Polyethylene composite shielding bar based on boron carbide

Abstract

The invention discloses a polyethylene composite shielding bar based on boron carbide, and belongs to the technical field of shielding materials. Comprising the following raw materials in parts by weight: 60-80 parts of high-density polyethylene, 12-28 parts of modified boron carbide, 2-4 parts of a processing aid and 4-8 parts of an antioxidant. The prepared shielding bar takes high-density polyethylene as a matrix, so that the bar is endowed with excellent comprehensive performance and certain shielding performance; the added antioxidant can play a synergistic role, so that the oxidation resistance of the bar is greatly enhanced; compared with common boron carbide, the prepared modified boron carbide is better in compatibility with a polyethylene matrix, the flame retardance, shielding property and mechanical property of the bar can be greatly enhanced, and the performance is long and stable; therefore, the prepared bar is good in comprehensive performance and oxidation resistance, stable and efficient in flame retardance, shielding performance and mechanical performance and has important application value in the technical field of shielding materials.

Description

Technical Field

[0001] The invention belongs to the technical field of shielding materials, and in particular relates to a polyethylene composite shielding rod based on boron carbide. Background Art

[0002] With the increasing demand for energy and the emphasis on the environment, new energy is developing rapidly. Nuclear energy, as a clean and efficient form of energy, has received widespread attention. The development and utilization of nuclear energy has brought great changes to mankind, but nuclear reactors will produce highly radioactive rays during operation, namely nuclear radiation. Nuclear radiation refers to the particles or electromagnetic waves released by atomic nuclei during decay, fission, fusion, etc., mainly including alpha particles, beta particles, gamma rays and neutrons. These rays have high energy and can affect surrounding substances, posing a serious threat to people's life, health and property safety. Therefore, shielding materials are needed to shield these radioactive substances.

[0003] Shielding materials refer to functional materials that can attenuate the propagation of electromagnetic wave energy by absorption, reflection, etc., so as to effectively suppress electromagnetic interference and pollution. Such materials are essential for protecting human health. Currently commonly used shielding materials include heavy metal shielding materials, metal-based shielding materials and polymer-based shielding materials. Among them, metal-based composite materials are usually based on heavy metals and their oxides, which can be used for neutron shielding in extreme temperatures and chemical environments. The characteristic of polymer-based composite materials is that they have a low density and are often used for neutron shielding in spacecraft and portable instruments, but their performance in shielding photons and heavy ions is poor, so heavy metal particles are usually mixed into them to improve their performance in shielding photons and heavy ions.

[0004] Polyethylene is a common matrix for polymer-based shielding materials. Polyethylene is widely used as a matrix for radiation shielding composite materials due to its high hydrogen content, mature processing technology, low cost, large elastic scattering cross section, light weight, and good chemical stability. However, polyethylene-based shielding materials use polyethylene as a matrix, and the flame retardant properties of polyethylene itself are poor, and the shielding performance of single polyethylene is insufficient. Therefore, it is urgent to solve the above problems to meet its higher demands in the field of shielding material technology. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a polyethylene composite shielding rod based on boron carbide.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A polyethylene composite shielding rod based on boron carbide is prepared by the following steps:

[0008] A1. Add high-density polyethylene, modified boron carbide, processing aid and antioxidant into a mixer and stir for 15 minutes to fully mix the raw materials to obtain a mixture;

[0009] A2. Add the mixed material into a twin-screw extruder, set the temperature to 210-220°C, melt blend for 20-40 minutes, extrude into a mold, wait for it to cool, and finally cut and shape to obtain a polyethylene composite shielding rod based on boron carbide.

[0010] Furthermore, the raw materials are calculated in parts by weight as follows: 60-80 parts of high-density polyethylene, 12-28 parts of modified boron carbide, 2-4 parts of processing aids, and 4-8 parts of antioxidants.

[0011] Furthermore, the antioxidant is prepared by compounding a hindered phenol antioxidant and a phosphite antioxidant in a mass ratio of 3:1.

[0012] Furthermore, the processing aid is one of paraffin and zinc stearate.

[0013] With high-density polyethylene as the matrix, the comprehensive performance is better than that of ordinary polyethylene. In addition, high-density polyethylene itself has a high hydrogen content and has a good ability to weaken fast neutrons, which can enhance the shielding performance of the material. The antioxidant is a hindered phenol main antioxidant and a phosphite auxiliary antioxidant. The two can play a synergistic role and greatly enhance the antioxidant performance of the matrix.

[0014] Furthermore, the modified boron carbide is prepared by the following steps:

[0015] S1. Add sodium hydroxide to a three-necked round-bottom flask filled with methanol solution, stir and heat to 55°C, stir continuously to dissolve the sodium hydroxide, then add L-cystine, continue stirring to completely dissolve the L-cystine, then add glyoxal dropwise until the addition of glyoxal is complete, continue stirring, and heat the device to 75°C, reflux for 8h, and after the reaction is complete, filter, wash the filter residue with anhydrous ethanol, then wash three times with anhydrous ether, and vacuum dry to obtain intermediate 1; the ratio of the amount of methanol solution, sodium hydroxide, L-cystine, and glyoxal is 100mL:4.0g:24.0g:5.8g;

[0016] Sodium hydroxide is used as a condensing agent, and the amino group in the L-cystine molecule condenses with the aldehyde group in the glyoxal molecule to form an imine group (C=N Schiff base structure) to obtain intermediate 1; the specific reaction process is shown below:

[0017]

[0018] S2. In a three-necked flask equipped with a stirring device, the intermediate 1, n-decylamine, dicyclohexylcarbodiimide (dehydrating agent) and N,N-dimethylformamide (DMF) were mixed and stirred uniformly, and reacted for 5 hours in a 50°C water bath. After the reaction was completed, the mixture was filtered, and some solvents were removed by vacuum distillation. The mixture was purified by column chromatography (the eluent was a mixed solvent of petroleum ether / ethyl acetate in a volume ratio of 5:1), and the eluent was removed by rotary evaporation to obtain intermediate 2; the ratio of the amount of intermediate 1, n-decylamine, dicyclohexylcarbodiimide and N,N-dimethylformamide was 55.7 g:47.1 g:61.8 g:300 mL;

[0019] The carboxyl group on the intermediate 1 and the amino group on the n-decylamine undergo an amidation reaction. Under the action of a dehydrating agent, the reaction can be carried out under relatively mild conditions. By controlling the molar ratio of the intermediate 1 to the n-decylamine to be close to 1:3 and the intermediate 1 to be slightly excessive, only three carboxyl groups on the intermediate 1 participate in the reaction, and the intermediate 2 is obtained. The specific reaction process is as follows:

[0020]

[0021] S3, boron carbide, distilled water and ethanol solution are placed in a flask, and shaken vigorously to obtain a boron carbide dispersion, γ-aminopropyltriethoxysilane (KH-550) is added to the boron carbide dispersion, and the mixture is shaken in a constant temperature oscillator at 45° C. for 24 hours, filtered, dried, crushed, and passed through a 200-mesh sieve to obtain pre-modified boron carbide; the ratio of boron carbide, ethanol solution, distilled water, and γ-aminopropyltriethoxysilane is 1g:50mL:50mL:5.3g;

[0022] There are many -OH groups on the surface of boron carbide, which can be introduced into amino groups by reacting with γ-aminopropyltriethoxysilane to obtain pre-modified boron carbide;

[0023] S4. Add N,N-dimethylformamide, dicyclohexylcarbodiimide and pre-modified boron carbide to a flask, disperse them uniformly by ultrasonication for 45 minutes, add intermediate 2, slowly heat to 50°C, start magnetic stirring (speed 1200r / min), stop heating after stirring for 6 hours, filter after the temperature in the reaction bottle drops to 25°C, wash with anhydrous ethanol 3-4 times, and freeze-dry to obtain modified boron carbide; the ratio of N,N-dimethylformamide, dicyclohexylcarbodiimide, pre-modified boron carbide and intermediate 2 is 100mL:3.7g:1g:7.6g;

[0024] Under the action of dicyclohexylcarbodiimide, the amino group on the pre-modified boron carbide undergoes an amidation reaction with the carboxyl group on the intermediate 2 to obtain modified boron carbide;

[0025] Boron carbide can be used as an excellent shielding material because it contains boron. Boron can absorb thermal neutron energy and neutron radiation and convert it into heat or other forms of energy, thereby shielding neutron radiation and enhancing the shielding performance of the polyethylene matrix. By modifying boron carbide, the surface hydrophobicity of boron carbide can be enhanced, making it more compatible with the polyethylene matrix, making it easier to exert the performance of boron carbide. In addition, the modified boron carbide can well protect the organic molecular chain, making it difficult to migrate and seep out, and improving the durability of the performance. In addition, the modified boron carbide molecule also contains Schiff base and long carbon chain structure, among which Schiff base mainly refers to the imine or azomethine characteristic group. Due to its special structure, it can be used as a self-crosslinking unit to form a relatively stable crosslinking network in a lower temperature range. At the same time, when the matrix burns, NH 3 Nitrogen-containing non-flammable gases such as nitrogen can dilute combustible gases and reduce the oxygen concentration around the material, thereby producing a flame retardant effect on the gas phase. Moreover, since the flame retardant is a macrocyclic compound, it has better heat resistance and stability than ordinary Schiff bases. In addition, the introduced long carbon chain belongs to a flexible chain segment, which can not only enhance the mechanical properties of the matrix, but also can be interspersed in the macromolecular chain of the matrix, further improving the stability of the matrix.

[0026] Beneficial effects of the present invention:

[0027] 1. The shielding rod material prepared by the present invention is based on high-density polyethylene, which gives the rod material excellent comprehensive performance and certain shielding performance;

[0028] 2. The added antioxidant can play a synergistic role and greatly enhance the antioxidant properties of the rod;

[0029] 3. Compared with ordinary boron carbide, the modified boron carbide has better compatibility with the polyethylene matrix, can greatly enhance the flame retardancy, shielding and mechanical properties of the rod, and has long-term stable performance;

[0030] Therefore, the rod material prepared by the present invention has good comprehensive performance and anti-oxidation performance, and also has stable and efficient flame retardancy, shielding and mechanical properties, and has important application value in the field of shielding material technology. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Embodiment 1

[0033] Preparation of modified boron carbide:

[0034] S1. Add 4.0 g of sodium hydroxide to a three-necked round-bottom flask containing 100 mL of methanol solution, stir and heat to 55 ° C, stir continuously to dissolve the sodium hydroxide, then add 24.0 g of L-cystine, continue stirring to completely dissolve the L-cystine, then add 5.8 g of glyoxal dropwise until the addition of glyoxal is complete, continue stirring, and heat the device to 75 ° C, reflux for 8 hours, the reaction is complete, filter, wash the filter residue with anhydrous ethanol, and then wash it three times with anhydrous ether, and vacuum dry to obtain intermediate 1;

[0035] S2, in a three-necked flask equipped with a stirring device, 55.7g of intermediate 1, 47.1g of n-decylamine, 61.8g of dicyclohexylcarbodiimide and 300mL of N,N-dimethylformamide were mixed and stirred evenly, and reacted for 5h in a 50°C water bath. After the reaction was completed, the mixture was filtered, and part of the solvent was removed by distillation under reduced pressure. The mixture was purified by column chromatography (the eluent was a mixed solvent of petroleum ether / ethyl acetate in a volume ratio of 5:1), and the eluent was removed by rotary evaporation to obtain intermediate 2;

[0036] S3, 1g boron carbide, 50mL distilled water and 50mL ethanol solution were placed in a flask, and shaken vigorously to obtain a boron carbide dispersion, 5.3g γ-aminopropyltriethoxysilane was added to the boron carbide dispersion, and the mixture was shaken in a constant temperature oscillator at 45°C for 24h, filtered, dried, crushed, and passed through a 200-mesh sieve to obtain pre-modified boron carbide;

[0037] S4. Add 100 mL of N,N-dimethylformamide, 3.7 g of dicyclohexylcarbodiimide and 1 g of pre-modified boron carbide into a flask. After uniform dispersion by ultrasonication for 45 min, add 7.6 g of intermediate 2, slowly heat to 50 °C, start magnetic stirring (speed 1200 r / min), stop heating after stirring for 6 h, wait until the temperature in the reaction bottle drops to 25 °C, filter, wash 4 times with anhydrous ethanol, and freeze-dry to obtain modified boron carbide.

[0038] Embodiment 2

[0039] Preparation of modified boron carbide:

[0040] S1. Add 8.0 g of sodium hydroxide to a three-necked round-bottom flask containing 200 mL of methanol solution, stir and heat to 55 ° C, stir continuously to dissolve the sodium hydroxide, then add 48.0 g of L-cystine, continue stirring to completely dissolve the L-cystine, then add 11.6 g of glyoxal dropwise until the addition of glyoxal is complete, continue stirring, and heat the device to 75 ° C, reflux for 8 hours, the reaction is complete, filter, wash the filter residue with anhydrous ethanol, and then wash it three times with anhydrous ether, and vacuum dry to obtain intermediate 1;

[0041] S2, in a three-necked flask equipped with a stirring device, 111.4 g of intermediate 1, 94.2 g of n-decylamine, 123.6 g of dicyclohexylcarbodiimide and 600 mL of N, N-dimethylformamide were mixed and stirred evenly, and reacted for 5 h in a 50° C. water bath. After the reaction was completed, the mixture was filtered, and some solvents were removed by distillation under reduced pressure. The mixture was purified by column chromatography (the eluent was a mixed solvent of petroleum ether / ethyl acetate in a volume ratio of 5:1), and the eluent was removed by rotary evaporation to obtain intermediate 2;

[0042] S3, 2g of boron carbide, 100mL of distilled water and 100mL of ethanol solution were placed in a flask, and shaken vigorously to obtain a boron carbide dispersion, 10.6g of γ-aminopropyltriethoxysilane was added to the boron carbide dispersion, and the mixture was shaken in a constant temperature oscillator at 45°C for 24h, filtered, dried, crushed, and passed through a 200-mesh sieve to obtain pre-modified boron carbide;

[0043] S4. Add 200 mL of N,N-dimethylformamide, 7.4 g of dicyclohexylcarbodiimide and 2 g of pre-modified boron carbide into a flask. After uniform dispersion by ultrasonication for 45 min, add 15.2 g of intermediate 2, slowly heat to 50 °C, start magnetic stirring (speed 1200 r / min), stop heating after stirring for 6 h, wait until the temperature in the reaction bottle drops to 25 °C, filter, wash 3 times with anhydrous ethanol, and freeze-dry to obtain modified boron carbide.

[0044] Embodiment 3

[0045] A1. Add 60 g of high-density polyethylene, 12 g of modified boron carbide prepared in Example 1, 2 g of paraffin wax and 4 g of antioxidant (prepared by compounding 3 g of antioxidant 1010 and 1 g of antioxidant 168) into a blender, and stir for 15 min to fully mix the raw materials to obtain a mixture;

[0046] A2. Add the mixed material into a twin-screw extruder, set the temperature to 210° C., melt blend for 20 minutes, and extrude to obtain a polyethylene composite shielding material based on boron carbide.

[0047] Embodiment 4

[0048] A1. Add 70 g of high-density polyethylene, 20 g of modified boron carbide obtained in Example 2, 3 g of zinc stearate and 8 g of antioxidant (6 g of antioxidant 1010 and 2 g of antioxidant 168) into a blender, and stir for 15 min to fully mix the raw materials to obtain a mixture;

[0049] A2. Add the mixed material into a twin-screw extruder, set the temperature to 215° C., melt blend for 30 minutes, and extrude to obtain a polyethylene composite shielding material based on boron carbide.

[0050] The material is put into a mold, cooled, and finally cut into shape to obtain a polyethylene composite shielding rod based on boron carbide.

[0051] Embodiment 5

[0052] A1. Add 80 g of high-density polyethylene, 28 g of modified boron carbide obtained in Example 2, 4 g of zinc stearate and 8 g of antioxidant (prepared by compounding 6 g of antioxidant 1010 and 2 g of antioxidant 168) into a blender, and stir for 15 min to fully mix the raw materials to obtain a mixture;

[0053] A2. Add the mixed material into a twin-screw extruder, set the temperature to 220° C., melt blend for 40 minutes, and extrude to obtain a polyethylene composite shielding material based on boron carbide.

[0054] Embodiment 6

[0055] A1. Add 80 g of high-density polyethylene, 28 g of modified boron carbide obtained in Example 2, 4 g of zinc stearate and 8 g of antioxidant (prepared by compounding 6 g of antioxidant 1010 and 2 g of antioxidant 168) into a blender, and stir for 15 min to fully mix the raw materials to obtain a mixture;

[0056] A2. Add the mixed material into a twin-screw extruder, set the temperature to 220° C., melt blend for 40 minutes, extrude into a mold, wait for it to cool, and finally cut and shape to obtain a polyethylene composite shielding rod based on boron carbide.

[0057] Comparative Example 1

[0058] Ordinary boron carbide of equal mass is used to replace the modified boron carbide in Example 5, and the remaining steps are the same as those in Example 5.

[0059] Comparative Example 2

[0060] Use polyethylene shielding material.

[0061] Embodiments 3, 4, 5, and comparative examples 1 and 2 were made into corresponding shapes according to different test standards, and the following performance tests were performed:

[0062] The tensile strength is determined using the national standard GB / T 1040.2-2022 "Determination of tensile properties of plastics";

[0063] The oxygen index was determined using the national standard GB / T 2406.2-2009 "Determination of Combustion Behavior of Plastics Using Oxygen Index Method"; after leaving Examples 3, 4, and 5 at room temperature for 200 days, the limiting oxygen index was determined using the same standard;

[0064] A Cf-252 neutron radiation source was used, and a 12 cm paraffin block was added to moderate the thermal neutron source. A 3He proportional counter imported from LND, USA, was used to measure the thermal neutron attenuation coefficient of the sample.

[0065] Using 60CoY radiation source and NaI crystal detector, the γ radiation attenuation coefficient of the sample was measured;

[0066] The measured results are shown in the following table:

[0067]

[0068] It can be seen from the above table that the polyethylene shielding material prepared in the embodiment of the present invention has better flame retardancy, shielding properties and mechanical properties than the control example, and the performance is long-lasting and stable. Therefore, the present invention has important application value in the field of shielding material technology.

[0069] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0070] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A polyethylene composite shielding rod based on boron carbide, characterized in that: Prepared by the following steps: A1. Add high-density polyethylene, modified boron carbide, processing aid and antioxidant into a mixer and stir for 15 minutes to fully mix the raw materials to obtain a mixture; A2. Add the mixed material into a twin-screw extruder, set the temperature to 210-220°C, melt blend for 20-40 minutes, extrude into a mold, wait for it to cool, and finally cut and shape to obtain a polyethylene composite shielding rod based on boron carbide.

2. The boron carbide-based polyethylene composite shielding rod according to claim 1, characterized in that: The modified boron carbide is prepared by the following steps: S1. Add sodium hydroxide to a flask containing methanol solution, stir and heat to 55°C, stir continuously to dissolve the sodium hydroxide, then add L-cystine, continue stirring to completely dissolve the L-cystine, then add glyoxal dropwise until the addition of glyoxal is complete, continue stirring, reflux at 75°C for 8h, and after the reaction is complete, filter, wash and dry to obtain intermediate 1; S2, mixing intermediate 1, n-decylamine, dicyclohexylcarbodiimide and N,N-dimethylformamide, stirring evenly, reacting in a water bath at 50°C for 5 hours, filtering, distilling under reduced pressure, purifying by column chromatography, and rotary evaporating to obtain intermediate 2; S3, boron carbide, distilled water and ethanol solution are placed in a flask, and shaken vigorously to obtain a boron carbide dispersion, γ-aminopropyltriethoxysilane is added to the boron carbide dispersion, and the mixture is shaken in a constant temperature oscillator at 45° C. for 24 h, filtered, dried, crushed, and passed through a 200-mesh sieve to obtain pre-modified boron carbide; S4. Add N,N-dimethylformamide, dicyclohexylcarbodiimide and pre-modified boron carbide into a flask, disperse by ultrasonic, add intermediate 2, slowly heat to 50°C, start magnetic stirring, stop heating after stirring for 6 hours, let stand to cool, filter, wash, and freeze-dry to obtain modified boron carbide.

3. The boron carbide-based polyethylene composite shielding rod according to claim 2, characterized in that: In step S1, the ratio of the amount of methanol solution, sodium hydroxide, L-cystine and glyoxal is 100 mL: 4.0 g: 24.0 g: 5.8 g.

4. The boron carbide-based polyethylene composite shielding rod according to claim 2, characterized in that: In step S2, the ratio of the amount of intermediate 1, n-decylamine, dicyclohexylcarbodiimide, and N,N-dimethylformamide is 55.7 g:47.1 g:61.8 g:300 mL.

5. The boron carbide-based polyethylene composite shielding rod according to claim 2, characterized in that: In step S3, the ratio of boron carbide, ethanol solution, distilled water, and γ-aminopropyltriethoxysilane is 1 g:50 mL:50 mL:5.3 g.

6. The boron carbide-based polyethylene composite shielding rod according to claim 2, characterized in that: In step S4, the ratio of the amount of N,N-dimethylformamide, dicyclohexylcarbodiimide, pre-modified boron carbide, and intermediate 2 is 100 mL: 3.7 g: 1 g: 7.6 g.

7. The boron carbide-based polyethylene composite shielding rod according to claim 1, characterized in that: The raw materials are calculated in parts by weight as follows: 60-80 parts of high-density polyethylene, 12-28 parts of modified boron carbide, 2-4 parts of processing aids, and 4-8 parts of antioxidants.

8. The boron carbide-based polyethylene composite shielding rod according to claim 1, characterized in that: The antioxidant is prepared by compounding a hindered phenol antioxidant and a phosphite antioxidant in a mass ratio of 3:

1.

9. The boron carbide-based polyethylene composite shielding rod according to claim 1, characterized in that: The processing aid is one of paraffin wax and zinc stearate.

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