ₂ ) ₃ OCF(CF ₃ )CN.

[0047] In one embodiment, non- fluoropolymer particles or semi-crystalline or crystalline fluoropolymer particles, or a combination thereof may be admixed with the amorphous fluoropolymer particles in the fluoropolymer latex. Exemplary non-fluoropolymers include: polyvinyl chloride and polyacrylate.

Exemplary semi-crystalline or crystalline fluoropolymers include: polytetrafluoroethylene,

tetrafluoroethylene-propylene (FEP) copolymer, tetrafluoroethylene-perfluoroalkoxyvinylether (PFA) copolymers, tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers, ethylene- tetrafluoroethylene copolymers, polyvinylidene fluoride, propylene-chlorotrifluoroethylene copolymers, and ethylene-chlorotrifluoroethylene copolymers. In one embodiment, the fluoropolymer latex comprises less than 50%, 25%, 15%, 10%, 5%, 2%, 1%, 0.5%, 0.1%, or even 0.05% by weight of these non- fluoropolymers or semi-crystalline or crystalline fluoropolymers versus the total polymer solids in the fluoropolymer latex.

[0048] After coagulation of the fluoropolymer latex with the modified inorganic nanoparticles, the fluoropolymer composite comprising the coagulated amorphous fluoropolymer and modified inorganic nanoparticles is separated from the aqueous medium (e.g., by filtration) and may then be washed with water.

[0049] After collecting and washing, the fluoropolymer composite is dried at a temperature below the temperature at which thermal decomposition starts.

[0050] Because the fluoropolymer latex can be coagulated with modified inorganic nanoparticles instead of metal salts, the resulting fluoropolymer composite may comprise low amounts of metal ions. For example, in one embodiment, the fluoropolymer composite comprises less than 200, 100, or even 50 ppm of total metal ions. The total metal ion content may be reduced even further by the screening of the raw materials to ensure low metal ions.

[0051] After drying, the fluoropolymer composite can then be used to form articles. By the term "article" in connection with the present invention is meant a final article such as, for example, an O-ring as well as preforms from which a final shape is made, e.g. a tube from which a ring is cut. To form an article, the fluoropolymer composite can be extruded using a screw type extruder or a piston extruder. Alternatively, the fluoropolymer composite can be shaped into an article using injection molding, transfer molding or compression molding. Compression molding consists of placing a quantity of cold uncured

fluoropolymer composite into a heated mold cavity and subsequently closing the mold using adequate pressure to shape the article. After retaining the amorphous fluoropolymer composite at sufficient temperature during sufficient time to allow vulcanization to proceed it can then be demolded. Injection molding is a shaping technique whereby the amorphous fluoropolymer composite is first heated and masticated in an extruder screw then collected in a heated chamber from which it is then injected into a hollow mold cavity by means of a hydraulic piston. After vulcanization the article can then be demolded. Transfer molding is similar to injection molding with the difference being that the amorphous fluoropolymer composite is not preheated and masticated by an extruder screw, but introduced as a cold mass in the heated injection chamber. In some embodiments, molding is carried out simultaneously with crosslinking. In some embodiments, molding is carried out before crosslinking.

[0052] Articles derived from the fluoropolymer composite presently disclosed are useful for in the semiconductor industry for the microchip manufacturing process where the fluoroelastomer may be used in seals of microchip fabrication equipment. In industries such as the semi-conductor, biotechnology, and pharmaceutical industries, there is a desire for cleaner fluoroelastomer parts (such as O-rings, quick connect seals, gaskets). In other words fluoroelastomer parts having extremely low metal ion content. In the present disclosure it has been found that unmodified inorganic nanoparticles may be used to coagulate the amorphous fluoropolymer latex resulting in a fluoroelastomer having low metal content and the ability to reduce a process step.

[0053] Some embodiments/items of the present disclosure include:

[0054] Item 1. A method of coagulating a fluoropolymer latex comprising:

providing an amorphous fluoropolymer latex;

providing modified inorganic nanoparticles; and

contacting the amorphous fluoropolymer with a sufficient amount of modified inorganic nanoparticles to coagulate the amorphous fluoropolymer latex.

[0055] Item 2. The method of claim 1, wherein the method is substantially free of a traditional coagulating agent.

[0056] Item 3. The method of any one of items 1-2, wherein the amorphous fluoropolymer latex is perfluorinated.

[0057] Item 4. The method of any one of items 1-2, wherein the amorphous fluoropolymer latex is partially fluorinated.

[0058] Item 5. The method of any one of the previous items, wherein the modified inorganic nanoparticles are modified with a poly(alkylene oxide)-containing moeity.

[0059] Item 6. The method of item 5, wherein the poly(alkylene oxide) -containing moiety has a molecular weight of at least 170 g/mol. [0060] Item 7. The method of any one of the previous items, wherein the modified inorganic nanoparticle comprises at least 25 % surface modification.

[0061] Item 8. The method of any one of the previous items, wherein the amorphous fluoropolymer latex comprises polymerized monomers selected from tetrafluoroethylene, hexafluoropropylene,

perfluoromethyl vinyl ether, 3-methoxy perfluoropropylvinyl ether, CF ₂ CFOCF ₂ OCF ₂ CF ₂ CF ₂ CF ₃ , vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, and combinations thereof.

[0062] Item 9. The method of any one of the previous items, wherein the amorphous fluoropolymer latex comprises an iodine- or a bromine-containing cure site group.

[0063] Item 10. The method of any one of the previous items, wherein the amorphous fluoropolymer latex comprises a nitrogen-containing cure site group.

[0064] Item 11. The method of item 10, wherein the nitrogen-containing cure site is a nitrile, an amidine, an imidate, an amidoxime, or an amidrazone.

[0065] Item 12. The method of any one of the previous items, wherein the modified inorganic nanoparticles have an average diameter of less than 100 nm.

[0066] Item 13. The method of any one of the previous items, wherein the modified inorganic nanoparticles comprise silica, zirconia, almumina, zinc oxide and combinations thereof.

[0067] Item 14. The method of any one of the previous items, wherein modified inorganic nanoparticles is added in an amount of at least 7500 ppm relative to the amorphous fluoropolymer latex.

[0068] Item 15. The method of any one of the previous items, wherein the fluoropolymer latex further comprises non-fluorinated polymer particles, semi-crystalline polymer particles, crystalline polymer particles, or a combination thereof.

[0069] Item 16. The method of item 15, wherein the fluoropolymer latex comprises less than 25% by weight of non-fluorinated polymer particles, semi-crystalline polymer particles, crystalline and polymer particles versus the total polymer solids in the fluoropolymer latex.

[0070] Item 17. A fluoropolymer composite made according to the method described in any one of items 1-16.

[0071] Item 18. The fluoropolymer composite of item 17, wherein the fluoropolymer composite comprises less than 200 ppm of total metal ions.

[0072] Item 19. A cured article derived from the fluoropolymer composite of any one of items 17-18.

EXAMPLES

[0073] Advantages and embodiments of this disclosure are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. In these examples, all percentages, proportions and ratios are by weight unless otherwise indicated. [0074] These abbreviations are used in the following examples: g = gram, min = minute, mol=mole, hr = hour, mL = milliliter; wt = weight. If not otherwise indicated chemicals are available from Sigma- Aldrich, StXouis, MO.

Materials

Material Name Description

Latex of bromine cure site containing perfluoroelastomer prepared by aqueous emulsion polymerization having 66.2 mol % of tetrafluoroethylene, 33.7 mol% of perfluoromoethyl vinylether and 0.36 wt % bromine (based on total wt of

Latex A perfluoroelastomer) added as bromotrifluoroethylene. Solids content 34.38 wt %.

Latex of nitrile cure site containing perfluoroelastomer prepared by aqueous emulsion polymerization having 66.8 mol% TFE, 32.0 mol% perfluoromethylvinyl ether (PMVE) and 1.2 mol % of a nitrile-containing cure site monomer, CF ₂ =CFO(CF ₂ ) ₅ CN (MV5CN).

Latex B Solids content 30.3 wt %.

50 wt % solids colloidal solution of nanoparticle S1O ₂ commercially available commercially available under the trade designation "NALCO 1050" from Nalco Co.,

Silica sol #1 Naperville, IL, further diluted with deionized water to 15 wt % solids.

40 wt % solids colloidal solution of nanoparticle S1O ₂ commercially available under the

Silica sol #2 trade designation "NALCO 2327" (20 nm) from Nalco Co., Naperville, IL

(2-[methoxy(polyethyleneoxy) propyl]trimethoxysilane), average molecular weight 500

PEG-silane g/mol, commercially available from Gelest Inc. Morrisville, PA

Polyethylene glycol of average molecular wt 300, commercially available under the trade

PEG 300 designation "POLYETHYLENE GLYCOL 300" from EMD Chemicals, Gibbstown, NJ.

Nalco 2327 silica nanoparticles (200 g, 40wt%) was diluted to 10wt% with deionized water (600g). The solution was stirred for 15 minutes. Subsequently to the solution was

Modified silica sol

added PEG-silane (Mw=500, 24.8 g, 100 % surface coverage) and the resulting mixture #1

was continuously stirred for additional 3-4hrs at room temperature. The solution was then heated at 70°C overnight. The prepared 12.7wt% solid solution was diluted to 4 wt% with deionized water (1795.2g).

Nalco 2327 silica nanoparticles (100 g, 40wt%) was diluted to 20wt% with deionized

Modified silica sol water (100g). The solution was stirred for 15 minutes. Subsequently to the solution was

#2 added PEG-silane (Mw=500, 4.96g, 40 % surface coverage) and the resulting mixture was continuously stirred for additional 3-4hrs at room temperature. The solution was then heated at 70°C overnight.

Nalco 1050 silica nanoparticles (80 g, 50wt%) was diluted to 20 wt% with deionized water (120 g). The solution was stirred for 15 minutes. Subsequently to the solution was

Modified silica sol added PEG-silane (Mw=500, 3.1 g, 25 % surface coverage) and the resulting mixture was #3 continuously stirred for additional 3-4hrs at room temperature. The solution was then heated at 70°C overnight. The resulting solution contains 21.2wt% solid and was diluted to 12.5wt% with deionized water (141.7g). [0075] Comparative Example 1

[0076] 45.5 g of "silica sol #2" was stirred with a Cowles blade driven by a Laboratory

Disperserator series 2000 Model 90 (Premier Mill, Exton, PA) controlled by a VARIAC at a setting of 30. To this solution, 616.40 g of Latex B was added over the course of 25 min. No coagulation was observed. The wt% of nanoparticles versus the total weight (nanoparticle solution and fluoropolymer latex) was 2.750.

[0077] Comparative Example 2

[0078] 261.00 g of "silica sol #1 " was stirred at a high speed with a magnetic stir bar on an IKA magnetic stir plate. To this solution was added 861.00 g of Latex B over the course of 55 min. The mixture was stirred for an additional 5 min. No coagulation was observed. The wt% of nanoparticles versus the total weight (nanoparticle solution and fluoropolymer latex) was 3.489.

[0079] Comparative Example 3

[0080] A solution of 15 wt. % solids was made by diluting "PEG 300" with deionized water. 87.00 g of this solution was stirred with a Cowles blade driven by a Laboratory Disperserator series 2000 Model 90 (Premier Mill, Exton, PA) and 253.00 g of Latex A was added. No coagulation was observed.

[0081] Comparative Example 4

[0082] A solution of 4.5 wt % solids was made by diluting "PEG 300" with deionized water. 86.13 g of this solution was stirred with a Cowles blade driven by a Laboratory Disperserator series 2000 Model 90 (Premier Mill, Exton, PA) and 279.00 g of Latex A was added. No coagulation was observed.

[0083] Example 1

[0084] To 1363.70 g of "modified silica sol #1 " was added 1799.00 g of Latex B over the course of 20 min. The mixture was stirred with a Cowles blade driven by a Laboratory Disperserator series 2000 Model 90 (Premier Mill, Exton, PA) controlled by a VARIAC at a setting of 30. Initially there was foam in the mixture but the foam dimished after 7 min of mixing. After latex addition the mixture was stirred an additional 30 min followed by 60 min of settling. The solids were filtered through cheese cloth and washed with approximately 2000 g of hot deionized water for 60 min. The washing procedure was repeated and the solids were filtered a final time then dried in an oven at 100 °C for 16 hrs. The resulting yield was 44.02% by wt. The wt% of nanoparticles versus the total weight (nanoparticle solution and fluoropolymer latex) was 1.725.

[0085] Example 2

[0086] To 81.6 g of "modified silica sol #2" was added 529.2 g of Latex A over the course of 30 min while stirring at medium speed on a Cowles blade driven by a Laboratory Disperserator series 2000 Model 90 (Premier Mill, Exton, PA). A white, foamy mixture formed initially then the precipitate thickened into solids. The mixture was stirred for an additional 30 min after addition followed by 30 min of settling. The solids were filtered through a cheese cloth and washed with approximately 600 g of hot deionized water for 60 min by shaking in a closed jar on a laboratory shaker. The washing procedure was repeated two more times followed by a final filtration through cheese cloth. The solids were dried in a 104 °C oven for 16 hrs. The resulting yield was 95.64 % by wt. The wt% of nanoparticles versus the total weight (nanoparticle solution and fluoropolymer latex) was 2.978.

[0087] Example 3

[0088] Latex A was diluted with deionized water to form a latex with 10 % solids. 1818.18 g of this latex was added over the course of 30 min to 81.60 g of "modified silica sol #2" while stirring at medium speed of a Cowles blade driven by a Laboratory Disperserator series 2000 Model 90 (Premier Mill, Exton, PA). Initially a foam formed but then the precipitate thickened into solids. After the latex was added the mixture was stirred an additional 30 min followed by 30 min of settling. The solids were filtered through a cheese cloth and washed with approximately 2000 g of hot deionized water for 60 min by shaking in a closed jar on a laboratory shaker. The washing procedure was repeated two more times followed by a final filtration through cheese cloth. The solids were dried in a 104 °C oven for 16 hrs. The resulting yield was 48.00 % by wt. The wt% of nanoparticles versus the total weight (nanoparticle solution and fluoropolymer latex) was 0.957.

[0089] Example 4

[0090] 209.00 g of "modified silica sol #3" was stirred at a high speed with a magnetic stir bar on an IKA magnetic stir plate. To this solution was added 575.0 g of Latex B over the course of 40 min. Solid material formed on the stir bar after one minute and thickened with the addition of additional latex. The mixture was stirred for an additional 30 min during which time a thick gel formed. The mixture was allowed to settle for 5 min. Liquid was pressed out of a material through a cheese cloth. The resulting solids were washed by adding approximately 600 mL of hot deionized water and shaking in a closed container on a laboratory shaker. The washing procedure was repeated two more times followed by a final filtration through cheese cloth. The solids were dried in a 93 °C oven for 16 hrs. The resulting yield was 80.61 % by wt. The wt% of nanoparticles versus the total weight (nanoparticle solution and fluoropolymer latex) was 3.332.

[0091] Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes.