Wear-resistant compositions containing crosslinked aromatic polymers and methods for using same to improve wear resistance - Patents.com

Abstract

Disclosed are compositions and articles formed therefrom for use in forming articles subjected to frictional forces or for use in tribological systems. Such compositions include at least one crosslinkable aromatic polymer matrix material that remains operable at a PV of at least about 75,000 psi-ft. / min or more. Such at least one crosslinkable polymer may also be used as a filler in crosslinked form in the wear matrix material in further compositions herein. Wear resistance may be improved by about 200% up to about 850% compared to known wear compositions or with respect to the use of the same aromatic polymer filler that is not crosslinked. Methods for improving the wear resistance or PV limit of wear compositions are also disclosed. Further disclosed are methods and compositions for substantially retaining dimensional stability and avoiding catastrophic failure near a critical transition temperature using the compositions herein.

Description

[Technical Field]

[0001] Title of the invention Wear-resistant compositions containing crosslinked aromatic polymers and methods for using same to improve wear resistance

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS This non-provisional patent application claims the benefit under U.S.C. § 119(e) to U.S. Provisional Patent Application No. 63 / 306,257, filed February 3, 2022, entitled "Wear-Resistant Compositions Including Crosslinked Aromatic Polymers and Methods for Improving Wear Resistance Using the Same," the entire disclosure of which is incorporated herein by reference.

[0003] Background of the Invention FIELD OF THE INVENTION The present invention relates to the field of wear-resistant materials for use in end applications where frictional forces are generated between moving parts, and to the field of reducing wear due to frictional forces in tribological systems. [Background technology]

[0004] Description of Related Technical Fields

[0003] Many mechanical systems include moving parts that interact due to surface-to-surface contact or with materials in contact with the surfaces, causing frictional forces that over time result in wear on the moving parts and contacting surfaces. For example, in heavy machinery and material handling industries such as the aerospace and energy industries, there is a strong need for polymeric materials that exhibit high levels of wear resistance, especially at elevated temperatures, and can provide improved temperature durability.

[0005] Friction and wear also contribute significantly to energy losses in moving parts such as gears, bearings, downhole tools, drills, pulleys, etc., as well as surface damage in such parts and various tools that routinely come into contact with other surfaces during use.

[0006] Tribology is the study of frictional contact between surfaces. Energy losses and part wear and the need for replacement (as well as wear due to the use of metals and hard ceramics in components subjected to weight and surface-to-surface contact) inhibit the ability to make systems more efficient, reduce waste in manufacturing, and reduce the energy requirements needed to produce items. Traditionally, tribology has generally been studied using metal-to-material or ceramic-to-material surface contacts. The tribology of polymers against polymer surfaces is an increasingly important field, but is much more difficult to predict and develop, as factors affecting polymers are less relevant when predicting behavior in metal and ceramic surface contacts. For example, the coefficient of friction for a given metal surface is reasonably constant due to the strength and high heat resistance of most metals. When working with polymer materials, their tribological properties are greatly influenced by the polymer used and the tribological conditions. The coefficient of friction for a given polymer depends, in some cases, on the applied load, sliding speed, temperature of the system, and glass transition temperature (T g ) and melting temperature (T m The wear characteristics of polyarylene polymers, such as polyetheretherketone (PEEK) polymers, can be substantially affected by the critical transition temperature of the polymer. At the critical transition temperature(s), softening or melting of the polymer matrix can alter the wear characteristics. For example, polyarylene polymers, such as polyetheretherketone (PEEK) polymers, have particularly limited usefulness when the test temperature exceeds the critical wear temperature, either due to the end-use temperature employed or as a result of application temperatures combined with elevated temperatures of mating surfaces of bearings or other components subjected to friction due to frictional heating. See Jean-Fulcrand et al., "Effect of Temperature on Tribological Performance of Polyetheretherketone-Polybenzimidazole Blends," Tribology International 129 (2019) pp. 5-15.

[0007] As the applied load and / or temperature increase, a given polymer may deform and its coefficient of friction may decrease rapidly. Similarly, sliding speed can generate heat and frictional energy that can adversely affect the coefficient of friction and wear characteristics. The coefficient of friction of a polymer is also typically determined when the polymer reaches its critical transition temperature, T g and / or T m As the temperature approaches the critical transition temperature T g and / or T m There is a need in the art to develop polymer tribological materials and systems that can provide suitable wear characteristics and are stable in high pressure-velocity ("PV") end uses, so that they can be used to replace heavy metal parts, reduce wear and part replacement, and make systems more efficient.

[0008] Previous patents by the applicant have shown that crosslinking aromatic polymers generally increases their mechanical properties and transition temperatures. Furthermore, when highly crosslinked, components formed from such crosslinked polymers can be used at temperatures above the melting point of the semicrystalline phase of the polymer system. Prior art applications of compositions containing aromatic polymers and crosslinking compounds have been developed by the applicant and employed to achieve materials with higher glass transition temperatures compared to non-crosslinked polymers, such as those described in U.S. Pat. No. 9,006,353 B2. Such compositions have also been described by the applicant in U.S. Pat. No. 9,109,080 in combination with crosslinking additives to control the crosslinking rate to enable melt processing of parts, such as by extrusion or injection molding, and / or to achieve improved mechanical properties at high temperatures for use in extrusion-resistant sealing components. See U.S. Pat. Nos. 9,475,938 and 9,127,938.

[0009] Improved friction and wear resistance, especially in high-temperature, pressure, and velocity end-use applications, as well as increased temperature durability, improve the application temperature and sustainability applicable to mobility and transportation solutions. Products formed from wear-resistant polymeric materials that meet such requirements and can provide improved wear properties for high-PV applications include bearings, seals, fittings / connections, tools, moving parts, and engine parts used in industrial products and commercial goods, including vehicle and appliance components, as well as other items and products with moving parts. Such materials can be used in place of products typically made from other metal or ceramic wear substitutes, such as engineering plastics or other enhanced plastics (including fluoropolymers, e.g., high-molecular-weight polytetrafluoroethylene (PTFE) or modified PTFE). While such materials have good wear properties, they are not mechanically strong and must be filled or otherwise enhanced for wear applications. As a matrix material, PTFE is traditionally not melt-processable and must be molded into preforms and sintered to form parts. As a result, such materials are difficult to recycle and reuse once used, potentially presenting environmental concerns. Others are stronger but exhibit variable or poor wear characteristics, especially in high PV applications.

[0010] High-performance polymers, such as polyetheretherketone (PEEK), polyetherketone (PEK), polyetherketoneketone (PEKK), polyamideimide (PAI), polybutylene terephthalate (PBT), polybenzimidazole (PBI), polyphenylene sulfide (PPS), ultra-high molecular weight polyethylene (UHMWPE), PTFE, polyoxyalkylenes (such as polyoxymethylene (acetal)), polyetherimide (PEI), polyamide (PA), polyimide (PI), fluoropolymers (including melt-processible fluoropolymers such as copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ether, copolymers of tetrafluoroethylene and hexafluoropropylene, polychlorotrifluoroethylene (PCTFE), and polyvinylidene fluoride (PVDF)), and other polymers (including aromatic polyethers and polyketones), are commonly used in friction-resistant end uses. Such materials have temperature limitations for the reasons mentioned above. Amorphous polymers such as PEI and polyphenylsulfone (PPSU), and some grades of polyarylenes such as PEKK, cannot be used above their glass transition temperature (Tg) due to severe softening (approximately 90% to 99% loss of properties) which can increase uncontrolled friction of the surface in contact applications.

[0011] Semi-crystalline polymers can be used above their Tg, but due to the higher molecular mobility above Tg, they exhibit a significant degradation in both surface and bulk properties at these temperatures, which can lead to catastrophic wear due to melting. In many cases, such end uses also involve the possibility of fluid exposure, and as a result, the materials must be chemically resistant. This presents challenges and limitations to the use of materials such as wear matrix materials for tribological systems and wear applications, especially in high temperature and high PV applications. As mentioned above, materials such as PTFE have been adopted as PTFE matrix materials for friction end uses due to their excellent friction properties, including a very low coefficient of friction. However, they lack sufficient strength for many end uses and therefore perform poorly in more demanding applications, such as high-pressure, high-velocity applications ("PV applications"). To modify these properties, many such applications often provide PTFE with additives in the form of fillers or reinforcing agents. For example, PPS, PI, polyesters, and polysulfones (such as Ceramer® oxidized polyphenylsulfone) are added to PTFE, as well as carbon, coke, and / or graphite at levels up to about 15% to enhance wear resistance. PPS and PI are commonly used fillers, but PPS has a Tg of about 90°C (194°F), which weakens the compound, as it can lose 60–80% of its mechanical properties at temperatures above its Tg. PI as a filler can withstand higher temperatures, but any exposure to water or water vapor can cause irreversible hydrolysis that can weaken the overall wear compound.

[0012] Thus, there is a need in the art to provide improved polymeric wear materials for use as matrix materials and / or fillers for existing wear compounds (such as those formed from PTFE) in applications subject to wear, particularly in high temperature and / or high PV end uses, to enhance the ability to employ such materials in tribological systems, thereby resulting in greater energy and cost efficiency, reduced weight, more sustainable industrial and commercial parts and products, more efficient manufacturing processes, and increased recycling opportunities. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] U.S. Patent No. 9,006,353 [Patent Document 2] U.S. Patent No. 9,109,080 [Patent Document 3] U.S. Patent No. 9,475,938 [Patent Document 4] U.S. Patent No. 9,127,938 [Non-patent literature]

[0014] [Non-Patent Document 1] Jean-Fulcrand et al., “Effect of Temperature on Tribological Performance of Polyetheretherketone-Polybenzimidazole Blend”, Tribology International 129 (2019) pp. 5-15 Summary of the Invention [Means for solving the problem]

[0015] Summary of the Invention The invention herein provides a method for producing high PV values ​​and / or critical temperatures (T) while retaining dimensional stability and mechanical properties and providing greater efficiency and the ability to reduce the weight of parts otherwise formed from metal or ceramic, thereby making the process more energy efficient and cost effective. g The shortcomings of the prior art are addressed by providing compositions and articles that enable polymeric materials to be used in friction and wear applications at high temperatures (such as above their melting point or temperature). In preferred embodiments herein, such compositions and articles may also provide improved chemical resistance of such articles over a wide range of temperatures, and enable continued good mechanical, wear, and friction properties at high temperature and high PV conditions.

[0016] The invention herein includes a composition for use in forming an article subjected to frictional forces or for use in a tribological system, comprising at least one crosslinkable aromatic polymer matrix material that, when crosslinked, remains operable at a PV of at least about 75,000 psi-ft. / min. In a preferred embodiment, the at least one crosslinkable aromatic polymer matrix material, when crosslinked, can remain operable at a PV of from about 75,000 psi-ft. / min to about 100,100 psi-ft. / min. In a further embodiment, the at least one crosslinkable aromatic polymer matrix material, when crosslinked, has a PV limit, measured in psi-ft. / min at about 500°F, that is at least about 10% higher than the PV limit, measured in psi-ft. / min at about 500°F, of the same aromatic polymer matrix material in a non-crosslinkable form. Preferably, the PV limit is at least about 20% higher, more preferably about 50% higher.

[0017] In one embodiment, the at least one crosslinkable aromatic polymer matrix material is a crosslinkable polymer selected from polyarylenes, polysulfones, polyethersulfones, polyphenylene sulfides, polyphenylene oxides, polyimides, polyetherimides, thermoplastic polyimides, polybenzamides, polyamideimides, polyureas, polyurethanes, polyphthalamides, polybenzimidazoles, polyaramids, and blends, copolymers, and alloys thereof. The at least one crosslinkable aromatic polymer is preferably a crosslinkable polyarylene selected from polyetherketones, polyetheretherketones, polyetherdiphenyletherketones, polyetherketoneketones, and blends, copolymers, and alloys thereof.

[0018] The at least one crosslinkable aromatic polymer may include one or more functional groups for crosslinking. The at least one crosslinkable polymer may have the formula (I): [ka] (In the formula, Ar 1 , Ar 2 , Ar 3 and Ar 4 are the same or different aryl radicals, m=0-1, and n=1-m. The polyarylene ether may have repeat units of the structure: along its backbone.

[0019] In one embodiment, at least one crosslinkable aromatic polymer in the composition has the formula (II): [ka] or formula (IIa): [ka] The polymer may have repeat units along its backbone having the structure:

[0020] In further embodiments, the at least one crosslinkable polymer may comprise a first crosslinkable polymer that is one or more polyarylenes selected from polyetherketone, polyetheretherketone, polyetherdiephenyletherketone, polyetherketoneketone, and blends, copolymers, and alloys thereof; and a second crosslinkable polymer selected from the group consisting of one or more of: (i) polyphenylene sulfide; (ii) polysulfone, polyphenylsulfone, polyethersulfone, copolymers, and alloys thereof; and (iii) polyimide, thermoplastic polyimide, polyetherimide, and blends, copolymers, and alloys thereof.

[0021] The composition may include at least one crosslinkable aromatic polymer having the following formula: [ka] where A is a bond, alkyl, aryl, or arene moiety having a molecular weight of less than about 10,000 g / mol; R 1 , R 2 and R 3 are the same or different and are independently selected from the group consisting of hydrogen, hydroxyl (-OH), amine (NH), halide, ester, ether, amide, aryl, arene, or a branched or straight chain saturated or unsaturated alkyl group of 1 to about 6 carbon atoms; m is 0 to 2, n is 0 to 2, and m + n is equal to or greater than 0 and is less than or equal to 2; Z is selected from the group of oxygen, sulfur, nitrogen, and a branched or straight chain saturated or unsaturated alkyl group of 1 to about 6 carbon atoms; and x is from about 1 to about 6. The polymer may further comprise at least one cross-linking compound having a structure according to one of:

[0022] In such embodiments, at least one bridging compound may have a structure according to formula (IV): [ka] [ka] is selected from the group consisting of: It may also have at least one bridging compound having a structure according to formula (V): [ka] is selected from the group consisting of: Additionally, the at least one bridging compound may have a structure according to formula (VI): [ka] is selected from the group consisting of:

[0023] In one embodiment of the composition comprising a crosslinking compound, the crosslinking compound may have the formula set forth above in Formulas (IV), (V), and (VI), where A has a molecular weight of about 1,000 g / mol to about 9,000 g / mol. When used, the at least one crosslinking compound may be present in the composition in an amount of about 1% to about 50% by weight, based on the unfilled weight of the composition. A preferred weight ratio of crosslinkable aromatic polymer to crosslinking compound in the composition is about 1:1 to about 100:1.

[0024] When a crosslinking compound is used, the composition may further comprise a crosslinking reaction control additive selected from a cure inhibitor or a cure accelerator. The crosslinking reaction control additive may be present in the composition in an amount of about 0.01% to about 15% by weight based on the crosslinking compound. The crosslinking reaction control additive may be a cure inhibitor containing lithium acetate. The crosslinking reaction control additive may be a cure accelerator containing magnesium chloride.

[0025] The composition may also comprise one or more additives selected from continuous or discontinuous long or short reinforcing fibers selected from carbon fibers, glass fibers, woven glass fibers, woven carbon fiber fabric, aramid fibers, boron fibers, polytetrafluoroethylene fibers, ceramic fibers, polyamide fibers, and / or one or more fillers selected from carbon black, silicates, fiberglass, glass beads, glass spheres, crushed glass, calcium sulfate, boron, ceramic, polyamide, asbestos, fluorographite, aluminum hydroxide, barium sulfate, calcium carbonate, magnesium carbonate, silica, aluminum nitride, aluminum oxide, borax (sodium borax), activated carbon, perlite, zinc terephthalate, graphite, graphene, talc, mica, silicon carbide whiskers or platelets, nanofillers, molybdenum disulfide, fluoropolymer fillers, boron nitride, nanodiamonds, microdiamonds, carbon nanotubes, and fullerene tubes. Preferably, the one or more additives and / or one or more fillers comprise from about 0.5% to about 65% by weight of the composition. The composition of claim 19, wherein the one or more additives are selected from carbon fiber, glass fiber, PTFE, and graphite.

[0026] The present invention further includes articles formed from the above compositions. Such articles may be, for example, but not limited to, rotating and reciprocating components selected from downhole tool components, aerospace components, vehicle components, semiconductor manufacturing components, and tools having rotating or reciprocating components. Such components may be, for example, but not limited to, gears, rotors, drill bits, pulleys, bearings, and seals.

[0027] In a further embodiment herein, the present invention relates to a composition for use in forming an article that is subject to frictional forces or for use in a tribological system, comprising at least one crosslinkable aromatic polymer matrix material and continuous or discontinuous long or short reinforcing fibers selected from carbon fibers, glass fibers, woven glass fibers, woven carbon fibers, aramid fibers, boron fibers, polytetrafluoroethylene fibers, ceramic fibers, polyamide fibers, and / or carbon black, silicates, fiberglass, glass beads, glass spheres, crushed glass, calcium sulfate, boron, ceramic, polyamide and one or more additives selected from one or more fillers selected from asbestos, fluorographite, aluminum hydroxide, barium sulfate, calcium carbonate, magnesium carbonate, silica, aluminum nitride, aluminum oxide, borax (sodium borax), activated carbon, perlite, zinc terephthalate, graphite, graphene, talc, mica, silicon carbide whiskers or platelets, nanofillers, molybdenum disulfide, fluoropolymer fillers, boron nitride, nanodiamonds, microdiamonds, carbon nanotubes, and fullerene tubes.

[0028] In such embodiments, the composition may comprise from about 0.5% to about 65% by weight of one or more additives and / or one or more fillers, which may preferably be selected from carbon fiber, glass fiber, PTFE, and graphite.

[0029] In such an embodiment, the at least one crosslinkable aromatic polymer matrix material may be a crosslinkable polymer selected from polyarylenes, polysulfones, polyethersulfones, polyphenylene sulfides, polyphenylene oxides, polyimides, polyetherimides, thermoplastic polyimides, polybenzamides, polyamideimides, polyureas, polyurethanes, polyphthalamides, polybenzimidazoles, polyaramids, and blends, copolymers, and alloys thereof. The at least one crosslinkable may also be a crosslinkable polyarylene selected from polyetherketones, polyetheretherketones, polyetherdiphenyletherketones, polyetherketoneketones, and blends, copolymers, and alloys thereof. The at least one crosslinkable aromatic polymer may contain one or more functional groups for crosslinking. In one embodiment of such a composition, the at least one crosslinkable polymer is represented by Formula (I): [ka] (In the formula, Ar 1 , Ar 2 , Ar 3 and Ar 4 are the same or different aryl radicals, m=0-1, and n=1-m. The polyarylene ether has repeating units of the structure shown below along its backbone.

[0030] For example, at least one crosslinkable aromatic polymer in the composition in this embodiment may also be represented by the formula (II): [ka] or formula (IIa): [ka] The polymer may have repeat units along its backbone having the structure:

[0031] Further, in such embodiments of the composition, the at least one crosslinkable polymer comprises a first crosslinkable polymer that is one or more polyarylenes selected from polyetherketone, polyetheretherketone, polyetherdiephenyletherketone, polyetherketoneketone, and blends, copolymers, and alloys thereof, and a second crosslinkable polymer selected from the group consisting of one or more of: (i) polyphenylene sulfide, (ii) polysulfone, polyphenylsulfone, polyethersulfone, copolymers, and alloys thereof, and (iii) polyimide, thermoplastic polyimide, polyetherimide, and blends, copolymers, and alloys thereof.

[0032] The composition may include at least one crosslinkable aromatic polymer having the following formula: [ka] where A is a bond, alkyl, aryl, or arene moiety having a molecular weight of less than about 10,000 g / mol; R 1 , R 2 and R 3 are the same or different and are independently selected from the group consisting of hydrogen, hydroxyl (-OH), amine (NH), halide, ester, ether, amide, aryl, arene, or a branched or straight chain saturated or unsaturated alkyl group of 1 to about 6 carbon atoms; m is 0 to 2, n is 0 to 2, and m + n is equal to or greater than 0 and is less than or equal to 2; Z is selected from the group of oxygen, sulfur, nitrogen, and a branched or straight chain saturated or unsaturated alkyl group of 1 to about 6 carbon atoms; and x is from about 1 to about 6. The polymer may further comprise at least one cross-linking compound having a structure according to one of:

[0033] The present invention further includes a method for improving the wear resistance of an article formed from a composition, the article being for use in a high PV end use where the article is subjected to frictional forces or used in a tribological system, the method comprising providing the composition with at least one crosslinkable aromatic polymer matrix material, which when crosslinked remains capable of operating at a PV of at least about 75,000 psi-ft. / min; crosslinking the at least one crosslinkable aromatic polymer in the composition; and forming the article. In one embodiment, the at least one crosslinkable aromatic polymer matrix material, when crosslinked, remains capable of operating at a PV of from about 75,000 psi-ft. / min to about 100,100 psi-ft. / min. In this method, the PV limit of the composition for forming the article can also be increased by providing the composition with at least one crosslinkable aromatic polymer matrix material that, when crosslinked, has a PV limit, measured in psi-ft. / min. at about 500°F, that is at least about 10% higher than the PV limit, measured in psi-ft. / min. at about 500°F, of the same aromatic polymer matrix material in a non-crosslinkable form. Preferably, the PV limit can be at least about 20% higher, more preferably about 50% higher. The method can further include providing the composition with one or more additives selected from carbon fiber, glass fiber, PTFE, and graphite.

[0034] In still further embodiments, the present invention comprises a composition for use in forming an article subjected to frictional forces or for use in a tribological system, said composition comprising a matrix material selected from polytetrafluoroethylene, modified polytetrafluoroethylene, and at least one aromatic polymer, and at least one crosslinked aromatic polymer filler material, wherein said at least one crosslinked aromatic polymer filler material.

[0035] In such compositions, the abrasion resistance of the composition may be at least about 200% greater than a composition having the same matrix material and the same non-crosslinked aromatic polymeric filler material, preferably at least about 250% greater than a composition having the same matrix material and the same non-crosslinked aromatic polymeric filler material, and even more preferably up to about 850% greater than a composition having the same matrix material and the same non-crosslinked aromatic polymeric filler material. The at least one crosslinked aromatic polymeric filler material may further have a PV limit, measured in psi-ft. / min at about 500°F, that is at least about 20% higher than the PV limit of the same non-crosslinked aromatic polymeric matrix material, and preferably the PV limit is at least about 50% higher than the PV limit of the same non-crosslinked aromatic polymeric matrix material.

[0036] The at least one crosslinked aromatic polymer filler can be formed by providing a composition comprising at least one or more crosslinkable aromatic polymers, crosslinking at least one of the crosslinkable aromatic polymers in the composition, and forming the composition into at least one of pellets, platelets, or particles.

[0037] The at least one crosslinkable aromatic polymer may include one or more functional groups for crosslinking. The at least one crosslinkable polymer may include a first crosslinkable polymer that is one or more polyarylenes selected from polyetherketone, polyetheretherketone, polyetherdiephenyletherketone, polyetherketoneketone, and blends, copolymers, and alloys thereof, and a second crosslinkable polymer selected from the group consisting of one or more of: (i) polyphenylene sulfide, (ii) polysulfone, polyphenylsulfone, polyethersulfone, copolymers, and alloys thereof, and (iii) polyimide, thermoplastic polyimide, polyetherimide, and blends, copolymers, and alloys thereof.

[0038] The at least one crosslinked aromatic polymer filler material is a crosslinked polymer that may be selected from polyarylenes, polysulfones, polyethersulfones, polyphenylene sulfides, polyphenylene oxides, polyimides, polyetherimides, thermoplastic polyimides, polybenzamides, polyamideimides, polyureas, polyurethanes, polyphthalamides, polybenzimidazoles, polyaramids, and blends, copolymers, and alloys thereof.

[0039] The at least one crosslinked aromatic polymer filler material may be a crosslinked polyarylene selected from polyether ketone, polyether ether ketone, polyether diphenyl ether ketone, polyether ketone ketone, and blends, copolymers, and alloys thereof. The at least one crosslinkable polymer may be, for example, ... [ka] (wherein Ar1, Ar2, Ar3 and Ar4 are the same or different aryl radicals, m=0 to 1, and n=1-m). The polyarylene ether may be a polyarylene ether having repeating units of the structure shown below along its backbone.

[0040] The at least one crosslinkable aromatic polymer has the formula (II): [ka] or formula (IIa): [ka] The polymer may further have repeat units along its backbone having the structure:

[0041] The composition may also comprise a compound of the formula: [ka] where A is a bond, alkyl, aryl, or arene moiety having a molecular weight of less than about 10,000 g / mol; R 1 , R 2 and R 3 are the same or different and are independently selected from the group consisting of hydrogen, hydroxyl (-OH), amine (NH), halide, ester, ether, amide, aryl, arene, or a branched or straight chain saturated or unsaturated alkyl group of 1 to about 6 carbon atoms; m is 0 to 2, n is 0 to 2, and m + n is equal to or greater than 0 and is less than or equal to 2; Z is selected from the group of oxygen, sulfur, nitrogen, and a branched or straight chain saturated or unsaturated alkyl group of 1 to about 6 carbon atoms; and x is from about 1 to about 6. The compound may comprise at least one cross-linking compound having a structure according to one of:

[0042] Examples of the at least one bridging compound include those having a structure according to formula (IV): [ka] may be selected from the group consisting of:

[0043] At least one bridging compound may have a structure according to formula (V): [ka] may be selected from the group consisting of:

[0044] At least one bridging compound may have a structure according to formula (VI): [ka] may be selected from the group consisting of:

[0045] In the above formula, A may have a molecular weight of about 1,000 g / mol to about 9,000 g / mol. The at least one crosslinking compound may be present in the composition in an amount of about 1% to about 50% by weight, based on the unfilled weight of the composition. A preferred weight ratio of crosslinkable aromatic polymer to crosslinking compound in the composition is about 1:1 to about 100:1.

[0046] The composition may further comprise a crosslinking reaction control additive selected from a cure inhibitor or a cure accelerator. The crosslinking reaction control additive may be present in the composition in an amount of about 0.01% to about 15% by weight based on the crosslinking compound. The crosslinking reaction control additive may be a cure inhibitor comprising lithium acetate. The crosslinking reaction control additive may be a cure accelerator comprising magnesium chloride.

[0047] The composition may comprise one or more additives selected from continuous or discontinuous long or short reinforcing fibers selected from carbon fibers, glass fibers, woven glass fiber fabric, woven carbon fiber fabric, aramid fibers, boron fibers, polytetrafluoroethylene fibers, ceramic fibers, polyamide fibers, and / or one or more fillers selected from carbon black, silicates, fiberglass, glass beads, glass spheres, crushed glass, calcium sulfate, boron, ceramic, polyamide, asbestos, fluorographite, aluminum hydroxide, barium sulfate, calcium carbonate, magnesium carbonate, silica, aluminum nitride, aluminum oxide, borax (sodium borax), activated carbon, perlite, zinc terephthalate, graphite, graphene, talc, mica, silicon carbide whiskers or platelets, nanofillers, molybdenum disulfide, fluoropolymer fillers, boron nitride, nanodiamonds, microdiamonds, carbon nanotubes, and fullerene tubes.

[0048] The composition may contain from about 0.5% to about 65% by weight of one or more additives and / or one or more fillers. Preferred additives include carbon fiber, glass fiber, PTFE, and graphite.

[0049] Also included in the present invention are articles formed from the above compositions. The article that undergoes wear during use may be selected from rotating and reciprocating components selected from, but not limited to, downhole tool components, aerospace components, vehicle components, semiconductor manufacturing components, and tools having rotating or reciprocating components. For example, the article may be, but is not limited to, a gear, a rotor, a drill bit, a pulley, a bearing, and a seal.

[0050] The present invention also includes a method for improving the wear resistance of a composition for use in forming an article subjected to frictional forces or for use in a tribological system, comprising providing a matrix material selected from polytetrafluoroethylene, modified polytetrafluoroethylene, and at least one aromatic polymer, and adding to the matrix a filler material comprising at least one crosslinked aromatic polymer. The composition may have a wear resistance at least about 200% greater than a composition having the same matrix material and a filler material of the same aromatic polymer that is not crosslinked, preferably at least about 250% greater than a composition having the same matrix material and a filler material of the same aromatic polymer that is not crosslinked, and may be up to about 850% greater than a composition having the same matrix material and a filler material of the same aromatic polymer that is not crosslinked. The at least one crosslinked aromatic polymer filler material may have a PV limit, measured in psi-ft. / min at about 500°F, that is at least about 10% higher than the PV limit of the same aromatic polymer matrix material that is not crosslinked, preferably at least about 20% higher, and most preferably at least about 50% higher than the PV limit of the same aromatic polymer matrix material that is not crosslinked.

[0051] The present invention also includes a composition for use in forming an article subjected to frictional forces or for use in a tribological system, comprising at least one crosslinkable aromatic polymer matrix material that, when crosslinked, substantially maintains its dimensional stability after heating above a critical transition temperature. The critical transition temperature may be a glass transition temperature or a melting point temperature. When the at least one crosslinkable aromatic polymer matrix material is crosslinked, it also preferably avoids catastrophic failure at temperatures above the critical transition temperature.

[0052] Also provided herein is a method for maintaining dimensional stability and / or avoiding catastrophic failure above a critical transition temperature of an article subjected to frictional forces and / or used in a tribological system, the method comprising forming the article from a composition comprising a crosslinked aromatic polymer and incorporating the article into an application where the temperature of the article is above the critical transition temperature of the aromatic polymer in the article, the application being subjected to frictional forces and / or used in a tribological system. The crosslinked aromatic polymer is preferably a matrix material in the article. In one embodiment, the composition may comprise a polymer matrix material, and the crosslinked aromatic polymer is a filler in the polymer matrix material. The critical transition temperature is a glass transition temperature or a melting temperature.

[0053] Also included in the present invention is a composition for use in forming an article subjected to frictional forces or for use in a tribological system, comprising at least one crosslinkable aromatic polymer matrix material that, when crosslinked and incorporated into an article subjected to frictional forces or a tribological system, substantially retains its dimensional stability above the critical transition temperature of the crosslinked aromatic polymer in the article.

[0054] A brief description of some of the figures in the drawing(s) The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the accompanying drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. [Brief explanation of the drawings]

[0055] [Figure 1A] FIG. 1A is a photographic representation of a thrust washer of Example 1 herein formed from an uncrosslinked PEEK wear composition prior to testing.

[0056] [Figure 1B] FIG. 1B is a photographic representation of the thrust washer of FIG. 1A after testing.

[0057] [Figure 1C] FIG. 1C is a photographic representation of a thrust washer of Example 1 herein formed from a crosslinked PEEK wear composition prior to testing.

[0058] [Figure 1D] FIG. 1D is a photographic representation of the thrust washer of FIG. 1C after testing.

[0059] [Figure 2] FIG. 2 is a graphical representation of the effect of wear coefficient (10-10 in3 min / ft.-lb. hr) as a function of PV (psi ft. / min) for Comparative Samples A and B and Inventive Sample C in Example 2.

[0060] [Figure 3] FIG. 3 is a graphical representation of the normalized abrasion resistance (1 / K) for the wear compound of Comparative Sample E formed from PTFE with PPS filler of Example 3 and for Inventive Sample D comprising PTFE filled with crosslinked PEEK filler.

[0061] [Figure 4]FIG. 4 is a graphical representation of the wear coefficient of inventive Sample H (using the crosslinked PEEK filler of inventive Sample D of Example 3) compared to PTFE samples filled with uncrosslinked PEEK (Sample F) and PPS (Sample G) as Example 4.

[0062] [Figure 5] FIG. 5 is a graphical representation of the change in thickness gap (mm) over time during DMA compression testing of Example 5.

[0063] [Figure 6A] FIG. 6A is a photographic representation of the thrust washer of Sample 2 (uncrosslinked material) of Example 5 before testing.

[0064] [Figure 6B] FIG. 6B is a photographic representation of the thrust washer of Sample 2 (uncrosslinked material) after testing in Example 5.

[0065] [Figure 6C] FIG. 6C is a photographic representation of the thrust washer of Sample 1 (crosslinked material) of Example 5 before testing.

[0066] [Figure 6D] FIG. 6D is a photographic representation of the thrust washer of Sample 1 (crosslinked material) after testing in Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0067] Detailed Description of the Invention The present invention relates to compositions for making articles comprising aromatic polymer materials for use as matrix materials and / or as friction additives in existing matrix materials, and articles made therefrom, when such articles are used in friction and wear applications, particularly when employed in high PV end uses. When employed as a matrix material, such compositions retain dimensional stability and mechanical properties, providing greater efficiency and the ability to reduce the weight of parts otherwise formed from metal or ceramic, thereby making the process more energy-efficient and cost-effective. Furthermore, when used as an additive in an existing matrix material or in place of an existing matrix material with an uncrosslinked aromatic material, such compositions can improve existing friction and wear properties, particularly at high PV conditions. In preferred embodiments herein, such compositions and articles also provide improved chemical resistance for such articles over a wide range of temperatures and enable continued good mechanical, wear, and friction properties at high temperatures and high PV conditions.

[0068] In one embodiment, compositions can be formed that can be employed to form articles that will be subjected to frictional forces in their intended end use or for use in tribological systems. Such compositions can be formed to include at least one crosslinkable aromatic polymer matrix material. The employed matrix material, when crosslinked, provides a PV limit, measured at about 500°F in psi-ft. / min, that is at least about 10% higher than the PV limit, measured at about 500°F in psi-ft. / min, of the same non-crosslinkable aromatic polymer matrix material. Preferably, the PV limit is at least about 20% higher, and more preferably about 50% higher. For example, the use of crosslinked polyetheretherketone as the matrix material in such compositions can provide a PV limit that is at least about 50% higher than that of standard uncrosslinked polyetheretherketone.

[0069] Such crosslinked aromatic polymers as matrix materials enable the formation of articles with improved tribological and wear properties, particularly for use of such compositions at high temperatures, improving friction properties, including PV limits, so that the polymeric materials can be employed in end uses where other wear materials of the prior art cannot be used.

[0070] As used herein, the terms "a" and "at least one" may mean "one or more" in the absence of language to the contrary, such as a language indicating a specific number.

[0071] As used herein, an "aromatic polymer" is a polymer that contains aromatic moieties along or attached to its polymer backbone, preferably one that incorporates aromatic moieties (cyclic moieties derived from aromatic compounds) into the polymer backbone. Such aromatic moieties may be monocyclic and / or polycyclic structures and may be linked together directly on the backbone or may be connected via linking species or elements such as oxygen, sulfur, hydrogen, alkyl, or other groups.

[0072] As used herein, a "crosslinkable polymer" means a polymer having groups that can react with each other (self-crosslinking), react through the application of heat, radiation, or light, or react with a crosslinking agent or compound. Such groups may be present on the polymer when formed by polymerization, or may be provided to the polymer via functional or other crosslinking groups located along the length of the polymer chain or along substituents extending from the polymer chain, including terminal groups.

[0073] The crosslinked polymers herein may be formed from compositions containing at least one crosslinkable polymer and one or more additives, crosslinking compounds, reaction control agents, or other additives or fillers. The compositions thus formed may be crosslinked using a variety of acceptable crosslinking techniques, such as thermally induced crosslinking, radiation-induced crosslinking, grafting crosslinkable groups on the polymer, and reacting the polymer with one or more other materials and / or chemically induced crosslinking reactions. Crosslinking may occur during and / or after molding or forming the crosslinkable aromatic polymer in the composition into a part, component, or portion thereof. As used herein, incorporating the compositions herein into an "article" may mean that the composition forms the entire article or any part, component, element, feature, surface coating, fastener, or other portion of the article. Furthermore, the compositions herein may be used as a matrix material for such an article or portion thereof, or as a filler for the article or portion thereof.

[0074] The crosslinkable aromatic composition may also be in solvent form and applied to an existing part or core-forming composition, such as a formed outer layer or coating on a part or composition of an article, and then the coating or outer layer may be dried and cured to form part of the composition.

[0075] Compositions useful as matrix materials and / or polymer fillers include one or more crosslinkable aromatic polymers. The crosslinkable aromatic polymer(s) herein may be any of a variety of crosslinked aromatic polymers. In a preferred embodiment, the crosslinkable aromatic polymer is a polyarylene polymer, such as polyarylene ether (PAE), polyarylene ketone (PAK), or polyarylene ether ketone (PAEK), and various copolymers thereof known or to be developed in the art. The aromatic polymer composition includes a crosslinkable aromatic polymer and may optionally include at least one crosslinking compound.

[0076] Crosslinking of the crosslinkable aromatic polymers herein is preferably achieved by modifying the polymer for graft crosslinking and then exposing the aromatic polymer to a temperature high enough to induce self-crosslinking of the polymer, and / or by use of a crosslinkable aromatic polymer with the use of one or more crosslinking compounds.

[0077] Aromatic polymers can be crosslinked by grafting functional groups onto the polymer backbone that can be thermally induced to crosslink the polymer, as further described, for example, in U.S. Patent No. 6,060,170, the relevant portions of which are incorporated herein by reference. Alternatively, crosslinkable aromatic polymers may be crosslinked by the action of heat at temperatures greater than about 350°C or greater, as disclosed in U.S. Patent No. 5,658,994, the relevant portions of which are incorporated herein by reference. Examples of preferred materials for use in thermal crosslinking are listed below. [ka] 1,2,4,5 tetra(phenylethynyl)benzene.

[0078] In a preferred embodiment of the present application, the composition used to form the matrix material may include at least one crosslinkable polymer that is crosslinked using the addition of at least one crosslinking compound capable of crosslinking the aromatic polymer to chains within the polymer matrix or to itself, and / or the filler may include or be formed from said at least one crosslinkable polymer. Such polymers may contain groups that allow for self-crosslinking, either by polymerization or functionalization. Grafted crosslinking may also be used, provided that the resulting crosslinked polymer can be formed into an article or portion thereof, such as by using thermoforming or other part-forming processes.

[0079] The crosslinkable aromatic polymer in the compositions used herein can be any of a variety of amorphous and / or semi-crystalline aromatic polymers and copolymers. Preferred examples for use herein include, but are not limited to, polyarylene ethers and / or polyarylene ketones, such as polyether ketone (PEK), polyether ketone ketone (PEKK), polyether ether ketone (PEEK), polyether diephenyl ether ketone (polyether diephenyl ether ketone), and the like. and polyarylene homopolymers or copolymers, including polyarylene ketone (PEDEK), and the like, and preferred examples for use herein are various polysulfones (PSU); polyethersulfones (PES); polyphenylene sulfide (PPS); polyphenylene oxide (PPO); polyphenylsulfone (PPSU); polyimides (PI); polyetherimides (PEI) and thermoplastic polyimides (TPI); polybenzamides (PBA); polyamideimides (PAI); aromatic polyureas; polyurethanes (PU); polyphthalamides (PPA); polybenzimidazoles (PBI); polyaramids; aromatic copolymers of polyoxyalkylenes such as polyoxymethylene (POM), thermoplastic aromatic polymers such as polyaramids, or similar aromatic polymers known in the art or to be developed, including various copolymers and functionalized or derivatized versions of such polymers, including blends or alloys, and may also be included in blend form with polyarylene homopolymers or copolymers. Examples of various polyketone and polysulfone homopolymers and copolymers suitable for the methods described herein are reviewed in McGrail, "Polyaromatics," Polymer International 41 (1996), pp. 103-120.

[0080] Such polymers that are at least partially semi-crystalline exhibit improved wear properties. However, crosslinking such polymers enhances their ability to function in wear applications without catastrophic failure at what would otherwise be their critical transition point, allowing for the retention of dimensional stability. For example, amorphous aromatic polymers (which, in their uncrosslinked form, have a T g The crosslinking of the (catastrophic softening at T) g This allows its use in high PV wear applications which further increase the surface temperature beyond

[0081] The crosslinkable aromatic polymer(s) may or may not be functionalized as desired to achieve specific properties or to form articles with specific operational uses or end uses. For example, functional groups such as hydroxyl, mercapto, amine, amide, ether, ester, halogen, sulfonyl, aryl, and functional aryl groups or other functional groups can be provided depending on the intended final effect and properties. The aromatic polymer may also be a polymer blend, alloy, or copolymer, or other multi-monomer polymerization of two or more such aromatic polymers, provided that one such monomer in each case allows the formation of a crosslinkable polymer, or that in the blend, alloy, or copolymer, at least one of the polymers is crosslinkable. Preferably, when the aromatic polymer is a blend or alloy, the aromatic polymer is selected to be processable within a compatible processing temperature range.

[0082] In embodiments herein, the composition comprises a compound of formula (I): [ka] The crosslinkable aromatic polymer(s) may be poly(arylene ether)s comprising along their backbone polymer repeat units having the general structure:

[0083] In the formula, Ar1 , Ar 2 , Ar 3 and Ar 4 may be the same or different aryl radicals, m=0-1, and n=1-m, and such polymers may be of various molecular weights and chain lengths depending on the intended end use, as is known in the relevant aromatic polymer art.

[0084] The Ar radical in formula (I) includes, but is not limited to, biphenyl, terphenyl, L anthracene, naphthyl, and other polyaromatic moieties.The larger aryl structure for the purpose of increasing Tg is known in the art, and therefore, the polymer can be selected or modified to be more suitable as a polymer or copolymer structure depending on the end-use temperature and the desired PV limit of the wear article or tribological component.See McGrail above.

[0085] In a further embodiment, the crosslinkable aromatic polymer(s) may be a poly(arylene ether) according to formula (I) where m is 1 and n is 0, and said aromatic polymer has formula (II) shown below: [ka] or formula (IIa): [ka] The polymer has repeating units along its backbone having the structure:

[0086] In a preferred embodiment, the crosslinkable aromatic polymer is one or more of polyaryletherketones (PAEKs), including polyetherketones (PEKs), polyetheretherketones (PEEKs), polyetherketoneketones (PEKKs), polyetherdiphenyletherketones (PEDEKs), and polyetherketoneetherketoneketones (PEKEKKs). The crosslinkable aromatic polymer may be a commercially available crosslinkable aromatic polymer, as described above. PAEKs for use in the present invention are commercially available, for example, from Victrex TM PEEK is available from Victrex, plc under the name PEEK, KetaSpire® PEEK is available from Solvay, and Vestakeep® is available from Evonik. Suitable copolymers of such materials, including ketones and / or sulfones and other biphenyl, diphenyl, and triphenyl derivatives, may also be used.

[0087] In embodiments herein where optional cross-linking compound(s) are used, such cross-linking compound(s) can be any such compound capable of initiating chemical cross-linking of aromatic polymers.Preferred cross-linking compounds for use with cross-linkable aromatic polymers are described in the applicant's U.S. Patent Nos. 9,006,353 and 9,109,075, each of which is incorporated herein by reference in relevant parts with respect to useful polymers and cross-linking compounds and cross-linking control additives that can be used herein.One such cross-linking compound has the general structure: [ka] where R is OH, NH, halide, ester, amine, ether, or amide, x is 1 to 6, and A is an arene moiety having a molecular weight of less than about 10,000 g / mol. Such cross-linking compounds, when reacted with aromatic polymers such as polyarylene ketones, form thermally stable cross-linked oligomers or polymers.

[0088] Such crosslinking techniques allow aromatic polymers, which would otherwise be difficult to crosslink, to be formed in crosslinkable forms that are thermally stable to temperatures in excess of 260°C, and even 400°C or higher, depending on the polymer so modified (i.e., polysulfones, polyimides, polyamides, polyether ketones and other polyarylene ketones, polyphenylene sulfides, polyureas, polyurethanes, polyphthalamides, polyamideimides, aramids, and polybenzimidazoles).

[0089] Further crosslinking compounds for crosslinking aromatic polymers are described in Applicant's co-pending US Patent Application Publication Nos. 2020-0172667 A1 and 2020-0172669 A1, including: [ka] wherein Q is a bond and A can be Q, an alkyl, an aryl, or an arene moiety having a molecular weight of less than about 10,000 g / mol. R 1 , R 2 , and R 3 may be the same or different and may be independently selected from the group consisting of hydrogen, hydroxyl (-OH), amine (-NH), halide, ester, ether, amide, aryl, arene, or branched or straight chain saturated or unsaturated alkyl group (preferably branched or straight chain saturated or unsaturated alkyl group of 1 to about 6 carbon atoms). Formula (IIIa) can be prepared by replacing the moiety A in formula (III) with Q (representing a bond) and R in formula (IIIa) 1 is substantially the same as formula (III) above, except that is defined differently from R in formula (III).

[0090] In formula (V), m is preferably 0 to 2, n is preferably 0 to 2, and m+n is equal to or greater than 0 and less than or equal to 2. Furthermore, in formula (V), Z is preferably selected from the group consisting of oxygen, sulfur, nitrogen, and a branched or straight-chain saturated or unsaturated alkyl group of 1 to about 6 carbon atoms. In all of formulas (IIIa), (V), and (VI), x is also about 1 to about 6, as in formula (III).

[0091] Compositions used in the articles and methods of the present invention to form articles or tribological components subject to wear, preferably capable of operating at high PV conditions, may comprise a blend of aromatic crosslinkable polymer(s) and one or more crosslinking compounds. In another embodiment, a composition may be used that comprises a single crosslinking compound, which may be selected based on the aromatic polymer in the composition that comprises at least one crosslinkable polymer.

[0092] In a further embodiment, the bridging compound is: [ka] may be added to a composition comprising at least one crosslinkable polymer for use in forming a crosslinked polymer suitable as a matrix material or filler that is part of an article according to the present invention, which may comprise a structure according to one of the formulas

[0093] In each of formulas (IV)-(VI), A can be a bond, alkyl, aryl, or arene moiety (preferably having a molecular weight of less than about 10,000 g / mol). A molecular weight of less than about 10,000 g / mol allows the overall structure to be more miscible with the aromatic polymer, allowing for uniform distribution with few or no domains within the composition comprising the aromatic polymer and the crosslinking compound. More preferably, A has a molecular weight of about 1,000 g / mol to about 9,000 g / mol. Most preferably, A has a molecular weight of about 2,000 g / mol to about 7,000 g / mol.

[0094] Part A is: [ka] [ka] The flexural members may be altered to have different structures, including but not limited to:

[0095] Additionally, moiety A may be functionalized, if desired, with one or more functional groups such as, but not limited to, sulfate, phosphate, hydroxyl, carbonyl, ester, halide, or mercapto, or other functional groups described above.

[0096] In formulas (IV) and (VI), R 1 is preferably selected from the group consisting of hydrogen, hydroxyl (-OH), amine (NH), halide, ester, ether, amide, aryl, arene, or a branched or straight chain saturated or unsaturated alkyl group (preferably a branched or straight chain saturated or unsaturated alkyl group of 1 to about 6 carbon atoms).

[0097] In formula (V), R 1 , R 2 , and R 3 may be the same or different and are preferably independently selected from the group consisting of hydrogen, hydroxyl (-OH), amine (-NH), halide, ester, ether, amide, aryl, arene, or branched or straight chain saturated or unsaturated alkyl group (preferably branched or straight chain saturated or unsaturated alkyl group of 1 to about 6 carbon atoms). 1 , R 2 and R 3 may be different, and R 1 , R 2 and R 3 Two of the are the same, the third may be different, and R 1 , R 2 and R 3may be the same. Furthermore, in formula (V), m is preferably 0 to 2, n is preferably 0 to 2, and m+n is preferably equal to or greater than 0, and less than or equal to 2. Therefore, in formula (V), one or two R 2 groups may be present, and one or two R 3 groups may be present, and one R 2 group and one R 3 groups may be present, and R 2 and R 3 may not both be present. In formula (V), Z is preferably selected from the group consisting of oxygen, sulfur, nitrogen, and a branched or straight chain, saturated or unsaturated alkyl group of 1 to about 6 carbon atoms. In any of formulas (IV) to (VI), x is preferably about 1 to about 6.

[0098] In embodiments having a bridging compound according to formula (IV), the bridging compound is: [ka] [ka] The structure may be one or more of:

[0099] The above listed bridging compounds are not intended to be limiting and are provided merely as examples of bridging compounds according to formula (IV). In the above bridging compounds of formula (IV), R 1 is shown to be a hydroxyl group. The moiety A is shown to be any of a variety of aryl groups, and x is shown to be either 2 or 4.

[0100] In embodiments having a bridging compound of formula (V), the bridging compound is: [ka] The structure may be one or more of:

[0101] The above listed crosslinking compounds are not intended to be limiting and are provided merely as examples of crosslinking compounds according to formula (V). In the above crosslinking compounds of formula (V), Z is shown to be an alkyl group having one carbon atom or O. R 1 is shown to be a hydroxyl group. 2 and R 3 are shown to be the same, different, or absent. The moiety A is shown to be a bond or an aryl group. Furthermore, x is shown to be 1 or 2.

[0102] In embodiments where the bridging compound has a structure according to formula (VI), the bridging compound has the following structure: [ka] The suffix may have one or more of:

[0103] The above listed bridging compounds are not intended to be limiting and are provided merely as examples of bridging compounds according to formula (VI). 1 is shown as a hydroxyl group. Moiety A is shown to be a bond or an aryl group. Additionally, x is shown to be 2.

[0104] The amount of crosslinking compound(s) for use with the crosslinkable aromatic polymer in the compositions used to form the articles and / or matrix materials described herein is preferably from about 1% to about 50%, 5% to about 30%, or from about 10% to about 35%, or from about 8% to about 24% by weight (collectively), based on the total weight of the unfilled composition of the crosslinkable aromatic polymer and crosslinking compound.

[0105] The compositions used herein may preferably have a weight ratio of crosslinkable aromatic polymer to crosslinking compound of from about 1:1 to about 100:1. More preferably, the weight ratio of aromatic crosslinkable polymer to crosslinking compound in the composition is from about 3:1 to about 10:1.

[0106] The composition may optionally further comprise a crosslinking reaction additive to control the cure reaction rate during formation of the wear article and / or component in the tribological system and during any post-treatment processing. Such additive(s) may be incorporated into the composition in various amounts depending on the final properties and crosslink density desired for the wear article. The use of crosslinking reaction control additive(s) to control the cure reaction rate, i.e., crosslinking rate and extent, also depends on the cure reaction rate of the particular aromatic polymer and crosslinking compound used.

[0107] The amount of crosslinking compound typically affects the degree of crosslinking, so that the use of a specific level of crosslinking compound can provide the desired degree of crosslinking and crosslink density. The use of crosslinking reaction control additives to control the curing reaction rate, i.e., the crosslinking rate and degree, also depends on the curing reaction kinetics of the specific aromatic polymer and the crosslinking compound used, and can be adjusted to help control the reaction rate of a given composition. Generally, the higher the degree of crosslinking and crosslink density, the higher the PV conditions that can be tolerated without failure.

[0108] Thus, the included crosslinking reaction control additive may be a cure inhibitor (Lewis base agent) such as lithium acetate for reactions with high reaction rates, or the crosslinking reaction additive may be a cure accelerator (Lewis acid agent) such as magnesium chloride or other rare earth metal halides if the cure reaction rate is too slow. When the composition includes a crosslinking reaction control additive, the amount of crosslinking reaction control additive in the composition is preferably about 0.01% to about 5% by weight based on the weight of the crosslinking compound, but can be adjusted depending on the reaction rate achieved in a given system.

[0109] The compositions may be formed to have a blend of crosslinkable aromatic polymers in the composition. Such blends include two or more such polymers. By providing control over the reaction, the process and article of formation may be modified to achieve desired hardness, T gOr other critical transition points, compressive modulus, shear modulus, toughness (elongation at break), tensile strength and other desirable properties, as well as physical properties such as consistency, dimensional stability and surface hardness properties for wear articles, allowing reactions to occur faster or slower in the process to provide variations in these properties.

[0110] When using a blend of two or more crosslinkable aromatic polymers, a crosslinking compound may not be necessary if the aromatic polymers are self-crosslinkable and / or many are thermally crosslinked; crosslinkable aromatic polymers with different crosslinking reaction rates may be used together to modify or control the overall crosslinking rate. This is described in detail in applicant's co-pending U.S. Patent Application Publication No. 2021-0388216 A1, which is incorporated herein by reference.

[0111] The level of crosslinking can be adjusted to achieve the desired mechanical and wear properties for use in wear articles and / or as components in tribological systems. Generally, higher levels of crosslinking compound tend to form harder products with lower ductility after a full cure cycle. To form wear articles and / or components in tribological systems, the compositions herein can be used to balance the desired physical and wear properties with the need to process the composition (i.e., its processability). Higher levels of crosslinking improve friction and wear properties and the ability to retain performance and dimensional stability in high PV applications, but in some cases, this can come at the expense of the processability and moldability of the article or component. Thus, depending on the physical properties of a given composition, if higher processability is desired, the crosslinking level can be adjusted to balance the desired friction and / or wear properties of the resulting component and / or article, and / or reaction rates or additives can be used to slightly modify those properties. Furthermore, if material blending is used to control reaction rates, the blend can be adjusted as well.

[0112] Compositions for use as matrix materials to form the polymeric wear articles herein and / or for use in forming polymeric fillers that may be used in forming the polymeric wear articles herein may be further filled or reinforced with one or more additives to improve or otherwise modify the modulus of elasticity, impact strength, adhesive strength, dimensional stability, heat resistance, and / or insulating properties, and / or to further modify the wear or tribological properties of articles formed using the compositions described herein. Preferably, such additives are selected from one or more of continuous or discontinuous long or short reinforcing fibers selected from one or more of carbon fibers, glass fibers, woven glass fiber fabric, woven carbon fiber fabric, aramid fibers, boron fibers, polytetrafluoroethylene (PTFE) fibers, ceramic fibers, polyamide fibers, and / or one or more fillers selected from carbon black, silicates, fiberglass, glass beads, glass spheres, crushed glass, calcium sulfate, boron, ceramic, polyamide, asbestos, fluorographite, aluminum hydroxide, barium sulfate, calcium carbonate, magnesium carbonate, silica, aluminum nitride, borax (sodium borax), activated carbon, perlite, zinc terephthalate, graphite, graphene, talc, mica, silicon carbide whiskers or platelets, nanofillers, molybdenum disulfide, fluoropolymer fillers, boron nitride, nanodiamonds, microdiamonds, carbon nanotubes, and fullerene tubes. Particularly preferred for use in forming such additives in the formation of wear articles are carbon fiber, graphite, and PTFE fillers. Additives may also be selected to help modify the coefficient of thermal expansion (CTE) for dimensional stability of the formed article, including fillers that, if desired, lower the CTE of the polymer in the compositions for the articles herein, such as glass fiber, crushed glass, glass beads, mica, aluminum oxide, and / or talc.

[0113] The additives may additionally or alternatively include nanodiamonds and other thermal management fillers, including, but not limited to, other carbon allotropes, polyhedral oligomeric silsesquioxanes ("POSS") and variants thereof, silicon oxide, boron nitride, and aluminum oxide. The additives may additionally or alternatively include flow modifiers, such as ionic or non-ionic chemicals.

[0114] The additive may include optional CTE-reducing additives as described above and / or optional reinforcing fibers, either continuous or discontinuous, long or short fibers, i.e., carbon fiber, PTFE fiber, glass fiber, and / or graphite. Most preferably, the additive is a continuous, long fiber reinforcing fiber. For example, if it is indicated to minimize the CTE in a specific direction, such a continuous, long fiber additive is indicated. If it is desired to minimize the overall CTE, a more isotropic filler, such as graphite or crushed fiber, may be preferred.

[0115] The crosslinkable polymer composition may comprise from about 0.5% to about 65% by weight of additives in the composition, more preferably from about 5% to about 40% by weight of additives in the composition. The crosslinkable polymer composition may further comprise one or more of stabilizers, tribology or rheology modifying additives, flame retardants, pigments, colorants, plasticizers, surfactants, or dispersants. Preferred additives include friction modifiers such as PTFE, graphite, molybdenum sulfide, and fibrous fillers for increasing modulus and / or hardness and CTC modification. Most preferably, PTFE, graphite, and carbon fibers are incorporated into compositions for use in forming wear articles and / or components for use in tribological systems.

[0116] In one embodiment herein, the present invention provides a composition for use in forming an article that is subject to frictional forces or for use in the tribological systems described above, comprising at least one or more of the crosslinkable aromatic polymers described herein as a matrix material, and containing continuous or discontinuous long or short reinforcing fibers selected from carbon fibers, glass fibers, woven glass fibers, woven carbon fibers, aramid fibers, boron fibers, polytetrafluoroethylene fibers, ceramic fibers, polyamide fibers, and / or carbon black, silicates, fiberglass, glass beads, glass spheres, crushed glass, calcium sulfate, boron, ceramic, polyamide fibers, and / or other materials selected from the group consisting of carbon black, silicates, fiberglass, glass beads, glass spheres, crushed glass, calcium sulfate, boron, ceramic, polyamide, and the like. The present invention provides a composition comprising, in addition to such a polymer, one or more additives selected from one or more fillers selected from the group consisting of cellulose, asbestos, fluorographite, aluminum hydroxide, barium sulfate, calcium carbonate, magnesium carbonate, silica, aluminum nitride, aluminum oxide, borax (sodium borax), activated carbon, perlite, zinc terephthalate, graphite, graphene, talc, mica, silicon carbide whiskers or platelets, nanofillers, molybdenum disulfide, fluoropolymer fillers, boron nitride, nanodiamonds, microdiamonds, carbon nanotubes, and fullerene tubes. Other additives, such as the crosslinking compounds described herein, may also be used. The one or more additives should be present in a total amount of about 0.5% to about 65% by weight, based on the weight of the entire composition. Preferred additives in such embodiments of the present invention are carbon fiber, glass fiber, PTFE, and / or graphite, which improve the property performance of the crosslinked polymer in articles formed from the compositions herein, especially at higher PV levels (e.g., levels at or above 75,000 psi-ft. / min, and up to about 100,100 psi-ft. / min, etc.). In such compositions, preferred crosslinkable aromatic polymers are those described herein above, and such polymers may include functional group(s) for crosslinking. Such compositions may also include crosslinkable polymer blends as described herein, and may use various crosslinking compounds as described herein.

[0117] The compositions herein can be prepared by providing a crosslinkable aromatic polymer(s) and, if necessary, a crosslinking compound capable of crosslinking the aromatic polymer(s), and combining the aromatic polymer(s) with the crosslinking compound. When a self-crosslinking polymer or a grafted polymer is used, the crosslinking compound may be omitted. When a crosslinking compound is used in the composition, the crosslinking compound is preferably combined with the aromatic polymer to preferably form a substantially homogeneous composition.

[0118] Incorporation of the crosslinking compound(s) into the crosslinkable aromatic polymer(s) can be accomplished by various methods, such as solvent precipitation, mechanical blending, or melt blending. Preferably, the crosslinkable polymer composition is formed by dry powder blending of the crosslinking compound with the aromatic polymer, such as by conventional non-crosslinking polymer compounding processes, including twin-screw compounding. The resulting composition can be extruded into filaments or fibers, or used as a powder, platelets, or pellets for use as a polymer filler or in forming articles. However, articles can also be formed from the composition directly or while crosslinking, without first forming pellets or the like.

[0119] Blending (including blending of more than one crosslinkable aromatic polymer) can further be achieved by the use of an extruder (e.g., a twin-screw extruder), a ball mill, or a cryogrinder. Blending of the crosslinkable aromatic polymer(s) with the crosslinking compound(s) is preferably carried out at a temperature during blending not exceeding about 250°C to avoid premature curing during the blending process. If a melt process is used, care should be taken to ensure that thermal history and temperature exposure are minimized; i.e., it is preferable to use the lowest temperature and / or shortest residence time possible to achieve material flow. Alternatively, the use of rate-controlling additives as described above and / or blending of crosslinkable aromatic polymers with different reaction kinetics may be used to inhibit curing and / or control the curing rate, minimizing crosslinking resulting from compounding and conversion to pellet or fiber form.

[0120] Depending on the selected polymer and components in the composition, the material can be formed into powder, fiber, filament, platelet, or pellet form for use in a matrix material, such as the matrix materials herein, or in the matrix of other known wear compositions, such as those formed from polytetrafluoroethylene or modified polytetrafluoroethylene or blends of such materials. As used herein, "modified polytetrafluoroethylene" or "modified PTFE" is intended to encompass both polymerized TFE or copolymer types of PTFE, as well as homopolymerized PTFE modified by external physicochemical impulses, or by other chemical modifications, such as chemical grafting or providing functional groups for specific purposes. To form articles from the compositions herein containing crosslinkable polymer(s) and selected optional additive components, such articles for wear use can be first formed as fibers, filaments, platelets, pellets, or powders and then thermoformed, extruded, or otherwise formed into an article, or can be formed by direct crosslinking without first being formed into pellets or the like.

[0121] When forming fillers and / or articles from the compositions herein, crosslinking may occur at least partially or completely during and / or after the formation of the article. Suitable crosslinking additives are known in the art and are described in the above-referenced U.S. Patent No. 9,109,080, the relevant portions of which are incorporated herein with respect to crosslinking control additives.

[0122] The blending process may be exothermic, so the temperature must be controlled, which may be adjusted as needed and as indicated depending on the particular crosslinkable aromatic polymer(s) selected for use. In mechanical blending of the aromatic polymer with the crosslinking compound, it is preferred that the resulting composition be substantially homogeneous to obtain uniform crosslinking.

[0123] When the composition is prepared, it can be cured by exposure to temperatures above 250°C, for example, from about 250°C to about 500°C. However, the timing and extent to which the composition is heated and crosslinked during the formation process depends on the desired properties to be achieved in the final product. For example, greater crosslinking may result in higher levels of mechanical strength or hardness, but may affect processability or ductility. A preferred crosslinking level is from about 1% to about 50%, which can be achieved by modifying the level of crosslinking compound, adjusting any crosslinking reaction control additives, and / or modifying any blend ratios when blend polymers are used to control crosslinking.

[0124] Thus, the crosslinkable polymers in such compositions can be used to form desired articles and crosslinked during formation, such as by thermoforming, for example, by injection molding, extrusion, or insert molding a part or portion of a part, followed by further curing and completion of the crosslinking for shaping. It is also possible to fully crosslink the material and then thermoform the part. Finally, it is possible to form portions of a different underlying core material, which can also be performed in high temperature applications, and in which the composition can be applied to the outside of the core material, such as by coating or molding a layer on the outside of the core material, or by otherwise joining or molding the parts or materials together.

[0125] When forming articles from the compositions herein using the above-mentioned hot forming techniques, including injection molding, care should be taken to control process parameters to ensure successful formation of the crosslinked and / or blended compositions into articles. For crosslinked compositions, careful control of temperature and shear rate should be maintained to avoid exceeding the composition's critical temperature and to determine and control the critical shear rate, including when the crosslinked aromatic polymer is used as a wear matrix material or as a filler in a wear matrix material. Thus, processing within controlled shear and temperature parameters (as well as control of crosslinking rate as discussed elsewhere herein) avoids exceeding such critical temperature and shear limits.

[0126] If such critical limits are exceeded, premature initiation of the crosslinking reaction may occur during the formation process, or excessive process crosslinking may occur, resulting in improper or insufficient formation of the resulting article or its component parts. Control of these parameters, which may vary depending on the crosslinkable aromatic polymer used and its crosslinking reaction rate and conditions, can avoid adverse effects on processability and article formation, such as partial or underfilling in the final article (i.e., short shots), excessive foaming of the heated polymer composition in the article, and / or excessive or premature initiation of crosslinking of the crosslinkable aromatic polymer in the feed fixture of a thermoforming apparatus, such as the barrel of an injection molding machine, which may damage machine components and result in an unsuccessful part formation. Such parameters can be evaluated within the ability of one skilled in the art by using its critical temperature and critical shear rate, depending on the crosslinkable aromatic polymer selected, and by evaluating the associated crosslinking reaction and any associated crosslinking compounds employed. Modeling of compositions and / or their properties using DMA or other similar evaluation techniques can be used to provide guidance and estimates of key parameters of crosslinkable aromatic polymer properties and crosslinked material properties prior to establishing critical process control parameters for specific compositions within the scope of the inventive compositions described herein. Consideration of such control parameters may also be used to influence the design or modification of equipment for processes incorporating the inventive compositions herein, such as, for example, in determining runner and / or screw design in plasticizing a heated composition prior to molding an article from the composition.

[0127] With respect to the desired wear article properties, the degree of crosslinking (crosslink density) may be varied or adjusted to provide different properties to the top of the wear article and avoid potential cracking and warping during use. Such properties include hardness, T gThe crosslinking density can be controlled by varying the concentration of the crosslinking compound and / or by controlling the amount of any optional crosslinking reaction additives used in combination with the crosslinking compound. The degree of cure, i.e., the completion of the crosslinking reaction, is related to both the thermal activation of the reaction when driven by temperature changes, and practical concerns, including the cure rate.

[0128] In embodiments using a blend of two crosslinkable polymers with different kinetics, as described herein and in applicant's pending U.S. Patent Application Publication No. 2021-0388216 A1, the crosslinking rate can be controlled not only by modifying the amount of any crosslinking compound used, but also by changing the amount of crosslinking polymer with a slower cure kinetics used in the blend. The level of crosslinking can be adjusted to achieve the desired final mechanical properties. In general, higher levels of crosslinking compound tend to form a harder product with less ductility after a full cure cycle. Crosslinking levels of about 1% to about 50% are recommended for forming wear articles, although they may vary depending on the hardness, T g or other critical transition points, compressive modulus, shear modulus, toughness (elongation at break), tensile strength and other desired properties, as well as consistency, dimensional stability, and surface hardness and friction properties, such as abrasion resistance and a desired coefficient of friction, and a sufficiently high PV limit, depending on the desired final properties such as those mentioned above.

[0129] In some examples herein, the compositions may be blended or used in a liquid system. In such cases, the compositions may be further prepared by dissolving both the crosslinkable aromatic polymer and any optional crosslinking compound in a common solvent, removing the common solvent via evaporation or by adding a non-solvent, and precipitating both the polymer and any optional crosslinking compound from the solvent. For example, depending on the aromatic polymer and crosslinking compound selected, the common solvent may be tetrahydrofuran, and the non-solvent may be water. A further option for polymers and crosslinking additives that are soluble in the same solvent is the use of solvent casting or dip coating of substrates, such as those from which wear articles are formed. The interior or core of the article does not need to be a crosslinked aromatic polymer; the aromatic polymer may be applied to the exterior of a molded core in a thickness sufficient to provide the desired wear and mechanical properties for the exterior of the article, subject to wear and high-temperature operation, as long as the core of the article is not adversely affected by the conditions of use. In such cases, the crosslinkable polymer(s) and any optional crosslinking compound and / or additive are dissolved in a suitable solvent and then applied to a molded core made of a high-PV material or metal, having a shape that may be the same or different from the outer dip-coated portion of the article. The solvent is removed in a controlled manner, and the uncured outer portion of the article can then be cured using various techniques, such as the use of heat or radiation, and / or by chemically induced crosslinking. For example, an inner molding core of any suitable shape may be formed from a different polymer, and an outer coating of at least one crosslinked aromatic polymer may be formed around the core to provide the article with the desired contour and curved characteristics as desired.

[0130] Suitable core materials may be formed from other materials such as ceramics, e.g., alumina, metals, metal alloys, organic or inorganic core materials, or various polymeric materials, such as non-crosslinked or crosslinked polymers; the core material may have certain desired properties suitable for the intended end use, such as adequate strength or other physical properties, but may lack surface friction and / or wear properties desirable for the intended end use. The crosslinked polymer compositions herein may be used to coat or encapsulate the core material to improve such surface friction and / or wear properties of the core material.

[0131] In preparing compositions for forming articles herein as matrix materials and / or polymer fillers, it is preferred to add any optional additives to the composition together with or simultaneously with combining the crosslinking compound with the crosslinkable aromatic polymer(s) to create a crosslinkable polymer composition. However, the particular manner in which reinforcing fibers or fillers are provided in the composition prior to further forming can be subject to a variety of techniques for incorporating such materials and should not be considered limiting of the scope of the present invention.

[0132] Articles formed from such compositions can be highly diverse and are useful in end uses that are subject to friction and wear and / or as one or more component surfaces that form a tribological system. Such articles may be, for example, but are not limited to, downhole tool components, aerospace components, vehicle components, semiconductor manufacturing components, and rotating or reciprocating components or tools having end uses. Examples include, but are not limited to, gears, rotors, drill bits, pulleys, bearings, and seals.

[0133] Such compositions described herein can further be used in a method for improving the PV limit of a composition for use in forming an article subjected to frictional forces or for use as one or more sliding friction surfaces in a tribological system. This can be done by providing such a composition with at least one crosslinkable aromatic polymer matrix material that, when crosslinked, has a PV limit, measured in psi-ft. / min at about 500°F, that is at least about 10% higher than the PV limit, measured in psi-ft. / min at about 500°F, of the same aromatic polymer matrix material in a non-crosslinkable form, and crosslinking at least one crosslinkable aromatic polymer in the composition. Preferably, the PV limit in this method is at least about 20% higher, more preferably about 50% higher.

[0134] Similarly, existing wear compositions, such as those having a matrix material formed from the compositions herein, or existing prior art matrix materials for wear components (e.g., PTFE, or modified PTFE alone or combined with other polymers, or other non-crosslinked aromatic polymers, etc.), can be improved by incorporating therein fillers formed from the compositions herein with crosslinked aromatic polymers. Such fillers may be incorporated by blending or addition during article formation to improve the wear properties of the matrix material, increase its PV limit, modify its K factor, or decrease its coefficient of friction. Such materials also provide chemical resistance to the matrix material and, in most cases, provide enhanced mechanical properties.

[0135] The compositions known herein can also be used to form articles subjected to frictional forces and / or for use in tribological systems. Such compositions can include at least one crosslinkable aromatic polymer matrix material described herein that, when crosslinked, substantially maintains its dimensional stability after heating above a critical transition temperature. As used herein, "substantially maintains dimensional stability" means that the article retains an operable shape and configuration, does not suffer catastrophic failure in the end use in which it is employed, does not integrate into any operating device, and preferably continues to operate within acceptable tolerances or performance levels in the friction end use or tribological system. Such tolerance levels or performance standards may be those established by industry standard-setting organizations, such as, but not limited to, ISO standards or other acceptable standards used or applicable in various technical industries in which wear end uses are employed. The critical transition temperature may be a glass transition temperature or melting point temperature, as described above. When the at least one crosslinkable aromatic polymer matrix material is crosslinked, it preferably also avoids catastrophic failure above a critical transition temperature.

[0136] A method for maintaining dimensional stability and / or avoiding catastrophic failure above the critical transition temperature of an article subjected to frictional forces and / or used in a tribological system can be practiced herein by forming such an article from a composition herein containing a crosslinked aromatic polymer, and then using or otherwise incorporating the article in an end use application where the article is subjected to frictional forces and / or used in a tribological system. The temperature of the article in the end use application may exceed the critical transition temperature of the aromatic polymer in the article. The article preferably further still maintains stability as well as avoids catastrophic failure in the end use application. The crosslinked aromatic polymer is preferably the matrix material in the article, although the composition may, in one embodiment, be a composition such as the wear compositions described herein that may incorporate a polymer matrix material in which the crosslinked aromatic polymer is incorporated as a filler into the polymer matrix material. The critical transition temperature in such a method is the glass transition temperature or melting temperature, as discussed elsewhere herein.

[0137] The invention will now be described with reference to the following non-limiting examples. [Example]

[0138] Example 1 A thrust washer sample (Sample 1) was formed using a composition according to the present invention by thermoforming the crosslinkable composition described herein using a commercially available crosslinked aromatic polymer based on crosslinkable polyetheretherketone, i.e., Arlon® 3000 XT, which has 12% crosslinking at 0% in the matrix (so that a 70% matrix with 30% additive contains 8.4% crosslinking), and contains wear additives of 10% PTFE, 10% graphite, and 10% carbon fiber for use in PEEK grades. A comparative thrust washer sample (Comparative Sample 2) was formed from the same base polymer, polyetheretherketone, but without crosslinking, and containing the same amounts of the same wear additives as used in Sample 1. Thrust washer samples Sample 1 and Comparative Sample 2 were formed according to ASTM D-3702 and subjected to the thrust washer test of that standard. The samples were not heated, but were subjected to frictional energy that raised the temperature at the contact surface above the melting point of the polymer. They were subjected to 75,000 PV cycles (60 hours at a speed of 150 ft / min). After testing, the cross-linked material, Sample 1, substantially retained its original dimensions and shape and was functional after 16 hours of testing (see Figures 1C and 1D). The uncross-linked material that formed Sample 2 melted, causing the sample to distort at failure. Photographic images of the test sample, uncross-linked material, Sample 2, before and after testing are shown in Figures 1A and 1B. Photographic images of the test sample (Sample 1) with a matrix material formed from Arlon 3000XT before and after testing are shown in Figures 1C and 1D, respectively.

[0139] Example 2 In this example, three wear compositions were prepared: Comparative Samples A and B, and Inventive Example C. Comparative Sample A was a commercially available uncrosslinked PEEK wear compound from RTP (RTP 2299 X 81382). Sample B was an uncrosslinked PEEK wear compound containing 10% graphite, 10% carbon fiber, and 10% PTFE filler. Sample C contained the same additives as described above for Sample B, but used 17% crosslinked PEEK as the matrix material within the PTFE matrix. The resulting wear factors, K, as shown in Figure 2, show an increase in wear factor with PV up to about 25,100 PV, then plateau to about 50,000 PV, but as PV increased to 75,000, Sample A was no longer operable. Sample B failed above 75,000 PV, while Sample C remained operable and substantially retained its dimensional shape up to an additional 100,100 PV. Sample C shows improved wear factor as well as the ability to function at higher PVs where the same polymer in uncrosslinked format in Sample B was unable to remain operable.

[0140] Example 3 In this example, all samples were tested using the ASTM D3702 abrasion test described in Example 1, at PV conditions ranging from 10,000 PV to 50,000 PV. The output of this test is the wear factor K (thickness), J (weight), and coefficient of friction. A sample of the present invention (Sample D) was prepared by providing crosslinked PEEK as the polymer filler. In this example, commercially available Arlon® 3000XT crosslinked PEEK was used, ground to a 50-100 micron powder, and added to the PTFE wear matrix material. Other fillers, including carbon powder and molybdenum disulfide present as minor components, were used at comparable wear ratings. In Sample D, a crosslinked aromatic polymer filler was added to the PTFE wear matrix at a 10% level.

[0141] Comparative Sample E was used, which was a PTFE wear material with polyphenylene sulfide (PPS) filler and carbon powder as a minor wear-grade additive. Sample D was compared to Sample E to calculate the wear factor K / thickness change. The normalized wear resistance (1 / K) for each sample is shown in Figure 3. The samples were tested using the D3702 thrust washer test described above, and the wear factor was collected. The wear resistance was then calculated as the reciprocal of the wear factor. The 1 / k values ​​were normalized to the inventive sample to better compare relative improvements.

[0142] FIG. 3 shows a 210% improvement in wear resistance for inventive Sample D, which has a crosslinked aromatic polymer additive along with other fillers in a PTFE wear matrix, compared to a typical wear-grade PTFE material (Comparative Sample E).

[0143] Example 4 In this example, Comparative Samples F and G were prepared, each containing a PTFE wear matrix. Additionally, Inventive Sample H was prepared by blending a PTFE wear matrix filled with the crosslinked filler used in Inventive Sample D of Example 3. Comparative Sample F was similarly formed using uncrosslinked PEEK filler, and Comparative Sample G was similarly formed using PPS filler. Thus, this example utilized three binary blends conventional in the art for the comparative evaluation of new additives with commercially available filler grades already in use. The uncrosslinked PEEK fillers in Comparative Sample F, the PPS fillers in Comparative Sample G, and the crosslinked PEEK fillers in Sample H were each added to their respective PTFE matrices in nominally equal amounts, at 15% of the PTFE matrix in the binary blends.

[0144] The wear coefficient was evaluated using the same ASTM D-3702 test run at 10,000 PV. The wear resistance was then calculated as the inverse of the wear coefficient. To better compare relative improvements, the 1 / k values ​​were normalized to the inventive samples. The normalized wear resistance (1 / k) of each of the comparative samples F and G and sample H is shown in Figure 4.

[0145] FIG. 4 shows that unlike other representative polymer fillers used in known wear compounds of the prior art, namely uncrosslinked PEEK (in Comparative Sample F) and PPS (in Comparative Sample G), binary blends made incorporating the crosslinked polyetheretherketone filler of Samples D and H of the present invention exhibited 850% higher wear resistance.

[0146] In summary, Figures 3 and 4 of Examples 3 and 4 above show significant improvements in wear resistance and wear coefficient for Sample D of the present invention having a crosslinked aromatic polymer additive in a representative PTFE wear matrix material with other standard wear compound fillers, and Sample H (using the same crosslinked aromatic polymer filler as Sample D) further demonstrates a significant increase in wear resistance over a composition having the same matrix but a different prior art wear additive.

[0147] Example 5 Dynamic mechanical analysis (DMA) testing was used to simulate temperatures above the critical wear transition temperature. Thrust washer samples (Samples 1 and 2) from Example 1 were further simulated to test the dimensional stability of the samples above the critical transition temperature under static pressure. A temperature above the melting point of the material was selected as the critical transition temperature to simulate the extreme surface temperatures experienced in aggressive applications to evaluate minimizing catastrophic failure. Using a compression fixture in an RSA G2 DMA (manufactured by TA Instruments), the thrust washer samples were subjected to 380°C and 16 psi for 30 minutes. The thickness change of the samples during this time was recorded as gap displacement, as shown in Figure 5. In Figure 5, the solid line represents uncrosslinked Sample 2, and the dashed line represents crosslinked Sample 1.

[0148] The samples were immersed prior to the 16 psi hold, and after the hold, uncrosslinked Sample 2 experienced catastrophic failure during the soaking stage after only a 5-minute hold, as shown in the photographs in Figures 5 and 6. Crosslinked Sample 1 advantageously maintained its dimensional stability even above the critical transition temperature, demonstrating the retention of dimensional stability and minimal catastrophic failure under aggressive conditions.

[0149] Those skilled in the art will appreciate that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that the invention is not limited to the particular embodiments disclosed, but that it is intended to cover modifications within the spirit and scope of the invention as defined by the appended claims.

Claims

1. 1. A composition for use in forming an article that is subject to frictional forces or for use in a tribological system, comprising:

1. A composition comprising at least one crosslinkable aromatic polymer matrix material, wherein the at least one crosslinkable aromatic polymer matrix material, when crosslinked, remains operable at a PV of at least about 75,000 psi-ft. / min.

2. 10. The composition of claim 1, wherein the at least one crosslinkable aromatic polymer matrix material, when crosslinked, remains operable at a PV of from about 75,000 psi-ft. / min to about 100,100 psi-ft. / min.

3. 10. The composition of claim 1, wherein the at least one crosslinkable aromatic polymer matrix material, when crosslinked, has a PV limit, measured in psi-ft / min at about 500°F, that is at least about 10% higher than the PV limit, measured in psi-ft / min at about 500°F, of the same aromatic polymer matrix material in a non-crosslinkable form.

4. 4. The composition of claim 3, wherein when crosslinked, the PV limit measured in psi-ft. / min at about 500°F is at least about 20% higher than the PV limit of the same aromatic polymer matrix material in a non-crosslinkable form.

5. 5. The composition of claim 4, wherein when crosslinked, the PV limit measured in psi-ft. / min at about 500°F is at least about 50% higher than the PV limit of the same aromatic polymer matrix material in a non-crosslinkable form.

6. 10. The composition of claim 1, wherein the at least one crosslinkable aromatic polymer matrix material is a crosslinkable polymer selected from polyarylenes, polysulfones, polyethersulfones, polyphenylene sulfides, polyphenylene oxides, polyimides, polyetherimides, thermoplastic polyimides, polybenzamides, polyamideimides, polyureas, polyurethanes, polyphthalamides, polybenzimidazoles, polyaramids, and blends, copolymers, and alloys thereof.

7. 7. The composition of claim 6, wherein the at least one crosslinkable aromatic polymer is a crosslinkable polyarylene selected from polyetherketone, polyetheretherketone, polyetherdiphenyletherketone, polyetherketoneketone, and blends, copolymers, and alloys thereof.

8. The composition of claim 7 , wherein the at least one crosslinkable aromatic polymer comprises one or more functional groups for crosslinking.

9. The at least one crosslinkable aromatic polymer has the formula (II): 【Transformation 34】 Or formula (IIa): 【Chemistry 35】 7. The composition of claim 6, having along its backbone repeat units having the structure:

10. 7. The composition of claim 6, wherein the at least one crosslinkable polymer comprises a first crosslinkable polymer that is one or more polyarylenes selected from polyetherketone, polyetheretherketone, polyetherdiphenyletherketone, polyetherketoneketone, and blends, copolymers, and alloys thereof; and a second crosslinkable polymer selected from the group consisting of one or more of: (i) polyphenylene sulfide, (ii) polysulfone, polyphenylsulfone, polyethersulfone, copolymers, and alloys thereof, and (iii) polyimide, thermoplastic polyimide, polyetherimide, and blends, copolymers, and alloys thereof.

11. The composition comprising the at least one crosslinkable aromatic polymer has the following formula: 【Transformation 36】 where A is a bond, alkyl, aryl, or arene moiety having a molecular weight of less than about 10,000 g / mol; R １ , R ２ and R ３ are the same or different and independently represent hydrogen, hydroxyl (—OH), amine (NH ２ ), halides, esters, ethers, amides, aryls, arenes, or branched or straight chain saturated or unsaturated alkyl groups of 1 to about 6 carbon atoms, m is 0 to 2, n is 0 to 2, m+n is equal to or greater than 0 and is less than or equal to 2, Z is selected from the group of oxygen, sulfur, nitrogen, and branched or straight chain saturated or unsaturated alkyl groups of 1 to about 6 carbon atoms, and x is from about 1 to about 6.

7. The composition of claim 6, further comprising at least one cross-linking compound having a structure according to one of:

12. The at least one bridging compound has a structure according to formula (IV): 【Chemistry 37】 【Transformation 38】 The composition of claim 11 selected from the group consisting of:

13. The at least one bridging compound has a structure according to formula (V), as follows: 【Chemistry 39】 【Chemistry 40】 The composition of claim 11 selected from the group consisting of:

14. The at least one bridging compound has a structure according to formula (VI), as follows: 【Chemistry 41】 The composition of claim 11 selected from the group consisting of:

15. The composition of claim 11, wherein the at least one cross-linking compound is present in the composition in an amount of from about 1% to about 50% by weight based on the unfilled weight of the composition.

16. 12. The composition of claim 11, wherein the weight ratio of the aromatic polymer to the crosslinking compound in the composition is from about 1:1 to about 100:

1.

17. 10. The composition of claim 9, wherein the composition further comprises from about 0.01% to about 15% by weight of a crosslinking reaction control additive selected from a cure inhibitor or a cure accelerator.

18. 18. The composition of claim 17, wherein the crosslinking reaction control additive is a cure inhibitor comprising lithium acetate, or the crosslinking reaction control additive is a cure accelerator comprising magnesium chloride.

19. 7. The composition of claim 6, wherein the composition comprises one or more additives selected from continuous or discontinuous long or short reinforcing fibers selected from carbon fibers, glass fibers, woven glass fibers, woven carbon fibers, aramid fibers, boron fibers, polytetrafluoroethylene fibers, ceramic fibers, polyamide fibers, and / or one or more fillers selected from carbon black, silicates, fiberglass, glass beads, glass spheres, crushed glass, calcium sulfate, boron, ceramic, polyamide, asbestos, fluorographite, aluminum hydroxide, barium sulfate, calcium carbonate, magnesium carbonate, silica, aluminum nitride, aluminum oxide, borax (sodium borax), activated carbon, perlite, zinc terephthalate, graphite, graphene, talc, mica, silicon carbide whiskers or platelets, nanofillers, molybdenum disulfide, fluoropolymer fillers, boron nitride, nanodiamonds, microdiamonds, carbon nanotubes, and fullerene tubes.

20. An article formed from the composition of claim 1.

21. 21. The article of claim 20, wherein the article that is subject to wear in use is selected from rotating and reciprocating components selected from downhole tool components, aerospace components, vehicle components, semiconductor manufacturing components, and tools having rotating or reciprocating components.

22. 22. The article of claim 21, wherein the article is a gear, a rotor, a drill bit, a pulley, a bearing, and a seal.

23. 1. A composition for use in forming an article that is subject to frictional forces or for use in a tribological system, comprising: at least one crosslinkable aromatic polymer matrix material, wherein the at least one crosslinkable aromatic polymer matrix material is a crosslinkable polymer selected from polyarylenes, polysulfones, polyethersulfones, polyphenylene sulfides, polyphenylene oxides, polyimides, polyetherimides, thermoplastic polyimides, polybenzamides, polyamideimides, polyureas, polyurethanes, polyphthalamides, polybenzimidazoles, polyaramids, and blends, copolymers, and alloys thereof; continuous or discontinuous long or short reinforcing fibers selected from carbon fibers, glass fibers, woven glass fiber fabrics, woven carbon fiber fabrics, aramid fibers, boron fibers, polytetrafluoroethylene fibers, ceramic fibers, polyamide fibers, and / or one or more additives selected from one or more fillers selected from carbon black, silicates, fiberglass, glass beads, glass spheres, crushed glass, calcium sulfate, boron, ceramic, polyamide, asbestos, fluorographite, aluminum hydroxide, barium sulfate, calcium carbonate, magnesium carbonate, silica, aluminum nitride, aluminum oxide, borax (sodium borax), activated carbon, perlite, zinc terephthalate, graphite, graphene, talc, mica, silicon carbide whiskers or platelets, nanofillers, molybdenum disulfide, fluoropolymer fillers, boron nitride, nanodiamonds, microdiamonds, carbon nanotubes, and fullerene tubes; A composition comprising:

24. 24. The composition of claim 23, wherein the composition comprises from about 0.5% to about 65% by weight of the one or more additives and / or one or more fillers.

25. 24. The composition of claim 23, wherein the one or more additives are selected from carbon fiber, glass fiber, PTFE, and graphite.

26. 24. The composition of claim 23, wherein the at least one crosslinkable aromatic polymer is a crosslinkable polyarylene selected from polyetherketone, polyetheretherketone, polyetherdiphenyletherketone, polyetherketoneketone, and blends, copolymers, and alloys thereof.

27. 27. The composition of claim 26, wherein the at least one crosslinkable aromatic polymer comprises one or more functional groups for crosslinking.

28. 24. The composition of claim 23, wherein the at least one crosslinkable polymer comprises a first crosslinkable polymer that is one or more polyarylenes selected from polyetherketone, polyetheretherketone, polyetherdiphenyletherketone, polyetherketoneketone, and blends, copolymers, and alloys thereof; and a second crosslinkable polymer selected from the group consisting of one or more of: (i) polyphenylene sulfide, (ii) polysulfone, polyphenylsulfone, polyethersulfone, copolymers, and alloys thereof, and (iii) polyimide, thermoplastic polyimide, polyetherimide, and blends, copolymers, and alloys thereof.

29. The composition comprising the at least one crosslinkable aromatic polymer has the following formula: 【Chemistry 45】 where A is a bond, alkyl, aryl, or arene moiety having a molecular weight of less than about 10,000 g / mol; R １ , R ２ and R ３ are the same or different and independently represent hydrogen, hydroxyl (—OH), amine (NH ２ ), halides, esters, ethers, amides, aryls, arenes, or branched or straight chain saturated or unsaturated alkyl groups of 1 to about 6 carbon atoms, m is 0 to 2, n is 0 to 2, m+n is equal to or greater than 0 and is less than or equal to 2, Z is selected from the group of oxygen, sulfur, nitrogen, and branched or straight chain saturated or unsaturated alkyl groups of 1 to about 6 carbon atoms, and x is from about 1 to about 6.

24. The composition of claim 23, further comprising at least one cross-linking compound having a structure according to one of:

30. 1. A method for improving the wear resistance of an article formed from a composition, said article being for use in a high PV end use where it is subjected to frictional forces or used in a tribological system, said method comprising: providing said composition with at least one crosslinkable aromatic polymer matrix material, wherein the at least one crosslinkable aromatic polymer matrix material, when crosslinked, remains operable at a PV of at least about 75,000 psi-ft. / min; crosslinking the at least one crosslinkable aromatic polymer in the composition; and forming the article.

31. 31. The method of claim 30, wherein the at least one crosslinkable aromatic polymer matrix material, when crosslinked, remains operable at a PV of from about 75,000 psi-ft. / min to about 100,100 psi-ft. / min.

32. 31. The method of claim 30, wherein the at least one crosslinkable aromatic polymer matrix material has a PV limit, measured in psi-ft. / min. at about 500°F, that is at least about 10% higher than the PV limit, measured in psi-ft. / min. at about 500°F, of the same non-crosslinkable aromatic polymer matrix material.

33. 33. The method of claim 32, wherein when crosslinked, the PV limit measured in psi-ft. / min at about 500°F is at least about 50% higher than the PV limit of the same aromatic polymer matrix material in a non-crosslinkable form.

34. 31. The method of claim 30, further comprising providing the composition with one or more additives selected from carbon fiber, glass fiber, PTFE, and graphite.

35. 1. A composition for use in forming an article that is subject to frictional forces or for use in a tribological system, comprising: a matrix material selected from polytetrafluoroethylene, modified polytetrafluoroethylene, and at least one aromatic polymer; at least one crosslinked aromatic polymer filler material, wherein said at least one crosslinked aromatic polymer filler material is formed by providing a composition comprising at least one or more crosslinkable aromatic polymers, crosslinking at least one of said crosslinkable aromatic polymers in said composition, and forming said composition into at least one of pellets, platelets, or particles; A composition comprising:

36. 36. The composition of claim 35, wherein the composition has an abrasion resistance that is at least about 200% greater than a composition having the same matrix material and the same aromatic polymeric filler material that is not crosslinked.

37. 37. The composition of claim 36, wherein the composition has an abrasion resistance that is up to about 850% greater than a composition having the same matrix material and the same aromatic polymeric filler material that is not crosslinked.

38. 36. The composition of claim 35, wherein the at least one crosslinked aromatic polymer filler material has a PV limit, measured in psi-ft. / min at about 500°F, that is at least about 20% higher than the PV limit of the same non-crosslinkable aromatic polymer matrix material.

39. 36. The composition of claim 35, wherein the at least one crosslinked aromatic polymer filler material is a crosslinked polyarylene selected from polyetherketone, polyetheretherketone, polyetherdiphenyletherketone, polyetherketoneketone, and blends, copolymers, and alloys thereof.

40. The composition comprising the at least one crosslinkable aromatic polymer has the following formula: 【Chemistry 49】 [Transformation 50] where A is a bond, alkyl, aryl, or arene moiety having a molecular weight of less than about 10,000 g / mol; R １ , R ２ and R ３ are the same or different and independently represent hydrogen, hydroxyl (—OH), amine (NH ２ ), halides, esters, ethers, amides, aryls, arenes, or branched or straight chain saturated or unsaturated alkyl groups of 1 to about 6 carbon atoms, m is 0 to 2, n is 0 to 2, m+n is equal to or greater than 0 and is less than or equal to 2, Z is selected from the group of oxygen, sulfur, nitrogen, and branched or straight chain saturated or unsaturated alkyl groups of 1 to about 6 carbon atoms, and x is from about 1 to about 6.

36. The composition of claim 35, further comprising at least one cross-linking compound having a structure according to one of:

41. 36. The composition of claim 35, wherein the composition comprises one or more additives selected from carbon fiber, glass fiber, PTFE, and graphite, and the one or more additives are present in an amount from about 0.5% to about 65% by weight.

42. 36. An article formed from the composition of claim 35.

43. 43. The article of claim 42, wherein the article that is subject to wear in use is selected from rotating and reciprocating components selected from downhole tool components, aerospace components, vehicle components, semiconductor manufacturing components, and tools having rotating or reciprocating components.

44. 43. The article of claim 42, wherein the article is a gear, a rotor, a drill bit, a pulley, a bearing, and a seal.

45. 1. A method for improving the wear resistance of a composition for use in forming an article that is subjected to frictional forces or for use in a tribological system, comprising: providing a matrix material selected from polytetrafluoroethylene, modified polytetrafluoroethylene, and at least one aromatic polymer; adding to said matrix a filler material comprising at least one crosslinked aromatic polymer.

46. 1. A composition for use in forming an article that is subject to frictional forces or for use in a tribological system, comprising:

1. A composition comprising at least one crosslinkable aromatic polymer matrix material that, when crosslinked, substantially maintains its dimensional stability after heating above a critical transition temperature, the critical transition temperature being a glass transition temperature or a melting point temperature.

47. 1. A method for maintaining dimensional stability and / or avoiding catastrophic failure above a critical transition temperature of an article subjected to frictional forces and / or used in a tribological system, said method comprising: forming the article from a composition comprising a crosslinked aromatic polymer; incorporating the article into an application in which it is subjected to frictional forces and / or used in a tribological system, wherein the temperature of the article in the application exceeds the critical transition temperature of the aromatic polymer in the article.

48. 48. The method of claim 47, wherein the crosslinked aromatic polymer is a matrix material in the article.

49. 1. A composition for use in forming an article that is subject to frictional forces or for use in a tribological system, comprising: At least one crosslinkable aromatic polymer matrix material is crosslinked and when incorporated into an article or tribological system subjected to frictional forces, substantially retains its dimensional stability above the critical transition temperature of the crosslinked aromatic polymer in said article. A composition comprising:

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