Composite modified calcium sulfate whisker as well as preparation method and application thereof

Abstract

The invention 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. Tetraethyl orthosilicate is adopted as a first-layer modifier, a titanate coupling agent HY201 is adopted as a second-layer modifier, the modification direction of the calcium sulfate whisker is provided by utilizing the action mechanism of a to-be-reinforced matrix, and a substance capable of reacting with rubber is introduced to the surface of the calcium sulfate whisker, so that the surface modification effect of the whisker is ensured, and meanwhile, the strength of the whisker is improved. And a promoting synergistic effect can also be achieved on a rubber system, strong-strong combination is achieved, and the efficiency of a better level is achieved. The obtained composite modified calcium sulfate whisker can partially or completely replace a traditional carbon black reinforcing agent, and a sustainable solution is provided for development of high-performance rubber composite materials.

Description

Technical Field

[0001] The invention belongs to the technical field of natural rubber reinforcing agent materials, and specifically relates to a composite modified calcium sulfate whisker and a preparation method and application thereof. Background Art

[0002] Rubber and its composites are widely used in the fields of automobiles, aerospace, construction, etc., with excellent elasticity, wear resistance and shock resistance. However, rubber often finds it difficult to meet higher mechanical requirements in many high-performance fields. In order to improve the mechanical properties of rubber and enhance its strength, toughness and durability, researchers usually use reinforcing agents. Carbon black, as a traditional reinforcing agent, has a significant effect in improving the mechanical properties of rubber, but its use has certain negative effects on the environment, and the cost of carbon black is relatively high. In recent years, scholars have paid more and more attention to the development of alternative materials. Calcium sulfate whisker (CSW), as a natural mineral material, has gradually become a potential reinforcing agent in rubber composites due to its excellent structural properties and good compatibility.

[0003] Calcium sulfate whiskers are fibrous in shape, with a high aspect ratio and good reinforcement properties. By surface modification of calcium sulfate whiskers, the bonding force between them and the rubber matrix can be effectively improved, thereby improving the mechanical properties of the rubber. However, the compatibility between calcium sulfate whiskers and rubber is poor, which limits their application effect.

[0004] At present, various surface modifiers such as composite modification, coupling agent, surfactant, etc. are mainly used to modify the surface of calcium sulfate whisker at home and abroad. Their mechanism of action and mode are different, but they are all to improve the surface morphology of calcium sulfate whisker, reduce the interfacial energy difference between it and the matrix, and enhance the bonding force and compatibility between it and the matrix. By utilizing the adsorption of surfactant on the surface of calcium sulfate whisker, a molecular film can be generated to change its physicochemical properties, thereby reducing the interfacial energy between whisker and matrix. Commonly used surfactants include borate and stearate. In addition, coupling agent effectively enhances the bonding force between whisker and materials such as resin by reacting with the surface of calcium sulfate whisker, improves the mechanical properties, thermal stability and chemical corrosion resistance of composite materials, and common coupling agents include silane and titanate. Composite modifier combines multiple modification means to improve the compatibility and performance of calcium sulfate whisker by organic-organic and inorganic-inorganic modes, thereby improving the modification effect. Therefore, according to demand, it is key to select suitable organic or inorganic modifier for modification. Summary of the invention

[0005] In view of this, the present invention aims at the problems existing in the prior art, proposes a modification direction of calcium sulfate whiskers by utilizing the action mechanism of the matrix to be reinforced, introduces a substance capable of reacting with rubber on the surface of the calcium sulfate whiskers, enhances the bonding force between the whiskers and the rubber interface, and further provides a composite modified calcium sulfate whisker that can be used to replace carbon black and serve as a natural rubber reinforcing agent, as well as a preparation method and application thereof.

[0006] In order to achieve the above-mentioned object, the first object of the present invention is to provide a method for preparing a composite modified calcium sulfate whisker, which improves the compatibility with an organic matrix by changing the surface polarity of the calcium sulfate whisker. The following technical scheme is adopted:

[0007] A method for preparing a composite modified calcium sulfate whisker comprises taking tetraethyl orthosilicate as a first layer modifier and taking a coupling agent selected from stearic acid, sodium stearate, titanate coupling agent HY201, aluminate coupling agent DL411 and aluminate coupling agent HYA1 as a second layer modifier to obtain the composite modified calcium sulfate whisker.

[0008] Considering that in the modification process of CSW in the prior art, the coating of CSW is mainly completed by the reaction of the modifier with the hydroxyl group, calcium ion, calcium sulfate, etc. on the surface of CSW to form chemical bonds, hydrogen bonds and other forces. Among them, the surfactant is mainly used to change the affinity of the CSW surface to water, and cannot interact with the matrix, resulting in insufficient bonding between the whisker and the matrix, and thus unable to transmit and transfer stress well. The production cost of coupling agent-modified calcium sulfate whiskers is relatively high, which will lead to its relatively high price. The use of composite modifiers is highly targeted, and suitable modifiers must be selected based on the characteristics of the reinforced matrix or the specific scope of use.

[0009] Based on this, the present invention introduces a substance capable of reacting with rubber on the surface of calcium sulfate whiskers through chemical modification and physical enhancement mechanisms, thereby enhancing the bonding force between the composite modified calcium sulfate whiskers (2-CSW) and the rubber interface, thereby 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 is added to anhydrous ethanol to adjust the solution pH, then calcium sulfate whiskers CSW are weighed and added to the mixed solution, and tetraethyl orthosilicate TEOS is added dropwise to the reaction system for reaction. After the reaction is completed, vacuum filtration is performed, and solid-liquid separation is performed to retain the solid product as the first modified product 1-CSW;

[0012] (2) Second layer modification: A certain amount of coupling agent is added to anhydrous ethanol and ultrasonically stirred. Then, 1-CSW is weighed and added to the mixed solution. The mixture is subjected to a constant temperature homogenization reaction. After the reaction is completed, vacuum filtration is performed. The solid-liquid separation and the retained solid is the composite modified calcium sulfate whisker 2-CSW.

[0013] Furthermore, in the 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 drop volume of tetraethyl orthosilicate TEOS 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 the present invention adopts room temperature reaction. Compared with other modification methods, no heating is required throughout the process, which truly realizes the simplification of reaction conditions.

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

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

[0017] It is worth noting that in some embodiments using titanate coupling agent HY201 as 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 constant temperature homogeneous reaction is 15-20min, and the reaction temperature is 70-80°C.

[0018] Therefore, the present invention selects tetraethyl orthosilicate (TEOS) as the first layer modifier, and realizes the nano-SiO by changing the experimental conditions. 2 Coating the surface of calcium sulfate whiskers is equivalent to introducing a large number of hydroxyl groups on the surface of the whiskers, providing attachment points for the subsequent second-layer modification. At the same time, the hydroxyl groups make its surface reactive centers exist, which can interact with the hydrogen bonds of siloxane 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 have a certain degree of hydrophobicity, which makes them have obvious advantages in powder modification applications. Compared with the prior art, the present invention uses a simple process to develop a suitable reinforcing agent by utilizing the characteristics of the matrix to be reinforced. It can not only realize the application of this type of whisker in rubber, but also provide a new idea for the development of different types of reinforcing agents.

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

[0020] A third object of the present invention is to provide an application of the composite modified calcium sulfate whisker as described above.

[0021] The invention relates to an application of the composite modified calcium sulfate whisker as described above to partially or completely replace the carbon black reinforcing agent in the preparation of natural rubber composite materials.

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

[0023] First, from a chemical point of view, the organic long chains contained in the surface of the modified 2-CSW react chemically with the chemical groups in NR to form strong chemical bonds. In particular, the O-Ti-O groups in the titanate coupling agent can react with the sulfur bonds [-Sn-] in NR to enhance the binding force between the two. The titanate coupling agent on the surface of 2-CSW makes it more affinity with the organic chains in the NR matrix, improving the interfacial compatibility between CSW and NR. The change in contact angle shows that the compatibility of the modified whiskers with the organic medium is significantly increased, further improving the dispersibility and stability of the composite material.

[0024] Secondly, from a physical point of view, 2-CSW has the morphology of short fibers and an anisotropic crystal structure. During the mixing process, due to the action of shear force, 2-CSW will be embedded in NR along a certain direction to form an orderly distribution. This directional arrangement enables 2-CSW to better disperse stress in the direction of force. In addition, 2-CSW has a large specific surface area and good interfacial adhesion, forming a strong interface in the NR matrix. This strong interface will generate a contraction force F toward the inside of the matrix under the action of external force, hindering the generation and expansion of cracks, thereby improving the crack resistance and fatigue resistance of the composite material. Due to the uniform distribution of 2-CSW in NR and strong interfacial adhesion, the composite material forms a tighter network structure, which significantly improves the tensile strength and elongation at break of the composite material.

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

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

[0027] (1) The natural rubber (NR) composite material was mixed in an internal mixer, the NR was plasticized by roller pressing for 5 times, and then zinc oxide, stearic acid and accelerators (DM, M) were added in sequence;

[0028] (2) placing the rubber material on an open mixing mill, adding carbon black, the composite modified calcium sulfate whisker (2-CSW), and sulfur for internal mixing;

[0029] (3) Vulcanizing the natural rubber using a vulcanizer.

[0030] It is worth noting that the present invention first utilizes a synergistic promotion mechanism to introduce active substances (such as Si-O-Ca and Ti-O-Ca) that can chemically react with natural rubber on the surface of the composite modified calcium sulfate whisker, which not only improves the interfacial compatibility of the whisker, but also promotes the vulcanization process of the rubber system, thereby achieving a strong combination of the reinforcing agent and the matrix. Moreover, 2-CSW significantly improves the tensile strength, hardness and maximum stress of the composite material at a moderate addition amount (such as 10phr), while maintaining excellent ductility, showing a reinforcing effect similar to or even better than carbon black. At the same time, considering that natural rubber mainly uses carbon black as a reinforcing agent, but the production of carbon black depends on oil extraction, it is very necessary to find alternative materials for it, and the present invention provides a green and sustainable solution.

[0031] Furthermore, in the step (1), mixing is performed in an internal mixer at 50-70°C, and NR is plasticized by rolling 5 times; and the step (3) is vulcanization performed at 150°C×1h.

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

[0033] The present invention partially or completely replaces carbon black by composite modified calcium sulfate whisker (2-CSW), which is 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 composite materials. On the other hand, compared with traditional carbon black, the composite modified calcium sulfate whisker (2-CSW) can make the natural rubber composite material have better heat resistance and can effectively reduce production costs, which is helpful to promote the development of rubber products in the field of environmental protection and has broad market prospects.

[0034] Compared with the prior art, the present invention uses tetraethyl orthosilicate as the first layer modifier and titanate coupling agent HY201 as the second layer modifier, proposes the modification direction of calcium sulfate whiskers by using the action mechanism of the matrix to be reinforced, introduces substances that can react with rubber on the surface of calcium sulfate whiskers, and while ensuring the modification effect of whisker surface, it can also promote the synergistic effect of rubber system, achieve a higher level of performance by combining strong forces. The obtained composite modified calcium sulfate whiskers can partially or completely replace the traditional carbon black reinforcing agent, and provide a sustainable solution for the development of high-performance rubber composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without creative work.

[0036] Figure 1 It is the zeta potential value of the orthogonal experimental result of the first layer of modified calcium sulfate whisker (1-CSW) in Example 1.

[0037] Figure 2 The contact angles of the composite modified calcium sulfate whiskers (2-CSW) prepared with different coupling agents in Example 1, wherein: 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 of 16 groups of orthogonal experimental results of the composite modified calcium sulfate whisker (2-CSW) in Example 2.

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

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

[0041] Figure 6 These are the TEM photo of 1-CSW in Example 3 (a), the HRTEM photo of 1-CSW (b), the electron diffraction SAED photo selected by 1-CSW (c), the TEM photo of 2-CSW (d), the crystal plane spacing of 2-CSW (e), and the electron diffraction SAED photo selected by 2-CSW (f).

[0042] Figure 7 (a) FI-TR spectrum, (b) full XPS spectrum 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 of HH-CSW, XPS analysis of (g) carbon, (h) calcium, (i) sulfur, (j) oxygen, and (k) silicon of 1-CSW, and XPS analysis of (l) carbon, (m) calcium, (n) sulfur, (o) oxygen, (p) titanium, and (q) phosphorus of 2-CSW.

[0043] Figure 8This is the TG-DSC curve of the composite modified calcium sulfate whisker 2-CSW in Example 3.

[0044] Fig. 9 It is the vulcanization characteristic curve of NR composite materials with different reinforcing agent addition amounts in Examples 4-5 and Comparative Example 2.

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

[0046] Fig.11 1 and 2 are the vulcanization characteristic curves of the composite materials in Example 6 and Comparative Example 3, wherein: (a) NR-HH-CSW composite material, and (b) NR-2-CSW composite material.

[0047] Fig.12 The mechanical properties of the natural rubber composite materials with different CSW addition amounts prepared in Comparative Example 3 are as follows: a. tensile strength b. maximum stress c. elongation at break.

[0048] Fig.13 1 and 2 are stress-strain curves of the NR-HH-CSW / 2-CSW composite materials prepared in Example 6 and Comparative Example 3, wherein (a) is the NR-HH-CSW composite material and (b) is the NR-2-CSW composite material.

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

[0050] Fig.15 These are cross-sectional SEM images of the NR-HH-CSW / 2-CSW composite materials and NR prepared in Example 6 and Comparative Example 3, wherein: a. NR b. NR-HH-CSW composite material c. NR-2-CSW composite material. DETAILED DESCRIPTION

[0051] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] The word "embodiment" used here as an "exemplary" does not necessarily mean that any embodiment described is superior to or better than other embodiments. Unless otherwise specified, the performance index tests in the embodiments of this application are performed using conventional test methods in the art. It should be understood that the terms described in this application are only used to describe specific implementation methods and are not used to limit the content disclosed in this application.

[0053] Unless otherwise specified, the technical and scientific terms used in this document have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs; other experimental methods and technical means not specifically specified in this application refer to experimental methods and technical means commonly used by ordinary technicians in this field.

[0054] In order to better illustrate the content of the present application, numerous specific details are provided in the specific examples below. It should be understood by those skilled in the art that the present application can also be implemented without certain specific details. In the embodiments, some methods, means, instruments, equipment, etc. well known to those skilled in the art are not described in detail in order to highlight the main purpose of the present application.

[0055] Under the premise of no conflict, the technical features disclosed in the embodiments of the present application can be combined arbitrarily, and the resulting technical solutions belong to the contents disclosed in the embodiments of the present application.

[0056] The present invention discloses a composite modified calcium sulfate whisker and a preparation method and application thereof, belonging to the technical field of natural rubber reinforcing agent materials. The present invention adopts tetraethyl orthosilicate as the first layer modifier and titanate coupling agent HY201 as the second layer modifier, proposes the modification direction of calcium sulfate whiskers by using the action mechanism of the matrix to be reinforced, introduces a substance that can react with rubber on the surface of the calcium sulfate whisker, and while ensuring the modification effect of the whisker surface, it can also promote the synergistic effect on the rubber system, and achieve a higher level of efficiency by combining the two. The obtained composite modified calcium sulfate whisker can partially or completely replace the traditional carbon black reinforcing agent, and provide a sustainable solution for the development of high-performance rubber composite materials.

[0057] In order to better understand the present invention, the present invention is further specifically described below through the following examples, but it should not be understood as a limitation of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above invention content 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 solution pH to 9, 10, 11, 12, then weigh 20 g / L CSW and add it to the mixed solution, use a rubber-tipped dropper to add 0, 2, 4, 6 mL of TEOS dropwise to the beaker, and set the reaction time to 10, 15, 20, 25 min, respectively. The reaction time A, TEOS addition amount B, and pH value C were investigated separately, and a three-factor four-level orthogonal experiment was designed. The surface Zeta potential of the first layer modified calcium sulfate whisker (1-CSW) was used as the investigation index, and L16 (4 3 ) The orthogonal experimental results are shown in Table 1. After the reaction is completed, vacuum filtration is performed to obtain a filter residue, which is 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 thereof is measured as follows: Figure 1 shown.

[0061] Table 1 Orthogonal experimental results of the first layer of modified calcium sulfate whiskers

[0062]

[0063] Therefore, the present invention selects the reaction time of 15-20min, the amount of TEOS added of 3-5mL, and the reaction system pH of 10-11 as the optimal conditions for preparing the first layer of modified calcium sulfate whiskers (1-CSW) used in subsequent examples.

[0064] (2) Second layer modification: Add 100 mL of anhydrous ethanol to a beaker, take 15% of the amount of 1-CSW of stearic acid, sodium stearate, titanate coupling agent HY201, aluminate coupling agent DL411 and aluminate coupling agent HYA1 and add them to the beaker and stir ultrasonically, then weigh 20 g / L 1-CSW and add it to the mixed solution, put the beaker into a water bath for heating reaction, set the reaction temperature to 80°C, the reaction time to 25 min, and the stirring speed to 400 r / min. After the reaction is completed, wash and filter with anhydrous ethanol, and finally dry at 100°C. After drying, the composite modified calcium sulfate whisker (2-CSW) can be obtained. The contact angle is measured as follows Figure 2 shown.

[0065] It can be seen that the contact angle of stearic acid modified 2-CSW is 60.20°, the contact angle of sodium stearate modified 2-CSW is 83.05°, the contact angle of titanate coupling agent HY201 modified 2-CSW is 93.15°, the contact angle of aluminate coupling agent DL411 modified 2-CSW is 72.90°, and the contact angle of aluminate coupling agent HYA1 modified 2-CSW is 71.90°. Considering that only the modification effect of titanate coupling agent is the most obvious, and the contact angle is greater than 90°, therefore, the present invention preferably uses titanate coupling agent HY201 as the organic modifier of the second layer of CSW.

[0066] Example 2

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

[0068] (1) First layer modification: The first layer of modified calcium sulfate whiskers (1-CSW) was prepared using the same steps and optimal reaction conditions as step (1) in Example 1.

[0069] (2) Second layer modification: Add 100 mL of anhydrous ethanol to a beaker, add 10%, 15%, 20%, and 25% of the mass of 1-CSW to the beaker and perform ultrasonic stirring, then weigh 20 g / L 1-CSW and add it to the mixed solution, put the beaker into 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. The reaction time A, the amount of coupling agent added B, and the reaction temperature C were investigated separately, and a three-factor four-level orthogonal experiment was designed. The contact angle of 2-CSW was used as the investigation index, and L16 (4 3 ) The orthogonal experimental results are shown in Table 2. After the reaction, the mixture was washed and filtered with anhydrous ethanol, and finally dried at 100°C. After drying, the composite modified calcium sulfate whisker (2-CSW) was obtained. The contact angle was measured as follows Figure 3 shown.

[0070] Table 2 Orthogonal experimental results of the second layer modified calcium sulfate whiskers

[0071]

[0072] Therefore, the present invention selects the reaction conditions of 20-25 min, 20-25% coupling agent addition, and 70-80° C. as the optimal conditions for preparing the composite modified calcium sulfate whiskers (2-CSW) used in the 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 to the CSW that has not been modified with TEOS into the beaker and perform ultrasonic stirring, then weigh 20 g / L of CSW and add it to the mixed solution, put the beaker into a water bath for heating reaction, set the reaction temperature to 80°C, and the reaction time to 20 min. After the reaction is completed, wash and filter with anhydrous ethanol, and finally dry at 100°C. After drying, a single modified CSW can be obtained.

[0076] The contact angles of the single modified CSW prepared in Comparative Example 1 and the composite modified calcium sulfate whisker 2-CSW obtained in Example 2 were measured as follows: Figure 4 As shown in the figure, it can be seen that the contact angle of 2-CSW after TEOS modification increased from 94.95° to 117.2°, which is better than the surface modification effect of CSW without TEOS modification, and the hydrophobicity improvement effect is excellent, which proves that the composite modification is meaningful. Because TEOS modification increases the degree of hydroxylation on the whisker surface, it provides more attachment sites for the subsequent modification of the titanate coupling agent on the whisker surface, which plays a role in enhancing the modification effect.

[0077] Example 3

[0078] A composite modified calcium sulfate whisker is prepared by using the optimal conditions disclosed in Example 1 and Example 2. The calcium sulfate whisker HH-CSW before modification, the first layer modified calcium sulfate whisker 1-CSW and the composite modified calcium sulfate whisker 2-CSW are tested, and the results are as follows: Figures 5 to 8 shown.

[0079] Figure 5 The XRD patterns and SEM images of HH-CSW and its modified products 1-CSW and 2-CSW are shown. XRD analysis shows that the characteristic diffraction peaks of HH-CSW before modification appear at 14°, 25° and 29°, corresponding to the (200), (020) and (400) crystal planes, which are consistent with the monoclinic CaSO in the standard card (JCPDS#98-000-0108). 4 0.5H 2 After modification, the characteristic peak positions of 1-CSW and 2-CSW did not change, indicating that the organic modification did not affect the crystal structure of the whiskers, and the modifiers were mainly attached to the whisker surface in an amorphous form. The weakening of the peak intensity can be attributed to the amorphous nature of Si-OH and titanate coupling agents and their low atomic scattering intensity.

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

[0081] In order 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) is the TEM of 1-CSW. A dense but uneven modified layer can be seen on the surface of the whisker. Since the modified layer is less dense than the whisker, the electrons are less blocked when the electron beam passes through. The shadow at the edge of the whisker is lighter, showing the modified layer. The thinnest part of the modified layer is 48.85nm and the thickest part is 105.81nm as measured by Digital Micrograph software. The darker shadows in some areas indicate that the electron beam is blocked more when passing through. Figure 6 (b) is the HRTEM image of 1-CSW, and the interplanar spacing was measured to be 0.3519 nm. Figure 6 (d) is the TEM image of 2-CSW, showing that the modified layer has a dense and uniform structure and an average thickness of 770 nm. Figure 6 (e) The measured interplanar spacing of 2-CSW is 0.2862nm. The interplanar spacing of CSW modified by the two modifiers is similar to the standard PDF card of HH-CSW (CaSO 4 ·0.5H2O: #98-000-0108) has similar (400) and (020) interplanar spacings of 0.3006nm and 0.3465nm, 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 spectrum. Figure 6 The electron diffraction patterns (SEAD) in (c) and (f) show clear transmission spots and the crystal plane index is marked, which is consistent with the XRD analysis results. In summary, the TEM analysis of 1-CSW and 2-CSW confirms the successful modification of CSW by the composite modification of TEOS and titanate coupling agent from a deeper level.

[0082] Figure 7 (a) is the FT-IR spectra of HH-CSW before and after modification. As can be seen from the figure, the unmodified HH-CSW has a peak at 472 cm -1 SO 42- Symmetrical angle-shifted vibration peak, shifted to 480 cm in 2-CSW -1 , indicating that the addition of the modifier leads to changes in the chemical bonds on the whisker surface. -1 and 658cm -1 For SO 4 2- Asymmetric angle-variable vibration peak, 1153 cm -1 For SO 4 2- After modification, these peaks became broadened, indicating that SO 4 2- In addition, 1-CSW at 799 cm -1 and 1094cm -1 The Si-O symmetric stretching vibration peak and the Si-OH bending vibration peak appeared at 2874 cm -1 、2928cm -1 and 2959cm -1 -CH 2 -and-CH 3 The stretching vibration peaks at 1467 cm -1 The carboxylate absorption peak indicates that the titanate coupling agent is chemically bonded to CSW and the long chain of organic molecules is successfully grafted.

[0083] Figure 7 (b) is the full XPS spectrum before and after modification, and (c)-(q) are the XPS spectra of different elements. 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 -Ca-SO 4Chemical environment. After modification, the XPS (gk) 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 that the chemical environment of the calcium element changed, and Ca-O-Si or Ca-COOR compounds may be formed; the S2p peak moved 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. The XPS spectrum (lq) of 2-CSW further shows that the second layer modification is successful: a new CC peak at 286.22 eV is added to C1s, indicating that the organic chain is grafted; the Ca2p peak shift changes slightly; the S2p peak is located at 169.80 eV, indicating that the chemical state of sulfur has changed; the center of the O1s peak is located at 531.9 eV, indicating that the bridging oxygen (SO-Ti) is combined with the sulfate oxygen; the Ti2p peak (459.41 eV / 465.17 eV) indicates that -Ti-O coupling is formed, and the final state is 3d2 of Ti and 2p5 of O; the P2p peak (133.59 eV) represents the organic phosphorus compound, which further proves that the titanate coupling agent is stably grafted on the whisker surface.

[0084] Figure 8 The TG-DSC curve of 2-CSW. 2-CSW experienced three weight loss changes. The first stage of weight loss occurred between 25.00℃ and 124.62℃, with a weight loss rate of 1.42%. This stage was mainly due to the volatilization of a small amount of adsorbed water on the whisker surface. The second stage of weight loss occurred between 124.62℃ and 285.35℃, with a weight loss rate of 9.23%. This stage was the decomposition process of the titanate coupling agent on the surface of 2-CSW. The third stage 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 stage can be divided into two steps: first, the removal of ethoxy groups to generate ethyleneoxysilane; then, the further decomposition of ethyleneoxysilane to generate silicon dioxide and ethylene. This analysis further proves the successful modification of CSW by the composite modification of TEOS and titanate coupling agent.

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

[0086] (1) First, cut off 100g of the original rubber material for use, and weigh the active agent ZnO, stearic acid, accelerator M and accelerator DM. Preheat the rubber internal mixer, press the safety cover and the pressure cover to open the internal mixer, put the original rubber material in, and then press the safety cover and the pressure cover. Press the main motor forward, the timer switch, set the temperature to 50-70℃ to internally mix the rubber material, and press the timer switch to stop the main motor. Complete the first round of internal mixing. Then press the safety cover and the pressure cover to open the internal mixer, and add ZnO and stearic acid. Follow the above steps, and then add accelerators M and DM in turn. Set the temperature to 50-70℃ to internally mix the rubber material. Take out the rubber material and place it at room temperature for a period of time to cool down, completing the first step.

[0087] (2) After the rubber compound has cooled at room temperature for 30 minutes, the rubber mill is opened, the distance between the two rollers is adjusted to 1 mm, the rubber compound is rolled 2 to 3 times, and sulfur is added. Then the reinforcing agent is added, the rubber compound is rolled 5 times, and the left and right cutters are cut 3 to 5 times until the sulfur and filler are completely added to the mixed rubber. Then, seamless triangle rolls are made 5 to 7 times. The rubber is then rolled to obtain a preliminary natural rubber composite material.

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

[0089] Example 4

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

[0091] Example 5

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

[0093] Comparative Example 2

[0094] The natural rubber composite material is traditionally prepared using white carbon black CB as a reinforcing agent, the difference being that 10 phr of white carbon black CB is added in step (2) as a reinforcing agent to prepare the natural rubber composite material NR-CB.

[0095] The performance tests of the natural rubber composite materials obtained in Examples 4-5 and Comparative Example 2 were carried out:

[0096] (1) Vulcanization performance analysis

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

[0098]

[0099] Through Table 3 and Fig. 9 It can be seen that different ratios of reinforcing agents have a significant effect on the vulcanization properties of NR composites. First, the maximum torque (M H ) increases significantly with the increase of the content of composite modified calcium sulfate whisker (2-CSW), indicating that 2-CSW can effectively enhance the hardness of the composite after vulcanization. L ) varies little in different ratios, showing the relative stability of the initial viscosity, but the torque difference (M H -M L ) increases significantly with the increase of CSW content, further indicating that CSW contributes more to the hardness improvement during the vulcanization process. 90 and t 10 ) data show that as the CSW content increases, t 90 significantly reduced, indicating that CSW can accelerate the vulcanization process, while t 10 The variation is small, indicating the stability of the initial cure rate. The Cure Rate Index (CRI) shows that the composite containing 10 parts of CSW has the highest CRI, indicating that it has the fastest cure rate.

[0100] (2) Mechanical properties analysis

[0101] Table 4 Mechanical properties of NR composites with different reinforcing agent additions

[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 193.17N and the tensile strength is 186.46MPa, while the maximum stress and tensile strength of NR-2-CSW (5phr)-CB (5phr) increase to 217.03N and 208.69MPa, respectively, and the maximum stress and tensile strength of NR-2-CSW further increase to 234.52N and 225.50MPa, respectively. This shows that 2-CSW is more effective than CB as a reinforcing agent, especially in improving the strength of composites. For elongation at break, NR-CB is 460.12%, 5CB+5CSW increases to 494.94%, and NR-2-CSW is 490.81%. This shows that the addition of CSW did not significantly reduce the ductility of NR, but slightly increased the toughness of the material, which has a positive effect on improving the comprehensive mechanical properties of the composite material. In terms of modulus, the 100% modulus of NR-CB is 14.07MPa, and the 300% modulus is 64.55MPa, while the 100% modulus of NR-2-CSW (5phr)-CB (5phr) is reduced to 12.00MPa, and the 300% modulus is also reduced to 52.25MPa, and the 100% modulus of NR-2-CSW is 14.39MPa, and the 300% modulus is 59.87MPa. The NR composite material of pure CB shows a higher modulus, but after adding 2-CSW, the modulus is slightly reduced, which may be because 2-CSW improves the uniformity and toughness of the matrix and reduces the stress concentration in the high modulus area. The overall modulus changes little, indicating that the reinforcement effect of 2-CSW is still obvious. In terms of hardness, NR- is 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, which may be because the rigidity of 2-CSW enhances the overall rigidity of the composite, making it show higher hardness. In summary, 2-CSW performs better than CB as a reinforcing agent in NR composites, especially in improving strength, hardness and toughness. Therefore, 2-CSW can be used as a preferred reinforcing agent to replace CB, especially for NR composite applications requiring high strength and high hardness.

[0104] The stress-strain curves of NR composites with different reinforcing agent additions are shown in Figure 2. Fig.10 As shown in the figure, from the stress-strain curve and the corresponding fracture energy, it can be seen that the fracture energy of the NR-2-CSW system is the highest (31104.29 J / m 2 ), followed by NR-2-CSW (5phr)-CB (5phr) (28380.82J / m2 ), NR-CB is the lowest (26332.18 J / m 2 ). This further confirms that the reinforcement effect of CSW is significantly better than that of traditional carbon black. Compared with CB, 2-CSW shows a more significant reinforcement effect in the high strain stage, indicating that it has a better effect in improving the strength and toughness of the material. The surface modification of 2-CSW improves its chemical interaction with the NR matrix and enhances the interfacial bonding force, so that the material can still maintain high strength and toughness in the high strain stage. The rigid structure and uniform dispersion performance can effectively transfer stress, reduce stress concentration, and further improve the mechanical properties of the material.

[0105] Example 6

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

[0107] Comparative Example 3

[0108] The natural rubber composite material is prepared by using unmodified calcium sulfate whisker HH-CSW as a reinforcing agent, the difference being that 0-20phr 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 composite materials 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 composites

[0111]

[0112] Table 6 Vulcanization performance parameters of NR-2-CSW composites

[0113]

[0114] Table 5-6 shows the curing performance parameters of NR-HH-CSW / 2-CSW composite materials. As the addition amount of NR-HH-CSW composite materials increases, the torque difference (M H -M L ) first decreased and then slightly increased, especially at 5phr and 10phr, which decreased significantly, indicating that the crosslinking density and mechanical properties weakened at low additions, but recovered at high additions. 90 ) increases with the addition amount, especially when the amount is 5phr-15phr, it increases significantly, indicating that the vulcanization reaction rate slows down. 10) did not change much, the vulcanization start time was relatively stable, but the CRI showed a downward trend overall, and the vulcanization rate slowed down. As the addition amount of NR-2-CSW composite material increased, the torque difference increased significantly, and the crosslinking density and mechanical properties were significantly enhanced. 90 It decreases significantly with the increase of addition amount, especially when the addition amount is 10phr or above, the vulcanization rate is significantly accelerated. 10 As the addition amount increases, the curing starts more quickly and the CRI increases significantly. Therefore, the NR-HH-CSW composite material is suitable for applications that require high addition amounts to achieve higher crosslink density and mechanical properties. Although the curing time is longer, the start-up is stable and the rate is slow; while the NR-2-CSW composite material is suitable for applications that require fast curing and excellent mechanical properties. Its curing reaction starts and completes quickly, and the crosslink density and mechanical properties are significantly enhanced at high addition amounts.

[0115] The influence of the curing characteristic curve of the composite material is as follows Fig.11 shown. Fig.11 (a) is the vulcanization characteristic curve of NR-HH-CSW composite material. There is a small amount of fluctuation in the flat area of ​​NR. 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 continues to decrease and the stiffness of the composite material decreases. This result is consistent with Table 5. Fig.11 (b) is the vulcanization characteristic curve of NR-2-CSW composite material. Compared with NR-HH-CSW composite material, the platform area of ​​NR-2-CSW composite material in the flat vulcanization stage is smoother. This phenomenon shows that the addition of NR-2-CSW can better promote the vulcanization process of natural rubber, and the processing performance of natural rubber is the best at this time. Through the double-layer modification of TEOS and titanate coupling agent, 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 NR-2-CSW composite material to show excellent mechanical properties and shorter vulcanization time at high addition.

[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 properties of NR composites with different addition amounts of HH-CSW and 2-CSW

[0118]

[0119] By analyzing Fig.12The reinforcement effect of HH-CSW and 2-CSW on natural rubber (NR) composites was evaluated by the mechanical properties test results shown in Table 7. 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 5phr, the strength was slightly improved, but when the addition amount increased to 10-20phr, the strength decreased significantly. This is mainly attributed to the incompatibility between the surface hydrophilicity of HH-CSW and the hydrophobicity of NR, resulting in poor interfacial bonding. In contrast, 2-CSW showed excellent reinforcement effect. When the addition amount was 5phr, the maximum stress and tensile strength were significantly improved; the peak value (234.52N, 225.50MPa) was reached at 10phr, which was about 37% higher than the blank NR. Although the performance decreased slightly at high addition amounts (15-20phr), it was still higher than that of the unfilled sample. This shows that the surface modification of 2-CSW effectively improved the compatibility and interfacial bonding with NR.

[0121] The addition of HH-CSW destroyed the cross-linked network of NR, which was manifested by a significant increase in elongation at break (671.19%) at high addition (15phr). However, the elongation at break of 2-CSW remained stable (490%-505%) within the addition range of 5-15phr, and decreased slightly at high addition (20phr), reflecting a higher cross-linking density and stiffness enhancement effect. Modulus testing further confirmed this trend. HH-CSW caused a significant decrease in modulus at 10-20phr, while 2-CSW increased the 100% modulus and 300% modulus by 13.22% and 21.56% (10phr) at an addition of 5-15phr, respectively. This shows that 2-CSW is uniformly dispersed in the NR matrix, effectively improving the stiffness and mechanical properties of the composite material. Hardness testing shows that the addition of HH-CSW causes a decrease in NR hardness, while 2-CSW significantly increases the hardness at 10phr and above, up to 50. This is consistent with the modulus results, further confirming the significant reinforcing effect of 2-CSW in NR.

[0122] Stress-strain curve Fig.13 It shows that the reinforcement effect is obvious when the HH-CSW filling amount is low, while the performance decreases when the filling amount is high. 2-CSW shows the best strength and toughness in the range of 5-15phr, especially at 10phr, the fracture energy of the composite material is increased by about 29.15% compared with the blank NR. This is attributed to the uniform dispersion and excellent fiber reinforcement structure of 2-CSW, which can effectively alleviate stress concentration and improve the fracture energy and overall stability of the composite material.

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

[0124] Fig.14 (b) 2957.8cm -1 (CH 3 Asymmetric stretching vibration) and 2912.7cm -1 (CH 2 The peak of asymmetric stretching vibration exists in all samples, confirming the stability of the rubber molecular chain. -1 (C=O absorption peak) and 943.2cm -1 (Si-O stretching vibration peak) was significantly enhanced, indicating that ethyl silicate and titanate modifiers formed new chemical bonds on the surface of calcium sulfate whiskers, significantly improving the interfacial bonding between whiskers and rubber matrix. -1 The (S=O stretching vibration peak) is stronger in NR-HH-CSW but weakened in NR-2-CSW, indicating that the surface modification reduces the exposure of sulfate groups and further strengthens the interfacial compatibility.

[0125] like Fig.14 As shown in (c), the main weight loss stage of NR, NR-HH-CSW and NR-2-CSW occurs between 250-450℃, but there are differences in weight loss rate: 85.95% for NR, 85.98% for NR-HH-CSW, and significantly reduced to 82.67% for NR-2-CSW. The residual mass of 2-CSW is the highest, indicating that the surface modification significantly improves the thermal stability of the rubber, which is due to the protective layer formed by the modifier effectively inhibiting the thermal decomposition rate. The DSC curve shows that the endothermic peak at 300-450℃ corresponds to the thermal decomposition of the rubber matrix. The endothermic peaks of NR-HH-CSW and NR-2-CSW at 600-700℃ are attributed to the decomposition or phase transition of calcium sulfate whiskers. It is worth noting that the exothermic peak of NR-2-CSW at 800-900℃ is weaker and simpler, indicating that the calcium sulfate whiskers after surface modification have higher thermal stability and effectively reduce side reactions at high temperatures.

[0126] Fig.15The cross-sectional morphology of different natural rubber composites is shown, revealing the relationship between whisker distribution and reinforcement mechanism. Fig.15 a) The cross section is smooth and the structure is uniform, but the lack of filler reinforcement leads to low mechanical properties. NR-HH-CSW composite material ( Fig.15 b), the whiskers are unevenly distributed and easy to agglomerate, and the interface between the whiskers and the matrix is ​​weak, resulting in stress concentration and crack source formation, which limits the improvement of mechanical properties. Fig.15 In c), the whiskers are evenly distributed and arranged in a specific direction, the whiskers are well bonded to the substrate interface, the surface is flat and the interface is fuzzy, indicating that the directional distribution and uniform filling of 2-CSW can effectively improve the stress transfer path. This optimized microstructure further verifies the strengthening mechanism of 2-CSW.

[0127] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one 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 present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a composite modified calcium sulfate whisker, characterized in that: The composite modified calcium sulfate whisker is obtained by using tetraethyl orthosilicate as the first layer modifier and using stearic acid, sodium stearate, titanate coupling agent HY201, aluminate coupling agent DL411 and aluminate coupling agent HYA1 as the second layer modifier.

2. The preparation method according to claim 1, characterized in that: The specific steps include: (1) First layer modification: NaOH solution is added to anhydrous ethanol to adjust the solution pH, then calcium sulfate whiskers CSW are weighed and added to the mixed solution, and tetraethyl orthosilicate TEOS is added dropwise to the reaction system for reaction. After the reaction is completed, vacuum filtration is performed, and solid-liquid separation is performed to retain the solid product as the first modified product 1-CSW; (2) Second layer modification: A certain amount of coupling agent is added to anhydrous ethanol and ultrasonically stirred. Then, 1-CSW is weighed and added to the mixed solution. The mixture is subjected to a constant temperature homogenization reaction. After the reaction is completed, vacuum filtration is performed. The solid-liquid separation and the retained solid is the composite modified calcium sulfate whisker 2-CSW.

3. The preparation method according to claim 2, characterized in that: In the 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 drop volume of tetraethyl orthosilicate TEOS is 4%-6% of the volume of anhydrous ethanol, and the reaction time is 10-30 min.

4. The preparation method according to claim 2, characterized in that: The mass of the coupling agent added in step (2) is 10%-25% of the mass of 1-CSW added, and the reaction time of the constant temperature homogenization reaction is 15-30min, the reaction temperature is 60-90°C, and the stirring speed is 200-400r / min.

5. The preparation method according to claim 4, characterized in that: The coupling agent is titanate coupling agent HY201.

6. the composite modified calcium sulfate whisker obtained by the preparation method as described in any one of claim 1-5.

7. The application of the composite modified calcium sulfate whisker as claimed in claim 6, characterized in that, The composite modified calcium sulfate whisker is used to partially or completely replace the carbon black reinforcing agent in the preparation of natural rubber composite materials.

8. The use according to claim 7, characterized in that: The preparation method of the natural rubber composite material is: (1) The natural rubber composite material was mixed on an internal mixer, the NR was plasticized by roller pressing for 5 times, and then zinc oxide, stearic acid and accelerator were added in sequence; (2) placing the rubber material on an open mixing mill, adding carbon black and the composite modified calcium sulfate whisker and sulfur for internal mixing; (3) Vulcanizing the natural rubber using a vulcanizer.

9. The use according to claim 8, characterized in that: In the step (1), mixing is performed in an internal mixer at 50-70° C., and NR is plasticized by rolling for 5 times; and in the step (3), vulcanization is performed at 150° C. for 1 h.

10. The use according to claim 8, characterized in that: In the step (2), the total amount of carbon black and composite modified calcium sulfate whisker added is 10 parts by weight per hundred parts of rubber, and the amount of composite modified calcium sulfate whisker added is 5-10 parts by weight per hundred parts of rubber.

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