A low breakage rate high uniformity solvent-free high molecular weight polyethylene fiber and a method for preparing the same

Abstract

This invention discloses a solvent-free high molecular weight polyethylene fiber with low breakage rate and high uniformity, and its preparation method, belonging to the technical field of polyethylene fiber preparation. To address the difficulty in balancing melt plasticization and molecular chain degradation in solvent-free polyethylene spinning technology, and to improve the mechanical properties of the finished fiber, this invention provides a solvent-free high molecular weight polyethylene fiber with low breakage rate and high uniformity, and its preparation method. This invention employs a twin-screw low-shear plasticization system, a stepped gradient negative pressure devolatilization process, and a three-stage gradient cooling zone. While fully preserving the integrity of the long polyethylene molecular chains, it effectively removes melt impurities, regulates the crystal structure, and thus improves the mechanical properties of the finished fiber.

Description

Technical Field

[0001] This invention belongs to the field of polyethylene fiber preparation technology, specifically relating to a solvent-free high molecular weight polyethylene fiber with low breakage rate and high uniformity, and its preparation method. Background Technology

[0002] High molecular weight polyethylene (HMWPE) possesses excellent comprehensive properties such as high strength, high modulus, impact resistance, corrosion resistance, and wear resistance, and is widely used in bulletproof protection, aerospace, and composite materials. Currently, the mainstream manufacturing process is gel spinning followed by super-stretching. Gel spinning utilizes organic solvents to swell and dissolve polyethylene resin powder, reducing the system viscosity, simplifying processing, and achieving stable spinnability.

[0003] During gel spinning, organic solvents are difficult to completely remove during the extrusion, cooling, and stretching processes of spinning preparation. Residual organic solvents can form micropores, voids, and interface defects inside the fiber, resulting in poor fiber size uniformity and large dispersion of mechanical properties. The gel spinning system also contains defects such as dissociated molecular chains, insufficiently swollen particles, and local gel agglomeration, which can cause uneven viscosity of the gel melt and extremely poor rheological stability. During extrusion, the instantaneous viscosity of the melt fluctuates, and the melt flow rate fluctuations can easily cause fuzzy fibers, floating fibers, and sudden changes in the thickness of the fibers, leading to frequent fiber breakage.

[0004] In solvent-free processing systems, high molecular weight polyethylene melt has extremely high viscosity. If the shear rate is too low, the powder plasticization will be incomplete, resulting in poor mixing uniformity. If the shear rate is too high, it will cause the macromolecular bonds to break and degrade, leading to a decrease in the mechanical properties of the fiber. How to balance the melt plasticization effect and the molecular chain degradation is an urgent problem to be solved in the solvent-free polyethylene fiber process.

[0005] Patent CN109306541B discloses a method for preparing high-strength, high-modulus polyethylene fiber. This patent involves blending polyethylene raw materials with a weight-average molecular weight of 600,000 to 1,200,000, obtained by polymerization with a single-active-center catalyst, with additives. The blend is then extruded into undrawn polyethylene filaments using a screw extruder. After cooling, the undrawn filaments undergo high-temperature, multi-stage stretching in a hot runner. The multi-stage stretched polyethylene fibers are then wound up to obtain polyethylene fibers with a tensile strength of ≥25 cN / dtex and a tensile modulus of ≥900 cN / dtex. However, this method suffers from the difficulty in fully removing trace volatile components and thermal degradation byproducts generated during processing, resulting in the presence of microbubbles in the melt, which can lead to fiber breakage during subsequent spinning and stretching.

[0006] In summary, to address the problem of poor mechanical properties of finished fibers due to the difficulty in balancing melt plasticization and molecular chain degradation in existing solvent-free polyethylene spinning technologies, this paper proposes a solvent-free high molecular weight polyethylene fiber with low breakage rate and high uniformity, along with its preparation method, with the aim of improving the mechanical properties of the finished fiber. Summary of the Invention

[0007] The purpose of this invention is to provide a solvent-free high molecular weight polyethylene fiber with low breakage rate and high uniformity, and a method for preparing the same, in order to solve the problems mentioned in the background art.

[0008] The above-mentioned technical objective of this invention is achieved through the following technical solution: a solvent-free high molecular weight polyethylene fiber with low breakage rate and high uniformity, wherein the solvent-free high molecular weight polyethylene fiber with low breakage rate and high uniformity meets the following parameters: molecular weight is 1.2 × 10⁻⁶. 5 ~5.8×10 5 The apparent density is 0.36~0.62 g / cm³. 3 The melting temperature is 126℃~137℃.

[0009] A method for preparing the aforementioned low breakage rate, high uniformity, solvent-free high molecular weight polyethylene fiber includes the following steps: S1: The linear polyethylene resin powder is compressed to remove air and subjected to negative pressure extraction. It is then dispersed by low-speed stirring and conveyed into the twin-screw extruder under N2 environment. S2: A loss-in-weight feeding metering device is used to transport the hindered phenolic primary antioxidant and phosphite secondary antioxidant to the front preheating section of the twin-screw extruder; S3: Dicumyl peroxide initiator and acrylate multifunctional monomers are fed to the melting zone of a twin-screw extruder using a side feeder; the twin-screw extruder is equipped with a barrier zone and a low-shear mixing zone; the maximum temperature of the extrusion equipment is controlled at 210℃; S4: The melt flows through the multi-stage vacuum channel of the twin-screw extruder and undergoes multi-stage vacuum devolatilization. The processed melt is then conveyed to the devolatilization kettle, melt pump, graded filter, metering pump, and finally to the spinning box. S5: The spinning box operates at a constant temperature. The melt inside the box is extruded from the spinneret holes to form a continuous gel-state filament. The filament enters the cooling channel for gradient cooling and shaping. The cooling channel is equipped with a high-precision infrared temperature feedback system. After cooling and shaping, the filament is oiled by the oiling roller. S6: The filament bundle is stretched in three stages in sequence: the first pre-stretch temperature is 112℃~126℃, the second main stretch temperature is 128℃~134℃, and the third stretch temperature is 132℃~137℃. The total stretch ratio is 8~16 times. The tension fluctuation range during the stretching process is controlled within ±2cN to obtain filaments.

[0010] Furthermore, the twin-screw extruder has a screw sequentially equipped with a conveying element, a barrier element, a 45° staggered kneading block, and a 60° staggered kneading block along the material transport direction; the screw compression ratio is 1.8~2.5, and the screw forms a low-shear distribution mixing structure; the melt residence time in the twin-screw extruder is 80~100s, and the screw speed is 180-240r / min; the twin-screw end integrates a multi-stage series vacuum devolatilization system.

[0011] The conveying element pushes the powder to be fed evenly, and the barrier element extends the powder's heating and mixing time. The 45° and 60° staggered kneading blocks adopt a mixing mode dominated by stretching rheology and assisted by weak shear, continuously compressing, stretching, and folding the melt to achieve uniform mixing. The screw compression ratio is 1.8~2.5, and the screw constitutes a low-shear distribution mixing structure. The residence time of the melt in the twin-screw extruder is 80~100s, and parameters such as the screw speed of 180-240r / min are used to control the mechanical work intensity of the screw, so that mechanical energy is smoothly converted into controllable viscous heat dissipation.

[0012] Furthermore, in S2, the stirring rate of the low-speed stirring dispersion is 30~50 r / min, and the stirring time is 3~5 min.

[0013] Furthermore, in S3, the primary antioxidant is N,N'-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hexanediamine, and the secondary antioxidant is dodecyl thiodipropionate, with a ratio of 1:1.5 to 1:2; based on the total mass of the linear polyethylene resin powder, the total addition amount of the primary antioxidant and the secondary antioxidant is 0.2wt% to 0.6wt%.

[0014] Hindered phenolic antioxidants capture free radicals and terminate the oxidation chain reaction; dodecanol thiodipropionate, a secondary antioxidant, decomposes peroxides, and the two work synergistically to inhibit the thermal oxidative degradation of the melt.

[0015] Furthermore, in S3, the amount of dicumyl peroxide added is 150~500ppm; based on the total mass of the linear polyethylene resin powder, the amount of acrylate multifunctional monomer added is 0.2wt%~0.8wt%.

[0016] Adding a trace amount of initiator can controllably generate free radicals, triggering the micrografting of acrylate monomers on the surface of polyethylene molecules, increasing the intermolecular interaction forces, and improving the rheological uniformity of high-viscosity melts.

[0017] Furthermore, in S4, the negative pressure of the vacuum devouring system is gradually increased from -0.05 to -0.08 MPa to -0.1 MPa.

[0018] The boiling points of low-molecular-weight volatiles and thermal degradation byproducts produced during processing are different. Low pressure can remove large molecules from volatile components, while high pressure can remove trace amounts of small molecules that are difficult to remove.

[0019] Furthermore, in S4, the graded filter adopts a multi-layer composite filter with a filter precision of 200-300 mesh.

[0020] Furthermore, in S5, the cooling channel is divided into three cooling zones along the direction of the filament: a homogeneous nucleation control zone, a crystal orientation growth zone, and a structure locking zone. The temperature of each cooling zone gradually decreases along the direction of the filament.

[0021] Furthermore, in S5, the temperature of the homogeneous nucleation control zone in the cooling channel is 128℃~135℃, the cooling rate is 2-5℃ / min, the temperature of the crystal orientation growth zone is 115℃~125℃, the temperature of the structure locking zone is 95℃~110℃, and the temperature fluctuation range of the cooling air is controlled within ±1℃.

[0022] The three cooling zones—homogeneous nucleation control zone, crystal orientation growth zone, and structure locking zone—correspond to the three stages of nucleation, growth, and shaping of gel-state precursor fibers, respectively. Different crystallization stages of gel precursor fibers exhibit significant differences in sensitivity to cooling rates. Independent temperature control in each zone allows for precise regulation of the fiber's microcrystalline structure, resulting in a highly uniform internal structure.

[0023] The beneficial effects of this invention are: 1. This invention employs a low-shear screw structure composed of a conveying element, a barrier element, and staggered kneading blocks. Through the moderate shearing, extrusion, and friction of the melt during the operation of the twin-screw extruder, this invention smoothly converts mechanical shear work into heat energy, achieving uniform plasticization of the melt through controllable viscous heat dissipation. This structure ensures uniform mixing of the polyethylene melt under low-shear and low-temperature rise process conditions, preserving the integrity of the long molecular chain structure of polyethylene to the greatest extent.

[0024] 2. This invention employs a step-by-step gradient negative pressure devolatilization process from low to high to remove low-molecular-weight volatiles and thermal degradation byproducts generated during polyethylene spinning, effectively eliminating microbubbles and impurities inside the melt, significantly reducing internal voids and structural defects after fiber forming, and significantly improving the overall density and mechanical load-bearing capacity of the finished fiber.

[0025] 3. This invention sets up a three-stage gradient cooling zone to match the cooling requirements of the three stages of nucleation, crystal growth and shaping of gel filaments according to their crystallization characteristics. It is equipped with a high-precision infrared temperature measurement feedback system and air temperature control to make the crystallization behavior of the filaments precise and controllable, effectively improve the problem of uneven crystal structure inside the fiber and improve the overall uniformity of the product fiber.

[0026] Appendix Explanation Table 1 is a performance comparison table of each sample in the embodiments of the present invention. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the appendix.

[0028] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. 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 are within the scope of the claims of the present invention.

[0029] Example 1 S1: Linear polyethylene resin powder with a weight-average molecular weight of 3.5 × 10⁻⁶. 5 After being vented by a compression device and impurities removed by negative pressure extraction, the speed is controlled at 40 r / min, and the mixture is stirred and dispersed at low speed for 4 minutes. Under N2 protection, it is then conveyed to a twin-screw extruder.

[0030] S2: Using a loss-in-weight feeding metering device, the main antioxidant N,N'-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hexanediamine and the auxiliary antioxidant disodium thiodipropionate are uniformly mixed at a mass ratio of 1:1.8. Based on the total mass of polyethylene powder, the total amount of the compounded antioxidant system is 0.4wt%, and it is uniformly conveyed to the preheating section at the front end of the twin-screw extruder.

[0031] S3: 300 ppm of dicumyl peroxide and 0.5 wt% of acrylate multifunctional monomers are fed into the molten zone of the extruder via a side feeder; the twin-screw extruder is equipped with a conveying element, a barrier element, a 45° staggered kneading block, and a 60° staggered kneading block in sequence; the screw compression ratio is 2.1; the screw forms a low-shear distribution mixing structure; the melt residence time in the screw is 90 s; the screw speed is 210 r / min; the maximum temperature of the extrusion equipment is controlled at 210℃.

[0032] S4: The melt flows through a multi-stage series vacuum devolatilization system at the end of the twin screw, where it undergoes step negative pressure devolatilization, with the negative pressure gradually increasing from -0.06MPa to -0.1MPa. After being filtered through a 250-mesh multi-layer composite filter, it is delivered to the spinning box by a melt pump and a metering pump with stable pressure.

[0033] S5: The spinning box operates at a constant temperature. The melt is extruded from the spinneret to form a continuous gel-state filament, which enters the cooling channel equipped with a high-precision infrared temperature feedback system. The cooling channel is divided into a homogeneous nucleation control zone, a crystal orientation growth zone, and a structure locking zone along the filament's travel direction. The temperature of the homogeneous nucleation control zone is 132℃, and the cooling rate is 3.5℃ / min. The temperature of the crystal orientation growth zone is 120℃. The temperature of the structure locking zone is 102℃. The temperature fluctuation of the cooling air is controlled within ±1℃ throughout the process. After cooling and shaping, the filament is uniformly oiled by the oiling roller.

[0034] S6: After oiling, the filament bundles are subjected to three-stage gradient heating and stretching: the first pre-stretching temperature is 118℃, the second main stretching temperature is 131℃, and the third stretching temperature is 134℃, with a total stretching ratio of 12 times; the tension fluctuation is strictly controlled within ±2cN throughout the stretching process, and finally sample 1 is obtained.

[0035] Example 2 S1: Linear polyethylene resin powder with a weight-average molecular weight of 3×10⁻⁶. 5 After being vented by a compression device and impurities removed by negative pressure extraction, the speed is controlled at 30 r / min, and the mixture is stirred and dispersed at low speed for 5 minutes. Under N2 protection, it is then conveyed to a twin-screw extruder.

[0036] S2: Using a loss-in-weight feeding metering device, the main antioxidant N,N'-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hexanediamine and the auxiliary antioxidant dodecanol thiodipropionate are uniformly mixed at a mass ratio of 1:1.5. Based on the total mass of polyethylene powder, the total amount of the compounded antioxidant system is 0.2wt%, and it is uniformly conveyed to the preheating section at the front end of the twin-screw extruder.

[0037] S3: 150 ppm of dicumyl peroxide and 0.2 wt% of acrylate multifunctional monomers are fed into the molten zone of the extruder via a side feeder; the twin-screw extruder is equipped with a conveying element, a barrier element, a 45° staggered kneading block, and a 60° staggered kneading block in sequence; the screw compression ratio is 1.8; the screw forms a low-shear distribution mixing structure; the melt residence time in the screw is 80 s; the screw speed is 180 r / min; the maximum temperature of the extrusion equipment is controlled at 210℃.

[0038] S4: The melt flows through a multi-stage series vacuum devolatilization system at the end of the twin screw, where it undergoes step negative pressure devolatilization, with the negative pressure gradually increasing from -0.05MPa to -0.1MPa. After being filtered through a 200-mesh multi-layer composite filter, it is delivered to the spinning box by a melt pump and a metering pump with stable pressure.

[0039] S5: The spinning box operates at a constant temperature. The melt is extruded from the spinneret to form a continuous gel-state filament, which enters the cooling channel equipped with a high-precision infrared temperature feedback system. The cooling channel is divided into a homogeneous nucleation control zone, a crystal orientation growth zone, and a structure locking zone along the filament's travel direction. The temperature of the homogeneous nucleation control zone is 128℃, and the cooling rate is 2℃ / min. The temperature of the crystal orientation growth zone is 115℃, and the temperature of the structure locking zone is 95℃. The temperature fluctuation of the cooling air is controlled within ±1℃ throughout the process. After cooling and shaping, the filament is uniformly oiled by the oiling roller.

[0040] S6: After oiling, the filament bundles are subjected to three-stage gradient heating and stretching: the first pre-stretching temperature is 112℃, the second main stretching temperature is 128℃, and the third stretching temperature is 132℃, with a total stretching ratio of 8 times; the tension fluctuation is strictly controlled within ±2cN throughout the stretching process, and finally sample 2 is obtained.

[0041] Example 3 S1: Select linear polyethylene resin powder with a weight-average molecular weight of 4×105. After being vented by a compression device and impurities removed by negative pressure extraction, the powder is dispersed at a speed of 50 r / min and stirred at low speed for 3 min. Under N2 protection, it is then conveyed to a twin-screw extruder.

[0042] S2: Using a loss-in-weight feeding metering device, the main antioxidant N,N'-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hexanediamine and the auxiliary antioxidant dodecanol thiodipropionate are uniformly mixed at a mass ratio of 1:2. Based on the total mass of polyethylene powder, the total amount of the compounded antioxidant system is 0.6wt%, and it is uniformly conveyed to the preheating section at the front end of the twin-screw extruder.

[0043] S3: 500 ppm of dicumyl peroxide and 0.8 wt% of acrylate multifunctional monomers are fed into the molten section of the extruder via a side feeder; the twin-screw extruder is equipped with a conveying element, a barrier element, a 45° staggered kneading block, and a 60° staggered kneading block in sequence on the screw; the screw compression ratio is 2.5; the screw forms a low-shear distribution mixing structure; the melt residence time in the screw is 100 s; the screw speed is 240 r / min; the maximum temperature of the extrusion equipment is controlled at 210℃.

[0044] S4: The melt flows through a multi-stage series vacuum devolatilization system at the end of the twin screw, where it undergoes step negative pressure devolatilization, with the negative pressure gradually increasing from -0.08MPa to -0.1MPa. After being filtered through a 200-mesh multi-layer composite filter, it is delivered to the spinning box by a melt pump and a metering pump with stable pressure.

[0045] S5: The spinning box operates at a constant temperature. The melt is extruded by the spinneret to form a continuous gel-state filament, which enters the cooling channel equipped with a high-precision infrared temperature feedback system. The cooling channel is divided into a homogeneous nucleation control zone, a crystal orientation growth zone, and a structure locking zone along the filament's travel direction. The temperature of the homogeneous nucleation control zone is 135℃, and the cooling rate is 5℃ / min. The temperature of the crystal orientation growth zone is 125℃. The temperature of the structure locking zone is 110℃. The temperature fluctuation of the cooling air is controlled within ±1℃ throughout the process. After cooling and shaping, the filament is uniformly oiled by the oiling roller.

[0046] S6: After oiling, the filament bundles are subjected to three-stage gradient heating and stretching: the first pre-stretching temperature is 126℃, the second main stretching temperature is 134℃, and the third stretching temperature is 137℃, with a total stretching ratio of 16 times; the tension fluctuation is strictly controlled within ±2cN throughout the stretching process, and finally sample 3 is obtained.

[0047] Comparative Example 1 S1: Linear polyethylene resin powder with a weight-average molecular weight of 3.5 × 10⁻⁶. 5 After being vented by a compression device and impurities removed by negative pressure extraction, the speed is controlled at 40 r / min, and the mixture is stirred and dispersed at low speed for 4 min. Under N2 protection, it is then conveyed to a twin-screw extruder. S2: Using a loss-in-weight feeding metering device, the main antioxidant N,N'-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hexanediamine and the auxiliary antioxidant disodium thiodipropionate are uniformly mixed at a mass ratio of 1:1.8. Based on the total mass of polyethylene powder, the total amount of the compounded antioxidant system is 0.4wt%, and it is uniformly conveyed to the preheating section at the front end of the twin-screw extruder. S3: 300 ppm of dicumyl peroxide and 0.5 wt% of acrylate multifunctional monomers are fed into the molten zone of the extruder via a side feeder; the twin-screw extruder screws are sequentially equipped with conveying elements, barrier elements, 45° staggered kneading blocks, and 60° staggered kneading blocks, with a screw compression ratio of 2.1. The screws form a low-shear distribution mixing structure, the melt residence time in the screw is 90 s, and the screw speed is 210 r / min; the maximum temperature of the extrusion equipment is controlled at 210℃; S4: The melt flows through the multi-stage series vacuum devolatilization system at the end of the twin screw, and is treated by a single fixed negative pressure of -0.1MPa. After being filtered by a 200-mesh multi-layer composite filter, it is delivered to the spinning box by a melt pump and a metering pump under stable pressure.

[0048] S5: The spinning box operates at a constant temperature. The melt is extruded from the spinneret to form a continuous gel-state filament, which enters the cooling channel equipped with a high-precision infrared temperature feedback system. The cooling channel is divided into a homogeneous nucleation control zone, a crystal orientation growth zone, and a structure locking zone along the filament's travel direction. The temperature of the homogeneous nucleation control zone is 132℃, and the cooling rate is 3.5℃ / min. The temperature of the crystal orientation growth zone is 120℃. The temperature of the structure locking zone is 102℃. The temperature fluctuation of the cooling air is controlled within ±1℃ throughout the process. After cooling and shaping, the filament is uniformly oiled by the oiling roller.

[0049] S6: After oiling, the filament bundles are subjected to three-stage gradient heating and stretching: the first pre-stretching temperature is 118℃, the second main stretching temperature is 131℃, and the third stretching temperature is 134℃, with a total stretching ratio of 12 times; the tension fluctuation is strictly controlled within ±2cN throughout the stretching process, and finally sample 4 is obtained.

[0050] Comparative Example 2 S1: Select linear polyethylene resin powder with a weight-average molecular weight of 3.5×105. After being vented by a compression device and impurities removed by negative pressure extraction, the powder is dispersed at a speed of 40 r / min and stirred at low speed for 4 min. Under N2 protection, it is then conveyed to a twin-screw extruder.

[0051] S2: Using a loss-in-weight feeding metering device, the main antioxidant N,N'-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hexanediamine and the auxiliary antioxidant disodium thiodipropionate are uniformly mixed at a mass ratio of 1:1.8. Based on the total mass of polyethylene powder, the total amount of the compounded antioxidant system is 0.4wt%, and it is uniformly conveyed to the preheating section at the front end of the twin-screw extruder.

[0052] S3: 300ppm of dicumyl peroxide and 0.5wt% of acrylate multifunctional monomers are fed into the molten section of the extruder via a side feeder; a single-screw mixing structure is adopted, with a screw compression ratio of 2.1, a melt residence time in the screw of 90s, and a screw speed of 210r / min; a multi-stage series vacuum devolatilization system at the end of the screw, and the maximum temperature of the extrusion equipment is controlled at 210℃.

[0053] S4: The melt flows through a multi-stage series vacuum devolatilization system at the end of the screw, where it undergoes step negative pressure devolatilization, with the negative pressure gradually increasing from -0.06MPa to -0.1MPa. After being filtered through a 250-mesh multi-layer composite filter, it is delivered to the spinning box by a melt pump and a metering pump with stable pressure.

[0054] S5: The spinning box operates at a constant temperature. The melt is extruded from the spinneret to form a continuous gel-state filament, which enters the cooling channel equipped with a high-precision infrared temperature feedback system. The cooling channel is divided into a homogeneous nucleation control zone, a crystal orientation growth zone, and a structure locking zone along the filament's travel direction. The temperature of the homogeneous nucleation control zone is 132℃, and the cooling rate is 3.5℃ / min. The temperature of the crystal orientation growth zone is 120℃. The temperature of the structure locking zone is 102℃. The temperature fluctuation of the cooling air is controlled within ±1℃ throughout the process. After cooling and shaping, the filament is uniformly oiled by the oiling roller.

[0055] S6: After oiling, the filament bundles are subjected to three-stage gradient heating and stretching: the first pre-stretching temperature is 118℃, the second main stretching temperature is 131℃, and the third stretching temperature is 134℃, with a total stretching ratio of 12 times; the tension fluctuation is strictly controlled within ±2cN throughout the stretching process, and finally sample 5 is obtained.

[0056] Comparative Example 3 S1: Select linear polyethylene resin powder with a weight-average molecular weight of 3.5×105. After being vented by a compression device and impurities removed by negative pressure extraction, the powder is dispersed at a speed of 40 r / min and stirred at low speed for 4 min. Under N2 protection, it is then conveyed to a twin-screw extruder.

[0057] S2: Using a loss-in-weight feeding metering device, the main antioxidant N,N'-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hexanediamine and the auxiliary antioxidant disodium thiodipropionate are uniformly mixed at a mass ratio of 1:1.8. Based on the total mass of polyethylene powder, the total amount of the compounded antioxidant system is 0.4wt%, and it is uniformly conveyed to the preheating section at the front end of the twin-screw extruder.

[0058] S3: 300 ppm of dicumyl peroxide and 0.5 wt% of acrylate multifunctional monomers are fed into the molten zone of the extruder via a side feeder; the twin-screw extruder is equipped with a conveying element, a barrier element, a 45° staggered kneading block, and a 60° staggered kneading block in sequence; the screw compression ratio is 2.1; the screw forms a low-shear distribution mixing structure; the melt residence time in the screw is 90 s; the screw speed is 210 r / min; the maximum temperature of the extrusion equipment is controlled at 210℃.

[0059] S4: The melt flows through a multi-stage series vacuum devolatilization system at the end of the twin screw, where it undergoes step negative pressure devolatilization, with the negative pressure gradually increasing from -0.06MPa to -0.1MPa. After being filtered through a 250-mesh multi-layer composite filter, it is delivered to the spinning box by a melt pump and a metering pump with stable pressure.

[0060] S5: The spinning box operates at a constant temperature. The melt is extruded from the spinneret to form a continuous gel-state filament, which enters the cooling channel. The overall temperature of the cooling channel is fixed at 118℃, and natural cooling with a constant wind speed is used throughout the process.

[0061] S6: After oiling, the filament bundles are subjected to three-stage gradient heating and stretching: the first pre-stretching temperature is 118℃, the second main stretching temperature is 131℃, and the third stretching temperature is 134℃, with a total stretching ratio of 12 times; the tension fluctuation is strictly controlled within ±2cN throughout the stretching process, and finally sample 6 is obtained. Table 1 As shown in Table 1, the molecular weight of samples 1-3 is 1.2 × 10⁻⁶. 5 ~5.8×10 5 The apparent density is 0.36~0.62 g / cm³. 3 The melting temperature is 130℃~137℃, and the molecular weight of sample 1 is 3.5×10⁻⁶. 5 Compared to a melting temperature of 133℃, sample 5 has a molecular weight of 2.6 × 10⁻⁶. 5 The medium fracture strength and melting temperature of 124℃ indicate that the molecular chains of sample 5 have broken down and degraded, and the molecular thermal structure and structural integrity have deteriorated significantly.

[0062] The fracture strength of samples 1-3 was 32.2-34.8 cN / dtex, and the elastic modulus was 1026-1180 cN / dtex. Among them, the fracture strength of sample 1 (34.8 cN / dtex) and the elastic modulus (1180 cN / dtex) were much higher than those of samples 4-6 (26.5-29.4 cN / dtex) and the elastic modulus (868-1043 cN / dtex). Sample 5 showed the most significant performance degradation. The fracture strength of sample 4 (29.4 cN / dtex) and the elastic modulus (1043 cN / dtex) were lower than those of sample 1, indicating that residual bubbles and impurities in the melt of sample 4 led to a decrease in density.

[0063] The batch dispersion coefficients of samples 1-3 were 1.8-2.5%, and the spinning breakage rate was 0.12-0.21 times / 1000km, which were significantly lower than those of samples 4-6, which were 4.3-6.7% and 0.64-1.12 times / 1000km.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A solvent-free high molecular weight polyethylene fiber with low breakage rate and high uniformity, characterized in that, The low breakage rate, high uniformity, solvent-free high molecular weight polyethylene fiber described herein meets the following parameters: molecular weight of 1.2 × 10⁻⁶. 5 ~5.8×10 5 The apparent density is 0.36~0.62 g / cm³. 3 The melting temperature is 126℃~137℃.

2. A method for preparing solvent-free high molecular weight polyethylene fiber with low breakage rate and high uniformity according to claim 1, characterized in that, Includes the following steps: S1: The linear polyethylene resin powder is compressed to remove air and subjected to negative pressure extraction. It is then dispersed by low-speed stirring and conveyed into the twin-screw extruder under N2 environment. S2: A loss-in-weight feeding metering device is used to transport the hindered phenolic primary antioxidant and phosphite secondary antioxidant to the front preheating section of the twin-screw extruder; S3: Dicumyl peroxide initiator and acrylate multifunctional monomers are fed to the melting zone of a twin-screw extruder using a side feeder; the twin-screw extruder is equipped with a barrier zone and a low-shear mixing zone; the maximum temperature of the extrusion equipment is controlled at 210℃; S4: The melt flows through the multi-stage vacuum channel of the twin-screw extruder and undergoes multi-stage vacuum devolatilization. The processed melt is then conveyed to the devolatilization kettle, melt pump, graded filter, and metering pump to the spinning box. S5: The spinning box operates at a constant temperature. The melt inside the box is extruded from the spinneret holes to form a continuous gel-state filament. The filament enters the cooling channel for gradient cooling and shaping. The cooling channel is equipped with a high-precision infrared temperature feedback system. After cooling and shaping, the filament is oiled by the oiling roller. S6: The filament bundle is stretched in three stages in sequence: the first pre-stretch temperature is 112℃~126℃, the second main stretch temperature is 128℃~134℃, and the third stretch temperature is 132℃~137℃. The total stretch ratio is 8~16 times. The tension fluctuation range during the stretching process is controlled within ±2cN to obtain filaments.

3. The method for preparing low-breakage, high-uniformity, solvent-free high molecular weight polyethylene fiber according to claim 2, characterized in that, In S2, the stirring rate of the low-speed stirring dispersion is 30~50 r / min, and the stirring time is 3~5 min.

4. The method for preparing low-breakage, high-uniformity, solvent-free high molecular weight polyethylene fiber according to claim 2, characterized in that, The twin-screw extruder has a screw sequentially equipped with a conveying element, a barrier element, a 45° staggered kneading block, and a 60° staggered kneading block along the material transport direction; the screw compression ratio is 1.8~2.5, and the screw forms a low-shear distribution mixing structure; the melt residence time in the twin-screw extruder is 80~100s, and the screw speed is 180-240r / min; the end of the twin screw integrates a multi-stage series vacuum devolatilization system.

5. The method for preparing low-breakage, high-uniformity, solvent-free high molecular weight polyethylene fiber according to claim 2, characterized in that, In S3, the primary antioxidant is N,N'-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hexanediamine, and the secondary antioxidant is dodecyl thiodipropionate, with a ratio of 1:1.5 to 1:2; based on the total mass of the linear polyethylene resin powder, the total addition amount of the primary antioxidant and the secondary antioxidant is 0.2wt% to 0.6wt%.

6. The method for preparing low-breakage, high-uniformity, solvent-free high molecular weight polyethylene fiber according to claim 2, characterized in that, In S3, the amount of dicumyl peroxide added is 150~500ppm; based on the total mass of the linear polyethylene resin powder, the amount of acrylate multifunctional monomer added is 0.2wt%~0.8wt%.

7. The method for preparing low-breakage, high-uniformity, solvent-free high molecular weight polyethylene fiber according to claim 2, characterized in that, In S4, the negative pressure of the vacuum devouring system is gradually increased from -0.05 to -0.08 MPa to -0.1 MPa.

8. The method for preparing low-breakage, high-uniformity, solvent-free high molecular weight polyethylene fiber according to claim 2, characterized in that, In S4, the graded filter uses a multi-layer composite filter with a filter precision of 200-300 mesh.

9. The method for preparing low-breakage, high-uniformity, solvent-free high molecular weight polyethylene fiber according to claim 2, characterized in that, In S5, the cooling channel is divided into three cooling zones along the direction of the filament: a homogeneous nucleation control zone, a crystal orientation growth zone, and a structure locking zone. The temperature of each cooling zone gradually decreases along the direction of the filament.

10. The method for preparing low-breakage, high-uniformity, solvent-free high molecular weight polyethylene fiber according to claim 2, characterized in that, In S5, the temperature of the homogeneous nucleation control zone in the cooling channel is 128℃~135℃, the cooling rate is 2-5℃ / min, the temperature of the crystal orientation growth zone is 115℃~125℃, the temperature of the structure locking zone is 95℃~110℃, and the temperature fluctuation range of the cooling air is controlled within ±1℃.

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