Method for improving the thermal aging performance and compression fatigue performance of low-protein natural rubber

Abstract

The application belongs to the field of natural rubber manufacturing, and particularly relates to a method for improving the thermal oxygen aging performance and compression fatigue performance of low-protein natural rubber. The method uses fresh latex as raw material, adds an anionic surfactant, a long-carbon-chain alkyl phenol polyoxyethylene ether surfactant and an alkaline protease to perform deproteinization treatment on the latex to obtain the low-protein natural rubber. The low-protein natural rubber has excellent thermal oxygen aging performance and a lower compression flexing temperature rise.

Description

Technical Field

[0001] This invention belongs to the field of natural rubber manufacturing, and specifically relates to a method for improving the thermo-oxidative aging properties and compression fatigue properties of low-protein natural rubber. Background Technology

[0002] Natural rubber (NR) is a high-performance natural polymer biosynthesized from the Brazilian rubber tree (Hevea brasiliensis). It possesses excellent comprehensive properties and is widely used in everyday life, medical and health care, transportation, national defense, and aerospace, among other cutting-edge technology fields. Natural rubber consists of rubber hydrocarbons and non-rubber components, with protein being the main non-rubber component. Fresh natural latex contains approximately 1%–2% protein. Studies have shown that reducing protein content can not only reduce contact allergies but also decrease the hygroscopicity, electrical conductivity, and internal heat generation of the products, thereby expanding its applications in tires, electrical engineering, medical applications, and other specialized fields.

[0003] Methods for deproteinizing natural rubber mainly include protease treatment, urea denaturation, multiple centrifugation, and leaching. (Gao Tianming et al.) [1] Using concentrated natural latex as raw material, alkaline protease and the surfactant sodium dodecyl sulfate (SDS) were added. The mixture was cured at room temperature for 24 hours, then coagulated with acetic acid. The wet gel sheets were soaked in water and filtered for 3 days. Finally, the sheets were pressed, dehydrated, granulated, and dried to prepare low-protein natural rubber (LPNR). The nitrogen content was only 0.094%, lower than that of acid-coagulated NR (nitrogen content 0.214%). Compared with centrifugal deproteinization, leaching retained more protein hydrolysis products. These products accelerate vulcanization and promote cross-linking, resulting in faster vulcanization of LPNR and higher cross-linking density and tensile strength compared to acid-coagulated NR. Simultaneously, deproteinization of NR reduced the internal heat of the material, decreasing the internal heat of the vulcanized rubber from 21.15℃ to 14.63℃. However, this study did not report the thermo-oxidative aging properties of the vulcanized rubber. (Zhang Guimei et al.) [2] Using fresh natural latex as raw material, low-protein natural rubber (LPNR) was prepared by coagulating the fresh latex with papain. The latex pH value was 7.0-8.5, and the amount of papain used was 0.10%-0.12%. Under this process, the nitrogen content of the prepared LPNR was 0.17%-0.18%, which is much lower than that of acid-coagulated NR (nitrogen content 0.40%). The LPNR vulcanizates prepared by this process showed better tensile stress, tensile strength, thermo-oxidative aging properties, and resistance to compression heat generation than acid-coagulated natural rubber. (Huang Honghai et al.) [3]Using fresh natural latex as raw material, SDS and protease are added and reacted for a certain period of time. After centrifugation, the solidified sheets are dried at low temperature to obtain LPNR with a nitrogen content of 0.06%-0.5%. The deproteinization treatment can reduce the compression flexural temperature rise of the vulcanizate from 16.2℃ to 12.8℃, but its thermo-oxidative aging performance decreases. Summary of the Invention

[0004] The first technical problem to be solved by the present invention is to provide a method for improving the thermo-oxidative aging properties and compression fatigue properties of low-protein natural rubber. The method includes the following steps: using fresh latex as raw material, adding anionic surfactant, long-chain hydrocarbon phenol polyoxyethylene ether surfactant and alkaline protease to deproteinize the latex until the nitrogen content is 0.12-0.17 wt% (relative to the mass of NR dry rubber), and then performing post-treatment to obtain the low-protein natural rubber.

[0005] Preferably, the above method includes the following steps: diluting fresh latex with water, adjusting the pH to 8.0-8.5 with alkali, adding anionic surfactant and long-chain hydrocarbon phenol polyoxyethylene ether surfactant, mixing well, then adding alkaline protease to carry out proteolytic hydrolysis until the latex nitrogen content is 0.12-0.17 wt% (relative to the dry weight of NR rubber), then adding acid or allowing it to solidify naturally, pressing, leaching, and drying to obtain the low-protein natural rubber.

[0006] Furthermore, in the above method, the alkali is KOH.

[0007] Furthermore, in the above method, the long-chain hydrocarbon phenol polyoxyethylene ether surfactant is selected from surfactants with a carbon chain length of 14-18 carbon atoms and an HLB of 10-15.

[0008] Preferably, in the above method, the long-chain hydrocarbon phenolic polyoxyethylene ether surfactant is selected from the NSF series surfactants.

[0009] Furthermore, in the above method, the anionic surfactant is selected from carboxylic acid, sulfonic acid, and sulfate ester surfactants.

[0010] Preferably, in the above method, the anionic surfactant is selected from sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS).

[0011] Furthermore, in the above method, the total amount of the anionic surfactant and the long-chain hydrocarbon phenol polyoxyethylene ether surfactant added is 0.1-0.5 wt% of NR (calculated by dry adhesive mass).

[0012] Furthermore, in the above method, the amount of the anionic surfactant added is 0.05-0.25 wt% of NR (calculated by dry adhesive mass).

[0013] Furthermore, in the above method, the amount of the long-chain hydrocarbon phenol polyoxyethylene ether surfactant added is 0.05-0.3 wt% of NR (calculated by dry adhesive mass).

[0014] Furthermore, in the above method, the fresh latex is diluted with water to a dry latex content of 20-30 wt%.

[0015] Furthermore, in the above method, the anionic surfactant is diluted with water to a concentration of 5-20 wt% before being added to the system.

[0016] Furthermore, in the above method, the long-chain hydrocarbon phenol polyoxyethylene ether surfactant is diluted with water to a concentration of 5-20 wt% before being added to the system.

[0017] Furthermore, in the above method, the amount of alkaline protease added is 0.1-0.15 wt% of NR (calculated by dry gel mass).

[0018] Furthermore, in the above method, the alkaline protease is diluted with water to a concentration of 5-15 wt% before being added to the system.

[0019] Furthermore, in the above method, the hydrolysis reaction temperature is 30-50°C, and the hydrolysis reaction time is 10-48 hours.

[0020] Furthermore, in the above method, the acid is formic acid, acetic acid, or hydrochloric acid.

[0021] Furthermore, in the above method, the acid is an aqueous solution of formic acid, acetic acid, or hydrochloric acid with a concentration of 2-5 wt%.

[0022] Furthermore, in the above method, the amount of acid added is such that when flocculation occurs in the system, acid addition is stopped. Then, after standing for 12-24 hours, a clump forms.

[0023] The second technical problem to be solved by the present invention is to provide a low-protein natural rubber prepared by the above method.

[0024] The third technical problem to be solved by this invention is to point out the use of long-chain hydrocarbon phenol polyoxyethylene ether surfactants in improving the thermo-oxidative aging properties and compression fatigue properties of low-protein natural rubber. Furthermore, in a method for preparing low-protein natural rubber, fresh latex is used as raw material, and anionic surfactants, long-chain hydrocarbon phenol polyoxyethylene ether surfactants, and alkaline proteases are introduced to deproteinize the latex until the nitrogen content is 0.12-0.17 wt% (relative to the mass of NR dry rubber).

[0025] Furthermore, in the above-mentioned applications, the long-chain hydrocarbon phenol polyoxyethylene ether surfactant is selected from surfactants with a carbon chain length of 14-18 carbon atoms and an HLB value of 10-15. Preferably, the long-chain hydrocarbon phenol polyoxyethylene ether surfactant is selected from the NSF series surfactants.

[0026] The beneficial effects of this invention are:

[0027] Most of the low-protein natural rubber on the market is produced by secondary processing of concentrated latex, which is costly and not conducive to widespread application. The process of obtaining low-protein natural rubber by multiple centrifugations of fresh latex is more complicated and has a lower yield. This invention uses fresh latex as raw material and adds two surfactants and alkaline protease to deproteinize the latex. Compared with the process of adding only protease in reference [2], the nitrogen content of the natural rubber obtained is lower, with a nitrogen content of 0.12%-0.17%. The anionic surfactant SDS and the nonionic surfactant NSF are used together to carry out the protein hydrolysis reaction with alkaline protease, and then acid is added for coagulation and protein is removed by leaching. Compared with the centrifugation method for protein removal in reference [3], the LPNR prepared by leaching has a higher tensile strength retention rate and better thermo-oxidative aging performance. At the same time, the addition of NSF surfactant has a significant effect on improving the internal heat of rubber compression flexure, and the obtained LPNR has a lower compression flexure temperature rise than that obtained by using a single surfactant SDS.

[0028] The low-protein natural rubber prepared by the present invention has a simple process and produces LPNR with excellent tensile properties, thermo-oxidative aging properties and compression fatigue properties, which expands the application field of low-protein natural rubber and is of great significance for improving the performance of tire raw materials. Attached Figure Description

[0029] Figure 1 Comparison chart of vulcanization characteristics of compound rubber in the examples and comparative examples

[0030] Figure 2 Tensile stress-strain diagrams of vulcanizates in the examples and comparative examples

[0031] Figure 3 Tensile stress-strain diagrams of vulcanized rubber after aging in the examples and comparative examples

[0032] Figure 4 Comparison of temperature rise in compression flexural tests of vulcanized rubber specimens in the examples and comparative examples Detailed Implementation

[0033] This invention mainly provides a method for improving the thermo-oxidative aging properties and compression fatigue properties of low-protein natural rubber. The method includes the following steps: Fresh natural rubber latex is diluted with deionized water to a dry rubber content of 20-30 wt%; alkali is added to adjust the pH to 8.0-8.5; anionic surfactant and long-chain hydrocarbon phenol polyoxyethylene ether surfactant are added, with the total amount of the two surfactants being 0.1-0.5 wt% of the dry rubber content (NR), wherein the amount of the anionic surfactant is 0.05-0.25 wt% of the NR (NR) (based on dry rubber weight), and the amount of the long-chain hydrocarbon phenol polyoxyethylene ether surfactant is 0.05-0.3 wt% of the NR (NR) (based on dry rubber weight); the surfactants are diluted with deionized water to a concentration of 5% before addition. -20wt%, stir at room temperature to mix the surfactant and natural latex evenly (e.g., mix for 30-60 min), then add 0.1-0.15wt% alkaline protease of NR (based on dry rubber mass). Before adding the alkaline protease, dilute it with deionized water to a concentration of 5-15wt%. Then, the entire system is subjected to protease hydrolysis at 30-50°C until the nitrogen content is 0.12-0.17wt% (relative to the dry rubber mass of NR) (e.g., react for 10-48 h). Then, allow it to stand and solidify naturally or add 2-5wt% aqueous solution of acetic acid, formic acid or hydrochloric acid to solidify it. After pressing the solidified material into crepes, it is leached for 24-72 h. The crepes are then removed and hung to dry indoors, and then dried in an oven at 60-80°C to obtain LPNR samples.

[0034] The surfactants used in the following examples are NSF-9, a product of Changshu Naisu Biomaterials Technology Co., Ltd.; SDS, a product of Shanghai Aladdin Biochemical Technology Co., Ltd.; and alkaline protease, S10154, with a purity of 200 U / mg, a product of Shanghai Yuanye Biotechnology Co., Ltd.

[0035] Table 1 Sample Composition

[0036]

[0037] Examples 1-2:

[0038] Fresh latex was diluted with deionized water to a dry latex content of 30%. A 20wt% potassium hydroxide aqueous solution was added to adjust the pH to approximately 8.4. Then, 10wt% sodium dodecyl sulfate (SDS) and 10wt% cashew phenol polyoxyethylene ether surfactant NSF-9 (hereinafter referred to as NSF) were added. The mixture was stirred at room temperature for 30 minutes to ensure uniform mixing. Then, 5wt% alkaline protease was added. The mass ratios of each component are shown in Table 1. The protease hydrolysis reaction was carried out at 39°C for 24 hours. Then, 5wt% acetic acid was added. After the latex flocculated, it was allowed to stand for 16 hours. The clumps were then removed and pressed into crepes. The crepes were then leached for 48 hours. The crepes were then hung indoors to dry. After drying, they were dried in a 75°C oven for 6 hours to obtain LPNR samples.

[0039] In Example 1, the amounts of SDS and NSF added (relative to the mass of NR dry adhesive) were 0.1% and 0.2% respectively; in Example 2, the amount of SDS added was 0.2% and the amount of NSF added was 0.3%.

[0040] Comparative Examples 1-2:

[0041] The preparation method is the same as in the examples, except that only sodium dodecyl sulfate (SDS) is added as a surfactant. The mass of each component is shown in Table 1.

[0042] Comparative Examples 3-5:

[0043] The preparation method is the same as in the examples, except that only NSF is added as a surfactant. The mass of each component is shown in Table 1.

[0044] Comparative Example 6:

[0045] Fresh natural latex was diluted with deionized water to a dry latex content of 30%, and then acetic acid with a concentration of 5wt% was added. After the latex flocculated, it was left to stand for 16 hours. The clumps were then removed and pressed into crepes. The crepes were then leached for 48 hours. The crepes were then hung indoors to dry. After drying, they were dried in an oven at 75℃ for 6 hours to obtain undeproteinized NR samples.

[0046] Comparison of deproteinization effects prepared by different methods

[0047] The nitrogen content of NR and LPNR uncured rubber samples was determined according to GB / T 8088-2008, and the protein content was 6.25 times the measured nitrogen content. The nitrogen content of uncured rubber prepared by different methods is shown in Table 2. The nitrogen content of the NR sample was approximately 0.43%. By adjusting the type and amount of surfactant, low-protein natural rubber samples with a nitrogen content between 0.12% and 0.17% could be obtained.

[0048] Table 2 Nitrogen content of unvulcanized rubber samples

[0049]

[0050] Oxidation induction period test of uncured rubber

[0051] Differential scanning calorimetry (DSC) can be used to test the oxidation induction time (OIT) of uncured rubber samples at 170°C, thereby evaluating the thermo-oxidative stability of uncured rubber. [4] The OIT times of different samples are shown in Table 3.

[0052] Table 3 Oxidation induction time of uncured rubber samples

[0053]

[0054] The OIT times of uncured LPNR samples S1 and S2, with the addition of surfactant SDS, were both increased compared to the NR samples, indicating improved thermo-oxidative stability. However, the OIT values ​​of samples N1, N2, and N3, prepared using surfactant NSF, were all decreased compared to the NR samples. Since protein is a natural antioxidant in NR and can delay rubber aging, the protein content of the samples decreased with increasing SDS or NSF addition, leading to a gradual decrease in OIT time and thermo-oxidative stability. For samples SN1 and SN2, which had both SDS and NSF added, their OIT times were lower than the NR samples but higher than the samples with only NSF added.

[0055] Preparation and vulcanization characteristics analysis of compound rubber

[0056] Table 4. Curing characteristics of compound rubber

[0057]

[0058] The samples were compounded at room temperature on an open twin-roll mill using a standard rubber vulcanization formulation. The vulcanization formulation was as follows: NR 100 phr, sulfur 3.5 phr, zinc oxide 6 phr, stearic acid 0.5 phr, and 2-mercaptobenzothiazole (accelerator M) 0.5 phr. The vulcanization characteristics of the compound were characterized using a rotorless rotational rheometer at 143 ºC, 1.67 Hz, and a strain amplitude of 0.5 degrees arc (6.98%). Table 4 shows the vulcanization induction period (t) for different compound samples. 10 ), positive vulcanization time (t) 90 Maximum torque (M) H Minimum torque (M) L ) value and torque difference (M H -M L Torque difference (M)H -M L This indicates the degree of chemical cross-linking of the vulcanized sample.

[0059] M during the vulcanization process of LPNR compound H The values ​​are all higher than those of the NR sample, indicating that the strength of the LPNR compound is higher than that of NR. Meanwhile, the M value of LPNR is also higher. H -M L The value is also higher than that of NR, indicating that the vulcanization crosslinking density of LPNR is higher than that of NR, which is consistent with the results of the tensile test of the vulcanizate. The M value of LPNR prepared using NSF surfactant is also higher than that of NR. H -M L The values ​​are all higher than those of samples prepared using SDS, indicating that the former has a higher crosslinking density. This higher crosslinking density restricts slippage and friction between rubber molecular chains, reducing the internal heat generated in the rubber, which is consistent with the test results of compression flexure temperature rise. Meanwhile, the t values ​​of LPNR are also higher than those of samples prepared using SDS. 90 All were lower than NR, because the amino acids generated from protein breakdown promote sulfidation. The t of the samples prepared with SDS... 90 and t 10 The values ​​were all higher than those of samples prepared with the same mass fraction of NSF. 10 A reduced scorch time leads to a shorter scorch time, which is detrimental to the vulcanization process of the rubber compound. Compared to samples with only NSF surfactant, samples with both SDS and NSF have a lower scorch time. 10 The time increased significantly, approaching the value of the NR sample, thus improving the vulcanization process of LPNR.

[0060] Preparation and tensile property testing of vulcanized rubber samples

[0061] A flat vulcanizing apparatus was used at 143℃ with a vulcanizing time of 1.2 times the normal value (1.2 × t). 90 The compound rubber was vulcanized to obtain vulcanized rubber samples with a thickness of 2 mm. The vulcanized rubber was cut into dumbbell-shaped strips, and the tensile properties of the vulcanized rubber film were determined using a universal tensile testing machine according to GB / T528-2009 (tensile speed 500 mm / min). The thermo-oxidative aging properties of the vulcanized rubber were tested by accelerated hot air aging at 100℃ for 24 hours according to GB / T3512-2001. Table 5 shows the tensile strength, 100% constant elongation stress, 300% constant elongation stress, 500% constant elongation stress, and tensile strength retention rate of different vulcanized rubber samples before and after aging, where the tensile strength retention rate = tensile strength after aging / tensile strength before aging × 100%.

[0062] In Table 5 below, A represents tensile strength (MPa), B represents elongation at break (%), C represents 100% constant elongation stress (MPa), D represents 300% constant elongation stress (MPa), E represents 500% constant elongation stress (MPa), F represents tensile strength after aging (MPa), G represents elongation at break after aging (%), H represents 100% constant elongation stress after aging (MPa), I represents 300% constant elongation stress after aging (MPa), J represents 500% constant elongation stress after aging (MPa), and K represents tensile strength retention rate (%).

[0063] Table 5 Comparison of tensile properties of vulcanized rubber samples before and after aging

[0064]

[0065] The tensile strength, 100% elongation stress, and 300% elongation stress of the LPNR vulcanizate samples were all higher than those of NR. In particular, the LPNR vulcanizate prepared with NSF showed higher tensile strength, 100%, 300%, and 500% elongation stress than the samples prepared with SDS. However, the tensile strength retention rate of the NSF-prepared LPNR after aging was lower than that of the NR samples, and the tensile strength retention rate gradually decreased with increasing NSF dosage, consistent with the decrease in the thermo-oxidative stability of its unvulcanized rubber. The tensile strength retention rates of the S1 and S2 vulcanizates prepared with SDS after aging were 78.68% and 76.84%, respectively, higher than the 71.54% retention rate of the NR samples, which is consistent with the analysis results of the thermo-oxidative induction period of unvulcanized rubber. However, the tensile strength retention rates of SN1 and SN2 vulcanizates prepared using two surfactants were 83.00% and 85.10%, respectively, which were higher than those of LPNR and NR vulcanizates prepared using a single surfactant, which were 116.02% and 118.95% of the tensile strength retention rates of NR vulcanizates, respectively.

[0066] Comparison of compression flex temperature rise of vulcanized rubber

[0067] Table 6 Temperature rise at the bottom of vulcanized rubber samples

[0068]

[0069] The temperature rise during the compression flexural test of vulcanized rubber was tested using an RH-2000N thermal analyzer according to GB / T 1687.3-2016. The specimen diameter was 17.8±0.15 mm; height was 25±0.25 mm; the test mold cavity was kept at a constant temperature of 55℃; the frequency was 30 Hz; a prestress of 1 MPa was applied, with a stroke of 4.45 mm. A temperature sensor at the bottom of the instrument could monitor temperature changes in real time.

[0070] Under compression and flexure, the rubber experiences a continuous temperature rise due to internal heat generation. This heat causes irreversible deformation of the network structure, and the increased temperature accelerates aging, leading to material failure and shortening its service life. Table 6 shows the temperature rise at the bottom of different vulcanized rubber samples after 25 minutes of testing. The bottom temperature rise of LPNR vulcanized rubber was lower than that of NR, especially for samples prepared with the surfactant NSF. The temperature rises of N1, N2, and N3 were only 7.7℃, 7.3℃, and 7.0℃, respectively, representing decreases of 52.47%, 54.94%, and 56.79% compared to the NR samples. The compression temperature rise of samples prepared with the surfactant SDS was higher than that of NSF, with S1 and S2 samples showing temperature rises of 12.6℃ and 11.2℃, respectively. The temperature rise values ​​of SN1 and SN2 prepared using two different surfactants were 10.4℃ and 9.5℃, respectively, which were lower than those of S1 and S2. This reduced the temperature rise of the NR sample by 35.80% and 41.36%, respectively, and significantly improved its compressive fatigue performance.

[0071] In summary, using both SDS and NSF surfactants combined with alkaline protease for deproteinization of fresh natural rubber not only enhances the deproteinization effect but also results in low-protein rubber with superior thermo-oxidative aging performance compared to undeproteinized NR and LPNR prepared with a single surfactant (SDS or NSF). Furthermore, its compression flexural temperature rise is significantly lower than that of LPNR and NR samples prepared with SDS alone. The combined use of these two surfactants can improve the overall thermo-oxidative aging and compression fatigue performance of LPNR samples.

[0072] [1] Gao Tianming, Lü Zhen, Xia Jialiang, Hui Yonghai, Chen Jing, Luo Yongyue, Performance characterization of low-protein natural rubber prepared by leaching method, Polymer Materials Science and Engineering 36(1) (2020) 70-74.

[0073] [2] Zhang Guimei, Yan Li, Jiang Shikuan, Zhu Ao, Zou Jianyun, Preparation and properties of low-protein natural rubber, Elastomer 32(01) (2022) 10-15.

[0074] [3] Huang Honghai, Gui Hongxing, Huang Maofang, Ding Li, Wang Yuekun, Study on the properties of deproteinized natural rubber, Rubber Industry 65(9) (2018) 1012-1015.

[0075] [4] M. Wang, R. Wang, X. Chen, Y. Kong, Y. Huang, Y. Lv, G. Li,Effect of non-rubber components on the crosslinking structure and thermo-oxidative degradation of natural rubber, Polym. Degrad. Stab. 196 (2022)109845。

Claims

1. A method for improving the thermo-oxidative aging properties and compression fatigue properties of low-protein natural rubber, characterized in that: Includes the following steps: Fresh natural latex is diluted with water, and the pH is adjusted to 8.0-8.5 with alkali. Anionic surfactant and long-chain hydrocarbon phenol polyoxyethylene ether surfactant are added and mixed well. Then, alkaline protease is added to carry out proteolytic hydrolysis until the nitrogen content of the latex is 0.12-0.17 wt%. Acid is then added or the mixture is left to solidify naturally. The latex is then pressed, pleated, filtered, and dried to obtain the low-protein natural rubber. The long-chain hydrocarbon phenol polyoxyethylene ether surfactant is selected from NSF series surfactants; the anionic surfactant is selected from sodium dodecyl sulfate; the amount of the anionic surfactant added is 0.05-0.25 wt% of the dry NR rubber mass; the amount of the long-chain hydrocarbon phenol polyoxyethylene ether surfactant added is 0.05-0.3 wt% of the dry NR rubber mass; and the amount of the alkaline protease added is 0.1-0.15 wt% of the dry NR rubber mass.

2. The method according to claim 1, characterized in that: The total amount of the anionic surfactant and the long-chain hydrocarbon phenol polyoxyethylene ether surfactant added is 0.1-0.5 wt% of the NR dry adhesive mass.

3. The method according to claim 1, characterized in that: The hydrolysis reaction temperature is 30-50℃; the hydrolysis reaction time is 10-48h.

4. The method according to claim 1, characterized in that: The acid is formic acid, acetic acid, or hydrochloric acid.

5. The method according to claim 1, characterized in that: The acid is an aqueous solution of formic acid, acetic acid, or hydrochloric acid with a concentration of 2-5 wt%.

6. The use of long-chain hydrocarbon phenol polyoxyethylene ether surfactants in improving the thermo-oxidative aging properties and reducing the compression flexural temperature rise of low-protein natural rubber; wherein the long-chain hydrocarbon phenol polyoxyethylene ether surfactant is selected from the NSF series surfactants; the long-chain hydrocarbon phenol polyoxyethylene ether surfactant is used in the preparation of low-protein natural rubber, using fresh natural latex as raw material, and simultaneously introducing anionic surfactants, long-chain hydrocarbon phenol polyoxyethylene ether surfactants, and alkaline protease to deproteinize the latex until the nitrogen content is 0.12-0.17 wt%; wherein, The anionic surfactant is selected from sodium dodecyl sulfate; the amount of the anionic surfactant added is 0.05-0.25 wt% of the NR dry adhesive mass; the amount of the long-chain hydrocarbon phenol polyoxyethylene ether surfactant added is 0.05-0.3 wt% of the NR dry adhesive mass; and the amount of the alkaline protease added is 0.1-0.15 wt% of the NR dry adhesive mass.

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