Composite modified calcium sulfate whisker, and preparation method and application thereof

Abstract

The application belongs to the technical field of natural rubber reinforcing agent materials, and particularly relates to a composite modified calcium sulfate whisker as well as a preparation method and application thereof. The application uses ethyl orthosilicate as a first layer modifier, and titanium acid ester coupling agent HY201 as a second layer modifier, proposes a modification direction of the calcium sulfate whisker by using a mechanism of a to-be-reinforced matrix, introduces a substance capable of reacting with rubber on the surface of the calcium sulfate whisker, and can promote a synergistic effect on the rubber system while ensuring the modification effect of the surface of the whisker, so that strong-strong combination is achieved, and a better level of efficiency is achieved. The obtained composite modified calcium sulfate whisker can partially or completely replace a traditional carbon black reinforcing agent, and provides a sustainable solution for the development of high-performance rubber composite materials.

Description

Technical Field

[0001] This invention belongs to the technical field of natural rubber reinforcing agent materials, specifically relating to a composite modified calcium sulfate whisker and its preparation method and application. Background Technology

[0002] Rubber and its composites are widely used in the automotive, aerospace, and construction industries, exhibiting excellent elasticity, wear resistance, and shock resistance. However, rubber often struggles to meet higher mechanical requirements in many high-performance applications. To improve the mechanical properties of rubber and enhance its strength, toughness, and durability, researchers typically employ reinforcing agents. Carbon black, as a traditional reinforcing agent, has significant effects on improving the mechanical properties of rubber, but its use has certain negative environmental impacts, and carbon black is relatively expensive. In recent years, scholars have increasingly focused on the development of alternative materials. Calcium sulfate whiskers (CSW), as a natural mineral material, are gradually becoming a potential reinforcing agent in rubber composites due to their excellent structural characteristics and good compatibility.

[0003] Calcium sulfate whiskers have a fibrous morphology and a high aspect ratio, exhibiting excellent reinforcing properties. Surface modification of calcium sulfate whiskers can effectively improve their bonding strength with the rubber matrix, thereby enhancing the mechanical properties of the rubber. However, the poor compatibility between calcium sulfate whiskers and rubber limits their application effectiveness.

[0004] Currently, both domestically and internationally, various surface modifiers, such as composite modifiers, coupling agents, and surfactants, are mainly used to modify the surface of calcium sulfate whiskers. While their mechanisms of action and methods differ, they all aim to improve the surface morphology of calcium sulfate whiskers, reduce the interfacial energy difference between them and the matrix, and enhance their bonding strength and compatibility. Utilizing the adsorption effect of surfactants on the surface of calcium sulfate whiskers, molecular films can be formed, altering their physicochemical properties and thus reducing the interfacial energy between the whiskers and the matrix. Commonly used surfactants include borate esters and stearates. Furthermore, coupling agents, through reaction with the surface of calcium sulfate whiskers, effectively enhance the adhesion between whiskers and materials such as resins, improving the mechanical properties, thermal stability, and chemical corrosion resistance of composite materials. Common coupling agents include silanes and titanates. Composite modifiers combine multiple modification methods, improving the compatibility and properties of calcium sulfate whiskers through organic-organic and inorganic-inorganic approaches, thereby enhancing the modification effect. Therefore, selecting appropriate organic or inorganic modifiers based on specific needs is crucial. Summary of the Invention

[0005] In view of this, the present invention addresses the problems existing in the prior art by proposing a modification direction for calcium sulfate whiskers based on the mechanism of the matrix to be reinforced. A substance that can react with rubber is introduced on the surface of the calcium sulfate whiskers to enhance the bonding force between the whiskers and the rubber interface. This provides a composite modified calcium sulfate whisker that can be used to replace carbon black as a reinforcing agent for natural rubber, as well as its preparation method and application.

[0006] To achieve the above objectives, the first objective of this invention is to provide a method for preparing composite-modified calcium sulfate whiskers, which improves compatibility with organic matrices by altering the surface polarity of the calcium sulfate whiskers. The following technical solution is adopted:

[0007] A method for preparing composite modified calcium sulfate whiskers, using tetraethyl orthosilicate as the first layer modifier and one of the following coupling agents as the second layer modifier: stearic acid, sodium stearate, titanate coupling agent HY201, aluminate coupling agent DL411, and aluminate coupling agent HYA1, to obtain composite modified calcium sulfate whiskers.

[0008] In existing CSW modification techniques, the main process involves modifiers reacting with hydroxyl groups, calcium ions, and calcium sulfate on the CSW surface to form chemical bonds and hydrogen bonds, thus coating the CSW. Surfactants, primarily used to alter the water affinity of the CSW surface, cannot interact with the matrix, resulting in insufficient bonding between the whiskers and the matrix, hindering stress transfer and transmission. Furthermore, the production cost of coupling agent-modified calcium sulfate whiskers is high, leading to a relatively high price. Composite modifiers, on the other hand, require highly targeted application, necessitating the selection of appropriate modifiers based on the characteristics of the matrix being reinforced or the specific application scope.

[0009] Based on this, the present invention introduces substances that can react with rubber on the surface of calcium sulfate whiskers through chemical modification and physical reinforcement mechanisms, thereby enhancing the bonding force between the composite modified calcium sulfate whiskers (2-CSW) and the rubber interface, and further improving the mechanical properties of the rubber.

[0010] Furthermore, the specific steps of the preparation method include:

[0011] (1) First layer modification: NaOH solution was added to anhydrous ethanol to adjust the pH of the solution. Then, calcium sulfate whiskers CSW were weighed and added to the mixed solution. Tetraethyl orthosilicate TEOS was added dropwise to the reaction system to carry out the reaction. After the reaction was completed, vacuum filtration was performed, and the solid product was retained as the first-modified product 1-CSW after solid-liquid separation.

[0012] (2) Second layer modification: Add a certain amount of coupling agent to anhydrous ethanol and stir ultrasonically. Then weigh 1-CSW and add it to the mixed solution. React at a constant temperature and homogenize. After the reaction is completed, vacuum filter and separate the solid and liquid to retain the solid, which is the composite modified calcium sulfate whisker 2-CSW.

[0013] Furthermore, in step (1), the pH value of the reaction system is 9-13, the concentration of calcium sulfate whiskers (CSW) in the reaction system is 20 g / L, the volume of tetraethyl orthosilicate (TEOS) added is 4%-6% of the volume of anhydrous ethanol, and the reaction time is 10-30 min.

[0014] It is worth noting that the first layer modification of this invention adopts a room temperature reaction, which, compared with other modification methods, does not require heating throughout the process, truly achieving a simplified treatment of reaction conditions.

[0015] Furthermore, in step (2), the mass of the coupling agent added is 10%-25% of the mass of 1-CSW added, and the reaction time of the isothermal homogenization reaction is 15-30 min, the reaction temperature is 60-90℃, and the stirring speed is 200-400 r / min.

[0016] Furthermore, the coupling agent is a titanate coupling agent HY201.

[0017] It is worth noting that in some embodiments using titanate coupling agent HY201 as the coupling agent, the mass of titanate coupling agent HY201 added in step (2) is 20% of the mass of 1-CSW added, the reaction time of the isothermal homogenization reaction is 15-20 min, and the reaction temperature is 70-80℃.

[0018] Therefore, this invention selects tetraethyl orthosilicate (TEOS) as the first-layer modifier. By changing the experimental conditions, nano-SiO2 is coated on the surface of calcium sulfate whiskers, which is equivalent to introducing a large number of hydroxyl groups on the whisker surface, providing adhesion sites for the subsequent second-layer modification. At the same time, the hydroxyl groups make its surface a reactive center, which can interact with the hydrogen bonds of siloxanes in the silicon skeleton structure, thereby improving the strength of natural rubber and achieving a reinforcing effect. The second-layer modification uses titanate coupling agent HY201. Organic long-chain fatty acids all have a certain degree of hydrophobicity, which makes them advantageous in powder modification applications. Compared with the prior art, this invention develops suitable reinforcing agents by utilizing the characteristics of the matrix to be reinforced through a simple process. It not only realizes the application of this type of whisker in rubber, but also provides new ideas for the development of different types of reinforcing agents.

[0019] The second objective of this invention is to provide a composite modified calcium sulfate whisker prepared by the preparation method described above.

[0020] A third objective of this invention is to provide an application of the composite modified calcium sulfate whiskers as described above.

[0021] Application of a composite modified calcium sulfate whisker, as described above, as a partial or complete replacement of carbon black reinforcing agent in the preparation of natural rubber composites.

[0022] It is worth noting that the composite modified calcium sulfate whiskers (2-CSW) provided by this invention can form a close composite material with natural rubber (NR) through chemical modification and physical reinforcement mechanisms.

[0023] First, from a chemical perspective, the long organic chains on the modified 2-CSW surface react with the chemical groups in the NR matrix to form strong chemical bonds. In particular, the O-Ti-O groups in the titanate coupling agent react with the sulfur bonds [-Sn-] in the NR, enhancing the bonding force between the two. The titanate coupling agent on the 2-CSW surface makes it more compatible with the organic chains in the NR matrix, improving the interfacial compatibility between CSW and NR. The change in contact angle indicates that the modified whiskers have significantly increased compatibility with the organic medium, further improving the dispersibility and stability of the composite material.

[0024] Secondly, from a physical perspective, 2-CSW possesses a short fiber morphology and an anisotropic crystal structure. During the mixing process, due to shear forces, 2-CSW embeds itself into the NR matrix along certain directions, forming an ordered distribution. This directional arrangement allows 2-CSW to better disperse stress in the direction of force application. Furthermore, 2-CSW has a large specific surface area and good interfacial adhesion, forming a strong interface within the NR matrix. This strong interface generates a contraction force F towards the matrix under external forces, hindering crack initiation and propagation, thereby improving the composite material's crack resistance and fatigue resistance. Due to the uniform distribution of 2-CSW in the NR and its strong interfacial adhesion, the composite material forms a denser network structure, significantly improving its tensile strength and elongation at break.

[0025] Therefore, the composite modified calcium sulfate whiskers (2-CSW) enhance the interfacial compatibility and chemical bonding between CSW and the NR matrix through chemical modification, while the physical reinforcement mechanism hinders crack propagation through directional alignment and strong interfacial adhesion, thereby significantly improving the mechanical properties of the composite material.

[0026] Furthermore, the preparation method of the natural rubber composite material is as follows:

[0027] (1) The natural rubber (NR) composite material is mixed in an internal mixer. The NR is plasticized by rolling five times. Then zinc oxide, stearic acid and accelerators (DM, M) are added in sequence.

[0028] (2) Place the rubber compound on a two-roll mill, add carbon black, the composite modified calcium sulfate whiskers (2-CSW), and sulfur, and mix them thoroughly.

[0029] (3) Vulcanize the natural rubber using a vulcanizing machine.

[0030] It is worth noting that this invention first utilizes a synergistic promoting mechanism to introduce active substances (such as Si-O-Ca and Ti-O-Ca) that can chemically react with natural rubber onto the surface of the composite modified calcium sulfate whiskers. This not only improves the interfacial compatibility of the whiskers but also promotes the vulcanization process of the rubber system, achieving a strong bond between the reinforcing agent and the matrix. Furthermore, 2-CSW at moderate addition levels (e.g., 10 phr) significantly improves the tensile strength, hardness, and maximum stress of the composite material while maintaining excellent ductility, exhibiting a reinforcing effect similar to or even better than that of carbon black. Meanwhile, considering that natural rubber primarily uses carbon black as a reinforcing agent, but carbon black production relies on oil extraction, finding alternative materials is essential. This invention provides a green and sustainable solution.

[0031] In step (1), the internal mixer is used to mix at 50-70°C, and NR is plasticized by rolling 5 times; step (3) is vulcanization at 150°C for 1 hour.

[0032] Furthermore, in step (2), the total amount of carbon black and composite modified calcium sulfate whiskers added is 10 parts by weight per 100 parts of rubber, and the amount of composite modified calcium sulfate whiskers added is 5-10 parts by weight per 100 parts of rubber.

[0033] This invention uses composite modified calcium sulfate whiskers (2-CSW) to partially or completely replace carbon black as a low-cost, environmentally friendly reinforcing material. On the one hand, it can reduce the dependence on carbon black in the preparation of natural rubber composites. On the other hand, compared with traditional carbon black, composite modified calcium sulfate whiskers (2-CSW) can make natural rubber composites have better heat resistance and effectively reduce production costs. It helps to promote the development of rubber products in the field of environmental protection and has broad market prospects.

[0034] Compared with existing technologies, this invention uses tetraethyl orthosilicate as the first-layer modifier and titanate coupling agent HY201 as the second-layer modifier. It utilizes the mechanism of action of the matrix to be reinforced to propose a modification direction for calcium sulfate whiskers, introducing substances that can react with rubber onto the surface of the calcium sulfate whiskers. While ensuring the surface modification effect of the whiskers, it also has a synergistic effect on promoting the rubber system, achieving a higher level of performance through a powerful combination. The resulting composite modified calcium sulfate whiskers can partially or completely replace traditional carbon black reinforcing agents, providing a sustainable solution for the development of high-performance rubber composite materials. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0036] Figure 1 The ZETA potential value is the result of the orthogonal experiment of the first layer of modified calcium sulfate whiskers (1-CSW) in Example 1.

[0037] Figure 2 The contact angles of the composite modified calcium sulfate whiskers (2-CSW) prepared by different coupling agents in Example 1 are: a. stearic acid, b. sodium stearate, c. titanate coupling agent HY201, d. aluminate coupling agent DL411, e. aluminate coupling agent HYA1.

[0038] Figure 3 The contact angles are the results of 16 orthogonal experiments on the composite modified calcium sulfate whiskers (2-CSW) in Example 2.

[0039] Figure 4 The contact angles are those of the single-modified CSW (a) and the composite-modified calcium sulfate whiskers 2-CSW (b) in Comparative Example 1.

[0040] Figure 5 The images shown are XRD patterns and SEM images of HH-CSW and its modified products 1-CSW and 2-CSW in Example 3.

[0041] Figure 6 The images shown are: TEM image (a) of 1-CSW, HRTEM image (b) of 1-CSW, SAED electron diffraction image (c) of 1-CSW, TEM image (d) of 2-CSW, interplanar spacing (e) of 2-CSW, and SAED electron diffraction image (f) of 2-CSW in Example 3.

[0042] Figure 7 The following are the FI-TR spectra, XPS full spectra, (a) of HH-CSW and its modified products 1-CSW and 2-CSW in Example 3; XPS analysis of (c) carbon, (d) calcium, (e) sulfur, and (f) oxygen in HH-CSW; XPS analysis of (g) carbon, (h) calcium, (i) sulfur, (j) oxygen, and (k) silicon in 1-CSW; and XPS analysis of (l) carbon, (m) calcium, (n) sulfur, (o) oxygen, (p) titanium, and (q) phosphorus in 2-CSW.

[0043] Figure 8The image shows the TG-DSC curve of the composite modified calcium sulfate whiskers 2-CSW in Example 3.

[0044] Figure 9 These are the vulcanization characteristic curves of NR composite materials with different reinforcing agent addition amounts in Examples 4-5 and Comparative Example 2.

[0045] Figure 10 The stress-strain curves are for NR composite materials with different amounts of reinforcing agent added in Examples 4-5 and Comparative Example 2.

[0046] Figure 11 These are the vulcanization characteristic curves of the composite materials in Example 6 and Comparative Example 3, where (a) is the NR-HH-CSW composite material and (b) is the NR-2-CSW composite material.

[0047] Figure 12 The mechanical properties of natural rubber composites with different CSW addition amounts prepared in Comparative Example 3 are: a. tensile strength, b. maximum stress, and c. elongation at break.

[0048] Figure 13 These are the stress-strain curves of the NR-HH-CSW / 2-CSW composite materials prepared in Example 6 and Comparative Example 3, where (a) is the NR-HH-CSW composite material and (b) is the NR-2-CSW composite material.

[0049] Figure 14 Characterization analysis (a. XRD b. FT-IR c. TG-DSC) of NR / HH-CSW / 2-CSW-NR prepared in Example 6 and Comparative Example 3.

[0050] Figure 15 These are SEM images of the NR-HH-CSW / 2-CSW composite materials and NR cross sections prepared in Example 6 and Comparative Example 3, where a. NR, b. NR-HH-CSW composite material, and c. NR-2-CSW composite material. Detailed Implementation

[0051] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in the embodiments of this application, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in this application is merely for describing particular implementations and is not intended to limit the scope of this disclosure.

[0053] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; other experimental methods and technical means not specifically mentioned herein refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0054] To better illustrate the content of this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail in order to highlight the main points of this application.

[0055] Without conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of this application.

[0056] This invention discloses a composite modified calcium sulfate whisker, its preparation method, and its application, belonging to the technical field of natural rubber reinforcing materials. This invention uses tetraethyl orthosilicate as the first-layer modifier and titanate coupling agent HY201 as the second-layer modifier. Utilizing the mechanism of action with the matrix to be reinforced, the modification direction of the calcium sulfate whisker is proposed. Substances that can react with rubber are introduced onto the surface of the calcium sulfate whisker. While ensuring the surface modification effect of the whisker, it also has a synergistic effect on promoting the rubber system, achieving a higher level of performance through a powerful combination. The resulting composite modified calcium sulfate whisker can partially or completely replace traditional carbon black reinforcing agents, providing a sustainable solution for the development of high-performance rubber composite materials.

[0057] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0058] Example 1

[0059] A method for preparing composite modified calcium sulfate whiskers:

[0060] (1) First layer modification: Add 100 mL of anhydrous ethanol to a beaker, then add 5% NaOH solution to the beaker and stir. Adjust the pH of the solution to 9, 10, 11, and 12. Then weigh 20 g / L CSW and add it to the mixed solution. Use a dropper to add 0, 2, 4, and 6 mL of TEOS dropwise to the beaker. The reaction time is set to 10, 15, 20, and 25 min, respectively. The reaction time (A), the amount of TEOS added (B), and the pH value (C) are investigated separately. A three-factor, four-level orthogonal experiment is designed. The surface Zeta potential of the first-layer modified calcium sulfate whiskers (1-CSW) is used as the evaluation index. L16(4 3 The results of the orthogonal experiments are shown in Table 1. After the reaction, vacuum filtration was performed to obtain the filter residue. The filter residue was washed with anhydrous ethanol and dried in a constant temperature drying oven for 6-12 hours to obtain the first layer of modified calcium sulfate whiskers (1-CSW). The zeta potential value was measured as follows: Figure 1 As shown.

[0061] Table 1. Results of orthogonal experiments on the first layer of modified calcium sulfate whiskers.

[0062]

[0063] Therefore, the optimal reaction conditions selected in this invention are a reaction time of 15-20 min, a TEOS addition amount of 3-5 mL, and a reaction system pH of 10-11, to prepare the first layer of modified calcium sulfate whiskers (1-CSW) used in subsequent examples.

[0064] (2) Second-layer modification: 100 mL of anhydrous ethanol was added to a beaker. 15% of the amount of 1-CSW added, including stearic acid, sodium stearate, titanate coupling agent HY201, aluminate coupling agent DL411, and aluminate coupling agent HYA1, were added to the beaker and ultrasonically stirred. Then, 20 g / L of 1-CSW was weighed and added to the mixed solution. The beaker was placed in a water bath for heating and reaction. The reaction temperature was set at 80℃, the reaction time at 25 min, and the stirring speed at 400 r / min. After the reaction, the mixture was washed and filtered with anhydrous ethanol, and finally dried at 100℃. After drying, the composite-modified calcium sulfate whiskers (2-CSW) were obtained. The contact angle was measured as follows: Figure 2 As shown.

[0065] As can be seen, the contact angle of stearic acid-modified 2-CSW is 60.20°, that of sodium stearate-modified 2-CSW is 83.05°, that of titanate coupling agent HY201-modified 2-CSW is 93.15°, that of aluminate coupling agent DL411-modified 2-CSW is 72.90°, and that of aluminate coupling agent HYA1-modified 2-CSW is 71.90°. Considering that only titanate coupling agents show the most significant improvement in modification effect and have a contact angle greater than 90°, this invention preferably uses titanate coupling agent HY201 as the organic modifier for the second layer of CSW.

[0066] Example 2

[0067] A method for preparing composite modified calcium sulfate whiskers:

[0068] (1) First layer modification: Calcium sulfate whiskers (1-CSW) with the first layer modification were prepared by using the same steps as step (1) in Example 1 and the optimal reaction conditions.

[0069] (2) Second layer modification: Add 100 mL of anhydrous ethanol to a beaker. Add 10%, 15%, 20%, and 25% by mass of 1-CSW titanate coupling agent HY201 to the beaker and stir ultrasonically. Then weigh 20 g / L 1-CSW and add it to the mixed solution. Place the beaker in a water bath for heating reaction. Set the reaction temperature to 60, 70, 80, and 90 °C, the reaction time to 15, 20, 25, and 30 min, and the stirring speed to 400 r / min. Investigate the reaction time (A), the amount of coupling agent added (B), and the reaction temperature (C) separately. Design a three-factor, four-level orthogonal experiment. Use the contact angle of 2-CSW as the evaluation index. Take L16(4 3 The results of the orthogonal experiments are shown in Table 2. After the reaction, the mixture was washed and filtered with anhydrous ethanol, and finally dried at 100℃ to obtain the composite-modified calcium sulfate whiskers (2-CSW). The contact angles were measured as follows: Figure 3 As shown.

[0070] Table 2. Results of orthogonal experiments on the second layer of modified calcium sulfate whiskers.

[0071]

[0072] Therefore, the optimal reaction conditions selected in this invention are a reaction time of 20-25 min, a coupling agent addition of 20-25%, and a reaction temperature of 70-80 °C, to prepare the composite modified calcium sulfate whiskers (2-CSW) used in subsequent examples.

[0073] Comparative Example 1

[0074] A method for preparing a single modified calcium sulfate whisker:

[0075] Add 100 mL of anhydrous ethanol to a beaker, then add 20% of the titanate coupling agent (unmodified CSW) to the beaker and ultrasonically stir. Then weigh 20 g / L CSW and add it to the mixed solution. Place the beaker in a water bath for heating and reaction. Set the reaction temperature to 80 °C and the reaction time to 20 min. After the reaction is complete, wash and filter with anhydrous ethanol. Finally, dry at 100 °C. After drying, you can obtain the single-modified CSW.

[0076] The contact angles of the single modified CSW prepared in Comparative Example 1 and the composite modified calcium sulfate whiskers 2-CSW obtained in Example 2 were measured as follows: Figure 4 As shown, the contact angle of 2-CSW modified with TEOS increased from 94.95° to 117.2°, demonstrating better surface modification effect compared to CSW without TEOS modification. The improvement in hydrophobicity is also significant, proving that composite modification is meaningful. This is because TEOS modification increases the degree of hydroxylation on the whisker surface, providing more adhesion sites for subsequent modification of the titanate coupling agent on the whisker surface, thus enhancing the modification effect.

[0077] Example 3

[0078] A composite-modified calcium sulfate whisker was prepared using the optimal conditions disclosed in Examples 1 and 2. Tests were performed on the unmodified calcium sulfate whisker HH-CSW, the first-layer modified calcium sulfate whisker 1-CSW, and the composite-modified calcium sulfate whisker 2-CSW. The results are as follows: Figures 5-8 As shown.

[0079] Figure 5 XRD patterns and SEM images of HH-CSW and its modified products 1-CSW and 2-CSW are shown. XRD analysis revealed that the characteristic diffraction peaks of the unmodified HH-CSW appeared at 14°, 25°, and 29°, corresponding to the (200), (020), and (400) crystal planes, respectively, consistent with the characteristics of monoclinic CaSO4·0.5H2O in the standard card (JCPDS#98-000-0108). After modification, the characteristic peak positions of 1-CSW and 2-CSW remained unchanged, indicating that the organic modification did not affect the crystal structure of the whiskers, and the modifier mainly adhered to the whisker surface in an amorphous form. The decrease in peak intensity can be attributed to the amorphous nature of Si-OH and the titanate coupling agent and their low atomic scattering intensity.

[0080] SEM images further revealed the surface morphology changes of HH-CSW before and after modification. Unmodified HH-CSW had a smooth and uniform surface, while 1-CSW had particles attached to its surface, forming a rough modified layer, indicating that the Si-OH nanostructure successfully covered the whisker surface. The presence of Si in the EDS spectra further verified the attachment of TEOS hydrolysis products. Furthermore, the detection of Na was related to the alkaline environment during TEOS hydrolysis. In contrast, the 2-CSW whisker surface was rougher and formed a dense and uniform modified layer, indicating the successful introduction of the titanate coupling agent. The detection of Ti in the EDS spectra further confirmed this result.

[0081] To further clarify the effect of CSW modification, TEM was used to analyze the state and thickness of the CSW-modified layer. Figure 6 (a) TEM image of 1-CSW shows a dense but uneven modification layer on the whisker surface. Because the modifier-modified layer is less dense than the whiskers, it causes less electron obstruction, resulting in a lighter shadow at the whisker edges, indicating the modification layer. Measurements using Digital Micrograph software show the modification layer to be 48.85 nm thin and 105.81 nm thick. The darker shadows in some areas indicate greater electron beam obstruction. Figure 6 (b) is an HRTEM image of 1-CSW, with the interplanar spacing measured to be 0.3519 nm. Figure 6 (d) is a TEM image of 2-CSW, showing that the modified layer has a dense and uniform structure with an average thickness of 770 nm. Figure 6 (e) The interplanar spacing of 2-CSW was measured to be 0.2862 nm. The interplanar spacing of CSW modified by the two modifiers is close to that of (400) and (020) interplanar spacings of 0.3006 nm and 0.3465 nm in the standard PDF card of HH-CSW (CaSO4·0.5H2O:#98-000-0108), but there are still deviations. This nanoscale deviation may be due to the strain of the structural unit combination of the crystal, which in turn affects the interplanar spacing and causes changes in the peak intensity in the XRD pattern. Figure 6 The electron diffraction (SEAD) patterns in (c) and (f) show clear transmission spots and are labeled with crystal plane indices, consistent with the XRD analysis results. In summary, the TEM analysis of 1-CSW and 2-CSW further confirms the successful modification of CSW by the composite modification of TEOS and titanate coupling agent.

[0082] Figure 7 (a) shows the FT-IR spectra of HH-CSW before and after modification. As can be seen from the figure, the unmodified HH-CSW at 472 cm⁻¹... -1 SO4 at the location 2-The symmetrical variable-angle vibration peak shifts to 480 cm⁻¹ in 2-CSW. -1 This indicates that the addition of the modifier caused changes in the chemical bonds on the whisker surface. 600cm -1 and 658cm -1 SO4 2- Asymmetric variable-angle vibration peak, 1153 cm⁻¹ -1 SO4 2- The antisymmetric stretching vibration peaks. After modification, these peaks broaden, indicating that SO42-... 2- It interacts with the active groups of the modifier. Furthermore, 1-CSW at 799 cm⁻¹... -1 and 1094cm -1 The presence of Si-O symmetric stretching vibration peaks and Si-OH bending vibration peaks at 2874 cm⁻¹ confirms that TEOS was successfully coated on the HH-CSW surface. Meanwhile, 2-CSW shows a peak at 2874 cm⁻¹. -1 2928cm -1 and 2959cm -1 Stretching vibration peaks of -CH2- and -CH3 appear at 1467 cm⁻¹. -1 The absorption peak of the carboxylate indicates that the titanate coupling agent chemically bonds with CSW, successfully grafting long organic molecular chains.

[0083] Figure 7(b) shows the full XPS spectra before and after modification, and (c)-(q) show the XPS partial spectra of different elements, respectively. In the unmodified HH-CSW(cf), C1s, Ca2p, S2p, and O1s are located at 284.8 eV, 347.66 eV / 351.24 eV, 163.83 eV, and 531.96 eV, respectively, corresponding to the -Ca-SO4 chemical environment. After modification, XPS (gk) analysis of 1-CSW showed that: a new C=O peak at 289.1 eV was added to the C1s peak, and the Ca2p peak shifted to 348.26 eV / 351.89 eV, indicating a change in the chemical environment of calcium, which may lead to the formation of Ca-O-Si or Ca-COOR compounds; the S2p peak shifted from 163.83 eV to 169.53 eV, and the O1s peak was located at 532.52 eV; the appearance of the Si2p peak (102.70 eV) further verified that TEOS successfully modified the whisker surface. XPS spectra (lq) of 2-CSW further demonstrate the success of the second-layer modification: a new C1s peak at 286.22 eV indicates organic linking; the Ca2p peak shift is relatively small; the S2p peak is located at 169.80 eV, indicating a change in the chemical state of sulfur; the O1s peak is centered at 531.9 eV, indicating the combination of bridging oxygen (SO-Ti) and sulfate oxygen; the Ti2p peak (459.41 eV / 465.17 eV) indicates the formation of -Ti-O coupling, with the final state being 3d2 of Ti and 2p5 of O; the P2p peak (133.59 eV) represents an organophosphorus compound, further proving that the titanate coupling agent is stably grafted onto the whisker surface.

[0084] Figure 8 The image shows the TG-DSC curve of 2-CSW. 2-CSW underwent three weight loss phases. The first phase of weight loss occurred between 25.00℃ and 124.62℃, with a weight loss rate of 1.42%, primarily due to the evaporation of a small amount of adsorbed water on the whisker surface. The second phase of weight loss occurred between 124.62℃ and 285.35℃, with a weight loss rate of 9.23%, representing the decomposition of the titanate coupling agent on the 2-CSW surface. The third phase of weight loss occurred between 285.35℃ and 1000℃, with a weight loss rate of 6.59%. The thermal decomposition reaction of TEOS in this phase can be divided into two steps: first, the removal of the ethoxy group, generating ethoxysilane; then, the further decomposition of the ethoxysilane, generating silica and ethylene. This analysis further demonstrates the successful modification of CSW by the composite modification of TEOS and the titanate coupling agent.

[0085] The preparation method of the natural rubber composite material used in this invention is as follows:

[0086] (1) First, cut 100g of raw rubber compound for later use. Weigh out the activator ZnO, stearic acid, accelerator M, and accelerator DM. Preheat the rubber mixer, and simultaneously press the safety cover and pressure cover to open the mixer. Place the raw rubber compound in, and then press the safety cover and pressure cover down. Press the main motor forward and the timer switch to set the temperature to 50-70℃ for mixing. Simultaneously press the timer switch to stop the main motor. This completes the first mixing cycle. Afterward, press the safety cover and pressure cover to open the mixer and add ZnO and stearic acid. Follow the above steps, and then add accelerator M and DM in sequence. Set the temperature to 50-70℃ for mixing. Remove the rubber compound and let it cool at room temperature for a period of time to complete the first step.

[0087] (2) After the rubber compound has cooled to room temperature for 30 minutes, open the rubber mixing mill, adjust the gap between the two rollers to 1 mm, wrap the rubber compound around the rollers 2 to 3 times, and add sulfur. Then add reinforcing agent, wrap the rubber compound around the rollers 5 times, and cut the rollers 3 to 5 times on each side until the sulfur and filler are completely added to the compound. Then perform seamless triangular wrapping 5 to 7 times. Then proceed with the rubber extrusion to obtain the preliminary natural rubber composite material.

[0088] (3) After drying at room temperature for 24 hours, the natural rubber composite material is vulcanized at 140°C for 30 minutes using a flat vulcanizing machine.

[0089] Example 4

[0090] The application of a composite modified calcium sulfate whisker 2-CSW completely replacing carbon black CB reinforcing agent in the preparation of natural rubber composite materials, wherein the reinforcing agent in step (2) is 10 phr composite modified calcium sulfate whisker 2-CSW, and the natural rubber composite material prepared is NR-2-CSW composite material.

[0091] Example 5

[0092] The application of a composite modified calcium sulfate whisker 2-CSW partially replacing carbon black CB as a reinforcing agent in the preparation of natural rubber composite materials, wherein 5 phr of white carbon black CB and 5 phr of composite modified calcium sulfate whisker 2-CSW are added as reinforcing agents in step (2) to prepare natural rubber composite material NR-2-CSW(5 phr)-CB(5 phr).

[0093] Comparative Example 2

[0094] The natural rubber composite material prepared by traditional silica CB as a reinforcing agent is different in that 10 phr of silica CB is added in step (2) as a reinforcing agent to prepare the natural rubber composite material NR-CB.

[0095] The performance of the natural rubber composite materials obtained in Examples 4-5 and Comparative Example 2 was tested:

[0096] (1) Analysis of vulcanization performance

[0097] Table 3. Vulcanization performance parameters of NR composites with different reinforcing agent addition amounts.

[0098]

[0099] Through Table 3 and Figure 9 As can be seen, different reinforcing agent ratios have a significant impact on the vulcanization performance of NR composites. Firstly, the maximum torque (M...) H The hardness of the composite material increased significantly with the increase of the content of modified calcium sulfate whiskers (2-CSW), indicating that 2-CSW can effectively enhance the hardness of the composite material after vulcanization. Although the minimum torque (M...) L The viscosity does not change much in different proportions, showing relative stability of the initial viscosity, but the torque difference (M) H -M L The hardness increased significantly with increasing CSW content, further indicating that CSW contributes more to the hardness improvement during vulcanization. Vulcanization time (t) 90 and t 10 Data shows that as CSW content increases, t 90 The significant reduction indicates that CSW can accelerate the vulcanization process, while t 10 The changes were small, indicating the stability of the initial vulcanization rate. The vulcanization rate index (CRI) showed that the composite containing 10 parts CSW had the highest CRI, indicating that it had the fastest vulcanization rate.

[0100] (2) Mechanical property analysis

[0101] Table 4 Mechanical property parameters of NR composites with different reinforcing agent addition amounts

[0102]

[0103] By comparing the mechanical properties of NR composites with different amounts of reinforcing agents, the following conclusions can be drawn: Compared with pure CB, the addition of 2-CSW significantly improves the maximum stress and tensile strength of NR composites. The maximum stress of NR-CB is 193.17 N and the tensile strength is 186.46 MPa, while the maximum stress and tensile strength of NR-2-CSW(5 phr)-CB(5 phr) increase to 217.03 N and 208.69 MPa, respectively. The maximum stress and tensile strength of NR-2-CSW further increase, reaching 234.52 N and 225.50 MPa, respectively. This indicates that 2-CSW is more effective as a reinforcing agent than CB, especially in improving the strength of composites. Regarding elongation at break, NR-CB is 460.12%, 5CB+5CSW increases to 494.94%, and NR-2-CSW is 490.81%. This indicates that the addition of CSW did not significantly reduce the ductility of NR, but rather slightly increased the toughness of the material, thus having a positive effect on improving the overall mechanical properties of the composite material. Regarding modulus, the 100% modulus of NR-CB was 14.07 MPa, and the 300% modulus was 64.55 MPa, while the 100% modulus of NR-2-CSW(5phr)-CB(5phr) decreased to 12.00 MPa, and the 300% modulus also decreased to 52.25 MPa. The 100% modulus of NR-2-CSW was 14.39 MPa, and the 300% modulus was 59.87 MPa. The pure CB NR composite material exhibited a high modulus, but the modulus decreased slightly after the addition of 2-CSW. This may be because 2-CSW improved the uniformity and toughness of the matrix, reducing stress concentration in high-modulus regions. The overall change in modulus was small, indicating that the reinforcing effect of 2-CSW remained significant. In terms of hardness, NR- has a hardness of 45, NR-2-CSW(5phr)-CB(5phr) increases to 47, and NR-2-CSW further increases to 48. The addition of CSW improves the hardness of the NR composite material, possibly because the rigidity of 2-CSW enhances the overall rigidity of the composite material, resulting in higher hardness. In summary, 2-CSW performs better than CB as a reinforcing agent in NR composites, especially in significantly improving strength, hardness, and toughness. Therefore, 2-CSW can be considered a preferred reinforcing agent to replace CB, particularly suitable for NR composite applications requiring high strength and high hardness.

[0104] The stress-strain curves of NR composites with different amounts of reinforcing agents are shown below. Figure 10 As shown, the stress-strain curves and corresponding fracture energies indicate that the NR-2-CSW system exhibits the highest fracture energy (31104.29 J / m). 2 ), followed by NR-2-CSW(5phr)-CB(5phr)(28380.82J / m2 ), NR-CB has the lowest (26332.18 J / m). 2 This further confirms that the reinforcing effect of CSW is significantly superior to that of traditional carbon black. Compared to CB, 2-CSW exhibits a more significant reinforcing effect at high strain stages, indicating its better performance in improving material strength and toughness. Surface modification of 2-CSW enhances its chemical interaction with the NR matrix, strengthening interfacial bonding and enabling the material to maintain high strength and toughness even at high strain stages. Rigid structure and uniform dispersion effectively transfer stress, reducing stress concentration and further improving the material's mechanical properties.

[0105] Example 6

[0106] The natural rubber composite material prepared by using composite modified calcium sulfate whiskers 2-CSW as a reinforcing agent, wherein 0-20 phr of 2-CSW is added as a reinforcing agent in step (2), the natural rubber composite material prepared is NR-2-CSW composite material.

[0107] Comparative Example 3

[0108] The natural rubber composite material prepared by using unmodified calcium sulfate whiskers HH-CSW as a reinforcing agent is different in that 0-20 phr of HH-CSW is added as a reinforcing agent in step (2) to prepare the natural rubber composite material NR-HH-CSW.

[0109] The vulcanization properties of the natural rubber composites obtained in Example 6 and Comparative Example 3 were tested, and the results are shown in Tables 5-6.

[0110] Table 5. Vulcanization performance parameters of NR-HH-CSW composite materials

[0111]

[0112] Table 6. Vulcanization performance parameters of NR-2-CSW composite material

[0113]

[0114] Table 5-6 shows the vulcanization performance parameters of NR-HH-CSW / 2-CSW composite materials. The torque difference (M) of the NR-HH-CSW composite material increases with increasing additive content. H -M L The crosslinking density and mechanical properties initially decreased and then increased slightly, particularly at 5 phr and 10 phr, indicating a significant decrease. This suggests that low addition levels weaken crosslinking density and mechanical properties, but these properties recover somewhat at higher addition levels. Its positive vulcanization time (t...) 90 The overall duration of scorch time increases with increasing addition amount, especially showing a significant increase between 5 phr and 15 phr, indicating a slower vulcanization reaction rate. (t) 10The changes were not significant, and the vulcanization start-up time remained relatively stable, but the CRI (Curvage Intensity Ratio) showed an overall downward trend, indicating a slower vulcanization rate. With increasing addition, the torque difference of the NR-2-CSW composite material increased significantly, and the crosslinking density and mechanical properties were significantly enhanced. 90 The curing rate decreases significantly with increasing addition amount, especially at addition amounts of 10 phr and above, while the vulcanization rate increases significantly. 10 The crosslinking density and mechanical properties decrease significantly with increasing addition amount, but the vulcanization initiation is faster and the CRI increases significantly. Therefore, the NR-HH-CSW composite material is suitable for applications requiring high addition amount to achieve high crosslinking density and mechanical properties. Although the vulcanization time is longer, the initiation is stable and the rate is slower. On the other hand, the NR-2-CSW composite material is suitable for applications requiring rapid vulcanization and excellent mechanical properties. Its vulcanization reaction starts and completes rapidly, and the crosslinking density and mechanical properties are significantly enhanced with high addition amount.

[0115] The influence of the vulcanization characteristic curve of the composite material as follows Figure 11 As shown. Figure 11 (a) shows the vulcanization characteristic curve of the NR-HH-CSW composite material. NR exhibits slight fluctuations in the flat region. The vulcanization characteristic curve of NR after adding HH-CSW is not smooth, which reduces the stability of NR during the vulcanization process. As the amount of HH-CSW continues to increase, the maximum torque of natural rubber decreases continuously, and the stiffness of the composite material decreases. This result is consistent with Table 5. Figure 11 (b) shows the vulcanization characteristic curves of the NR-2-CSW composite material. Compared with the NR-HH-CSW composite material, the plateau region of the NR-2-CSW composite material is smoother in the flat vulcanization stage. This phenomenon indicates that the addition of NR-2-CSW can better promote the vulcanization process of natural rubber, at which point the natural rubber has the best processing performance. Through bilayer modification with TEOS and titanate coupling agents, stable and high-energy Si-O-Si, Si-O-Ca, Ti-O-Ca, and Ti-O-Si bonds are formed on the surface of calcium sulfate whiskers. The formation of these chemical bonds significantly improves the dispersibility and compatibility of calcium sulfate whiskers in the NR matrix, enhances the mechanical properties and vulcanization behavior of the composite material, and enables the NR-2-CSW composite material to exhibit excellent mechanical properties and a shorter vulcanization time even at high addition levels.

[0116] The mechanical properties of the natural rubber composite materials obtained in Example 6 and Comparative Example 3 were tested, and the results are shown in Table 7.

[0117] Table 7 Mechanical property parameters of NR composites with different addition amounts of HH-CSW and 2-CSW

[0118]

[0119] Through analysis Figure 12The mechanical property test results in Table 7 were used to evaluate the reinforcing effect of HH-CSW and 2-CSW on natural rubber (NR) composites. The maximum stress and tensile strength of the NR blank sample were 171.10 N and 164.52 MPa, respectively.

[0120] When HH-CSW was added at 5 phr, the strength increased slightly, but when the addition amount increased to 10-20 phr, the strength decreased significantly. This is mainly attributed to the incompatibility between the hydrophilicity of the HH-CSW surface and the hydrophobicity of NR, resulting in poor interfacial bonding. In contrast, 2-CSW exhibited excellent reinforcing effects. At an addition amount of 5 phr, the maximum stress and tensile strength were significantly improved; they reached their peak values ​​at 10 phr (234.52 N, 225.50 MPa), which was about 37% higher than the blank NR. Although the performance decreased slightly at higher addition amounts (15-20 phr), it was still higher than the unfilled sample. This indicates that the surface modification of 2-CSW effectively improved the compatibility and interfacial bonding with NR.

[0121] The addition of HH-CSW disrupted the crosslinking network of NR, resulting in a significant increase in elongation at break (671.19%) at high addition levels (15 phr). In contrast, 2-CSW maintained a stable elongation at break (490%-505%) within the addition range of 5-15 phr, with a slight decrease at high addition levels (20 phr), reflecting higher crosslinking density and enhanced rigidity. Modulus testing further confirmed this trend. HH-CSW at 10-20 phr significantly reduced the modulus, while 2-CSW at 5-15 phr increased the 100% and 300% modulus by 13.22% and 21.56% (10 phr), respectively. This indicates that 2-CSW is uniformly dispersed within the NR matrix, effectively improving the stiffness and mechanical properties of the composite material. Hardness testing showed that the addition of HH-CSW led to a decrease in NR hardness, while 2-CSW at 10 phr and above significantly increased the hardness, reaching a maximum of 50. This is consistent with the modulus results, further confirming the significant enhancement effect of 2-CSW in NR.

[0122] Stress-strain curve Figure 13 The results show that HH-CSW provides significant reinforcement at low filler levels, while high filler levels lead to a decrease in performance. 2-CSW exhibits the best strength and toughness in the 5-15 phr range, especially at 10 phr, where the fracture energy of the composite material is approximately 29.15% higher than that of blank NR. This is attributed to the uniform dispersion and excellent fiber-reinforced structure of 2-CSW, which effectively mitigates stress concentration and improves the fracture energy and overall stability of the composite material.

[0123] analyze Figure 14XRD pattern (a): The broad peaks of natural rubber (NR) at 2θ = 12°–26° are attributed to the characteristics of the amorphous cis-1,4-polyisoprene molecular chains. The diffraction peaks of the ZnO filler match the standard card (PDF#97-006-5120), indicating that no other inorganic fillers were introduced into the system. The characteristic peaks of HH-CSW and 2-CSW match the standard whisker card (PDF#98-000-0108), with the strongest peaks appearing on the (200) and (400) crystal planes, respectively, confirming that the whiskers were successfully embedded in the NR matrix. Furthermore, the masking phenomenon of the NR diffraction peaks indicates the high crystallinity and good dispersibility of the whiskers.

[0124] Figure 14 (b) In this case, 2957.8cm -1 (CH3 asymmetric stretching vibration) and 2912.7 cm -1 The (CH2 asymmetric stretching vibration) peak was present in all samples, confirming the stability of the rubber molecular chain. The peak at 1698.8 cm⁻¹ was observed in NR-2-CSW. -1 (C=O absorption peak) and 943.2 cm⁻¹ -1 The significantly enhanced Si-O stretching vibration peak indicates that ethyl silicate and titanate modifiers formed new chemical bonds on the surface of calcium sulfate whiskers, significantly improving the interfacial bonding between the whiskers and the rubber matrix. Meanwhile, the 1152 cm⁻¹ peak... -1 The S=O stretching vibration peak is stronger in NR-HH-CSW but weaker in NR-2-CSW, indicating that surface modification reduces sulfate exposure and further enhances interfacial compatibility.

[0125] like Figure 14 As shown in (c), the main weight loss phases of NR, NR-HH-CSW, and NR-2-CSW occurred between 250-450℃, but the weight loss rates differed: NR was 85.95%, NR-HH-CSW was 85.98%, while NR-2-CSW significantly decreased to 82.67%. 2-CSW had the highest residual mass, indicating that surface modification significantly improved the thermal stability of the rubber, as the protective layer formed by the modifier effectively suppressed the thermal decomposition rate. The DSC curves showed that the endothermic peak at 300-450℃ corresponded to the thermal decomposition of the rubber matrix. The endothermic peaks at 600-700℃ for NR-HH-CSW and NR-2-CSW were attributed to the decomposition or phase transition of calcium sulfate whiskers. Notably, the exothermic peak at 800-900℃ for NR-2-CSW was weaker and simpler, indicating that the surface-modified calcium sulfate whiskers had higher thermal stability and effectively reduced side reactions at high temperatures.

[0126] Figure 15 The cross-sectional morphology of different natural rubber composites is shown, revealing the relationship between whisker distribution and reinforcement mechanism. Pure natural rubber ( Figure 15a) The cross-section is smooth and the structure is uniform, but the lack of filler reinforcement results in lower mechanical properties. NR-HH-CSW composite material ( Figure 15 In (b), the whiskers are unevenly distributed and prone to agglomeration, resulting in weak bonding between the whiskers and the matrix. This leads to stress concentration and crack initiation, limiting the improvement of mechanical properties. In contrast, the NR-2-CSW composite material ( Figure 15 In c), the whiskers are uniformly distributed and aligned along a specific direction, exhibiting good bonding between the whiskers and the matrix interface. The surface is smooth with a blurred interface, demonstrating that the directional distribution and uniform filling of 2-CSW can effectively improve the stress transfer path. This optimized microstructure further validates the reinforcement mechanism of 2-CSW.

[0127] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing composite modified calcium sulfate whiskers, characterized in that, Composite modified calcium sulfate whiskers were obtained by using tetraethyl orthosilicate as the first layer modifier and titanate coupling agent HY201 as the second layer modifier. The specific steps include: (1) First layer modification: Add 5wt% NaOH solution to anhydrous ethanol to adjust the pH of the solution to 10-11. Then weigh 20g / L calcium sulfate whiskers CSW and add them to the mixed solution. Add 3-5mL tetraethyl orthosilicate TEOS dropwise to the reaction system and react for 15-20min. After the reaction is completed, vacuum filter and separate the solid and liquid products to retain the product 1-CSW after the first layer modification. (2) Second layer modification: A certain amount of second layer modifier is added to anhydrous ethanol and ultrasonically stirred. Then, 1-CSW is weighed and added to the mixed solution. The mixture is homogenized at a constant temperature for 20-25 min and 70-80℃. After the reaction, the mixture is vacuum filtered and the solid is separated to obtain the composite modified calcium sulfate whiskers 2-CSW. The amount of the second layer modifier added is 20-25%.

2. The preparation method according to claim 1, characterized in that, In step (1), the pH value of the reaction system is 9-13, the concentration of calcium sulfate whiskers (CSW) in the reaction system is 20 g / L, the volume of tetraethyl orthosilicate (TEOS) added is 4%-6% of the volume of anhydrous ethanol, and the reaction time is 10-30 min.

3. The composite modified calcium sulfate whiskers obtained by the preparation method described in claim 1 or 2.

4. The application of the composite modified calcium sulfate whiskers as described in claim 3, characterized in that, The application of the composite modified calcium sulfate whiskers as a partial or complete replacement of carbon black reinforcing agent in the preparation of natural rubber composite materials.

5. The application according to claim 4, characterized in that, The preparation method of the natural rubber composite material is as follows: (1) The natural rubber composite material is mixed on a mixer, and NR is plasticized by rolling five times. Then zinc oxide, stearic acid and accelerator are added in sequence. (2) Place the rubber compound on a two-roll mill, add carbon black and the composite modified calcium sulfate whiskers and sulfur, and mix them thoroughly. (3) Vulcanize the natural rubber using a vulcanizing machine.

6. The application according to claim 5, characterized in that, In step (1), the internal mixer is used to mix at 50-70℃, and NR is plasticized by rolling 5 times; step (3) is to vulcanize at 150℃ for 1 hour.

7. The application according to claim 6, characterized in that, In step (2), the total amount of carbon black and composite modified calcium sulfate whiskers added is 10 parts by weight per 100 parts of rubber, and the amount of composite modified calcium sulfate whiskers added is 5-10 parts by weight per 100 parts of rubber.

Images