Neutron radiation shielding material and preparation method thereof

Abstract

The invention discloses a neutron radiation shielding material and a preparation method thereof, the neutron radiation shielding material comprises a neutron radiation protection coating agent, and the neutron radiation protection coating agent comprises the following raw materials: polyvinyl alcohol, N, N-dihydroxyethyl-2-methacrylamide, di (carborane methoxy ester) phthalate, a dispersant, a cross-linking agent and an accelerant. According to the neutron radiation protection coating agent, N, N-dihydroxyethyl-2-methacrylamide is introduced and can be polymerized under the thermal action to form a Gel-PMA and PVA hydrogel system, a PVA-boric acid ester covalent network system is further constructed under the action of boric acid ester, and the neutron radiation protection coating agent is prepared. And a strong bisamide hydrogen bond interpenetrating network is generated under complete dispersion of phthalic acid di (carborane methoxyl ester) in a Gel-PMA polymer system, and the dual effects of mechanical property improvement and efficient neutron shielding effectiveness are synergistically realized.

Description

Technical Field

[0001] This invention relates to the field of radiation protection materials technology, and in particular to a neutron radiation shielding material and its preparation method. Background Technology

[0002] The development and utilization of nuclear technology are often accompanied by nuclear radiation and the leakage of radioactive materials. This radiation ionizes matter, and without effective protection, it can damage equipment and seriously threaten human health. Among nuclear radiation, neutrons, being uncharged and having a complex mechanism of action, possess strong penetrating power and are more harmful to the human body than equivalent doses of X-rays and gamma rays. Therefore, neutron protection has become a key focus and challenge in the field of nuclear radiation protection.

[0003] Current neutron protection typically achieves its effect through two processes: first, slowing down fast neutrons using hydrogen-containing materials, and then absorbing thermal neutrons using elements with high neutron absorption cross-sections. Currently, hydrogen-containing organic polymers are commonly used as the matrix, with boron-containing substances introduced to achieve neutron absorption. A common method is to mechanically blend boron powder, boron oxide, or boron carbide powder with the polymer to prepare boron-containing polymer-based neutron protection materials. However, this method has significant drawbacks: due to the poor compatibility between inorganic boron-containing substances and the polymer matrix, their dispersion in the material is poor, leading to difficulties in processing and molding, and also easily causing a decrease in the material's mechanical properties, thus limiting the application performance and widespread use of the protective materials. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an improved neutron radiation shielding material and its preparation method.

[0005] The technical solution adopted by this invention to solve its technical problem is: to provide a neutron radiation shielding material, comprising a neutron radiation protective coating agent, wherein the neutron radiation protective coating agent comprises raw materials and their mass fractions as follows: 5-15 parts of polyvinyl alcohol; 5-10 parts of N,N-dihydroxyethyl-2-methylacrylamide; Di(carborane methoxy ester) phthalate 30-45 parts; 1-5 parts of dispersant; 1-15 parts of crosslinking agent; Accelerator 1-5 parts.

[0006] Preferably, the dispersant is selected from at least one of polyethylene glycol monoethyl ether, polyethylene glycol monomethyl ether, polypropylene glycol monomethyl ether, and polypropylene glycol monoethyl ether.

[0007] Preferably, the crosslinking agent is selected from at least one of triethyl borate, trimethyl borate, tripropyl borate, and tributyl borate.

[0008] Preferably, the accelerator is selected from at least one of amine oxide, lauryl dimethyl amine oxide, cocamidopropyl amine oxide, tetradecyl dimethyl amine oxide, hexadecyl dimethyl amine oxide, octadecyl dimethyl amine oxide, morpholine, and N-methylmorpholine.

[0009] Preferably, the neutron radiation protection coating agent further includes an appropriate amount of co-solvent; the co-solvent is selected from at least one of ethanol, methanol, ethylene glycol monomethyl ether, isopropanol, tetrahydrofuran, acetone and formamide.

[0010] Preferably, the neutron radiation shielding material further includes a substrate, and the neutron radiation protective coating is applied to the substrate by impregnation.

[0011] Preferably, the substrate comprises a nonwoven fabric.

[0012] This invention also provides a method for preparing a neutron radiation shielding material, comprising the following steps: S1. Polyvinyl alcohol is dissolved in water to form a polyvinyl alcohol aqueous solution. The polyvinyl alcohol aqueous solution is mixed with N,N-dihydroxyethyl-2-methylacrylamide to prepare a base adhesive. S2. Add dispersant, crosslinking agent and accelerator to the base adhesive and mix evenly to form a mixture; S3. After adding the neutron shielding solution to the mixture, stir and mix at high speed at a predetermined temperature to form a uniform and transparent sol, which is the neutron radiation protection coating agent. The neutron shielding solution is prepared from dicarborane methyl phthalate.

[0013] Preferably, the method for preparing the neutron radiation shielding material further includes the following steps: S4. Immerse the pretreated substrate in the neutron radiation protection coating agent; S5. Roll the substrate impregnated with neutron radiation protection coating agent to ensure that the neutron radiation protection coating agent is evenly loaded onto the substrate, and then dry and cure it.

[0014] Preferably, in step S4, the pretreatment includes: immersing the substrate in anhydrous ethanol solution, adding a surfactant, then rinsing with water and drying.

[0015] The beneficial effects of this invention are as follows: In the neutron radiation protection coating, N,N-dihydroxyethyl-2-methylacrylamide is introduced and polymerized under heat to form a Gel-PMA and PVA hydrogel system. Furthermore, under the action of borate ester, a covalent network system of PVA-boronate ester is constructed, realizing the generation of a strong diamide hydrogen bond interpenetrating network under the complete dispersion of phthalic acid di(carborane methoxy ester) in the Gel-PMA polymer system, thus synergistically achieving the dual effects of improving mechanical properties and high neutron shielding efficiency. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is the infrared spectrum corresponding to the polymer hydrogel formation path in this invention; Figure 2 This is a diagram of the microstructure of the polymer hydrogel in this invention; Figure 3 This is a SEM image of a neutron radiation shielding material according to an embodiment of the present invention at 500x magnification; Figure 4 This is a SEM image of a neutron radiation shielding material according to an embodiment of the present invention at 1000x magnification; Figure 5 This is a SEM image of a neutron radiation shielding material according to an embodiment of the present invention at 5000x magnification; Figure 6 This is a SEM image of the nonwoven fabric at 400x magnification; Figure 7 This is a SEM image of the nonwoven fabric at 3000x magnification. Detailed Implementation

[0017] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0018] The neutron radiation shielding material of the present invention includes a neutron radiation protective coating agent. The neutron radiation protective coating agent comprises the following raw materials and their mass fractions as follows: 5-15 parts of polyvinyl alcohol (PVA); 5-10 parts of N,N-dihydroxyethyl-2-methylacrylamide (MA); 30-45 parts of di(carborane methoxy ester) phthalate; 1-5 parts of dispersant; 1-15 parts of crosslinking agent; and 1-5 parts of accelerator.

[0019] Polyvinyl alcohol (PVA) serves as a sol-carrier, acting as an adhesive to the substrate. In the preparation of the neutron radiation shielding coating, PVA is used in its aqueous solution. N,N-dihydroxyethyl-2-methylacrylamide, as a neutron shielding agent, is preferably added in solution form during the preparation of the neutron radiation shielding coating.

[0020] The dispersant disperses the raw materials of the neutron radiation protection coating, especially those that are insoluble in water. The dispersant can be at least one of polyethylene glycol (200-300) monoethyl ether, polyethylene glycol (200-300) monomethyl ether, polypropylene glycol monomethyl ether, and polypropylene glycol monoethyl ether; preferably, the degree of polymerization n of the above dispersant is 4-5.

[0021] The crosslinking agent may be at least one of triethyl borate, trimethyl borate, tripropyl borate, and tributyl borate. The accelerator may be at least one of amine oxide, lauryl dimethyl amine oxide, cocamidopropyl amine oxide, tetradecyl dimethyl amine oxide, hexadecyl dimethyl amine oxide, octadecyl dimethyl amine oxide, morpholine, and N-methylmorpholine.

[0022] The neutron radiation protection coating also includes an appropriate amount of co-solvent to dissolve the neutron shielding agent. The co-solvent is selected from at least one of ethanol, methanol, ethylene glycol monomethyl ether, isopropanol, tetrahydrofuran, acetone, and formamide. From an environmental, safety, and health perspective, ethanol is preferred as the co-solvent.

[0023] The preparation of a neutron radiation protection coating may include the following steps: S1. Polyvinyl alcohol is dissolved in water to form a polyvinyl alcohol aqueous solution. The polyvinyl alcohol aqueous solution is mixed with N,N-dihydroxyethyl-2-methylacrylamide to prepare a base adhesive.

[0024] The mass concentration of the polyvinyl alcohol aqueous solution is 1%-5%.

[0025] S2. Add dispersant, crosslinking agent and accelerator to the base adhesive in sequence, and mix evenly to form a mixture.

[0026] S3. After adding the neutron shielding solution to the mixture, stir at high speed at a predetermined temperature (e.g., 20℃~80℃) to ensure that the neutron shielding solution and the mixture are uniformly mixed under high-speed shear force and form a homogeneous and transparent sol, thus obtaining a neutron radiation protection coating agent with high boron content. The neutron shielding solution is prepared by dissolving bis(carborane methoxy ester) phthalate in a co-solvent (ethanol, etc.).

[0027] The above-mentioned neutron radiation protection coating agent can be prepared in a high-shear mixer. The stirring speed is 200 rpm to 1500 rpm.

[0028] In the neutron radiation protection coating, the neutron shielding powder (i.e., bis(carborane methoxy ester) of phthalate) is dispersed in a network system integrated by a hydrogel constructed from borate ester (boric acid formed by the hydrolysis of triethyl borate) and polymethyl methacrylate (Gel-PMA) and polyvinyl alcohol (PVA). Accompanying the formation of an interpenetrating polymer network and the secondary hydrogen bonding (strong / weak H bonds, the carborane structure contains a large number of H elements) between molecules due to the large number of hydroxyl groups in the polymer network, the dual effects of synergistically improving mechanical properties and obtaining high-efficiency neutron shielding performance are achieved.

[0029] The infrared spectra of the polymer hydrogel formation pathways of Gel-PMA and PVA in neutron radiation protective coatings are as follows: Figure 1 As shown. Figure 1 In the diagram, the two curves a1 from top to bottom represent the reaction start point and the initial formation stage of the polymer hydrogel, respectively. a2, a3, and a4 represent the states of the polymer hydrogel after a 2-hour interval. The microstructure diagrams of the polymer hydrogel corresponding to a1 (initial hydrogel formation stage) to a4 are shown below. Figure 2 As shown.

[0030] In one embodiment, the neutron radiation shielding material further includes a substrate. The neutron radiation protection coating agent is impregnated and adsorbed onto the substrate, effectively adhering to the fiber gaps and surface of the substrate to form a dense, uniform, and density-controllable coating composite fabric (shielding fabric). Compared with the neutron radiation protection coating agent alone, it can further improve the shielding performance and mechanical properties.

[0031] The substrate includes nonwoven fabric. This neutron radiation shielding material (shielding fabric) is suitable for manufacturing protective clothing and other applications in radiation protection situations.

[0032] The method for preparing the neutron radiation shielding material in this embodiment mainly includes the preparation of a neutron radiation protective coating agent and its impregnation and loading on a substrate. Specific steps include: S1. Polyvinyl alcohol is dissolved in water to form a polyvinyl alcohol aqueous solution. The polyvinyl alcohol aqueous solution is mixed with N,N-dihydroxyethyl-2-methylacrylamide to prepare a base adhesive.

[0033] S2. Add dispersant, crosslinking agent and accelerator to the base adhesive in sequence, and mix evenly to form a mixture.

[0034] S3. After adding the neutron shielding solution to the mixture, stir and mix at high speed at a predetermined temperature to form a homogeneous and transparent sol, thus obtaining a neutron radiation protection coating agent with high boron content. The neutron shielding solution is prepared by dissolving bis(carborane methoxy ester) phthalic acid in a co-solvent (ethanol, etc.).

[0035] S4. Immerse the pretreated substrate in a neutron radiation protection coating.

[0036] Because nonwoven fabrics have high molecular crystallinity, tight molecular arrangement and no hydrophilic groups, and high surface polarity, they are prone to static electricity. In order to facilitate the subsequent impregnation process and improve the protective function, nonwoven fabrics need to be pretreated to change their surface polarity, thereby obtaining nonwoven fabrics with surface hydrophilicity.

[0037] The pretreatment of the nonwoven fabric includes: immersing the substrate (i.e., the nonwoven fabric) in anhydrous ethanol solution, preferably with a liquor ratio of 1:300; adding surfactant (1 ml / 1 g fabric), immersing for 6 hours, then removing the substrate, rinsing with water, and drying.

[0038] The optimal parameters for obtaining the highest solids loading when the substrate is impregnated with the neutron radiation protection coating are as follows: impregnation time 35 min; impregnation bath ratio 1:120; impregnation temperature 50℃.

[0039] S5. Roll the substrate impregnated with neutron radiation protection coating agent to ensure that the neutron radiation protection coating agent is evenly loaded onto the substrate, and then dry and cure.

[0040] The neutron radiation protection coating agent on the substrate, after being heated and dried, contains Gel-PMA and PVA as its main components. The heating and drying process enables Gel-PMA and PVA to undergo a polymerization reaction, further forming a PVA-boron ester covalent network. At the same time, a coating film structure of a strong diamide hydrogen bond interpenetrating network of Gel-PMA-phthalic acid di(carborane methoxy ester) is formed between the substrate surface and the fabric structure. This can achieve the dual purpose of improving the mechanical strength of the shielding fabric and enhancing the shielding effect.

[0041] The preferred parameters for the rolls are as follows: the roll pressure is 0.1 MPa and the rotation speed is 2 m / min.

[0042] In the neutron radiation shielding material (which can be called shielding fabric) obtained after step S5, the mass ratio of neutron shielding powder (di(carborane methoxy ester) phthalate) to polyethylene glycol is preferably 100:1-5.

[0043] The above impregnation parameters were determined using a combination of single-factor analysis and orthogonal experiments, as detailed below: ① The effect of impregnation bath ratio on the protective performance of fabrics The impregnation bath ratio refers to the ratio of nonwoven fabric to neutron radiation protection coating agent (referred to as coating agent), and is an important indicator in the impregnation process. The solid load of shielding materials prepared with bath ratios of 1:60, 1:90, 1:120, 1:150, and 1:180 at an impregnation temperature of 40℃ and an impregnation time of 40 min were studied to clarify the influence of the bath ratio on the shielding effectiveness of the nonwoven fabric. The results are shown in Table 1 below.

[0044] Table 1. Effect of liquor ratio on the load capacity of nonwoven fabrics As the liquor ratio increases, the solids content of the nonwoven fabric shows a trend of first increasing and then decreasing. With the increase of the liquor ratio, the fabric is more thoroughly impregnated in the coating agent, and the protective powder is more evenly loaded on the fabric. When the liquor ratio reaches 1:120, as the liquor ratio increases, the loading of the protective powder on the nonwoven fabric gradually reaches saturation. When the liquor ratio is further increased beyond the critical value, the solids content decreases due to the relative reduction of the effective component content in the coating agent.

[0045] Therefore, according to the results shown in Table 1, the solid load is the largest when the liquor ratio is 1:120.

[0046] ② The effect of impregnation temperature on the protective performance of fabrics The effect of impregnation temperature on the protective performance of the fabric is shown in Table 2. The results in Table 2 show that at lower temperatures (below 40℃), the uniformity of the coating agent dispersion is poor (the difference in the unit areal density of the tested dried fabric samples), and the solubility in the PVA solution is relatively low. At higher temperatures, the uniformity of the coating agent dispersion is better. At the same time, the higher the temperature, the higher the load fastness of the coating agent and the better the protective performance. When the temperature exceeds 40℃, the increase in load fastness with increasing temperature is smaller, because the load fastness is basically saturated at this point.

[0047] Table 2. Effect of impregnation temperature on the load capacity of nonwoven fabrics Therefore, according to the results shown in Table 2, the solid load is the largest when the impregnation temperature is 40℃.

[0048] ③ The effect of impregnation time on fabric functionality Impregnation time represents the sufficient contact time between the nonwoven fabric and the coating agent. The load-bearing capacity of the shielding material prepared with impregnation time of 5 min, 15 min, 25 min, 35 min and 45 min was studied when the impregnation bath ratio was 1:120 and the impregnation temperature was 40℃. The influence of impregnation time on the shielding effectiveness of nonwoven fabric was clarified. The results are shown in Table 3 below.

[0049] Table 3. Effect of impregnation time on the load capacity of nonwoven fabrics The data in Table 3 show that as the impregnation time increases, the protective performance of the impregnated nonwoven fabric first increases, then levels off, and finally decreases. This is because in the initial stage, as the impregnation time increases, the protective powder loaded on the fabric increases, and the protective performance of the fabric increases. When the impregnation time is extended to 35 minutes, the protective powder loaded on the fabric reaches relative saturation. If the impregnation time is too long, the powder may agglomerate or fall off, resulting in a decrease in the protective function of the fabric.

[0050] Therefore, according to the results shown in Table 3, the solid load is the largest when the impregnation time is 35 min.

[0051] To further optimize the immersion parameters, the optimal parameter combination was obtained by combining the single-factor analysis with the orthogonal experimental method. The three parameters, namely immersion time, immersion bath ratio and immersion temperature, were used as experimental factors. Three different levels were used for each factor. Therefore, the orthogonal table L9 (43) was selected to determine the experimental scheme, and nine experiments were conducted. The orthogonal experimental factors and level table are shown in Table 4, and the orthogonal experimental scheme is shown in Table 5.

[0052] Table 4. Factor Level Table Table 5. Orthogonal Experiment Scheme Therefore, according to the experimental results in Table 5, when the impregnation time is 35 min, the impregnation bath ratio is 1:120, and the impregnation temperature is 50℃, the nonwoven fabric has a high load-bearing capacity, which is beneficial to ensuring the overall shielding performance of the shielding material.

[0053] The optimized process parameters for the rolling mill are determined as follows: After the neutron radiation protection coating agent is fully impregnated into the nonwoven fabric, it needs to be rapidly squeezed through two rollers to perform a rolling operation. Given that single-layer nonwoven fabric is relatively thin and has low tensile strength, surface cracking may occur due to accidental stretching during processing. Therefore, the gap width between the upper and lower pressure rollers is adjusted to ensure minimal tension during rolling, resulting in uniform pressure and liquid coverage across the left, center, and right sides of the fabric surface. This ensures the coating agent is evenly loaded onto the nonwoven fabric, achieving efficient and uniform neutron protection performance. Simultaneously, it ensures the surface smoothness and quality uniformity of the fabric after rolling. Through multiple experiments, the roller pressure was ultimately determined to be 0.1 MPa, and the rotation speed 2 m / min.

[0054] The characterization and testing performance of the neutron radiation shielding material obtained by impregnating a substrate (non-woven fabric) with a neutron radiation protection coating agent in this invention are as follows: a. Surface morphology of neutron radiation shielding materials SEM microstructure of neutron radiation shielding materials, such as Figures 3-5As shown, Figure 3 , Figure 4 and Figure 5 These are SEM images of the neutron radiation shielding material at 500x, 1000x, and 5000x magnification. Figure 6 and Figure 7 SEM images of a substrate (nonwoven fabric) without neutron radiation shielding coating are shown at 400x and 3000x magnification. From... Figures 3-5 and Figures 6-7 The comparison shows that the single-layer cross-sectional surface of the neutron radiation shielding material is dense (crack width is less than 0.1μm), and the shielding requirements can be met through multi-layer coverage.

[0055] b. Testing the neutron protection performance of neutron radiation shielding materials The unit area mass and thickness of the neutron radiation shielding material (shielding fabric) were tested according to standards GB / T 24218.1-2009 "Textiles - Nonwovens - Test Methods - Part 1: Determination of Unit Area Mass" and GB / T 24218.2-2009 "Textiles - Nonwovens - Test Methods - Part 2: Thickness". The thermal neutron shielding performance (neutron spectral lines between 0.025 eV and 24.4 keV) at 0.042 eV was tested for shielding fabrics with three different thickness gradients, and the shielding efficiency was ≥90%, as detailed in Table 6 below.

[0056] Table 6. Test results of neutron protection efficiency of shielding fabric The tear strength acceptance index for shielding fabric is ≥10N, and the corresponding test results are shown in Table 7 below.

[0057] Table 7. Results of Fracture Strength Test The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A neutron radiation shielding material, characterized in that, The coating includes a neutron radiation protection agent, which comprises the following raw materials and their mass fractions: 5-15 parts of polyvinyl alcohol; 5-10 parts of N,N-dihydroxyethyl-2-methylacrylamide; Di(carborane methoxy) phthalate 30-45 parts; 1-5 parts of dispersant; 1-15 parts of crosslinking agent; Accelerator 1-5 parts.

2. The neutron radiation shielding material according to claim 1, characterized in that, The dispersant is selected from at least one of polyethylene glycol monoethyl ether, polyethylene glycol monomethyl ether, polypropylene glycol monomethyl ether, and polypropylene glycol monoethyl ether.

3. The neutron radiation shielding material according to claim 1, characterized in that, The crosslinking agent is selected from at least one of triethyl borate, trimethyl borate, tripropyl borate, and tributyl borate.

4. The neutron radiation shielding material according to claim 1, characterized in that, The accelerator is selected from at least one of amine oxide, lauryl dimethyl amine oxide, cocamidopropyl amine oxide, tetradecyl dimethyl amine oxide, hexadecyl dimethyl amine oxide, octadecyl dimethyl amine oxide, morpholine, and N-methylmorpholine.

5. The neutron radiation shielding material according to claim 1, characterized in that, The neutron radiation protection coating agent also includes an appropriate amount of co-solvent; the co-solvent is selected from at least one of ethanol, methanol, ethylene glycol monomethyl ether, isopropanol, tetrahydrofuran, acetone and formamide.

6. The neutron radiation shielding material according to any one of claims 1-5, characterized in that, The neutron radiation shielding material also includes a substrate, and the neutron radiation protection coating agent is impregnated and adsorbed onto the substrate.

7. The neutron radiation shielding material according to claim 6, characterized in that, The substrate includes nonwoven fabric.

8. A method for preparing the neutron radiation shielding material according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Polyvinyl alcohol is dissolved in water to form a polyvinyl alcohol aqueous solution. The polyvinyl alcohol aqueous solution is mixed with N,N-dihydroxyethyl-2-methylacrylamide to prepare a base adhesive. S2. Add dispersant, crosslinking agent and accelerator to the base adhesive and mix evenly to form a mixture; S3. After adding the neutron shielding solution to the mixture, stir and mix at a predetermined temperature to form a uniform and transparent sol, which is the neutron radiation protection coating agent. The neutron shielding solution is prepared from di(carborane methoxy ester) phthalate.

9. The method for preparing the neutron radiation shielding material according to claim 8, characterized in that, It also includes the following steps: S4. Immerse the pretreated substrate in the neutron radiation protection coating agent; S5. Roll the substrate impregnated with neutron radiation protection coating agent to ensure that the neutron radiation protection coating agent is evenly loaded onto the substrate, and then dry and cure it.

10. The method for preparing the neutron radiation shielding material according to claim 8, characterized in that, In step S4, the pretreatment includes: immersing the substrate in anhydrous ethanol solution, adding a surfactant, then rinsing with water and drying.

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