A high-density flexible radiation-resistant composite material, a preparation method and application thereof

Abstract

The application provides a high-density flexible radiation-proof composite material and a preparation method and application thereof, and belongs to the technical field of radiation-proof polymer composite materials and powder surface modification. In the application, bismuth oxide is used as a high-energy cutoff layer, tungsten oxide is used as a sub-high-energy reinforcing layer, gadolinium oxide is used as a medium-energy leak repairing layer, and lanthanum oxide is used as a low-energy scattering layer. The particle sizes of the bismuth oxide, the tungsten oxide, the gadolinium oxide and the lanthanum oxide are limited. A 'three-stage particle size dense packing' strategy is adopted to solve the mechanical brittleness problem under high filling. The high-density flexible radiation-proof composite material can cover a wide energy spectrum of 30-120keV, has no shielding dead angle, and still has excellent flexibility under super high filling. The application is especially suitable for medical intervention protection, nuclear industry and CBRN (chemical, biological, radioactive and nuclear) flexible protection and other high filling radiation shielding scenes with strict requirements on material light weight, flexibility and long-term reliability.

Description

Technical Field

[0001] This invention relates to the field of radiation-resistant polymer composite materials and powder surface modification technology, and particularly to a high-density flexible radiation-resistant composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of medical diagnostic technologies (such as X-ray fluoroscopy and CT-guided interventional surgery), the health risks of long-term exposure to scattered radiation for medical personnel are becoming increasingly prominent. Traditional radiation protection equipment mainly uses lead rubber materials. However, lead not only has heavy metal toxicity, posing potential hazards to the environment and human body, but lead protective clothing is also extremely heavy, easily leading to severe spinal and muscle strain in medical personnel who wear it for extended periods. Therefore, the development of lightweight, non-toxic "lead-free flexible radiation protection materials" has become an inevitable trend in the industry.

[0003] Currently, lead-free radiation shielding materials mainly use high atomic number heavy metal oxides (such as bismuth oxide and tungsten oxide) as shielding fillers, which are then blended into a polymer matrix. However, existing lead-free flexible shielding materials still face the following three major technical bottlenecks in practical applications: 1. Absorption Limit Defects Leading to Protection Low Points in Specific Frequency Bands: In interventional radiology, the most commonly used X-ray tube voltage range is 60–80 kVp. However, due to their inherent physical properties, commonly used bismuth oxide and tungsten oxide exhibit absorption low points in this energy range, specifically at the point of mass attenuation. Using only the bismuth-tungsten system would cause a surge in X-ray transmittance in this critical frequency band, failing to provide effective protection across the entire frequency range.

[0004] 2. Severe Brittleness and Loss of Flexibility Due to Extremely High Filling Rates: To achieve lead equivalent to traditional lead rubber (e.g., 0.5 mmPb), the filling rate of lead-free powder in the polymer matrix often needs to reach 80% or even 85% or more. At such extreme filling rates, if a traditional one-step blending process is used, the micron- and nano-sized heavy metal powders with extremely high surface energy are prone to severe agglomeration. These agglomerates form huge macroscopic and microscopic pores in the matrix (i.e., a worsening of the "island effect"), blocking the stress transmission of the polymer chains. Macroscopically, this manifests as a precipitous drop in the material's elongation at break (often below 70% or even 40%), making the material extremely brittle and prone to brittle fracture under slight stretching or folding, completely losing the flexibility and ductility required for protective clothing.

[0005] 3. Poor Aging Resistance and "Powdering" Phenomenon Due to Weak Interfacial Bonding: Heavy metal oxides are inorganic rigid particles, exhibiting natural interfacial incompatibility with organic polymer matrices (such as ordinary TPU or PVC). Existing coupling processes often fail to achieve uniform monolayer encapsulation of powders in highly filled systems. This results in numerous microscopic capillary channels between the inorganic framework and the organic matrix. During long-term use (such as contact with human sweat), salts and weak acids in sweat can easily penetrate the interface through capillary action, damaging the already fragile physical encapsulation. After repeated bending and erosion, the material exhibits significant interfacial debonding and stress whitening, ultimately leading to the release of internal heavy metal powder (powdering). This not only pollutes the environment but also causes a catastrophic decline in the material's physical and mechanical properties and radiation protection effectiveness.

[0006] In summary, how to overcome the limitations of existing technologies, achieve lightweighting while eliminating the protection trough in specific frequency bands, and completely solve the problems of brittle fracture and powder precipitation caused by powder agglomeration and interface debonding under large intervention (such as 85% filling), and prepare flexible radiation shielding materials with both excellent mechanical ductility and long-term reliability, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a high-density flexible radiation shielding composite material, its preparation method, and its application. The high-density flexible radiation shielding composite material provided by this invention can cover a wide energy spectrum of 30~120keV, has no shielding dead zones, and maintains excellent flexibility even with ultra-high filling.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a high-density flexible radiation-shielding composite material, which is lead-free and comprises the following raw materials by mass percentage: Polymer matrix 10-15%, inorganic radiation shielding skeleton filler 80-88%, compound flame retardant 1-5%, and functional additives 0.5-4%; The inorganic radiation shielding skeleton filler includes bismuth oxide, tungsten oxide, gadolinium oxide, and lanthanum oxide. The mass percentage of bismuth oxide in the inorganic radiation shielding skeleton filler is 35-55%, the mass percentage of tungsten oxide is 30-50%, the mass percentage of gadolinium oxide is 8-22%, and the mass percentage of lanthanum oxide is 0.5-8%. The particle size of bismuth oxide and tungsten oxide is 3-5 μm, the particle size of gadolinium oxide is 0.8-1.5 μm, and the particle size of lanthanum oxide is 100-300 nm.

[0009] Preferably, the compound flame retardant comprises the following components by mass percentage: 55-70% nitrogen-phosphorus intumescent flame retardant, 5-10% inorganic metal hydroxide, and 20-35% char-forming synergist.

[0010] Preferably, the nitrogen-phosphorus intumescent flame retardant includes one or more of ammonium polyphosphate, melamine cyanurate, and aluminum hypophosphite.

[0011] Preferably, the inorganic metal hydroxide includes aluminum hydroxide and / or magnesium hydroxide.

[0012] Preferably, the char-forming synergist includes pentaerythritol and / or zinc borate.

[0013] Preferably, the functional additives include coupling agents, antioxidants, and lubricants, wherein the mass ratio of the coupling agent, antioxidant, and lubricant is 0.6~2.5:0.1~0.5:0.1~1.2.

[0014] This invention also provides a method for preparing the high-density flexible radiation-shielding composite material described in the above technical solution, comprising the following steps: Inorganic radiation shielding skeleton filler, compound flame retardant and functional additives are mixed and activated to obtain activated powder; The activated powder is melt-blended with a polymer matrix to obtain a melt; The melt is calendered and shaped to obtain the high-density flexible radiation-shielding composite material.

[0015] Preferably, the calendering and shaping is a three-roll calendering, which includes an upper roll, a middle roll, and a lower roll. The temperature of the upper roll is 150~170℃, the temperature of the middle roll is 140~160℃, and the temperature of the lower roll is 35~45℃.

[0016] Preferably, the distance between the upper roller and the middle roller is 0.55~1.8mm, and the distance between the middle roller and the lower roller is 0.48~1.5mm.

[0017] The present invention also provides the application of the high-density flexible radiation shielding composite material described in the above technical solution or the high-density flexible radiation shielding composite material prepared by the preparation method described in the above technical solution in the fields of medical interventional protection, nuclear industry and flexible protection.

[0018] This invention provides a high-density flexible radiation-shielding composite material, which is lead-free and comprises the following raw materials by mass percentage: 10-15% polymer matrix, 80-88% inorganic radiation-shielding skeleton filler, 1-5% compound flame retardant, and 0.5-4% functional additives; the inorganic radiation-shielding skeleton filler includes bismuth oxide, tungsten oxide, gadolinium oxide, and lanthanum oxide, wherein the mass percentage of bismuth oxide in the inorganic radiation-shielding skeleton filler is 35-55%, the mass percentage of tungsten oxide is 30-50%, the mass percentage of gadolinium oxide is 8-22%, and the mass percentage of lanthanum oxide is 0.5-8%. The particle size of bismuth oxide and tungsten oxide is 3-5 μm, the particle size of gadolinium oxide is 0.8-1.5 μm, and the particle size of lanthanum oxide is 100-300 nm.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: In this invention, bismuth oxide (Bi₂O₃) is used as a high-energy cutoff layer, utilizing its 90.5 keV K-edge to intercept high-energy straight rays, ensuring an absolute cutoff rate for high-energy rays above 90 keV. Tungsten oxide (WO₃) is used as a secondary high-energy reinforcement layer, utilizing its 69.5 keV K-edge to fill the 70-90 keV range, forming a smooth joint attenuation curve with bismuth oxide. Gadolinium oxide (Gd₂O₃) is used as a mid-energy leakage filler layer, utilizing its 50.2 keV K-edge to achieve strong absorption in the 50-80 keV transmission window of the traditional Bi-W system, precisely filling the absorption trough in this energy range without... To address the impact on the mechanical framework of the material, lanthanum oxide (La2O3) was used as a low-energy scattering layer. Its 38.9keV K-edge absorbed low-energy scattered photons, effectively eliminating low-energy primary or secondary scattered rays. The particle sizes of bismuth oxide, tungsten oxide, gadolinium oxide, and lanthanum oxide were limited. Coarse powder (bismuth oxide and tungsten oxide) of 3~5μm was used as the framework, medium powder (Gd2O3) of 0.8~1.5μm was used to fill the voids, and fine powder (La2O3) of 100~300nm was used as micro "balls" to achieve complete wetting of the inorganic radiation shielding framework filler by the polymer matrix. A "three-level particle size dense packing" strategy was adopted to solve the mechanical brittleness problem under high filling. The high-density flexible radiation shielding composite material of the present invention can cover a wide energy spectrum of 30~120keV without any shielding dead angles, and still maintains excellent flexibility under ultra-high filling. The present invention is particularly suitable for high-filling radiation shielding scenarios with stringent requirements for material lightweighting, flexibility and long-term reliability, such as medical interventional protection, nuclear industry and CBRN (chemical, biological, radioactive, nuclear) flexible protection.

[0020] The present invention also provides a method for preparing the high-density flexible radiation-shielding composite material described in the above technical solution. The preparation method of the present invention is simple to operate and suitable for industrial application. Detailed Implementation

[0021] This invention provides a high-density flexible radiation-shielding composite material, which is lead-free and comprises the following raw materials by mass percentage: Polymer matrix 10-15%, inorganic radiation shielding skeleton filler 80-88%, compound flame retardant 1-5%, and functional additives 0.5-4%; The inorganic radiation shielding skeleton filler includes bismuth oxide, tungsten oxide, gadolinium oxide, and lanthanum oxide. The mass percentage of bismuth oxide in the inorganic radiation shielding skeleton filler is 35-55%, the mass percentage of tungsten oxide is 30-50%, the mass percentage of gadolinium oxide is 8-22%, and the mass percentage of lanthanum oxide is 0.5-8%. The particle size of bismuth oxide and tungsten oxide is 3-5 μm, the particle size of gadolinium oxide is 0.8-1.5 μm, and the particle size of lanthanum oxide is 100-300 nm.

[0022] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0023] In this invention, the mass percentage of the polymer matrix in the raw materials can be specifically 10%, 11%, 12%, 13%, 14%, or 15%. By limiting the mass percentage of the polymer matrix to 10-15%, it is possible to ensure that the proportion of inorganic radiation shielding skeleton filler reaches 80%-88%. This allows the composite material to meet high lead equivalent requirements even with an extremely thin thickness (e.g., 0.5 mm), achieving lightweight protective clothing. 10% is the bottom line for the polymer matrix to completely "wet" and encapsulate the inorganic radiation shielding skeleton filler. Below 10%, the polymer matrix cannot form a continuous phase, and the material will collapse from an "island structure" into loose particle accumulation, leading to severe powdering and brittle fracture. Furthermore, within the range of 10%-15%, the processing rheology is good, and the melt has sufficient viscoelasticity and strength to support pressures above 220 kN / m in the three-roll calendering process.

[0024] In this invention, the polymer matrix in the raw material preferably includes thermoplastic polyurethane (TPU), and the TPU preferably includes one or more of polyether-type thermoplastic polyurethane, polyester-type thermoplastic polyurethane, polycaprolactone-type thermoplastic polyurethane, and polycarbonate-type thermoplastic polyurethane.

[0025] In this invention, the polymer matrix is ​​preferably modified before use to obtain a modified polymer matrix with polar side groups. The modification treatment can improve the wettability of the matrix to high surface energy heavy metal oxide particles, ensuring that even under extreme conditions where the proportion of inorganic radiation shielding skeleton filler is as high as 80% to 88%, the matrix can still form a continuous and stable coating phase, thereby giving the material excellent mechanical ductility.

[0026] In this invention, the modification treatment is preferably reactive polarization modification, more preferably graft modification of thermoplastic polyurethane with maleic anhydride (MAH) to obtain modified TPU (TPU-g-MAH). The graft modification is intended to completely solve the interfacial compatibility problem between organic polymers and high-density inorganic powders, including the following three aspects: a) Achieving chemical bonding and deep physical entanglement: In the activation process of the inorganic radiation-shielding skeleton filler, the powder surface is coated with a coupling agent. The anhydride groups on the modified TPU chains, in the molten state at 160~185℃, can chemically react with the coupling agent groups on the powder surface (or form strong hydrogen bonds). After the melt blending feeding section, high-shear kneading is preferably performed to provide strong mechanical force, forcing these long molecular chains with extremely strong affinity to tightly wrap around the activated skeleton. The parameters of the high-shear kneading preferably include: screw speed 350~550 r / min; specific energy consumption 0.18~0.28 kWh / kg; average shear rate 200~800 s. -1 The kneading process uses a combination of offset angles from 45° / 5 / 28 to 60° / 5 / 28.

[0027] b) Enhance the "wetting" and dispersion capabilities under ultra-high filler: The inorganic radiation shielding skeleton filler has a high density and a surface energy that is significantly different from that of pure TPU. After the introduction of polar groups through modification, the surface tension of the TPU melt decreases, allowing it to perfectly wet and encapsulate each activated inorganic radiation shielding skeleton filler like a water-wetted sponge, ensuring that the powder is uniformly dispersed in the polymer matrix.

[0028] c) Maintaining the flexibility and mechanical strength of composite materials: Excessive filling with inorganic radiation shielding skeleton fillers can easily lead to material embrittlement (i.e., defect amplification in the "island effect"). The robust "interface bridge" established through modification can effectively and uniformly transfer external mechanical stress from the soft TPU to the rigid inorganic skeleton, thereby maintaining the material's excellent tensile strength and flexibility even under high-density radiation shielding or flame retardant requirements.

[0029] In this invention, the grafting modification preferably includes the following steps: a) Raw material premixing: TPU particles, polar monomer maleic anhydride, and initiator are uniformly mixed in a mixer; b) Reactive extrusion: The resulting premix is ​​subjected to a grafting modification reaction; c) Deviation and granulation: Vacuum exhaust is turned on in the post-extrusion zone to remove unreacted polar monomer maleic anhydride and small molecule byproducts. After cooling and granulation, TPU-g-MAH is obtained. TPU-g-MAH is a modified TPU particle with highly active polar side groups.

[0030] In this invention, the initiator preferably includes dicumyl peroxide (DCP).

[0031] The present invention does not impose any special limitation on the amount of the polar monomer maleic anhydride and the initiator, and any amount known to those skilled in the art can be used.

[0032] In this invention, the grafting modification reaction is preferably carried out in a twin-screw extruder.

[0033] In this invention, the temperature of the grafting modification reaction is preferably 170~190℃, specifically 170, 180, or 190℃. The grafting modification reaction is preferably carried out under high shear conditions, and the parameters of the high shear conditions preferably include: screw speed 350~550 r / min; specific energy consumption 0.18~0.28 kWh / kg; and average shear rate 200~800 s. -1 The kneading process employs a combination of misaligned angles of 45° / 5 / 28 to 60° / 5 / 28. During the grafting modification reaction, the initiator decomposes upon heating to generate free radicals. These free radicals capture active hydrogen atoms from the main chain or side chain of the TPU macromolecule, forming macromolecular free radicals. Subsequently, these free radicals initiate a grafting modification reaction in the polar monomers, "hanging" polar anhydride groups onto the TPU chain.

[0034] In this invention, the mass percentage of the inorganic radiation shielding skeleton filler in the raw material can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, or 88%. The mass percentage of the inorganic radiation shielding skeleton filler can ensure that the composite material meets the core conditions of 25% to 30% weight reduction while meeting the standards IEC61331 or GBZ130-2020, such as 0.5mmPb equivalent. If it is less than 80%, the thickness of the composite material must be increased to achieve the same shielding level, which will result in rigid and heavy protective equipment, losing the meaning of flexible protection.

[0035] In this invention, the mass percentage of bismuth oxide in the inorganic radiation shielding skeleton filler can be 35%, 40%, 45%, 50%, or 55%. The mass percentage of bismuth oxide ensures that the composite material has an extremely high linear decay coefficient in the high-energy radiation range (such as above 90 keV). While maintaining the high atomic number metal atom density, it serves as a coarse powder skeleton support phase in the "tertiary particle size dense packing" strategy, providing stable filling space for medium and fine powders. The particle size of the bismuth oxide can be 3, 4, or 5 μm. The bismuth oxide is the main shielding agent, utilizing its 90.5 keV K-edge to intercept high-energy direct radiation.

[0036] In this invention, the mass percentage of tungsten oxide in the inorganic radiation shielding skeleton filler can be 30%, 35%, 40%, 45%, or 50%. The mass percentage of tungsten oxide ensures that the composite material forms an efficient and continuous shielding barrier in the 70-90 keV energy range. Together with bismuth oxide, it constitutes the first-level coarse powder skeleton in the three-level particle size packing system. While achieving high filling volume, it maintains the rheological stability of the melt during extrusion and calendering. The particle size of the tungsten oxide can be 3, 4, or 5 μm. Tungsten oxide is the main shielding agent, a secondary high-energy reinforcing layer, and a broadband absorption layer. Its 69.5 keV K-edge fills the 70-90 keV range, forming a smooth joint attenuation curve with bismuth oxide.

[0037] In this invention, the mass percentage of gadolinium oxide in the inorganic radiation shielding skeleton filler can specifically be 8%, 10%, 12%, 14%, 16%, 18%, 20%, or 22%. The mass percentage of gadolinium oxide can provide precise gain shielding in the critical energy spectrum range of 50~80kVp. At the same time, as the medium-powder filling phase in the "three-level particle size dense packing" structure, it effectively fills the primary microscopic gaps formed by the coarse powder skeleton (bismuth oxide, tungsten oxide), significantly improving the atomic surface density of heavy metals inside the material. The particle size of gadolinium oxide can specifically be 0.8, 1, 1.2, or 1.5μm. The gadolinium oxide is a complementary shielding agent and a medium-energy complementary layer. It utilizes the absorption limit of Gd element to construct a complementary gradient and eliminate the protection trough in the 50~80kVp frequency band.

[0038] In this invention, the mass percentage of lanthanum oxide in the inorganic radiation shielding skeleton filler can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%. The mass percentage of lanthanum oxide can synergistically improve the rheological properties of the ultra-high filling system at the microscopic level by accurately capturing low-energy secondary scattered rays. As micro-balls filling extremely fine gaps, it significantly improves the mechanical ductility and interfacial density of the composite material under large deformation conditions. The particle size of the lanthanum oxide can be 100, 150, 200, 250, or 300 nm. The lanthanum oxide is an auxiliary shielding agent that uses its 38.9 keV K-edge to absorb low-energy scattered photons and effectively eliminate low-energy primary or secondary scattered rays.

[0039] This invention uses coarse powder (bismuth oxide, tungsten oxide) of 3~5μm as the skeleton, medium powder (Gd2O3) of 0.8~1.5μm to fill the gaps, and fine powder (La2O3) of 100~300nm as micro-balls to achieve complete wetting of the inorganic radiation shielding skeleton filler by the polymer matrix. It adopts a "three-level particle size dense packing" strategy to solve the mechanical brittleness problem under high filling.

[0040] In this invention, the compound flame retardant preferably comprises the following components by mass percentage: 55-70% nitrogen-phosphorus intumescent flame retardant, 5-10% inorganic metal hydroxide, and 20-35% char-forming synergist. The compound flame retardant is a halogen-free intumescent or synergistic flame retardant system to ensure the fire safety and low-smoke, non-toxic properties of the material in extreme environments. The nitrogen-phosphorus intumescent flame retardant, inorganic metal hydroxide, and char-forming synergist are added simultaneously with the inorganic radiation-shielding skeleton filler during the activation process of the preparation method to prevent premature decomposition or cross-linking failure of the flame retardant.

[0041] In this invention, the mass percentage of nitrogen-phosphorus intumescent flame retardant in the compound flame retardant can be 55%, 60%, 65%, or 70%. The mass percentage of nitrogen-phosphorus intumescent flame retardant can ensure the rapid formation of a uniform and dense intumescent protective layer in a composite system with extremely high filling rate through an efficient dehydration and char formation mechanism, even with a very low polymer matrix ratio. This endows the composite material with excellent self-extinguishing performance and fire safety without compromising the macroscopic flexibility of the material. The nitrogen-phosphorus intumescent flame retardant acts as the main flame retardant, promoting the dehydration and char formation of the polymer matrix. The nitrogen-phosphorus intumescent flame retardant preferably includes one or more of ammonium polyphosphate (APP), melamine cyanurate (MCA), and aluminum hypophosphite (AHP). The melamine cyanurate also acts as a gas-phase synergist, decomposing upon heating to absorb heat and release non-flammable gases, thus diluting the oxygen concentration.

[0042] In this invention, the mass percentage of inorganic metal hydroxide in the compound flame retardant can be 5%, 6%, 7%, 8%, 9%, or 10%. The mass percentage of inorganic metal hydroxide can reduce the surface temperature of the matrix through its unique endothermic decomposition mechanism without compromising the macroscopic flexibility of the composite material, and can synergistically react with the char layer generated by the nitrogen-phosphorus flame retardant at high temperature, further enhancing the physical strength and smoke suppression performance of the char layer. The inorganic metal hydroxide preferably includes aluminum hydroxide and / or magnesium hydroxide, wherein the aluminum hydroxide is preferably nano-sized aluminum hydroxide (ATH), and the magnesium hydroxide is preferably nano-sized magnesium hydroxide (MDH).

[0043] In this invention, the mass percentage of the char-forming synergist in the compound flame retardant can be 20%, 25%, 30%, 32%, or 35%. The mass percentage of the char-forming synergist can produce a highly efficient physical and chemical synergistic effect with the nitrogen-phosphorus flame retardant, constructing a high-strength porous expanded char layer structure under the condition of low polymer matrix ratio (10~15%), effectively anchoring an ultra-high proportion of inorganic radiation-shielding skeleton filler, and preventing structural collapse and powdering caused by interface failure during high-temperature combustion. The char-forming synergist preferably includes pentaerythritol (PER) and / or zinc borate. The zinc borate also has a smoke-suppressing effect, stabilizes the expanded char layer structure, and prevents metal powder from agglomerating and collapsing at high temperatures.

[0044] In this invention, the functional additives preferably include coupling agents, antioxidants, and lubricants. The mass ratio of the coupling agent, antioxidant, and lubricant is preferably 0.6~2.5:0.1~0.5:0.1~1.2, specifically 0.67:0.17:0.16. The amount of coupling agent is sufficient to ensure complete monolayer coverage of the inorganic radiation shielding skeleton filler surface at an extremely high filling rate (80%~88%). By constructing a strong chemical bonding interface between the inorganic powder and the modified polymer matrix, the incompatibility problem of the organic / inorganic phase interface is completely solved. The coupling agent preferably includes one or more of silane coupling agents, titanate coupling agents, and aluminate coupling agents, used to activate the inorganic radiation shielding skeleton filler.

[0045] In this invention, the amount of antioxidant used is sufficient to effectively inhibit the breakage and crosslinking of thermoplastic polyurethane chain segments by synergistically capturing active free radicals generated by the oxidation of the polymer matrix and decomposing hydroperoxides under high shear processing conditions of 160~185℃ and during long-term service, thereby maintaining the color stability and mechanical ductility of the composite material. The antioxidant preferably includes a compound of hindered phenolic antioxidant and phosphite auxiliary antioxidant to prevent thermo-oxidative aging of the polymer matrix during high-temperature melt blending and long-term use. The mass ratio of hindered phenolic antioxidant to phosphite auxiliary antioxidant in the compound is preferably 1:1 to 1:2. The hindered phenolic antioxidant is preferably antioxidant 1010, and the phosphite auxiliary antioxidant is preferably antioxidant 168.

[0046] In this invention, the amount of lubricant used can significantly balance the internal and external lubrication requirements of the ultra-high filler system without reducing the interfacial bonding strength, giving the high viscosity melt excellent processing rheology and interfacial roll release performance, and ensuring high surface finish and dimensional stability of the sheet. The lubricant preferably includes one or more of pentaerythritol stearate (PETS), EBS wax and silicone powder. The lubricant is used to improve the melt flowability and calender roll release performance of the ultra-high filler system.

[0047] In this invention, the high-density flexible radiation-shielding composite material is preferably a sheet, and the thickness of the sheet is preferably 0.5~2.0mm, specifically 0.5, 1, 1.5, 1.8, 1.9 or 2.0mm.

[0048] This invention also provides a method for preparing the high-density flexible radiation-shielding composite material described in the above technical solution, comprising the following steps: Inorganic radiation shielding skeleton filler, compound flame retardant and functional additives are mixed and activated to obtain activated powder; The activated powder is melt-blended with a polymer matrix to obtain a melt; The melt is calendered and shaped to obtain the high-density flexible radiation-shielding composite material.

[0049] This invention involves mixing and activating an inorganic radiation shielding skeleton filler, a compound flame retardant, and functional additives to obtain an activated powder.

[0050] In this invention, bismuth oxide and tungsten oxide are preferably fed into a high-speed mixer and heated to 110°C. Then, a portion of the coupling agent is sprayed on for the first activation. The resulting first activated product, gadolinium oxide, lanthanum oxide and a compound flame retardant are mixed and then sprayed on the remaining coupling agent for the second activation to obtain the activated powder.

[0051] In this invention, the mass of the coupling agent is 60% of the mass of the coupling agent.

[0052] In this invention, the first activation is preferably carried out under high-speed stirring, the speed of the high-speed stirring is preferably 1500~3000 r / min, specifically 1500, 2000, 2500 or 3000 r / min, and the first activation time is preferably 5~15 min, specifically 5, 10 or 15 min.

[0053] After the first activation is completed, it is preferable to cool down to 80°C to obtain the first activated product.

[0054] In this invention, the second activation is preferably carried out under low-speed stirring, and the stirring speed is preferably 300~800 r / min, specifically 300, 400, 500, 600, 700 or 800 r / min. The second activation time is preferably 10~20 min, specifically 10, 15 or 20 min.

[0055] In this invention, the activation process ensures the wettability of the large particle skeleton of bismuth oxide and tungsten oxide, while preventing the agglomeration of small particles of gadolinium oxide and lanthanum oxide. The antioxidant is pre-coated on the powder surface during the activation stage, which ensures that it can immediately capture free radicals generated by local overheating when entering the melt blending stage, thereby precisely protecting the TPU molecular chains from thermal degradation. The lubricant is added at this stage and can be evenly distributed between the inorganic filler particles. In the subsequent calendering process, it can more effectively balance the internal and external lubrication, reduce the melt viscosity, prevent sticking to the rollers, and ensure the high gloss of the sheet surface.

[0056] After obtaining the activated powder, the present invention melt-blends the activated powder with a polymer matrix to obtain a melt.

[0057] In this invention, the melt blending temperature is preferably 160~185℃, specifically 160, 165, 170, 175, 180 or 185℃.

[0058] In this invention, the melt blending is preferably carried out in a twin-screw extruder.

[0059] In this invention, the activated powder and the polymer matrix are preferably fed into a twin-screw extruder via a loss-in-weight balance for melt blending.

[0060] In this invention, a high-shear kneading block is preferably provided after the feeding section of the twin-screw extruder to promote deep interfacial physical entanglement between the modified TPU segments with polar anhydride groups and the activated powder with strong mechanical shear force.

[0061] In this invention, the preferred parameters of the high-shear kneading block include: screw speed 350~550 r / min; specific energy consumption 0.18~0.28 kWh / kg; average shear rate 200~800 s. -1 The kneading process uses a combination of offset angles from 45° / 5 / 28 to 60° / 5 / 28.

[0062] After obtaining the melt, the present invention performs calendering and shaping on the melt to obtain the high-density flexible radiation-proof composite material.

[0063] In this invention, the calendering and shaping is preferably a three-roll calender, which preferably includes an upper roll, a middle roll, and a lower roll. The temperature of the upper roll is preferably 150~170℃, specifically 150, 160, or 170℃; the temperature of the middle roll is preferably 140~160℃, specifically 140, 150, or 160℃; and the temperature of the lower roll is preferably 35~45℃, specifically 35, 40, or 45℃. Rapid cooling from the upper roll to the lower roll suppresses the crystal growth of the polymer matrix, thereby maximizing the preservation of the substrate's flexibility and producing the highly dense flexible radiation-resistant composite material with a thickness ranging from 0.5 to 1.5 mm.

[0064] In this invention, the gap between the upper roller and the middle roller (first gap) is preferably 0.55~1.8mm, specifically 0.55, 0.6, 0.8, 1, 1.2, 1.4, 1.6 or 1.8mm, providing a 10%~20% pre-pressing allowance to maintain the stability of the melt. The gap between the middle roller and the lower roller (second gap) is preferably 0.48~1.5mm, specifically 0.5, 0.7, 0.9, 1.1, 1.3 or 1.5mm, to offset the physical shrinkage rate and control the final shaping thickness.

[0065] In this invention, the base line speed of the three-roll calender is preferably 0.5~3.0 m / min, specifically 0.5, 1, 1.5, 2, 2.5 or 3.0 m / min. The base line speed is inversely proportional to the thickness. When the thickness is too large, it is preferable to reduce the base line speed of the roller to ensure thorough cooling of the core.

[0066] In this invention, the roller speed ratio of the upper roller, the middle roller and the lower roller is preferably 1:(1.02~1.05):(1.05~1.1) to reduce internal residual tensile stress.

[0067] In this invention, the pressure of the three-roll calender is preferably 150~300kN / m, specifically 150, 200, 250 or 300kN / m, to eliminate internal microscopic phase interface voids.

[0068] In this invention, the traction winding tension of the three-roll calender is preferably 10~50N, specifically 10, 20, 30, 40 or 50N, to prevent the sheet in a highly elastic state from being overstretched and thinned, and to ensure that the winding is flat and does not deform.

[0069] The present invention also provides the application of the high-density flexible radiation shielding composite material described in the above technical solution or the high-density flexible radiation shielding composite material prepared by the preparation method described in the above technical solution in the fields of medical interventional protection, nuclear industry and flexible protection.

[0070] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0071] Example 1 A high-density, flexible radiation-shielding composite material was prepared. This high-density, flexible radiation-shielding composite material is lead-free and comprises the following raw materials by mass percentage: The high-density flexible radiation-shielding composite material contains 12% TPU-g-MAH, 84% inorganic radiation-shielding skeleton filler, 3% compound flame retardant, and 1% functional additives. The raw materials used in its preparation include 42% bismuth oxide, 29.4% tungsten oxide, 10.08% gadolinium oxide, and 2.52% lanthanum oxide. The inorganic radiation shielding skeleton filler includes bismuth oxide, tungsten oxide, gadolinium oxide, and lanthanum oxide. The inorganic radiation shielding skeleton filler contains 50% bismuth oxide, 35% tungsten oxide, 12% gadolinium oxide, and 3% lanthanum oxide. The particle size of bismuth oxide and tungsten oxide is 4.0 μm, the particle size of gadolinium oxide is 1.2 μm, and the particle size of lanthanum oxide is 200 nm. The compound flame retardant includes a nitrogen-phosphorus intumescent flame retardant, an inorganic metal hydroxide, and a char-forming synergist. The mass percentage of bismuth oxide in the raw materials for preparing the high-density flexible radiation-proof composite material is: 1.8% nitrogen-phosphorus intumescent flame retardant, 0.24% inorganic metal hydroxide, and 0.96% char-forming synergist. The nitrogen-phosphorus intumescent flame retardant is ammonium polyphosphate, the inorganic metal hydroxide is nano-sized aluminum hydroxide, and the char-forming synergist is pentaerythritol. The functional additives include coupling agents, antioxidants, and lubricants, with a mass ratio of 0.67:0.17:0.16. The coupling agent is a silane coupling agent KH-550, the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 with a mass ratio of 1:2, and the lubricant is pentaerythritol stearate. The preparation process is as follows: Polyether-type thermoplastic polyurethane particles, polar monomer maleic anhydride, and an initiator are uniformly mixed in a mixer. The resulting premix is ​​then subjected to a graft modification reaction. Vacuum exhaust is activated in the post-extrusion zone to remove unreacted polar monomer maleic anhydride and small molecule byproducts. After cooling and pelletizing, the TPU-g-MAH is obtained. The preferred initiator is dicumyl peroxide. The parameters for the graft modification reaction include: temperature 170℃, screw speed 550 r / min, specific energy consumption 0.28 kWh / kg, and average shear rate 800 s⁻¹. -1 ; Bismuth oxide and tungsten oxide were stirred in a high-speed mixer at 3000 r / min for 5 min, heated to 110°C, and then a portion of the coupling agent was sprayed on for the first activation. The mixture was then cooled to 80°C. The resulting first activated product, gadolinium oxide, lanthanum oxide, and a compound flame retardant were mixed, and the remaining coupling agent was sprayed on for the second activation (800 r / min, 10 min) to obtain activated powder. The mass of the portion of coupling agent was 60% of the total mass of the coupling agent. The activated powder and polymer matrix are fed into a twin-screw extruder via a loss-in-weight balance. A high-shear kneading block is installed after the feeding section of the twin-screw extruder. The parameters of the high-shear kneading block include: screw speed 550 r / min, specific energy consumption 0.28 kWh / kg, and average shear rate 800 s. -1 The kneading process employs a 60° / 5 / 28° misalignment angle combination, followed by melt blending at 185°C to obtain a melt. The melt is fed into a three-roll calender for calendering and shaping. The three-roll calender includes an upper roll, a middle roll, and a lower roll. The temperature of the upper roll is 160℃, the temperature of the middle roll is 150℃, and the temperature of the lower roll is 40℃. The roll gap between the upper and middle rolls is 1.8mm, and the roll gap between the middle and lower rolls is 1.5mm. The basic linear speed of the three-roll calender is 3.0m / min, and the roll speed ratio of the upper, middle, and lower rolls is 1:1.05:1.1. The pressure of the three-roll calender is 300kN / m, and the traction winding tension is 50N. The resulting high-density flexible radiation-shielding composite material has a thickness of 1.9mm and an areal density of 6.3kg / m³. 2 .

[0072] Comparative Example 1 A traditional lead-free formulation with 0.5 mmPb includes polyether thermoplastic polyurethane, bismuth oxide, and tungsten oxide, with the bismuth oxide comprising 60% of the mass of the polyether thermoplastic polyurethane and the tungsten oxide comprising 25% of the mass of the polyether thermoplastic polyurethane.

[0073] Preparation method: Polyether-type thermoplastic polyurethane, bismuth oxide, and tungsten oxide were mixed without activation.

[0074] Comparative Example 2 Standard lead rubber material with 0.5mmPb, thickness: 2.1mm, areal density: 7kg / m³ 2 .

[0075] Comparative Example 3 Similar to Example 1, the only difference is that the activation process in the preparation process is a one-step activation, that is, a one-step coupling, in which the inorganic radiation shielding skeleton filler, compound flame retardant and functional additives are activated in one step (the one-step activation temperature is 110°C and the time is 15 min) to obtain activated powder.

[0076] Comparative Example 4 Same as Example 1, except that the particle size of bismuth oxide and tungsten oxide in the inorganic radiation shielding skeleton filler is 50 μm, gadolinium oxide is 10.0 μm, and lanthanum oxide is 5 μm.

[0077] Comparative Example 5 Same as Example 1, except that the first activation temperature is 80°C.

[0078] Example 2 Same as Example 1, except that the raw materials are as follows: The composition includes 10% TPU-g-MAH, 88% inorganic radiation shielding skeleton filler, 1% compound flame retardant, and 1% functional additives. The inorganic radiation shielding skeleton filler contains 50% bismuth oxide, 35% tungsten oxide, 12% gadolinium oxide, and 3% lanthanum oxide. The compound flame retardant contains 60% nitrogen-phosphorus intumescent flame retardant, 8% inorganic metal hydroxide, and 32% char-forming synergist.

[0079] Breakthrough in the molding limits of elastomers: When the inorganic radiation shielding skeleton filler content reaches 88%, the melt viscosity of Example 2 is extremely high. However, under the synergistic effect of 0.16% lubricant and a roller speed ratio of 1:1.05:1.1 described in this invention, stable calendering and shaping can still be achieved.

[0080] Comparative Example 6: 90% Critical Line of Inorganic Radiation Shielding Framework Filler: Same as Example 2, except that the raw materials are as follows: The formula consists of 8% TPU-g-MAH, 90% inorganic radiation shielding skeleton filler, 1% compound flame retardant, and 1% functional additives.

[0081] When the amount of inorganic radiation shielding skeleton filler is increased to 90% (beyond the scope of this invention), the TPU-g-MAH matrix is ​​less than 10%, which cannot form a continuous encapsulation phase. This results in a severe "drying" phenomenon in the melt in the extruder, a surge in torque, and obvious "peeling" and cracks on the sheet surface.

[0082] Comparative Example 7 Similar to Example 2, the only difference is that the activation process in the preparation process is a one-step activation, that is, a one-step coupling, in which the inorganic radiation shielding skeleton filler, compound flame retardant and functional additives are activated in one step (the one-step activation temperature is 110°C and the time is 15 min) to obtain activated powder.

[0083] Comparison of elongation at break: The high-density flexible radiation shielding composite material prepared in Example 1 has a breaking elongation of 165%.

[0084] The high-density flexible radiation-shielding composite material prepared in Example 2 has a breaking elongation of 115%.

[0085] Physical property loss: Although the elongation at break of Example 2 decreased compared to Example 1, it was still far higher than the brittle fracture level of 38.4% in Comparative Example 7 under the same filler conditions achieved by the traditional one-step process. This demonstrates that even under conditions of extreme matrix scarcity, the "tertiary particle size packing" can still ensure that the material possesses the basic flexibility for making protective clothing through the "ball bearing" lubrication effect of nano-lanthanum oxide.

[0086] Interface stability: Example 2 ensured that 88% of the powder surface was completely covered by the full activation of the coupling agent at a dosage of 0.67%.

[0087] Comparison of powder separation risks: After 5000 flexural cycles, no particles were observed to precipitate on the surface of Example 2. If the inorganic radiation shielding skeleton filler content reaches 90%, the interfacial bonding force will be unable to resist the propagation of microcracks under high loads, leading to the free precipitation of heavy metal powder (i.e., the "powder precipitation" phenomenon mentioned in the background art).

[0088] Example 3 Same as Example 1, except that the raw materials are as follows: The composition includes 15% TPU-g-MAH, 80% inorganic radiation shielding skeleton filler, 2% compound flame retardant, and 3% functional additives. The inorganic radiation shielding skeleton filler contains 50% bismuth oxide, 35% tungsten oxide, 12% gadolinium oxide, and 3% lanthanum oxide. The compound flame retardant contains 60% nitrogen-phosphorus intumescent flame retardant, 8% inorganic metal hydroxide, and 32% char-forming synergist.

[0089] Verification of its high toughness advantage: Mechanical performance: With 80% inorganic radiation shielding skeleton filler, the elongation at break of the material is 225% due to the increase of polymer matrix content to 15%.

[0090] The ample continuous phase matrix not only completely impregnates the inorganic radiation-shielding framework filler, but also forms a thicker and more elastic interfacial buffer layer between the powder particles. This allows the material to dissipate stress through the full extension of the TPU molecular chains when subjected to severe tension or ultra-high frequency bending, exhibiting excellent wearing comfort and physical durability.

[0091] Lead equivalent decrease: Tests show that, at the same thickness of 1.9 mm, the lead equivalent of Example 3 at 120 kVp is 0.48 mmPb, which is lower than the 0.51 mmPb of Example 1.

[0092] Radiation shielding effectiveness comparison test The test was conducted according to IEC 61331-1:2014 standard, examining the lead equivalent (Pb) at different tube voltages. eq The stability, especially the performance in the "transmission window" region, is shown in Table 1.

[0093] Table 1. Comparison Test Results of Radiation Shielding Effectiveness

[0094] Physical and mechanical property comparison test The tests were conducted according to ASTM D412 / ISO 37:2024 / GB / T 528-2009 standards, verifying that the combined effect of step coupling and three-stage gradation improved the ductility of the material. The results are shown in Table 2.

[0095] Table 2 Comparison of Physical and Mechanical Properties Test Results

[0096] Aging resistance and powder precipitation test (reliability) The results of the aging resistance and powder precipitation tests are shown in Table 3.

[0097] Table 3 Results of Aging Resistance and Powder Separation Tests

[0098] Artificial sweat immersion (37℃, 72h) The results of the artificial sweat immersion test are shown in Table 4.

[0099] Table 4 Results of Artificial Sweat Immersion Test

[0100] In summary, Example 1 not only successfully eliminated the protection trough in the 60-80kVp frequency band by introducing Gd elements to construct complementary absorption limits, but also completely eliminated powder agglomeration and interfacial voids at the microscopic level through the synergistic effect of stepwise activation and three-level gradation. This dual construction of a dense skeleton and a strong interface enables the material to achieve 10% weight reduction while maintaining extremely high mechanical integrity (165% elongation at break) and excellent anti-powder aging performance, fully meeting the high standard requirements of medical and nuclear biological and chemical protective clothing.

[0101] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A highly dense, flexible radiation-shielding composite material, characterized in that, The high-density flexible radiation-shielding composite material is lead-free and comprises the following raw materials by mass percentage: Polymer matrix 10-15%, inorganic radiation shielding skeleton filler 80-88%, compound flame retardant 1-5%, and functional additives 0.5-4%; The inorganic radiation shielding skeleton filler includes bismuth oxide, tungsten oxide, gadolinium oxide, and lanthanum oxide. The mass percentage of bismuth oxide in the inorganic radiation shielding skeleton filler is 35-55%, the mass percentage of tungsten oxide is 30-50%, the mass percentage of gadolinium oxide is 8-22%, and the mass percentage of lanthanum oxide is 0.5-8%. The particle size of bismuth oxide and tungsten oxide is 3-5 μm, the particle size of gadolinium oxide is 0.8-1.5 μm, and the particle size of lanthanum oxide is 100-300 nm.

2. The high-density flexible radiation-shielding composite material according to claim 1, characterized in that, The compound flame retardant comprises the following components by mass percentage: 55-70% nitrogen-phosphorus intumescent flame retardant, 5-10% inorganic metal hydroxide, and 20-35% char-forming synergist.

3. The high-density flexible radiation-shielding composite material according to claim 2, characterized in that, The nitrogen-phosphorus intumescent flame retardant includes one or more of ammonium polyphosphate, melamine cyanurate, and aluminum hypophosphite.

4. The high-density flexible radiation-shielding composite material according to claim 2, characterized in that, The inorganic metal hydroxides include aluminum hydroxide and / or magnesium hydroxide.

5. The high-density flexible radiation-shielding composite material according to claim 2, characterized in that, The char-forming synergist includes pentaerythritol and / or zinc borate.

6. The high-density flexible radiation-shielding composite material according to claim 1, characterized in that, The functional additives include coupling agents, antioxidants, and lubricants, wherein the mass ratio of the coupling agent, antioxidant, and lubricant is 0.6~2.5:0.1~0.5:0.1~1.

2.

7. The method for preparing the high-density flexible radiation-shielding composite material according to any one of claims 1 to 6, characterized in that, Includes the following steps: Inorganic radiation shielding skeleton filler, compound flame retardant and functional additives are mixed and activated to obtain activated powder; The activated powder is melt-blended with a polymer matrix to obtain a melt; The melt is calendered and shaped to obtain the high-density flexible radiation-shielding composite material.

8. The preparation method according to claim 7, characterized in that, The calendering and shaping process is a three-roll calendering process, which includes an upper roll, a middle roll, and a lower roll. The temperature of the upper roll is 150~170℃, the temperature of the middle roll is 140~160℃, and the temperature of the lower roll is 35~45℃.

9. The preparation method according to claim 8, characterized in that, The distance between the upper roller and the middle roller is 0.55~1.8mm, and the distance between the middle roller and the lower roller is 0.48~1.5mm.

10. The application of the high-density flexible radiation shielding composite material according to any one of claims 1 to 6 or the high-density flexible radiation shielding composite material prepared by the preparation method according to any one of claims 7 to 9 in the fields of medical interventional protection, nuclear industry and flexible protection.

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