Stable polyetheretherketone (PEEK) compositions

Abstract

The invention relates to a polyetheretherketone (PEEK) composition (I), and the PEEK composition (I) contains lanthanum hydroxide. Lanthanum hydroxide was found to be useful for long-term stabilization of PEEK compositions at temperatures of 210 DEG C to 300 DEG C, preferably 230 DEG C to 270 DEG C, for a time period of 500 hours or longer, preferably 1000 to 3000 hours or longer. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to a polymer composition comprising polyetheretherketone (PEEK) and a rare earth compound. The present invention further relates to the use of said rare earth compound as a heat stabilizer in a polymer composition comprising PEEK. Background Art

[0002] Thermoplastic polymers are widely used in engineering. Their suitability for temperature-based reprocessing opens up a vast field of extensive manufacturing methods such as casting, molding, cupping, etc., which are generally more superior in terms of production volume compared to non-thermal processing. On the other hand, this temperature sensitivity limits the high-temperature performance of thermoplastics, especially when exposed to these temperatures for a period of time.

[0003] Therefore, various heat stabilizer additives are known, which either mechanically enhance the compound or chemically impede thermal degradation.

[0004] Regarding the latter option, it should be mentioned that over time, the main driver of the reduction in mechanical properties after exposure to elevated temperatures is the degradation reaction of polymer chains initiated by free radicals. To address this issue, both organic free radical interceptors and inorganic free radical interceptors are used.

[0005] It has been demonstrated that rare earth elements such as cerium and lanthanum are capable of capturing free radicals, thereby stabilizing thermoplastics thermally.

[0006] For example, WO 2021 / 074178 A1 discloses the thermal stabilizing effect of cerium-oxide-hydrate and lanthanum hydroxide on thermoplastic polyesters. This effect was observed based on the tensile strength of thermoplastic polyesters during thermal aging over an extended period of time.

[0007] Other examples where plastics (especially thermoplastic polymers) are usually mixed with additives such as stabilizers, fillers, plasticizers, and colorants to adjust properties according to the desired application fields include the following:

[0008] EP 1 832 624 Al discloses the use of cerium dioxide to stabilize organic polymers against degradation caused by free radicals, which mainly originate from UV-radiation, although heat is also mentioned as a possible source. This patent does not disclose the use of lanthanum.

[0009] US 9,969,882 B2 describes the use of rare earth compounds (preferably cerium tetrahydroxide and lanthanum trihydroxide) as inorganic free radical capturers in polyamides for long-term thermal stabilization at temperatures of at least 180°C.

[0010] CN 106279646 A relates to heat-resistant poly(butylene succinate), which contains a nucleating agent (such as, in particular, kaolin, mica, titanium dioxide, carbon nanotubes), cyclodextrin or lanthanum cyclic phosphate.

[0011] US 3 621 074 A discloses a method for polycondensing diglycol terephthalate, in which lanthanum phosphate can be used as a catalyst.

[0012] Other documents that disclose, in particular, the use of cerium salts as stabilizers are GB 904,972, EP 3 006 500, WO2019 / 191574A1, CN 110183638 A, KR 20170063159 A, CN 104086877 B, CN 108329573 A, WO 2004 / 106311, "Plastics Additives Handbook" (H. Zweifel, R.D. Maier, M. Schiller, 6th edition, Carl Hanser Verlag, Munich, 2009), CN 102775635 A, CN 101200556B and Yang et al. (2015) Ind. Eng. Chem. Res. 54(44):11048 - 11055.

[0013] Polyetheretherketone (PEEK) is a thermoplastic semi-crystalline polymer with excellent mechanical properties. The structural units of the monomers of PEEK are as follows:

[0014]

[0015] Although the glass transition temperature is approximately 150 °C, PEEK is suitable for many high-temperature applications because it can still maintain most of its mechanical properties at temperatures up to 200 °C to 260 °C. The melting point is approximately at 340 °C.

[0016] Therefore, PEEK is essentially a relatively heat-resistant thermoplastic polymer. Therefore, those skilled in the art would not primarily envision adding a heat stabilizer to PEEK.

[0017] US 3,925,307 discloses adding antioxidants to polyaryletherketones. PEEK is not mentioned in this document. This document particularly mentions lanthanum hydroxide (La(OH) 3 ) and cerium oxide hydroxide (CeO 2 .xH 2O) As an antioxidant. At a temperature of 400 °C (i.e., above the melting point of the polymer), heat resistance was observed only within a time period of 30 minutes. Thus, this document relates to the short-term stability of the polymer under processing conditions. This document does not mention the long-term stability of PEEK under operating conditions (i.e., elevated temperature, but below the melting point).

[0018] In Material Properties Guide( Material Properties Guide)”( https: / / www.victrex.com / - / media / downloads / literature / en / material-properties-guide_us- 4-20.pdf , downloaded on October 13, 2022) and “ PEEK Design&Processing Guide( PEEK Design and Processing Guide)”( https: / / content.solvay.com / ketaspire-peek- design-and-processing-guide.pdf ; downloaded on October 13, 2022), the properties of two commercially available PEEK materials are disclosed.

[0019] Regarding the long-term stability under thermal stress, according to these publications, PEEK does not show a significant decrease in tensile strength during long-term thermal aging, which is contrary to what is observed in thermoplastic polyesters studied, for example, in WO 2021 / 074178.

[0020] Furthermore, regarding the maximum elongation at break after long-term thermal aging, according to these publications, no significant decrease was observed at temperatures in the range of 180 °C to 220 °C.

[0021] These temperatures are lower than the currently recommended maximum continuous operating temperature of 240 °C.

[0022] However, it has been found that at a temperature of 210 °C (especially at temperatures close to 240 °C or even above 240 °C), after long-term thermal aging, PEEK does exhibit a decrease in the maximum elongation at break.

[0023] The maximum elongation at break is a measure of the toughness of the polymer, and thus it is particularly desirable to maintain this property under the invasive temperature conditions that usually cause aging. SUMMARY OF THE INVENTION

[0024] The object of the present invention is to improve the heat aging resistance of polyetheretherketone (PEEK), especially the long-term heat aging resistance.

[0025] This object is solved by a polyetheretherketone (PEEK) composition according to claim 1. Preferred embodiments are set forth in the dependent claims.

[0026] Furthermore, according to claim 4, the present invention relates to the use of lanthanum hydroxide for the long-term stabilization of PEEK compositions. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Shows the results of long-term thermal aging of PEEK compositions in terms of tensile strength.

[0028] Figure 2 Shows the effect of incorporating cerium-oxide hydrate and lanthanum hydroxide into PEEK on the elongation at break after thermal aging at 230 °C for 500 hours.

[0029] Figure 3 Shows the effect of incorporating lanthanum hydroxide (standard grade and fine grade) on the elongation at break quotient during thermal aging at 230 °C for 500 hours.

[0030] Figure 4 Shows the effect of incorporating lanthanum hydroxide (standard grade and fine grade) on the elongation at break quotient during thermal aging at 230 °C for 3000 hours.

[0031] Figure 5 Shows the effect of incorporating lanthanum hydroxide (standard grade and fine grade) on the elongation at break quotient during thermal aging at 270 °C for 3000 hours.

[0032] Figure 6 Shows the effect of different incorporation amounts of lanthanum hydroxide on the elongation at break quotient during thermal aging at 230 °C for 500 hours.

[0033] Figure 7 Shows the effect of different incorporation amounts of lanthanum hydroxide on the elongation at break quotient during thermal aging at 270 °C for 500 hours.

[0034] Figure 8 Shows the effect of different incorporation amounts of lanthanum hydroxide on the elongation at break quotient during thermal aging at 230 °C for 1500 hours.

[0035] Figure 9 Shows the effect of incorporating different lanthanum hydroxides on the elongation at break quotient during thermal aging at 270 °C for 1500 hours.

[0036] Figure 10 Compares the effect of incorporating lanthanum hydroxide (fine grade) on the elongation at break quotient during thermal aging in PEEK, polybutylene terephthalate (PBT), and polyamide 66 (PA66) at temperatures above the respective recommended maximum temperatures for continuous use. DETAILED DESCRIPTION

[0037] In a first aspect, the present invention provides a polyetheretherketone (PEEK)

[0038]

[0039] composition, the PEEK composition containing lanthanum hydroxide.

[0040] In a second aspect, the present invention further provides the use of lanthanum for long-term stabilizing a PEEK composition at a temperature of 210 °C to 300 °C, preferably 230 °C to 270 °C, for a period of 500 hours or longer, preferably 1000 to 3000 hours or longer.

[0041] The following disclosure similarly applies to the first aspect and the second aspect.

[0042] Under "PEEK composition", it is to be understood as a polymer composition containing at least 50%, preferably at least 70% by degree of PEEK.

[0043] As is well known to those skilled in the art, polymer compositions may contain a large number of additives, such as fillers, binders or reinforcing materials.

[0044] The compositions of the present invention may contain PEEK as the only polymer matrix-forming component. Especially in the case of composite materials, the polymer composition may contain one or more polymer matrix-forming components and a reinforcing material (such as a fiber), which may also be a polymer. In a preferred embodiment of the present invention, PEEK is the only polymer matrix-forming component.

[0045] The compositions of the present invention are especially PEEK or consist essentially of PEEK.

[0046] Surprisingly, it has been found that lanthanum hydroxide (La(OH) 3 ) has a long-term thermal stabilizing effect on PEEK with respect to the maximum elongation at break.

[0047] Based on the literature cited above, one can assume that the industry has mainly focused on Ce-based rare earth heat stabilizers rather than La-based rare earth heat stabilizers. The basic principle may lie in the remarkable redox properties of cerium hydrate in the form of stable Ce 3+ and Ce 4+ and the well-known phenomenon that even formally tetravalent (oxidized) cerium-(IV)-hydrate more precisely shows a non-stoichiometric Ce(OH) 4-n molecular formula. Ce also occupies the f orbitals, which helps to better delocalize electrons when capturing free radicals.

[0048] Since none of these standards apply to lanthanum, using lanthanum hydroxide as a heat stabilizer for PEEK does not seem straightforward, and experts could not have anticipated the effects described here.

[0049] Even more surprisingly, it has been found that other known heat stabilizers (such as especially cerium hydrate oxide) are substantially ineffective in stabilizing the maximum elongation at break of PEEK during long-term thermal aging.

[0050] In the context of the present invention, improved long-term heat aging resistance should be understood as a decrease in the percentage of mechanical property values after long-term thermal aging at elevated temperatures compared to the initial values before said thermal aging.

[0051] For the context of the present invention, the mechanical property values are preferably the Young's modulus, the tensile strength, and especially the elongation at break.

[0052] In the context of the present invention, thermal aging (especially long-term thermal aging) should be understood as being caused by placing the polymer composition (i.e., the PEEK polymer contained therein) at an elevated temperature.

[0053] The elevated temperature should be understood as being slightly below and even above the known highest working temperature of PEEK. The currently known highest continuous working temperature of PEEK is 240 °C and is thus below the melting point.

[0054] A particular aspect of the present invention is to improve the heat aging resistance of PEEK at temperatures in the range of 210 °C to 300 °C, preferably up to 230 °C to 270 °C.

[0055] In one embodiment of the present invention, by adding lanthanum hydroxide, the maximum elongation at break after thermal aging at temperatures in the range of 210 °C to 300 °C, preferably up to 230 °C to 270 °C, for 500 h to 3000 h or longer, preferably 1000 h to 3000 h, more preferably 2000 h to 3000 h, is increased.

[0056] Surprisingly, the PEEK composition according to the present invention exhibits very good heat aging, especially for long-term thermal stress. This effect is due to the lanthanum hydroxide used according to the present invention. Thermal aging is generally based on a thermal oxidative degradation mechanism via a free radical chain reaction. Due to the influence of heat and oxygen, free radicals are formed within the polymer. It has been found that the lanthanum hydroxide used according to the present invention can improve the long-term heat aging resistance of PEEK. Such an effect has not been reported before.

[0057] In the following, the preferred features of the present invention are outlined by way of examples.

[0058] The amount of lanthanum hydroxide can range from 0.05 wt% to 20 wt%. Additionally, the amount of lanthanum hydroxide can range from 0.05 wt% to 10 wt%. The amount of lanthanum hydroxide is preferably from 0.05 wt% to 5.0 wt%, more preferably from 0.1 wt% to 5.0 wt%, and most preferably from 0.3 wt% to 5 wt%, for example 0.5 wt%.

[0059] Other amounts of lanthanum hydroxide can be, for example, 5.0 wt%, 1.0 wt%, 0.7 wt%, 0.3 wt% or 0.1 wt%. The preferred amount of lanthanum hydroxide can also range from 0.1 wt% to 3.0 wt%, more preferably from 0.3 wt% to 3 wt%, and most preferably from 0.3 wt% to 0.7 wt%.

[0060] Lanthanum hydroxide preferably has a pH value of 7.5 to 11.5, more preferably 8.5 to 11.

[0061] Lanthanum hydroxide preferably has 2 m 2 / g to 20 m 2 / g, more preferably 6 m 2 / g to 13 m 2 / g of BET specific surface area.

[0062] Lanthanum hydroxide preferably has a D of 0.3 μm to 6.0 μm, more preferably 0.5 μm to 5.0 μm, further preferably 0.5 μm to 3.5 μm, and most preferably 0.5 μm to 1 μm 50 .

[0063] It has been found that, compared to particles with a higher average particle size, those with a lower average particle size, especially lanthanum hydroxide particles with a D of 0.5 μm to 1 μm 50 have a stronger effect.

[0064] All D 50 values given herein refer to volume-based representations, i.e., the particle diameter at "x" volume% in the cumulative distribution (e.g., D 50 of at least 1 μm means that 50 volume% of the particles have a diameter less than 1 μm).

[0065] Lanthanum hydroxide preferably has an LOI of 8.0% to 15.0%, more preferably 10.0% to 15.0% and most preferably 12.0% to 14.5%.

[0066] In particular, lanthanum hydroxide has all of the above parameters, i.e., a specific pH value, BET surface, D 50 and LOI.

[0067] Examples

[0068] PEEK-based molding compounds are available from several suppliers on the market. In the current example, a PEEK-based molding compound with medium viscosity, suitable for injection molding processes, was used (Vestakeep 2000G, non-reinforced grade; producer EVONIK).

[0069] Cerium hydrate (for comparison) and lanthanum hydroxide (according to the present invention) were incorporated into the PEEK

[0070] By gravimetric feeding, the incorporation of cerium hydrate and lanthanum hydroxide was carried out in a separate compounding step by a co-rotating twin-screw extruder Coperion ZSK 26Mcc produced by Coperion of Stuttgart.

[0071] The diameter (D) of the screw was 26 mm and the L / D ratio was 48. Vestakeep 2000G was provided in pellet form and did not require adjustment before compounding. To achieve a constant mass flow rate of 0.5 wt% of cerium hydrate or lanthanum hydroxide over time, a production rate of >50 kg / h was required.

[0072] Materials:

[0073] Cerium hydrate: pH was 6.8, BET surface area was 64.7 m 2 / g, D 50 was 1.1 μm, LOI was 5.5%

[0074] Lanthanum hydroxide: pH was 9.6, BET surface area was 8.2 m 2 / g, D 50 was 3.2 μm, LOI was 14.2%

[0075] Lanthanum hydroxide “fine”: pH was 9.8, BET surface area was 9.7 m 2 / g, D 50 was 0.8 μm, LOI was 13.6%

[0076] For gravimetric feeding, a Loss-in-Weight-Brabender dosing unit was used for the basic molding compound Vestakeep 2000G and cerium hydrate or lanthanum hydroxide.

[0077] There were two devolatilization openings at the twin-screw extruder to remove any residual moisture during the compounding step.

[0078] Cylindrical pellets with a diameter of approximately 2 mm and a length of 2 to 5 mm were produced using a strand cutter and were then used to produce test specimens by injection molding.

[0079] The following compounds were used / manufactured:

[0080] - Compound A – PEEK Vestakeep 2000G – injection molding grade

[0081] - Compound B – PEEK Vestakeep 2000G + 0.5 wt% cerium hydrate oxide

[0082] - Compound C – PEEK Vestakeep 2000G + 0.5 wt% lanthanum hydroxide

[0083] - Compound D – PEEK Vestakeep 2000G + 0.5 wt% “fine” lanthanum hydroxide

[0084] - Compound E – PEEK Vestakeep 2000G + 0.05 wt% “fine” lanthanum hydroxide

[0085] - Compound F – PEEK Vestakeep 2000G + 0.1 wt% “fine” lanthanum hydroxide

[0086] - Compound G – PEEK Vestakeep 2000G + 0.3 wt% “fine” lanthanum hydroxide

[0087] - Compound H – PEEK Vestakeep 2000G + 0.7 wt% “fine” lanthanum hydroxide

[0088] - Compound I – PEEK Vestakeep 2000G + 1.0 wt% “fine” lanthanum hydroxide

[0089] - Compound J – PEEK Vestakeep 2000G + 3.0 wt% “fine” lanthanum hydroxide

[0090] - Compound K – PEEK Vestakeep 2000G + 5.0 wt% “fine” lanthanum hydroxide

[0091] Compounding conditions - ZSK 26 twin-screw compounder:

[0092] Production rate = 60 kg / h

[0093] Speed = 900 rpm

[0094] Table 1: Temperature distribution in the heating zones of ZSK 26, in [°C]

[0095] Region 1 Region 2 Region 3 Region 4 Region 5 Region 6 100 390 390 385 385 380 Region 7 Region 8 Region 9 Region 10 Region 11 Region 12 380 380 380 375 375 375

[0096] Lanthanum hydroxide is incorporated into polyester and polyamide (comparison)

[0097] Lanthanum hydroxide (“fine”) is incorporated into polymer compositions different from PEEK, namely

[0098] - Polybutylene terephthalate (PBT) (PBT Ultradur B 4520, manufacturer: BASF) and

[0099] - Polyamide 66 (PA66) (PA66 Zytel E 42, manufacturer: DuPont)

[0100] The production process is similar to that for incorporation into PEEK. However, of course, the possible processing temperatures of these different polymers are taken into account.

[0101] The following compounds were used / manufactured:

[0102] - Compound L – PBT Ultradur B 4520 + 0.5 wt% lanthanum hydroxide “fine”

[0103] - Compound M – PA66 Zytel E 42 + 0.5 wt% lanthanum hydroxide “fine”

[0104] Production of test specimens:

[0105] PEEK:

[0106] Tensile test bars were manufactured by injection molding according to DIN EN ISO 527-1 using an Engel Victory 330 / 80 injection molding machine. Before the injection molding process, the granules of the compositions (compounds A to D) were dried at 150 °C for 6 h.

[0107] PBT / PA66:

[0108] Test specimens were manufactured similar to the PEEK specimens.

[0109] Thermal aging:

[0110] PEEK:

[0111] The thermal aging process was carried out in an oven from Treibacher Industrie AG. For 500, 1000, 1500, and 3000 h, the defined temperatures were 230 °C, 270 °C, and 300 °C. For 230 °C and 270 °C, an oven from Heraeus (model: Function line T 5042EK) was used, and for 300 °C, an oven from Memmert (model: UF160) was used.

[0112] PBT:

[0113] The applied thermal aging temperature was 170 °C (which is higher than the recommended maximum temperature for continuous use).

[0114] PA66:

[0115] The applied thermal aging temperature was 190 °C (which is higher than the recommended maximum temperature for continuous use).

[0116] The mechanical properties of the test specimens after thermal aging were tested on a universal testing machine manufactured by Zwick Z 150 Allround-Linie.

[0117] Before the mechanical testing after thermal aging, the test specimens were conditioned in water at 80 °C for 72 h.

[0118] Test conditions:

[0119] The tensile test was carried out in accordance with DIN EN ISO 527. The speed was 1 mm / min until the yield strength, and then 50 mm / min until fracture. The Young's modulus, tensile strength, and elongation at break were determined.

[0120] Results:

[0121] At temperatures below 240°C, long-term thermal aging has no significant effect on the tensile strength of PEEK:

[0122] Figure 1 And Table 1 below shows the results of the long-term thermal aging of the PEEK composition in terms of tensile strength. It can be seen that after a period of 3000 hours at 230 °C, no significant effect on the tensile strength (MPa) was observed. This applies to unmodified PEEK (Compound A) and the PEEK composition containing lanthanum hydroxide (Compound C).

[0123] Table 1

[0124] Time (hours) 0 500 1000 1500 3000 Compound A - 230°C 86 92 104 102 110 Compound C - 230°C 85 92 102 102 103

[0125] Effect of long-term thermal aging on the elongation at break of PEEK

[0126] Figure 2 And Table 2 below shows the effect of incorporating cerium hydrate and lanthanum hydroxide into PEEK on the elongation at break (%) after thermal aging at 230 °C for 500 hours.

[0127] Unmodified PEEK (Compound A) showed a significant decrease in elongation at break after thermal aging at 500 h / 230 °C.

[0128] PEEK modified with cerium hydrate (Compound B) also showed a significant decrease.

[0129] However, PEEK modified with lanthanum hydroxide according to the present invention (Compound C) shows almost no deterioration in the elongation at break.

[0130] It is noteworthy that the addition of both cerium hydrate and lanthanum hydroxide results in a decrease in the elongation at break of the starting material. However, this decrease is tolerable.

[0131] Table 2

[0132] Time (hours) 0 500 Compound A - 230°C 22 10 Compound B - 230°C 14 7 Compound C - 230°C 16 14

[0133] Figure 3 And Table 3 shows the same results based on the elongation at break quotient ("relative elongation at break", determined as the quotient of the elongation at break values before the end of thermal aging (100%) and after the end of thermal aging) as Figure 2 the same.

[0134] The amazing effect of lanthanum hydroxide (Compound C) becomes even more apparent here compared to unmodified PEEK (Compound A) and PEEK modified with cerium hydrate (Compound B).

[0135] It is known to those skilled in the art that for polymer compositions, it is important to maintain their properties substantially stable during use relative to the initial state (i.e., before use).

[0136] Table 3

[0137] Time (hours) 0 500 Compound A - 230°C 100 43 Compound B - 230°C 100 45 Compound C - 230°C 100 91

[0138] Figures 4 to 5 And the following Table 4 shows the effect of the particle size of lanthanum hydroxide on the elongation at break quotient. This was tested at three different temperatures: 230 °C, 270 °C and 300 °C for up to 3000 hours.

[0139] For each temperature, unmodified PEEK (Compound A) was compared with PEEK modified with lanthanum hydroxide (Compound C) and PEEK modified with "fine" lanthanum hydroxide (Compound D).

[0140] Table 4

[0141] Time (hours) 0 500 1000 1500 3000 Compound A - 230°C 100 40 33 36 31 Compound C - 230°C 100 44 54 48 44 Compound D - 230°C 100 83 87 79 79 Compound A - 270°C 100 23 20 11 12 Compound C - 270°C 100 49 37 37 31 Compound D - 270°C 100 84 61 84 45

[0142] For each temperature, the better effect of the "fine" lanthanum hydroxide (Compound D) used is evident.

[0143] In addition, it was found that at very high temperatures (300 °C), a decrease in the tensile strength of PEEK could also be observed during the time period between 500 and 1000 hours. It was found that this decrease could also be counteracted by incorporating lanthanum hydroxide into PEEK.

[0144] Figure 6 and 7 And Table 5 below shows the effect of the amount of lanthanum hydroxide on the elongation at break quotient. This was tested for 500 hours at two temperatures: 230 °C and 270 °C.

[0145] In particular, for each temperature, unmodified PEEK (Compound A) was compared with PEEK modified with different amounts of lanthanum hydroxide (Compounds D to K).

[0146] Table 5

[0147] Time (hours) 0 500 Compound A - 230°C 100 40 Compound D - 230°C 100 83 Compound E - 230°C 100 26 Compound F - 230°C 100 62 Compound G - 230°C 100 77 Compound H - 230°C 100 43 Compound I - 230°C 100 90 Compound J - 230°C 100 97 Compound K - 230°C 100 131 Compound A - 270°C 100 23 Compound D - 270°C 100 84 Compound E - 270°C 100 22 Compound F - 270°C 100 32 Compound G - 270°C 100 84 Compound H - 270°C 100 50 Compound I - 270°C 100 69 Compound J - 270°C 100 91 Compound K - 270°C 100 116

[0148] Some compounds were also tested for 1500 hours. The results are summarized in Table 6 below and Figure 8 and Figure 9 in:

[0149] Table 6

[0150] Time (h) 0 1500 Compound A - 230°C 100 36 Compound D - 230°C 100 79 Compound E - 230°C 100 89 Compound K - 230°C 100 111 Compound A - 270°C 100 11 Compound D - 270°C 100 84 Compound E - 270°C 100 34 Compound K - 270°C 100 92

[0151] The results show that, compared with unmodified PEEK (Compound A), amounts of lanthanum hydroxide between 0.05 wt% and 5.0 wt% (Compounds D to K) have a stabilizing effect at both 230 °C and 270 °C for 500 hours and up to 1500 hours.

[0152] Effect on different polymers:

[0153] Figure 10 And Table 7 below shows the results of a comparison based on the elongation at break quotient of incorporating lanthanum hydroxide "fine" into PEEK (Compound D), into PBT (Compound L), and into PA66 (Compound M), respectively. For all polymers, the temperature was slightly above the recommended maximum temperature for continuous use.

[0154] It can be seen that lanthanum hydroxide has a significant stabilizing effect on PEEK compared to PBT (slightly stabilized) and PA.

[0155] Table 7

[0156] Time (hours) 0 500 1500 3000 Compound D - 270°C 100 84 61 84 Compound L - 170°C 100 10 6 4 Compound M - 190°C 100 1 1 0

[0157] Characterization of Lanthanum Hydroxide

[0158] In the following text, a test method for characterizing lanthanum hydroxide according to the present invention is described. All analyses were repeated.

[0159] Determination of pH value

[0160] A 10 wt% slurry of lanthanum hydroxide in deionized water was prepared and stirred for 30 min. Thereafter, the pH value was measured at 20 °C (+ / -1 °C) using a pH meter (model: SevenExcellence from Mettler Toledo) while stirring.

[0161] Determination of BET surface area

[0162] Before measurement, 1 g of lanthanum hydroxide was dried by purging with nitrogen at 250 °C for 60 min.

[0163] The BET surface area was determined using a Tristar 3020 surface area and porosity analyzer (from Micromeritics) with nitrogen as the analysis gas.

[0164] Determination of particle size distribution D by laser diffraction method 50

[0165] D represents the diameter of the powder particles. D 50 is referred to as the median diameter or the median value of the particle size distribution, i.e., the particle diameter at 50% in the cumulative distribution (e.g., a D of 2.0 μm 50 means that 50% of the particles have a diameter less than 2.0 μm).

[0166] Lanthanum hydroxide (0.5 g) in powder form was introduced into a laser particle size analyzer.

[0167] Before measurement, the sample was also sonicated at 50 W for 60 s.

[0168] Determination of loss on ignition

[0169] The loss on ignition (LOI) was determined using a muffle furnace (model: N11HR from Nabertherm) by heating 20 g of lanthanum hydroxide from room temperature to 1000 °C and holding at 1000 °C for 2 hours.

Claims

1. A polyetheretherketone (PEEK) composition, the PEEK composition containing lanthanum hydroxide.

2. The PEEK composition according to claim 1, wherein the amount of the lanthanum hydroxide is 0.05% to 5.0% by weight, more preferably 0.1% to 5.0% by weight, most preferably 0.3% to 0.5% by weight, for example 0.5% by weight.

3. The PEEK composition according to claim 1, wherein The lanthanum hydroxide has a D measured by laser diffraction analysis according to the specification of 0.5 to 1 μm 50 .

4. Use of lanthanum hydroxide for long-term stabilization of a PEEK composition at a temperature of 210°C to 300°C, preferably 230°C to 270°C, for a period of 500 hours or longer, preferably 1000 to 3000 hours or longer.

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