A polyethylene composite shielding material for nuclear radiation protection

Abstract

This invention discloses a polyethylene composite shielding material for nuclear radiation protection, belonging to the technical field of shielding materials. The composite shielding material is composed of lead powder, boron carbide, ultra-high molecular weight polyethylene, and a modifier solution. The modifier is prepared via Schiff base reaction, DOPO addition, and Mannich condensation, and its molecular structure simultaneously contains silane coupling groups, phosphorus-containing phenanthrene flame-retardant groups, and compliant siloxane segments. This modifier can chemically modify the surface of inorganic fillers, improving their dispersion state and interfacial bonding strength in the polyethylene matrix, and exerting a synergistic effect of gas-phase flame retardancy and condensed-phase char formation. This results in a material with excellent radiation and neutron shielding performance, superior mechanical strength, and flame retardant properties, suitable for applications with stringent radiation protection and fire safety requirements.

Description

Technical Field

[0001] This invention belongs to the field of shielding materials technology, specifically, it relates to a polyethylene composite shielding material for nuclear radiation protection. Background Technology

[0002] Currently, nuclear radiation shielding materials are generally prepared by combining a polymer matrix with heavy metals or neutron-absorbing fillers. A common technique involves using polyethylene as the matrix and filling it with inorganic particles such as lead powder and boron carbide. These materials utilize the attenuation effect of lead on gamma rays and the absorption capacity of boron carbide for thermal neutrons to achieve a certain degree of protection against mixed radiation fields. However, in practical applications, the above-mentioned composite system has obvious technical shortcomings: On the one hand, lead powder and boron carbide are both inorganic particles with high surface energy, and their interfacial properties differ greatly from those of the hydrophobic polyethylene matrix. When directly mechanically blended, the filler is difficult to disperse evenly and is prone to agglomeration. This not only causes uneven distribution of the shielding functional phase and weakens the overall shielding efficiency, but also forms a large number of stress concentration points in the matrix, resulting in a significant deterioration of the material's tensile strength, impact toughness, and other mechanical properties. On the other hand, in order to improve dispersibility, existing technologies often use silane coupling agents (such as γ-aminopropyltriethoxysilane) to treat the filler surface. However, such simple treatment can only improve affinity to a limited extent, and the coating of the filler is incomplete. Moreover, the coupling agent molecules lack functional structures and cannot solve the problem of insufficient interfacial bonding strength at the same time. Furthermore, it fails to take into account the inherent flammability of polyethylene materials. In application scenarios such as nuclear facilities and nuclear waste transportation, fire safety is also a key indicator. Conventional polyethylene composite shielding materials are not modified for flame retardancy, and their limiting oxygen index is usually below 20%. They are easily ignited and produce molten droplets when exposed to fire, posing a serious fire hazard.

[0003] Therefore, existing technologies cannot simultaneously meet the multiple requirements of uniform filler dispersion, strong interfacial bonding, maintenance of mechanical properties, and improvement of flame retardant properties, which restricts the development and application of high-performance integrated shielding materials. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a polyethylene composite shielding material for nuclear radiation protection.

[0005] The objective of this invention can be achieved through the following technical solutions: A polyethylene composite shielding material for nuclear radiation protection comprises the following components: by weight, 40-70 parts lead powder, 10-20 parts boron carbide, 20-35 parts ultra-high molecular weight polyethylene, 0.3-1 part antioxidant, 0.5-1 part lubricant, and 7-8 parts modifier solution. The preparation process of the modifier solution is as follows: S1: Under an inert atmosphere, γ-aminopropyltriethoxysilane and p-hydroxybenzaldehyde were added to anhydrous toluene, followed by the addition of glacial acetic acid. The mixture was stirred at 80°C for 8 hours. Subsequently, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was added, and the mixture was heated to 100°C and reacted for another 10 hours. After the reaction was completed, the solvent was removed by concentration under reduced pressure. The residue was purified by silica gel column chromatography to obtain intermediate A. S2: Under an inert atmosphere, intermediate A, paraformaldehyde, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and anhydrous ethanol were mixed and stirred until homogeneous. The temperature was then raised to 90°C and refluxed for 12 hours. After the reaction was completed, the solvent was removed by vacuum concentration. The residue was purified by silica gel column chromatography to obtain the modifier. S3: Add the modifier to anhydrous ethanol, stir until homogeneous, and obtain the modifier solution.

[0006] In the scheme, under an inert atmosphere and anhydrous conditions, the primary amino group of γ-aminopropyltriethoxysilane and the aldehyde group of p-hydroxybenzaldehyde first undergo a nucleophilic addition-elimination reaction catalyzed by glacial acetic acid, resulting in dehydration to generate a Schiff base intermediate containing an imine bond. Subsequently, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is added, utilizing its pH bond to nucleophilically add to the C=N double bond of the Schiff base, introducing the phosphaphenanthrene-containing structure into the molecule to form intermediate A. Intermediate A is then subjected to further analysis... After purification, the material undergoes a Mannich condensation reaction with paraformaldehyde and 1,3-bis(3-aminopropyl)tetramethyldisiloxane in anhydrous ethanol. Upon heating, the paraformaldehyde depolymerizes, releasing formaldehyde monomers, which act as methylene bridging agents to connect the active hydrogen at the para-position of the phenolic hydroxyl group in intermediate A to the primary amino groups at both ends of the disiloxane, constructing a symmetrical modifier with a siloxane segment as the central backbone and symmetrically introduced DOPO-based phosphorus-containing flame-retardant units at both ends. Finally, the modifier is dissolved in anhydrous ethanol to obtain a homogeneous solution. The entire synthesis process is carried out in an anhydrous environment to avoid the hydrolytic condensation of the terminal silylacetyl groups of γ-aminopropyltriethoxysilane. The resulting modifier molecule possesses silane coupling groups, phosphorus-containing flame-retardant groups, and flexible siloxane segments, thus exhibiting multiple functions including promoting filler dispersion, enhancing interfacial compatibility, and improving the flame-retardant properties of the material.

[0007] The structure of the modifier is shown below:

[0008] In a more optimized manner, in step S1, the ratio of the amounts of γ-aminopropyltriethoxysilane, p-hydroxybenzaldehyde, anhydrous toluene, glacial acetic acid, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 22.1g:12.2g:200mL:6g:21.6g.

[0009] In a more optimized manner, in step S2, the ratio of intermediate A, paraformaldehyde, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and anhydrous ethanol is 54.1g:3.3g:12.4g:200mL.

[0010] In a more optimized manner, in step S3, the ratio of modifier to anhydrous ethanol is 60g:200mL.

[0011] More preferably, the antioxidant is selected from at least one of antioxidant 1010, antioxidant 1076, antioxidant 168, antioxidant BHT, and antioxidant 2246.

[0012] Ideally, the lubricant is zinc stearate.

[0013] Ideally, the lead powder has a particle size of 10-30 μm.

[0014] Ideally, the boron carbide has a particle size of 2-10 μm.

[0015] The beneficial effects of this invention are: The polyethylene composite shielding material provided in this application achieves multiple performance enhancements by introducing a phosphorus-nitrogen-silicon modifier solution into the formulation, utilizing its unique molecular structure. One end of the modifier molecule contains a silane ethoxy group, which, during processing, can condense with the hydroxyl groups on the surface of lead powder and boron carbide fillers to form stable chemical bonds. This transforms the surface of the inorganic filler particles from hydrophilic to oleophilic, effectively reducing the interfacial tension between the filler and the ultra-high molecular weight polyethylene matrix, breaking up the agglomeration of filler particles, and ensuring uniform dispersion of lead powder and boron carbide in the matrix. This reduces stress concentration points caused by filler aggregation, improving the overall mechanical integrity and shielding uniformity of the material. Simultaneously, the symmetrical structure of the modifier molecule, with siloxane segments as the central backbone, endows it with good molecular flexibility, enabling the formation of a stable interfacial layer on the filler surface, further enhancing the compatibility and interfacial bonding strength between the filler and the resin matrix. Furthermore, the phosphorus-containing phenanthrene structure introduced through DOPO in the modifier molecule can decompose thermally during combustion, releasing phosphorus-containing free radicals that effectively capture hydrogen and hydroxyl radicals in the combustion chain reaction, thus interrupting the combustion reaction. Simultaneously, the nitrogen-containing components and siloxane segments in the molecule synergistically promote the formation of a dense, expanded char layer on the polymer matrix surface. This char layer acts as a barrier, both isolating heat transfer and preventing the escape of combustible gases, thereby endowing the polyethylene composite material with excellent dual flame-retardant effects in both the gas and condensed phases. Overall, this material possesses good gamma-ray and neutron shielding properties, excellent mechanical strength, and flame-retardant properties, making it suitable for applications with high requirements for radiation protection and fire safety. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1: A polyethylene composite shielding material for nuclear radiation protection, comprising the following steps: Step 1: Add 40 parts lead powder (10μm particle size), 10 parts boron carbide (10μm particle size), 20 parts ultra-high molecular weight polyethylene, and 0.3 parts antioxidant (antioxidant 1010) to a high-speed mixer. Premix at low speed for 5 minutes. Then switch to high speed and add 6 parts modifier solution dropwise in batches while continuously stirring. After the addition is complete, continue stirring at high speed for 15 minutes. Then add 0.5 parts lubricant (zinc stearate) and continue stirring at high shear mode for 12 minutes. After stirring, discharge the material, allow it to cool naturally to room temperature, and sieve to break up any agglomerates to obtain the modified composite powder. Step 2: Fill the modified composite powder into a steel mold, place it in a hot press, and hot press it (temperature 170℃, pressure 10MPa, time 100min). Then, maintain the mold closing pressure and introduce cooling medium to cold press and shape it. After cooling, demold to obtain polyethylene composite shielding material. The preparation process of the modifier solution is as follows: S1: Under an inert atmosphere, 22.1 g of γ-aminopropyltriethoxysilane and 12.2 g of p-hydroxybenzaldehyde were added to 200 mL of anhydrous toluene, followed by 6 g of glacial acetic acid. The mixture was stirred at 80 °C for 8 h. Subsequently, 21.6 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was added, and the mixture was heated to 100 °C and reacted for another 10 h. After the reaction was completed, the solvent was removed by concentration under reduced pressure. The residue was purified by silica gel column chromatography to obtain intermediate A. S2: Under an inert atmosphere, 54.1 g of intermediate A, 3.3 g of paraformaldehyde, 12.4 g of 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and 200 mL of anhydrous ethanol were mixed and stirred until homogeneous. The temperature was then raised to 90 °C and refluxed for 12 h. After the reaction was completed, the solvent was removed by vacuum concentration. The residue was purified by silica gel column chromatography to obtain the modifier. S3: Add 60g of modifier to 200mL of anhydrous ethanol, stir well to obtain a modifier solution.

[0018] Example 2: A polyethylene composite shielding material for nuclear radiation protection, comprising the following steps: Step 1: Add 70 parts lead powder (particle size 10μm), 20 parts boron carbide (particle size 10μm), 35 parts ultra-high molecular weight polyethylene, and 1 part antioxidant (antioxidant 1010) to a high-speed mixer. Premix at low speed for 5 minutes. Then switch to high speed and add 7 parts modifier solution dropwise in batches while continuously stirring. After the addition is complete, continue stirring at high speed for 15 minutes. Then add 0.8 parts lubricant (zinc stearate) and continue stirring at high shear mode for 12 minutes. After stirring, discharge the material, allow it to cool naturally to room temperature, and sieve to break up any agglomerates to obtain the modified composite powder. Step 2: Fill the modified composite powder into a steel mold, place it in a hot press, and hot press it (temperature 170℃, pressure 10MPa, time 100min). Then, maintain the mold closing pressure and introduce cooling medium to cold press and shape it. After cooling, demold to obtain polyethylene composite shielding material. The preparation process of the modifier solution is as follows: S1: Under an inert atmosphere, 22.1 g of γ-aminopropyltriethoxysilane and 12.2 g of p-hydroxybenzaldehyde were added to 200 mL of anhydrous toluene, followed by 6 g of glacial acetic acid. The mixture was stirred at 80 °C for 8 h. Subsequently, 21.6 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was added, and the mixture was heated to 100 °C and reacted for another 10 h. After the reaction was completed, the solvent was removed by concentration under reduced pressure. The residue was purified by silica gel column chromatography to obtain intermediate A. S2: Under an inert atmosphere, 54.1 g of intermediate A, 3.3 g of paraformaldehyde, 12.4 g of 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and 200 mL of anhydrous ethanol were mixed and stirred until homogeneous. The temperature was then raised to 90 °C and refluxed for 12 h. After the reaction was completed, the solvent was removed by vacuum concentration. The residue was purified by silica gel column chromatography to obtain the modifier. S3: Add 60g of modifier to 200mL of anhydrous ethanol, stir well to obtain a modifier solution.

[0019] Example 3: A polyethylene composite shielding material for nuclear radiation protection, comprising the following steps: Step 1: Add 50 parts lead powder (particle size 10μm), 15 parts boron carbide (particle size 10μm), 30 parts ultra-high molecular weight polyethylene, and 0.8 parts antioxidant (antioxidant 1010) to a high-speed mixer. Premix at low speed for 5 minutes. Then switch to high speed and add 6.5 parts modifier solution dropwise in batches while continuously stirring. After the addition is complete, continue stirring at high speed for 15 minutes. Then add 0.6 parts lubricant (zinc stearate) and continue stirring at high shear mode for 12 minutes. After stirring, discharge the material, allow it to cool naturally to room temperature, and sieve to break up any agglomerates to obtain the modified composite powder. Step 2: Fill the modified composite powder into a steel mold, place it in a hot press, and hot press it (temperature 170℃, pressure 10MPa, time 100min). Then, maintain the mold closing pressure and introduce cooling medium to cold press and shape it. After cooling, demold to obtain polyethylene composite shielding material. The preparation process of the modifier solution is as follows: S1: Under an inert atmosphere, 22.1 g of γ-aminopropyltriethoxysilane and 12.2 g of p-hydroxybenzaldehyde were added to 200 mL of anhydrous toluene, followed by 6 g of glacial acetic acid. The mixture was stirred at 80 °C for 8 h. Subsequently, 21.6 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was added, and the mixture was heated to 100 °C and reacted for another 10 h. After the reaction was completed, the solvent was removed by concentration under reduced pressure. The residue was purified by silica gel column chromatography to obtain intermediate A. S2: Under an inert atmosphere, 54.1 g of intermediate A, 3.3 g of paraformaldehyde, 12.4 g of 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and 200 mL of anhydrous ethanol were mixed and stirred until homogeneous. The temperature was then raised to 90 °C and refluxed for 12 h. After the reaction was completed, the solvent was removed by vacuum concentration. The residue was purified by silica gel column chromatography to obtain the modifier. S3: Add 60g of modifier to 200mL of anhydrous ethanol, stir well to obtain a modifier solution.

[0020] Comparative Example 1: Directly add γ-aminopropyltriethoxysilane, as follows: A polyethylene composite shielding material for nuclear radiation protection includes the following steps: Step 1: Add 50 parts lead powder (particle size 10μm), 15 parts boron carbide (particle size 10μm), 30 parts ultra-high molecular weight polyethylene, and 0.8 parts antioxidant (antioxidant 1010) to a high-speed mixer. Premix at low speed for 5 minutes. Then switch to high speed and add 6.5 parts γ-aminopropyltriethoxysilane dropwise in batches while continuously stirring. After the addition is complete, continue stirring at high speed for 15 minutes. Then add 0.6 parts lubricant (zinc stearate) and continue stirring in high-shear mode for 12 minutes. After stirring, discharge the material, allow it to cool naturally to room temperature, and sieve to break up any agglomerates to obtain the modified composite powder. Step 2: Fill the modified composite powder into a steel mold, place it in a hot press, and hot press it (temperature 170℃, pressure 10MPa, time 100min). Then, maintain the mold closing pressure and introduce cooling medium to cold press and shape it. After cooling, demold to obtain polyethylene composite shielding material.

[0021] Testing Experiment (I): The polymer materials obtained from the examples and comparative examples were prepared into corresponding samples according to different testing standards, and relevant tests were conducted: (1) The oxygen index was determined according to the national standard GB / T2406.2-2009; (2) Tensile strength was determined according to national standard GB / T 1040.2-2022; The obtained data is shown in Table 1: Table 1

[0022] Test (II): The polymer materials obtained in the examples and comparative examples were prepared into corresponding samples with a thickness of 25 mm according to different test standards, and relevant tests were carried out at room temperature: (1) Thermal neutron shielding performance test A thermal neutron field was generated using a Cf-252 neutron source through a 12 cm thick paraffin moderation layer, employing LND Corporation. 3 He proportional counters are used to determine the thermal neutron shielding efficiency of materials (characterized by attenuation coefficients). (2) Fast neutron shielding performance test Fast neutrons emitted directly from the Cf-252 neutron source, through 3 He counters are used to quantitatively analyze the attenuation ability of materials for fast neutrons; (3) Gamma-ray shielding performance test use 60 The gamma rays emitted by the Co radioactive source were used in conjunction with a NaI crystal detector to accurately measure the material's shielding effectiveness against gamma radiation (expressed as attenuation coefficient); the data obtained are shown in Table 2. Table 2

[0023] Conclusion: Based on the comparison of test data from Examples 1 to 3 and Comparative Example 1, the following conclusions can be drawn: The polyethylene composite shielding material prepared by this invention is significantly superior to the comparative example with directly added γ-aminopropyltriethoxysilane in terms of mechanical properties, flame retardant properties, and radiation shielding properties. In terms of mechanical properties, the tensile strength of Example 3 reached 27.2 MPa, which is approximately 41% higher than the 19.3 MPa of Comparative Example 1. This indicates that treating the inorganic filler with the modifier solution effectively improves the interfacial compatibility and dispersion uniformity between the filler and the ultra-high molecular weight polyethylene matrix, reduces stress concentration, and thus significantly enhances the structural integrity of the material. Regarding flame retardant properties, the limiting oxygen index of Example 3 was 28.3%, far higher than the 20.3% of Comparative Example 1. This proves that the phosphorus-containing phenanthrene structure and the nitrogen- and silicon-containing components introduced into the modifier molecule play a good synergistic role in gas-phase flame retardancy and condensed-phase char formation during combustion, significantly improving the flame resistance of the material. Regarding radiation shielding performance, Example 3 showed attenuation coefficients of 0.75, 0.58, and 0.95 for thermal neutrons, fast neutrons, and gamma rays, respectively, all higher than those of Comparative Example 1 (0.55, 0.42, and 0.78), demonstrating superior overall shielding effectiveness. This is attributed to the modifier promoting the uniform dispersion of lead powder and boron carbide in the matrix, thereby ensuring sufficient interaction between radiation particles and shielding filler.

[0024] In summary, this invention, by introducing a modifier with a specific structure into the formulation, successfully achieves effective surface modification and interface strengthening of inorganic fillers, resulting in a polyethylene composite shielding material that possesses excellent mechanical strength, efficient flame retardant properties, and outstanding gamma-ray and neutron shielding capabilities, thus meeting the application environments with stringent requirements for both radiation protection and fire safety.

[0025] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0026] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A polyethylene composite shielding material for nuclear radiation protection, characterized in that, It includes the following components by weight: 40-70 parts lead powder, 10-20 parts boron carbide, 20-35 parts ultra-high molecular weight polyethylene, 0.3-1 part antioxidant, 0.5-1 part lubricant, and 7-8 parts modifier solution. The preparation process of the modifier solution is as follows: S1: Under an inert atmosphere, γ-aminopropyltriethoxysilane and p-hydroxybenzaldehyde were added to anhydrous toluene, followed by the addition of glacial acetic acid. The mixture was stirred at 80°C for 8 hours. Subsequently, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was added, and the mixture was heated to 100°C and reacted for another 10 hours. After the reaction was completed, the solvent was removed by concentration under reduced pressure. The residue was purified by silica gel column chromatography to obtain intermediate A. S2: Under an inert atmosphere, intermediate A, paraformaldehyde, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and anhydrous ethanol were mixed and stirred until homogeneous. The temperature was then raised to 90°C and refluxed for 12 hours. After the reaction was completed, the solvent was removed by vacuum concentration. The residue was purified by silica gel column chromatography to obtain the modifier. S3: Add the modifier to anhydrous ethanol, stir until homogeneous, and obtain the modifier solution.

2. The polyethylene composite shielding material for nuclear radiation protection according to claim 1, characterized in that, In step S1, the ratio of the amounts of γ-aminopropyltriethoxysilane, p-hydroxybenzaldehyde, anhydrous toluene, glacial acetic acid, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 22.1g:12.2g:200mL:6g:21.6g.

3. The polyethylene composite shielding material for nuclear radiation protection according to claim 1, characterized in that, In step S2, the ratio of intermediate A, paraformaldehyde, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and anhydrous ethanol is 54.1g:3.3g:12.4g:200mL.

4. The polyethylene composite shielding material for nuclear radiation protection according to claim 1, characterized in that, In step S3, the ratio of modifier to anhydrous ethanol is 60g:200mL.

5. A polyethylene composite shielding material for nuclear radiation protection according to claim 1, characterized in that, The antioxidant is selected from at least one of antioxidant 1010, antioxidant 1076, antioxidant 168, antioxidant BHT, and antioxidant 2246.

6. A polyethylene composite shielding material for nuclear radiation protection according to claim 1, characterized in that, The lubricant is zinc stearate.

7. A polyethylene composite shielding material for nuclear radiation protection according to claim 1, characterized in that, The lead powder has a particle size of 10-30 μm.

8. A polyethylene composite shielding material for nuclear radiation protection according to claim 1, characterized in that, The boron carbide has a particle size of 2-10 μm.

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