A method for forming ultra-high molecular weight polyethylene strips

Abstract

This application discloses a method for forming ultra-high molecular weight polyethylene (UHMWPE) strips, comprising the following steps: Step 1: Mixing UHMWPE resin with a low molecular weight solvent to prepare a uniform suspension, then extruding at high temperature, and finally cooling and shaping to obtain a gel film; Step 2: Performing uniaxial high-temperature ultra-high-stretching on the gel film; Step 3: Extracting away the low molecular weight solvent from the stretched gel film, and then drying it with hot air to obtain a dried film; Step 4: Longitudinally cutting the dried film to form strips; Step 5: Performing low-magnification uniaxial thermal stretching on the strips to remove pores, obtaining the final UHMWPE strip. Performing uniaxial thermal stretching on the gel film without removing the low molecular weight solvent helps promote the orientation of the retained fibrous extended chain crystals and the formation of highly oriented crystals such as subsequent extended chain crystals in the gel film, thereby helping to improve the tensile mechanical properties and other properties of the final strip.

Description

Technical Field

[0001] This application relates to the field of polymer technology, and more specifically, to a method for molding ultra-high molecular weight polyethylene strips. Background Technology

[0002] Ultra-high molecular weight polyethylene (UHMWPE) is a thermoplastic engineering plastic with excellent comprehensive properties, typically ranging from 1 million to 6 million or even higher. Films made from UHMWPE exhibit excellent wear resistance and good anti-adhesion properties, finding wide applications in civilian, medical, and military fields. Therefore, its industrial production is of great significance. For many years, technicians in UHMWPE materials and related fields have been exploring methods suitable for the industrial production of UHMWPE films. In particular, obtaining high-performance UHMWPE strips has become a technical challenge that researchers in related fields have been eager to solve.

[0003] To prepare ultra-high molecular weight polyethylene (UHMWPE) strips with excellent mechanical properties, a gel molding method can be used. First, UHMWPE is mixed with a suitable solvent and dissolved at high temperature to form a solution. Then, a gel film is generated through gel molding. The gel film is first extracted and dried, and then the dried film is cut to form strips. Finally, uniaxial multi-stage thermal stretching is performed to obtain the finished UHMWPE strips.

[0004] Because the resin has an extremely high molecular weight, the viscosity is very high when all the resin is completely dissolved, and the conditions for preparing a homogeneous solution are harsh, making it difficult to obtain a high-concentration homogeneous solution. Moreover, because the resin requires a very high dissolution temperature, the molecular weight of ultra-high molecular weight polyethylene decreases significantly, affecting the mechanical properties of the final strip.

[0005] Patent CN115302751A discloses a process for preparing ultra-high molecular weight polyethylene (UHMWPE) films while retaining extended chain crystals. By precisely controlling the temperature during the preparation of the UHMWPE solution, only the lower-melting-point folded chain lamellar crystals in the UHMWPE are dissolved at low temperatures, while the partial dissolution of extended chain crystals in the resin is retained. This reduces the viscosity of the UHMWPE solution and minimizes the molecular weight reduction caused by high processing temperatures. The extended chain crystals retained during the dissolution process act as highly efficient nucleating agents for UHMWPE crystallization, inducing the formation of both extended chain crystals and folded chain lamellar crystals during the hot stretching process after extraction and drying.

[0006] Through in-depth and systematic research on the stretching process of ultra-high molecular weight polyethylene (UHMWPE) with retained extended chain crystals, it was found that if the gel film is subjected to uniaxial thermal stretching, the retained fibrous extended chain crystals are more easily oriented due to the presence of low molecular weight solvents, and the formation of highly oriented crystals such as extended chain crystals is more easily promoted. This significantly improves the tensile mechanical properties and other properties of the final strip, forming a unique UHMWPE strip forming process. Summary of the Invention

[0007] To further improve the mechanical properties of ultra-high molecular weight polyethylene (UHMWPE) strips, this application provides a method for molding UHMWPE strips.

[0008] This application provides a method for forming ultra-high molecular weight polyethylene strips, comprising the following steps:

[0009] Step 1: Mix ultra-high molecular weight polyethylene resin with low molecular weight solvent to prepare a uniform suspension, then extrude at high temperature, and then cool and shape to obtain a gel film.

[0010] Step 2: Perform uniaxial high-temperature super-stretching on the gel film;

[0011] Step 3: Extract the low molecular weight solvent from the stretched gel film, and then dry it with hot air to obtain a dried film;

[0012] Step 4: Cut the dried film longitudinally to form strips;

[0013] Step 5: Perform low-magnification uniaxial thermal stretching on the strip to remove pores, obtaining the final ultra-high molecular weight polyethylene strip.

[0014] By adopting the above technical solution, the gel film is uniaxially thermally stretched without removing the low molecular weight solvent. In this way, the low molecular weight solvent helps to promote the orientation of the fibrous extended chain crystals retained in the gel film and the formation of highly oriented crystals such as subsequent extended chain crystals, thereby helping to significantly improve the tensile properties and other properties of the final strip.

[0015] Preferably, in the high-temperature extrusion process of step 1, the temperature of the feeding section of the twin-screw extruder is 80-130℃, the temperature of the compression section is 130-200℃, the temperature of the homogenization section is 130-200℃, the temperature of the die head is 130-200℃, and the rotation speed of the twin-screw extruder is 30-400 r / min.

[0016] By adopting the above technical solution, when the temperature of the compression section, homogenization section, and die of the twin-screw extruder exceeds 200°C, most of the extended chain crystals in the ultra-high molecular weight polyethylene resin will be dissolved. However, when the temperature is below 130°C, almost all the lamellar crystals in the ultra-high molecular weight polyethylene resin will be retained, which will affect the dissolution effect of the ultra-high molecular weight polyethylene resin, resulting in decreased fluidity and consequently uneven extruded gel film.

[0017] Preferably, the temperature of the compression section, homogenization section, and die of the twin-screw extruder is 130–170°C.

[0018] By adopting the above technical solution, when the temperature of the compression section, homogenization section and die head of the twin-screw extruder is controlled at 130-170℃, it is beneficial for most of the extended chain crystals in the ultra-high molecular weight polyethylene resin to be retained without being dissolved, while also ensuring the fluidity of the ultra-high molecular weight polyethylene resin after dissolution, so that the gel film is uniform.

[0019] Preferably, in step 2, the temperature of uniaxial super-stretching is 90–130°C, the stretching rate is 5–80 m / min, and the stretching ratio is 6–18 times.

[0020] Preferably, the temperature for uniaxial super-stretching is 100–120°C.

[0021] By adopting the above technical solution, the low hot stretching temperature results in insufficient orientation of the retained extended chain crystals and an insignificant promoting effect on the subsequent formation of highly oriented crystals; the high hot stretching temperature makes the ultra-high molecular weight polyethylene gel film prone to detangling, leading to a decrease in the mechanical properties of the strip, instability in the hot stretching process, and instability in the film quality.

[0022] Preferably, the stretching rate of uniaxial high-temperature super-expansion hot stretching is 10 to 60 m / min.

[0023] By adopting the above technical solution, the low stretching rate makes the oriented molecular chains more prone to deorientation under the action of low molecular weight solvent, thus affecting the mechanical properties of the final ultra-high molecular weight polyethylene strip and also affecting production efficiency; while excessive stretching rate will affect the stretching stability of the gel film.

[0024] Preferably, the stretching ratio of uniaxial high-temperature super-stretching is 10 to 15 times.

[0025] By adopting the above technical solution, the uniaxial thermal stretching ratio of the gel film is low, and the number of newly formed extended chain crystals retained during the stretching process is insufficient, which cannot significantly improve the mechanical properties of the final strip; if the uniaxial stretching ratio of the gel film is too high, it will affect the stretching stability.

[0026] Preferably, the low molecular weight solvent is one or more of decahydronaphthalene, white oil, or long straight-chain alkanes.

[0027] By adopting the above technical solutions, the aforementioned low molecular weight solvents can easily dissolve ultra-high molecular weight polyethylene resin, thereby facilitating the orientation of the retained fibrous extended chain crystals and the formation of highly oriented crystals such as subsequent extended chain crystals during the hot stretching process of the gel film.

[0028] Preferably, the low molecular weight solvent is a long straight-chain alkane.

[0029] By adopting the above technical solution, since long straight-chain alkanes are C12 to C16 n-alkanes, and the chain structure of long straight-chain alkanes is similar to that of ultra-high molecular weight polyethylene, it is easier to precisely control the retention of extended chain crystals during the dissolution of ultra-high molecular weight polyethylene resin and the formation of highly oriented crystals during the thermal stretching of the gel film.

[0030] Preferably, the mass ratio of ultra-high molecular weight polyethylene to low molecular weight solvent in step 1 is (0.18-0.45):1.

[0031] By employing the above technical solution, the method of partially dissolving a small amount of ultra-high molecular weight polyethylene (UHMWPE) resin reduces the actual dissolved concentration. The high rigidity of the retained extended-chain crystals allows the solution to exhibit characteristics similar to a liquid crystal solution, significantly reducing the viscosity of the UHMWPE solution. However, excessively low resin content leads to insufficient entanglement within the prepared gel film, affecting its mechanical properties; excessively high resin content, on the other hand, affects the partial dissolution effect. To balance the UHMWPE resin dissolution effect with the mechanical properties of the strip, the above-mentioned range is preferred.

[0032] Preferably, the temperature for hot stretching the strip after extraction and drying in step 5 is 120-150°C, and the stretching ratio is 1.5-4 times.

[0033] By employing the above technical solutions, the low hot stretching temperature and weak melt recrystallization effect mean that the porosity caused by extraction and drying cannot be completely eliminated; the high hot stretching temperature makes it easy for de-entanglement to occur in the ultra-high molecular weight polyethylene film, causing problems such as instability in the hot stretching process and film quality. At the same time, the low longitudinal hot stretching ratio cannot completely eliminate the porosity in the dried film, affecting the mechanical properties of the final film; and the excessively high uniaxial stretching ratio will affect the stability of film stretching.

[0034] In summary, this application has the following beneficial effects:

[0035] 1. Since the gel film in this application is subjected to uniaxial high-temperature super-stretching without removing the low molecular weight solvent, this not only helps to promote the orientation of the fibrous extended chain crystals retained in the gel film, but also facilitates the formation of highly oriented crystals such as extended chain crystals in the subsequent process, thereby greatly improving the tensile properties and other properties of the final ultra-high molecular weight polyethylene strip.

[0036] 2. In this application, the temperature of the compression section, homogenization section and die head of the twin-screw extruder is controlled at 130-170℃, which is beneficial to the retention of most of the extended chain crystals in the ultra-high molecular weight polyethylene resin without being dissolved, and also ensures the fluidity of the ultra-high molecular weight polyethylene resin after dissolution, so that the produced gel film is more uniform.

[0037] 3. In this application, long-chain alkanes are selected as low-molecular-weight solvents because long-chain alkanes are C12 to C16 n-alkanes. The chain structure of long-chain alkanes is similar to that of ultra-high molecular weight polyethylene, making it easier to precisely control the retention of extended chain crystals during the dissolution of ultra-high molecular weight polyethylene resin and the formation of highly oriented crystals during the thermal stretching of the gel film;

[0038] 4. In this application, the uniaxial high-temperature super-stretching ratio of the gel film is 10 to 15 times. This can ensure the orientation of the fibrous extended chain crystals in the ultra-high molecular weight polyethylene resin, thereby guaranteeing the mechanical properties of the ultra-high molecular weight polyethylene strip, while not affecting the stability of the uniaxial high-temperature super-stretching of the gel film. Attached Figure Description

[0039] Figure 1 This is an X-ray diffraction pattern of the ultra-high molecular weight polyethylene strip in Example 1 of this application.

[0040] Figure 2 This is the X-ray diffraction pattern of the ultra-high molecular weight polyethylene strip in Comparative Example 1 of this application. Detailed Implementation

[0041] The present application will be further described in detail below with reference to the accompanying drawings, embodiments and comparative examples. Example 1

[0042] A method for forming ultra-high molecular weight polyethylene strips includes the following steps:

[0043] Step 1: The viscosity-average molecular weight is 7.12 × 10⁻⁶. 6 A uniform suspension was prepared by mixing g / mol of ultra-high molecular weight polyethylene resin with long straight-chain alkanes at a mass ratio of 0.32:1. The suspension was then fed into a twin-screw extruder to dissolve the solution at high temperature. The solution was then passed through a metering pump and a slit die, and cooled and shaped by a polishing cold roller at 20°C to obtain a gel film.

[0044] Step 2: Perform uniaxial high-temperature super-stretching on the gel film;

[0045] Step 3: Immerse the stretched gel film in an ultrasonic extraction tank to remove long-chain alkanes, and then dry it with hot air to obtain a dried film.

[0046] Step 4: Cut the dried film longitudinally to form strips;

[0047] Step 5: The strip is subjected to uniaxial thermal stretching at a temperature of 135℃ to remove pores, with a stretching ratio of 3 times, thereby obtaining the final ultra-high molecular weight polyethylene strip.

[0048] The twin-screw extruder has a feeding section temperature of 105℃, a compression section temperature of 170℃, a homogenization section temperature of 170℃, and a die temperature of 170℃. The twin-screw extruder rotates at a speed of 200 r / min. The uniaxial super-stretching temperature of the gel film is 100℃, the stretching rate is 45 m / min, and the stretching ratio is 10 times. The long straight-chain alkanes are typically C12 to C16 n-alkanes, and can be single-length straight-chain n-alkanes or mixtures of long straight-chain alkanes. Unless otherwise specified, n-pentadecane is preferred in the following examples. Example 2

[0049] A method for forming ultra-high molecular weight polyethylene strips includes the following steps:

[0050] Step 1: The viscosity-average molecular weight is 7.12 × 10⁻⁶. 6 Ultra-high molecular weight polyethylene resin (g / mol) and decahydronaphthalene were mixed at a mass ratio of 0.18:1 to form a uniform suspension. The suspension was then fed into a twin-screw extruder to dissolve at high temperature to obtain a solution. The solution was then passed through a metering pump and a slit die, and cooled and shaped by a polishing cold roller at 10°C to obtain a gel film.

[0051] Step 2: Perform uniaxial high-temperature super-stretching on the gel film;

[0052] Step 3: Immerse the stretched gel film in an ultrasonic extraction tank to remove decahydronaphthalene, and then dry it with hot air to obtain a dried film.

[0053] Step 4: Cut the dried film longitudinally to form strips;

[0054] Step 5: The strip is subjected to uniaxial thermal stretching at 120℃ to remove pores, with a stretching ratio of 4 times, to obtain the final ultra-high molecular weight polyethylene strip.

[0055] The twin-screw extruder has a feeding section temperature of 80℃, a compression section temperature of 130℃, a homogenization section temperature of 130℃, and a die temperature of 130℃. The twin-screw extruder rotates at a speed of 30 r / min. The uniaxial super-stretching temperature of the gel film is 90℃, the stretching rate is 5 m / min, and the stretching ratio is 6 times. Example 3

[0056] A method for forming ultra-high molecular weight polyethylene strips includes the following steps:

[0057] Step 1: The viscosity-average molecular weight is 7.12 × 10⁻⁶. 6 Ultra-high molecular weight polyethylene resin (UHMWPE) at a mass ratio of g / mol was mixed with white oil at a mass ratio of 0.45:1 to form a uniform suspension. The suspension was then fed into a twin-screw extruder to dissolve at high temperature to obtain a solution. The solution was then passed through a metering pump and a slit die, and cooled and shaped by a polishing cold roller at 30°C to obtain a gel film.

[0058] Step 2: Perform uniaxial high-temperature super-stretching on the gel film;

[0059] Step 3: Immerse the stretched gel film in an ultrasonic extraction tank to remove the white oil, and then dry it with hot air to obtain a dried film.

[0060] Step 4: Cut the dried film longitudinally to form strips;

[0061] Step 5: The strip is subjected to uniaxial hot stretching at 150℃ to remove pores, with a stretching ratio of 1.5 times, thereby obtaining the final ultra-high molecular weight polyethylene strip.

[0062] The twin-screw extruder has the following temperature settings: feeding section temperature 130℃, compression section temperature 200℃, homogenization section temperature 200℃, and die temperature 200℃. The extruder's rotation speed is 400 r / min. The uniaxial super-stretching temperature of the gel film is 130℃, the stretching rate is 80 m / min, and the stretch ratio is 18 times. The white oil used here is Total Lyran C360B No. 70 white oil.

[0063] Comparative Example 1

[0064] The only difference between this comparative example and Example 1 is that it does not include step 2, and in step 5, it is stretched to 30 times in multiple stages at 120-150°C.

[0065] Comparative Example 2

[0066] The only difference between this comparative example and Example 2 is that it does not include step 2, and in step 5, it is stretched to 24 times in multiple stages at 120-150°C.

[0067] Comparative Example 3

[0068] The only difference between this comparative example and Example 3 is that it does not include step 2, and in step 5, it is stretched to 27 times in multiple stages at 120-150°C.

[0069] The tensile mechanical properties, thermal properties, and crystallinity properties of the ultra-high molecular weight polyethylene strips from Examples 1 to 3 and Comparative Examples 1 to 3 were tested. The specific testing methods are as follows.

[0070] Thermal performance test

[0071] Cut the ultra-high molecular weight polyethylene strip into small pieces, weigh 5-10 mg and place them in a standard aluminum crucible. Protect the crucible with a dry nitrogen gas flow and test the thermal properties of the ultra-high molecular weight polyethylene strip using a differential scanning calorimeter (DSC). Heat the strip from 25 °C to 200 °C at a heating rate of 10 °C / min and scan the temperature. Record the thermal property curve of the strip.

[0072] Crystallinity and orientation tests

[0073] The crystallinity and orientation of the ultra-high molecular weight polyethylene (UHMWPE) strips were measured using wide-angle X-ray diffraction (WAXD) at a wavelength of 0.124 nm. Two-dimensional WAXD results were collected using a Pilatus 900K detector with a resolution of 172 × 172 μm. 2 The distance from the detector to the sample was 210 mm. WAXD data was obtained by processing the data using FIT2D software. One-dimensional integration was performed on the two-dimensional WAXD image to obtain the intensity distribution curve in the 2θ direction. Then, peak fitting was performed on the curve to calculate the ratio of amorphous to crystalline regions, and subsequently, the crystallinity was calculated. The calculation formula is as follows: Xc = Ac / (Ac + Aa), where Ac and Aa represent the areas under the crystalline peak and amorphous peak of the I(2θ)~2θ curve, respectively.

[0074] The Hermans method was used to determine the crystal orientation of ultrathin molecular weight polyethylene strips. Taking the strip stretching direction as the reference direction, and assuming the crystal plane is hkl, the orientation parameters can be expressed as:

[0075]

[0076] in, Ф For azimuth, I( Ф The scattering intensity is along the azimuth angle. Orientation. f It can be calculated using the following formula:

[0077]

[0078] when f When = -0.5, the normal direction of the crystal plane is perpendicular to the reference direction; when fWhen = 1, the normal direction of the crystal plane is parallel to the reference direction; when f When = 0, the normals of the crystal planes are freely oriented.

[0079] Tensile mechanical property testing:

[0080] The tensile mechanical properties of ultra-high molecular weight polyethylene strips were tested at room temperature using a universal mechanical testing machine. The strips were stretched at a speed of 50 mm / min to characterize their mechanical properties. At least five samples were used for each strip to obtain the average value and standard deviation.

[0081] Based on the above detection method, the test results of Examples 1 to 3 and Comparative Examples 1 to 3 were obtained, as shown in Table 1 below:

[0082] Table 1

[0083] Testing items Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Melting point (°C) 150.5 148.2 149.1 145.5 143.0 144.2 Crystallinity (%) 96.9 94.4 95.2 93.1 91.1 92.0 Orientation 0.95 0.93 0.94 0.91 0.89 0.90 Tensile strength (GPa) 5.04±0.25 4.29±0.21 4.64±0.22 3.51±0.18 3.10±0.16 3.31±0.17 Tensile modulus (GPa) 185.16±9.32 152.67±7.68 159.74±7.89 132.3±6.58 121.8±6.02 125.8±6.12

[0084] The detection results of Examples 1 to 3 and Comparative Examples 1 to 3 were compared respectively, and the results were attached. Figure 1 and attached Figure 2 As demonstrated, when the low molecular weight solvent is not removed, uniaxial high-temperature super-stretching of the gel film makes it easier to retain the orientation of the fibrous extended chain crystals and promotes the formation of highly oriented crystals such as the extended chain crystals, thereby effectively improving the tensile strength and tensile modulus of the final ultra-high molecular weight polyethylene strip. Example 4

[0085] The only difference between this comparative example and Example 1 is that the temperature of the compression section, homogenization section, and die of the twin-screw extruder is 200°C. Example 5

[0086] The only difference between this comparative example and Example 1 is that the temperature of the compression section, homogenization section, and die of the twin-screw extruder is 130°C.

[0087] Comparative Example 4

[0088] The only difference between this comparative example and Example 1 is that the temperature of the compression section, homogenization section, and die of the twin-screw extruder is 120°C.

[0089] Comparative Example 5

[0090] The only difference between this comparative example and Example 1 is that the temperature of the compression section, homogenization section, and die of the twin-screw extruder is 210°C.

[0091] The ultra-high molecular weight polyethylene (UHMWPE) strips of Examples 4 and 5, as well as Comparative Examples 4 and 5, were tested according to the testing methods described in Table 1 above. The test results for the UHMWPE strips are shown in Table 2 below.

[0092] Table 2

[0093] Testing items Example 4 Example 5 Comparative Example 4 Comparative Example 5 Melting point (°C) 150.6 148.1 / 145.2 Crystallinity (%) 96.8 93.4 / 91.4 Orientation 0.94 0.93 / 0.91 Tensile strength (GPa) 4.89±0.29 4.14±0.24 / 3.45±0.19 Tensile modulus (GPa) 178.23±11.25 140.34±8.98 / 134.65±6.68 Film-forming properties Film formation was relatively smooth and stable. Successful and stable film formation Unable to form a stable film Successful and stable film formation

[0094] Comparing the test results of Examples 1, 4, and 5, as well as Comparative Examples 4 and 5, it can be seen that when the temperature of the compression section, homogenization section, and die head of the twin-screw extruder is controlled at 130–200°C, especially at 130–170°C, the ultra-high molecular weight polyethylene strips finally prepared have good tensile strength and tensile modulus. Example 6

[0095] The only difference between this embodiment and Example 1 is that the low molecular weight solvent is decahydronaphthalene. Example 7

[0096] The only difference between this embodiment and Example 1 is that the low molecular weight solvent is white oil.

[0097] The ultra-high molecular weight polyethylene strips of Examples 6 and 7 were tested according to the testing methods in Table 1 above, and the test results are shown in Table 3 below.

[0098] Table 3

[0099] Testing items Example 6 Example 7 Melting point (°C) 149.1 149 Crystallinity (%) 95.2 95 Orientation 0.94 0.94 Tensile strength (GPa) 4.89±0.26 4.81±0.26 Tensile modulus (GPa) 174.8±9.23 173.9±9.21

[0100] A comparison of the test results from Examples 1, 6, and 7 shows that using long-chain alkanes as low-molecular-weight solvents is beneficial for improving the mechanical properties of the final ultra-high molecular weight polyethylene strips. Example 8

[0101] The only difference between this embodiment and Embodiment 1 is that the stretching ratio of the gel film in the uniaxial super-stretching is 15 times. Example 9

[0102] The only difference between this embodiment and Embodiment 1 is that the stretching ratio of the gel film in the uniaxial super-stretching is 6 times. Example 10

[0103] The only difference between this embodiment and Embodiment 1 is that the stretching ratio of the gel film in the uniaxial super-stretching is 18 times.

[0104] The ultra-high molecular weight polyethylene strips from Examples 8 to 10 were tested according to the testing methods described in Table 1 above. The specific test results are shown in Table 4 below.

[0105] Table 4

[0106] Testing items Example 8 Example 9 Example 10 Melting point (°C) 151.2 148.9 151.3 Crystallinity (%) 97.4 94.9 97.5 Orientation 0.96 0.93 0.96 Tensile strength (GPa) 5.48±0.29 4.23±0.20 5.54±0.58 Tensile modulus (GPa) 197.63±11.24 155.21±7.84 199.88±21.44 Film-forming properties Successful and stable film formation Successful and stable film formation The membrane is prone to breakage during stretching.

[0107] A comparison of the test results from Examples 1, 8 to 10 shows that when the stretching rate of the gel film during uniaxial super-stretching is 10 to 15 times, it can ensure the mechanical properties of the ultra-high molecular weight polyethylene strip without affecting the stretching stability of the ultra-high molecular weight polyethylene gel film. Example 11

[0108] The only difference between this embodiment and Embodiment 1 is that the temperature for uniaxial super-stretching of the gel film is 120°C. Example 12

[0109] The only difference between this embodiment and Embodiment 1 is that the temperature for uniaxial super-stretching of the gel film is 90°C. Example 13

[0110] The only difference between this embodiment and Embodiment 1 is that the temperature for uniaxial super-stretching of the gel film is 130°C.

[0111] The ultra-high molecular weight polyethylene strips of Examples 11 to 13 were tested according to the testing methods in Table 1 above. The specific test results are shown in Table 5 below.

[0112] Table 5

[0113] Testing items Example 11 Example 12 Example 13 Melting point (°C) 151.5 148.3 149.4 Crystallinity (%) 97.3 94.4 95.8 Orientation 0.96 0.93 0.94 Tensile strength (GPa) 5.42±0.25 4.42±0.28 4.82±0.26 Tensile modulus (GPa) 195.65±9.37 164.18±10.52 179.54±10.24

[0114] A comparison of the test results from Examples 1 and 11 to 13 shows that when the temperature of uniaxial super-tense thermal stretching of the gel film is 100-120°C, the retained extended chain crystals can be rapidly oriented and promote the formation of subsequent highly oriented crystals. Moreover, the molecular chains in the gel film are not prone to de-entanglement during the stretching process, and the thermal stretching process is stable. Therefore, the mechanical properties of the final ultra-high molecular weight polyethylene strip are better.

[0115] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for forming ultra-high molecular weight polyethylene strips, characterized in that: Includes the following steps, Step 1: Mix ultra-high molecular weight polyethylene resin with long straight-chain alkanes to form a uniform suspension, then extrude it at high temperature, and then cool and shape it through a polishing cold roller at 20°C to obtain a gel film. Step 2: Perform uniaxial high-temperature super-stretching on the gel film; Step 3: Extract the long-chain alkanes from the stretched gel film, and then dry it with hot air to obtain a dried film; Step 4: Cut the dried film longitudinally to form strips; Step 5: Perform low-magnification uniaxial thermal stretching on the strip to remove pores, and obtain the final ultra-high molecular weight polyethylene strip; In step 2, the uniaxial high-temperature super-expansion temperature is 90-130℃, the stretching rate is 5-80m / min, and the stretching ratio is 6-18 times. In step 1, the high-temperature extrusion is achieved by a twin-screw extruder. The temperature of the feeding section of the twin-screw extruder is 80-130℃, the temperature of the compression section is 130-170℃, the temperature of the homogenization section is 130-170℃, and the temperature of the die is 130-170℃. The rotation speed of the twin-screw extruder is 30-400r / min. In step 1, the mass ratio of ultra-high molecular weight polyethylene resin to long straight-chain alkanes is (0.18-0.45):

1.

2. The method for forming ultra-high molecular weight polyethylene strips according to claim 1, characterized in that: The temperature for uniaxial high-temperature super-stretching of the gel film is 100-120℃.

3. The method for forming ultra-high molecular weight polyethylene strips according to claim 1, characterized in that: The stretching ratio during uniaxial high-temperature super-stretching is 10 to 15 times.

4. The method for forming ultra-high molecular weight polyethylene strips according to claim 1, characterized in that: In step 5, the temperature for uniaxial thermal stretching of the strip after extraction and drying is 120–150℃, and the stretching ratio is 1.5–4 times.

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