Composite vulcanization accelerator, preparation method and application thereof in natural rubber latex and rubber compound

Abstract

The application discloses a composite vulcanization accelerator, a preparation method and application of the composite vulcanization accelerator to natural latex and mixed rubber, wherein the composite vulcanization accelerator comprises a thioketone derivative and a pyridine compound, the pyridine compound is selected from 3-hydroxypyridine, 2-methylpyridine, 4-ethylpyridine, 2-nitropyridine, 3-nitropyridine, 2-aminopyridine and 3-aminopyridine, and the thioketone derivative is selected from sodium pyrithione, 3-methylthiazoline-2-thione, N-hydroxypyridine-2-thione, 5-dodecyl dithio-3-phenyl-1,3,4-thiadiazole-2-thione, 1,3-thiazolidine-2-thione, tetrahydropyrrole-2-thione and 5-(4-methylbenzoyl)-3,4-dihydropyrimidine-2-thione. The composite vulcanization accelerator does not generate harmful substances, has the properties of safety, high efficiency, low toxicity and environmental protection, and can promote vulcanization of the natural latex and the mixed rubber and improve the physical and mechanical properties of vulcanized rubber films.

Description

Technical Field

[0001] The present invention relates to the technical field of rubber vulcanization, in particular to a composite vulcanization accelerator, a preparation method and application thereof to natural rubber latex and rubber compound. Background Art

[0002] Natural rubber is an important industrial raw material, and concentrated natural latex and rubber compounds are widely used in many fields. Vulcanization is the process by which linear chain molecules of rubber form three-dimensional spatial network macromolecules through chemical cross-linking reactions. Unvulcanized natural rubber has many defects, such as low strength, poor wear resistance, heat resistance and aging resistance, which limit its scope of application. Vulcanization not only improves the physical and mechanical properties of rubber, but also gives it good dimensional stability and aging resistance. The vulcanization of rubber is a complex chemical process involving multiple components. Researchers have conducted extensive research on it and established a systematic kinetic model to clarify the reaction mechanism. The vulcanization process can be divided into three stages: the vulcanization process, the cross-linking reaction period and the network formation period. The study of kinetic models can optimize the vulcanization process and improve the performance of vulcanized rubber.

[0003] Vulcanization accelerators play a crucial role in the vulcanization process. They accelerate the vulcanization reaction, shorten the vulcanization time, and reduce the vulcanization temperature, thereby optimizing the physical and mechanical properties of the vulcanized rubber. Selecting the right vulcanization accelerator is crucial for improving the quality of rubber products. Common vulcanization accelerators on the market include sulfenamides, thiazoles, and thiurams, each with specific applications and advantages. For example, sulfenamide vulcanization accelerators exhibit excellent delayed vulcanization properties, making them suitable for a variety of rubber products; thiazole vulcanization accelerators are known for their rapid vulcanization characteristics, making them suitable for high-speed vulcanization processes. However, these traditional vulcanization accelerators also have drawbacks, such as the potential for containing hazardous substances and requiring harsh operating conditions. For example, thiazole and sulfenamide accelerators can easily generate nitrosamines during the vulcanization process, a potent carcinogen that poses a threat to human health. Furthermore, these accelerators are prone to decomposition at high temperatures, resulting in unstable vulcanized rubber properties. Therefore, the development of new, efficient, low-toxic, and environmentally friendly composite vulcanization accelerators has become a research priority. Summary of the Invention

[0004] In view of the above-mentioned defects of the prior art, the present invention proposes a composite vulcanization accelerator, a preparation method and its application in natural rubber latex and rubber compound to solve the problems raised by the above-mentioned background technology.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A composite vulcanization accelerator comprises a thioketone derivative and a pyridine compound, wherein the pyridine compound is selected from any one of 3-hydroxypyridine, 2-methylpyridine, 4-ethylpyridine, 2-nitropyridine, 3-nitropyridine, 2-aminopyridine and 3-aminopyridine.

[0007] Preferably, the thione derivative is selected from any one of sodium pyrithione, 3-methylthiazoline-2-thione, N-hydroxypyridine-2-thione, 5-dodecyldithio-3-phenyl-1,3,4-thiadiazole-2-thione, 1,3-thiazolidine-2-thione‌, tetrahydropyrrole-2-thione, and 5-(4-methylbenzoyl)-3,4-dihydropyrimidine-2-thione.

[0008] Preferably, the mass ratio of the thione derivative to the pyridine compound in the composite vulcanization accelerator is 1:15.

[0009] Preferably, the mass ratio of the thione derivative to the pyridine compound in the composite vulcanization accelerator is 1:3.

[0010] Preferably, the usage of the composite vulcanization accelerator is 2.5 mmol / Kg to 7.5 mmol / Kg.

[0011] Preferably, the usage of the composite vulcanization accelerator is 3 mmol / Kg to 6 mmol / Kg.

[0012] Preferably, the usage of the composite vulcanization accelerator is 5.0 mmol / Kg.

[0013] Preferably, the preparation method of the composite vulcanization accelerator comprises the following steps: adding a thioketone derivative to a pyridine compound, and stirring the mixture uniformly to obtain the composite vulcanization accelerator.

[0014] Preferably, the composite vulcanization accelerator involved in the present application is used to promote the vulcanization of natural rubber latex and rubber compound, accelerate the vulcanization rate, improve their physical and mechanical properties, and inhibit bacteria and mildew.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The composite vulcanization accelerator TK-PY mainly includes thione derivatives and pyridine compounds. The thione derivatives include sodium pyridinethione, and the pyridine compounds include 3-hydroxypyridine. TK-PY contains thione, pyridine and other groups, among which the thione group and pyridine group are the main vulcanization accelerators. In this study, TAA, ETU and 3-Hp were introduced into concentrated latex as vulcanization accelerators. The results showed that when added at 5mmol / Kg, ETU and 3-Hp could also improve the film properties at the same dosage, but the effect was slightly inferior to that of TK-PY. TAA had little effect on the film properties. This shows that the composite vulcanization accelerator TK-PY has a better effect on improving the mechanical strength of the film than ETU and 3-Hp, that is, it is better than the promotion effect of any single group. This shows that the thione group and pyridine group have a superimposed effect on the vulcanization acceleration of natural rubber. TK-PY can effectively enhance the tensile strength, modulus of tensile stress and hardness of concentrated latex vulcanized film, with the tensile strength reaching 34.18MPa, while shortening the vulcanization time.

[0017] (2) As a new type of composite vulcanization accelerator, TK-PY can significantly enhance the mechanical properties of natural rubber films. The use of TK-PY is not only safe, environmentally friendly, and low-cost, but also can promote the vulcanization reaction of rubber, improve the physical and mechanical properties of rubber and product quality, and has high application value.

[0018] (3) The raw rubber prepared by adding TK-PY to the fresh latex through wet mixing has a low number average molecular weight and a wide molecular weight distribution; the weight average molecular weight of the ETU sample is also low, and the molecular weight distribution coefficient is relatively small; and the weight average molecular weight of the 3-Hp sample is also low, and its molecular weight distribution coefficient is the lowest. The results of infrared spectroscopy analysis show that the characteristic peaks of the five samples are basically the same, and no significant migration or strength changes are observed, indicating that the vulcanization accelerator has little effect on the main chain structure of natural rubber. The raw rubber samples with the addition of TK-PY and 3-Hp have an improvement in the storage modulus (G'), indicating that the rigidity of the rubber has increased; at the same time, the loss factor (Tanδ) curve is also low, especially the 3-Hp sample shows a low Tanδ value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The following are the curing curves of the concentrated latex and film of the two preservation systems at 100℃ for 3000s;

[0020] Figure 2 The vulcanization curves of the composite films at 143°C after adding 5mmol / Kg of different vulcanization accelerators are shown;

[0021] Figure 3The influence of adding 5mmol / Kg different vulcanization accelerators on the structure and performance of dry rubber film; wherein (a) is the relative molecular mass distribution diagram; (b) is the infrared curve diagram; (c) is the TG curve diagram; (d) is the DTG curve diagram;

[0022] Figure 4 (a) is the radar chart of performance index of dry rubber film after adding different vulcanization accelerators; Figure 4 (b) is the radar chart of vulcanization parameters and mechanical strength index of rubber film after adding different vulcanization accelerators;

[0023] Figure 5 The influence of four vulcanization accelerators on the (a) M L , (b) M H , (c) M H -M L and (d) T 90 vulcanization time of rubber compound;

[0024] Figure 6 The influence of (a) TK-PY, (b) TAA, (c) ETU and (d) 3-HP on the vulcanization curve of rubber compound under different addition amounts;

[0025] Figure 7 The change trend of the modulus of natural rubber vulcanized rubber with the increase of the amount of four vulcanization accelerators; wherein (a) is the 100% modulus, (b) is the 300% modulus and (c) is the 500% modulus;

[0026] Figure 8 The change trend of the physical and mechanical properties of natural rubber vulcanized rubber with the change of the amount of four vulcanization accelerators; wherein (a) is the tensile strength, (b) is the elongation at break, (c) is the tear strength and (d) is the hardness;

[0027] Figure 9 The vulcanization curve of rubber compound for preparing natural rubber raw rubber by different vulcanization accelerators;

[0028] Figure 10 The molecular weight distribution map of natural rubber raw rubber prepared by adding four vulcanization accelerators by wet mixing of fresh latex;

[0029] Figure 11 The infrared spectrum of natural rubber raw rubber prepared by adding four vulcanization accelerators by wet mixing of fresh latex;

[0030] Figure 12 The TG and DTG spectrum of rubber raw rubber prepared by adding four different vulcanization accelerators by wet mixing;

[0031] Figure 13 The (a) G' and (b) Tanδ curves of natural rubber raw rubber after adding four vulcanization accelerators. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical content of the present invention, the technical solution of the present invention is further described in detail below in conjunction with specific implementation methods.

[0033] Examples 1 to 13

[0034] The composite vulcanization accelerator was prepared according to the following components and addition amounts, as shown in Table 1:

[0035] Table 1 Components and addition amounts of different composite vulcanization accelerators

[0036]

[0037] The preparation method of the composite vulcanization accelerator comprises the following steps: mixing a thioketone derivative and a pyridine compound in proportion and stirring them uniformly to obtain the composite vulcanization accelerator.

[0038] Experimental Example 1: Effect of Vulcanization of Natural Rubber Latex

[0039] 1 Experimental materials and test methods

[0040] 1.1 Experimental Materials

[0041] Natural rubber latex (NRL) was collected from the experimental farm of the Chinese Academy of Tropical Agricultural Sciences. The natural rubber latex additives TAA (thioacetamide), ETU (2-imidazolidinethione), and 3-Hp (3-hydroxypyridine) were industrial-grade, with chemical structures shown in Table 2, and were purchased from Shandong Yousuo Chemical Technology Co., Ltd. The composite vulcanization accelerator TK-PY (Example 1) was laboratory-prepared. Analytical-grade tetrahydrofuran and 25% aqueous ammonia were purchased from Guangdong Xilong Chemical Co., Ltd. The vulcanization accelerators used in the experiment included KOH, peregal (O), ZnO, sulfur, and the accelerator ZDC.

[0042] Table 2 Chemical structures of TAA, ETU and 3-Hp

[0043]

[0044] 1.2 Test Method

[0045] 1.2.1 Preparation of concentrated latex samples

[0046] A certain amount of natural fresh rubber latex (NRL) was centrifuged in a continuous centrifuge to prepare a blank ammonia-free concentrated latex (Blank). This was stored in TK-PY. A high-ammonia concentrated latex (HA) was simultaneously prepared as a control (HA was prepared by centrifuging the natural fresh rubber latex and then adding liquid ammonia to a concentration of 0.7 wt%). These were labeled TK-PY and HA, respectively, and stored for three months before use. Concentrated latex samples were prepared by adding appropriate amounts of the blank ammonia-free concentrated latex according to the formulation in Table 3.

[0047] Table 3 Composition and dosage of concentrated latex vulcanization accelerator

[0048]

[0049] 1.2.2 Preparation of concentrated latex dry film, compound film and vulcanized film samples

[0050] Preparation of concentrated latex dry film: Refer to ISO 498:1992. Slowly inject natural fresh latex (NRL) into the inner groove of a 3mm glass mold (cover). After standing for 1 minute, scrape off excess NRL with a ruler. Dry the mold at room temperature for 16 hours, then dry in a 35°C oven until completely transparent.

[0051] Prepare the compound film sample: Take an appropriate amount of concentrated latex sample, add the following vulcanizing agent according to the following formula, slowly stir for 2 hours, and dry at room temperature. The vulcanizing agent formula (dry basis, parts by weight) is: 100 parts concentrated latex, 1 part sulfur, 0.1 part KOH, 0.1 part Peregal (O), 0.5 part ZDC, and 0.4 part ZnO. Test the compound film vulcanization parameters.

[0052] Preparation of vulcanized film samples: First, place an appropriate amount of NRL in a clean beaker and dilute it to 50% with deionized water. Second, stir and disperse the vulcanizing agent in the diluted NRL in a 40°C water bath. Third, heat the mixture to 60°C, then cool and filter to prepare pre-vulcanized latex. Fourth, pour an appropriate amount of pre-vulcanized latex into a clean glass dish and level it. Then, dry the pre-vulcanized latex at room temperature until transparent, and then soak the film in deionized water for 24 hours. Finally, heat the film at 80°C for 6 hours until it becomes translucent to obtain a vulcanized film.

[0053] 1.2.3 Determination of curing speed of adhesive film

[0054] The vulcanization rate of the compound film was determined by using a high-speed MD-3000A rotorless vulcanometer. The thickness of the compound film was about 4 mm. The vulcanization curve of the compound film with concentrated latex of different vulcanization accelerator systems was determined at a temperature of 100 ° C and a measurement time of 50 min.

[0055] 1.2.4 Testing of physical and mechanical properties of dry and vulcanized films

[0056] The tensile strength, elongation at break, modulus of tensile strength, and tear strength of dry and cured films were determined in accordance with ISO 37:2017 and ISO 34-1:2015. Tensile strength test specimens were dumbbell-shaped, with five replicates prepared for each sample. Five tests were performed and the average value was recorded. The tensile test machine speed was set at 500 mm / min.

[0057] 1.2.5 Infrared test of dry rubber film

[0058] The test was directly performed by using TENSOR 27 Fourier infrared spectrometer, the detection range was set to 4000~370cm –1 , the resolution was 4cm –1 , and the scanning times were 32.

[0059] 1.2.6 Thermal gravimetric analysis of dry rubber film

[0060] The raw rubber sample was cut into particles, 10mg sample was weighed and placed in a crucible, and the STA449 type thermal gravimetric analyzer was used for testing. The test conditions were as follows: nitrogen was used as the external atmosphere, the flow rate was set to 50mL / min; the protective gas was high-purity nitrogen, the flow rate was set to 25mL / min; the test temperature range was 25~600℃, and the heating rate was 10K / min.

[0061] 1.2.7 Determination of low temperature characteristics of dry rubber film

[0062] The glass transition temperature of the dry rubber film was determined by differential scanning calorimetry (DSC method), and the temperature section was set to -90~100℃, and the heating rate was 10K / min.

[0063] 1.2.8 Test of molecular weight and distribution of dry rubber film

[0064] The molecular weight and distribution of the rubber were detected by GPC gel permeation chromatograph, 3g dry rubber was cut into fine strips, soaked in appropriate amount of tetrahydrofuran for one week until completely dissolved, and the solution was filtered by a needle filter, and detected by gel permeation chromatograph at 30℃.

[0065] 2. Test results and analysis

[0066] 2.1 Effect of different storage systems on vulcanization performance of concentrated latex

[0067] 2.1.1 Vulcanization speed of concentrated latex with different storage systems

[0068] As shown in Figure 1 and Table 4, the two rubber film samples S' continuously increased with the extension of the vulcanization time, but there were certain differences in the rising speed and the rising amplitude. Among them, the TK-PY composite vulcanization accelerator system rubber film sample S' had the largest rising amplitude, the maximum torque M H value and the torque difference M H -M L were the highest. The torque difference M H -M LThe torque difference of the film prepared by the TK-PY composite vulcanization accelerator system is 1.68, which is 41.18% higher than that of the HA sample, and is basically consistent with the change of the vulcanization curve. It is shown that compared with the HA system, the TK-PY composite vulcanization accelerator system has a faster vulcanization speed and a higher vulcanization degree.

[0069] Table 4 vulcanization characteristics of concentrated latex prepared by different storage systems at 100°C

[0070]

[0071] 2.1.2 Physical and mechanical properties of vulcanized film of concentrated latex with different storage systems

[0072] As shown in Table 5, the vulcanized film is prepared by pre-vulcanized latex, and the vulcanization degree reaches the third elementary level. The mechanical properties of the vulcanized film of the two concentrated latexes are quite different. The hardness, tensile strength and tensile stress of the vulcanized film of the TK-PY composite vulcanization accelerator concentrated latex are higher, among which the tensile strength reaches 34.18 MPa, which is 30.26% higher than that of the high ammonia concentrated latex vulcanized film; the 500% tensile stress reaches 1.81 MPa, which is 32.12% higher than that of the high ammonia concentrated latex; the tear strength and elongation at break are also relatively high, which is basically consistent with the change of the medium vulcanization curve. Comprehensive analysis shows that the physical and mechanical properties of the vulcanized film of the TK-PY composite vulcanization accelerator ammonia-free concentrated latex are the best. Figure 1

[0073] Table 5 Physical and mechanical properties of vulcanized film of concentrated latex with different storage systems

[0074]

[0075] 2.1.3 Effect of TK-PY dosage on the mechanical properties of concentrated latex dry film

[0076] As shown in Table 6, the strength of the dry film can to some extent represent the gel strength of the latex, and has a great influence on the production process performance of the immersed product. By comparing the mechanical properties of the dry film of the blank ammonia-free concentrated latex, it is shown that TK-PY has a significant effect on the mechanical strength of the concentrated latex dry film. With the increase of the dosage of TK-PY, the tensile strength and elongation at break of the concentrated latex dry film increase continuously, and the mechanical properties are the highest when the dosage of TK-PY is about 5 mmol / Kg. With the continuous increase of the dosage of TK-PY, the tear strength, tensile stress and hardness of the vulcanized film all show a trend of first increasing and then decreasing. It is shown that the mechanical properties are the highest when the dosage of TK-PY is about 5 mmol / Kg.

[0077] Table 6 Effect of TK-PY with different dosages on the mechanical properties of concentrated latex dry film ​

[0078]

[0079] Note: The concentrated latex was added with TK-PY and stored for 3 months before preparing the dry film.

[0080] 2.2 Comparison of different vulcanization accelerators

[0081] 2.2.1 Effects of different vulcanization accelerators on the physical and mechanical properties of concentrated latex dry films

[0082] As shown in Table 7, the addition of 5 mmol / Kg of TK-PY, TAA, ETU and 3-HP improved the tensile strength of the dry film, but generally reduced the elongation at break, tear strength and Mooney viscosity. The tensile strength of the concentrated latex dry film increased, the modulus of tensile stress and elongation at break generally decreased, and the tear strength all decreased.

[0083] TK-PY: Provides the highest tensile strength, 77% higher than the Blank control, but reduces tear strength and Mooney viscosity. TK-PY forms crosslinks in NR through covalent bonds / hydrogen bonds, forming a network that enhances tensile strength.

[0084] TAA: minimal effect on physical and mechanical properties, with results comparable to the Blank control. The limited reactivity of TAA may not produce sufficient crosslinking.

[0085] ETU: Compared to the Blank control, tensile strength increased by 69%, but tear strength and Mooney viscosity decreased. ETU promotes crosslinking through intermediate or free radical mechanisms.

[0086] 3-HP: has limited effect on tensile strength, but significantly reduces elongation at break and tear strength. The hydroxyl and pyridine groups of 3-HP disrupt the hydrogen bonding / molecular stacking of NR through competition or electronic interactions, weakening cohesion and reducing tear strength.

[0087] Table 7 Effects of different vulcanization accelerators on the physical and mechanical properties of concentrated latex dry films

[0088]

[0089] 2.2.2 Effect of different vulcanization accelerators on the vulcanization speed of compound films

[0090] like Figure 2As shown in the figure, although the vulcanization curves of the five compound film samples are basically the same, there are obvious differences in the highest torque peaks. TK-PY improves the vulcanization speed of the compound film most significantly, as can be seen from the highest peak of the vulcanization curve and the shorter vulcanization time. ETU and 3-Hp also significantly promote the vulcanization process. In contrast, TAA has the least effect on the vulcanization speed and does not show a significant enhancement effect. Table 8 shows the characteristic parameters of the vulcanization of the concentrated latex compound film after adding four vulcanization accelerators. As shown in Table 8, TK-PY can significantly improve the minimum torque M of the compound film. L and the maximum value M H , where M L The value increases with the amount of TK-PY, and when the amount of TK-PY is 5mmol / Kg, M H In addition, ETU and 3-Hp can also significantly improve the M value of the composite film when added at 5mmol / Kg. H and torque difference. TK-PY, ETU and 3-Hp can greatly reduce the vulcanization time and increase the vulcanization speed, but TAA has little effect on the vulcanization process. Among them, with the increase of TK-PY dosage, the vulcanization time has a trend of first decreasing and then increasing. When the dosage is 5mmol / Kg, the vulcanization time is the shortest and the vulcanization speed is the fastest; ETU and 3-Hp can also greatly reduce the vulcanization time and increase the vulcanization speed when added at 5mmol / Kg, and the difference in vulcanization time with the same dosage of TK-PY is very small. The four vulcanization accelerators can shorten the vulcanization time, but combined with the torque difference analysis, TK-PY shortens the vulcanization time and increases the vulcanization speed while significantly increasing the torque difference.

[0091] Table 8 Characteristic vulcanization parameters of concentrated latex with different additives and film

[0092]

[0093] 2.2.3 Effects of different vulcanization accelerators on the physical and mechanical properties of vulcanized films

[0094] Table 9 shows that TK-PY, ETU, and 3-Hp all effectively improve the tensile stress, tensile strength, elongation at break, and hardness of the vulcanized film. The sample with TK-PY has the highest tensile stress, tensile strength, and hardness. The 500% tensile stress reaches 1.45 MPa, a 12.4% increase over the blank sample, and the tensile strength increases to 19.26 MPa, a 31.38% increase over the blank sample. The sample with ETU has the highest tear strength, reaching 59.72 kN·m. -1 , which is 8.9% higher than that of the Blank sample. The modulus of tensile stress and tensile strength are also improved. 3-Hp significantly improves the tensile strength and modulus of the vulcanized film. TAA has the least effect on the physical and mechanical properties of the vulcanized film.

[0095] TK-PY increases crosslinking density and intermolecular interactions by forming disulfide bonds from active sulfur, thus improving the properties of the rubber. This enhances the tensile strength and hardness while maintaining the elongation at break by uniform network distribution, mitigating stress concentration. The sulfur groups further enhance bonding through coordination and hydrogen bonding with the rubber double bonds. ETU promotes polysulfide formation by lowering the activation energy for vulcanization. Its moderate sulfur bridge length creates a dense, directional crosslinking that improves tear strength and intra-chain cohesion while maintaining elongation. The hydroxyl groups of Hp improve tensile strength through hydrogen bonding but can cause brittleness and uneven crosslinking, thus promoting crack propagation. Overall, the results indicate that TK-PY exhibits superior mechanical properties in enhancing the mechanical properties of the film.

[0096] Table 9 Effect of different vulcanization accelerators on the physical and mechanical properties of concentrated latex vulcanized rubber film

[0097]

[0098] 2.2.4 Effect of different vulcanization accelerators on the relative molecular mass of concentrated latex dry rubber film

[0099] The addition of vulcanization accelerators enhances the strength of the NRL film, possibly due to changes in their relative molecular mass. Figure 3 (a) shows that the molecular weight distribution patterns of the five NRL samples are essentially consistent, showing a typical unimodal distribution. After the addition of the four vulcanization accelerators, the overall rubber molecular weight distribution pattern shifts to the left, and notably, the molecular weight distribution peak of the samples with TK-PY and ETU increases, while the molecular weight distribution peak of the samples with TAA and 3-Hp further shifts to the left, increasing the content of small molecules and reducing the average molecular weight, as shown in Figure 3 (a) and Table 10, the number average relative molecular mass of the dry rubber film after the addition of these four substances differs little within the normal error range. However, the weight average relative molecular mass of all samples decreases slightly, indicating that the mechanism of improving the physical and mechanical properties is not due to an increase in relative molecular mass. At the same time, the decrease in the distribution coefficient also indicates an increase in the content of low molecular weight components.

[0100] Table 10 Characteristic relative molecular mass of concentrated latex sample dry rubber film

[0101]

[0102] 2.2.5 Infrared spectra of concentrated latex dry rubber film treated with different vulcanization accelerators

[0103] As shown in Figure 3(b) shows that no obvious shift of the peaks occurred in the infrared spectra of the five concentrated latex dry rubber film samples, and the intensity of the peaks did not change significantly. The characteristic peaks appeared in the same waveband, and the overall infrared curve was relatively close, with small differences. The C=C double bond stretching vibration peak of the natural rubber molecule was at 1645 cm -1 , the bending vibration peak was at 840 cm -1 , the stretching vibration peaks of -CH3 and -CH2 were at 2959 cm -1 and 2851 cm -1 , and the bending vibration peaks were at 1443 cm -1 and 1375 cm -1 , respectively. There were some minor differences in the characteristic peaks of the five spectra, indicating that the incorporation of the four substances had minimal effect on the structure of the NRL dry film. Figure 3 (b) shows that there is no significant shift in the characteristic peaks, which rules out the possibility of changes in polymer chain length as the main factor.

[0104] 2.2.6 Effect of different vulcanization accelerators on the thermal stability of concentrated latex dry rubber film

[0105] Figure 3 (c) and Figure 3 (d) are the TG and DTG curves of the concentrated latex dry rubber film samples after the addition of the four substances, respectively. The improvement in the mechanical strength of the concentrated latex dry rubber film is related to the change in its crosslinking density, and the improvement in crosslinking density will inevitably improve its thermal stability. Compared with the blank sample, the degradation curves of the dry rubber film samples after the addition of the four vulcanization accelerators all showed some changes, but were basically consistent, with very small differences. The DTG degradation curve of natural rubber is mainly used to characterize its thermal stability and thermal decomposition process, and shows the relationship between the mass loss rate and the temperature. The peaks on the curve represent the key steps in the thermal decomposition process. As can be seen from Figure 3 (d), the DTG curve of natural rubber basically presents a shoulder peak shape. The peak area is directly proportional to the mass lost in the corresponding temperature interval, and can be used to quantify the percentage of mass lost in each step of the decomposition reaction. Combined with Figure 3 (c) and Figure 3 (d) analysis, the pre-degradation rate of the samples is basically consistent, but the maximum degradation rate of the TK-PY sample is higher, and the secondary degradation peak rate is lower.

[0106] Table 11 shows the characteristic degradation temperatures of concentrated latex dry film samples after adding different vulcanization accelerators. There are some variations in the characteristic degradation temperatures of the five samples. After adding the four vulcanization accelerators, the initial degradation stability of the concentrated latex dry film samples increased, but the subsequent maximum degradation stability and terminal degradation stability showed some fluctuations. The initial degradation temperature of the dry film with the addition of TK-PY increased, but T50% decreased significantly. In addition, ETU and 3-HP also increased the initial degradation temperature of the dry film, and T50% was also relatively high. The initial degradation temperature and maximum degradation temperature of the TK-PY sample were almost the same, with a difference of <1%. TK-PY (T f =407.7°C) was 1.7% lower than the blank, which is within the experimental error (±2%). These multi-parameter comparisons confirm that the TK-PY additive does not substantially impair the thermal stability of the NRL membrane.

[0107] Table 11 Characteristic degradation temperature of concentrated latex dry film samples

[0108]

[0109] 2.2.7 Effects of different vulcanization accelerators on the low-temperature properties of concentrated latex dry films

[0110] As shown in Table 12, if a vulcanization accelerator promotes the vulcanization of natural rubber and produces crosslinks in the dry film, the film's glass transition temperature will increase to a certain extent. Compared to the blank control sample, the addition of a vulcanization accelerator to the concentrated latex dry film samples did not significantly change the glass transition temperature. Furthermore, the addition of ETU and 3-HP increased the thermal conductivity of the dry film.

[0111] Table 12 Glass transition temperature of dry films of concentrated latex with different vulcanization accelerators

[0112]

[0113] 2.2.8 Influence of concentrated latex film on physical and mechanical properties

[0114] Figure 4 (a) shows a radar chart comparing the performance indexes of dry adhesive films after adding various accelerators. The blank concentrated latex dry adhesive film sample has the highest tear strength, 500% modulus, weight-average molecular weight and distribution coefficient. Compared with the blank dry adhesive film sample, the concentrated latex dry adhesive film added in Example 1 has the best tensile strength and elongation at break. The dry adhesive film added with ETU has the highest number-average molecular weight and excellent tensile strength. The dry adhesive film added with 3-Hp has only a higher molecular weight distribution coefficient.

[0115] Figure 4(b) Radar chart of the four different accelerators on the vulcanization parameters and mechanical strength indicators of the vulcanized rubber film, the blank concentrated latex compounded rubber film and the vulcanized rubber film are all relatively poor; the M L , M H , M H -M L , T 90 , the tensile strength and tensile stress indicators are the highest, and the physical and mechanical properties are the highest; the torque difference and T 90 indicators of the ETU latex compounded rubber film are higher, and the tear strength and elongation at break indicators of the vulcanized rubber film are the highest, indicating that the physical and mechanical properties are excellent and reach a high level; on the contrary, the indicators of the 3-HP sample are lower, and the TAA sample statistics show that the indicator coefficients are the lowest.

[0116] TK-PY can induce uniform high crosslinking density by gradually releasing active sulfur, leading to the formation of extended sulfur bridges, which enhances network stability, resulting in only a slight increase in elongation at break. In contrast, ETU accelerates vulcanization, producing a dense network of short sulfur bonds, resulting in a flexible yet robust network. This results in an 8.9% increase in tear strength, with less tensile enhancement than TK-PY. The selective crosslinking of 3-Hp leads to local over-densification, increasing tensile strength. However, the brittleness caused by hydrogen bonds leads to a sharp decrease in tear strength of 14.0%, and TAA shows no significant effect due to its low reactivity. While crosslinking density has a positive impact on strength and hardness, tear performance is influenced by sulfur bridge length and uniformity. The flexible structure of ETU is superior to the uneven distribution of 3-Hp, while TK-PY strikes a balance between high strength and moderate elongation. Among the four accelerators, TK-PY exhibits the most significant promotion of NR vulcanization, producing the highest rubber film M H , tensile strength, and constant tensile stress values. While ETU and 3-Hp both promote vulcanization, their effects are less pronounced.

[0117] Summary: This application studies the influence mechanism of composite vulcanization accelerator TK-PY on the mechanical properties of natural rubber latex dry rubber film, the vulcanization characteristics of compounded rubber film, and the mechanical properties of vulcanized rubber film. The results show that the composite vulcanization accelerator TK-PY can effectively promote the vulcanization process of concentrated latex compounded rubber film, improve the vulcanization degree, shorten the vulcanization time, and greatly improve the mechanical properties of dry rubber film and vulcanized rubber film. The TK-PY addition amount is 5 mmol / Kg, and the mechanical properties of the rubber film are the highest.

[0118] The vulcanization accelerator system TK-PY mainly includes thioketone derivatives and pyridine compounds, the thioketone derivatives include sodium pyrithione, the pyridine compounds include 3-hydroxypyridine, TK-PY contains thioketone, pyridine and other groups, among which the main vulcanization promotion is the thioketone group and the pyridine group. In this study, TAA, ETU and 3-Hp were introduced into the concentrated latex as vulcanization accelerators, and the results showed that when 5 mmol / Kg was added, ETU and 3-Hp could also improve the performance of the rubber film at the same dosage, but the effect was slightly inferior to TK-PY. It is shown that the vulcanization accelerator system TK-PY has better effect on improving the mechanical strength of the rubber film than ETU and 3-Hp, that is, better than any single group promotion, so it is speculated that the thioketone group and the pyridine group have a superimposed effect on the vulcanization promotion of natural rubber. In summary, TK-PY is a new type of composite vulcanization accelerator, which not only improves the corrosion prevention efficiency of NRL, but also significantly improves the mechanical properties of the vulcanized film. The application of TK-PY has safety, ecological friendliness and cost effectiveness. In addition, it also accelerates the rubber vulcanization process, thereby improving the physical and mechanical properties of natural rubber and improving the overall quality of the product, so TK-PY has great practical application potential in the rubber industry.

[0119] Experimental Example 2 on the vulcanization effect on the mixed rubber

[0120] 1. Experimental materials and test methods

[0121] 1.1 Experimental materials: the same as described in 1.1 of Example 1;

[0122] 1.2 Test methods

[0123] 1.2.1 Preparation of natural rubber raw rubber samples

[0124] A certain amount of fresh natural latex was taken in the rubber garden and stored using 0.1% ammonia water. Subsequently, the corresponding vulcanization accelerator was added according to the formula in Table 13, and after being fully stirred and uniform, it was left for 24 hours. According to the calculation formula of the amount of acid required for coagulation, the appropriate amount of acid was determined to coagulate the fresh latex. After 1 day of standing, it was subjected to wrinkle dehydration treatment and completely dried under hot air at 70°C to prepare raw rubber samples.

[0125] Table 13 Fresh latex wet mixing to prepare raw rubber vulcanization accelerator composition and dosage

[0126]

[0127] Note: The vulcanization accelerator is an aqueous solution or colloidal suspension.

[0128] 1.2.2 Preparation of mixed rubber and vulcanized rubber samples

[0129] The natural raw rubber was mixed on an open mill to prepare a mixed rubber according to the ACSI formula and mixing procedure in GB / T 15340-1994. The curing characteristics of the mixed rubber were tested using a rotorless vulcanizer, the curing temperature was 143°C, and the test time was 60 min. The mixed rubber was vulcanized using a flat vulcanizing machine, the vulcanizing temperature was 143°C, and the vulcanizing time was the positive vulcanizing time t90+5 min, to obtain a vulcanized rubber sheet.

[0130] 1.2.3 Preparation of test samples of mixed rubber

[0131] The mixed rubber 3.9 kg was prepared according to the pure rubber formula, and was evenly divided into 13 parts, each of 300 g. Then, the vulcanization accelerators were added according to the formula in Table 14, and were mixed thoroughly. After standing for 12 h, the curing characteristics of the mixed rubber were detected, and the vulcanized rubber film was prepared to evaluate the physical and mechanical properties thereof.

[0132] Table 14 Types and amounts of vulcanization accelerators for mixed rubber

[0133]

[0134] 1.2.4 Detection of raw rubber

[0135] Plastic initial value (P0) and plastic retention rate (PRI): measured according to GB / T 3517-2014 and GB / T 3510-2006 using a rapid plasticity tester; Mooney viscosity ML (1+4) 100°C: tested according to GB / T 1232.1-2016 using a Mooney viscometer; nitrogen content: measured according to GB / T 8088-2008 using a Kjeldahl nitrogen determination apparatus. Directly tested using a TENSOR 27 Fourier infrared spectrum tester, the detection range was set to 4000~370 cm –1 , the resolution was 4 cm –1 , and the scanning number was 32 times. The raw rubber sample was cut into particles, 10 mg of the sample was weighed and placed in a crucible, and was tested using a STA449 thermal gravimetric analyzer. The test conditions were as follows: nitrogen was used as the external atmosphere, the flow rate was set to 50 mL / min; high-purity nitrogen was used as the protective gas, the flow rate was set to 25 mL / min; the test temperature range was 25~600°C, and the heating rate was 10 K / min. The glass transition temperature of the dry rubber film was determined using differential scanning calorimetry (DSC method), the temperature section was set to -90~100°C, and the heating rate was 10 K / min. The molecular weight and distribution of the rubber were detected using a GPC gel permeation chromatograph, 3 g of the dry rubber was cut into fine strips, soaked in a proper amount of tetrahydrofuran for one week until dissolved, and the solution was filtered using a needle filter, and was detected at 30°C using a gel permeation chromatograph.

[0136] 1.2.5 Determination of mixed rubber and vulcanized rubber

[0137] The vulcanization rate of the rubber mix was measured using a high-speed MD-3000A rotorless vulcanometer at 143°C for 50 minutes. The tensile strength, elongation at break, and modulus of tensile strength of the vulcanized rubber film were determined using an electronic universal testing machine according to GB / T 528-2009, and the tear strength was determined according to GB / T 528-2008. Dumbbell-shaped and right-angled test specimens were prepared according to ISO 527, and the stress-strain curves and related values ​​of the samples were measured using a universal electronic testing machine.

[0138] 2. Results and Analysis

[0139] 2.1 Effects of different vulcanization accelerators on the vulcanization characteristics and physical and mechanical properties of rubber compounds

[0140] 2.1.1 Effect of different vulcanization accelerator addition amounts on the vulcanization characteristics of rubber compounds

[0141] like Figure 5 and Figure 6 The trend of the vulcanization characteristics of the pure rubber compound with the change of the amount of the four vulcanization accelerators is shown. L It reflects the viscosity or fluidity of the rubber compound at the initial stage of vulcanization. L The lower the value, the better the processability. H The increase in the value will result in a torque difference (M H -M L The torque differential directly affects the physical and mechanical properties of the vulcanized rubber, such as hardness and elasticity, and is an important indicator for evaluating the degree of hardening during the vulcanization process of the rubber compound. A larger torque differential generally indicates good vulcanization responsiveness. The vulcanization time can be used to determine whether the additive accelerates or retards the vulcanization process.

[0142] like Figure 5 As shown in (a), M L With the increase of the dosage of the four vulcanization accelerators, there is a trend of first decreasing, then increasing and then decreasing to varying degrees. The four vulcanization accelerators can reduce the M L The values ​​indicate that adding four kinds of vulcanization accelerators can optimize its processing performance. L The order is TAA>3-HP>TK-PY>ETU, which means that under the same conditions, TAA has the worst processing performance and ETU has the best processing performance. Figure 5 As shown in (b) and (c), M H With M H -M L There is a similar trend, that is, with the increase of the content of the four vulcanization accelerators, M H With M H -M LAll of them showed an upward trend, and the M H With M H -M L The lowest TK-PY is the highest, which shows that TK-PY has the best vulcanization response and can give the material more excellent performance. Figure 5 (d) shows that TK-PY can significantly reduce the vulcanization time of the material and promote vulcanization.

[0143] Figure 6 As shown, TK-PY has the most significant effect on the improvement of the vulcanization curve, the vulcanization degree improves the fastest, and the torque value reaches the highest level. At the same time, with the increase of the amount of TK-PY, the torque value rises, and the vulcanization time is significantly shortened, but all of them appear vulcanization reversion phenomenon. Second, 3-Hp also has obvious promoting effect on vulcanization, the vulcanization speed is faster, and the torque value is higher. Compared with TK-PY, the vulcanization reversion phenomenon is lighter. In contrast, ETU has a weak promoting effect on the vulcanization of natural rubber, and even may reduce the vulcanization speed when the amount is low. Finally, TAA has no promoting effect on the vulcanization of the rubber compound, but it reduces the vulcanization degree to some extent. Among the four vulcanization accelerators, only the vulcanization time of TK-PY rubber compound is shortened with the increase of TK-PY amount, which significantly speeds up the vulcanization process, and the other three vulcanization accelerators have little effect on the vulcanization time.

[0144] 2.1.2 Effect of different amounts of vulcanization accelerators on the vulcanization curve of rubber compound

[0145] The modulus of vulcanized rubber is closely related to its crosslinking density. From Figure 7 It can be seen that with the increase of the amount of vulcanization accelerator, except TAA, the other three vulcanization accelerators all have a certain degree of improvement on the modulus of natural rubber vulcanized rubber. Among them, the modulus of the vulcanized rubber film of TK-PY group and 3-Hp group increases continuously with the increase of the amount of vulcanization accelerator, showing similar change law, but the TK-PY group has more significant speed and amplitude; The modulus of the vulcanized rubber of ETU group first increases and then decreases; After adding TAA, the modulus of the vulcanized rubber of natural rubber hardly changes. This shows that the improvement of modulus mainly depends on the pyridine group, and other functional groups play an important auxiliary synergistic role.

[0146] The physical and mechanical properties mainly include tensile strength, elongation at break, tear strength and hardness. According to Figure 8As shown, the tensile strength of natural rubber vulcanizates significantly increases with increasing TK-PY dosage. At lower dosages, 3-Hp also has a modest effect on tensile strength, but the increase ceases when the dosage exceeds 5 mmol / kg. TAA and ETU have almost no significant effect on tensile strength. The elongation at break of rubber vulcanizates increases initially and then decreases with increasing TK-PY dosage. TAA has minimal effect, with a slight improvement at higher dosages. With increasing 3-Hp dosage, the elongation at break continuously decreases, while increasing ETU dosage shows a trend of first decreasing and then increasing. The tear strength of natural rubber vulcanizates increases continuously with increasing TK-PY dosage, with the largest increase. However, 3-Hp stabilizes after reaching a certain level. Increasing ETU dosage shows an initial increase and then a decrease, while TAA has a minimal effect. The hardness of the vulcanized rubber increases with increasing amounts of TK-PY and 3-Hp, while the hardness initially increases and then decreases with increasing ETU. TAA also has a minimal effect on hardness. Analysis suggests that the improvement in the mechanical properties of the material after adding TK-PY is primarily due to the pyridine groups contained in TK-PY.

[0147] 2.1.3 Analysis of the effects of different vulcanization accelerators on vulcanization characteristics and physical and mechanical properties

[0148] As shown in Table 15:

[0149] The performance differences among the four vulcanization accelerators (TK-PY, 3-HP, ETU, and TAA) are mainly due to the effects of their chemical structures on the vulcanization reaction and cross-linking network.

[0150] Table 15 Comprehensive association table

[0151]

[0152] TK-PY: Thioketone group + pyridine group work synergistically to quickly release sulfur free radicals and coordinate Zn ions to form a high cross-linking density (M H -M L The highest) and shortest curing time (T 90 shortest), significantly improves the tensile stress, tensile strength and tear strength. However, polysulfide bonds (-S X -) The high proportion of it leads to easy breakage at high temperatures and poor stability.

[0153] 3-HP: Pyridine group coordination promotes cross-linking, and hydroxyl hydrogen bonds enhance network uniformity, but the release of sulfur radicals is insufficient, resulting in the second highest cross-linking density (M H -M L higher), slower vulcanization speed (T 90 Short sulfur bonds (-S- / -SS-) increase brittleness and lower tear strength.

[0154] ETU: Thioketone group releases sulfur radicals quickly, and the initial viscosity is the lowest (M L lowest), but lacks coordination groups and has low cross-linking density (M H -M L Moderate). Short sulfur bonds dominate the network, resulting in moderate tensile strength but high energy dissipation under dynamic loading (high tear strength).

[0155] TAA: The thioamide group is not active enough, the vulcanization reaction is not sufficient, and the cross-linking density is the lowest (M H -M L The lowest), the slowest vulcanization speed (T 90 Extension), the performance is close to that of unvulcanized rubber.

[0156] 2.2 Properties of natural rubber prepared by wet mixing of four vulcanization accelerators

[0157] 2.2.1 Conventional indicators of natural rubber

[0158] Fresh latex was wet-mixed and then added with four additives to produce natural rubber raw rubber. Mooney viscosity is an important parameter for assessing rubber processing fluidity and reflects the shear properties of rubber during mixing. As shown in Table 16, the raw rubber sample with ETU exhibited the highest Mooney viscosity, while the Mooney viscosity decreased after the addition of TAA, 3-HP, and TK-PY. Plasticity measures the plasticity of rubber, while plasticity retention is an important indicator of rubber stability. The data in Table 16 show that the initial plasticity of the raw rubber changed little after the addition of the four vulcanization accelerators. With the exception of TK-PY, which saw a slight increase, the other three decreased to some extent. All four vulcanization accelerators reduced the plasticity retention of the raw rubber, with ETU and 3-HP showing a greater decrease, while TK-PY and TAA showed a relatively smaller decrease. Finally, the change in nitrogen content may be due to the nitrogen contained in the additives themselves or to their inhibition of microbial degradation, thereby retaining a high protein content. Specifically, the nitrogen content of the raw rubber sample with TK-PY added was the highest, which may be related to the good antibacterial and mildew-proof effect of TK-PY.

[0159] Table 16 Conventional indicators of raw rubber prepared by wet mixing of fresh latex and adding four vulcanization accelerators

[0160]

[0161] 2.2.2 Effect of different vulcanization accelerators on the vulcanization characteristics of rubber compounds

[0162] Figure 9 Table 17 shows the vulcanization characteristics of the natural rubber raw rubber prepared by wet mixing of fresh latex with the addition of four vulcanization accelerators. Figure 9As shown in Table 17, all four vulcanization accelerators can improve the minimum viscosity (M L ) of the rubber compound. Among them, ETU and TK-PY have the largest improvement on the M L of the rubber compound. There is a high correlation between the maximum viscosity (M H ) and the minimum viscosity difference (M H -M L ) of the rubber compound. The rubber compound added with 3-HP performs best in M H and M H -M L , followed by TK-PY, while ETU has relatively small effect on M H and M H -M L , and TAA leads to the decrease of M H and M H -M L . In terms of vulcanization time, the 3-HP sample has the shortest vulcanization time and the fastest vulcanization speed in all vulcanization stages; TK-PY is second; ETU and TAA also accelerate the vulcanization process, but the effect is relatively weak.

[0163] Table 17 Effect of different vulcanization accelerators on the vulcanization properties of rubber compound prepared from fresh latex

[0164]

[0165] 2.2.3 Effect of different vulcanization accelerators on the physical and mechanical properties of vulcanized rubber prepared from raw rubber

[0166] Table 18 is the detection results of the physical and mechanical properties of natural rubber vulcanizate prepared by adding four additives to fresh latex by wet mixing. For the vulcanized rubber, the physical and mechanical properties are important indicators for evaluating the final quality of the product. Several key performance indicators including constant tensile stress, tensile strength, elongation at break, tear strength and hardness are listed in the table below. From Table 18, it can be seen that the samples added with TK-PY and 3-HP exhibit higher tensile stress at 100%, 300% and 500% elongation, especially 3-HP, which reaches the highest value at each constant elongation stress. This indicates that these two vulcanization accelerators can more effectively improve the load-carrying capacity of the material during deformation under stress. In contrast, the constant elongation stress of the sample added with TAA decreases. The samples added with TK-PY and 3-HP also exhibit higher tensile strength, reaching 25.90 MPa and 26.49 MPa, respectively, while the tensile strength of the sample added with TAA is 18.47 MPa, which is lower than the blank control group. The elongation at break of the samples of the four vulcanization accelerators is maintained at a similar high level, indicating good elastic recovery characteristics. Among them, the sample added with ETU has the highest elongation at break, reaching 902.0%, but the difference between it and other samples is not significant. The sample added with 3-HP has the highest tear strength, reaching 27.9 KN / m, followed by the TK-PY sample, reaching 26.4 KN / m, which also has a relatively high level, the sample added with ETU also performs well, while the tear strength of the TAA sample is relatively low. The hardness of the samples added with TK-PY and 3-HP is higher, while the hardness of the samples added with ETU and TAA changes less.

[0167] Based on the above vulcanization characteristics and physical and mechanical properties, the reasons for the above are analyzed as follows:

[0168] TK-PY shows better performance in improving mechanical properties, proving that the pyridine group has a role in promoting vulcanization. TK-PY forms a network that enhances tensile strength by covalent / hydrogen bonding in NR, TK-PY can enhance rubber properties by forming disulfide bonds through the release of reactive sulfur, increasing crosslinking density and intermolecular interactions. This not only improves tensile strength / hardness, but also reduces stress concentration through uniform network distribution, thereby maintaining elongation at break. The sulfur group further strengthens the bond through coordination and hydrogen bonding with rubber double bonds.

[0169] The hydroxyl group of 3-Hp enhances tensile strength through hydrogen bonding, but can cause brittleness and uneven crosslinking, promoting crack propagation. The structural stability of TAA hinders the formation of effective sulfur bonds, resulting in low vulcanization participation. Compared with the strength-brittleness trade-off of 3-Hp and the inertness of TAA, ETU and TK-PY show better effects in network optimization.

[0170] ETU effectively accelerates curing by lowering the activation energy of vulcanization and promoting polysulfide bond formation. Its moderate sulfur bridge length forms dense, directional crosslinks, enhancing tear strength and interchain cohesion while maintaining elongation. Although ETU cures faster than TK-PY, its limited sulfur elongation limits the increase in tensile stress.

[0171] TAA has the worst mechanical properties, corresponding to the lower vulcanization performance, and has a lower hardness. The reason may be that the degree of cross-linking is low, less cross-linking network is formed, and the limited reactivity of TAA may not produce sufficient cross-linking.

[0172] Table 18 Effects of different vulcanization accelerators on the mechanical properties of vulcanized natural rubber prepared from fresh latex

[0173]

[0174] 2.2.4 Effects of different vulcanization accelerators on the molecular weight and distribution of raw natural rubber

[0175] Molecular weight has an important influence on the processing properties of rubber materials and the mechanical properties of the final product. Figure 10 Table 19 and Table 19 respectively show the relative molecular mass distribution and molecular weight test results of natural rubber raw rubber prepared by wet mixing and adding four vulcanization accelerators. Figure 10 As shown, the molecular weight distribution of raw natural rubber treated with vulcanization accelerators is not significantly different from that of the control, and both exhibit similar trends, showing bimodal distribution characteristics. The sample treated with 3-HP exhibits a significant difference in the distribution, with a higher content of the low molecular weight fraction and a lower content of the high molecular weight fraction. In contrast, the sample treated with TK-PY exhibits similar low molecular weight distribution to the 3-HP sample, but also exhibits a lower content of the high molecular weight fraction.

[0176] The weight average molecular weight of the natural rubber prepared by wet mixing and adding four vulcanization accelerators decreased compared with the control group, among which TK-PY did not decrease significantly, and 3-HP had the most obvious downward trend. The addition of TAA increased the number average molecular weight to a certain extent, but the number average molecular weight decreased after adding ETU and TK-PY, with TK-PY decreasing the most, while the number average molecular weight after adding 3-HP was consistent with the control group. The distribution coefficient increased after adding TK-PY, but decreased after adding the other three vulcanization accelerators, with 3-HP decreasing the most significantly. The results showed that after adding TK-PY, the content of small molecular weight components increased, the molecular weight of large molecular weight components became larger, and at the same time the molecular weight distribution became wider, and the difference in molecular weight of rubber molecular chains became larger; after adding 3-HP, the small molecular weight components became more and the molecular weight became smaller, and the number of large molecules was small and the molecular weight was low, and the molecular weight distribution was the most compact, which was consistent with the control group. Figure 9 consistent.

[0177] Table 19 Effect of different vulcanization accelerators on the relative molecular mass and distribution coefficient of raw rubber prepared from fresh latex

[0178]

[0179] 2.2.5 Effects of different vulcanization accelerators on the infrared spectra of natural rubber

[0180] Figure 11 The infrared spectrum of natural rubber raw rubber was prepared by wet mixing and adding four additives to fresh latex. Figure 11 As shown in the infrared spectra of the five natural rubber samples, no significant peak migration was observed, and the peak intensity did not change significantly. The characteristic peaks basically appeared in the same band number, and the infrared curves were relatively close as a whole with little difference. The peak wave number of the C=C double bond stretching vibration peak of the natural rubber molecule is 1645cm -1 , the bending vibration peak is 840cm -1 ; The stretching vibration wave number of -CH3 and -CH2 is 2959cm -1 and 2851cm -1 , and their bending vibration peaks are at wave numbers 1443 cm -1 and 1375cm -1 There are some slight differences in some characteristic peaks of the six spectra, indicating that the addition of the four vulcanization accelerators has little effect on the structure of natural rubber, making it difficult to determine their effects on the properties of the dry film.

[0181] 2.2.6 Effects of different vulcanization accelerators on the thermal stability of raw natural rubber

[0182] Figure 12 Table 20 shows the TG and DTG spectra and characteristic temperatures of natural rubber raw rubber prepared by adding four different vulcanization accelerators during wet mixing. Figure 12 As shown in Table 20, the samples with TK-PY and 3-Hp added showed slightly higher initial decomposition temperatures, indicating that these two additives may help improve the initial thermal stability of natural rubber. In contrast, the initial decomposition temperatures of the samples with TAA and ETU were similar to those of the sample without any additives (Blank), which means that their effect on improving the initial thermal stability of natural rubber was not significant. 50% ), among all the vulcanization accelerators, 3-Hp makes natural rubber have the highest T 50% , i.e. 386.28°C, showing that it has a significant positive effect on the thermal stability of rubber, and TK-PY makes the T 50%decrease, indicating that the thermal decomposition rate in the middle stage is faster, and the rest of the additives have less effect on T 50% The peak temperature (Tp) is the temperature that measures the most active decomposition stage of the material during heating. From the data, it can be seen that the sample with TK-PY has the highest T p , reaching 382.00°C, followed by 3-HP, again proving their importance in improving the thermal stability of natural rubber, while the sample with TAA has the lowest T p , and ETU is not much different from the blank control group. Finally, considering the final decomposition temperature (T f ), the samples with TAA and ETU are even slightly higher than the blank sample, 3-HP is not much different from the blank control group, and TK-PY is lower than the control group.

[0183] According to the above phenomenon, all vulcanization accelerators can improve the initial decomposition temperature to some extent, but TK-PY has poor thermal stability in general, and the rest of the vulcanization accelerators have slightly better thermal stability than the control group. The reasons are as follows: TK-PY: the pyridine group improves the initial stability, but the degradation effect and uneven crosslinking lead to a decrease in thermal stability in the middle and late stages. 3-HP: hydrogen bonds and pyridine groups synergistically enhance the stability of molecular chains, and the middle thermal stability is optimal. TAA: low reactivity leads to no significant improvement in thermal stability, and the residue only delays the final decomposition. ETU may be that it is easy to vulcanize with double bonds in rubber at high temperatures to generate short sulfur bonds, which slightly enhances its thermal stability.

[0184] Table 20 Characteristic temperatures of natural rubber raw rubber prepared after adding four different vulcanization accelerators

[0185]

[0186] 2.2.7 Effect of different vulcanization accelerators on RPA data of prepared natural rubber raw rubber

[0187] The changes in G' (storage modulus) and Tan δ (loss factor) curves are very important for understanding the dynamic mechanical properties of rubber materials. They reflect the elastic behavior and energy dissipation characteristics of the material at different frequencies or temperatures. From Figure 13 (a) and Figure 13(b) It can be seen that the addition of TK-PY, 3-HP, and ETU may lead to an increase in G' values ​​across the entire test range, with 3-HP showing the most significant increase, followed by TK-PY. This indicates an increase in rubber rigidity, likely due to TK-PY and 3-HP promoting the formation of crosslinks, thereby strengthening the network structure. Furthermore, changes in the Tanδ curve reflect changes in the material's viscoelasticity; if the peak shifts to higher temperatures or frequencies, it indicates an increase in the material's glass transition temperature (Tg), implying decreased flexibility and enhanced thermal stability. TAA has little effect on the G' and Tanδ values ​​of the raw rubber samples. The addition of ETU increases the G' curve while decreasing the Tanδ value, with minimal differences from the TK-PY curve. The sample with 3-HP exhibits the highest G' curve and the lowest Tanδ value.

[0188] The reasons are analyzed as follows:

[0189] (1) TK-PY: ① Thioketone group promotes cross-linking: Thioketone group (RC=S) releases active sulfur free radicals, accelerates cross-linking, and increases cross-linking density (G'↑). ② Coordination effect of pyridine group: Pyridine and Zn 2+ Coordination enhances the rigidity of the cross-linked network, but cross-linking may be locally uneven, resulting in incomplete restriction of molecular chain motion (limited reduction in Tanδ). ③ Degradation side reactions: Thioketone groups may induce partial chain breakage during the vulcanization process, forming micro-defects and slightly increasing energy dissipation.

[0190] (2) ETU (ethylene thiourea): ① Rapid cross-linking to form short sulfur bonds: ETU efficiently promotes sulfur cross-linking, but mainly generates monosulfide bonds (-S-) or disulfide bonds (-SS-), resulting in a high brittle cross-linked network. ② Bond reorganization under dynamic load: Short sulfur bonds are easily broken and reconnected during deformation, resulting in a certain amount of viscous dissipation (Tanδ↓ is not as large as 3-HP). ③ Trade-off between cross-linking density and uniformity: Although the cross-linking density is high, the network uniformity is poor, which limits the optimization of elastic response.

[0191] (3) TAA (thioacetamide): ① Low reactivity limits crosslinking: The thioamide group of TAA has low activity and cannot effectively participate in the vulcanization reaction, and has no significant effect on the crosslinking network. ② Unrestricted molecular chain movement: No additional crosslinking points are formed, and the rubber maintains its original viscoelastic behavior (G'≈blank, tanδ≈blank).

[0192] (4) 3-HP (3-hydroxypyridine): ① Hydrogen bond enhances the interaction between molecular chains: Hydroxyl (-OH) forms reversible hydrogen bonds with rubber molecular chains, improving the interchain bonding force and increasing the crosslinking point density, thereby significantly improving the rigidity (G'↑). ② Coordination stabilization effect of pyridine group: Pyridine ring and Zn 2+ Coordination (such as Zn(C5H5N) 2+), optimize the uniformity of crosslinking network, reduce the local movement of molecular chain, and reduce energy dissipation (Tanδ↓). ③ Synergistic effect: hydrogen bonding and coordination interaction jointly form a uniform and stable crosslinking network, which not only improves the elastic energy storage capacity, but also inhibits viscous dissipation.

[0193] Summary: Through systematic experiments, the specific performance and mechanism of different vulcanization accelerators (TK-PY, TAA, ETU and 3-Hp) in the preparation process of natural rubber mixed rubber and vulcanized rubber were analyzed. The results show that TK-PY can effectively shorten the vulcanization time and show strong vulcanization promotion ability; Compared with TAA, it has almost no positive effect on vulcanization, and may even inhibit the vulcanization process; and ETU and 3-Hp show different degrees of vulcanization promotion effect. TK-PY and 3-Hp have a significant improvement on the modulus, tensile strength, tear strength and hardness of the vulcanized rubber, among which TK-PY samples show faster vulcanization speed and higher vulcanization degree at higher dosage; The improvement of TAA on the performance of vulcanized rubber is almost negligible, and the effect of ETU is also relatively limited. The raw rubber prepared by adding TK-PY to fresh latex through wet mixing has a lower number average molecular weight and a wider molecular weight distribution; The weight average molecular weight of the ETU sample is also low, and the molecular weight distribution coefficient is relatively small; The weight average molecular weight of the 3-Hp sample is also low, and its molecular weight distribution coefficient is the lowest. The infrared spectrum analysis results show that the characteristic peaks of the five samples are basically the same, and no significant migration or intensity change is observed, indicating that the vulcanization accelerator has little effect on the main chain structure of natural rubber. The raw rubber samples added with TK-PY and 3-Hp have improved storage modulus (G'), indicating that the rigidity of the rubber increases; At the same time, the loss factor (Tanδ) curve is also lower, especially the 3-Hp sample shows a lower Tanδ value.

[0194] In summary, TK-PY not only can significantly accelerate the vulcanization speed of natural rubber, improve the vulcanization degree, but also can significantly improve the physical and mechanical properties of vulcanized natural rubber.

[0195] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A composite vulcanization accelerator TK-PY, characterized in that: Composed of a thione derivative and a pyridine compound, wherein the pyridine compound is selected from any one of 3-hydroxypyridine, 2-methylpyridine, 4-ethylpyridine, 2-nitropyridine, 3-nitropyridine, 2-aminopyridine and 3-aminopyridine; The thione derivative is selected from any one of sodium pyridinethione, 3-methylthiazoline-2-thione, N-hydroxypyridine-2-thione, 5-dodecyldithio-3-phenyl-1,3,4-thiadiazole-2-thione, 1,3-thiazolidine-2-thione, tetrahydropyrrole-2-thione, and 5-(4-methylbenzoyl)-3,4-dihydropyrimidine-2-thione; The mass ratio of the thione derivative and the pyridine compound in the composite vulcanization accelerator is 1:(1-15); The usage of the composite vulcanization accelerator is 2.5 mmol / Kg to 7.5 mmol / Kg.

2. The composite vulcanization accelerator according to claim 1, characterized in that The mass ratio of the thione derivative to the pyridine compound in the composite vulcanization accelerator is 1:

3.

3. The composite vulcanization accelerator according to claim 1, characterized in that The usage of the composite vulcanization accelerator is 3 mmol / Kg to 6 mmol / Kg.

4. The composite vulcanization accelerator according to claim 3, characterized in that The dosage of the composite vulcanization accelerator is 5 mmol / Kg.

5. The method for preparing the composite vulcanization accelerator according to claim 1, wherein The following steps are involved: The composite vulcanization accelerator is obtained by adding the thioketone derivative into the pyridine compound and stirring evenly.

6. Use of the composite vulcanization accelerator according to any one of claims 1 to 4 or the composite vulcanization accelerator prepared by the preparation method according to claim 5 in promoting the vulcanization of natural rubber latex, accelerating the vulcanization rate, improving its physical and mechanical properties, and inhibiting bacteria and mildew.

7. Use of the composite vulcanization accelerator according to any one of claims 1 to 4 or the composite vulcanization accelerator prepared by the preparation method according to claim 5 in promoting the vulcanization of rubber mix, accelerating the vulcanization rate, improving its physical and mechanical properties, and inhibiting bacteria and mildew.

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