Preparation method of silica-coated calcium carbonate core-shell structure nanocomposite and application thereof in natural latex gloves

Abstract

This invention relates to the fields of inorganic nanocomposite material preparation technology and natural latex glove production technology, specifically to a method for preparing a core-shell structured nanocomposite material with densely coated calcium carbonate (MgCO3) and its high-filling application in natural latex gloves. The invention involves adding an aqueous sodium silicate solution to a MgCO3 nanoparticle slurry, followed by the addition of a polyol and mixing. Then, carbon dioxide gas is introduced under ultrasonic conditions until the pH of the system reaches 8-10. Finally, the mixture is ultrasonically treated at 40-80 °C, thereby preparing the MgCO3 core-shell structured nanomaterial. This invention uses this MgCO3 core-shell structured nanomaterial as a filler in natural latex gloves, solving problems such as low addition amounts of MgCO3 in natural latex gloves, easy agglomeration leading to localized defects causing performance degradation, and poor process stability.

Description

Technical Field

[0001] This invention relates to the fields of inorganic nanocomposite material preparation technology and natural latex glove production technology, specifically to a method for preparing a core-shell structured nanocomposite material with silica densely coated calcium carbonate and its high-filling application in natural latex gloves. Background Technology

[0002] Natural latex gloves are widely used in medical examinations, surgery, industrial protection, and daily life due to their excellent elasticity, fit, biocompatibility, and good barrier properties. Adding inorganic fillers to natural latex is a common industry practice to reduce production costs, improve processing performance, and impart necessary mechanical strength to the products.

[0003] Calcium carbonate (CaCO3) is the most commonly used additive filler due to its low price and wide availability. With the development of nanotechnology, nano-calcium carbonate (particle size <100 nm) has become a research hotspot due to its unique size effect and surface effect, which theoretically have both reinforcing and toughening effects. However, nano-calcium carbonate faces three major problems in practical applications: (1) Nano-calcium carbonate has a large specific surface area and high surface energy, and it is very easy to aggregate to form secondary agglomerates, losing its nanoscale advantages. When added to natural latex, the agglomerated nano-calcium carbonate forms stress concentration points, which not only cannot play a reinforcing role, but also become the source of material damage. (2) Nano-calcium carbonate has a hydrophilic surface, while natural latex is oily after cross-linking reaction. The polarity difference between the two is significant, resulting in weak interfacial bonding. (3) The calcium ions on the surface of nano-calcium carbonate have two positive charges. When added to natural latex, it will compress the electric double layer and reduce the Zeta potential, which will disrupt the electrostatic stability of latex particles. In addition, calcium ions have high chemical activity and can interact with components such as proteins and fatty acids in latex, causing a decrease in latex stability and flocculation.

[0004] Existing surface modification techniques often employ organic acids (such as stearic acid) to coat nano-calcium carbonate. While this can partially reduce surface energy, the extremely strong hydrophobicity after modification prevents it from dispersing in natural latex emulsion systems. Furthermore, it is difficult to effectively shield against the effects of calcium ion dissolution. In addition, studies have shown that stearic acid coatings are not stable enough in the natural latex environment (pH 9-11) and are prone to hydrolysis and desorption, causing the calcium carbonate surface to become hydrophilic again and aggregate, thereby weakening the interfacial bonding between the filler and the latex matrix. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a core-shell structured nanomaterial of silica-coated calcium carbonate in order to address the shortcomings of the prior art. This method solves the problems of low addition amount of nano-calcium carbonate in natural latex gloves, easy agglomeration leading to local defects and poor performance and process stability.

[0006] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: A method for preparing a core-shell structured nanomaterial with silica-coated calcium carbonate includes the following steps: (1) Add sodium silicate aqueous solution dropwise to nano calcium carbonate slurry while stirring; after the sodium silicate aqueous solution is added, add polyol and stir thoroughly to mix evenly; (2) In the ultrasonic state, carbon dioxide gas is introduced into the mixed solution obtained in step (1) until the pH value of the system reaches 8~10, and then the introduction of carbon dioxide gas is stopped. (3) The system obtained in step (2) is subjected to ultrasonic treatment at 40~80 ℃ for 0.5~1.5 h. At this time, a slurry of core-shell structured nanomaterials of calcium carbonate coated with silica is obtained. The solid product is separated and washed with ethanol and water to obtain core-shell structured nanomaterials of calcium carbonate coated with silica.

[0007] According to the above scheme, in step (1), the mass ratio of silicon dioxide to nano-calcium carbonate is 1:30~1:10. The amount of sodium silicate precursor of silicon dioxide is calculated based on the amount of nano-calcium carbonate used. The amount of polyol added is 1%~10% of the mass of sodium silicate.

[0008] According to the above scheme, in step (1), the solid content of the nano-calcium carbonate slurry is 5%~15%, and the concentration of the sodium silicate aqueous solution is 0.05~0.2 mol / L.

[0009] According to the above scheme, in step (1), the polyol is one or more of mannitol, sorbitol, ethylene glycol, glycerol, erythritol, xylitol or inositol.

[0010] According to the above scheme, in step (2), the ultrasonic conditions are: ultrasonic power 70~90 W, ultrasonic frequency 14~18kHz; carbon dioxide gas ventilation rate is 80~120 mL / min. According to the above scheme, in step (3), the ultrasonic conditions are: ultrasonic power 70~90 W, ultrasonic frequency 14~18 kHz.

[0011] The silica-coated calcium carbonate core-shell nanomaterial prepared by the above method has a silica shell and a calcium carbonate core, with the silica shell continuously, uniformly, and densely coating the surface of the calcium carbonate core. The primary particle size of the calcium carbonate core is 80–150 nm, and the thickness of the silica shell is 8–10 nm. The silica shell forms chemical bonds with calcium ions on the surface of the calcium carbonate core, passivating the surface of the calcium carbonate particles and preventing the dissolution of calcium ions. This ensures that the aqueous dispersion of the silica-coated calcium carbonate core-shell nanomaterial has ultra-low calcium ion activity. Furthermore, the calcium ion activity of the silica-coated calcium carbonate core-shell nanomaterial, measured by the calcium ion concentration in the supernatant of its aqueous dispersion (with a solid content of 12–15%), is less than 0.05 mmol / L.

[0012] The silica-coated calcium carbonate core-shell nanomaterials prepared by the above method were added to a phthalate buffer solution with a pH of 5-6. It exhibits good acid resistance with a pH less than 0.5. The concentration of the silica-coated calcium carbonate core-shell nanomaterial is 0.1–0.3 g / mL; the phthalate buffer solution is prepared with potassium hydrogen phthalate and sodium hydroxide.

[0013] Based on the above, the present invention also provides a natural latex glove filled with the silica-coated calcium carbonate core-shell structured nanomaterial of the present invention, wherein the raw materials include, by mass parts: 100 parts of natural latex, 10-40 parts of the silica-coated calcium carbonate core-shell structured nanomaterial of the present invention, 0.1-1.5 parts of defoamer, and 3-5 parts of mixing additives.

[0014] Furthermore, the natural latex has a dry rubber mass percentage of 55% to 65% and an ammonia content of 0.3% to 0.5%.

[0015] The preparation method of the natural latex gloves filled with the silica-coated calcium carbonate core-shell structured nanomaterial described in this invention includes the following steps: 1) Add the mixed additives to the natural latex and stir at 40~45 ℃ for 3.5~4 h to obtain pre-vulcanized natural latex; 2) The silica-coated calcium carbonate core-shell structured nanomaterial (CaCO3@SiO2 nanocomposite material) and defoamer described in this invention are added to the pre-vulcanized natural latex obtained in step 1). After stirring evenly, the mixture is ultrasonically treated for 20 to 40 minutes under ultrasonic power of 180~220W and frequency of 30~50 kHz to obtain a uniformly mixed material. 3) After cleaning the glove mold, preheat it to 60~70 ℃, immerse it in the coagulant, control the immersion time to 6~8 s, after immersion, remove the glove mold, shake off the excess coagulant, and then put it into a 70~80 ℃ oven for drying time of 3~5 min. 4) Immerse the glove mold obtained in step 3) into the mixture obtained in step 2) for 5-10 seconds. Remove the glove mold and let the excess mixture drip off. Then put it into an oven at 70-80 ℃ and dry it for 3-5 minutes. 5) Immerse the glove mold obtained in step 4) in warm water at 50~60 ℃ for 15~20 s. Remove the glove mold, shake off excess water, roll the edges and put it into an oven at 70~80 ℃ for 3~5 min. 6) Immerse the glove mold obtained in step 5) in a 2%-10% polyurethane solution (i.e., coating solution) for 2-3 seconds. Remove the glove mold, discard the excess coating solution, and then place it in an oven at 110-120 ℃ for vulcanization treatment for 10-20 minutes. After vulcanization, demold to obtain a natural latex glove with high filling of CaCO3@SiO2 nanocomposite material.

[0016] In the preparation of silica-coated calcium carbonate core-shell nanomaterials, this invention involves the hydrolysis of sodium silicate to form silicic acid. A polyol containing adjacent hydroxyl groups is added, which can undergo an esterification reaction with the silicic acid formed by the hydrolysis of sodium silicate under weakly acidic conditions, forming a soluble chelate complex. This significantly reduces the concentration of free silicic acid and inhibits the homogeneous nucleation of silicic acid to form free silica precipitate. Furthermore, carbon dioxide carbonization is used to control the pH of the system, allowing silica to undergo heterogeneous nucleation on the surface of the nano-calcium carbonate, thus forming a dense nano-silica shell. This preparation process combines sonochemical technology with carbon dioxide carbonization precipitation, achieving efficient and uniform silica coating on the surface of nano-calcium carbonate in a short time, reducing the preparation time from several hours to tens of minutes. In addition, the ultrasonic cavitation effect of sonochemical technology is utilized; the collapse of cavitation bubbles instantly generates localized high temperature, high pressure, and strong microjets to disperse particle agglomerates in real time, further promoting the uniform diffusion of the reactant sodium silicate onto the surface of the nano-calcium carbonate particles, thereby forming a silica shell. The present invention controls the average particle size of the silica-coated calcium carbonate core-shell structured nanomaterial to be 90~160 nm and in a highly dispersed state. This morphology enables it to exert excellent reinforcing effect as a natural latex glove filler.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention relates to a method for preparing silica-coated calcium carbonate core-shell structured nanomaterials. By adding polyols to reduce the free silicic acid concentration, homogeneous nucleation is effectively suppressed. Furthermore, carbon dioxide carbonization is used to control the pH of the system, promoting heterogeneous nucleation of silica nanoparticles. The ultrasonic cavitation effect of sonochemical technology is then utilized to further promote the uniform diffusion of reactants onto the surface of the calcium carbonate nanoparticles. Simultaneously, the microjets generated by cavitation can disperse particle agglomerates in real time. Therefore, this invention combines sonochemical technology with carbon dioxide carbonization precipitation to achieve efficient and uniform silica coating on the surface of calcium carbonate nanoparticles in a short time, resulting in a dispersed silica-coated calcium carbonate core-shell structured nanocomposite material, significantly improving production efficiency.

[0018] 2. The silica-densely coated calcium carbonate core-shell nanomaterial prepared by this invention has a complete and dense silica shell, which not only effectively inhibits the aggregation of calcium carbonate nanoparticles but also passivates surface calcium ions through a dual effect of chemical bonding and physical shielding. This significantly blocks direct contact between the core calcium carbonate nanoparticles and the external medium, reducing the overall calcium ion activity of the material to an extremely low level. This characteristic gives it a significant advantage in applications sensitive to free calcium ions, especially since it does not cause flocculation when added to natural latex, thus ensuring the stable operation of the production process.

[0019] 3. The silica-densely coated calcium carbonate core-shell nanomaterial prepared by this invention has a silica surface rich in silanol groups, which can form strong bonds with latex molecular chains, significantly improving the mechanical properties of natural latex gloves. Therefore, this invention effectively overcomes the shortcomings of existing technologies, such as limited inorganic filler addition, insufficient reinforcement, and poor process stability, providing a new approach to balancing the cost and performance of natural latex gloves. Attached Figure Description

[0020] Figure 1 This is a process flow diagram for preparing the silica-densely coated calcium carbonate core-shell nanocomposite material of the present invention.

[0021] Figure 2 The images are transmission electron microscope (TEM) images of the silica-densely coated calcium carbonate core-shell nanocomposite material prepared in Example 1, where (a) is a low-magnification image and (b) is a high-magnification image.

[0022] Figure 3 The images show a comparison of scanning electron microscopy (SEM) images of the silica-dense calcium carbonate core-shell nanocomposite material prepared in Example 1 and the uncoated calcium carbonate nanocomposite material, where (a) is the uncoated calcium carbonate nanocomposite material and (b) is the silica-dense calcium carbonate core-shell nanocomposite material.

[0023] Figure 4The image shows a comparison of the Fourier Transform Infrared (FT-IR) spectra of the silica-densely coated calcium carbonate core-shell nanocomposite material prepared in Example 1 with those of uncoated nano-calcium carbonate and silica.

[0024] Figure 5 The image shows the X-ray photoelectron spectroscopy (XPS) of the silica-densely coated calcium carbonate core-shell nanocomposite material prepared in Example 1, where (a) is the full spectrum and (b) is the Si 2p fine spectrum.

[0025] Figure 6 SEM images of the silica-densely coated calcium carbonate core-shell nanocomposites prepared in Examples 2-4, where (a) is Example 2, (b) is Example 3, and (c) is Example 4.

[0026] Figure 7 SEM images of CaCO3@SiO2 nanocomposites prepared in Comparative Examples 1-5, where (a) is Comparative Example 1, (b) is Comparative Example 2, (c) is Comparative Example 3, (d) is Comparative Example 4, and (e) is Comparative Example 5.

[0027] Figure 8 The tensile cross-section scanning electron microscope image of the CaCO3@SiO2 nanocomposite high-filled natural latex glove prepared in Example 1.

[0028] Figure 9 Photograph of the CaCO3@SiO2 nanocomposite high-filled natural latex gloves prepared in Example 1. Detailed Implementation

[0029] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the present invention is not limited to the following embodiments.

[0030] In the following examples, the polyols and sodium silicate were commercially available analytical grade reagents.

[0031] In the following examples, the nano-calcium carbonate slurry was purchased from Guangxi Huibin Calcium Industry Technology Co., Ltd., model: HB20, and the solid content of the slurry was 15%.

[0032] In the following examples, carbon dioxide is an industrial gas with a purity of 99.9%.

[0033] In the following examples, the natural latex was purchased from TAVORN RUBBERINDUSTRY (1982) CO., LTD, with a dry rubber content of 55% to 65% and an ammonia content of 0.3% to 0.5%.

[0034] In the following examples, the defoamer is an organosilicone defoamer, purchased from Shanghai Sangjing Chemical Co., Ltd., model DF-963.

[0035] In this invention, the mixed additive comprises the following components by mass: 100 parts solvent water, 20-40 parts sulfur, 15-25 parts zinc oxide, 5-15 parts accelerator, 0.5-1.5 parts antioxidant, and 3-5 parts dispersant. The components are dispersed using a high-speed disperser and then ground in a high-speed ball mill or roller mill for 5-6 hours to obtain the mixed additive. Sulfur is a vulcanizing agent, and zinc oxide is a vulcanizing activator; the accelerator is one or more of accelerator M, accelerator D, or accelerator PX; and the antioxidant is one or more of antioxidant 4020, antioxidant 264, or antioxidant 2246.

[0036] Specifically, in the following embodiments, the mixed additives, by weight, consist of 30 parts sulfur, 20 parts zinc oxide, 10 parts accelerator D, 1 part antioxidant 4020, 4 parts dispersant NNO, and 100 parts deionized water. The aforementioned additives were dispersed using a high-speed disperser and then ground in a high-speed ball mill or roller mill for 4 hours. The sulfur was purchased from Linyi Houpu Chemical Co., Ltd., and its product name was rubber sulfur powder; the zinc oxide was purchased from Weifang Aolong Zinc Industry Co., Ltd., and its product name was zinc oxide for rubber and plastics; accelerator D was diphenylguanidine, CAS number 102-06-7; antioxidant 4020 was N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, CAS number 793-24-8; and dispersant NNO was sodium methylene bis(naphthalene)sulfonate, CAS number 36290-04-7.

[0037] Example 1 A method for preparing a silica-densely coated calcium carbonate core-shell nanocomposite material, the specific steps of which are as follows: S1. Take a nano-calcium carbonate slurry with a solid content of 8%, and slowly add a 0.1 mol / L sodium silicate aqueous solution to it under stirring. After the sodium silicate aqueous solution is added, add glycerol and stir to ensure the mixture is fully mixed. Calculate the theoretical amount of sodium silicate precursor required to generate silica, based on a silica to nano-calcium carbonate mass ratio of 1:20. Then prepare a 0.1 mol / L sodium silicate aqueous solution for addition, with glycerol at 5% of the sodium silicate mass.

[0038] S2. Place the mixed solution obtained in step S1 in an ultrasonic environment, and introduce carbon dioxide gas into the system under ultrasonic conditions until the pH value of the system reaches pH=9, then stop the gas introduction; wherein, the ultrasonic power is 80 W and the ultrasonic frequency is 16 kHz.

[0039] S3. The mixed solution obtained in step S2 is subjected to ultrasonic treatment at 60°C for 1 h, with an ultrasonic power of 80 W and an ultrasonic frequency of 16 kHz.

[0040] S4. Filter the product obtained in step S3, wash it multiple times with anhydrous ethanol and high-purity water to remove residual sodium ions and by-products, and obtain a silica-densely coated calcium carbonate core-shell structure nanocomposite slurry with a solid content of 20%~25%, namely CaCO3@SiO2 nanocomposite material.

[0041] Figure 2 The image shows a transmission electron microscope (TEM) image of the CaCO3@SiO2 nanocomposite material prepared in this embodiment. It can be clearly observed from the image that a uniform shell is formed on the surface of the nano-calcium carbonate. The primary particle size of the nano-calcium carbonate core is 80~150 nm, and the thickness of the shell is 8~10 nm, showing a distinct core-shell structure.

[0042] Figure 3 Scanning electron microscope (SEM) images of the CaCO3@SiO2 nanocomposite material and uncoated nano-calcium carbonate prepared for this embodiment are shown. The images show that the CaCO3@SiO2 nanocomposite material has a clear particle interface and good dispersion.

[0043] Figure 4 The Fourier Transform Infrared (FT-IR) spectra of the CaCO3@SiO2 nanocomposite and the uncoated nano-calcium carbonate and silica were prepared for this embodiment. The results show that the CaCO3@SiO2 nanocomposite exhibits high performance at 1100 cm⁻¹. -1 Characteristic absorption peaks of Si-O-Si appear nearby. Figure 5 The X-ray photoelectron spectroscopy (XPS) spectrum of the CaCO3@SiO2 nanocomposite material prepared in this embodiment shows that, compared with the uncoated calcium carbonate nanocomposite material, the CaCO3@SiO2 nanocomposite material exhibits Si 2p and Si 2s peaks. Fine-sampling analysis of the Si 2p peak reveals that the single peak at 103.4 eV corresponds to the Si-O bond in SiO2. The combined FT-IR and XPS results confirm that silica was successfully coated on the surface of the calcium carbonate nanocomposite material.

[0044] The CaCO3@SiO2 nanocomposite material prepared in this example was dispersed in high-purity water to form a slurry with a solid content of 15%. The supernatant was collected by centrifugation, and the calcium ion concentration was measured to be 0.042 mmol / L. Meanwhile, the uncoated nano-calcium carbonate slurry with a solid content of 15% was centrifuged, and the supernatant was measured to have a calcium ion concentration of 0.598 mmol / L. This indicates that the calcium ion activity of nano-calcium carbonate was significantly reduced after being coated with a SiO2 shell.

[0045] Acid resistance test: A 500 mL buffer solution with a pH of approximately 5.5 was prepared using 125 mL of 0.1 mol / L potassium hydrogen phthalate and 97 mL of 0.1 mol / L sodium hydroxide. 0.2 g of the CaCO3@SiO2 nanocomposite material and uncoated calcium carbonate nanoparticles prepared in this example were dispersed in 100 mL of the above buffer solution. The pH of the uncoated calcium carbonate nanoparticle system increased rapidly, and at 120 min, relative to the initial time (0 min), the pH increased significantly. The pH can reach 0.9; however, the pH increase of the CaCO3@SiO2 nanocomposite system is significantly reduced, reaching 0.9 after 120 min. With a pH of 0.2, it exhibits good acid resistance. This also indicates that silica has a good coating effect on nano-calcium carbonate.

[0046] Example 2 This embodiment provides a method for preparing a silica-densely coated calcium carbonate core-shell structured nanocomposite material, which differs from Embodiment 1 in that: in step S1, the solid content of the nano-calcium carbonate is 5%, the concentration of the sodium silicate aqueous solution is 0.05 mol / L, the polyol used is mannitol, and the amount of mannitol added is 1% of the mass of sodium silicate (based on the effective dry basis of sodium silicate); in step S2, the gas is stopped when the system is carbonized to a pH of 10; in step S3, the ultrasonic treatment temperature is 40 ℃ and the treatment time is 1.5 h.

[0047] Example 3 This embodiment provides a method for preparing a silica-densely coated calcium carbonate core-shell structured nanocomposite material, which differs from Embodiment 1 in that: in step S1, the solid content of the nano-calcium carbonate is 15%, the concentration of the sodium silicate aqueous solution is 0.2 mol / L, the added polyol is xylitol, and the amount of xylitol added is 10% of the dry basis of sodium silicate; in step S2, the gas is stopped when the system is carbonized to a pH of 8; in step S3, the ultrasonic treatment temperature is 80 ℃ and the treatment time is 0.5 h.

[0048] Example 4 This embodiment provides a method for preparing a silica-densely coated calcium carbonate core-shell structured nanocomposite material, which differs from Embodiment 1 in that: in step S1, the solid content of the nano-calcium carbonate is 10%, the concentration of the sodium silicate aqueous solution is 0.15 mol / L, the added polyol is ethylene glycol, and the amount of ethylene glycol added is 8% of the dry basis of sodium silicate; in step S3, the ultrasonic treatment temperature is 50 ℃, and the treatment time is 1.2 h.

[0049] Figure 6 The images show SEM images of the CaCO3@SiO2 nanocomposites prepared in Examples 2-4. The images show clear particle interfaces of the CaCO3@SiO2 nanocomposites, distinct from the uncoated nano-calcium carbonate (SiO2). Figure 3 (a) Good dispersibility. The CaCO3@SiO2 nanocomposites prepared in Examples 2-4 were dispersed in high-purity water to obtain a slurry with a solid content of 15%. The supernatant was centrifuged and its calcium ion activity was tested. The calcium ion concentration of the sample obtained in Example 2 was 0.044 mmol / L, the calcium ion concentration of the sample obtained in Example 3 was 0.045 mmol / L, and the calcium ion concentration of the sample obtained in Example 4 was 0.044 mmol / L. The calcium ion activity of all samples was very low.

[0050] The CaCO3@SiO2 nanocomposites prepared in Examples 2-4 were weighed and subjected to acid resistance tests, following the procedures outlined in Example 1. Specifically, the CaCO3@SiO2 nanocomposite of Example 2 showed a stable pH value after 100 min in a buffer solution. pH=0.4; the CaCO3@SiO2 nanocomposites of Examples 3 and 4 showed a stable pH value in the buffer solution after 110 min. All of them have good acid resistance at pH=0.3.

[0051] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in both steps S2 and S3, mechanical stirring was used to prepare silica-coated calcium carbonate core-shell nanocomposite materials, the stirring speed was 500 rpm, and ultrasonic treatment was not performed.

[0052] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that step S3 involves ultrasonic preparation of silica-coated calcium carbonate core-shell nanocomposite material at room temperature of 25 °C.

[0053] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in step S2, CO2 gas is introduced until the pH value of the system reaches pH=11 to prepare a silica-coated calcium carbonate core-shell structured nanocomposite material.

[0054] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that in step S2, CO2 gas is introduced until the pH value of the system reaches pH=7 to prepare a silica-coated calcium carbonate core-shell structured nanocomposite material.

[0055] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that in step S1, the theoretical amount of sodium silicate precursor required to generate silica is calculated based on a mass ratio of silica to nano-calcium carbonate of 1:100 to prepare silica-coated calcium carbonate core-shell structured nanocomposite material.

[0056] Figure 7The SEM images of the CaCO3@SiO2 nanocomposites prepared for Comparative Examples 1-5 show that the free SiO2 particles in Comparative Examples 1 and 4 are significantly increased, with agglomerates appearing in some areas. The uniformity of the composite particle coating layer is reduced, and the surface roughness of the particles is increased. The microstructures of the samples obtained in Comparative Examples 2, 3, and 5 are different from those of uncoated nano-calcium carbonate (CCO3@SiO2). Figure 3 (a) There is not much difference.

[0057] The CaCO3@SiO2 nanocomposites prepared in Comparative Examples 1-5 were dispersed in high-purity water to form a slurry with a solid content of 15%. The supernatant was collected by centrifugation to test its calcium ion activity. The calcium ion concentration of the material in Comparative Example 1 was 0.325 mmol / L, that of Comparative Example 2 was 0.432 mmol / L, that of Comparative Example 3 was 0.354 mmol / L, that of Comparative Example 4 was 0.156 mmol / L, and that of Comparative Example 5 was 0.362 mmol / L.

[0058] The CaCO3@SiO2 nanocomposites prepared in Comparative Examples 1-5 were weighed and subjected to acid resistance tests, following the procedures outlined in Example 1. In Comparative Example 1, the pH value of the solution tended to stabilize after 120 minutes of the acid resistance test. pH=0.6; in Comparative Example 2, the pH value of the solution tended to stabilize after 120 min of acid resistance testing. pH=0.7; the pH value of the solution in Comparative Example 3 tended to stabilize after 120 min of acid resistance testing. pH=0.7; in Comparative Example 4, the pH value of the solution tended to stabilize after 120 min of acid resistance testing. pH=0.6; in Comparative Example 5, the pH value of the solution tended to stabilize after 120 min of acid resistance testing. pH=0.8. In summary, the CaCO3@SiO2 nanocomposites prepared in Comparative Examples 1-5 all exhibit high calcium ion activity but poor acid resistance.

[0059] Application examples The CaCO3@SiO2 nanocomposite material prepared in the above embodiments was added to natural latex to prepare high-filler natural latex gloves. The specific process for preparing the CaCO3@SiO2 nanocomposite material high-filler natural latex gloves is as follows: P1. By weight, add 4.5 parts of mixed additives to 100 parts of natural latex and stir at 40~45 ℃ for 3.5~4 h to obtain pre-vulcanized natural latex.

[0060] P2. Add 10-40 parts of CaCO3@SiO2 nanocomposite material and 0.12 parts of defoamer to the mixture obtained in step 1, stir evenly, and sonicate for 0.5 h (ultrasonic power 200 W, frequency 40 kHz) to obtain a uniformly mixed material.

[0061] P3. After cleaning the glove mold, preheat it to 60~70 ℃, immerse it in coagulant (10% calcium chloride solution), control the immersion time to 6~8 s, after immersion, remove the glove mold, shake off the excess coagulant, and then send it into a 70~80 ℃ oven for drying time of 3~5 min.

[0062] P4. Immerse the glove mold from step 3 into the mixture obtained in step 2, controlling the immersion time to be 5-10 seconds. Remove the glove mold and allow the excess emulsion to drip off. Then, place it in an oven at 70-80°C and dry it for 3-5 minutes. P5. Immerse the glove mold treated in step 4 in warm water at 50~60 ℃ for 15~20 s. Remove the glove mold, shake off the water, roll the edges, and put it into an oven at 70~80 ℃ for 3~5 min.

[0063] P6. Immerse the glove mold film treated in step 5 into the coating solution, control the immersion time to be 2~3 s, remove the glove mold, shake off the excess coating solution, and then send it into the oven and set the oven temperature to 110~120 ℃. When the oven temperature reaches the set temperature, control the vulcanization time to be 10~20 min.

[0064] P7. After vulcanization, the product is demolded to obtain natural latex gloves with high filling amount of CaCO3@SiO2 nanocomposite material.

[0065] Multiple experiments were conducted by adjusting the amount of CaCO3@SiO2 nanocomposite material added in step P2 above. (1) The CaCO3@SiO2 nanocomposite material prepared in Example 1 was added at a rate of 40 phr (phr represents the amount of CaCO3@SiO2 nanocomposite material added per 100 parts of natural latex, specifically, 40 phr represents 40g of CaCO3@SiO2 nanocomposite material added per 100g of natural latex); (2) The CaCO3@SiO2 nanocomposite material prepared in Example 2 was added at a rate of 10 phr; (3) The CaCO3@SiO2 nanocomposite material prepared in Example 3 was added at a rate of 22 phr; (4) The CaCO3@SiO2 nanocomposite material prepared in Example 4 was added at a rate of 30 phr. Meanwhile, a control was established by replacing the CaCO3@SiO2 nanocomposite material in step P2 with commercially available water-milled light calcium carbonate or uncoated nano calcium carbonate, with an addition amount of 22 phr.

[0066] like Figure 8 As shown, the tensile cross-sectional micrograph of the natural latex glove obtained by adding the CaCO3@SiO2 nanocomposite material prepared in Example 1 shows that the CaCO3@SiO2 nanocomposite material is uniformly dispersed at the nanoscale in the latex matrix; as shown in the micrograph. Figure 9 As shown in the macroscopic photograph, the gloves have a uniform color, with no obvious spots, holes, or bubbles.

[0067] Performance tests were conducted on the natural latex gloves prepared from CaCO3@SiO2 nanocomposites in each embodiment. Ten gloves were taken from each group. The natural latex gloves were type M, weighing approximately 7g each. The performance of the natural latex gloves was tested according to the requirements of Chinese standard GB 10213, as shown in Table 1. For those without coated nano-calcium carbonate, glove samples could not be prepared due to latex flocculation; therefore, no performance evaluation was conducted on these samples.

[0068] Table 1

[0069] Note: The filler refers to the silica-densely coated calcium carbonate core-shell nanocomposite material prepared in the examples, or commercially available water-milled light calcium carbonate added in proportion.

[0070] As shown in Table 1, the tensile strength of the natural latex gloves prepared in the embodiments of the present invention before aging was 14.1~15.4 N, and the elongation at break was 721%~910%; after aging, the tensile strength was 13.4~14.8 N, and the elongation at break was 718%~835%. Among them, the tensile strength and elongation at break of the natural latex gloves prepared in Examples 1, 2, 3, and 4, and those prepared with commercially available water-milled light calcium carbonate, were significantly higher than the requirements of GB 10213 standard (in which, before aging: minimum tensile strength 7 N, minimum elongation at break 650%; after aging: minimum tensile strength 6 N, minimum elongation at break 500%). In contrast, the natural latex gloves made using commercially available water-milled light calcium carbonate, while maintaining a good level of tensile strength (higher than the standard requirement of 7 N), showed a significant decrease in elongation at break, indicating poor softness. This precisely explains why it is difficult to further increase the addition amount of commercially available water-milled light calcium carbonate in the production formula of natural latex gloves.

[0071] As the amount of silica-densely coated calcium carbonate core-shell nanocomposite material prepared according to this invention is further increased (see Examples 3 and 4, with addition amounts of 22 phr and 30 phr, respectively), the tensile strength and elongation at break are still far higher than the requirements of GB 10213 standard. When further increased to 40 phr (see Example 1), the elongation of the natural latex gloves decreases significantly, but still meets the requirements of GB 10213 standard, and exhibits higher mechanical properties than natural latex gloves made with commercially available water-milled light calcium carbonate with 22 phr added. Compared to latex gloves with the same mass fraction of water-milled light calcium carbonate, the gloves prepared using this invention show a 29.1% increase in tensile strength and a 16.3% increase in elongation at break. Moreover, based on achieving equivalent mechanical properties, compared to using water-milled light calcium carbonate as a filler, the cost reduction of the silica-densely coated calcium carbonate core-shell nanocomposite material prepared according to this invention reaches 15%, significantly saving production costs. Furthermore, while maintaining performance in accordance with standard requirements, the filler loading can be increased to 40 phr, achieving a low formulation cost for natural latex gloves.

[0072] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing a core-shell structure nanomaterial of silica-coated calcium carbonate, characterized in that, Includes the following steps: (1) Add sodium silicate aqueous solution dropwise to nano calcium carbonate slurry while stirring; after the sodium silicate aqueous solution has been added, add polyol and mix well; (2) In the ultrasonic state, carbon dioxide gas is introduced into the mixed solution obtained in step (1) until the pH value of the system reaches 8~10, and then the introduction of carbon dioxide gas is stopped. (3) The system obtained in step (2) is subjected to ultrasonic treatment at 40~80 °C, and then the solid product is separated, which is the core-shell structured nanomaterial of calcium carbonate coated with silica.

2. The method for preparing a core-shell structured nanomaterial of silica-coated calcium carbonate according to claim 1, characterized in that, In step (1), the mass ratio of silicon dioxide to nano-calcium carbonate is 1:30 to 1:

10. The amount of sodium silicate precursor is calculated based on the amount of nano-calcium carbonate used. The amount of polyol added is 1% to 10% of the mass of sodium silicate.

3. The method for preparing a core-shell structured nanomaterial of silica-coated calcium carbonate according to claim 1, characterized in that, In step (1), the solid content of the nano-calcium carbonate slurry is 5%~15%, and the concentration of the sodium silicate aqueous solution is 0.05~0.2 mol / L; the polyol is one or more of mannitol, sorbitol, ethylene glycol, glycerol, erythritol, xylitol or inositol.

4. The method for preparing a core-shell structured nanomaterial of silica-coated calcium carbonate according to claim 1, characterized in that, In step (2), the carbon dioxide gas ventilation rate is 80~120 mL / min; the ultrasonic conditions are: ultrasonic power 70~90 W, ultrasonic frequency 14~18 kHz.

5. The method for preparing a core-shell structured nanomaterial of silica-coated calcium carbonate according to claim 1, characterized in that, In step (3), the ultrasonic conditions are: ultrasonic power 70~90 W, ultrasonic frequency 14~18 kHz, and ultrasonic treatment time 0.5~1.5 h.

6. The silica-coated calcium carbonate core-shell nanomaterial prepared by any one of claims 1 to 5.

7. The silica-coated calcium carbonate core-shell nanomaterial according to claim 6, characterized in that, The material consists of a shell of nano-silica and a core of nano-calcium carbonate. The silica shell is continuously, uniformly and densely coated on the surface of the nano-calcium carbonate core. The primary particle size of the nano-calcium carbonate core is 80~150 nm, and the thickness of the silica shell is 8~10 nm.

8. The silica-coated calcium carbonate core-shell nanomaterial according to claim 6, characterized in that, The calcium ion activity of the silica-coated calcium carbonate core-shell nanomaterial, measured by the calcium ion concentration in the supernatant of its aqueous dispersion, is less than 0.05 mmol / L.

9. The silica-coated calcium carbonate core-shell nanomaterial according to claim 6, characterized in that, The silica-coated calcium carbonate core-shell nanomaterial was added to a phthalate buffer solution with a pH of 5-6. The pH is less than 0.5; wherein the concentration of the silica-coated calcium carbonate core-shell nanomaterial is 0.1~0.3 g / mL.

10. The application of the silica-coated calcium carbonate core-shell structured nanomaterial of claim 6 as a filler in natural latex gloves, characterized in that, The amount of the silica-coated calcium carbonate core-shell nanomaterial is in the range of 10 to 40 parts per 100 parts by weight of natural latex.

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