Lead-free radiation-proof PVC composite board and preparation method thereof

Abstract

The application discloses a lead-free anti-radiation PVC composite board and a preparation method thereof, and belongs to the technical field of composite boards. First, sheet-shaped bismuth oxide is in-situ grown on boron nitride nanosheets through a hydrothermal method, and then the lead-free anti-radiation filler is obtained by modifying the sheet-shaped bismuth oxide with a silane coupling agent. Then, magnesium-silver co-doped hydroxyapatite powder is synthesized through a wet chemical method with hydroxyapatite as a carrier. Then, the lead-free anti-radiation filler is used as inner layer functional filler, and the magnesium-silver co-doped hydroxyapatite powder and magnesium hydroxide are used as outer layer functional fillers. The PVC resin, the plasticizer and the stabilizer are mixed respectively, and then the mixed materials are subjected to melt blending, three-layer co-extrusion compounding and hot-pressing forming processes, so as to obtain the lead-free anti-radiation PVC composite board. The lead-free anti-radiation PVC composite board has excellent anti-radiation performance, long-acting antibacterial property, high mechanical strength and good flame-retardant and heat-insulating characteristics.

Description

Technical Field

[0001] This invention belongs to the field of composite board technology, specifically relating to a lead-free radiation-proof PVC composite board and its preparation method. Background Technology

[0002] PVC composite panels are multi-layered structural panels with polyvinyl chloride as the core material. They are lightweight, moisture-proof, and corrosion-resistant, and are widely used in decoration, furniture manufacturing, and construction. PVC composite panels are generally easy to install, and can be spliced ​​or seamlessly welded. They are particularly suitable for public places such as hospitals, as they can reduce maintenance and construction cycles and avoid excessive impact on the daily operation of the hospital.

[0003] However, in the medical field, including hospital CT scan rooms, X-ray rooms, and radiotherapy rooms, medical imaging rooms emit significant radiation when the equipment is running. To minimize the impact of this radiation on the human body, it is necessary to use decorative panels with radiation shielding capabilities. Common examples include lead-boron polyethylene panels, which have high lead content and pose serious health and environmental risks. These panels are unsuitable for extensive use outside medical imaging rooms or for exposure to environments accessible to the human body, and strict international regulations have been implemented. In hospitals, industrial clean areas, and other locations with high environmental standards, lead-free radiation shielding panels are required to achieve both radiation shielding and pollution prevention.

[0004] Chinese patent application CN112225956A discloses a radiation-shielding composite material, its preparation method, and its application. It uses non-toxic metal oxides such as bismuth trioxide as lead-free radiation-shielding fillers, applied to rubber materials to provide radiation shielding. However, when these lead-free radiation-shielding fillers are applied to polymer systems such as PVC, their dispersibility remains poor, and they are prone to agglomeration, leading to uneven filler distribution and localized radiation protection failure. Summary of the Invention

[0005] The purpose of this invention is to provide a lead-free radiation-shielding PVC composite board and its preparation method. First, a hydrothermal method is used to firmly anchor bismuth oxide flakes onto boron nitride nanosheets. Through spatial hindrance, the aggregation of bismuth oxide itself is prevented at the source, forming a uniformly dispersed radiation-shielding and heat-insulating network. Then, through the bridging effect of a silane coupling agent, the interfacial compatibility between the inorganic filler and the organic PVC matrix is ​​improved, the interfacial bonding force is enhanced, and secondary aggregation during processing is prevented. This allows the composite filler to form a continuous and dense protective network in the matrix, synergistically achieving excellent radiation protection efficiency.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing a lead-free radiation-shielding PVC composite board includes the following steps:

[0008] Step 1: Plate-like bismuth oxide is grown in situ on boron nitride nanosheets using a hydrothermal method, and then modified with a silane coupling agent to obtain a lead-free radiation shielding filler.

[0009] Step 2: Using hydroxyapatite as a carrier, magnesium-silver co-doped hydroxyapatite powder is synthesized by wet chemical method.

[0010] Step 3: Lead-free radiation shielding filler is used as the inner functional filler, and magnesium-silver co-doped hydroxyapatite powder and magnesium hydroxide are used as the outer functional fillers. They are mixed with PVC resin, plasticizer and stabilizer respectively. After melt blending, the three-layer co-extrusion composite and hot pressing molding process is used to obtain lead-free radiation shielding PVC composite board.

[0011] Furthermore, the specific preparation steps for lead-free radiation shielding filler are as follows:

[0012] Add the flake-shaped bismuth oxide / boron nitride composite powder to toluene and stir for 20-30 minutes. Slowly add the silane coupling agent and reflux at 100°C for 24 hours under nitrogen protection. Allow it to cool naturally to room temperature, filter, collect the product, and wash it 3-5 times each with toluene, ethanol, and deionized water. Vacuum dry to constant weight, grind, and pass through a 200-mesh sieve to obtain the lead-free radiation shielding filler.

[0013] Furthermore, the ratio of flake bismuth oxide / boron nitride composite powder, toluene, and silane coupling agent is 15-20g: 300-400mL: 16.5-18.5mL.

[0014] Furthermore, the silane coupling agent is either silane coupling agent KH550 or silane coupling agent KH560.

[0015] Furthermore, the specific preparation steps for the flake-shaped bismuth oxide / boron nitride composite powder are as follows:

[0016] Boron nitride nanosheets were added to ethanol and sonicated for 30-40 min to obtain a boron nitride nanosheet dispersion. Bismuth salt was added to a dilute nitric acid solution prepared from nitric acid and deionized water and stirred continuously at 80-90℃. Then, the boron nitride nanosheet dispersion was added and stirred for 30-40 min. Then, 10wt% ammonia water was slowly added dropwise to adjust the pH of the solution to 10. The solution was transferred to a hydrothermal reactor and kept at 180-190℃ for 10-12 h. After cooling, the product was filtered and washed alternately with deionized water and ethanol 3-5 times. It was then vacuum dried to constant weight and transferred to a high-temperature tube furnace. The temperature was increased to 400-500℃ at a rate of 5℃ / min and calcined for 3-5 h. After cooling, the product was ground and passed through a 200-mesh sieve to obtain a flaky bismuth oxide / boron nitride composite powder.

[0017] Furthermore, the ratio of boron nitride nanosheets to ethanol is 4-6g:80-100mL.

[0018] Furthermore, the ratio of bismuth salt, nitric acid, deionized water, and boron nitride nanosheet dispersion is 48.8-52.2 g: 100-120 mL: 300-330 mL: 52-56 mL.

[0019] Furthermore, the bismuth salt is either bismuth nitrate pentahydrate or bismuth chloride.

[0020] Furthermore, the specific preparation steps for magnesium-silver co-doped hydroxyapatite powder are as follows:

[0021] Add calcium nitrate tetrahydrate, magnesium nitrate, and silver nitrate to deionized water and stir until completely clear to obtain a mixed cation solution; add diammonium hydrogen phosphate to deionized water and stir for 20-30 minutes, then slowly add 10wt% ammonia water until the pH of the solution is 10 to obtain a phosphorus source solution.

[0022] The phosphorus source solution was heated to 90-95℃, and the mixed cation solution was slowly added at 600-700 rpm. During the reaction, 10wt% ammonia water was continuously added dropwise to keep the pH of the solution at around 10. The dropping rate was controlled to make the whole process last for 2-3 hours. Then, stirring was stopped and the mixture was allowed to stand for 24 hours. The mixture was filtered, and the product was repeatedly washed with a large amount of deionized water, vacuum dried to constant weight, ground, and passed through a 200-mesh sieve to obtain magnesium-silver co-doped hydroxyapatite powder.

[0023] Furthermore, the ratio of calcium nitrate tetrahydrate, magnesium nitrate, silver nitrate, and deionized water is 46.1-48.2g: 1-1.5g: 0.2-0.5g: 100-120mL.

[0024] Furthermore, the ratio of diammonium hydrogen phosphate to deionized water is 13.2-14.6g: 200-300mL.

[0025] Furthermore, the volume ratio of the phosphorus source solution to the mixed cation solution is 10-15:5-6.

[0026] Furthermore, the specific preparation steps for lead-free radiation-shielding PVC composite sheets are as follows:

[0027] PVC resin, plasticizer, calcium-zinc stabilizer, magnesium-silver co-doped hydroxyapatite powder and magnesium hydroxide are mixed and stirred evenly to obtain the outer layer formulation powder; PVC resin, plasticizer, calcium-zinc stabilizer and lead-free radiation shielding filler are mixed and stirred evenly to obtain the inner layer formulation powder.

[0028] The outer layer formulation powder and the inner layer formulation powder are mixed separately and stirred at 120-130℃ and 1000-1200rpm for 5-8 minutes, then stirred at 70-80℃ and 700-800rpm for 5-8 minutes, then stirred at 40-50℃ and 500-600rpm for 3-5 minutes, and then cooled to 30-35℃ to obtain the outer and inner layer mixture. This mixture is then transferred to a screw extruder and subjected to a three-layer co-extrusion composite and hot-press molding process to obtain lead-free radiation-proof PVC composite board.

[0029] Furthermore, the three-layer co-extrusion composite and hot-pressing process specifically includes the following steps:

[0030] The plastic molten material of the outer layer, inner layer, and outer layer is simultaneously supplied through a three-layer co-extrusion die head and extruded at 160-170℃ to form a three-layer composite sheet. The sheet is then placed in a flat vulcanizing machine and held at 150-160℃ and 10-12MPa for 10-15 minutes before cooling and depressurization.

[0031] Furthermore, the mass ratio of PVC resin, plasticizer, calcium-zinc stabilizer, and lead-free radiation-shielding filler is 100-120:40-50:4-6:15-20.

[0032] Furthermore, the mass ratio of PVC resin, plasticizer, calcium-zinc stabilizer, magnesium-silver co-doped hydroxyapatite powder and magnesium hydroxide is 100-120:45-50:4-6:10-12:15-18.

[0033] The beneficial effects of this invention are:

[0034] 1. This invention achieves a balance of multifunctionality, high performance, and environmental safety in lead-free radiation-shielding PVC composite panels through material design and structural innovation. First, a stable "sheet-on-sheet" structure is constructed using a hydrothermal method, eliminating the need for traditional toxic lead materials and achieving highly efficient synergistic shielding against X / γ rays and neutrons. Then, through the synergistic effect of magnesium-silver co-doped hydroxyapatite and magnesium hydroxide, the material is endowed with highly efficient flame retardancy, significant smoke suppression, and long-lasting broad-spectrum antibacterial functions, greatly improving the safety of the panel applications.

[0035] The three-layer co-extruded composite structure precisely combines a high-radiation-shielding inner layer with a high-flame-retardant and antibacterial outer layer, achieving functional zoning and performance optimization of the material. With the help of silane coupling agent surface modification and step-by-step processing technology, the uniform dispersion and firm bonding of each component in the matrix are ensured, resulting in excellent radiation protection performance, long-lasting antibacterial properties and good flame-retardant and heat insulation characteristics. It is suitable for fields with multiple protection requirements, such as medical, nuclear industry and high-end buildings.

[0036] 2. The lead-free radiation shielding filler in this invention is achieved by in-situ loading bismuth oxide flakes onto boron nitride nanosheets and surface modification with silane coupling agent KH-550. Functionally, the "sheet-on-sheet" composite structure utilizes the high atomic number of bismuth oxide to shield X / γ rays and the boron nitride nanosheets to achieve neutron protection, thus synergistically constructing a highly efficient lead-free radiation shielding system. In terms of performance, the modification with the silane coupling agent improves the interfacial compatibility and bonding force between the inorganic filler and the organic PVC matrix, ensuring uniform and stable dispersion of the filler in the matrix, avoiding agglomeration, and significantly enhancing the mechanical strength, toughness, and durability of the composite board. At the same time, the excellent dispersibility also improves the processing fluidity, laying the foundation for obtaining a high-quality board with a smooth surface and uniform performance.

[0037] 3. The magnesium-silver co-doped hydroxyapatite powder in this invention achieves multifunctional integration of flame retardancy, smoke suppression, and antibacterial properties through ion doping. Hydroxyapatite itself, as an environmentally friendly flame retardant, can promote the formation of a dense ceramic layer during combustion, playing a core role in heat insulation and oxygen isolation. The doping of magnesium ions significantly refines the crystal particles of hydroxyapatite by inducing lattice distortion, increasing its specific surface area and improving flame retardant efficiency. Silver ions replace lattice sites in an atomically dispersed manner, enabling slow and sustained release, giving the material broad-spectrum and long-lasting antibacterial function, and effectively inhibiting bacterial growth. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments in 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.

[0039] Example 1: A method for preparing a lead-free radiation-shielding PVC composite board, comprising the following steps:

[0040] S1: Add 4g of boron nitride nanosheets to 80mL of ethanol and sonicate for 30min to obtain a boron nitride nanosheet dispersion; add 48.8g of bismuth nitrate pentahydrate to a dilute nitric acid solution prepared by 100mL of nitric acid and 300mL of deionized water, stir continuously at 80℃, then add 52mL of the boron nitride nanosheet dispersion and stir for 30min, then slowly add 10wt% ammonia water to make the pH of the solution 10, transfer to a hydrothermal reactor with a polytetrafluoroethylene liner, keep at 180℃ for 10h, cool naturally to room temperature, filter the product, wash three times alternately with deionized water and ethanol, vacuum dry at 60℃ for 10h, transfer to a high-temperature tube furnace, heat to 400℃ at a rate of 5℃ / min, calcine for 3h, cool naturally to room temperature, grind, and pass through a 200-mesh sieve to obtain flake-shaped bismuth oxide / boron nitride composite powder.

[0041] Using bismuth ions adsorbed on the surface of boron nitride as nucleation sites, bismuth ions are hydrolyzed under alkaline conditions to generate bismuth hydroxide precipitate in situ, which is then loaded onto the surface of boron nitride nanosheets. The bismuth hydroxide precursor is then dissolved and recrystallized by hydrothermal method, transforming it into a sheet-like structure that is tightly composited with the boron nitride support.

[0042] S2: Add 15g of flaky bismuth oxide / boron nitride composite powder to 300mL of toluene, stir for 20min, slowly add 16.5mL of silane coupling agent KH-550, reflux and condense at 100℃ for 24h under nitrogen protection, cool naturally to room temperature, filter, collect the product, wash with toluene, ethanol and deionized water three times each, vacuum dry at 80℃ for 6h, grind, and pass through a 200-mesh sieve to obtain lead-free radiation shielding filler.

[0043] Surface modification of flake-shaped bismuth oxide / boron nitride composite powder was carried out using silane coupling agent KH-550.

[0044] S3: Add 46.1g of calcium nitrate tetrahydrate, 1g of magnesium nitrate and 0.2g of silver nitrate to 100mL of deionized water and stir until completely clear to obtain a mixed cation solution; add 13.2g of diammonium hydrogen phosphate to 200mL of deionized water and stir for 20min, then slowly add 10wt% ammonia water until the pH of the solution is 10 to obtain a phosphorus source solution;

[0045] 200 mL of phosphorus source solution was heated to 90 °C, and 100 mL of mixed cation solution was slowly added at 600 rpm. During the reaction, 10 wt% ammonia water was continuously added dropwise to keep the pH of the solution at around 10. The dropping rate was controlled to make the whole process last for 2 hours. Then, stirring was stopped and the mixture was allowed to stand for 24 hours. The mixture was filtered, and the product was repeatedly washed with a large amount of deionized water. It was then vacuum dried at 100 °C for 24 hours, ground, and passed through a 200-mesh sieve to obtain magnesium-silver co-doped hydroxyapatite powder.

[0046] By using a wet chemical method, the mixed cation solution is placed in an alkaline environment to promote the reaction of PO4. 3- Complete dissociation and guidance of preferential crystal growth along the C-axis, Mg 2+ Ag refines grains and improves thermal stability through lattice distortion effects. + Antibacterial function is achieved through atomic-level dispersion via lattice substitution.

[0047] S4: Mix 100g PVC resin, 45g plasticizer, 4g calcium-zinc stabilizer, 10g magnesium-silver co-doped hydroxyapatite powder and 15g magnesium hydroxide evenly to obtain the outer layer formulation powder; mix 100g PVC resin, 40g plasticizer, 4g calcium-zinc stabilizer and 15g lead-free radiation shielding filler evenly to obtain the inner layer formulation powder;

[0048] The outer layer formulation powder and the inner layer formulation powder are mixed separately and stirred at 120℃ and 1000rpm for 5 minutes, then stirred at 70℃ and 700rpm for 5 minutes, and then stirred at 40℃ and 500rpm for 3 minutes. After cooling to 30℃, the mixture of outer and inner layers is obtained and transferred to a screw extruder. The outer, inner, and outer layers of plastic molten material are simultaneously supplied through a three-layer co-extrusion die head and extruded at 160℃ to form a three-layer composite sheet. The sheet is placed in a flat vulcanizing machine and held at 150℃ and 10MPa for 10 minutes. After cooling and depressurization, a lead-free radiation-proof PVC composite sheet with an "outer-inner-outer" three-layer structure is obtained.

[0049] Example 2: A method for preparing a lead-free radiation-shielding PVC composite board, comprising the following steps:

[0050] S1: Add 5g of boron nitride nanosheets to 90mL of ethanol and sonicate for 35min to obtain a boron nitride nanosheet dispersion; add 50.5g of bismuth nitrate pentahydrate to a dilute nitric acid solution prepared by 110mL of nitric acid and 315mL of deionized water, stir continuously at 85℃, then add 54mL of the boron nitride nanosheet dispersion and stir for 35min. Then slowly add 10wt% ammonia water to make the pH of the solution 10. Transfer to a hydrothermal reactor with a polytetrafluoroethylene liner, keep at 185℃ for 11h, cool naturally to room temperature, filter the product, wash with deionized water and ethanol alternately 4 times, vacuum dry at 65℃ for 11h, transfer to a high-temperature tube furnace, heat to 450℃ at a rate of 5℃ / min, calcine for 4h, cool naturally to room temperature, grind, and pass through a 200-mesh sieve to obtain flake-shaped bismuth oxide / boron nitride composite powder.

[0051] S2: Add 17.5g of flaky bismuth oxide / boron nitride composite powder to 350mL of toluene, stir for 25min, slowly add 17.5mL of silane coupling agent KH-550, reflux and condense at 100℃ for 24h under nitrogen protection, cool naturally to room temperature, filter, collect the product, wash with toluene, ethanol and deionized water 4 times each, vacuum dry at 85℃ for 7h, grind, and pass through a 200-mesh sieve to obtain lead-free radiation shielding filler.

[0052] S3: Add 47.15g of calcium nitrate tetrahydrate, 1.25g of magnesium nitrate and 0.35g of silver nitrate to 110mL of deionized water and stir until completely clear to obtain a mixed cation solution; add 13.9g of diammonium hydrogen phosphate to 250mL of deionized water and stir for 25min, then slowly add 10wt% ammonia water until the pH of the solution is 10 to obtain a phosphorus source solution;

[0053] 250 mL of phosphorus source solution was heated to 92.5 °C, and 110 mL of mixed cation solution was slowly added at 650 rpm. During the reaction, 10 wt% ammonia water was continuously added dropwise to keep the pH of the solution at around 10. The dropping rate was controlled to make the whole process last for 2.5 h. Then, stirring was stopped and the mixture was allowed to stand for 24 h. After filtration, the product was washed repeatedly with a large amount of deionized water, dried under vacuum at 105 °C for 24 h, ground, and passed through a 200-mesh sieve to obtain magnesium-silver co-doped hydroxyapatite powder.

[0054] S4: Mix 110g of PVC resin, 47.5g of plasticizer, 5g of calcium-zinc stabilizer, 11g of magnesium-silver co-doped hydroxyapatite powder and 16.5g of magnesium hydroxide evenly to obtain the outer layer formulation powder.

[0055] Mix 110g of PVC resin, 45g of plasticizer, 5g of calcium-zinc stabilizer and 17.5g of lead-free radiation-proof filler evenly to obtain the inner layer formula powder.

[0056] The outer layer formulation powder and the inner layer formulation powder are mixed separately and stirred at 125℃ and 1100rpm for 6.5min, then at 75℃ and 750rpm for 6.5min, and then at 45℃ and 550rpm for 4min. The mixture is then cooled to 32.5℃ to obtain the outer and inner layer mixture. This mixture is then transferred to a screw extruder and fed through a three-layer co-extrusion die head, simultaneously supplying the molten plastic streams of the outer layer, inner layer, and outer layer. The mixture is extruded at 165℃ to form a three-layer composite sheet. This sheet is then placed in a flat vulcanizing machine and held at 155℃ and 11MPa for 12.5min. After cooling and depressurization, the lead-free radiation-proof PVC composite sheet is obtained.

[0057] Example 3: A method for preparing a lead-free radiation-shielding PVC composite board, comprising the following steps:

[0058] S1: Add 6g of boron nitride nanosheets to 100mL of ethanol and sonicate for 40min to obtain a boron nitride nanosheet dispersion; add 52.2g of bismuth nitrate pentahydrate to a dilute nitric acid solution prepared by 120mL of nitric acid and 330mL of deionized water, stir continuously at 90℃, then add 56mL of the boron nitride nanosheet dispersion and stir for 40min, then slowly add 10wt% ammonia water to make the pH of the solution 10, transfer to a hydrothermal reactor with a polytetrafluoroethylene liner, keep at 190℃ for 12h, cool naturally to room temperature, filter the product, wash it 5 times alternately with deionized water and ethanol, vacuum dry at 70℃ for 12h, transfer to a high-temperature tube furnace, heat to 500℃ at a rate of 5℃ / min, calcine for 5h, cool naturally to room temperature, grind, and pass through a 200-mesh sieve to obtain flake-shaped bismuth oxide / boron nitride composite powder.

[0059] S2: Add 20g of flaky bismuth oxide / boron nitride composite powder to 400mL of toluene, stir for 30min, slowly add 18.5mL of silane coupling agent KH-550, reflux and condense at 100℃ for 24h under nitrogen protection, cool naturally to room temperature, filter, collect the product, wash with toluene, ethanol and deionized water 5 times each, vacuum dry at 90℃ for 8h, grind, and pass through a 200-mesh sieve to obtain lead-free radiation shielding filler.

[0060] S3: Add 48.2g of calcium nitrate tetrahydrate, 1.5g of magnesium nitrate and 0.5g of silver nitrate to 120mL of deionized water and stir until completely clear to obtain a mixed cation solution; add 14.6g of diammonium hydrogen phosphate to 300mL of deionized water and stir for 30min, then slowly add 10wt% ammonia water until the pH of the solution is 10 to obtain a phosphorus source solution;

[0061] 300 mL of phosphorus source solution was heated to 95 °C, and 120 mL of mixed cation solution was slowly added at 700 rpm. During the reaction, 10 wt% ammonia water was continuously added dropwise to keep the pH of the solution at around 10. The dropping rate was controlled to make the whole process last for 3 h. Then, stirring was stopped and the mixture was allowed to stand for 24 h. After filtration, the product was washed repeatedly with a large amount of deionized water, dried under vacuum at 110 °C for 24 h, ground, and passed through a 200-mesh sieve to obtain magnesium-silver co-doped hydroxyapatite powder.

[0062] S4: Mix 120g of PVC resin, 50g of plasticizer, 6g of calcium-zinc stabilizer, 12g of magnesium-silver co-doped hydroxyapatite powder and 18g of magnesium hydroxide evenly to obtain the outer layer formulation powder.

[0063] Mix 120g of PVC resin, 50g of plasticizer, 6g of calcium-zinc stabilizer and 20g of lead-free radiation-proof filler evenly to obtain the inner layer formula powder.

[0064] The outer layer formulation powder and the inner layer formulation powder are mixed separately and stirred at 130℃ and 1200rpm for 8 minutes, then stirred at 80℃ and 800rpm for 8 minutes, and then stirred at 50℃ and 600rpm for 5 minutes. After cooling to 35℃, the mixture of outer and inner layers is obtained and transferred to a screw extruder. The outer layer, inner layer and outer layer plastic molten material are simultaneously supplied through a three-layer co-extrusion composite die head and extruded at 170℃ to form a three-layer composite sheet. The sheet is placed in a flat vulcanizing machine and held at 160℃ and 12MPa for 15 minutes. After cooling and depressurization, lead-free radiation-proof PVC composite sheet is obtained.

[0065] Example 4: This example provides a method for preparing lead-free radiation-proof PVC composite board. The difference from Example 1 is that bismuth chloride is used instead of bismuth nitrate pentahydrate in step S1 to prepare lead-free radiation-proof PVC composite board.

[0066] Example 5: This example provides a method for preparing lead-free radiation-proof PVC composite board. The difference from Example 1 is that in step S3, silane coupling agent KH-560 is used instead of silane coupling agent KH-550 to prepare lead-free radiation-proof PVC composite board.

[0067] In Examples 1-5, the outer layer thickness was 0.5 mm, the inner layer thickness was 4.0 mm, and the total thickness of the lead-free radiation-proof PVC composite board was 5 mm. Boron nitride nanosheets were selected from Forsmann Technology (Beijing) Co., Ltd., brand name Forsmann. Bismuth nitrate pentahydrate was selected from the flagship store of Maclean, item number B802763. Calcium nitrate tetrahydrate was selected from Tianfeng Chemical (Shanxi) Group Co., Ltd. Diammonium hydrogen phosphate was selected from Jinan Weixing Chemical Technology Co., Ltd., brand name Yuanlian. The PVC resin model was SG-5, brand name Xinfa, CAS number 9002-86-2. The plasticizer was dibutyl phthalate, selected from Zhengzhou Yufeng Nanomaterials Co., Ltd. The calcium-zinc stabilizer is a composite stabilizer with calcium soap (calcium fatty acid) and zinc soap (zinc fatty acid) as the main active ingredients, purchased from Shandong Yunxin New Material Technology Co., Ltd. The remaining raw materials were commercially available products.

[0068] Comparative Example 1: The difference from Example 1 is that boron nitride nanosheets are not added in step S1, while the other steps remain unchanged, and lead-free radiation-proof PVC composite board is prepared.

[0069] Comparative Example 2: The difference from Example 1 is that step S1 is omitted. Referring to the boron / bismuth molar ratio of the flaky bismuth oxide / boron nitride composite powder in step S1, in step S2, the flaky bismuth oxide / boron nitride composite powder is replaced with a physical mixture of commercially available boron nitride nanosheets and bismuth oxide in the same ratio. The remaining steps remain unchanged, and lead-free radiation-proof PVC composite board is prepared.

[0070] Comparative Example 3: The difference from Example 1 is that step S2 is omitted, and the lead-free radiation shielding filler in step S4 is replaced with the flake bismuth oxide / boron nitride composite powder in step S1. The remaining steps remain unchanged, and a lead-free radiation shielding PVC composite board is prepared.

[0071] Comparative Example 4: The difference from Example 1 is that step S3 is omitted, and commercially available hydroxyapatite powder is used to replace the magnesium-silver co-doped hydroxyapatite powder in step S4. The remaining steps remain unchanged, and lead-free radiation-proof PVC composite board is prepared.

[0072] The following performance tests were performed on the lead-free radiation-shielding PVC composite sheets prepared in Examples 1-5 and Comparative Examples 1-4:

[0073] Radiation shielding rate: The test was conducted in accordance with GBZ / T147-2017 "Determination of Attenuation Performance of X-ray Shielding Materials". A medical diagnostic X-ray machine was used. Under fixed tube voltage (100 kV) and filtration conditions, the radiation dose rate before protection was measured without placing the sample. Then, the plate sample was placed and the radiation dose rate after protection was measured. The radiation shielding rate was calculated using the formula: Radiation shielding rate = (1 - after protection / before protection) × 100%. The higher the value, the better the radiation shielding efficiency.

[0074] Inhibition rate of Staphylococcus aureus and Escherichia coli: The test was conducted in accordance with GB / T 31402-2015 "Test Method for Antibacterial Properties of Plastic Surfaces". A specific concentration of bacterial solution was evenly covered on the surface of the sample and control sample. After incubation at (37±1)℃ and high humidity for 24 hours, the colonies were washed off with neutralization solution and viable bacteria were counted. The inhibition rate was calculated using the formula: Inhibition rate = (number of colonies in control sample - number of colonies in sample) / number of colonies in control sample × 100%. The higher the value, the better the antibacterial effect.

[0075] Internal bond strength: The test is conducted in accordance with GB / T17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels". The sample is cut into the specified size, and it is bonded to a special tensile clamp with a high-strength adhesive. Then, it is stretched at a uniform speed perpendicular to the board surface on a universal testing machine until the interlayer of the sample is pulled apart and fails. The maximum load is recorded and the strength is calculated using the formula: Internal bond strength = Maximum failure load / Bonded area. The higher the value, the better, indicating that the material is denser.

[0076] Static bending strength: The test is conducted in accordance with GB / T9341-2008 "Determination of bending properties of plastics". The rectangular specimen is placed on the testing machine with two-point support. Then, the indenter is used to apply a load downward at a constant rate in the middle of the specimen until the specimen breaks. The static bending strength is calculated based on the maximum load, specimen size and support span. The higher the value, the better, indicating that the sheet is more rigid and less likely to be bent.

[0077] Combustion growth rate index: The test is conducted in accordance with GB / T20284-2022 "Single Combustion Test of Building Materials or Products". The sample is placed vertically in a combustion device in a corner position, and its edge is impacted by a specified propane burner flame. The combustion exhaust gas is collected and the heat release rate (HRR) is continuously measured over time. The FIGRA index (the maximum value of the heat release rate to time quotient) is calculated. The smaller the value, the better, indicating that the flame spread and heat release are slower and the fire hazard is lower.

[0078] Oxygen Index: The test is conducted in accordance with GB / T2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test". The sample is vertically fixed in a transparent combustion tube filled with a mixture of oxygen and nitrogen. It is ignited from the top with an igniter. The lowest oxygen concentration that can just support the material to continue burning for a certain period of time is found by the "small amount rise and fall method". The higher the value, the better, indicating that the material is more difficult to burn in air. Generally, an oxygen index greater than 28% is considered to have flame retardancy.

[0079] The results are shown in Table 1:

[0080] Table 1 Performance Test Results of Lead-Free Radiation-Proof PVC Composite Sheets

[0081]

[0082] As can be seen from Table 1, the lead-free radiation-proof PVC composite boards prepared in Examples 1-5 are significantly superior to those in Comparative Examples 1-4. First, bismuth oxide sheets are grown in situ on boron nitride nanosheets as a substrate to construct a highly efficient and stable radiation-proof and heat-insulating network. Then, the composite powder is surface-modified by a silane coupling agent to optimize the interfacial bonding force. Finally, magnesium-silver co-doped hydroxyapatite is added to the outer layer. By utilizing the atomic-level dispersion and synergistic effect of silver ions, the material is endowed with antibacterial function, thus achieving lead-free radiation-proof PVC composite boards with excellent radiation protection performance, long-lasting antibacterial properties, and good flame-retardant and heat-insulating characteristics.

[0083] The significant deterioration in radiation shielding efficiency and oxygen index in Comparative Example 1 is likely due to the lack of boron nitride nanosheets. Without boron nitride as a substrate, bismuth oxide particles severely agglomerate during synthesis, failing to form a dense and continuous shielding network, resulting in a significant decrease in radiation shielding efficiency. At the same time, the lack of boron nitride nanosheets and their synergistic effect on the dense and stable char layer during combustion deteriorates the flame retardancy of the material and reduces the oxygen index. Furthermore, boron nitride nanosheets have the effect of inhibiting heat conduction, and their absence leads to a significant reduction in phonon scattering effect.

[0084] In Comparative Example 2, the radiation shielding efficiency, oxygen index, and combustion growth rate deteriorated. This may be because the boron nitride nanosheets and bismuth oxide were not prepared into a composite structure. The simple physical mixing led to the filler agglomerating and unevenly dispersing within the PVC matrix, resulting in defects in the radiation shielding network, reduced X-ray absorption efficiency, and consequently, a decrease in radiation shielding efficiency. Simultaneously, poor interfacial bonding weakened the synergistic flame-retardant effect between the filler and the matrix during combustion, failing to form an effective barrier layer, thus lowering the oxygen index and accelerating the combustion growth rate. Furthermore, the agglomeration of the filler and weakened interfacial bonding also affected the material's density, leading to a decrease in internal bond strength and static bending strength.

[0085] The significant deterioration in internal bond strength and static bending strength in Comparative Example 3 may be due to the lack of surface modification with silane coupling agent. The unmodified flake bismuth oxide / boron nitride composite powder has a serious interfacial incompatibility problem with the organic PVC matrix, resulting in uneven dispersion and agglomeration of the filler in the matrix. This greatly weakens the interfacial bonding force between the filler and the resin. When the material is subjected to external force, these fragile interfaces become stress concentration points, which cannot effectively transfer and disperse stress, resulting in a sharp decrease in interlayer bonding rate and overall bending strength.

[0086] The antibacterial rate and combustion growth rate in Comparative Example 4 showed significant deterioration, possibly because ordinary hydroxyapatite was used instead of magnesium-silver co-doped hydroxyapatite. This resulted in the material losing both the inherent antibacterial properties of silver ions and the synergistic flame-retardant effect of magnesium ions. The absence of silver ion doping caused the material to lose its core ability to destroy bacterial cell structure. The increase in the combustion growth rate was due to the decreased thermal stability of hydroxyapatite after the absence of magnesium ions, which prevented it from effectively synergizing with magnesium hydroxide to form a dense char layer, ultimately leading to a reduction in flame-retardant performance.

[0087] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a lead-free radiation-shielding PVC composite board, characterized in that, Includes the following steps: Step 1: Plate-like bismuth oxide is grown in situ on boron nitride nanosheets using a hydrothermal method, and then modified with a silane coupling agent to obtain a lead-free radiation shielding filler. Step 2: Using hydroxyapatite as a carrier, magnesium-silver co-doped hydroxyapatite powder is synthesized by wet chemical method; Step 3: Use lead-free radiation shielding filler as the inner functional filler, and magnesium-silver co-doped hydroxyapatite powder and magnesium hydroxide as the outer functional filler. Mix them with PVC resin, plasticizer and stabilizer respectively. After melt blending, the mixture is obtained by three-layer co-extrusion and hot pressing. The specific preparation steps for the lead-free radiation shielding filler are as follows: Add the flake-shaped bismuth oxide / boron nitride composite powder to toluene, stir for 20-30 min, slowly add silane coupling agent, reflux and condense at 100℃ for 24 h under nitrogen protection, cool naturally to room temperature, filter, collect the product, wash with toluene, ethanol and deionized water 3-5 times each, vacuum dry to constant weight, grind, and pass through a 200-mesh sieve to obtain lead-free radiation shielding filler; The specific preparation steps for the flake-shaped bismuth oxide / boron nitride composite powder are as follows: Boron nitride nanosheets were added to ethanol and sonicated for 30-40 min to obtain a boron nitride nanosheet dispersion. Bismuth salt was added to a dilute nitric acid solution prepared from nitric acid and deionized water and stirred continuously at 80-90℃. Then, the boron nitride nanosheet dispersion was added and stirred for 30-40 min. Then, 10wt% ammonia water was slowly added dropwise to adjust the pH of the solution to 10. The solution was transferred to a hydrothermal reactor and kept at 180-190℃ for 10-12 h. After cooling, the product was filtered and washed alternately with deionized water and ethanol 3-5 times. It was then vacuum dried to constant weight and transferred to a high-temperature tube furnace. The temperature was increased to 400-500℃ at a rate of 5℃ / min and calcined for 3-5 h. After cooling, the product was ground and passed through a 200-mesh sieve to obtain a flaky bismuth oxide / boron nitride composite powder.

2. The method for preparing a lead-free radiation-shielding PVC composite board according to claim 1, characterized in that, The ratio of the flake-shaped bismuth oxide / boron nitride composite powder, toluene, and silane coupling agent is 15-20g: 300-400mL: 16.5-18.5mL; The silane coupling agent is either silane coupling agent KH550 or silane coupling agent KH560.

3. The method for preparing a lead-free radiation-shielding PVC composite board according to claim 1, characterized in that, The ratio of boron nitride nanosheets to ethanol is 4-6g:80-100mL; The ratio of the amount of bismuth salt, nitric acid, deionized water and boron nitride nanosheet dispersion is 48.8-52.2g: 100-120mL: 300-330mL: 52-56mL; The bismuth salt is either bismuth nitrate pentahydrate or bismuth chloride.

4. The method for preparing a lead-free radiation-shielding PVC composite board according to claim 1, characterized in that, The specific preparation steps for the magnesium-silver co-doped hydroxyapatite powder are as follows: Add calcium nitrate tetrahydrate, magnesium nitrate, and silver nitrate to deionized water and stir until completely clear to obtain a mixed cation solution; add diammonium hydrogen phosphate to deionized water and stir for 20-30 minutes, then slowly add 10wt% ammonia water until the pH of the solution is 10 to obtain a phosphorus source solution. The phosphorus source solution was heated to 90-95℃, and the mixed cation solution was slowly added at 600-700 rpm. During the reaction, 10wt% ammonia water was continuously added dropwise to keep the pH of the solution at around 10. The dropping rate was controlled to make the whole process last for 2-3 hours. Then, stirring was stopped and the mixture was allowed to stand for 24 hours. The mixture was filtered, and the product was repeatedly washed with a large amount of deionized water, vacuum dried to constant weight, ground, and passed through a 200-mesh sieve to obtain magnesium-silver co-doped hydroxyapatite powder.

5. The method for preparing a lead-free radiation-shielding PVC composite board according to claim 4, characterized in that, The ratio of the amount of calcium nitrate tetrahydrate, magnesium nitrate, silver nitrate and deionized water is 46.1-48.2g: 1-1.5g: 0.2-0.5g: 100-120mL; The ratio of diammonium hydrogen phosphate to deionized water is 13.2-14.6g: 200-300mL; The volume ratio of the phosphorus source solution to the mixed cation solution is 10-15:5-6.

6. The method for preparing a lead-free radiation-shielding PVC composite board according to claim 1, characterized in that, The specific preparation steps for the lead-free radiation-proof PVC composite board are as follows: PVC resin, plasticizer, calcium-zinc stabilizer, magnesium-silver co-doped hydroxyapatite powder and magnesium hydroxide are mixed and stirred evenly to obtain the outer layer formulation powder; PVC resin, plasticizer, calcium-zinc stabilizer and lead-free radiation shielding filler are mixed and stirred evenly to obtain the inner layer formulation powder. The outer layer formulation powder and the inner layer formulation powder are mixed separately and stirred at 120-130℃ and 1000-1200rpm for 5-8 minutes, then stirred at 70-80℃ and 700-800rpm for 5-8 minutes, then stirred at 40-50℃ and 500-600rpm for 3-5 minutes, and then cooled to 30-35℃ to obtain the outer and inner layer mixture. The mixture is then transferred to a screw extruder and subjected to a three-layer co-extrusion composite and hot-press molding process to obtain lead-free radiation-proof PVC composite board. The three-layer co-extrusion composite and hot-pressing process specifically includes the following steps: The plastic molten material of the outer layer, inner layer, and outer layer is simultaneously supplied through a three-layer co-extrusion die head and extruded at 160-170℃ to form a three-layer composite sheet. The sheet is then placed in a flat vulcanizing machine and held at 150-160℃ and 10-12MPa for 10-15 minutes before cooling and depressurization.

7. The method for preparing a lead-free radiation-shielding PVC composite board according to claim 6, characterized in that, The mass ratio of the PVC resin, plasticizer, calcium-zinc stabilizer, magnesium-silver co-doped hydroxyapatite powder and magnesium hydroxide is 100-120:45-50:4-6:10-12:15-18. The mass ratio of the PVC resin, plasticizer, calcium-zinc stabilizer, and lead-free radiation-shielding filler is 100-120:40-50:4-6:15-20.

8. A lead-free radiation-proof PVC composite board, prepared according to any one of claims 1-7.

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