Preparation method of high-performance natural rubber

Abstract

The invention discloses a preparation method of high-performance natural rubber, which belongs to the technical field of natural rubber production, and comprises the following steps: mixing and grinding zinc oxide and other vulcanizing aids to prepare a mixed dispersion; mixing the mixed dispersion with natural latex, and curing to obtain pretreated natural latex; pouring the pretreated natural latex into a mold, and performing freezing treatment under a low-temperature freezing condition; and unfreezing, pre-pressing, drying and vulcanizing the frozen natural latex to obtain the high-performance natural rubber. Under the condition of no reinforcing filler, the comprehensive performance of the natural rubber is improved by inducing movement and arrangement of colloidal particles in the natural latex through ice crystal growth and the low-temperature freezing and solidifying characteristic of the natural latex, the forming process is simple, the condition requirement is lower, production operation is easier, and the cost is lower.

Description

Technical Field

[0001] The invention relates to the technical field of natural rubber production, and in particular to a method for preparing high-performance natural rubber. Background Art

[0003] From natural latex to natural rubber film, there are many factors that affect its molding and performance, among which the coagulation process of natural latex and the vulcanization process of raw rubber are the most important. The performance of natural rubber is affected by the quality and processing technology of natural latex. When the quality of natural latex cannot be improved by environmental factors, the improvement and innovation of the processing technology has become another way to prepare domestic high-performance natural rubber. Traditional natural rubber is mostly coagulated by acid, and the most commonly used is formic acid. Acid coagulation is easy to cause damage to equipment and human body, pollute the environment, and needs to be washed with water after coagulation, which will waste a lot of water resources; there are also coagulation methods such as natural coagulation, microbial coagulation, and microwave coagulation, which also have the disadvantages of long time, high cost, and poor quality of clots. After the latex is coagulated, it also needs to be dehydrated, dried, and granulated, and then processed by an open mixer and an internal mixer to obtain rubber products. The process is cumbersome, time-consuming and labor-intensive. The present invention utilizes low-temperature freezing technology to improve the performance of natural rubber. First, a cold source is applied in a specific direction of natural latex, and the growth of ice crystals during the freezing process is utilized to promote the aggregation and arrangement of rubber particles to realize the freezing molding of natural latex. After molding, further freezing treatment is performed to complete the coagulation and fixing of natural latex. Finally, thawing, drying, pre-pressing and vulcanization treatment are used to obtain high-performance natural rubber. The molding process is simple, and the environmental pollution is small. It is expected to replace rubber reinforced by carbon black, white carbon black, etc. Summary of the invention

[0004] In view of the above problems, the object of the present invention is to provide a method for preparing a high-performance natural rubber in the field of natural rubber molding. In order to achieve these objects of the present invention, in the process of preparing natural rubber, a cold source is first applied in a specific direction of natural latex, and the growth of ice crystals in the freezing process is utilized to promote the aggregation and arrangement of rubber particles to realize the freezing molding of natural latex, and further freezing treatment is performed after molding to complete the coagulation and fixation of natural latex, and finally thawing, drying, pre-pressing and vulcanization are utilized to obtain high-performance natural rubber. Through this method, the performance of natural rubber can be improved, so that the tensile properties and elongation at break performance are excellent, and the problem of incompatibility between tensile strength and elongation at break existing in current rubber products is solved.

[0005] In order to achieve these purposes and other advantages of the present invention, the present invention provides a method for preparing high-performance natural rubber. The raw materials thereof, measured in parts by weight, include: 100 parts of natural latex, 1 to 10 parts of zinc oxide, 0.2 to 4 parts of sulfur, 0.5 to 4 parts of accelerator M, 0.5 to 8 parts of stearic acid, 5 to 30 parts of water, 0.02 to 0.5 parts of diffusant NF, 0.02 to 0.5 parts of potassium hydroxide, and 0.2 to 4 parts of casein.

[0006] Preferably, the concentration of natural rubber latex used is 20% to 65%.

[0007] Preferably, other auxiliary agents include but are not limited to any one or more of active agents, promoters, diffusants, sulfur, potassium hydroxide, and casein.

[0008] Preferably, the active agent is stearic acid, the accelerator is one or more of accelerator M and accelerator DZ; and the diffusant is diffusant NF.

[0009] The present invention provides a method for preparing high-performance natural rubber, comprising the following steps: Step 1, weighing natural rubber latex and preparing it into a solution of a certain concentration, and then removing ammonia from the natural rubber latex by formaldehyde method; Step 2, adding casein, diffusant NF and potassium hydroxide into water to prepare a solution with a concentration of 10-20%; Step 3, placing zinc oxide, sulfur, accelerator M, stearic acid, casein solution, diffusant NF solution, and potassium hydroxide solution in a ball mill for grinding, the ball mill speed is 800-4000 rpm, the ball milling time is 2-72 h, to obtain a dispersion; Step 4, adding the dispersion to the natural latex after ammonia removal treatment, stirring for a certain period of time and then aging at room temperature for 2 to 6 hours at a stirring speed of 100 to 300 rpm to obtain a pretreated natural latex; Step 5, pouring the natural latex obtained in step 4 into a mold, freezing it on a low-temperature cold source at -20 to -80°C, freezing it for 1 to 24 hours to obtain a frozen natural latex, and further freezing it on a low-temperature cold source at -20 to -80°C for 12 to 24 hours after freezing to obtain a frozen solidified natural latex; Step 6, thawing the natural rubber frozen in step 5 at room temperature, and after thawing, pre-pressing for 1 to 5 minutes at a pressure of 1 to 5 MPa for multiple times; Step 7, drying the pre-pressed natural rubber obtained in step 6 in a forced air drying oven at 20-80° C. for 3-50 h; Step 8: placing the natural rubber obtained in step 7 on a vulcanizer for hot pressing and vulcanization to obtain a natural rubber film, the vulcanization pressure is 5-15 MPa, the hot pressing temperature is 120-145° C., and the hot pressing time is 10-30 min.

[0010] Preferably, as required, the natural rubber can be vulcanized by hot pressing to form a film in the vulcanization stage to obtain a natural rubber film, or can be prepared into other required natural rubber by other molding processes.

[0011] Preferably, after the frozen natural latex is thawed naturally, it is pre-pressed multiple times to remove part of the moisture, and then air-dried (≤80° C.), freeze-dried or naturally dried.

[0012] Specifically, the low-temperature freezing technology includes but is not limited to any one or more of unidirectional freezing, bidirectional freezing, and homogeneous freezing.

[0013] Specifically, the cold source temperature used for low-temperature freezing is -20℃~-80℃.

[0014] Specifically, the use of formaldehyde method to remove ammonia from natural rubber latex is a common method, the basic principle of which is to remove ammonia in natural rubber latex through a chemical reaction between formaldehyde and ammonia.

[0015] The invention provides a high-performance natural rubber prepared by the preparation method.

[0016] In some embodiments, the natural rubber produced by the low-temperature freezing technology described above has significantly improved tensile strength and elongation at break compared to the natural rubber produced by the hot baking and coagulation molding technology.

[0017] In some embodiments, the maximum tensile strength of the natural rubber produced by the above-mentioned low-temperature freezing technology reaches 31.40 MPa, which has exceeded the highest strength of natural rubber published so far of 29.04 MPa, and the maximum elongation at break reaches 1885.10%.

[0018] The present invention has at least the following beneficial effects: 1. The method of improving the performance of natural rubber by using low-temperature freezing technology of the present invention can realize direct freezing and solidification of natural latex at a relatively low temperature, without the need to inject liquid carbon dioxide or secondary film pressing. The process is simpler, the conditions are less demanding, the production operation is easier, and the cost is lower.

[0019] 2. The method of using low-temperature freezing technology to improve the performance of natural rubber of the present invention, by regulating the low-temperature freezing mode, uses ice crystal growth to regulate the aggregation and arrangement of natural rubber particles, so that the tensile and tear properties of natural rubber products are excellent, and solves the problem of incompatibility between tensile strength and elongation at break of current rubber products. The method has the advantages of simple process and low cost, and can be used for industrial promotion.

[0020] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is an electron microscope image (1000 times - 10 μm) of a natural rubber film prepared by freeze solidification molding (non-directional freezing) in Example 1; Figure 2 This is an electron microscope image (1000 times - 10 μm) of a natural rubber film prepared by freeze coagulation molding (directional freezing) in Example 11; Figure 3 This is an electron microscope image (5000 times - 2μm) of the natural rubber film prepared by freeze-solidification molding (directional freezing) in Example 11. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with embodiments so that those skilled in the art can implement the invention with reference to the description.

[0023] Example 1 This example gives an example of a method for preparing natural rubber.

[0024] The raw material ratio of this embodiment is as follows: 100 parts of natural rubber latex; 2.5 parts of sulfur; 3 parts of zinc oxide; 1.5 parts of accelerator M; 3 parts of stearic acid; 0.1 parts of potassium hydroxide; 0.1 parts of diffusing agent NF; and 0.8 parts of casein.

[0025] The steps include: Step 1, weighing natural rubber latex and preparing it into a latex solution with a concentration of 60%, and then removing ammonia from the natural rubber latex by formaldehyde method; Step 2, adding casein, diffusant NF and potassium hydroxide into water to prepare a solution with a concentration of 10-20%; Step 3, the casein, diffusant NF, potassium hydroxide solution obtained in step 2 are placed in a ball mill together with sulfur, zinc oxide, accelerator M and stearic acid, the grinding time is 3h, the ball mill speed is 1500rpm, and a dispersion is obtained; Step 4, adding the dispersion ground in step 3 to the natural rubber latex after ammonia removal treatment, stirring evenly and aging at room temperature for 2 to 6 hours to obtain a pretreated natural latex; Step 5, pouring the pretreated natural latex obtained in step 4 into a mold, first uniformly freezing and forming in a -24°C cold box, and then continuing to uniformly freeze for 24 hours to obtain frozen natural rubber; Step 6, thawing the natural rubber frozen in step 5 at room temperature, and then pre-pressing to remove moisture for multiple times, with a pre-pressing pressure of 1 MPa and a pre-pressing time of 5 minutes; Step 7, subjecting the natural rubber pre-pressed in step 6 to air drying at a drying temperature of 50° C. for a drying time of 8 hours; Step 8: Place the raw rubber dried in step 7 on a flat vulcanizer, and hot-press vulcanize it at a pressure of 5 MPa and a temperature of 143° C. for 10 min to obtain a natural rubber film.

[0026] Example 2 This example gives an example of a method for preparing natural rubber.

[0027] The raw material ratio of this embodiment is as follows: 100 parts of natural rubber latex; 2.5 parts of sulfur; 5 parts of zinc oxide; 1.5 parts of accelerator M; 3 parts of stearic acid; 0.1 parts of potassium hydroxide; 0.1 parts of diffusing agent NF; and 0.8 parts of casein.

[0028] The steps include: Step 1, weighing natural rubber latex and preparing it into a latex solution with a concentration of 60%, and then removing ammonia from the natural rubber latex by formaldehyde method; Step 2, adding casein, diffusant NF and potassium hydroxide into water to prepare a solution with a concentration of 10-20%; Step 3, the casein, diffusant NF, potassium hydroxide solution obtained in step 2 are placed in a ball mill together with sulfur, zinc oxide, accelerator M and stearic acid, the grinding time is 3h, the ball mill speed is 1500rpm, and a dispersion is obtained; Step 4, adding the dispersion ground in step 3 to the natural rubber latex after ammonia removal treatment, stirring evenly and aging at room temperature for 2 to 6 hours to obtain a pretreated natural latex; Step 5, pouring the pretreated natural latex obtained in step 4 into a mold, first uniformly freezing and forming in a -24°C cold box, and then continuing to uniformly freeze for 24 hours to obtain frozen natural rubber; Step 6, thawing the natural rubber frozen in step 5 at room temperature, and then pre-pressing to remove moisture for multiple times, with a pre-pressing pressure of 1 MPa and a pre-pressing time of 5 minutes; Step 7, subjecting the natural rubber pre-pressed in step 6 to air drying at a drying temperature of 50° C. for a drying time of 8 hours; Step 8: Place the raw rubber dried in step 7 on a flat vulcanizer, and hot-press vulcanize it at a pressure of 5 MPa and a temperature of 143° C. for 10 minutes to obtain a natural rubber film.

[0029] Example 3 This example gives an example of a method for preparing natural rubber.

[0030] The raw material ratio of this embodiment is as follows: 100 parts of natural rubber latex; 2.5 parts of sulfur; 7 parts of zinc oxide; 1.5 parts of accelerator M; 3 parts of stearic acid; 0.1 parts of potassium hydroxide; 0.1 parts of diffusing agent NF; and 0.8 parts of casein.

[0031] The steps include: Step 1, weighing natural rubber latex and preparing it into a latex solution with a concentration of 60%, and then removing ammonia from the natural rubber latex by formaldehyde method; Step 2: Add casein, diffusant NF and potassium hydroxide into water to prepare a solution with a concentration of 10-20%.

[0032] Step 3, the casein, diffusant NF, potassium hydroxide solution obtained in step 2 are placed in a ball mill together with sulfur, zinc oxide, accelerator M and stearic acid, the grinding time is 3h, the ball mill speed is 1500rpm, and a dispersion is obtained; Step 4, adding the dispersion ground in step 3 to the natural rubber latex after ammonia removal treatment, stirring evenly and aging at room temperature for 2 to 6 hours to obtain a pretreated natural latex; Step 5, pouring the pretreated natural latex obtained in step 4 into a mold, first uniformly freezing and forming in a -24°C cold box, and then continuing to uniformly freeze for 24 hours to obtain frozen natural rubber; Step 6: Thaw the natural rubber frozen in step 5 at room temperature, and then pre-press it several times to remove moisture. The pre-pressing pressure is 1 MPa and the pre-pressing time is 5 minutes.

[0033] Step 7: subjecting the natural rubber pre-pressed in step 6 to air drying at a drying temperature of 50° C. for 8 hours.

[0034] Step 8: Place the raw rubber dried in step 7 on a flat vulcanizer, and hot-press vulcanize it at a pressure of 5 MPa and a temperature of 143° C. for 10 minutes to obtain a natural rubber film.

[0035] Example 4 This example gives an example of a method for preparing natural rubber.

[0036] The raw material ratio of the natural rubber film in this embodiment is as follows: natural latex: 100 parts; sulfur: 2 parts; zinc oxide: 3 parts; accelerator M: 1 part; stearic acid: 2.5 parts; sulfur zinc oxide diffuser NF: 0.1 part; potassium hydroxide: 0.1 part; casein: 0.8 part.

[0037] The steps include: Step 1, weighing natural rubber latex and preparing it into a latex solution with a concentration of 60%, and then removing ammonia from the natural rubber latex by formaldehyde method; Step 2, adding casein, diffusant NF and potassium hydroxide into water to prepare a solution with a concentration of 10-20%; Step 3, the casein, diffusant NF, potassium hydroxide solution obtained in step 2 are placed in a ball mill together with sulfur, zinc oxide, accelerator M and stearic acid, the grinding time is 3h, the ball mill speed is 1500rpm, and a dispersion is obtained; Step 4, adding the dispersion ground in step 3 to the natural rubber latex after ammonia removal treatment, stirring evenly and aging at room temperature for 2 to 6 hours to obtain a pretreated natural latex; Step 5, pouring the pretreated natural latex obtained in step 4 into a mold, first uniformly freezing and forming in a -24°C cold box, and then continuing to uniformly freeze for 24 hours to obtain frozen natural rubber; Step 6, thawing the natural rubber frozen in step 5 at room temperature, and then pre-pressing it several times to remove moisture, the pre-pressing pressure is 1 MPa, and the pre-pressing time is 5 minutes; Step 7: subjecting the natural rubber pre-pressed in step 6 to air drying at a drying temperature of 50° C. for 8 hours.

[0038] Step 8: Place the raw rubber dried in step 7 on a flat vulcanizer, and hot-press vulcanize it at a pressure of 5 MPa and a temperature of 143° C. for 10 minutes to obtain a natural rubber film.

[0039] Example 5 The raw material ratio of this embodiment is the same as that of embodiment 4, but the amount of sulfur is changed to 3 parts. The remaining steps are the same as those of embodiment 4.

[0040] Example 6 The raw material ratio of the embodiment is the same as that of the embodiment 4, but the amount of the accelerator M is changed to 3 parts, and the amount of sulfur is changed to 1 part. The remaining steps are the same as those of the embodiment 4.

[0041] Example 7 This example shows an example of preparing a natural rubber film using heat coagulation instead of freeze coagulation molding.

[0042] The raw material ratio of the embodiment of this embodiment is the same as that of embodiment 4. Implementation steps include: Step 1, weighing natural rubber latex and preparing it into a latex solution with a concentration of 60%, and then removing ammonia from the natural rubber latex by formaldehyde method; Step 2, adding casein, diffusant NF and potassium hydroxide into water to prepare a solution with a concentration of 10-20%; Step 3, the casein, diffusant NF, potassium hydroxide solution obtained in step 2 are placed in a ball mill together with sulfur, zinc oxide, accelerator M and stearic acid, the grinding time is 3h, the ball mill speed is 1500rpm, and a dispersion is obtained; Step 4, adding the dispersion ground in step 3 to the natural rubber latex after ammonia removal treatment, stirring evenly and aging at room temperature for 2 to 6 hours to obtain a pretreated natural latex; Step 5: Pour the pretreated natural rubber latex obtained in step 4 into a mold, first dry it in a 40° C. forced air drying oven for 48 hours, then adjust the temperature to 120° C. and dry it for 3 hours to obtain a vulcanized natural rubber film.

[0043] Example 8 The raw material ratio of the embodiment is the same as that of embodiment 4, but the uniform freezing temperature of step 5 is -10°C.

[0044] Example 9 The raw material ratio of the embodiment is the same as that of embodiment 4, but the uniform freezing temperature of step 5 is -15°C.

[0045] Example 10 The raw material ratio of the embodiment is the same as that of embodiment 4, but the uniform freezing temperature of step 5 is -20°C.

[0046] Comparative Example 1 The difference from Example 4 is that the raw materials do not contain sulfur, and the specific raw material ratio is: 100 parts of natural rubber latex; 3 parts of zinc oxide; 0.1 parts of potassium hydroxide; 0.1 parts of diffusing agent NF; 0.8 parts of casein.

[0047] The other steps are the same.

[0048] Comparative Example 2 The difference from Example 4 is that the raw materials do not contain sulfur, and the specific raw material ratio is: 100 parts of natural rubber latex; 4 parts of zinc oxide; 0.1 parts of potassium hydroxide; 0.1 parts of diffusing agent NF; 0.8 parts of casein.

[0049] The other steps are the same.

[0050] Comparative Example 3 The difference from Example 4 is that the raw materials do not contain sulfur, and the specific raw material ratio is: 100 parts of natural rubber latex; 5 parts of zinc oxide; 0.1 parts of potassium hydroxide; 0.1 parts of diffusing agent NF; 0.8 parts of casein.

[0051] The other steps are the same.

[0052] Embodiment 11 This embodiment provides an example of improving the properties of natural rubber by regulating the freezing process (directional freezing).

[0053] The raw material ratio of this embodiment is the same as that of embodiment 1.

[0054] Implementation steps include: Step 1 to step 4 are the same as in Example 1.

[0055] The difference is that in step 5, the matured natural latex is poured into the mold and first directionally frozen on a unidirectional cold source at -40°C for 1 hour (the unidirectional cold source contacts any side of the mold, such as the bottom or side, from top to bottom or from left to right or vice versa, for unidirectional freezing. For example, the mold containing the latex is placed on a cold table, and the cold source of the cold table only contacts the bottom, and is frozen from bottom to top), and then placed in a cold box and evenly frozen at -24°C for 24 hours.

[0056] Step 6 to step 8 are the same as in Example 1.

[0057] Example 12 This embodiment provides an example of improving the properties of natural rubber by regulating the freezing process (directional freezing).

[0058] The raw material ratio of this embodiment is the same as that of embodiment 1.

[0059] Implementation steps include: Step 1 to step 4 are the same as in Example 1.

[0060] The difference is that in step 5, the matured natural latex is poured into the mold and first directionally frozen on a unidirectional cold source at -50°C for 1 hour (the unidirectional cold source contacts any side of the mold, such as the bottom or side, from top to bottom or from left to right or vice versa, for unidirectional freezing. For example, the mold containing the latex is placed on a cold table, and the cold source of the cold table only contacts the bottom, and is frozen from bottom to top), and then placed in a cold box and evenly frozen at -24°C for 24 hours.

[0061] Step 6 to step 8 are the same as in Example 1.

[0062] Example 13 This embodiment provides an example of improving the properties of natural rubber by regulating the freezing process (directional freezing).

[0063] The raw material ratio of this embodiment is the same as that of embodiment 1.

[0064] Implementation steps include: Step 1 to step 4 are the same as in Example 1.

[0065] The difference is that in step 5, the matured natural latex is poured into the mold and first directionally frozen on a one-way cold source at -60°C for 1 hour (the one-way cold source contacts any side of the mold, such as the bottom or side, from top to bottom or from left to right or vice versa, for one-way direction freezing. For example, the mold containing the latex is placed on a cold table, and the cold source of the cold table only contacts the bottom, and is frozen from bottom to top), and then placed in a cold box and evenly frozen at -24°C for 24 hours.

[0066] Step 6 to step 8 are the same as in Example 1.

[0067] Effect comparison The mechanical properties of the natural rubber film products of the embodiment and the comparative example were measured. The product thickness was 2 mm. According to GB / T529-2008, the tensile properties of the natural rubber film were measured using a dumbbell-shaped tensile sample on an electronic tensile testing machine (Guanteng W05). The results are shown in Table 1 below: Table 1 Performance test of each embodiment product It can be seen from the above embodiments and comparative examples and Table 1 that: 1. In Examples 4 to 6, the natural rubber films prepared by low-temperature freezing technology have excellent tensile strength and elongation at break. Compared with the sample formed by hot baking and coagulation in Example 7, the strength is increased by 134.17% and the elongation at break is increased by 38.70%. This shows that the natural rubber film prepared by the present invention has the advantages of low material cost, high strength, high elongation at break, etc., and the preparation method is simple, the raw material source is abundant and renewable, and the cost is low.

[0068] 2. The freezing temperatures of Examples 8 to 10 are -10°C, -15°C, and -20°C, respectively. It can be seen that as the freezing temperature decreases from -10°C to -20°C, the tensile properties are significantly improved (21.22 MPa, 22.57 MPa, and 25.24 MPa, respectively), and the elongation at break also increases.

[0069] 3. No sulfur was added to the raw materials of Comparative Examples 1 to 3, and no cross-linking reaction occurred. The tensile strengths were extremely low (2.25 MPa, 1.60 MPa, and 2.97 MPa, respectively). Although the elongation at break was high, the overall mechanical properties of the products were poor.

[0070] 4. Embodiments 11, 12, and 13 adopt a directional freezing process, first directional freezing for 1 hour on a unidirectional cold source at a relatively low temperature (-40°C, -50°C, -60°C), and then uniformly freezing for 24 hours at -24°C. Compared with the embodiment without the directional freezing process, the tensile strength (respectively 29.05MPa, 30.04MPa, 31.40MPa) and elongation at break (respectively 1762.73%, 1885.10%, 1802.52%) are significantly improved, indicating that directional freezing has a significant improvement on the performance of rubber, and the maximum strength can be 31.40 MPa, which has exceeded the highest strength of 29.04 MPa published by natural rubber at present. This shows that the rubber film prepared by the process of improving the performance of natural rubber by regulating the freezing process (directional freezing) of the present invention has the advantages of low material cost, high strength and high elongation at break, and the preparation method is simple, low cost, and can be promoted on a large scale.

[0071] 5. In Examples 1 to 3, only the zinc oxide content was changed (3 parts, 5 parts, and 7 parts, respectively). As the zinc oxide content increased, the tensile properties decreased from 26.04 MPa to 23.25 MPa, the elongation at break first increased and then decreased, and the density increased from 0.96 g / cm³ to 1.02 g / cm³, indicating that the increase in the amount of zinc oxide will reduce the tensile strength of the rubber film and affect the density.

[0072] 6. In Examples 4 to 6, the amount of sulfur increased from 2 parts to 3 parts (Example 5), and the tensile properties increased from 20.94 MPa to 23.77 MPa; the accelerator M increased from 1 part to 3 parts (Example 6), and the tensile properties increased to 26.04 MPa, but the elongation at break decreased, indicating that changes in the amount of sulfur and accelerator M affect the tensile properties and elongation at break of natural rubber.

[0073] in addition, Figure 1 This is an electron microscope image (1000 times) of the natural rubber film prepared by freeze solidification molding (non-directional freezing) in Example 1; Figure 2 This is an electron microscope image (1000 times) of the natural rubber film prepared by freeze solidification molding (directional freezing) in Example 11 Figure 3 This is an electron microscope image (5000 times) of the natural rubber film prepared by freeze-solidification molding (directional freezing) in Example 11.

[0074] By comparison, it can be seen that the natural rubber film produced by directional freezing has an orderly arrangement, which can effectively improve the tensile strength, tear strength, impact strength and other properties of natural rubber.

[0075] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and the embodiments. They can be applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily realized.

Claims

1. A method for preparing high-performance natural rubber, characterized in that: include: According to the weight of the components: 100 parts of natural rubber latex, 1-10 parts of zinc oxide, 0.2-4 parts of sulfur, 0.5-4 parts of accelerator M, 0.5-8 parts of stearic acid, 5-30 parts of water, 0.02-0.5 parts of diffusant NF, 0.02-0.5 parts of potassium hydroxide, and 0.2-4 parts of casein; Step 1, weighing natural rubber latex to prepare a solution of a certain concentration, and removing ammonia from the natural rubber latex by formaldehyde method; Step 2, adding casein, diffusant NF and potassium hydroxide into water to prepare a solution with a concentration of 10-20%; Step 3, placing zinc oxide, sulfur, accelerator M, stearic acid, casein solution, diffusant NF solution, and potassium hydroxide solution in a ball mill for grinding, the ball mill speed is 800-4000 rpm, the ball milling time is 2-72 h, to obtain a dispersion; Step 4, adding the dispersion to the natural rubber latex after ammonia removal treatment, stirring for a certain period of time and then aging at room temperature for 2 to 6 hours at a stirring speed of 100 to 300 rpm to obtain a pretreated natural latex; Step 5, pouring the natural latex obtained in step 4 into a mold, freezing it on a low-temperature cold source for 1 to 24 hours to obtain frozen and solidified natural latex, the freezing temperature being -20°C to -80°C; Step 6, thawing the frozen natural rubber obtained in step 5 at room temperature, and pre-pressing at a pressure of 1-5 MPa for 1-5 minutes after thawing; Step 7, drying the pre-pressed natural rubber obtained in step 6 in a forced air drying oven at 20-80° C. for 3-50 h; Step 8: placing the natural rubber obtained in step 7 on a vulcanizer for hot pressing and vulcanization to obtain a natural rubber film, the vulcanization pressure is 5-15 MPa, the hot pressing temperature is 120-145° C., and the hot pressing time is 10-30 min.

2. The method for preparing a high-performance natural rubber according to claim 1, characterized in that: In the preparation process of natural rubber, a cold source is first applied in a specific direction of the natural latex, and the growth of ice crystals during the freezing process is used to promote the aggregation and arrangement of the rubber particles to achieve the freeze-forming of the natural latex. After forming, it is further frozen to complete the coagulation and fixing of the natural latex. Finally, thawing, drying, pre-pressing and vulcanization are used to obtain high-performance natural rubber.

3. A method for preparing a high-performance natural rubber as claimed in claim 1 or 2, characterized in that: The freezing technology is one of one-way freezing, two-way freezing and homogeneous freezing, and the cold source temperature used for freezing is -20°C to -80°C.

4. A method for preparing a high-performance natural rubber as claimed in claim 1 or 2, characterized in that: After the frozen natural latex is thawed naturally, some of the moisture is removed by multiple pre-pressing, and then it is air-dried at ≤80°C, freeze-dried or naturally dried.

5. A method for preparing a high-performance natural rubber as claimed in claim 1 or 2, characterized in that: The concentration of the natural rubber latex is 20-65%.

6. A method for preparing a high-performance natural rubber as claimed in claim 1 or 2, characterized in that: Other vulcanization aids include any one or more of activators, accelerators, dispersants, sulfur, potassium hydroxide, and casein.

7. The method for preparing a high-performance natural rubber according to claim 5, characterized in that: The active agent is stearic acid, and the accelerator is one or both of accelerator M and accelerator DZ.

8. A high-performance natural rubber obtained by the preparation method according to claim 1 or 2.

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