Polymer composition comprising UHMWPE and HDPE

Abstract

The present invention relates to a polymer composition comprising an ultra high molecular weight polyethylene (UHMWPE), relative to the total weight of the polymer composition, and > = 5.0 and < = 50.0 wt%, preferably > = 5.0 and < = 40.0 wt%, more preferably > = 5.0 and < = 30.0 wt%, even more preferably > = 5.0 and < = 20.0 wt% of a high density polyethylene (HDPE); preferably, the HDPE is a homopolymer of ethylene or a copolymer of ethylene and a comonomer, and the comonomer can be one selected from 1-butene, 1-hexene or 1-octene. Such polymer compositions allow for processing into desired shaped objects using common and economically effective forming techniques, such as injection molding and / or compression molding.

Description

[0001] The present invention relates to a polymer composition comprising ultra high molecular weight polyethylene and high density polyethylene. The present invention also relates to a method for producing such a composition and an object produced using such a composition.

[0002] Ultra-high molecular weight polyethylene (UHMWPE) is a special type of polyethylene material that exhibits many outstanding properties, such as high impact strength, low coefficient of friction and good biocompatibility. These properties make UHMWPE a suitable material for applications such as bone joint prostheses, bearings, high-performance fibers and pipelines. UHMWPE typically has a very high molecular weight, long polymer chains and a high degree of molecular entanglement.

[0003] However, the special molecular structure of UHMWPE may lead to difficulties in processing the material via melt processing techniques. When the molecular weight of the polyethylene polymer is above 500,000 g / mol, the polymer retains its solid state behavior even at temperatures above its melting point and therefore does not exhibit the appropriate fluid flow properties that would allow the material to be processed by typical melt processing techniques in the field of thermoplastic polymers such as melt extrusion and injection molding.

[0004] To avoid this, the forming methods of UHMWPE materials generally involve solid powder processing techniques such as compression molding and plunger extrusion. However, each of these technologies has its disadvantages. For example, compression molding is an intermittent method and is therefore not particularly suitable for high-speed large-scale production of products. Furthermore, it involves relatively long processing times, which may lead to oxidative degradation of the UHMWPE material during the compression molding method. Although plunger molding is a quasi-continuous method, further processing of the original shape obtained (usually a rod) is also required, which often leads to processing marks on the surface of the produced parts, which may affect the product aesthetics and mechanical properties, and this leads to the generation of waste processed from the rod extruded by the plunger.

[0005] Other limitations of processing UHMWPE materials in common extrusion or injection molding methods include, for example, the physical state of the UHMWPE materials that can be used for processing. From the polymerization process, UHMWPE materials are obtained in the form of fine powders with very low friction. When attempting to process such powders via extrusion or injection molding, the powders tend to rotate with (one or more) rotating screws in the barrel of an extruder or injection molding machine, and therefore cannot be conveyed along the screw and move forward toward the die outlet of the extruder or the nozzle of the injection molding machine. Therefore, it is a challenging task to transform UHMWPE powder into a material that is more suitable for processing, such as pellets. In this article, pellets are understood to be materials with sizes within the range of millimeters (mm), such as diameters of 2-7mm and lengths of 2-10mm. Such pellets are generally more convenient for processing than powdery materials, and therefore need to be obtained.

[0006] It would therefore be desirable to have a more convenient processing method for UHMWPE materials to produce objects of desired shapes, in particular a method for producing UHMWPE pellets.

[0007] In the field of polyethylene, some changes in the nomenclature of different types of polyethylene have appeared in the known literature. In order to avoid any ambiguity in this regard, a detailed description of the composition of UHMWPE is provided here. In the context of the present invention, UHMWPE is understood to be a polymer comprising repeating polymer units derived from ethylene, preferably consisting of repeating polymer units derived from ethylene, and having a viscosity average molecular weight (Mv) of at least 1,000,000 g / mol. Typical UHMWPE materials can have a viscosity average molecular weight of 1,000,000 to 10,000,000 g / mol, or 2,000,000 to 8,000,000 g / mol.

[0008] To determine the viscosity average molecular weight (Mv) of the UHMWPE material, in the context of the present invention, the viscosity average molecular weight (Mv) is calculated based on the intrinsic viscosity (η) in dl / g according to the Margolies equation:

[0009] Mv=5.37·10 4 ·η 1.49

[0010] Wherein, Mv is the viscosity average molecular weight of UHMWPE in g / mol, and η is the intrinsic viscosity of UHMWPE in dl / g. The calculation according to the Margolies equation is described in ASTM D4020-11 (Standard Specification for Ultra-High Molecular Weight Polyethylene Molding and Extrusion Materials). The determination of the intrinsic viscosity is carried out in decalin as solvent at a temperature of 135° C. according to the method described in ASTM D2857-95 (Re 2007) (Standard Practice for Dilute Solution Viscosity of Polymers).

[0011] The present invention provides a polymer composition comprising

[0012] Ultra-high molecular weight polyethylene (UHMWPE), and

[0013] ≥5.0 and ≤50.0 wt% of high-density polyethylene (HDPE),

[0014] Relative to the total weight of the polymer composition.

[0015] Such polymer compositions allow for processing into desired shaped objects using common and cost-effective forming techniques, such as injection molding and / or compression molding.

[0016] The composition preferably comprises ≥5.0 and ≤40.0 wt. %, more preferably ≥5.0 and ≤30.0 wt. %, even more preferably ≥5.0 and ≤20.0 wt. % of HDPE, relative to the total weight of the polymer composition. Alternatively, the composition preferably comprises ≥6.0 and ≤40.0 wt. %, more preferably ≥6.0 and ≤35.0 wt. %, even more preferably ≥15.0 and ≤35.0 wt. % of HDPE, relative to the total weight of the polymer composition.

[0017] The HDPE may, for example, have a molecular weight of ≥50,000 and ≤500,000 g / mol, preferably ≥50,000 and ≤300,000 g / mol, more preferably ≥75,000 and ≤250,000 g / mol.

[0018] HDPE can be a homopolymer of ethylene, or a copolymer of ethylene and a comonomer. The comonomer can be, for example, one selected from 1-butene, 1-hexene or 1-octene. Such a HDPE copolymer can, for example, contain ≥0.1 and ≤5.0 wt%, preferably ≥0.1 and ≤3.0 wt%, more preferably ≥0.3 and ≤3.0 wt% of polymer units derived from the comonomer, relative to the total weight of the HDPE copolymer.

[0019] HDPE may, for example, have a value of ≥946 and ≤975 kg / m 3 , preferably ≥950 and ≤970kg / m 3 , more preferably ≥950 and ≤965 kg / m 3 The density of the composite is as determined according to ASTM D792 (2008).

[0020] The HDPE may, for example, have a melt mass flow rate of ≥0.1 and ≤100 g / 10 min, preferably ≥0.5 and ≤50 g / 10 min, more preferably ≥1.0 and ≤25 g / 10 min, even more preferably ≥3.0 and ≤15.0 g / 10 min, yet even more preferably ≥5.0 and ≤10.0 g / 10 min, as determined according to ASTM D1238 (2013) at 190°C under a load of 2.16 kg.

[0021] The UHMWPE may, for example, have a viscosity average molecular weight (Mv) of ≥2,000,000 g / mol, preferably ≥2,000,000 and ≤8,000,000 g / mol, more preferably ≥3,000,000 and ≤8,000,000 g / mol, even more preferably ≥4,000,000 and ≤8,000,000 g / mol, still even more preferably ≥5,000,000 and ≤8,000,000 g / mol, wherein the Mv is calculated via the Margolies formula based on the intrinsic viscosity, wherein the intrinsic viscosity is determined according to the method set forth in ASTM D2857-95 (Re2007) at a temperature of 135°C in decalin as solvent.

[0022] UHMWPE may for example have a mass of ≥ 900 kg / m 3 , preferably ≥900kg / m 3 And ≤945kg / m 3 , more preferably ≥910kg / m 3 And ≤945kg / m 3 , even more preferably ≥910kg / m 3 And ≤935kg / m 3 , still even more preferably ≥ 915 kg / m 3 And ≤930kg / m3 density.

[0023] The UHMWPE may be a homopolymer of ethylene or a copolymer of ethylene and a comonomer. The comonomer may, for example, be one selected from 1-butene, 1-hexene or 1-octene. Such a UHMWPE copolymer may, for example, contain ≥0.1 and ≤5.0 wt%, preferably ≥0.1 and ≤3.0 wt%, more preferably ≥0.3 and ≤3.0 wt% of polymerized units derived from the comonomer, relative to the total weight of the UHMWPE copolymer.

[0024] The present invention also relates to a polymer object comprising or consisting of a composition according to any one of claims 1 to 5, wherein the object is a pellet having a diameter of 2 to 7 mm and a length of 2 to 10 mm, preferably a diameter of 3 to 5 mm and a length of 4 to 6 mm. Such pellets allow convenient molding of articles and shapes using the polymer composition. During the molding process, it is advantageous to use a moldable polymer material in the form of pellets, compared to using a powdered material, in view of the flow of the material into the molding unit. Another benefit of using pellets is the reduction of the dust tendency that powdered materials are usually prone to. Preferably, in such an object, UHMWPE and HDPE are evenly and indifferently distributed.

[0025] Preferably, the polymer composition comprises ≥ 95.0 wt.-% of the sum of UHMWPE and HDPE, relative to the total weight of the polymer composition, or the polymer composition consists of UHMWPE, HDPE and ≤ 1.0 wt.-%, preferably ≤ 0.5 wt.-%, of additives.

[0026] Such pellets of the polymer composition according to the invention can be obtained, for example, by a process comprising:

[0027] i. supplying a polymer composition to a polymer extruder component, the polymer composition comprising an ultra high molecular weight polyethylene (UHMWPE) and ≥5.0 and ≤50.0 wt%, preferably ≥5.0 and ≤40.0 wt%, more preferably ≥5.0 and ≤30.0 wt%, even more preferably ≥5.0 and ≤20.0 wt% HDPE, or ≥6.0 and ≤40.0 wt%, more preferably ≥6.0 and ≤35.0 wt%, even more preferably ≥15.0 and ≤35.0 wt% HDPE;

[0028] ii. conveying the polymer composition through a polymer extruder;

[0029] iii. conveying the polymer composition through a die assembly; and

[0030] iv. forming the polymer composition leaving the polymer extruder into pellets through the outlet of the die assembly, which is carried out as follows:

[0031] a) cooling the polymer composition to a temperature below the melting temperature, preferably below 100° C., and subsequently cutting the obtained cooled strands into pellets; or

[0032] b) cutting the polymer composition into pellets and subsequently cooling the pellets to below the melting temperature, preferably to below 100° C.;

[0033] wherein the polymer extruder assembly comprises a material inlet (6), an extruder barrel (7) comprising one or two extruder screws (8), and an outlet (9) for removing processed material from the extruder, wherein the outlet comprises a die assembly, the die assembly comprising a circularly enclosed straight channel (1), the straight channel comprising an inlet (2) and an outlet (3), the channel being configured so that material can be conveyed through the channel along a flow axis (4) from the inlet toward the outlet, wherein the channel comprises a housing (5) to form a shell that completely surrounds the channel;

[0034] wherein the channel comprises a buffer section having a length A and a compression section having a length B, the buffer section is located at an inlet side of the channel, and the compression section is located at an outlet side of the channel, and the buffer section and the compression section are connected to each other;

[0035] wherein the buffer section has a first diameter D1 perpendicular to the flow axis on one side of the inlet of the channel and a second diameter D2 perpendicular to the flow axis on the side facing the outlet of the channel, wherein D1>D2, preferably forming a tapered channel section at an angle α;

[0036] wherein the compression section has a first diameter D3 perpendicular to the flow axis on the side facing the inlet of the channel, which corresponds to D2, and a second diameter D4 perpendicular to the flow axis on the side facing the outlet of the channel, wherein D3>D4, forming a tapered channel section at an angle β;

[0037] Preferably, wherein the angle α>β; and

[0038] Preferably, D4 is a circular opening, and more preferably, each of D1 , D2 , D3 and D4 is circular.

[0039] In the die assembly according to the invention, the angle β may preferably be ≥1.0° and ≤10.0°, preferably ≥1.5° and ≤5.0°.

[0040] Preferably, the outlet diameter D4 of the die assembly is ≥2.0 and ≤8.0 mm, preferably ≥3.0 and ≤6.0 mm.

[0041] The length B of the compression section of the channel can be, for example, ≥20 and ≤100 mm, preferably ≥30 and ≤60 mm.

[0042] The ratio of length B / length A may, for example, be ≥2.0, preferably ≥4.0.

[0043] The ratio D3 / D4 may be, for example, ≥1.2 and ≤2.0, preferably ≥1.3 and ≤1.7.

[0044] The die assembly according to the present invention may be equipped with a cooling unit. Such a cooling unit may preferably be configured such that it is able to cool the die assembly to a temperature of ≤150° C., more preferably ≥100° C. and ≤150° C. The cooling unit may for example be a unit that provides cooled air to the die assembly, preferably wherein the cooling unit is an air gun.

[0045] The die assembly may include a plurality of channels (1).

[0046] The present invention also relates in certain embodiments to a polymer extruder assembly comprising a material inlet (6), an extruder barrel (7) comprising one or two extruder screws (8), and an outlet (9) for removing processed material from the extruder, wherein the outlet comprises a die assembly according to the present invention.

[0047] The extruder may comprise a cooling unit (10) for cooling the die assembly, preferably for cooling the die assembly to a temperature of ≤ 150° C., more preferably ≥ 100° C. and ≤ 150° C. The cooling unit may for example be a unit providing cooled air to the die assembly, preferably wherein the cooling unit is an air gun.

[0048] Preferably, the extruder barrel temperature in step ii) is ≥ 170° C. and ≤ 220° C. The extruder speed may, for example, be ≥ 50 and ≤ 150 rpm.

[0049] Preferably, the pressure at the inlet of the die assembly is ≥3.0 and ≤8.0 MPa.

[0050] In certain embodiments, the present invention also relates to a method for producing a shaped article, wherein the method comprises compression molding using a polymer object, the polymer object being a polymer pellet. Preferably such compression molding is performed by feeding the polymer object into an open and heated mold cavity, followed by closing the two mold halves, providing compression, and subsequently cooling to give the article a final shape.

[0051] The invention also relates to a compression-molded article comprising a polymer composition according to the invention or produced using a polymer object according to a compression-molding process.

[0052] In certain embodiments, the present invention also relates to a method for producing a shaped article, wherein the method comprises injection molding using a polymer object, the polymer object being a polymer pellet. Preferably such injection molding is performed by melting the polymer object in a machine barrel and then injecting the polymer melt under pressure into a closed cavity in a mold, where the polymer solidifies and forms the final article formed by the cavity.

[0053] The invention further relates to an injection-molded article comprising the polymer composition according to the invention or produced using a polymer object according to an injection-molding process.

[0054] A brief description of the drawings is provided here.

[0055] Figure 1 A die assembly according to an embodiment of the present invention is shown, which includes a tapered compression section. Figure 1 In the die assembly, a housing (5) includes a channel (1) having an inlet (2) and an outlet (3). A material can flow along the channel in the direction of a flow axis (4). The assembly includes a buffer region having a length A and a compression region having a length B. D1 represents the diameter of the inlet of the buffer region, and D2 represents the diameter of the outlet of the buffer region; D3 represents the diameter of the inlet of the compression region, and D4 represents the diameter of the outlet of the compression region.

[0056] Figure 2 An alternative configuration of the die assembly is shown, showing an alternative geometry of the buffer region. Figure 2 The markers 1-5, AB and D1-D4 correspond to Figure 1 , as explained above.

[0057] Figure 3 A polymer extruder assembly comprising a die assembly according to the present invention is shown, wherein the extruder comprises a material inlet (6), an extruder barrel (7) comprising one or two extruder screws and an outlet (9) for removing processed material from the extruder, wherein the outlet comprises a die assembly according to the present invention. Figure 3 The extruder assembly further shows a cooling unit (10) for cooling the die assembly.

[0058] Figure 4 A conventional die assembly is shown which does not include a compression zone as defined in accordance with the present invention.

[0059] Figure 5 The contents extruded from the barrel of the extruder by removing the die from the extruder are shown, thereby reflecting the processing state of the contents of the extruder during the processing of the UHMWPE material. Figure 5 The top image shows the extruder equipped with Figure 4The material obtained from the extraction of the extruder contents in the case of conventional die components; Figure 5 The bottom image in FIG. 1 shows the use of an extruder equipped with a die assembly according to the present invention. Figure 1 The material obtained by construction.

[0060] The invention will now be illustrated by the following non-limiting examples.

[0061] In the examples of the present invention, a Leistritz ZSE-18 co-rotating twin-screw extruder was used. The extruder was equipped with a tapered die, such as Figure 1 The tapered die has a compression zone length of 35 mm, a tapered angle of the compression zone of 2°, and a diameter of the outlet opening of 4.5 mm. The extruder is operated under a temperature profile in which each zone is heated to 180° C. except that the die zone is heated to 170° C. The extruder is operated at a speed of 80 rpm. The feed rate of the polymer composition to the extruder is 0.53 kg / h. The extruder is equipped with an air gun to provide cooled air to the tapered die.

[0062] As the material, a molten-carbon ... 3 UHMWPE with a density of 960kg / m 3 A density of 1.3 g / 10 min, a melt mass flow rate (190° C., 2.16 kg) of 7.6 g / 10 min and a Mv of 78,000 g / mol of HDPE. All formulations produced contained 0.5 wt % of an antioxidant (Irganox 1010). The experimental formulations prepared are listed in the table below.

[0063] During extrusion, the pressure at the inlet of the die assembly, also known as the back pressure, was measured. The results are shown in Table 1 below.

[0064] Table 1

[0065] Example UHMWPE HDPE 1 99.5% by weight 0% by weight 2 94.5% by weight 5.0 wt% 3 89.5% by weight 10.0 wt% 4 79.5% by weight 20.0 wt% 5 69.5% by weight 30.0 wt% 6 59.5% by weight 40.0% by weight 7 49.5% by weight 50.0% by weight 8 0% by weight 99.5% by weight

[0066] The product obtained was cut into pellets for further processing.

[0067] The samples of the products obtained in each example were then processed into test specimens via compression molding using a CARVER press (1NE100). The pellets were placed between two steel plates. Compression molding was performed at 200° C. and 10 MPa pressure for 20 min.

[0068] In addition, a sample of the product obtained in each example was subsequently processed into a test sample via injection molding using an Arburg Allrounder 270A machine with an ASTM D-638 V-type tensile test bar mold and an ASTM D-4020 impact test bar mold. The injection molding was carried out at a melt temperature of 235° C. and a mold temperature of 80° C. The injection speed was 20 cm 3 / s, injection pressure is 1700 bar, back pressure is 40 bar, holding pressure is 800 bar, holding time is 20 seconds, screw speed is 300 rpm.

[0069] In the samples obtained by compression molding and injection molding, tensile strength and impact strength were measured for each sample. According to ASTM D638-14 method, an Instron 5967 tester equipped with a 30 kN load cell was used to measure the tensile strength. The compression molded samples obtained by the above method were punched into V-shaped tensile bars for testing.

[0070] Impact strength was determined according to ASTM D4020-11 using a double notched cantilever beam specimen tested using a pendulum impact tester with a pendulum of 5.4 J from Custom Scientific Instruments. Impact test specimens with a thickness of 3 mm were processed from compression molded sheets. Impact test specimens from injection molded examples were used, as obtained by the above method. Impact strength tests were conducted at both room temperature (23° C.) and -40° C.

[0071] The tensile strength and impact strength test results are shown in Table 2 below, where CM refers to compression molded samples and IM refers to injection molded samples.

[0072] Table 2

[0073]

[0074] In order to determine the thermal properties of the materials, DSC analysis was performed on the materials in the examples. DSC analysis was performed using a TA instrument Q20 device according to ASTM F2625-10A standard. A sample of 5-10 mg was scanned from 30°C to 200°C at a rate of 10°C / min in a nitrogen atmosphere, kept for 3 min, cooled to a temperature of 30°C at 10°C / min, and then heated again to 200°C at the same heating rate of 10°C / min for a second time. The calculation of crystallinity (χ) was performed according to the following formula:

[0075]

[0076] Where ΔH f 0= 289.3 J / g, for a given example, ΔH f is the crystallization enthalpy of the sample obtained from DSC measurement.

[0077] The DSC measurement results are shown in Table 3 below.

[0078] Table 3

[0079] Example <![CDATA[T m (℃)]]> χ(%) <![CDATA[T c,开始 (℃)]]> <![CDATA[T c,峰值 (℃)]]> <![CDATA[T c,偏移 (℃)]]> 1 135.3 53.9 115.7 109.2 96.7 2 135.6 56.4 116.2 109.5 96.5 3 136.7 59.5 116.4 109.9 96.9 4 136.4 62.9 116.8 109.7 98.7 5 136.4 65.9 117.3 110.1 98.7 6 136.0 71.2 117.6 111.3 99.1 7 136.6 76.5 118.0 110.2 99.2 8 132.6 87.0 118.2 115.3 109.1

Claims

1. A polymer composition comprising Ultra-high molecular weight polyethylene (UHMWPE), and ≥5.0 and ≤50.0 wt. %, preferably ≥5.0 and ≤40.0 wt. %, more preferably ≥5.0 and ≤30.0 wt. %, even more preferably ≥5.0 and ≤20.0 wt. % of a high-density polyethylene (HDPE), or ≥6.0 and ≤40.0 wt. %, more preferably ≥6.0 and ≤35.0 wt. %, even more preferably ≥15.0 and ≤35.0 wt. % of said HDPE, Relative to the total weight of the polymer composition; Preferably, the HDPE is a homopolymer of ethylene or a copolymer of ethylene and a comonomer, wherein the comonomer may be one selected from 1-butene, 1-hexene or 1-octene.

2. The polymer composition according to claim 1, wherein the polymer composition comprises ≥ 95.0 wt.-% of the sum of the UHMWPE and the HDPE, relative to the total weight of the polymer composition, or wherein the polymer composition consists of the UHMWPE, the HDPE and ≤ 1.0 wt.-%, preferably ≤ 0.5 wt.-% of additives.

3. The polymer composition according to any one of claims 1 to 2, wherein the UHMWPE has a viscosity average molecular weight (Mv) of ≥ 2,000,000 g / mol, preferably ≥ 2,000,000 and ≤ 8,000,000 g / mol, more preferably ≥ 3,000,000 and ≤ 8,000,000 g / mol, even more preferably ≥ 4,000,000 and ≤ 8,000,000 g / mol, still even more preferably ≥ 5,000,000 and ≤ 8,000,000 g / mol, wherein Mv is calculated via the Margolies formula based on the intrinsic viscosity, wherein the intrinsic viscosity is determined according to the method set forth in ASTM D2857-95 (Re2007) at a temperature of 135°C in decalin as solvent.

4. The polymer composition according to any one of claims 1 to 3, wherein the HDPE has a hardness of ≥946 and ≤975 kg / m2 as determined according to ASTM D792 (2008). 3 , preferably ≥950 and ≤970kg / m 3 , more preferably ≥950 and ≤965kg / m 3 density.

5. The polymer composition of any one of claims 1-4, wherein the HDPE has: a molecular weight of ≥50,000 and ≤500,000 g / mol, preferably ≥50,000 and ≤300,000 g / mol, more preferably ≥75,000 and ≤250,000 g / mol; and / or A melt mass flow rate of ≥0.1 and ≤100 g / 10 min, preferably ≥0.5 and ≤50 g / 10 min, more preferably ≥1.0 and ≤25 g / 10 min, even more preferably ≥3.0 and ≤15.0 g / 10 min, still even more preferably ≥5.0 and ≤10.0 g / 10 min, measured at 190° C. under a load of 2.16 kg according to ASTM D1238 (2013).

6. A polymer object comprising or consisting of a composition according to any one of claims 1 to 5, wherein the object is a pellet having a diameter of 2 to 7 mm and a length of 2 to 10 mm, preferably a diameter of 3 to 5 mm and a length of 4 to 6 mm.

7. The polymer object according to claim 6, wherein the UHMWPE and the HDPE are uniformly and indifferently distributed.

8. The polymer object according to any one of claims 6-7, wherein the object is produced via a method comprising: i. supplying a certain amount of UHMWPE and ≥5.0 and ≤50.0 wt. %, preferably ≥5.0 and ≤40.0 wt. %, more preferably ≥5.0 and ≤30.0 wt. %, even more preferably ≥5.0 and ≤20.0 wt. % of said HDPE, or ≥6.0 and ≤40.0 wt. %, more preferably ≥6.0 and ≤35.0 wt. %, even more preferably ≥15.0 and ≤35.0 wt. % of said HDPE to a polymer extruder component; ii. conveying the polymer composition through the polymer extruder; iii. conveying the polymer composition through the die assembly; and iv. forming the polymer composition leaving the polymer extruder into pellets through the outlet of the die assembly, which is carried out as follows: a) cooling the polymer composition to a temperature below the melting temperature, preferably below 100° C., and subsequently cutting the obtained cooled strands into pellets; or b) cutting the polymer composition into pellets and subsequently cooling the pellets to below the melting temperature, preferably to below 100° C.; wherein the polymer extruder assembly comprises a material inlet (6), an extruder barrel (7) comprising one or two extruder screws (8), and an outlet (9) for removing processed material from the extruder, wherein the outlet comprises a die assembly, the die assembly comprising a circularly enclosed straight channel (1), the straight channel comprising an inlet (2) and an outlet (3), the straight channel being configured such that material can be conveyed through the channel along a flow axis (4) from the inlet toward the outlet, wherein the channel comprises a housing (5) to form a shell completely surrounding the channel; in, The channel comprises a buffer section having a length A and a compression section having a length B, the buffer section being located at an inlet side of the channel, and the compression section being located at an outlet side of the channel, the buffer section and the compression section being connected to each other; wherein the buffer section has a first diameter D1 perpendicular to the flow axis on one side of the inlet of the channel and a second diameter D2 perpendicular to the flow axis on the side facing the outlet of the channel, wherein D1>D2, preferably forming a tapered channel section at an angle α; wherein the compression section has a first diameter D3 perpendicular to the flow axis on the side facing the inlet of the channel, which corresponds to D2, and a second diameter D4 perpendicular to the flow axis on the side facing the outlet of the channel, wherein D3>D4, forming a tapered channel section at an angle β; Preferably, wherein the angle α>β; and Preferably, D4 is a circular opening, and more preferably, each of D1 , D2 , D3 and D4 is circular.

9. Method for producing a polymer object according to claim 8, wherein the angle β is preferably ≥ 1.0° and ≤ 10.0°, preferably ≥ 1.5° and ≤ 5.0°.

10. A method for producing a shaped article, wherein the method comprises compression molding using a polymer object according to any one of claims 6 to 8.

11. The method according to claim 10, wherein compression molding is performed by feeding the polymer object into an open and heated mold cavity, followed by closing the two mold halves, providing compression, and subsequent cooling to give the article a final shape.

12. A compression molded article comprising a polymer composition according to any one of claims 1 to 5 or produced using a polymer object according to any one of claims 6 to 8.

13. Method for producing a shaped article, wherein the method comprises injection molding using a polymer object according to any one of claims 6 to 8.

14. The method of claim 13, wherein the injection molding is performed by melting the polymer object in a machine barrel and then injecting the polymer melt under pressure into a closed cavity in a mold where the polymer solidifies and forms a final article shaped by the cavity.

15. An injection molded article comprising the polymer composition according to any one of claims 1 to 5 or produced using the polymer object according to any one of claims 6 to 8.

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