Natural rubber product with low zinc oxide content as well as preparation method and application of natural rubber product

Abstract

The invention relates to a natural rubber product with low zinc oxide content and a preparation method and application thereof, and belongs to the technical field of natural rubber materials. The preparation method of the natural rubber product with the low zinc oxide content comprises the following steps: (1) adding an activating agent into the purified natural latex, fully stirring and uniformly mixing to obtain a raw natural rubber product with the low zinc oxide content; (2) mixing the raw natural rubber product with low zinc oxide content, stearic acid, zinc oxide, an accelerant and sulfur in an open mill to obtain a rubber compound sample; and (3) vulcanizing the rubber compound sample to obtain the natural rubber product with low zinc oxide content. Soybean protein or lecithin is introduced as a novel activator, and specific groups in the soybean protein or lecithin are coordinated with zinc ions to form an active complex, so that the utilization rate of zinc oxide is increased, zinc oxide directly participates in the vulcanization reaction process, and 60% of zinc oxide is replaced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural rubber materials, in particular to a natural rubber product with low content of zinc oxide and a preparation method and application thereof. BACKGROUND

[0002] Natural rubber is a natural polymer material biosynthesized by Hevea brasiliensis, and its main component is cis-1,4-polyisoprene, and contains a small amount of non-rubber substances such as proteins and phospholipids.

[0003] Natural rubber has become an indispensable material in the application fields of automobile tires, aircraft tires, high-speed train bearings, shock absorbers, seals, etc. due to its excellent comprehensive performance. The wide application of natural rubber products is largely due to its key vulcanization cross-linking reaction.

[0004] In order to improve the processability and mechanical properties of natural rubber, vulcanization aids such as activators, accelerators, and vulcanizing agents need to be added during the mixing process of natural rubber. Among them, zinc oxide is considered to be the most effective activator and is the most widely used activator in the production of natural rubber industry. Zinc oxide not only promotes the vulcanization of natural rubber and improves the cross-linking density, but also improves the aging resistance of rubber. Therefore, a large amount of zinc oxide is needed in the processing and production of rubber products. However, the large amount of zinc oxide used will have a long-term adverse effect on the environment, causing environmental pollution, especially the toxic effect of zinc oxide on aquatic organisms, which endangers the survival of aquatic organisms. Under the drive of economic sustainable development, it is necessary to reduce or partially replace the amount of zinc oxide in rubber composites.

[0005] Currently, the following technical solutions are mainly used to reduce or partially replace the amount of zinc oxide: using other metal compounds to replace zinc oxide, such as magnesium oxide. However, the vulcanization activity of magnesium oxide is significantly lower than that of zinc oxide, which affects efficiency and performance and increases energy consumption in the production process. Nano-zinc oxide particles are used to replace zinc oxide. However, nano-particles have a small size and a large specific surface area, and they stay in the air for a long time, are easily inhaled into the respiratory tract, and pose a direct threat to the health of living organisms, which may cause greater harm. Organic zinc salts are used to replace zinc oxide, but organic zinc salts are prone to decomposition or volatilization, and the volatile organic compounds (VOCs) generated by decomposition may also pose new environmental and safety problems.

[0006] Therefore, it is urgent to develop a natural rubber product that can reduce the amount of zinc oxide while maintaining excellent mechanical properties, so as to achieve the goal of energy saving and emission reduction and green production. SUMMARY

[0007] Therefore, the application provides a natural rubber product with low content of zinc oxide and a preparation method and application thereof. By introducing soybean protein or lecithin as a new activator, specific groups in the soybean protein or lecithin are coordinated with zinc ions to form active complexes, which not only improves the utilization rate of zinc oxide but also directly participates in the vulcanization reaction process to maintain a high vulcanization rate. By using soybean protein or lecithin, 60% of zinc oxide is replaced, and the natural rubber product still maintains excellent mechanical properties. The application constructs a green and efficient new vulcanization system for natural rubber, which provides an industrialized feasible solution for solving the problem of zinc pollution and simultaneously ensuring the mechanical properties, and can effectively overcome the defects of the prior art.

[0008] The first aspect of the application provides a natural rubber product with low content of zinc oxide, which comprises the following raw materials in mass fraction: 100 parts of purified natural latex, 0.4-3 parts of an activator, 0.5-1 part of stearic acid, 2-5 parts of zinc oxide, 0.5-1 part of an accelerator, and 1-4 parts of sulfur.

[0009] Preferably, the activator is lecithin or soybean protein.

[0010] The second aspect of the application further provides a preparation method of the above-mentioned natural rubber product with low content of zinc oxide, which comprises the following steps:

[0011] (1) adding an activator to the purified natural latex, fully stirring, and uniformly mixing to obtain a natural rubber green product with low content of zinc oxide;

[0012] (2) mixing the natural rubber green product with low content of zinc oxide, stearic acid, zinc oxide, an accelerator, and sulfur on an open mill to obtain a rubber sample;

[0013] (3) vulcanizing the rubber sample to obtain the natural rubber product with low content of zinc oxide.

[0014] Preferably, in step (1), the preparation process of the purified natural latex is as follows: sodium dodecyl sulfate is added to natural latex diluted to 25-30%, fully stirred, and uniformly mixed, and then high-speed frozen centrifugation is performed in a high-speed frozen centrifuge to obtain centrifugally separated natural latex; the uppermost cream part is taken, diluted, and subjected to the above-mentioned operation again, and then centrifuged again to obtain purified natural latex free of non-rubber components.

[0015] Preferably, the temperature of the high-speed frozen centrifugation is 3-10℃, the rotation speed is 10000-15000 rpm, and the time is 48-72 min.

[0016] Preferably, the mass fraction of the sodium dodecyl sulfate is 0.2-0.8%.

[0017] Preferably, the specific process of step (1) is: adding soybean protein or lecithin into the purified natural latex, stirring for 20-60 min at room temperature, mixing uniformly, and drying into a film at room temperature until reaching a constant weight to obtain a low-zinc oxide natural rubber raw product.

[0018] Preferably, in step (2), the mixing is performed at room temperature.

[0019] Preferably, in step (3), the temperature of the vulcanization is 140-150℃, and the time of the vulcanization is t 90 .

[0020] The third aspect of the present application also provides an application of the above-mentioned low-zinc oxide natural rubber product in the fields of automobile tires, airplane tires, high-speed train bearings, shock absorbers, and sealing elements.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] The present application chooses to add soybean protein or lecithin as a new type of activator to achieve the purpose of partially replacing zinc oxide and reducing the amount of zinc oxide used; a small amount of non-rubber substances naturally present in natural rubber has been proven to effectively promote vulcanization, increase crosslinking density, and enhance mechanical properties, and these effects make it have the potential to become a new type of high-efficiency activator or accelerator; the small amount of non-rubber substances mainly includes proteins, phospholipids, etc., therefore, in order to study the effect of non-rubber substances as a new type of high-efficiency activator partially replacing zinc oxide, soybean protein and lecithin are added to the purified natural latex as a simulation of proteins and phospholipids; in the vulcanization process of natural rubber, specific groups in soybean protein or lecithin are easy to combine with zinc ions Zn 2+ released by zinc oxide to form a complex, and the formed complex can participate in the vulcanization reaction to effectively promote the generation of crosslinking precursors. Therefore, even in the case of reducing the amount of zinc oxide (replacing 60% of zinc oxide), the system can still achieve an efficient vulcanization process, ensuring that the rubber product maintains excellent mechanical properties, which builds a new vulcanization system that is more environmentally friendly (reduces zinc emissions) and provides an important scientific basis and technical approach for developing low-zinc oxide high-performance natural rubber products. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions, and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application.

[0024] The experimental methods used in the embodiments of the present application are conventional methods unless otherwise specified.

[0025] In the following examples, all raw materials can be obtained by commercial purchase or conventional methods unless otherwise specified.

[0026] Example 1

[0027] The low-zinc oxide content natural rubber product of the present embodiment comprises the following raw materials in mass fraction: 100 parts of purified natural latex, 3 parts of soybean protein, 0.5 parts of stearic acid, 5 parts of zinc oxide, 0.7 parts of accelerator, and 3 parts of sulfur.

[0028] The method for preparing the low-zinc oxide content natural rubber product of the present embodiment comprises the following steps:

[0029] (1) Add 0.5% of sodium dodecyl sulfate in mass fraction to the natural latex diluted to 30%, and mix well by stirring. Then, put it into a high-speed refrigerated centrifuge for high-speed refrigerated centrifugation. The temperature of the high-speed refrigerated centrifugation is 4℃, the rotation speed is 12000 rpm, and the time is 60 min. The centrifuged natural latex is obtained. Take the uppermost cream part, dilute it, and repeat the above operation for centrifugation again to obtain purified natural latex without non-rubber components;

[0030] (2) Add soybean protein or lecithin to the purified natural latex, and mix well by stirring at room temperature for 30 min. Dry it into a film at room temperature until a constant weight is reached to obtain a low-zinc oxide content natural rubber raw product;

[0031] (3) Mix the low-zinc oxide content natural rubber raw product, stearic acid, zinc oxide, accelerator M (2-mercaptobenzothiazole), and sulfur on an open mill at room temperature. The temperature of the vulcanization is 145℃, and the time of the vulcanization is t 90 , to obtain a rubber compound sample;

[0032] (4) Vulcanize the rubber compound sample to obtain a low-zinc oxide content natural rubber product.

[0033] Example 2

[0034] The natural rubber product and the method for preparing the same provided in the present embodiment can refer to Example 1, except that the low-zinc oxide content natural rubber product of the present embodiment comprises the following raw materials in mass fraction: 100 parts of purified natural latex, 3 parts of soybean protein, 0.5 parts of stearic acid, 4 parts of zinc oxide, 0.7 parts of accelerator, and 3 parts of sulfur.

[0035] Example 3

[0036] The natural rubber product and the preparation method thereof provided in the embodiment can refer to the embodiment 1, and the difference is that the natural rubber product with low content of zinc oxide in the embodiment comprises the following raw materials in mass fraction: purified natural latex 100 parts, soybean protein 3 parts, stearic acid 0.5 part, zinc oxide 3 parts, accelerator 0.7 part, and sulfur 3 parts.

[0037] Embodiment 4

[0038] The natural rubber product and the preparation method thereof provided in the embodiment can refer to the embodiment 1, and the difference is that the natural rubber product with low content of zinc oxide in the embodiment comprises the following raw materials in mass fraction: purified natural latex 100 parts, soybean protein 3 parts, stearic acid 0.5 part, zinc oxide 2 parts, accelerator 0.7 part, and sulfur 3 parts.

[0039] Embodiment 5

[0040] The natural rubber product and the preparation method thereof provided in the embodiment can refer to the embodiment 1, and the difference is that the natural rubber product with low content of zinc oxide in the embodiment comprises the following raw materials in mass fraction: purified natural latex 100 parts, lecithin 1.2 parts, stearic acid 0.5 part, zinc oxide 5 parts, accelerator 0.7 part, and sulfur 3 parts.

[0041] Embodiment 6

[0042] The natural rubber product and the preparation method thereof provided in the embodiment can refer to the embodiment 1, and the difference is that the natural rubber product with low content of zinc oxide in the embodiment comprises the following raw materials in mass fraction: purified natural latex 100 parts, lecithin 1.2 parts, stearic acid 0.5 part, zinc oxide 4 parts, accelerator 0.7 part, and sulfur 3 parts.

[0043] Embodiment 7

[0044] The natural rubber product and the preparation method thereof provided in the embodiment can refer to the embodiment 1, and the difference is that the natural rubber product with low content of zinc oxide in the embodiment comprises the following raw materials in mass fraction: purified natural latex 100 parts, lecithin 1.2 parts, stearic acid 0.5 part, zinc oxide 3 parts, accelerator 0.7 part, and sulfur 3 parts.

[0045] Embodiment 8

[0046] The natural rubber product and the preparation method thereof provided in the embodiment can refer to the embodiment 1, and the difference is that the natural rubber product with low content of zinc oxide in the embodiment comprises the following raw materials in mass fraction: purified natural latex 100 parts, lecithin 1.2 parts, stearic acid 0.5 part, zinc oxide 2 parts, accelerator 0.7 part, and sulfur 3 parts.

[0047] Comparative Example 1

[0048] The natural rubber product and the preparation method thereof provided by the present comparative example can refer to Example 1, and the difference is that the natural rubber product of the present comparative example comprises the following raw materials in mass parts: purified natural latex 100 parts, stearic acid 0.5 parts, zinc oxide 5 parts, accelerator 0.7 parts, and sulfur 3 parts.

[0049] The formulations of Examples 1-8 and Comparative Example 1 are shown in Table 1, and each raw material is in parts by weight.

[0050] Table 1

[0051]

[0052]

[0053] Test Example

[0054] In the present application, the vulcanization characteristics of the above-mentioned rubber compound are tested according to the Chinese national standard GB / T 16584-1996. Among them, t 10 is the scorch time, t 90 is the optimum vulcanization time, M L is the minimum torque value, M H is the maximum torque value.

[0055] In the present application, the above-mentioned vulcanized rubber sample is tested for tensile stress-strain performance according to the Chinese national standard GB / T 528-2009.

[0056] The test results of the vulcanization characteristics and stress-strain curves of Examples 1-4 are shown in Table 2.

[0057] Table 2

[0058]

[0059] The test results of the vulcanization characteristics and stress-strain curves of Examples 5-8 are shown in Table 3.

[0060] Table 3

[0061]

[0062]

[0063] The test results of the vulcanization characteristics and stress-strain curves of Comparative Example 1 are as follows, t 10 is 168 s, t 90 is 845 s, M L is 0.134 dN·m, M H is 2.047 dN·m, the tensile strength is 5.50 MPa, the elongation at break is 946.5%, and the 300% modulus is 0.44 MPa.

[0064] According to the test results of the vulcanization characteristics and stress-strain curves of the above-mentioned examples and the comparative examples, it is concluded that, with 3 parts of soybean protein or 1.2 parts of lecithin as a new activator partially replacing zinc oxide, the results show that, with the decrease of the amount of zinc oxide, t 10 and t 90 almost remain unchanged, slightly decrease; the tensile strength slightly increases, and the elongation at break and the modulus at 300% almost remain unchanged.

[0065] According to the above results, the following conclusions are obtained: the soybean protein and lecithin as a new activator can not only maintain high efficient vulcanization effect, but also guarantee excellent mechanical properties, thereby significantly reducing the amount of zinc oxide and replacing 60% of zinc oxide.

[0066] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that: they can still modify the technical solutions recorded in the above examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the examples of the present application.

Claims

1. A natural rubber product with low zinc oxide content, characterized in that: The invention comprises the following raw materials in parts by mass: 100 parts of purified natural rubber latex, 0.4-3 parts of activator, 0.5-1 parts of stearic acid, 2-5 parts of zinc oxide, 0.5-1 parts of accelerator and 1-4 parts of sulfur.

2. The natural rubber product with low zinc oxide content according to claim 1, characterized in that: The activator is lecithin or soy protein.

3. A method for preparing a natural rubber product with low zinc oxide content according to claim 1 or 2, characterized in that: The following steps are involved: (1) adding an activator to the purified natural rubber latex, stirring and mixing the mixture thoroughly to obtain a natural rubber product with a low zinc oxide content; (2) mixing the low-zinc oxide content natural rubber product, stearic acid, zinc oxide, an accelerator, and sulfur on an open mill to obtain a mixed rubber sample; (3) vulcanizing the rubber mix to obtain a natural rubber product with a low zinc oxide content.

4. The method for preparing a natural rubber product with low zinc oxide content according to claim 3, wherein: In step (1), the preparation process of the purified natural rubber latex is as follows: sodium lauryl sulfate is added to the natural rubber latex diluted to 25-30%, the mixture is fully stirred and evenly mixed, and then the mixture is placed in a high-speed refrigerated centrifuge for high-speed refrigerated centrifugation to obtain centrifugally layered natural rubber latex; the cream portion of the top layer is taken, the above operation is repeated after dilution, and the mixture is centrifuged again to obtain purified natural rubber latex free of non-rubber components.

5. The method for preparing a natural rubber product with low zinc oxide content according to claim 4, wherein: The temperature of the high-speed refrigerated centrifugation is 3-10° C., the rotation speed is 10,000-15,000 rpm, and the time is 48-72 min.

6. The method for preparing a natural rubber product with low zinc oxide content according to claim 4, characterized in that: The mass fraction of the sodium lauryl sulfate is 0.2-0.8%.

7. The method for preparing a natural rubber product with low zinc oxide content according to claim 3, wherein: The specific process of step (1) is: adding soybean protein or lecithin to the purified natural latex, stirring at room temperature for 20-60 minutes, mixing evenly, and spreading to form a film at room temperature until a constant weight is reached to obtain a low-zinc oxide content natural rubber raw rubber product.

8. The method for preparing a natural rubber product with low zinc oxide content according to claim 3, wherein: In step (2), the mixing is carried out at room temperature.

9. The method for preparing a natural rubber product with low zinc oxide content according to claim 3, wherein: In step (3), the vulcanization temperature is 140-150°C and the vulcanization time is t 90 .

10. Use of the natural rubber product with low zinc oxide content according to claim 1 or 2 in the fields of automobile tires, aircraft tires, high-speed train bearings, shock absorbers and seals.

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