Radiation low-crosslinking high-density polyethylene and preparation method thereof

Abstract

The invention relates to a preparation method of radiation low-crosslinking high-density polyethylene, which comprises the following steps: S1, a melting step: placing high-density polyethylene in an anaerobic environment, and heating the high-density polyethylene until the high-density polyethylene is completely molten; s2, irradiation: irradiating the high-density polyethylene by adopting a high-energy ionization radiation source under the condition that the high-density polyethylene is kept in a molten state and in an anaerobic environment, so as to crosslink molecular chains of the high-density polyethylene; s3, a cooling step: cooling the irradiated high-density polyethylene to obtain the low-crosslinking high-density polyethylene, according to the preparation method, moderate low crosslinking of molecular chains of the high-density polyethylene is ensured, the impact strength and wear resistance of the high-density polyethylene are improved, meanwhile, relatively good processing performance of the high-density polyethylene is reserved, other materials do not need to be added in the preparation process, the product purity is high, and the preparation process is environmentally friendly and free of pollution.

Description

Technical Field

[0001] This application relates to the field of high-density polyethylene technology, and in particular to a radiation-low crosslinked high-density polyethylene and its preparation method. Background Technology

[0002] High-density polyethylene (HDPE) is a widely used general-purpose resin material, extensively used in the manufacture of various blow-molded products, injection-molded products, films, wires and cables, and pipes. Due to the absence of micro-crosslinked structures in its molecular chains, the degree of molecular chain entanglement is relatively low. Compared with ultra-high molecular weight polyethylene (UHMWPE), it has better processing performance, but its impact strength and abrasion resistance are significantly lower than those of UHMWPE. In addition, the structural characteristics of HDPE determine its low melt strength, making it prone to deformation in melt stretching and extrusion molding processes, resulting in unstable thermoforming processing of HDPE products.

[0003] To improve the performance of high-density polyethylene (HDPE), it is typically cross-linked. Current technologies usually employ radiation cross-linking, where high-energy radiation induces ionization and activation of the molecular chains, enabling self-cross-linking. However, existing radiation cross-linking methods are generally performed at room temperature. During radiation cross-linking, the cross-linking reaction mainly occurs in the amorphous regions of HDPE, leading to uneven cross-linking. Furthermore, during radiation processing, oxygen in the air may cause radiation-induced oxidative cracking of HDPE, further affecting material properties. Summary of the Invention

[0004] In view of this, this application proposes a method for preparing radiation-induced low-crosslinking high-density polyethylene, comprising the following steps: S1. Melting step: The high-density polyethylene is placed in an oxygen-free environment and heated to a completely molten state; S2. Irradiation step: The high-density polyethylene is irradiated with a high-energy ionizing radiation source while maintaining the high-density polyethylene in a molten state and in an oxygen-free environment to cause the molecular chains of the high-density polyethylene to crosslink. S3. Cooling step: Cool the irradiated high-density polyethylene to obtain low-crosslinked high-density polyethylene.

[0005] According to another aspect of this application, a low-crosslinked high-density polyethylene is provided, which is obtained by the preparation method described in any of the above claims.

[0006] Beneficial effects of this application This application involves heating high-density polyethylene (HDPE) to a molten state and then irradiating it while maintaining the molten state. This results in a more uniform cross-linking reaction of the HDPE molecular chains, improving the overall consistency of the material's performance. Maintaining an oxygen-free environment throughout the entire preparation process effectively prevents oxidative cracking of HDPE during radiation processing, ensuring smooth cross-linking and reducing material performance degradation caused by oxidative cracking. This guarantees product quality stability. By setting the absorbed dose of the irradiation, the energy emitted by the high-energy ionizing radiation source induces cross-linking of the HDPE molecular chains while avoiding excessive cross-linking and gel formation due to excessive absorbed dose. This ensures moderately low cross-linking of the HDPE molecular chains, improving the impact strength and abrasion resistance of HDPE while retaining its relatively good processing performance. Furthermore, this invention requires no additional materials during preparation, resulting in high product purity and an environmentally friendly, pollution-free preparation process.

[0007] Other features and aspects of this application will become clear from the following detailed description of exemplary embodiments. Detailed Implementation

[0008] The various exemplary embodiments, features, and aspects of this application will be described in detail below.

[0009] It should be understood that the terms “center,” “longitudinal,” “lateral,” “length,” “width,” “up,” “down,” “front,” “back,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” “outer,” “clockwise,” “counterclockwise,” “axial,” “radial,” and “circumferential” are used only for the convenience of describing this application or simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application.

[0010] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0011] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0012] Furthermore, to better illustrate this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented without certain specific details. In some instances, methods, means, components, and circuits well-known to those skilled in the art have not been described in detail in order to highlight the main points of this application.

[0013] Slightly cross-linked high-density polyethylene (HDPE) exhibits high melt strength and significant strain hardening characteristics. Liu Zheng et al. (Research on Polyethylene Micro-crosslinking Technology and its Application in New Product Development, China University of Petroleum, Master's Thesis, 2020) found that slightly cross-linked HDPE can significantly improve its processing and performance. The slightly cross-linked molecular chain structure can increase the processing temperature range of HDPE and improve the edge curling and shrinkage behavior that occurs during high-speed extrusion. Gao Kejing et al. (Research on Chemical Micro-crosslinking of High-Density Polyethylene, ...) Synthetic resins and plastics A study published in 2021, 38(6):15, found that micro-crosslinking of high-density polyethylene (HDPE) produces long branched structures on the molecular chain, increasing the entanglement ability of the chain segments and thus significantly improving its impact resistance. Therefore, slight crosslinking of HDPE can simultaneously improve its thermal processing performance and mechanical properties.

[0014] This application discloses a method for preparing radiation-induced low-crosslinking high-density polyethylene, comprising the following steps: S1. Melting step: Place the high-density polyethylene in an oxygen-free environment and heat it until it is completely molten; S2. Irradiation step: High-density polyethylene is irradiated with a high-energy ionizing radiation source while maintaining the high-density polyethylene in a molten state and in an oxygen-free environment to crosslink the molecular chains of the high-density polyethylene. S3. Cooling step: Cool the irradiated high-density polyethylene to obtain low-crosslinked high-density polyethylene.

[0015] The preparation method of this application is carried out in an oxygen-free environment. Specifically, an oxygen-free environment refers to an environment in which oxygen is removed by physical or chemical means, such as by vacuum treatment followed by filling with an inert gas, or by using a sealed container filled with a non-oxidizing gas. The oxygen-free environment is designed to prevent oxygen from participating in the cross-linking reaction of the high-density polyethylene (HDPE) molecular chains and to prevent radiation oxidation and cracking of HDPE due to the presence of oxygen during subsequent irradiation. HDPE is placed in an oxygen-free environment and heated to completely melt it. In the molten state, the degree of freedom of movement of the HDPE molecular chains is significantly increased, providing conditions for the subsequent cross-linking reaction to occur uniformly throughout the material. This avoids the cross-linking reaction occurring only in the amorphous region of HDPE, which would lead to uneven cross-linking. A high-energy ionizing radiation source is suitable for providing energy to activate the HDPE molecular chains to carry out the cross-linking reaction. The high-energy ionizing radiation source emits energy to induce the ionization and activation of the HDPE molecular chains to generate free radicals. The highly active free radicals combine with each other to achieve cross-linking of the molecular chains.

[0016] By adjusting the intensity and irradiation time of the radiation source, the absorbed dose of irradiation can be controlled to achieve low-dose irradiation treatment of high-density polyethylene (HDPE). This allows the energy emitted by the high-energy ionizing radiation source to induce cross-linking of the HDPE molecular chains while avoiding excessive cross-linking and gel formation due to excessive absorbed dose. This results in improved impact strength and abrasion resistance of HDPE while retaining its relatively good processability. Absorbed dose is a standard term in the field of radiation processing, specifically referring to the energy value of radiation absorbed per unit mass of material (i.e., the energy value of the radiation emitted by the high-energy ionizing radiation source absorbed by HDPE). Typically, the absorbed dose for irradiating polyethylene and other polymer materials ranges from tens to hundreds of kGy. After irradiation, the HDPE is cooled, fixing the partially cross-linked molecular chains in the molten state, forming low-crosslinked HDPE with a certain cross-linking structure.

[0017] Furthermore, it should be noted that the absorbed dose of low-dose irradiation treatment is determined by preventing high-density polyethylene from gelling, i.e., it should not exceed the gel point dose of high-density polyethylene. The gel point dose of high-density polyethylene varies due to its molecular weight and molecular structure. The following experiments have confirmed that when the absorbed dose is controlled within the range of 20% to 100% of its gel point dose, the thermoplastic processing properties of polyethylene can be maintained while significantly improving its performance (such as melt strength and impact toughness). If the absorbed dose reaches or exceeds the gel point dose, due to the significant cross-linking of the molecular chains of high-density polyethylene, polyethylene gradually transforms from thermoplastic to thermosetting, resulting in a sharp decrease in processing properties and a rapid decrease in impact properties.

[0018] This application involves heating high-density polyethylene (HDPE) to a molten state and then irradiating it while maintaining the molten state. This results in a more uniform cross-linking reaction of the HDPE molecular chains, improving the overall consistency of the material's performance. Maintaining an oxygen-free environment throughout the entire preparation process effectively prevents oxidative cracking of HDPE during radiation processing, ensuring the smooth progress of the cross-linking reaction, reducing material performance degradation caused by oxidative cracking, and guaranteeing product quality stability. By controlling the absorbed dose of the irradiation, the energy emitted by the high-energy ionizing radiation source induces cross-linking of the HDPE molecular chains while avoiding excessive cross-linking and gel formation due to excessive absorbed dose. This ensures appropriate cross-linking of the HDPE molecular chains, improving the impact strength and abrasion resistance of HDPE while retaining its relatively good processing performance. Furthermore, this invention requires no additional materials during preparation, resulting in high product purity and an environmentally friendly, pollution-free preparation process.

[0019] In one possible implementation, the high-density polyethylene is either a homopolymer or a copolymer, and the melt index of the high-density polyethylene is 0.01-10 g / 10 min, and the density is 0.940-0.970 g / cm3; wherein the high-density polyethylene is in various shapes such as fine particles, blocks, films, fibers, and granules; it should be noted that when the high-density polyethylene is in solid block form, melting does not require an oxygen-free environment, but when irradiating the molten high-density polyethylene, it must be done in an oxygen-free environment.

[0020] In one possible implementation, the S1 melting step is as follows: S101. The high-density polyethylene is placed in an irradiation chamber, and the irradiation chamber is vacuum-treated and then filled with inert gas; S102. Heating the irradiation chamber to fully melt the high-density polyethylene inside the irradiation chamber; S103. After heating is completed, the irradiation tank and the molten high-density polyethylene are kept warm.

[0021] It should be noted that in step S101, vacuum treatment and the introduction of inert gas effectively remove residual air from the irradiation chamber, providing a reliable oxygen-free environment for subsequent melting and irradiation. Specifically, the inert gas refers to a chemically stable gas that does not readily react with high-density polyethylene (HDPE). The heating process in step S102 is conducted within this established oxygen-free environment, ensuring complete melting of the HDPE and highly mobile molecular chains, thus providing a uniform molten matrix for subsequent irradiation crosslinking. In step S103, heat preservation maintains the molten state of the HDPE, preventing cooling and solidification due to temperature fluctuations. This ensures the continuity and consistency of the irradiation process. The melting process design avoids radiation oxidation and cracking caused by residual oxygen interfering with irradiation crosslinking, improving the uniformity and stability of the crosslinking reaction.

[0022] In one possible implementation, the inert gas is any one of nitrogen, argon, or carbon dioxide.

[0023] In one possible implementation, the heating temperature in step S102 is 130℃-200℃; where heating temperature refers to the temperature range set when heating the irradiation chamber in the melting step; heating to a suitable temperature can ensure that the high-density polyethylene is completely melted, allowing the molecular chains of high-density polyethylene to fully extend and maintain high mobility, thereby providing a uniform reaction basis for subsequent irradiation crosslinking, while avoiding the high-density polyethylene from being exposed to excessively high temperatures for a long time in the molten state, suppressing the risk of thermal degradation, and maintaining the stability of the material structure.

[0024] Preferably, the heating temperature is 140℃-160℃.

[0025] In one possible implementation, the high-energy ionizing radiation source is a device capable of emitting electron beams, gamma rays, or X-rays of 0.01-10 MeV for radiation processing.

[0026] In one possible implementation, in step S2, the absorbed dose of the high-density polyethylene is controlled by adjusting the radiation intensity of the rays emitted by the high-energy ionizing radiation source.

[0027] It should be noted here that the radiation intensity of the rays emitted by a high-energy ionizing radiation source specifically refers to the radiation energy emitted by the high-energy ionizing radiation source in a specific direction in space per unit time. The radiation intensity can be converted into absorbed dose rate using energy absorption logic. The purpose of converting radiation intensity into absorbed dose rate is to provide clear process guidance for the regulation of the high-energy ionizing radiation source, ensuring that the absorbed dose of high-density polyethylene falls within a predetermined range, and ensuring the stability of the cross-linking of the high-density polyethylene molecular chains. The specific conversion formula and derivation logic are as follows: =Φ / (ρ×h), where, Here, Φ represents the absorbed dose rate, ρ represents the radiation intensity of the radiation, ρ represents the density of high-density polyethylene (HDPE), and h represents the thickness of HDPE. The density and thickness of HDPE are known. The radiation intensity of the radiation is directly proportional to the absorbed dose rate. When the radiation intensity of the radiation is stronger, the absorbed dose rate is greater, that is, the absorbed dose of HDPE is greater. Conversely, when the radiation intensity of the radiation is weaker, the absorbed dose rate is smaller, that is, the absorbed dose of HDPE is smaller. The radiation intensity of the radiation can be controlled by adjusting the parameters of the equipment. The specific methods for adjusting the equipment parameters are conventional techniques in this field and will not be described in detail here.

[0028] By adjusting the irradiation intensity of the radiation emitted by the high-energy ionizing radiation source, the absorbed dose of high-density polyethylene (HDPE) is controlled within the range of 0.5 kGy to 25 kGy. The appropriate absorbed dose design ensures that the energy input of the high-energy ionizing radiation source is sufficient to activate the molecular chains of HDPE to undergo cross-linking reactions, thereby effectively improving the impact strength and wear resistance of the material. This avoids the inability to undergo cross-linking reactions due to excessively low absorbed doses, while also avoiding excessive cross-linking and gel formation due to excessively high absorbed doses, thus ensuring the stability and reliability of the material's performance.

[0029] Preferably, the absorbed dose of high-density polyethylene is controlled within the range of 2 kGy to 10 kGy by adjusting the radiation intensity of the radiation emitted by the high-energy ionizing radiation source.

[0030] Furthermore, the methods for determining the radiation intensity of rays from different types of high-energy ionizing radiation sources are as follows: When the high-energy ionizing radiation source is an electron beam radiation source, the radiation intensity of the rays can be obtained through calculation: First, obtain the rated output power P and effective scanning area A of the electron beam radiation source. The rated output power P is obtained through equipment parameters, and the effective scanning area A is obtained through the product of the scanning width and the effective length of the transmission direction of the electron beam radiation source. Based on the data obtained above, the radiation intensity of the rays output by the electron beam radiation source is calculated. The calculation formula is: Φ = P / A; where P is the rated output power of the high-energy ionizing radiation source, and A is the effective scanning area of ​​the high-energy ionizing radiation source. P and A are known parameters that can be directly obtained from the equipment parameters.

[0031] When the high-energy ionizing radiation source is X-rays or gamma rays, the corresponding absorbed dose rate can be directly obtained from the spatial dose rate distribution map provided by the equipment manufacturer. Furthermore, the absorbed dose rate of the target processing object can also be measured and calculated using a standard dosimeter. The absorbed dose rate is obtained using a standard dosimeter. The method used is a conventional technique in this field and will not be described in detail here.

[0032] In one possible implementation, step S2 can also be achieved by adjusting the irradiation time of the high-energy ionizing radiation source to control the absorbed dose of high-density polyethylene.

[0033] It should be noted here that the absorbed dose of high-density polyethylene is controlled between 0.5 kGy and 25 kGy by adjusting the irradiation time of the high-energy ionizing radiation source; preferably, the absorbed dose of high-density polyethylene is controlled between 2 kGy and 10 kGy by adjusting the irradiation time of the high-energy ionizing radiation source.

[0034] In one possible implementation, the absorbed dose of high-density polyethylene (HDPE) can be controlled by synergistically regulating the absorbed dose rate (i.e., radiation intensity) and irradiation time of the high-energy ionizing radiation source; ensuring that the absorbed dose of HDPE is controlled between 0.5 kGy and 25 kGy. Specifically, the absorbed dose of HDPE is proportional to the radiation intensity (i.e., absorbed dose rate) and irradiation time of the radiation. By controlling the radiation intensity and irradiation time (i.e., controlling the absorbed dose rate and irradiation time), the absorbed dose of HDPE can be controlled. The smaller the absorbed dose rate output by the high-energy ionizing radiation source, the longer the corresponding irradiation time; conversely, the larger the absorbed dose rate output by the high-energy ionizing radiation source, the shorter the corresponding irradiation time. The specific mapping relationship between the absorbed dose rate output by the high-energy ionizing radiation source and the irradiation time is shown below. D = ×t; where D is the absorbed dose, The absorbed dose rate obtained above is given by t, which is the irradiation time. It should be noted that the absorbed dose of high-density polyethylene is a known value that should be between 0.5 kGy and 25 kGy.

[0035] In one possible implementation, to ensure that the high-density polyethylene (HDPE) remains in the required molten state during irradiation step S2, the invention further includes monitoring the temperature of the irradiation chamber. After the HDPE irradiation treatment in the chamber is completed, the temperature of the irradiated chamber is measured. (Since the irradiation chamber and the HDPE inside reach thermal equilibrium after sufficient heating, the outer wall temperature of the irradiation chamber can directly or indirectly reflect the actual state of the internal HDPE.) By measuring the temperature of the irradiation chamber, if the temperature is greater than 130°C, the HDPE inside the chamber remains in a molten state during irradiation, and the next step S3 (cooling) can proceed. If the temperature is less than 130°C, the HDPE inside the chamber solidifies or partially crystallizes during irradiation. In this case, the HDPE inside the chamber should be reheated until its temperature reaches the required heating temperature range before re-irradiation.

[0036] In one possible implementation, step S3 involves placing the irradiated high-density polyethylene in an oxygen-free environment and cooling it to 70°C.

[0037] It should be noted that the design of cooling to 70°C is based on the thermal behavior characteristics of high-density polyethylene (HDPE). This temperature is below the melting temperature range but above room temperature, which can prevent HDPE from reacting with oxidation during high-temperature cooling. Irradiated HDPE is in a highly reactive state. If it is directly exposed to an oxygen environment for cooling, the oxygen in the air will participate in the free radical reaction as a reactant, which will lead to the breakage of the HDPE molecular chains and performance degradation. By placing the irradiated HDPE in an oxygen-free environment for cooling, the material is completely isolated from oxygen during the cooling stage, thereby avoiding molecular chain breakage and performance degradation caused by oxidation reaction. This ensures that the low-crosslinked HDPE maintains a stable physicochemical state throughout the preparation process, thus ensuring the integrity of the obtained low-crosslinked HDPE structure and the consistency of its performance.

[0038] Furthermore, the cooling process in this invention employs conventional cooling methods in the art, namely, any one of programmed cooling, natural cooling, air cooling, or water cooling.

[0039] In the following examples and comparative examples, high-density polyethylene (melt index 6.3 g / 10 min, density 0.948 g / cm³) was used. 3 The granules were molded into test samples at a molding temperature of 190℃ and a pressure of 10 MPa for 10 min. The tensile strength of the samples was measured to be 25.3 MPa, the elongation at break was 495%, and the impact strength was 25.3 kJ / m. 2 The gel content is 0%.

[0040] In the following embodiments and comparative examples, the present invention employs the following testing methods; (1) Melt flow rate test: The melt flow rate of a polymer is the mass of the sample melt passing through a standard diameter capillary every 10 minutes under certain temperature and pressure. The melt flow rate is abbreviated as MFR and the unit is g·(10min). -1 When determining the melt flow index of HDPE, the temperature was set to 190℃, the load was 21.6kg, and the test was performed three times, with the average value taken. For specific testing, refer to standard GB / T3682-2000.

[0041] (2) Gel content test: Cross-linking reaction occurs between linear polyethylene molecular chains. Mild cross-linking reaction increases molecular weight. When the cross-linking density increases to the point that a network structure is formed between molecular chains, cross-linked polyethylene exhibits insoluble and infusible characteristics. Usually, the degree of cross-linking is higher when a network structure is formed. At this time, the degree of cross-linking can be calculated by the dissolution extraction method to determine its gel content. In this invention, the method of testing gel content is used to characterize the cross-linking situation. The experimental operation is as follows: Take a stainless steel sieve of appropriate size with a sieve mesh of 60 mesh, wash it with water and ethanol, dry it in a 100℃ drying oven for 1 hour, and weigh it, recording it as m1. Take 0.5-1.0g of sample, wrap it completely with the sieve, weigh it, and record it as m2. Pour xylene solution with a mass ratio of 200:1 to the mass of the sample to be tested into a round bottom flask, and add antioxidant 1010 at a ratio of 1%. Suspend the sample in a Soxhlet extractor, turn on the heating device, keep the solvent in a state of slight boiling, control the reflux rate at 20-40 drops / min, and extract for 24 hours. Remove the extracted sample and sieve, wash them twice with approximately 100 ml of ethanol, then place the sieve in a vacuum drying oven at 100°C for 3 hours. Remove the sieve and allow it to cool to room temperature. Weigh the total weight of the sieve and sample, record it as m³, and calculate the gel content (Gel) using the following formula.

[0042] Gel = (m3 - m1) / (m2 - m1) × 100% Where Gel is the sample gel content, m1 is the mass of the sieve, m2 is the total mass of the sieve and the sample before extraction, and m3 is the total mass of the sieve and the sample after extraction.

[0043] (3) Mechanical property testing: Mechanical property testing was conducted using the molding method. The sample was placed in a molding die and pressed at 190℃ and 10MPa for 10 minutes, then allowed to cool naturally to room temperature. The molding test was performed according to ASTM D638. The dumbbell sample was prepared according to the Type IV sample, with the following dimensions: length 115mm, thickness 3.2mm, and the narrow strip in the middle 33mm long and 6mm wide. Performance testing was conducted on an MTS microcomputer-controlled electronic universal testing machine (model CMT6503). During testing, the gauge length was 25mm, the tensile speed was 5.08cm / min, and at least 5 sets of tensile samples were tested, with the average value taken. Before testing, the samples needed to be placed in an environment with a temperature of 23±2℃ and a humidity of 50±5% for more than 24 hours. The specific tensile strength and elongation at break were tested according to ASTM D638 standard.

[0044] (4) Impact strength test: The impact strength test was conducted using a molding method, with the preparation method as described above. The impact strength was tested using a double-notch cantilever beam according to ASTM F648. The test sample size was 63.5 × 12.7 × 6.35 mm, with two notches, and 5 samples were used, with the average value taken. The cantilever beam impact tester was a Shanghai XJUD-5.5, with a maximum impact force of 5.5 J and an impact velocity of 3.5 m / s.

[0045] Example 1 Two kg of high-density polyethylene granules were placed in a cylindrical stainless steel irradiation chamber. Air was evacuated, and then nitrogen was introduced. The chamber was placed in an oven at 160°C for 2 hours. It was then removed and immediately covered with insulating cotton for heat preservation. The chamber was then placed in an X-ray field for irradiation for 30 minutes, with an absorbed dose of approximately 0.5 kGy. The temperature of the irradiation chamber after irradiation was measured at 142°C, indicating that the sample was in a molten state during irradiation. This X-ray field was an electron beam-targeted X-ray field used for radiation processing.

[0046] After irradiation, the irradiation chamber was removed and allowed to cool naturally to 70°C. The chamber was then opened, and the low-crosslinked high-density polyethylene was allowed to continue cooling to room temperature before the sample was removed. The sample was tested and found to have a melt flow index of 6.1 g / 10 min, a gel content of 0%, a tensile strength of 25.8 MPa, an elongation at break of 478%, and an impact strength of 26.1 kJ / m². 2 The results are listed in Table 1.

[0047] Example 2 Take 2 kg of high-density polyethylene granules and put them into a cylindrical stainless steel irradiation barrel. Evacuate the air and then purge with argon. Place the stainless steel barrel in an oven and bake at 160℃ for 2 hours. Then take it out and immediately cover it with insulation cotton to keep it warm. Place the stainless steel barrel in a cobalt-60 ray source and irradiate it with gamma rays for 40 min. The absorbed dose is about 5 kGy. The temperature of the irradiation barrel was measured at 140℃ after irradiation, indicating that the sample was in a molten state during the irradiation process.

[0048] After irradiation, the irradiation chamber was removed and allowed to cool naturally to 70°C. The chamber was then opened, and the low-crosslinked high-density polyethylene was allowed to continue cooling to room temperature before the sample was removed. The sample was tested and found to have a melt flow index of 4.3 g / 10 min, a gel content of 0%, a tensile strength of 26.1 MPa, an elongation at break of 446%, and an impact strength of 32.8 kJ / m². 2 The results are listed in Table 1.

[0049] Example 3 Take 2 kg of high-density polyethylene granules and put them into a cylindrical stainless steel irradiation barrel. Evacuate the air and then purge with argon. Place the stainless steel barrel in an oven and bake at 180℃ for 2 hours. Then take it out and immediately cover it with insulation cotton to keep it warm. Place the stainless steel barrel in a cobalt-60 ray source and irradiate it with gamma rays for 60 min. The absorbed dose is about 10 kGy. The temperature of the irradiation barrel was measured at 143℃ after irradiation, indicating that the sample was in a molten state during the irradiation process.

[0050] After irradiation, the irradiation chamber was removed and allowed to cool naturally to 70°C. The chamber was then opened, and the low-crosslinked high-density polyethylene was allowed to continue cooling to room temperature before the sample was removed. The sample was tested and found to have a melt flow index of 2.0 g / 10 min, a gel content of 0.03%, a tensile strength of 25.8 MPa, an elongation at break of 428%, and an impact strength of 42.3 kJ / m². 2 The results are listed in Table 1.

[0051] Example 4 Take about 1 kg of high-density polyethylene granules and place them in a flat stainless steel irradiation chamber. Evacuate the air and then purge with nitrogen. Place the stainless steel chamber in an oven at 150°C for 2 hours. Then remove it and immediately cover it with insulation cotton to keep it warm. Place it flat on the track of a 10MeV electron accelerator for irradiation. The sample placement method should ensure that the electron beam can penetrate and irradiate the entire sample. One irradiation cycle takes 10 minutes, and the absorbed dose is about 15 kGy. After irradiation, the temperature of the irradiation chamber was measured to be 145°C, indicating that the sample was in a molten state during the irradiation process.

[0052] After irradiation, the irradiation chamber was removed and allowed to cool naturally to 70°C. The chamber was then opened, and the low-crosslinked high-density polyethylene was allowed to continue cooling to room temperature before the sample was removed. The sample was tested and found to have a melt flow index of 2.1 g / 10 min, a gel content of 0.03%, a tensile strength of 27.3 MPa, an elongation at break of 436%, and an impact strength of 36.7 kJ / m². 2 The results are listed in Table 1.

[0053] Example 5 Approximately 1 kg of high-density polyethylene granules was placed in a flat stainless steel irradiation chamber. The chamber was evacuated and then filled with argon gas. The chamber was then placed in an oven at 150°C for 2 hours. Afterward, it was removed and immediately covered with insulating cotton for heat preservation. The chamber was then placed flat on the track of a 4.5 MeV electron accelerator for irradiation. The sample placement was designed to ensure that the electron beam could penetrate and irradiate the entire sample. One irradiation cycle lasted 10 minutes, with an absorbed dose of approximately 25 kGy. The temperature of the irradiation chamber after irradiation was measured at 145°C, indicating that the sample was in a molten state during irradiation.

[0054] After irradiation, the irradiation chamber was removed and allowed to cool naturally to 70°C. The chamber was then opened, and the low-crosslinked high-density polyethylene was allowed to continue cooling to room temperature before the sample was removed. The sample was tested and found to have a melt flow index of 1.0 g / 10 min, a gel content of 0.06%, a tensile strength of 28.7 MPa, an elongation at break of 395%, and an impact strength of 33.6 kJ / m². 2 The results are listed in Table 1.

[0055] Comparative Example 1 Compared with Example 5, conventional room temperature irradiation was used.

[0056] Take approximately 1 kg of high-density polyethylene granules, place them in a plastic bag, and lay them flat on the track of a 4.5 MeV electron accelerator for irradiation. The sample placement should ensure that the electron beam can penetrate and irradiate the entire sample. One irradiation cycle takes 10 minutes, with an absorbed dose of approximately 20 kGy.

[0057] After irradiation, the sample was tested. The melt flow index was 4.3 g / 10 min, the gel content was 0%, the tensile strength was 24.8 MPa, the elongation at break was 453%, and the impact strength was 26.3 kJ / m. 2 The results are listed in Table 1.

[0058] Comparative Example 2 Compared with Example 5, the high-dose irradiation treatment resulted in excessive cross-linking of high-density polyethylene.

[0059] Approximately 1 kg of high-density polyethylene granules was placed in a flat stainless steel irradiation chamber. The chamber was evacuated and then filled with argon gas. The chamber was then placed in an oven at 150°C for 2 hours. Afterward, it was removed and immediately covered with insulating cotton for heat preservation. The chamber was then placed flat on the track of a 4.5 MeV electron accelerator for irradiation. The sample placement was designed to ensure that the electron beam could penetrate and irradiate the entire sample. Two irradiation cycles were performed, lasting 25 minutes, with an absorbed dose of approximately 50 kGy. The temperature of the irradiation chamber after irradiation was measured at 148°C, indicating that the sample was in a molten state during the irradiation process.

[0060] After irradiation, the irradiation chamber was removed and allowed to cool naturally to room temperature. The chamber was then opened, and the sample was retrieved. The sample was tested, and the melt flow index was 0.1 g / 10 min, the gel content was 35.5%, the tensile strength was 28.6 MPa, the elongation at break was 368%, and the impact strength was 28.2 kJ / m². 2 The results are listed in Table 1.

[0061] Comparative Example 3 Compared with Example 3, the performance of HDPE deteriorated when treated with conventional gamma ray irradiation.

[0062] Take 2 kg of high-density polyethylene granules, put them in a plastic bag, place them in a cobalt-60 radiation source, and irradiate them with gamma rays for 60 min. The absorbed dose is about 10 kGy.

[0063] After irradiation, the sample was removed from the plastic bag. The sample was tested and found to have a melt flow index of 8.5 g / 10 min, a gel content of 0%, a tensile strength of 22.5 MPa, an elongation at break of 320%, and an impact strength of 21.4 kJ / m². 2 The results are listed in Table 1.

[0064] Table 1 As shown in the table, compared with Comparative Examples 1-3, the low-crosslinked high-density ethylene melts of Examples 1-5 have higher strength, lower gel content, and higher impact strength, exhibiting the best overall performance.

[0065] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing radiation-induced low-crosslinking high-density polyethylene, characterized in that, Includes the following steps: S1. Melting step: The high-density polyethylene is placed in an oxygen-free environment and heated to a completely molten state; S2. Irradiation step: The high-density polyethylene is irradiated with a high-energy ionizing radiation source while maintaining the high-density polyethylene in a molten state and in an oxygen-free environment to cause the molecular chains of the high-density polyethylene to crosslink. S3. Cooling step: Cool the irradiated high-density polyethylene to obtain low-crosslinked high-density polyethylene.

2. The method for preparing radiation-induced low-crosslinking high-density polyethylene according to claim 1, characterized in that, The specific steps of step S1 are as follows: S101. The high-density polyethylene is placed in an irradiation chamber, and the irradiation chamber is vacuum-treated and then filled with inert gas; S102. Heating the irradiation chamber to fully melt the high-density polyethylene inside the irradiation chamber; S103. After heating is completed, the irradiation tank and the molten high-density polyethylene are kept warm.

3. The method for preparing radiation-crosslinked high-density polyethylene according to claim 2, characterized in that, The inert gas in step S101 is any one of nitrogen, argon, or carbon dioxide.

4. The method for preparing radiation-induced low-crosslinking high-density polyethylene according to claim 3, characterized in that, The heating temperature in step S102 is 130℃-200℃.

5. The method for preparing radiation-crosslinked high-density polyethylene according to claim 1, characterized in that, In step S2, the absorbed dose of the high-density polyethylene is controlled by adjusting the radiation intensity of the rays emitted by the high-energy ionizing radiation source.

6. The method for preparing radiation-induced low-crosslinking high-density polyethylene according to claim 1, characterized in that, In step S2, the absorbed dose of the high-density polyethylene is controlled by adjusting the irradiation time of the high-energy ionizing radiation source.

7. The method for preparing radiation-induced low-crosslinking high-density polyethylene according to claim 1, characterized in that, The high-energy ionizing radiation source is an electron beam, gamma ray, or X-ray that can be used for radiation processing.

8. The method for preparing radiation-induced low-crosslinking high-density polyethylene according to claim 1, characterized in that, In step S3, the irradiated high-density polyethylene is placed in an oxygen-free environment and cooled to 70°C.

9. The method for preparing radiation-induced low-crosslinking high-density polyethylene according to claim 1, characterized in that, The high-density polyethylene is either a homopolymer or a copolymer, and the high-density polyethylene has a melt index of 0.01-10 g / 10 min and a density of 0.940-0.970 g / cm3.

10. A low-crosslinked high-density polyethylene, characterized in that, Low-crosslinked high-density polyethylene obtained by the preparation method according to any one of claims 1-9.

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