ULTRA-FAST AGING SOLUTION

Description

[0001] The invention relates to a method for the accelerated ageing of plastic articles using a liquid mixture, the use of the liquid mixture for the accelerated ageing of plastic articles and a liquid mixture for the accelerated ageing of plastic articles.

[0002] Plastic products are increasingly being considered as replacements for metallic materials in applications subject to high temperatures, such as in the automotive industry, to reduce weight. For example, polyamides can be used for transmissions such as oil pans and housings for transmission control units, thrust washers and solenoids, vehicle fuel tanks, and various hoses and casings in the fuel system.

[0003] When developing new plastic products, tests are conducted to determine aging properties based on customer requirements. These include material, semi-finished product, and product tests. Customer aging requirements range from dynamic pulsation tests to static or dynamic long-term aging. These tests are part of the product development process. The final design of the products must pass these tests to meet customer requirements.

[0004] The aging properties of the materials used as well as of the products are evaluated during the development phase in order to make necessary adjustments if the required properties are not achieved.

[0005] According to the state of the art, the duration of aging tests is 500–5,000 hours. These tests must be conducted on the finished products as described above. In such long-term tests, the components are subjected to conditions to which they are exposed in use, e.g., over a period of 3,000 hours. Subsequently, it is tested whether the aged samples meet the required properties. Currently, there is no way to provide an advance assessment of the success of such tests. In addition, new materials must also undergo this validation before it can be assessed whether they are suitable for use. Furthermore, the long test duration represents a long waiting time before production batches are released.

[0006] Bredäcs M. et al., Accelerated aging of polyethylene pipe grades in aqueous chlorine dioxide at constant concentration, Polymer Degradation and Stability, Vol. 157, November 2018, pages 80 to 89, investigates the effect of disinfected water on the degradation of polyethylene (PE) by immersion tests of two PE pipe materials in solutions at different temperatures containing chlorine dioxide (ClO 2 ) formed by sodium hypochlorite.

[0007] Roy PK et al., Accelerated aging of LDPE films containing cobalt complexes as prooxidants, Polymer Degradation and Stability, Vol. 91, No. 8, August 2006, pages 1791 to 1799, describes the synthesis and characterization of two cobalt complexes, namely cobalt styrene maleate copolymer (CSMA) and cobalt stearate (CS), and their effect on the degradation behavior of low-density polyethylene (LDPE).

[0008] Francesco Recupero et al., Free Radical Functionalization of Organic Compounds Catalyzed by N-Hydroxyphthalimide; Chemical Reviews, Vol. 107, No. 9, September 2007, pages 3800 to 3842, investigates reactions of various low-molecular-weight substrates under aerobic oxidation using N-hydroxyphthalimide and cobalt as the oxidation system for synthetic chemistry.

[0009] The object of the invention was therefore to provide a new accelerated aging process in order to improve the development cycles and the reliability of the statements on aging for plastic articles, in particular the finished products.

[0010] The inventors have found that this can be achieved by using a liquid mixture for the ageing treatment of plastic articles, wherein the liquid mixture comprises at least one oxidation catalyst or at least one oxidizing agent and an acid and optionally at least one cocatalyst for the oxidation catalyst.

[0011] The object was thus achieved by a method for the accelerated ageing of a plastic article, wherein the method comprises bringing the plastic article into contact with a liquid mixture, wherein the liquid mixture a) at least one oxidation catalyst and b) optionally at least one cocatalyst for the at least one oxidation catalyst and c) at least one acid and d) optionally water and / or at least one other solvent, wherein the at least one oxidation catalyst is an N-hydroxyimide.

[0012] In a preferred embodiment, the liquid mixture comprises: a) at least one oxidation catalyst selected from an N-hydroxyimide, in particular a cyclic N-hydroxyimide, preferably N-hydroxyphthalimide and / or N-hydroxysuccinimide, and b) at least one cocatalyst selected from a transition metal salt or a transition metal complex and c) at least one acid selected from an inorganic acid or an organic acid and d) optionally water and / or at least one other solvent.

[0013] With the aging process according to the invention, it is possible to transform plastic articles into the same aging state in a very short time, e.g., within 1 week or even within 50 hours, which is only achieved after 3000 hours of testing under service conditions according to standard protocols. This represents an enormous time saving, which can generally significantly reduce development times or the duration of material testing.

[0014] It has also been advantageously shown that the reproducibility of the results can be ensured.

[0015] The process described in this invention can be used for any type of plastic. The accelerated aging is based in particular on the principle of thermal oxidative aging, which is further accelerated by the acid. This can also involve attacking the aging inhibitors contained in plastics and causing their degradation. Age inhibitors can significantly influence the aging properties of plastics, especially polyamides. Hydrolysis reactions can also play a role in aging.

[0016] The liquid mixtures used according to the invention are conceivable for use in a variety of areas. Plastics age, and this must be taken into account during design. Therefore, initial assessments must be available as quickly as possible to further refine the product design. Thus, the application extends to all areas where plastics are subject to aging and these must be validated in advance.

[0017] The attached drawings show: Fig. 1The relative decrease in the modulus of elasticity of the plastic article during the aging treatment according to Example 1. Fig. 2The relative decrease in the breaking stress of the plastic article during the aging treatment according to Example 1. Fig. 3The relative decrease in the breaking elongation of the plastic article during the aging treatment according to Example 1. Fig. 4The change in the carbonyl index of the plastic article as a function of the treatment duration during the aging treatment according to Example 1. Fig. 5The relative decrease in the breaking stress of the plastic article during the aging treatment according to Examples 2 and 3.

[0018] The invention is described in detail below.

[0019] According to DIN 50035, the term "aging" refers to all irreversible physical and chemical changes in material properties over time. These changes can have various causes and be attributable to specific degradation mechanisms. In DIN 50035, aging processes are divided into chemical and physical aging processes.

[0020] Accelerated aging can, for example, represent aging compared to aging during storage under standard climate conditions according to DIN ISO 291. However, accelerated aging here is understood to mean accelerated aging compared to long-term aging according to the state of the art, in which the plastic article is subjected to conditions that correspond to those to which the plastic article is exposed during its intended use. Such long-term aging is generally carried out in test rigs in which the operating conditions for the plastic article are simulated, usually based on customer specifications.

[0021] The degree of aging of the plastic article can be determined using various parameters, e.g. mechanical parameters determined from tensile tests, which depend, among other things, on the chain length of the plastic polymers, or the proportion of degradation products contained, which can be determined by IR spectroscopy.

[0022] The liquid mixture comprises at least one oxidation catalyst.

[0023] The at least one oxidation catalyst is an N-hydroxyimide, preferably a cyclic N-hydroxyimide. In a cyclic N-hydroxyimide, the N-hydroxyimide structure is contained in a ring structure, preferably succinimide, which may optionally contain substituents.

[0024] Particularly preferably, the at least one oxidation catalyst is N-hydroxyphthalimide and / or N-hydroxysuccinimide, preferably N-hydroxyphthalimide or N-hydroxysuccinimide, with N-hydroxyphthalimide being particularly preferred. N-hydroxyphthalimide is abbreviated below as NHPI, as usual, and N-hydroxysuccinimide as NHS. NHPI showed a shorter induction period compared to NHS in the conversion of substrates and generally a greater acceleration of aging. NHS showed better solubility in hydrophilic solutions even at low temperatures compared to NHPI.

[0025] The use of N-hydroxyimide derivatives as catalysts for oxidation reactions represents a non-toxic and environmentally friendly alternative to catalysts made of toxic transition metals. After hydrogen abstraction from the -NOH group by oxygen, the N-hydroxyimide derivatives form the reactive N-oxy radical, e.g., a phthalimide-N-oxy radical (PINO), which can catalyze oxidation reactions.

[0026] In a particularly preferred embodiment, the liquid mixture comprises: a) at least one oxidation catalyst selected from an N-hydroxyimide, in particular a cyclic N-hydroxyimide, preferably N-hydroxyphthalimide and / or N-hydroxysuccinimide, and b) at least one cocatalyst selected from a transition metal salt or a transition metal complex and c) at least one acid selected from an inorganic acid or an organic acid and d) optionally water and / or at least one other solvent.

[0027] All information contained herein, including details of how to carry out the process, relates, where applicable, in particular to this particularly preferred embodiment, unless otherwise stated.

[0028] The liquid mixture comprises at least one acid. It can be an inorganic acid and / or an organic acid, with at least one organic acid being preferred. A preferred example of an inorganic acid is sulfuric acid. A preferred example of an organic acid is at least one C 1-4 carboxylic acid. Such short-chain carboxylic acids are preferred because they can penetrate the plastic material better.

[0029] The at least one acid is preferably selected from formic acid, acetic acid, propionic acid, or a mixture thereof, with formic acid and / or acetic acid being particularly preferred. When using the particularly preferred combination of formic acid and acetic acid, the volume ratio of acetic acid to formic acid can be, for example, in the range from 2:1 to 20:1, preferably 3:1 to 15:1.

[0030] The acids, especially the carboxylic acids, serve primarily as solvents for the oxidation catalyst and, optionally, the cocatalyst or oxidizing agent. Furthermore, the acids can have catalytic properties for hydrolysis reactions or other reactions. A particularly suitable acid when using sodium hypochlorite as an oxidizing agent is sulfuric acid, but the use of the aforementioned organic acids is also conceivable.

[0031] The liquid mixture optionally comprises at least one cocatalyst. The liquid mixture preferably contains at least one cocatalyst.

[0032] The at least one cocatalyst is preferably a transition metal salt or a transition metal complex. Suitable examples of transition metal salts or transition metal complexes are those in which the transition metal of the transition metal salt or transition metal complex is selected from Cu, e.g., Cu(II), Mn, e.g., Mn(II) or Mn(III), Co, e.g., Co(II) or Co(III), or Fe. The cocatalyst is particularly preferably a cobalt salt or a cobalt complex, in particular a cobalt(II) salt or a cobalt(II) complex.

[0033] Examples of suitable transition metal salts or complexes are halides, e.g., chlorides, sulfates, or acetates of Cu, Mn, Co, or Fe. Cobalt(II) acetate (Co(Ac) 2 ) is particularly preferred.

[0034] The cocatalysts, especially the transition metal salts or transition metal complexes, support the oxidizing effect of the oxidation catalyst. For example, they generate intermediate hydroperoxides, which promote the formation of N-oxy radicals in the aforementioned N-hydroxyimide derivatives.

[0035] The cocatalysts can also attack ageing inhibitors in plastics, such as ageing inhibitors contained in polyamides.

[0036] The liquid mixture may further contain water and / or another solvent. An example of a solvent other than water is alcohols, e.g., ethanol. It is preferred that the liquid mixture comprises water, ie, the liquid mixture is preferably an aqueous liquid mixture.

[0037] It is preferred that the at least one oxidation catalyst selected from an N-hydroxyimide and, if present, the at least one cocatalyst, in particular the transition metal salt or the transition metal complex, are present in dissolved form in the liquid mixture. This does not necessarily require that the oxidation catalyst and optionally cocatalyst are each completely dissolved, although this is advantageous. In general, for example, at least 80 to 100%, preferably at least 90 to 100%, of the oxidation catalyst and optionally cocatalyst, expediently almost 100%, should be present in solution. In this sense, the liquid mixture is preferably a solution. Undissolved constituents may optionally be present in the solution as flakes or particles, but as mentioned above, this should be avoided as far as possible.It should be noted that these specifications for the solution refer to the liquid mixture used in the process according to the invention, in which the liquid mixture preferably has an elevated temperature. It is known that the solubility of compounds typically increases with increasing temperature.

[0038] The liquid mixture, preferably the aqueous liquid mixture, preferably contains 0.03 to 0.75 mol / L, preferably 0.08 to 0.4 mol / L, of at least one oxidation catalyst selected from an N-hydroxyimide, in particular a cyclic N-hydroxyimide, preferably N-hydroxyphthalimide and / or N-hydroxysuccinimide. It is understood that this and the following concentration data refer to moles of oxidation catalyst or cocatalyst per liter of liquid mixture.

[0039] The liquid mixture, preferably the aqueous liquid mixture, preferably contains 0.001 to 0.1 mol / L, preferably 0.005 to 0.03 mol / L, of at least one cocatalyst selected from a transition metal salt or a transition metal complex, wherein the transition metal is preferably selected from Cu, Mn, Co or Fe, more preferably Co, in particular Co(II).

[0040] The liquid mixture, preferably the aqueous liquid mixture, preferably contains 35 to 80 vol.%, preferably 45 to 70 vol.%, of at least one acid selected from a C 1-4 carboxylic acid, preferably formic acid and / or acetic acid.

[0041] In a preferred embodiment, the liquid mixture, preferably the aqueous liquid mixture, a) 0.03 to 0.75 mol / L, preferably 0.08 to 0.4 mol / L, of at least one oxidation catalyst selected from an N-hydroxyimide, in particular a cyclic N-hydroxyimide, preferably N-hydroxyphthalimide and / or N-hydroxysuccinimide, and b) 0.001 to 0.1 mol / L, preferably 0.005 to 0.03 mol / L, of at least one cocatalyst selected from a transition metal salt or a transition metal complex, wherein the transition metal is preferably selected from Cu, Mn, Co or Fe, more preferably Co, in particular Co(II), and c) 35 to 80 vol.%, preferably 45 to 70 vol.%, of at least one acid selected from a C 1-4 carboxylic acid, preferably formic acid and / or acetic acid.

[0042] The plastic article to be treated can be, for example, the plastic itself, e.g. in the form of a test piece, a semi-finished product made of plastic or a component or a product which has at least one component made of the plastic. The component or product can be formed from the plastic alone or from a plastic component in combination with one or more components made of another material, with a component or product made of the plastic alone being preferred. The method according to the invention is particularly suitable for components or products. Examples of plastic articles to be tested are plastic couplings, gear components, thrust washers, components for magnetic coils, vehicle tanks as well as hoses, sleeves, connecting elements, e.g. for a tank system or a cooling circuit system.

[0043] It is understood that the plastic may contain one or more additives, as is customary in the field. Examples of additives include age inhibitors or stabilizers, plasticizers, pigments, reinforcing agents, e.g., fibers or particulates, e.g., glass fibers or mineral fillers, flame retardants, etc. It may, for example, be a glass-fiber-reinforced plastic, e.g., a glass-fiber-reinforced polyamide.

[0044] The plastic of the plastic article can be any plastic whose aging behavior is to be tested. The plastic of the plastic article is preferably a plastic obtained by a polyaddition or polycondensation reaction, i.e., a polycondensate plastic or a polyadduct plastic. The plastic of the plastic article is preferably a polyester or a polyamide, with polyamide being particularly preferred. Examples of polyamides (PA) are PA 6.6, PA 4.6, PA 6, PA6.12, and PA 11.

[0045] During the aging treatment of the method according to the invention, the plastic article is brought into contact with the liquid mixture. To bring the plastic article into contact with the liquid mixture, the plastic article can be immersed in the liquid mixture, the plastic article can be rinsed or flushed with the liquid mixture, or the plastic article can be filled with the liquid mixture. When rinsing or flushing or filling with the liquid mixture, it is possible to bring only one side of the plastic article, e.g., the inside, into contact with the liquid mixture. Rinsing or flushing or filling thus enables one-sided loading of the article, whereby a loading can be achieved that is more similar to practical operation.

[0046] Filling a plastic article depends on its geometry and may require sealing after filling. Typically, the plastic article will have at least one hollow body during filling. In some cases, sealing one side of the article before filling may also be necessary, for example, in the case of a hose.

[0047] In one embodiment of the aging treatment of the method according to the invention, the plastic article is immersed in the liquid mixture. The plastic article can optionally be immersed only partially in the liquid mixture, but it is generally more expedient for the entire plastic article to be immersed in the liquid mixture.

[0048] For dipping, the plastic article is expediently placed in a suitable container or flask, for example, or secured therein with appropriate fixing elements, and the liquid mixture is poured in. Of course, the sequence can also be reversed. It is advantageous if the liquid mixture is kept moving during the aging treatment, e.g., using a stirrer. If the aging treatment is carried out at elevated temperature, e.g., near the boiling point, and / or with the introduction of an oxygen-containing gas, it is often expedient to equip the container or flask with a reflux condenser to prevent liquid evaporation. It goes without saying that a suitable heating device must be provided for carrying out the treatment at elevated temperature.

[0049] The aging treatment, or bringing the plastic article into contact with the liquid mixture, e.g., by immersing, rinsing, or filling it with the liquid mixture, can be carried out at a temperature in the range of 15°C to 100°C. Aging treatment at a temperature above the boiling point of the liquid mixture or the components it contains is also possible, but this requires treatment under pressure, which requires more complex equipment, e.g., a pressure vessel. This is not preferred because the process should be kept as simple as possible.

[0050] The aging treatment or bringing the plastic article into contact with the liquid mixture, e.g., by immersion, rinsing, or filling in or with the liquid mixture, is preferably carried out at a temperature in the range of 60°C to 90°C, more preferably 70 to 85°C. A temperature of approximately 80°C has proven particularly favorable in practice.

[0051] In a preferred embodiment, an oxygen-containing gas, particularly air, can be introduced into the liquid mixture during the aging treatment. This can be easily accomplished using a pipe or hose immersed in the liquid mixture, which is connected to a pump and / or a source of the oxygen-containing gas.

[0052] The duration of the aging treatment can depend on several factors, e.g. composition of the liquid mixture or concentrations of the components contained, degree of aging to be achieved or temperature used. The aging treatment or bringing the plastic article into contact with the liquid mixture, e.g. by immersing, rinsing, purging or filling in or with the liquid mixture, can take place over a period of 6 hours to 300 hours, preferably 20 hours to 80 hours. A duration of approximately 50 hours has proven to be particularly useful in practice. If the aging treatment is carried out at an elevated temperature, such as the temperatures mentioned above, it may be possible to temporarily interrupt the aging treatment by stopping the heating of the liquid mixture and allowing it to cool to room temperature.The periods without heating are then not taken into account for the duration of the aging treatment.

[0053] After the aging treatment, the plastic article is removed from the liquid mixture, and any adhering residues of the liquid mixture are removed by rinsing with and / or storing it in a rinsing medium, such as water or deionized water. The practitioner can obtain indications of the degree of aging achieved by visually inspecting the resulting plastic article, for example, based on cracking or discoloration. However, for a more precise investigation of the degree of aging, analytical methods are generally used to determine at least one characteristic property of the plastic article.

[0054] Before conducting such analytical procedures, it may be appropriate to subject the plastic article subjected to aging treatment to a reconditioning treatment. This is a conditioning treatment to return the plastic article to its pre-aging condition with regard to certain parameters, e.g., water content. For example, certain plastics, such as polyamides, are capable of absorbing water or moisture from the environment, so the water content may increase during aging treatment. However, the water content can influence the results of analytical procedures, particularly mechanical tests. Therefore, reconditioning for standardization purposes is often appropriate or necessary to ensure comparability of the results with untreated samples.

[0055] For reconditioning or conditioning, the plastic article can be subjected to a conditioning climate until an equilibrium is established between the temperature and humidity of the article and the conditioning climate. Conditioning can be carried out, for example, according to the standard climate according to DIN EN ISO 291 (23°C, relative humidity of 55%).

[0056] Therefore, in a preferred embodiment, the method according to the invention further comprises analyzing the plastic article after removal from the liquid mixture and, if appropriate, a conditioning treatment in order to determine at least one property of the plastic article subjected to the aging treatment. It is understood that the properties to be determined are, in particular, properties that are characteristic of the degree of aging. Suitable analytical methods for determining the degree of aging of plastic articles are described, for example, in DE102018214235A1, DE102016213188A1, and DE102016213157A1, which are incorporated herein by reference.

[0057] Examples of other suitable analytical methods include mechanical tests to determine mechanical properties, e.g., mechanical tensile testing, differential scanning calorimetry, IR spectroscopy, and optical analytical methods, such as light microscopy and scanning electron microscopy (SEM). One or more analytical methods can be used. In a preferred embodiment, the analysis of the plastic article comprises at least one analytical method selected from mechanical tensile testing, differential scanning calorimetry, optical analysis, and IR spectroscopy, preferably mechanical tensile testing and / or IR spectroscopy.

[0058] IR spectroscopy, such as FTIR spectroscopy or FTIR-ATR spectroscopy, is suitable for detecting degradation products. The mechanical properties from tensile tests are, among other things, an indication of the length of the polymer chains. Differential scanning calorimetry provides information on the crystalline phases in the plastic.

[0059] The invention also relates to the use of a liquid mixture as an ageing medium for the accelerated ageing of a plastic article, wherein the liquid mixture a) at least one oxidation catalyst and b) optionally at least one cocatalyst for the at least one oxidation catalyst and c) at least one acid and d) optionally water and / or at least one other solvent, wherein the at least one oxidation catalyst is an N-hydroxyimide.

[0060] It is understood that for the use according to the invention, the above statements apply equally to the process for the liquid mixture, the plastic article and the process, so that reference is made thereto.

[0061] The invention also relates to a liquid mixture, preferably an aqueous liquid mixture, for the accelerated ageing of a plastic article, comprising a) 0.03 to 0.75 mol / L, preferably 0.08 to 0.4 mol / L, of at least one oxidation catalyst selected from an N-hydroxyimide, in particular a cyclic N-hydroxyimide, preferably N-hydroxyphthalimide and / or N-hydroxysuccinimide, and b) 0.001 to 0.1 mol / L, preferably 0.005 to 0.03 mol / L, of at least one cocatalyst selected from a transition metal salt or a transition metal complex, wherein the transition metal is preferably selected from Cu, Mn, Co or Fe, more preferably Co, and c) 35 to 80 vol.%, preferably 45 to 70 vol.%, of at least one acid selected from a C 1-4 carboxylic acid, preferably formic acid and / or acetic acid.

[0062] It is understood that the above statements regarding the liquid mixture apply equally to the liquid mixture according to the invention, where applicable, so that reference is made thereto.

[0063] The invention will now be further explained using exemplary embodiments. These specific exemplary embodiments are not intended to limit the invention in any way. Examples

[0064] Due to safety regulations, the tests could only be conducted at elevated temperatures during the day. However, it is assumed that the downtime at room temperature overnight has no significant impact on the test results and is therefore negligible. It is advisable to run the test overnight without interruption to further accelerate the aging process. Tensile test

[0065] Tensile testing can determine parameters such as Young's modulus, elongation at break, and stress at break. A Zwick Z010 materials testing machine was used for the measurement. A triple determination was performed according to test standard DIN EN ISO 527-2. 2012-06 at a tensile speed of 50 mm / s. Since the dimensions of the shoulder test pieces can change slightly after aging, corrections were made prior to the measurement. Before the measurement, the aged specimens were reconditioned as described below. FTIR-ATR spectroscopy

[0066] The shoulder bars were first removed from the water bath and pre-dried in air for 24 hours. They were then subjected to a final drying process at 80 °C for 12 hours in a drying cabinet. For the measurements on pipe couplings, sample pieces were cut out using a saw and then dried at 80 °C in a drying cabinet.

[0067] The Perkin Elmer "Spectrum Two" FTIR spectrometer was used. Diamond was used as the ATR crystal for the analysis. The wavenumber range from 4000 to 400 cm -1 was scanned in eight cycles per measurement (triple measurements at different locations on the shoulder rod).

[0068] For quantitative analysis, the measurement range between 1800 and 1700 cm -1 was examined in more detail. Typical absorption bands of the aging products are found in this range. The CH2 band, with a maximum at approximately 2928 cm -1 , served as the internal standard. Quantitative analysis is performed by calculating the ratio of the total peak area in the wavenumber range from 1800 to 1700 cm -1 to the peak area of ​​the internal standard (CH2; approximately 2928 cm -1 ). This ratio is referred to below as the "carbonyl index." Example 1

[0069] The samples tested are injection-molded shoulder bars made of glass fiber reinforced and carbon black colored polyamide 6.6 according to the test standards DIN EN ISO 527-2.

[0070] The liquid mixture or solution used as an aging medium had the following composition: NHPI 0.15 mol / L Co(Ac) 2 0.0075 mol / L acetic acid 50 vol.% Formic acid 5 vol.% distilled water rest

[0071] A pressure vessel from Kliewe GmbH was filled with 800 mL of the aging medium. The test rods were loosely placed in the solution. The medium was stirred with a PTFE stir bar. During the heating periods, air purified with a sterile filter was continuously introduced into the solution via a laboratory compressor. Since introducing atmospheric oxygen via a compressor can result in high vapor losses, a condensate collector cooled by a water bath was installed.

[0072] The aging medium was heated to 80 °C for approximately 10 hours per day and actively ventilated. Apart from the relatively short heating and cooling phases, the test specimens were stored in the aging medium at room temperature (approximately 20 °C) for the remainder of the time. The aging treatment was carried out over a period of 1 week. Only the times at elevated temperature are relevant for the duration of the aging treatment; the times at room temperature are not taken into account.

[0073] At regular intervals according to the following table, test bars were removed from the aging medium, rinsed with deionized water and stored in a water bath to remove diffused aging medium residues from the polyamide matrix. Taking sample series Duration of active heating at 80 °C [h] Storage time at RT in aging medium [h] N1 series 5,0 0 N2 series 10,0 11,0 N3 series 20,0 11,0 N4 series 30,0 23,0 N5 series 40,0 34,0 N6 series 50,0 44,5

[0074] To determine the mechanical properties, the samples were removed from the water bath and initially pre-dried in air for approximately eight hours. Since the mechanical properties vary greatly depending on the water content in the polyamide matrix, the test specimens were then reconditioned for at least 72 hours in a desiccator over a supersaturated magnesium nitrate solution at room temperature (approx. 20 °C) and a relative humidity between 49.9 and 55.0%.

[0075] For comparison, characteristic values ​​were determined on samples not subjected to aging treatment (= blank sample or 0-sample), which were taken as the 100% value. The ultimate stress of the blank sample was between 107 - 109 MPa with elongation at break values ​​of 4.5 - 5.9%. The results for the aged samples are presented below. Optical analysis

[0076] Macroscopically, severe damage to the shoulder rods in the NHPI / Co(Ac)2 solution could already be observed depending on their treatment time, which was confirmed by analysis of light microscopy and SEM images. Tensile test

[0077] The results of the N6 samples are to be regarded as tendencies, since notches in the area of ​​the web led to premature fatigue of the material.

[0078] Fig. 1 shows the relative decrease of the Young's modulus during the aging treatment, which shows a significant drop to approximately 80% after the first five hours of active heating.

[0079] The Fig. 2 The relative fracture stress also shows a steep decline within the first five hours. Subsequently, a linearly decreasing trend is evident. Already at the fifth sampling point, a fracture stress of only 60% is observed.

[0080] At the Fig. 3The elongation at break shown initially shows an improvement in the elongation at break during the first few hours, but then decreases drastically. At the third sampling point, a decrease in the elongation at break to approximately 95% is observed, and at the fifth sampling point, an elongation at break of only 70% of the original value is observed.

[0081] Both the decrease in breaking stress and elongation at break indicate a steady degradation of the polyamide matrix. FTIR-ATR spectroscopy

[0082] The change in the carbonyl index described above depending on the duration of treatment is in Fig. 4 The formation of the carbonyl index shows a significant increase with increasing treatment time. The results confirm that, in addition to the hydrolysis of the imide band, a progressive aging of the matrix has also occurred. Comparison

[0083] The results obtained in Example 1 were compared with measurement results for shoulder bars made of glass fiber reinforced polyamide 6.6 (for tensile tests) and pipe couplings (for FTIR measurements) that were aged in a mixture of water and coolant under conditions comparable to those prevailing in a test rig for a state-of-the-art coolant circuit (temperatures of approximately 120°C and increased pressure).

[0084] Overall, the fracture stress values ​​of Example 1 and the coolant-aged samples are within the same range. However, the samples aged according to Example 1 show significantly accelerated aging. Thus, according to the fracture stress values ​​determined, a treatment time of 30 hours of active heating in Example 1 corresponds to a treatment time of approximately 1750 hours for the coolant-aged samples.

[0085] A comparison with the temporal change of the elongation at break also shows a very good agreement between the two systems, although in significantly different time intervals (Example 1: 0-50 h (times at elevated temperature); samples aged in coolant: 0-3000 h).

[0086] A comparison of the carbonyl index of the coolant-aged pipe coupling with the samples from Example 1 shows that a comparable amount of degradation products is only reached after 2,861 h in the coolant-aged sample after approximately 50 h of active heating in Example 1.

[0087] The analysis of the images obtained by light and scanning electron microscopy also shows a good agreement between the samples aged in the coolant mixture and those from Example 1.

[0088] The investigations demonstrate that the NHPI / Co(Ac) 2 system enables rapid acceleration of the aging process of polyamide 6.6-GF30. A comparison with samples from aging tests in coolant / deionized water mixtures and pipe couplings from the test bench shows largely excellent agreement regarding the change in mechanical properties and comparability regarding the distribution of degradation products. Example 2

[0089] The samples tested were injection-molded shoulder bars made of glass fiber-reinforced polyamide 6.6 in accordance with the test standard DIN EN ISO 527-2. The plastic used was different from the polyamide type used in Example 1 (different manufacturers).

[0090] The liquid mixture or solution used as an aging medium had the following composition: NHS 0.2 mol / L Co(Ac)2 0.01 mol / L acetic acid 50 vol.% Formic acid 5 vol.% distilled water rest

[0091] A standard reflux apparatus consisting of a 2 L glass round-bottom flask with a Dimroth reflux condenser and a heating mantle was used for the experiments. A uniform temperature was achieved by thermal convection. Active aeration of the medium with atmospheric oxygen at elevated temperature was achieved using a laboratory compressor. The samples were threaded onto a flexible stainless steel wire and attached to a stainless steel mesh placed inside the flask. The flask was then filled with the liquid mixture.

[0092] The parameters and the type of test procedure, such as temperature profile and measurement method, otherwise corresponded to those of Example 1.

[0093] In Fig. 5The change in fracture stress during the aging treatment is shown as curve A. It should be noted that the time axis only considers the duration of the treatment at 80°C. This means that the standing time at room temperature is not taken into account.

[0094] The determined mechanical parameters confirm that the NHS-based system accelerates the aging process. Both increasing the catalyst concentration and increasing the temperature only slightly improved the acceleration effect. Example 3

[0095] For comparison, the same tests were carried out as in Example 2, except that the aging medium was replaced by the aging medium of Example 1. The resulting change in fracture stress during the aging treatment is also shown in Fig. 5 shown (curve B).

[0096] The comparison with the system of Example 2 based on NHS shows a significantly faster aging of the NHPI system according to Example 3 compared to the NHS system of Example 2 starting from approximately 20 hours of treatment. Example 4

[0097] Based on the results obtained, an accelerated aging process for plastic components such as a plastic coupling made of PA66-GF30 (Quick Connector) can be designed. Here, the coupling is immersed in an aging medium as described in Example 1. The solution is continuously agitated by a stirrer. Aging is initiated by exposure to an elevated temperature, e.g., 80°C, and the solution. Air is preferably introduced into the solution during the treatment. After the aging treatment (e.g., for 50 hours), the component is removed from the medium, rinsed, and reconditioned. These material testing results can be determined on this component.

Claims

1. Method of accelerated ageing of a plastics article, comprising contacting the plastics article with a liquid mixture comprising a) at least one oxidation catalyst and b) optionally at least one cocatalyst for at least one oxidation catalyst and c) at least one acid and d) optionally water and / or at least one other solvent, characterized in that the at least one oxidation catalyst is an N-hydroxyimide.

2. Method according to Claim 1, wherein the at least one oxidation catalyst is a cyclic N-hydroxyimide, preferably N-hydroxyphthalimide and / or N-hydroxysuccinimide.

3. Method according to either of the preceding claims, wherein the liquid mixture comprises: a) at least one oxidation catalyst selected from an N-hydroxyimide, in particular a cyclic N-hydroxyimide, preferably N-hydroxyphthalimide and / or N-hydroxysuccinimide, and b) at least one cocatalyst selected from a transition metal salt or a transition metal complex and c) at least one acid selected from an inorganic acid or an organic acid and d) optionally water and / or at least one other solvent.

4. Method according to any of the preceding claims, wherein the acid is sulfuric acid or at least one C1-4 carboxylic acid.

5. Method according to any of the preceding claims, wherein the acid is selected from formic acid, acetic acid, propionic acid or a mixture thereof, preferably formic acid and / or acetic acid.

6. Method according to Claim 3, wherein the transition metal of the transition metal salt or transition metal complex is selected from Cu, Mn, Co or Fe, preferably Co.

7. Method according to any of the preceding claims, wherein the liquid mixture comprises water, and / or wherein the at least one oxidation catalyst selected from an N-hydroxyimide, and, if present, at least one cocatalyst, in particular the transition metal salt or the transition metal complex, are in dissolved form in the liquid mixture.

8. Method according to any of the preceding claims, wherein the liquid mixture, preferably the aqueous liquid mixture, contains a) 0.03 to 0.75 mol / l, preferably 0.08 to 0.4 mol / l, of at least one oxidation catalyst selected from an N-hydroxyimide, in particular a cyclic N-hydroxyimide, preferably N-hydroxyphthalimide and / or N-hydroxysuccinimide, and b) 0.001 to 0.1 mol / l, preferably 0.005 to 0.03 mol / l, of at least one cocatalyst selected from a transition metal salt or a transition metal complex, where the transition metal is preferably selected from Cu, Mn, Co or Fe, more preferably Co, and c) 35% to 80% by volume, preferably 45% to 70% by volume, at least one acid selected from a C1-4 carboxylic acid, preferably formic acid and / or acetic acid.

9. Method according to any of the preceding claims, wherein the plastic of the plastics article is a polycondensate or a polyadduct, wherein the plastic is preferably a polyester or a polyamide, preferably a polyamide.

10. Method according to any of the preceding claims, wherein the plastics article is contacted with the liquid mixture at a temperature in the range from 15°C to 100°C, preferably in the range from 60°C to 90°C, more preferably from 70 to 85°C, and / or wherein the plastics article is contacted with the liquid mixture over a period of 6 hours to 300 hours, preferably 20 hours to 80 hours.

11. Method according to any of the preceding claims, wherein an oxygen-containing gas, in particular air, is introduced into the liquid mixture during the ageing treatment.

12. Method according to any of the preceding claims, further comprising analysing the plastics article after it has been removed from the liquid mixture for determination of at least one property of the plastics article subjected to the ageing treatment, wherein the removed plastics article is optionally subjected to a reconditioning treatment before the analysis.

13. Method according to Claim 12, wherein the analysis of the plastics article comprises at least one of mechanical tensile testing, dynamic differential calorimetry, IR spectroscopy, optical analysis or a combination thereof.

14. Method according to any of the preceding claims, wherein the plastics article is contacted with the liquid mixture by dipping the plastics article into the liquid mixture or rinsing or flushing the plastics article with the liquid mixture or filling the plastics article with the liquid mixture.

15. Use of a liquid mixture as ageing medium for accelerated ageing of a plastics article, wherein the liquid mixture comprises a) at least one oxidation catalyst and b) optionally at least one cocatalyst for at least one oxidation catalyst and c) at least one acid and d) optionally water and / or at least one other solvent, characterized in that the at least one oxidation catalyst is an N-hydroxyimide.

16. Use according to Claim 15, wherein the liquid mixture is as defined in any of Claims 2 to 8 and / or the plastics article is as defined in Claim 9 and / or the use is effected in a method according to any of Claims 1 to 14.

17. Liquid mixture, preferably an aqueous liquid mixture, for accelerated ageing of a plastics article, comprising a) 0.03 to 0.75 mol / l, preferably 0.08 to 0.4 mol / l, of at least one oxidation catalyst selected from an N-hydroxyimide, in particular a cyclic N-hydroxyimide, preferably N-hydroxyphthalimide and / or N-hydroxysuccinimide, and b) 0.001 to 0.1 mol / l, preferably 0.005 to 0.03 mol / l, of at least one cocatalyst selected from a transition metal salt or a transition metal complex, where the transition metal is preferably selected from Cu, Mn, Co or Fe, more preferably Co, and c) 35% to 80% by volume, preferably 45% to 70% by volume, at least one acid selected from a C1-4 carboxylic acid, preferably formic acid and / or acetic acid.