Method for CO2 foaming of high-temperature polymers using co-solvents, high-temperature polymer and its use as well as component

Abstract

This document describes a process for the production of high-temperature polymers, comprising the steps of providing high-temperature polymer material, treating the high-temperature polymer material with at least one co-solvene, wherein the at least one co-solvene is selected from the group consisting of limonene, triethanolamine, dimethyl sulfoxide (DMSO), and combinations thereof, and saturating the treated high-temperature polymer material with CO2. Furthermore, a high-temperature polymer, a component comprising a high-temperature polymer, and the use of a high-temperature polymer or a component are described.

Description

[0001] The invention relates to a method for producing high-temperature polymers, a high-temperature polymer, a component, and the use of the high-temperature polymer or the component.

[0002] Solvents such as the basic triethanolamine are known as CO2 absorbents and are used in so-called carbon capture processes, as described, for example, in Daniel Ohde et al., Chem. Ing. Tech., 91, No. 12, 1822-1826 (2019). The absorbing effect can be attributed to a more or less strong interaction between the CO2 and the solvent.

[0003] Polyetheretherketone (PEEK) foams are very useful for numerous technical processes, for example as recyclable, foamed thermoplastic materials for wire insulation.

[0004] It is well known that PEEK, and also polyetherketoneketone (PEKK), foams very poorly with CO2. Behrendt et al., Appl. Phys. A 85, 87-93 (2006) describes CO2 foaming processes of PEEK. Furthermore, it was found, for example in DE102015209275B4, that PEEK and PEKK often only become saturated with CO2 under extreme conditions.

[0005] However, new publications have recently appeared that utilize the solvent diphenyl sulfone and the addition of other chemicals for the foaming of PEEK and PEDEK (diphenyl polyetheretherketone) by phase separation (Lingcheng Meng et al., Macromol. Mater. Eng., 308, 2200559 (2023)). Rusakov et al., J. Appl. Polym. Sci. 2022;139:e51423 describe a similar approach using the solvent 4-phenylphenol.

[0006] A process for producing a thermoplastic fiber foamed with supercritical fluid is described, for example, in CN119458746A.

[0007] The object of the present invention is to provide a method, a high-temperature polymer, a component, and the use of the high-temperature polymer and the component that at least partially overcomes the aforementioned disadvantages.

[0008] This problem is solved by the inventive method according to claim 1, the high-temperature polymer according to claim 6, the component according to claim 8 and the use according to claim 9.

[0009] Further advantageous embodiments of the invention will become apparent from the dependent claims and the following description of preferred embodiments of the present invention.

[0010] A process according to the invention for the production of high-temperature polymers comprises the following steps: - Provision of high-temperature polymer material, - Treating the high-temperature polymer material with at least one co-solvene, wherein the at least one co-solvene is selected from the group consisting of limonene, triethanolamine, DMSO and combinations thereof, - Saturating the treated high-temperature polymer material with CO2, - Lowering the temperature and pressure, - sudden temperature increase to cause foaming of the high-temperature polymer material, wherein the treatment of the high-temperature polymer material with at least one co-solvent takes place within a period ranging from 24 hours to 200 hours before saturation with CO2, wherein the CO2 saturation of the high-temperature polymer material treated with the cosolvent(s) takes place at a pressure of at least 73.75 to 200 bar and a temperature of at least 30.9 °C to 80 °C for 5 to 40 minutes, wherein the CO2 dissolved in the high-temperature polymer material is converted into the liquid state by reducing the pressure to at least below 73.75 bar and the temperature to at least below 30.9 °C, and where the foaming occurs through an abrupt temperature increase to a temperature in the range of 140 °C to 260 °C for a period of 90 to 240 seconds.

[0011] High-temperature polymers are polymers that exhibit high temperature resistance and have a melting point of preferably at least 170 °C for semi-crystalline plastics and a glass transition temperature of at least 120 °C for amorphous plastics. The high-temperature polymers in question are preferably foamable. Therefore, the high-temperature polymer is preferably selected from the group consisting of polyphenylene sulfides (PPS), polyphenylene ethers (PPE), polyethersulfones (PES), polyetherimides (PEI), polysulfones (PSU), polyesters, including polyethylene naphthalates (PEN), polyetheretherketones (PEEK), polyetherketone ketones (PEKK), diphenyl polyetheretherketones (PEDEK), cycloolefin copolymers (COC), polyacrylonitrile (PAN), acrylonitrile butadiene styrene copolymers (ABS), polycarbonates (PC), foamable fluoropolymers, polystyrenes, and derivatives, mixtures, and copolymers thereof.Of these, PPS, PES, PEI, PEEK, PEDEK, and PEKK are particularly preferred. PPS is especially favored because it is ideally suited as an insulating material for electrical machines and, in addition to its good electrical properties, exhibits a high melting point (approx. 280–297 °C), very low moisture absorption, and good chemical resistance, for example, to gear oil. Furthermore, PPS foams very well. PES has similar properties to PPS but foams slightly less readily. PEI is even somewhat superior to PPS in terms of its electrical properties but has a slightly higher moisture absorption rate and is relatively expensive. PEEK materials have a very high melting point (approx. 334–343 °C) and also possess excellent mechanical properties. However, they exhibit comparatively moderate foamability and are also very expensive.An alternative to PEEK is polyetherketone ketone (PEKK) with a melting point of approximately 305 - 358 °C, which, in addition to good mechanical properties, exhibits better foamability.

[0012] Preferably, the high-temperature polymer is a polyetheretherketone polymer.

[0013] A further preferred high-temperature polymer is a polyetherketoneketone (PEKK) or a polyetherimide (PEI).

[0014] The high-temperature polymer can be the material alone, a component or workpiece made from it, or a workpiece coated with it, a coated wire, or a coated component.

[0015] A method according to the invention comprises the step of treating the high-temperature polymer material with at least one co-solvene. Treatment can be understood as complete immersion, spraying, or storage of a component made of high-temperature polymer material or a component coated with a high-temperature polymer in the co-solvene for a defined period, e.g., 48 hours.

[0016] The at least one cosolvent is selected from the group consisting of limonene, triethanolamine, DMSO (dimethyl sulfoxide) and combinations thereof.

[0017] In one embodiment, the at least one solvent is limonene or triethanolamine. Limonene is a natural product from the terpene group and is known, among other names, as 1-methyl-4-(prop-1-en-2-yl)cyclohex-1-ene. Triethanolamine is an amino alcohol and is also known as 2,2',2"-nitrilotriethanol.

[0018] In one embodiment, the at least one cosolvent is a combination of limonene and / or triethanolamine and / or dimethyl sulfoxide.

[0019] In another embodiment, the at least one cosolvent is a combination of limonene and triethanolamine.

[0020] In another embodiment, the at least one cosolvent is a combination of limonene, triethanolamine and DMSO.

[0021] The at least one cosolvent can be limonene, triethanolamine or a 1:1 mixture (by mass) of limonene and triethanolamine.

[0022] The cosolvant can also be a mixture of limonene, triethanolamine and DMSO, ranging from mixtures with a mass composition of 1 / 3 limonene, 1 / 3 triethanolamine and 1 / 3 DMSO (dimethyl sulfoxide) to mixtures of 45 wt% limonene, 45 wt% triethanolamine and 10 wt% DMSO (dimethyl sulfoxide).

[0023] In one embodiment, the treatment of the high-temperature polymer material with at least one co-solvent takes place over a period of 24 to 200 hours. Preferably, the treatment of the high-temperature polymer material with at least one co-solvent takes place over a period of 48 to 144 hours, more preferably over a period of 60 to 100 hours, and even more preferably over a period of 72 to 96 hours.

[0024] A process according to the invention further comprises the step of saturating the treated high-temperature polymer material with CO2. Preferably, the CO2 is supercritical CO2. Supercritical is defined as a state in which the fluid is neither liquid nor gaseous. The CO2 reaches this state at approximately 31 °C and 74 bar.

[0025] The high-temperature polymer material can be treated with carbon dioxide (CO2) under pressure and temperature. This process saturates the polymer with CO2, which is in a supercritical state due to the selected pressure and temperature conditions. To counteract the supercritical state of the CO2 after saturation, the temperature is preferably lowered. This slows the diffusion of the now liquid CO2, resulting in a longer retention time within the polymer during the physical foaming process. The high-temperature polymer can be placed in a reactor / autoclave for CO2 treatment.

[0026] In one embodiment of the inventive method, the CO2-treated high-temperature polymer material is saturated at a pressure of at least 73.75 to 200 bar and a temperature of at least 30.9°C to 80°C for 5 to 40 minutes.

[0027] In a further embodiment of the process according to the invention, the CO2 dissolved in the high-temperature polymer material is converted into the liquid state by reducing the pressure to at least below 73.75 bar and the temperature to at least below 30.9° C.

[0028] A supercritical state of CO2 can occur, for example, when the autoclave / reactor used for CO2 saturation maintains a temperature of at least 30.9 °C and a pressure of at least 73.75 bar. The supercritical state of CO2 can also be induced, for example, at a pressure of 80 bar and a temperature of 40 °C in the autoclave / reactor.

[0029] In one embodiment, the treated high-temperature polymer material can be saturated with CO2 at a pressure of at least 73.75 to 200 bar and a temperature of at least 30.9 °C, preferably from 40 °C to 80 °C, for 5 to 40 minutes. The temperature during CO2 saturation can be in the range of 40 °C to 80 °C, preferably in the range of 40 °C to 65 °C. The duration of the saturation can be in the range of 5 to 40 minutes, preferably in the range of 15 to 20 minutes.

[0030] In one embodiment, a method according to the invention comprises the following further steps: - Lowering the temperature and pressure, - sudden temperature increase to cause foaming of the high-temperature polymer material.

[0031] In one embodiment, a process according to the invention for the production of high-temperature polymers comprises the following steps: - Provision of high-temperature polymer material, - Treating the high-temperature polymer material with at least one co-solvene, wherein the at least one co-solvene is selected from the group consisting of limonene, triethanolamine, dimethyl sulfoxide (DMSO) and combinations thereof, - Saturating the treated high-temperature polymer material with CO2, - Lowering the temperature and pressure in order to leave the supercritical state of CO2, if supercritical CO2 is used, - sudden drop in pressure to atmospheric pressure and - sudden temperature increase to cause foaming of the high-temperature polymer material.

[0032] In one embodiment, the pressure on the CO2-saturated high-temperature polymer material is abruptly reduced to atmospheric pressure. The CO2-saturated high-temperature polymer material can be located in an autoclave or a reactor.

[0033] Following the CO2 saturation step, a cooling and pressure reduction phase can be implemented, whereby the temperature should fall below 30.9 °C and the pressure should be reduced to at least below 73.75 bar to exit the supercritical state of the CO2. This cooling and pressure reduction phase can take place within 10 minutes to 24 hours, preferably achieving a temperature of 20 °C, and more preferably 15 °C. The pressure is preferably reduced to 60 bar, and more preferably to 50 bar.

[0034] A subsequent, abrupt pressure drop in the autoclave / reactor to atmospheric pressure allows the CO2 initially dissolved in the polymer to transition into the gaseous state, preferably initiating phase separation of the CO2. CO2 initially dissolved in the polymer can act as a plasticizer, softening the high-temperature polymer and enabling the formation of foam pores. As the amount of CO2 in the polymer decreases during the rapid temperature treatment at temperatures of 160–260 °C, the plasticizing effect diminishes until the high-temperature polymer, in which the foam pores have formed, solidifies. The pore structure can then be described as "solidified." The temperature treatment can be carried out, for example, using an induction or resistance heating element placed in close proximity to the high-temperature polymer material.To improve the homogeneity of the temperature distribution, the aforementioned methods can be combined. The elevated temperature is set to a suitable value, which could be, for example, 180 °C, until the foaming process is complete.

[0035] In one embodiment, foaming takes place at a temperature in the range of 140 °C to 260 °C. Preferably, foaming takes place at a temperature in the range of 160 °C to 200 °C, and more preferably in the range of 170 °C to 190 °C.

[0036] The CO2 saturation in an autoclave can be a so-called "temperature pulse method," as described, for example, in DE102015209275B4. The high-temperature polymer material, treated with at least one co-solvent and saturated with CO2, is preferably subsequently subjected to a short-term temperature shock of 90 to 240 seconds at 140 to 260 °C, preferably 180 °C. The temperature shock can be achieved by the action of hot oil, or the high-temperature polymer can be heated directly by contact with an electric or inductive heating device.

[0037] In one embodiment of a method according to the invention, foaming takes place by abruptly increasing the temperature to a temperature in the range of 140 °C to 260 °C for a period of 90 to 240 seconds.

[0038] The process according to the invention enables efficient, fine-pored foaming of high-temperature polymers, in particular polyetherketones. The process, through the addition of cosolvents, improves the solubility of CO2 in the high-temperature polymer, resulting in significantly more effective and uniform foaming. A process according to the invention can enable particularly uniform and fine-pored foaming of high-temperature polymers (e.g., PEEK or PEKK materials) or coated wires, workpieces (made of or coated with high-temperature polymer), or components (made of or coated with high-temperature polymer).

[0039] Furthermore, the subject matter of the present invention is a high-temperature polymer which is produced according to a process according to the invention.

[0040] In one embodiment, the foamed high-temperature polymer produced according to the invention exhibits a density reduction of 30% to 80% compared to the compact material. Preferably, the foamed high-temperature polymer produced according to the invention exhibits a density reduction of 40% to 80% compared to the compact material; more preferably, the high-temperature polymer exhibits a density reduction of 50% to 80% compared to the compact material.

[0041] A compact high-temperature polymer is understood to be a non-foamed, pore-free high-temperature polymer.

[0042] A process according to the invention leads, due to the process steps, to a particularly uniform pore distribution in the high-temperature polymer, so that foamed high-temperature polymers with particularly uniform material properties can be obtained.

[0043] Furthermore, the subject matter of the present invention is a component comprising a foamed high-temperature polymer according to the invention. It can be a component consisting of foamed high-temperature polymer material or a component coated with a high-temperature polymer, e.g., a PEEK-coated wire in a stator of an electric machine or a PEEK-coated groove base of a stator of an electric machine.

[0044] An electric machine can be an electrical machine designed to generate mechanical rotary or translational motion from an electric current, or conversely, to convert electric current into mechanical motion. In particular, an electric machine can be an electric motor, a generator, a combination of the above, or similar devices. Specifically, an electric machine can be designed to power a motor vehicle. The electric machine can also be a separately excited synchronous machine.

[0045] Furthermore, the subject of the present invention is the use of a high-temperature polymer foam and / or a component according to the invention for thermally stressed coated wires, surfaces, workpieces or components, or as workpieces or components which are used in electric machines, in particular in stators of electric machines, in plain and ball bearings, valves, gears, fittings, motor bearing cages and prostheses, in particular hip joint prostheses.

[0046] A high-temperature polymer and / or a component according to the invention can be used, for example, in all electric machines where, according to the current state of the art, groove base and wire insulation is required.

[0047] The high-temperature polymers according to the invention can also be used in thermally resilient components and coatings, where compact polyetheretherketones can be replaced by, for example, polyetheretherketone foams.

[0048] A high-temperature polymer according to the invention, or components made therefrom according to the invention, can also be used in thermally resilient components and coatings in railway vehicles, in the mining industry, in chemical plant construction, in mechanical engineering or in robotics.

[0049] Exemplary embodiments of the invention are now described by way of example and with reference to the accompanying drawing, in which: Fig. 1 schematically an embodiment of a process for the production of high-temperature polymers without co-solvent, Fig. 2 schematically an embodiment of a process according to the invention for the production of high-temperature polymers and Fig. Figure 3 schematically shows an embodiment of a process for the production of high-temperature polymers.

[0050] Fig. Figure 1 schematically shows an embodiment of a process for producing high-temperature polymers 100 without co-solvene. This embodiment can also be referred to as the temperature pulse method. In this process, a high-temperature polymer material 101 is subjected to saturation with CO2 104, thus obtaining a CO2-saturated high-temperature polymer material 102. Alternatively, instead of a high-temperature polymer material 102, the material can also be coated wires, workpieces (made of or coated with the high-temperature polymer), or components (made of or coated with the high-temperature polymer). Preferably, the high-temperature polymer is PEEK. The CO2 saturation can be carried out with a temperature and pressure pulse of approximately 70 °C and approximately 80 bar for 30 minutes, followed by cooling and pressure reduction to 14 °C and 50 bar within 22.5 hours. Subsequently, foaming 105 takes place (e.g.,...(Temperature shock at 180 °C) to obtain a foamed high-temperature polymer 103.

[0051] Fig. Figure 2 schematically shows an embodiment of a process according to the invention for the production of high-temperature polymers 200. The process for the production of high-temperature polymers 200 comprises the steps of providing high-temperature polymer material 207, treating the high-temperature polymer material with at least one co-solvene 206 and saturating the treated high-temperature polymer material with CO2 204, wherein the at least one co-solvene is selected from the group consisting of limonene, triethanolamine, DMSO and combinations thereof.

[0052] Fig.Figure 3 schematically shows an embodiment of a process for producing high-temperature polymers 300. In this process, a high-temperature polymer material 301 is saturated with a co-solvant 306, thus yielding a co-solvene-saturated high-temperature polymer material 308. In particular, the surface or near-surface volume of the high-temperature polymer material is saturated with the co-solvene. The co-solvene can be limonene. Alternatively, instead of a high-temperature polymer material, the material can also be wires coated with a high-temperature polymer, workpieces (made of or coated with a high-temperature polymer), or components (made of or coated with a high-temperature polymer). The co-solvene-saturated high-temperature polymer material is then saturated with CO2 304, thus yielding a CO2-saturated high-temperature polymer material 302. Preferably, the high-temperature polymer is PEEK.CO2 saturation can be achieved with a temperature and pressure pulse of approximately 70 °C and 80 bar for 30 minutes, followed by cooling and pressure reduction to 14 °C and 50 bar within 22.5 hours. Subsequently, foaming (305) is carried out (by abruptly increasing the temperature to, for example, 180 °C) to obtain a foamed high-temperature polymer 303. It can be assumed that when the pressure reactor in which the process is carried out is depressurized to atmospheric pressure, the CO2 escapes very quickly from the high-temperature polymer material (e.g., PEEK) and is therefore no longer available for foaming. The CO2-dissolving cosolvents (e.g., limonene) lead to higher CO2 solubility in the polymer due to a carrier effect, and thus to improved foaming of the high-temperature polymer. Reference symbol list 100, 200, 300 Processes for the production of high-temperature polymers 101, 301 High-temperature polymer material 102, 302 CO2 saturated high-temperature polymer material 103, 303 foamed high-temperature polymer 104, 204, 304 Saturate with CO2 105, 305 Frothing 206, 306 Treating the high-temperature polymer material with at least one co-solvent 207 Provision of high-temperature polymer material 308 high-temperature polymer material saturated with cosolvent

Claims

[1] Process for the production of high-temperature polymers comprising the steps: - Provision of high-temperature polymer material, - Treating the high-temperature polymer material with at least one co-solvene, wherein the at least one co-solvene is selected from the group consisting of limonene, triethanolamine, dimethyl sulfoxide (DMSO) and combinations thereof, - Saturating the treated high-temperature polymer material with CO2 - Lowering the temperature and pressure, - sudden temperature increase to cause foaming of the high-temperature polymer material, wherein the treatment of the high-temperature polymer material with at least one co-solvent takes place within a period ranging from 24 hours to 200 hours before saturation with CO2, wherein the CO2 saturation of the high-temperature polymer material treated with the cosolvent(s) takes place at a pressure of at least 73.75 to 200 bar and a temperature of at least 30.9 °C to 80 °C for 5 to 40 minutes, wherein the CO2 dissolved in the high-temperature polymer material is converted into the liquid state by reducing the pressure to at least below 73.75 bar and the temperature to at least below 30.9 °C, and where the foaming occurs through an abrupt temperature increase to a temperature in the range of 140 °C to 260 °C for a period of 90 to 240 seconds. [2] The method of claim 1, wherein the high-temperature polymer material is a polymer selected from the group consisting of polyphenylene sulfides (PPS), polyphenylene ethers (PPE), polyethersulfones (PES), polyetherimides (PEI), polysulfones (PSU), polyesters, including polyethylene naphthalates (PEN), polyetheretherketones (PEEK), polyetherketone ketones (PEKK), diphenyl polyetheretherketones (PEDEK), cycloolefin copolymers (COC), polyacrylonitrile (PAN), acrylonitrile butadiene styrene copolymers (ABS), polycarbonates (PC), foamable fluoropolymers, polystyrenes, derivatives, mixtures and copolymers thereof. [3] Method according to claim 1 or 2, wherein the at least one cosolvene is limonene, triethanolamine or dimethyl sulfoxide. [4] Method according to claim 1 or 2, wherein the at least one cosolvent is a combination of limonene and / or triethanolamine and / or dimethyl sulfoxide. [5] Method according to at least one of claims 1 to 4, wherein the pressure which is applied to the high temperature polymer material saturated with CO2 is suddenly reduced to atmospheric pressure. [6] High-temperature polymer produced by a process according to at least one of claims 1 to 5. [7] High-temperature polymer according to claim 6, wherein the high-temperature polymer has a density reduction compared to the compact starting material of 30% to 80%, preferably of 40% to 80%, more preferably of 50% to 80%. [8] Component comprising a high-temperature polymer according to claim 6 or 7. [9] Use of a high-temperature polymer according to claim 6 or 7 and / or a component according to claim 8 for thermally stressed coated wires, surfaces, workpieces or components, or as workpieces or components, in electric machines, in particular in stators of electric machines, plain and ball bearings, valves, gears, fittings, motor bearing cages, prostheses, in particular hip joint prostheses.

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