Impact of Thioamide Derivative Composite Preservation System on Vulcanization of Natural Rubber

Impact of Thioamide Derivative Composite Preservation System on Vulcanization of Natural Rubber | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Impact of Thioamide Derivative Composite Preservation System on Vulcanization of Natural Rubber Liguang Zhao, Yiqun Liu, Liyang Zhao, Yazhong Song, Honghai Huang, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7015352/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The thioacetamide derivative (TD)-composite preservation system (TDCPS) exhibits superior preservation effects on natural rubber (NR) latex and significantly enhances its vulcanization efficiency and mechanical properties. This study assessed TDCPS for NR, with a particular focus on its effects in promoting vulcanization. The TD containing both pyridine and thioamide groups was evaluated against other additives, namely thione accelerator ETU, pyridine 3-HP, and thioacetamide TAA. The results indicated that TD significantly reduced vulcanization time and enhanced efficiency, surpassing the moderate effects of ETU and 3-HP, as well as the minimal activity of TAA. Furthermore, TD and 3-HP demonstrated a synergistic effect in enhancing the properties of vulcanized NR, including elongation stress, tensile strength, tear resistance, and hardness, with TD achieving more rapid and complete vulcanization at higher dosages. Both TD and 3-HP increased the energy storage modulus of raw NR, thereby enhancing rigidity, while maintaining low loss factor values. The superior performance of TD is attributed to the synergistic interaction of its pyridine and thioamide groups, which optimize vulcanization kinetics and mechanical integrity. These findings underscore TD's potential as an efficient vulcanization promoter for NR. Natural rubber Preservation system Vulcanization Physical and mechanical properties Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction In the current industrial context, the rubber sector holds a crucial position within the economy. Natural rubber (NR) products, renowned for their exceptional elasticity and durability, are extensively utilized across critical sectors such as automotive, structure, medical, and aviation [ 1 ]. However, NR latex is inherently prone to microbial degradation and deterioration, necessitating effective preservation strategies [ 2 ]. Traditionally, ammonia has been employed for this purpose; however, its high volatility and irritating properties pose significant environmental and safety challenges to its use [ 3 – 4 ]. In response to this challenge, the industry has developed ammonia-free preservatives, such as hexahydroxyethyl homotriazine, benzisothiazolinone, and bismorpholine methane, among others [ 5 – 7 ]. However, factors such as the preservation effect, toxicity of preservatives, and production costs hinder the large-scale dissemination and application of these preservatives. Among these, the thioamide derivative composite preservative system (TDCPS) emerges as a promising alternative, exhibiting significant advantages in terms of safety, low toxicity, consistent quality, and cost-effectiveness. A key feature of TDCPS is its ability to significantly enhance the quality of NR latex while improving its physical and mechanical performance [ 8 ]. The core component of the system is a thioamide derivative (TD), which is complemented by a minimal quantity of auxiliary additives. Analytical studies have revealed that TD is uniquely responsible for accelerating and enhancing vulcanization within TDCPS. This functionality is attributed to the synergistic interplay of thioamide and pyridine functional groups in its molecular structure. These groups not only facilitate efficient cross-linking but also optimize the kinetics and extent of vulcanization, ultimately contributing to the production of high-performance rubber materials with enhanced mechanical properties [ 9 – 13 ]. NR, a primary raw material for rubber products, has long been the cornerstone of the rubber industry owing to its superior mechanical properties and environmental adaptability. Nevertheless, unprocessed NR exhibits certain constraints, notably low hardness and suboptimal abrasion resistance, restricting its use in high-performance applications [ 13 ]. Vulcanization, the process of creating a three-dimensional mesh structure between linear macromolecular chains, enhances these properties. This is achieved by introducing sulfur or other vulcanizing agents to the rubber, initiating a chemical reaction at a specified temperature. Post-vulcanization, rubber undergoes significant enhancements in its physical and mechanical attributes, rendering it suitable for high-performance applications [ 14 ][ 15 ]. Within this process, the role of the vulcanization accelerator is pivotal [ 16 ]. Vulcanization accelerators expedite the vulcanization process, lower the required temperature, augment the mechanical characteristics of the vulcanized rubber, and decrease sulfur usage, thereby reducing costs. Additionally, they bolster the dynamic fatigue performance, abrasion resistance, and aging resilience of the vulcanized rubber. Consequently, judicious selection of vulcanization accelerators is paramount to elevating the quality of rubber products [ 17 ]. NR, a primary raw material for rubber products, has long been the cornerstone of the rubber industry owing to its superior mechanical properties and environmental adaptability. Nevertheless, unprocessed NR exhibits certain constraints, notably low hardness and suboptimal abrasion resistance, restricting its use in high-performance applications [ 13 ]. Vulcanization, which involves the formation of a three-dimensional mesh structure between linear macromolecular chains, enhances these properties. This is achieved by introducing sulfur or other vulcanizing agents into the rubber, initiating a chemical reaction at a specified temperature. Post-vulcanization, rubber undergoes significant enhancements in its physical and mechanical attributes, rendering it suitable for high-performance applications [ 14 – 15 ]. The vulcanization accelerator plays a pivotal role in this process [ 16 ]. Vulcanization accelerators expedite the vulcanization process, lower the required temperature, augment the mechanical characteristics of vulcanized rubber, and decrease sulfur usage, thereby reducing costs. Additionally, they bolster the dynamic fatigue performance, abrasion resistance, and aging resilience of vulcanized rubber. Consequently, the judicious selection of vulcanization accelerators is paramount for improving the quality of rubber products [ 17 ]. Vulcanization accelerators are chemicals that expedite the vulcanization reaction, thereby enhancing the physical attributes of vulcanized rubber. These accelerators not only reduce the vulcanization duration and lower the vulcanization temperature but also augment the aging and abrasion resistance of the resultant rubber. In the rubber industry, judicious selection and utilization of a vulcanization accelerator is paramount to elevating product quality. Currently, prevalent vulcanization accelerators in the market encompass hyposulfonamide, thiazole, and thiuram, each of which exhibits distinct characteristics and finds application in specific scenarios, offering unique advantages [ 18 ]. For instance, hyposulfonamide vulcanization accelerators possess commendable delayed-vulcanization properties, making them apt for an array of rubber products [ 19 ], whereas thiazole accelerators are acclaimed for their rapid vulcanization capabilities, rendering them suitable for high-speed vulcanization processes [ 20 ]. Nevertheless, these conventional accelerators are not devoid of shortcomings; they may contain potentially hazardous substances and necessitate stringent operational conditions. With the expanding application of rubber products in extreme environments, there emerges an escalating demand for vulcanization accelerators capable of functioning proficiently under such challenging conditions [ 21 ]. Previous studies have established that the enhancement of the mechanical properties of NR-vulcanized films via composite preservation systems is primarily governed by the concentration of thioamide derivatives (TD). Building on this foundation, this study aimed to identify the specific chemical groups within TD responsible for its vulcanization-promoting effects. To achieve this, four key compounds—thioacetamide (TAA), thioketone accelerators (ETU), pyridine compounds, and TD —were selected as model additives. Their influence on the vulcanization behavior of NR blends and the resulting physical and mechanical properties of the vulcanized rubbers were systematically evaluated [ 22 ][ 24 ]. The experimental approach involved incorporating these four substances into fresh NR latex through a wet mixing process, followed by the production of raw rubber samples. The effects of each additive on the quality of raw rubber and the mechanical performance of the vulcanized products were characterized. This study specifically targeted the identification of key functional groups in TD that drive vulcanization enhancement and elucidated the underlying reaction mechanisms. 2. Experimental 2.1 Materials NR latex was sourced from the Experimental Farm of the Chinese Academy of Tropical Agricultural Sciences in Hainan Province, China. Industrial-grade additives including TD, TAA, ETU, and 3-Hp (Table 1 ) were procured from Shandong Yusuo Chemical Technology Co. TDCPS was prepared in the laboratory. Analytical grade tetrahydrofuran and ammonia (25% wt) were supplied by Guangdong Xilong Chemical Co., Ltd. Additional materials commonly used in the rubber industry, including ammonia, acetic acid, stearic acid, zinc oxide (ZnO), sulfur, and accelerator M accelerators, were employed in the experiments. Table 1 Chemical structure of four additives Category TD TAA ETU 3-Hp Chemical structure 2.2 Methods 2.2.1 Preparation of NR raw rubber samples A certain amount of fresh latex was collected from the rubber plantation and preserved using 0.1% ammonia. Subsequently, according to the formula in Table 2 , the appropriate additives were added, mixed well, and left for 24 h. The appropriate amount of acid required to coagulate fresh latex was determined using the formula for calculating the amount of acid required for coagulation. After one day of standing, it was creased, dehydrated, and dried completely under hot air at 70°C to prepare raw latex samples (Fig. 1 ). Table 2 NR latex additive composition and dosage Additives Dosage/mmol∙L − 1 Blank - TD 5 TAA 5 ETU 5 3-Hp 5 Note: The additives utilized were either aqueous solutions or colloidal suspensions, with the dosage indicating the optimal quantity of preservative employed for the preservation of natural latex. 2.2.2 Sample Preparation of Rubber Mixing and Vulcanization The sample preparation adheres to the ACS I formula and mixing procedure as stipulated in GB/T 15340 − 1994. Natural raw rubber was mixed using an open kneader to obtain the rubber mixture. The vulcanization characteristics of this mixture were then examined using a rotorless vulcanizer at a set temperature of 143°C for 60 min. Subsequently, the mixed rubber was vulcanized using a plate vulcanizing machine, maintained at a temperature of 143°C. The vulcanization process was carried out for a positive vulcanization time of t 90 + 5 min, resulting in the formation of a vulcanized film. 2.2.3 Preparation of Test Sample for Rubber Mixing A pure rubber formulation was employed to produce 3.9 kilogram of compounded NR, which was subsequently divided into 13 equal 300 g portions. Subsequently, the additives were incorporated as per the specifications detailed in Table 3 , ensuring thorough mixing. After allowing the mixture to rest for 12 hours, its vulcanization characteristics were examined. Subsequently, a vulcanized rubber film was fabricated to assess its physical and mechanical properties. Table 3 Dosage of additives for compounded NR Additives Dosage/mmol∙L − 1 blank - TD 2.5, 5, 7.5 TAA 2.5, 5, 7.5 ETU 2.5, 5, 7.5 3-Hp 2.5, 5, 7.5 2.2.4 Testing of Raw Rubber Plasticity Initial Value (P 0 ) and Plasticity Retention Rate (PRI): These were measured using a rapid plasticity meter, in accordance with the GB/T 3517 − 2014 and GB/T 3510 − 2006 standards.Menni Viscosity M L (1 + 4) at 100 ℃: This was tested using a Menni viscometer, following the GB/T 1232.1–2016 standard. Nitrogen Content: The nitrogen content was measured using a Kjeldahl nitrogen tester, as prescribed by the GB/T 8088 − 2008 standard. A TENSOR 27 Fourier infrared spectroscopy tester was used for direct testing, with the detection range set at 4000 − 370 cm -1 , a resolution of 4 cm -1 , and 32 scans. The raw rubber sample was cut into small particles, and 10 mg of the sample was weighed and placed in a crucible for testing using an STA449 thermogravimetric analyzer. The test conditions included the use of nitrogen as the external atmosphere with a flow rate of 50 mL/min, high-purity nitrogen as the protective gas at a flow rate of 25 mL/min, a temperature range of 25–600 ℃, and a heating rate of 10 K/min. The glass transition temperature of the dry gel film was determined using both the Differential Scanning Calorimetry (DSC) method, with a temperature range of -90-100 ℃ and a heating rate of 10 K/min, and the GPC gelation method, under similar conditions.Furthermore, the molecular weight size and distribution of the rubber were detected by GPC gel permeation chromatography. For this process, A 3 g of dry rubber was cut into small strips and soaked in an appropriate amount of tetrahydrofuran for one week until fully dissolved. The solution was then filtered using a needle filter and analyzed by gel permeation chromatography at 30°C. 2.2.5 Determination of Mixing and Vulcanizing Rubber The vulcanization speed of the rubber mix was determined using an MRL MD-3000A rotorless vulcanometer. Subsequently, the vulcanization characteristics of the mix were examined at 143 ℃ for 40 min using the same instrument. The tensile strength, elongation at break, and constant tensile stress of the vulcanized film were measured using an electronic universal testing machine. Tear strength was determined using the same machine. Specimens for the tensile strength and right-angled tests were prepared in accordance with ISO 527. The tests were conducted using an electronic universal testing machine. The tensile strength, elongation at break, and constant elongation stress were evaluated according to the guidelines of GB/T 528–2009, while the tearing strength was assessed based on GB/T 528–2008. Dumbbell and right-angle specimens required for these tests were prepared according to ISO 527. Finally, the stress-strain curves and relevant values of the samples were obtained using a universal electronic testing machine. 3. Results and Discussion 3.1 Impact of the Four Additives on the Vulcanization Characteristics and Physical and Mechanical Properties of the Compound Rubber 3.1.1 Influence of the Four Additives on the Vulcanization Characteristics of the Compound Rubber Figures 2 and 3 depict the trends in the vulcanization characteristics of pure rubber formulations as the four additives were modified. The minimum torque (M L ) value serves as an indicator of the viscosity or fluidity of the compound rubber at the onset of vulcanization; a lower M L value indicates superior processability. An increase in the maximum torque (M H ) value results in an increased torque difference (M H -M L ), which has direct implications for the hardness, elasticity, and other physical and mechanical attributes of the vulcanized rubber. This torque difference is a crucial metric for gauging the extent of hardening during vulcanization of the compound. A substantial torque difference typically signifies the commendable vulcanization responsiveness of the compound. Furthermore, vulcanization time provides insights into whether the additives accelerate or decelerate the vulcanization process. Figure 2 (a) illustrates that as the dosage of the four different additives increases, the M L value initially declines, subsequently rises, and finally decreases again. This indicates that these four additives can effectively reduce the M L value of the rubber mix, thereby optimizing its processing performance. When comparing the M L values at the same additive content, the order was TAA > 3-HP > TD > ETU. This suggests that under identical conditions, TAA exhibits the poorest processing performance, whereas ETU exhibits the best. Figures 2 (b) and 2(c) reveal a consistent trend for M H and the M H -M L ; that is, an increase in the content of the four additives leads to a corresponding increase in M H and M H -M L . Furthermore, at the same additive content, the lowest values of MH and M H -M L were observed for TAA, and the highest for TD. This demonstrates that TD has superior vulcanization responsiveness, significantly enhancing the properties of the material. As illustrated in Fig. 3 , TD exhibited the most pronounced effect on enhancing the vulcanization curve, characterized by the swiftest rise in the degree of vulcanization and peak torque value. Concurrently, an increase in TD dosage elevates the torque value and markedly reduces the vulcanization time, although all exhibit vulcanization reversion. Subsequently, 3-Hp notably promoted vulcanization, as evidenced by the accelerated vulcanization speed and heightened torque value, with the reversion of vulcanization phenomenon being less pronounced than that with TD. Conversely, ETU exerts a comparatively weaker promoting effect on the vulcanization of NR and may even diminish the vulcanization speed at lower dosages. Finally, TAA did not enhance the vulcanization of the compound and, to a certain extent, reduced the degree of vulcanization. Among the four additives, only the vulcanization time of the TD compounds was curtailed with increasing TD dosage, thereby significantly expediting the vulcanization process, whereas the other three additives exerted a lesser impact on vulcanization time. 3.1.2 The Impact of Four Additives on the Physical and Mechanical Properties of Vulcanized Rubber The constant elongation stress of vulcanized rubber is intimately associated with its crosslink density. As illustrated in Fig. 4 , an increase in additive dosage, with the exception of TAA, results in varying degrees of enhancement in the constant elongation stress of vulcanized NR. Specifically, the samples of vulcanized rubber film treated with TD and 3-Hp exhibited a continuous rise in constant elongation stress as the additive dosage increased, demonstrating similar patterns of change. However, the rate and extent of improvement were notably more pronounced in the TD group. In contrast, the constant elongation stress for the vulcanized rubber in the ETU group showed an initial increase followed by a decrease, whereas the samples with TAA remained largely unchanged. Furthermore, it can be deduced that the enhancement in elongation provided by TD is primarily attributed to the pyridine group, with other groups offering significant auxiliary synergistic contributions. The physical and mechanical properties primarily encompass the tensile strength, elongation at break, tear strength, and hardness. As depicted in Fig. 5 , the tensile strength of vulcanized NR experienced a marked increased significantly with increasing TD dosage. However, at lower dosages, 3-Hp also enhanced the tensile strength, but this effect plateaued when the dosage exceeded 5 mmol/Kg. Conversely, TAA and ETU exerted minimal influence on the tensile strength. The elongation at break for the vulcanized rubber demonstrated an initial increase, followed by a decrease as the TD dosage increased. The impact of TAA on these properties was marginal. An increasing 3-Hp dosage led to a consistent reduction in the elongation at break, whereas an increasing ETU dosage exhibited an initial decrease, followed by an increase. The tear strength of vulcanized NR consistently improved with increasing TD dosage, showing the most significant increase. The effect of 3-Hp dosage stabilized after a certain point, whereas an increased ETU dosage initially increased and then decreased. The influence of TAA on the tear strength was notably less pronounced. The hardness of the vulcanized rubber augmented with both TD and 3-Hp dosages, yet the increase with ETU displayed a pattern of initial growth, followed by a decrease. The role of TAA in altering the hardness was relatively minor in this study. The analysis indicates that the enhanced physical and mechanical properties of the materials post-TD addition are predominantly attributed to the pyridine group within TD, with the thioamide group providing supplementary contributions. 3.1.3 Result analysis of vulcanization characteristics and physical and mechanical properties The variances in the properties of the four vulcanizing agents, TD, 3-HP, ETU, and TAA primarily arise from the impact of their distinct chemical structures on both the vulcanization reaction and the crosslinking network. The thioamide in conjunction with the pyridine group facilitates the rapid release of sulfur radicals and coordinates Zn²⁺, culminating in a pronounced cross-linking density and the briefest vulcanization time. This led to a marked enhancement in the constant tensile stress, tensile strength, and tear strength. However, the significant presence of polysulfide bonds (-Sₓ-) predisposes the material to easy fracture at elevated temperatures, compromising stability. In the 3-HP compound, pyridine group coordination encourages cross-linking, while hydroxyl hydrogen bonding boosts network uniformity. However, the release of sulfur radicals was insufficient, resulting in a suboptimal crosslinking density and slower vulcanization process. The presence of short sulfur bonds (-S-/-S-S-) increases the brittleness and reduces the tear strength. ETU is characterized by the rapid release of sulfur radicals from thione groups, resulting in the lowest initial viscosity. However, it lacks ligand groups and has a low crosslinking density. The network is dominated by short sulfur bonds, which contribute to medium tensile strength. However, it exhibits high energy dissipation under dynamic loading, resulting in high tear strength. Thioamide activity exhibits inadequate activity owing to the deficient performance of thioamide groups. This led to an insufficient vulcanization reaction, resulting in the lowest crosslinking density. Consequently, vulcanization takes longer, and its properties closely resemble those of unvulcanized rubber. 3.2 Characteristics of NR Prepared by Wet Mixing with Four Additives 3.2.1 Conventional Indicators of NR Raw Material Fresh latex was processed into raw NR through wet mixing with four distinct additives. Mooney viscosity is a critical parameter for evaluating the processing fluidity of rubber, as it indicates the shear characteristics of rubber during the mixing process. As shown in Table 4 , the raw rubber samples exhibited the highest Mooney viscosity upon the addition of ETU. Conversely, Mooney viscosity decreased with the incorporation of TAA, 3-HP, and TD. Plasticity provides insight into the malleability of rubber, and the retention of plasticity is a key index for assessing the stability of rubber. As shown in Table 4 , the initial plasticity value of the raw rubber displayed minimal variations upon the addition of the four additives. Notably, 3-HP and TAA reduced plasticity slightly. However, all four additives reduced the plasticity retention of raw rubber. Among them, ETU and 3-HP caused a more pronounced decline, whereas TD and TAA caused a relatively lesser decrease. Furthermore, alterations in nitrogen content could be attributed to either the inherent nitrogen in the additives or their potential to inhibit microbial degradation reactions, thereby preserving a higher protein content. Specifically, the elevated nitrogen content observed in the TD-enhanced raw rubber samples may be correlated with TD's potent antimicrobial and anti-mold properties of TD. Table 4 Conventional indexes of raw NR prepared by mixing fresh latex with the four additives Additives Mooney viscosity P 0 PRI/% Nitrogen content/% - 71.57 34.8 86.2 0.407 TD 68.74 35.2 82.61 0.478 TAA 70.20 33.7 83.14 0.466 ETU 73.58 34.4 77.21 0.399 3-Hp 69.62 32.1 73.13 0.419 3.2.2 The impact of various additives on the vulcanization properties of raw rubber. Figure 6 and Table 5 present the vulcanization characteristics of pure rubber formulations derived from fresh latex processed via wet mixing with four distinct additives. Contrary to the trend depicted in Fig. 2 (a), all four additives enhanced the Maximum Latent Hardness of the compounds. Notably, ETU and TD exhibited the most significant enhancement in the ML of the compounds. A strong correlation was observed between the Maximum Hardness and the difference between the Maximum Hardness and Maximum Latent Hardness of the compounds. The compounds into which 3-HP was incorporated demonstrated superior MH and M H -M L values, followed by TD. Meanwhile, ETU had a comparatively minor enhancing effect on MH and M H -M L values, whereas TAA reduced these values. With respect to vulcanization time, the samples containing 3-HP displayed the shortest duration and the fastest rate of vulcanization across all stages, followed by TD. Both ETU and TAA expedited the vulcanization process, albeit with relatively weaker effects. Table 5 Effects of different additives on vulcanization characteristics of fresh latex prepared compound Additives M L /dN∙m M H /dN∙m M H -M L /dN∙m T 10 /s T 50 /s T 90 /s - 0.42 5.62 5.2 130 350 1169 TD 0.69 6.35 5.66 91 226 826 TAA 0.49 5.47 4.98 142 367 1192 ETU 0.61 5.94 5.33 117 313 1097 3-Hp 0.47 6.47 6 80 208 774 3.2.3 Effects of different additives on the physical and mechanical properties of vulcanized rubber Table 6 presents the physical and mechanical properties of NR vulcanized from fresh latex using wet mixing with four additives. The quality of vulcanized rubber is determined by its physical and mechanical characteristics. Key metrics, such as constant tensile stress, tensile strength, elongation at break, tear strength, and hardness, are detailed. At 100%, 300%, and 500% elongations, the samples containing TD and 3-Hp displayed elevated tensile stresses, with 3-Hp achieving the highest values at each constant tensile stress, suggesting an enhanced load-bearing capacity. The constant tensile stress for the TAA samples diminished. For tensile strength, TD and 3-Hp samples exhibited values of 25.90 MPa and 26.49 MPa, respectively, while TAA samples showed 18.47 MPa, lower than that of the blank control group. The elongation at break remained consistent across the additives, with ETU showing the highest value at 902%. The highest tear strength was recorded for 3-Hp at 27.9 kN∙m − 1 , followed by TD at 26.4 kN∙m − 1 . While the ETU samples showed robust tear strength, the TAA samples showed notably lower strength. For hardness, TD and 3-Hp samples were stiffer, whereas ETU and TAA showed less variation. In conjunction with the previously discussed vulcanization characteristics and properties, the causes of these occurrences were analyzed as follows: TD exhibited superior performance in enhancing the mechanical properties through its pyridine group promoting vulcanization. TD creates cross-links in NR via covalent and hydrogen bonds, forming a network that increases the tensile strength. The TD improves the rubber properties by releasing reactive sulfur to form disulfide bonds, thereby increasing the crosslink density and interactions. This enhances the tensile strength and hardness while maintaining elongation through a uniform network distribution. The sulfur moiety strengthens the bonding by coordinating with the rubber double bond [ 25 – 27 ]. While 3-Hp's hydroxyl group improves the tensile strength via hydrogen bonding, it causes brittleness and uneven crosslinking. TAA's structural stability reduces vulcanization effectiveness. ETU and TD showed better network optimization than 3-Hp's strength-brittleness trade-off and TAA's inertness [ 28 ]. ETU accelerates vulcanization by reducing the activation energy and forming polysulfide bonds. Although ETU cures faster than TD, its limited sulfur elongation restricts the tensile stress [ 29 ]. TAA exhibited the weakest mechanical properties, confirming its poor vulcanization and hardness owing to reduced crosslinking and network formation [ 30 – 32 ]. Table 6 Effects of different additives on mechanical properties of vulcanized NR prepared from fresh latex Detection index Additives - TD TAA ETU 3-Hp Tensile stress at 100% elongation/MPa 0.59 0.68 0.55 0.61 0.70 Tensile stress at 300% elongation/MPa 1.21 1.50 1.14 1.31 1.57 Tensile stress at 500% elongation/MPa 2.49 3.29 2.34 2.80 3.55 Tensile strength/MPa 19.43 25.90 18.47 23.09 26.49 Elongation at break/% 882.4 898.7 899.7 902.0 881.0 Tear strength/kN∙m − 1 20.8 26.4 21.0 23.0 27.9 Hardness/HA 33.3 37.0 32.8 34.8 37.7 3.2.4 Effects of different additives on the relative molecular weight size and distribution of raw NR The molecular weight significantly influences the processing performance of rubber materials and the mechanical properties of the final product. Figure 6 and Table 7 present the relative molecular mass distribution and molecular weight detection results of raw NR prepared by wet mixing with the four additives, respectively. As shown in Fig. 6 , the relative molecular mass distributions of the additive-treated raw NR were not notably different from those of the control group, exhibiting a consistent bimodal distribution. The samples with 3-Hp showed differences in the distribution plots, with higher low-molecular-weight and lower high-molecular-weight fractions. Conversely, the TD-added samples showed minimal variation in the low-molecular-weight distribution compared to the 3-Hp samples, but their high-molecular-weight fractions were similarly reduced. The weight-average molecular weights of the raw NR with the four additives decreased compared to that of the control. TD showed an insignificant decline, whereas 3-HP displayed the most pronounced reduction. TAA led to a slight enhancement in the number-average molecular weight. However, these weights decreased with ETU and TD, with TD causing a greater decrease. The number-average molecular weight with 3-HP remained consistent with that of the control. The distribution coefficient increased due to TD but decreased with other additives, with 3-HP showing the sharpest decrease. These findings indicate that TD addition of TD increased the number of smaller molecular weight components. Concurrently, the molecular weight of the larger components increased, broadening the distribution and amplifying the molecular weight disparity among the rubber chains. With 3-HP introduction, smaller-molecular-weight components increased, larger molecules decreased, and the molecular weight distribution became more tightly clustered. These observations are consistent with the results shown in Fig. 6 . The weight-average molecular weight of raw NR, derived from fresh latex via wet mixing with four additives, decreased compared to that of the control. TD showed an insignificant decline, whereas 3-Hp displayed the most substantial reduction. The incorporation of TAA marginally increased the number-average molecular weight. However, it diminished with the inclusion of both ETU and TD, with TD witnessing a sharper drop. Notably, the number-average molecular weights after 3-Hp addition aligned with those of the control group. The distribution coefficient increased upon TD addition but decreased with the other three additives, with 3-Hp causing the most pronounced reduction. After TD addition, the proportion of smaller-molecular-weight components increased, the molecular weight of the larger components increased, and the molecular weight distribution broadened. Conversely, after 3-Hp addition, there was a surge in smaller molecular weight components and a decrease in the count and molecular weight of larger molecules, leading to the tightest molecular weight distribution. These observations are consistent with the results shown in Fig. 6 . Table 7 Relative molecular weight size and distribution coefficient of raw rubber with different additives Additives Mn/10 4 Mw/10 4 Distribution coefficient - 13.02 236.52 18.17 TD 11.35 235.96 20.79 TAA 14.14 232.58 16.45 ETU 12.48 221.26 17.72 3-Hp 13.02 195.54 15.02 3.2.5 Effects of different additives on the preparation of infrared spectrum of NR Figure 7 shows the infrared spectrum of NR derived from fresh latex prepared via wet mixing with four distinct additives. As shown in Fig. 7 , there are no noticeable shifts in the wave peaks of the infrared spectra of the five NR samples. Moreover, the intensities of these wave peaks did not exhibit significant changes. The characteristic peaks of all samples essentially fell within the same number of bands, and the overall infrared curve mappings were closely aligned, with minimal variance observed. The C = C double bond in the NR molecule corresponds to a wavenumber of 1645 cm − 1 , accompanied by a bending vibration peak at 840 cm − 1 . The -CH 3 and -CH 2 groups exhibit wave numbers of 2959 cm − 1 and 2851 cm − 1 , respectively, with their bending vibration peaks manifesting near wave numbers of 1443 cm − 1 and 1375 cm − 1 . Notably, the six profiles exhibited minor discrepancies in certain characteristic peaks, suggesting that the integration of the four molecules might not be optimal for the infrared profile. These slight variations in the characteristic peaks across the six profiles imply a marginal structural impact on NR after the addition of the four substances. Consequently, drawing definitive conclusions about their influence on the various properties of dried rubber films is challenging. 3.2.6 Influence of different additives on the thermal stability of raw NR The Thermogravimetric (TG) and Derivative Thermogravimetric (DTG) profiles of raw NR prepared from fresh latex with the four additives and their characteristic temperatures are presented in Fig. 8 and Table 8 . The impact of the additives on NR's thermal stability of NR was assessed using the initial decomposition temperature (T 0 ). Samples with TD and 3-Hp exhibited marginally higher onset decomposition temperatures, suggesting enhanced initial thermal stability. The TAA and ETU samples exhibited decomposition temperatures comparable to those of the blank samples, indicating a minimal effect on the initial thermal stability. For T 50 , 3-Hp recorded the highest value at 386.28°C, while TD displayed a lower T 50% , indicating faster mid-period decomposition. Other additives minimally influenced the T 50% . The peak decomposition temperature (Tp) varied with the additives, with TD showing the highest value at 382.00°C, followed by 3-HP, whereas TAA showed the lowest value. The final temperature (T f ) for the TAA and ETU samples was marginally higher than that of the blanks, with minor differences between the 3-HP and control samples, whereas the TD was lower. While all additives elevated the initial decomposition temperature, TD showed inferior overall thermal stability, whereas the others demonstrated slightly enhanced stability compared to the controls. For TD, despite the pyridine group improving the initial stability, thioamide degradation and uneven crosslinking reduced the thermal stability later [ 33 ]. With 3-HP, hydrogen bonding and pyridine group synergy enhanced the molecular chain stability [ 34 ]. TAA's low reactivity provided minimal thermal stability improvement. 32 ETU's early vulcanization due to rubber double bonds forms sulfur bonds, slightly improving the thermal stability [ 35 – 36 ]. Table 8 Characteristic degradation temperature of NR latex dry films incorporating various additives T 0 / o C T 50 / o C T p / o C T f / o C Blank 353.62 385.35 377.31 415.17 TD 354.69 383.58 382.00 411.98 TAA 353.88 385.39 376.51 418.01 ETU 353.98 385.70 377.85 416.20 3-Hp 354.61 386.28 380.08 415.97 3.2.7 Influence of different additives on RPA data of raw NR preparation The analysis of G' (energy storage modulus) and tan δ (loss factor) curves is crucial for understanding the dynamic mechanical properties of rubber materials. These curves provide insights into the elastic behavior and energy dissipation characteristics at varying frequencies and temperatures. As shown in Figs. 9 a and 9 b, the incorporation of TD, 3-HP, and ETU enhanced the G' values across the test range. 3-HP showed the strongest effect, followed by TD, suggesting increased rubber rigidity due to the synergistic effect of TD and 3-HP, which promotes cross-linking and strengthens the network structure. Changes in the tan δ curve indicate shifts in viscoelasticity. A peak shift to a higher temperature or frequency indicates an elevated glass transition temperature (Tg), indicating reduced flexibility and enhanced thermal stability. TAA minimally influences the G' and tanδ of raw rubber samples. ETU slightly elevated G' and reduced tanδ, which was similar to the TD effects. Samples with 3-HP showed the highest G' curve and lowest tanδ. The causes are: 3-HP: (1) Hydrogen bonding strengthens molecular chain interactions through reversible bonds between hydroxyl groups (-OH) and rubber chains, increasing crosslinking density and improving rigidity [ 28 ]. (2) Pyridine groups coordinate with Zn 2+ (Zn(C5H5N) 2+ ), optimizing the crosslinked network homogeneity and reducing energy dissipation [ 27 ]. (3) Hydrogen bonding and ligand interactions form a stable crosslinking network, enhancing elastic storage and suppressing viscous dissipation. Thioamide Derivatives (TD): (1) Thioamide enables cross-linking through sulfur radicals from R-C = S groups, accelerating sulfur cross-linking [ 25 ][ 26 ]. (2) Pyridine-Zn 2+ coordination increases network rigidity, although uneven crosslinking leads to incomplete chain movement restriction [ 28 ]. (3) Thioamides may cause partial chain breaks during vulcanization, thereby increasing energy dissipation. The properties of ethylene thiourea (ETU) are as follows: (1) Rapid crosslinking forms short sulfur bonds (-S- or -S-S-), creating a brittle network. (2) Short sulfur bonds break and reconnect during deformation, causing viscous dissipation [ 29 ]. (3) High crosslink density trades off with network uniformity, limiting the optimization of the elastic response. Thioacetamide (TAA): (1) Limited crosslinking: The thioamide group in TAA has low reactivity, preventing effective vulcanization and having a negligible impact on the crosslinked network. (2) Unrestricted Molecular Chain Movement: No cross-linking points are formed, maintaining the viscoelastic properties of the rubber (G' ≈ blank, tanδ ≈ blank) [ 30 – 31 ]. TD promotes a uniformly high crosslink density by slowly releasing reactive sulfur and forming long sulfur bridges. This process fully extends the sulfur bonds, enhancing network stability with only a slight increase in the elongation at break [ 37 ]. In contrast, ETU accelerates vulcanization, generating dense short sulfur bonds that form a dense and flexible network. This resulted in an 8.9% increase in the tear strength, although the magnitude of tensile enhancement was lower than that of the TD direction [ 29 , 38 ]. 3-Hp selective crosslinking leads to local overdensification and improves the tensile strength. However, hydrogen-bond-induced brittleness results in a 14.0% decrease in the tear strength [ 39 ]. TAA, owing to its low reactivity, had no significant effect on the tensile strength. However, hydrogen bonding-induced brittleness results in a 14.0% decrease in the tear strength [ 29 , 38 ]. The crosslink density positively enhanced the strength and hardness of the material. However, the tearing performance is dependent on the sulfur-bridge length and network homogeneity. The flexible structure of ETU is superior to the inhomogeneous distribution of 3-Hp, whereas TD balances high strength with moderate elongation. The mechanisms by which the three additives (TD, ETU, and 3-Hp) promoted NR vulcanization are shown in Fig. 10 . As depicted in this figure, all three components facilitated the crosslinking of rubber molecules, thereby significantly enhancing the mechanical properties of the rubber. 4. CONCLUSION This study aimed to examine the key chemical groups of thioamide derivative (TD) present in the composite preservation system to amplify the vulcanization properties of NR. The distinct impacts of various additives, namely TD, TAA, ETU, and 3-Hp, on the preparation of NR blends and vulcanized rubber were meticulously analyzed. The findings revealed that TD significantly reduced the vulcanization time and exhibited potent vulcanization-promoting capabilities. Conversely, TAA exerted virtually no beneficial influence on vulcanization, whereas ETU and 3-Hp exhibited varying degrees of vulcanization promotion. Notably, the TD samples demonstrated an accelerated vulcanization speed and a heightened degree of vulcanization at increased dosages. In contrast, TAA's influence of TAA on the performance of vulcanized rubber was virtually imperceptible, and the effect of ETU was also relatively constrained. The raw rubber produced by incorporating TD into fresh latex via wet mixing exhibited a reduced number-average molecular weight and a broader molecular weight distribution. Similarly, the ETU sample displayed a diminished weight-average molecular weight with a relatively narrow molecular weight distribution coefficient. The 3-Hp sample also presented a decreased weight average molecular weight, and its molecular weight distribution coefficient was notably the lowest among the samples. The infrared spectroscopy results revealed consistent characteristic peaks across the five samples, with no marked migration or intensity variations, suggesting a minimal impact of the additives on the primary chain structure of NR. Notably, the raw rubber samples treated with TD and 3-Hp exhibited an elevated energy storage modulus (G'), indicating increased rigidity of the rubber molecules. Concurrently, their loss factor (tanδ) curves diminished, with the 3-Hp samples showing particularly low tanδ values. In summary, the vulcanization promoted by TD is predominantly a synergistic result of the pyridine and thioamide groups. Consequently, the composite antibacterial and antifungal system, LS, not only markedly accelerated the vulcanization process and enhanced the degree of vulcanization of NR but also significantly improved the physical and mechanical properties of the vulcanized NR. Abbreviations NR Natural rubber TD Thioacetamide derivative TAA Thioacetic acid ETU Thioketone accelerators 3-Hp 3-Hydroxypyridine Mv Mooney viscosity M L The minimum torque M H The highest maximum torque phr Parts per hundred rubber Declarations Author Contribution Liguang Zhao: Conceptualization, Methodology, Writing—original draft. Yiqun Liu: Methodology, Writing—original draft preparation. Liyang Zhao: Validation. Yazhong Song: Project administration. Honghao Huang: Investigation, Methodology, Writing—review and editing. Jianwei Li: Data curation, Project administration, Validation. Tuo Dai: Data curation, Validation. Minmin Chen: Formal analysis. Tao Zhao: Formal analysis, Project administration. Hongxing Gui: Methodology, Resources. Zhenxiang Xin: Investigation, Resources, Writing—review and editing. Acknowledgments We would like to thank the Ministry of Agriculture and Rural Affairs of China and the Department of Science and Technology of Hainan Province for their support. This reearch was supported by the National Key R&D Program of China (2024YFD2300903; 2022YFD2301201), the Agricultural Technology Experiment Demonstration and Service Support Project of the Ministry of Agriculture and Rural Affairs (XJSHT2-02-02), the Hainan Province Science and Technology Special Fund [ZDYF2024XDNY284], and Earmarked Fund for China Agriculture Research System [CARS-33-JG1]. References Loykulnant S, Kongkaew C, Chaikumpollert O, Sanguanthammarong P, Na Ubol P, Suchiva K (2011) Study of chitosan and its derivatives as preservatives for field natural rubber. Journal of Applied Polymer Science Chaikumpollert O, Loykulnant S, Kongkaew C (2007) A novel preservative system for natural rubber latex. Proceedings of the 10th Pacific Polymer Conference, Kobe, Japan Afreen S, Haque KR, Huda MK (2013) Troubleshooting for the observed problems in processing latex concentrate from natural resource. 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Polym Test 129:108289 Surya I, Ismail H (2016) Alkanolamide as a novel accelerator and vulcanising agent in carbon black-filled polychloroprene rubber compounds. Plast Rubber Compos 45(7):287–293 Wang L, Fu W, Peng W (2020) Enhanced strength and toughness of polyurethane rubber by introducing hydrogen bond sacrificial units at rubber-graphene interfaces. Polym Compos 41(4):1242–1254 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7015352","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":498196352,"identity":"1157fa7b-5173-4572-9f47-2b85d838dd52","order_by":0,"name":"Liguang 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blends.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7015352/v1/fe471aa7a44fb6825c1acc43.png"},{"id":89084233,"identity":"7eea58bd-7149-4f51-b7c3-95fb9cc0d5aa","added_by":"auto","created_at":"2025-08-14 13:44:59","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":103104,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of the four additives with\u0026nbsp; 5 mmol/kg \u0026nbsp;on (A)M\u003csub\u003eL\u003c/sub\u003e, (B)M\u003csub\u003eH\u003c/sub\u003e, (C)M\u003csub\u003eH\u003c/sub\u003e-M\u003csub\u003eL\u003c/sub\u003e, and (D)T\u003csub\u003e90\u003c/sub\u003e\u0026nbsp;of compound NR \u0026nbsp;at 143 ℃ for 40 min.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7015352/v1/5a2cc3719bdbee1f000090ec.png"},{"id":89085467,"identity":"c434c11b-ada2-4415-b41f-da7bb07fbdce","added_by":"auto","created_at":"2025-08-14 14:00:59","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":115929,"visible":true,"origin":"","legend":"\u003cp\u003eVulcanization curves of compound NR with 5 mmol/Kg (A)TD, (B)TAA, (C)ETU, and (D)3-Hp at 143 °C for 2400s.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7015352/v1/a8bd865419ea792d8f30a3f8.png"},{"id":89085468,"identity":"31c5efe6-529d-42c3-aa9e-f989f4831606","added_by":"auto","created_at":"2025-08-14 14:00:59","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":71796,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of the four additives on NR vulcanizate tensile stress at (a)100%, (b)300% and (c)500% elongation.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7015352/v1/327dd2a966f3ebb3bf30c3f4.png"},{"id":89084540,"identity":"41adcf25-7aea-4656-8ac0-58140aa5e7c4","added_by":"auto","created_at":"2025-08-14 13:53:00","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":115502,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of the four additives on (a)tensile strength, (b)elongation at break, (c)tear strength, and (d)hardnessd of NR vulcanizate\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7015352/v1/c85c06c2f6396e9459514073.png"},{"id":89084246,"identity":"5a4dca3b-b835-4f35-91b9-7f1947742d85","added_by":"auto","created_at":"2025-08-14 13:44:59","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":18287,"visible":true,"origin":"","legend":"\u003cp\u003eVulcanization curves of compound NR with four additives at 143 °C for 2400s.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7015352/v1/6e7761df6e35080cce8263c5.png"},{"id":89084247,"identity":"8598cd55-46ae-4eeb-9cc1-5d6845d730c4","added_by":"auto","created_at":"2025-08-14 13:45:00","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":25224,"visible":true,"origin":"","legend":"\u003cp\u003eFig. 6 \u0026nbsp;Molecular weight distribution of raw NR prepared with different additives.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7015352/v1/52522e086fcf438d5b31bc6f.png"},{"id":89084527,"identity":"43780f74-c3d4-4506-8995-a09109d11a1d","added_by":"auto","created_at":"2025-08-14 13:52:59","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":35156,"visible":true,"origin":"","legend":"\u003cp\u003eFig. 7 \u0026nbsp;Infrared spectrum of raw NR prepared with different additives.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7015352/v1/b6efb9e53827f84a4f33b237.png"},{"id":89084242,"identity":"f9e36c81-0f16-4d53-97ef-174fe92cbace","added_by":"auto","created_at":"2025-08-14 13:44:59","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":26434,"visible":true,"origin":"","legend":"\u003cp\u003eFig. 8 The Thermogravimetric and derivative thermogravimetric curves of raw NR prepared with different additives.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-7015352/v1/9ea5ec2a8e8457ce9e718077.png"},{"id":89084528,"identity":"52d6b223-22d0-47cc-967f-9c3c739fbd19","added_by":"auto","created_at":"2025-08-14 13:52:59","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":35981,"visible":true,"origin":"","legend":"\u003cp\u003eFig. 9 (a) G 'and (b)tanδ curves of raw NR with the four additives.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-7015352/v1/525a6ac6a47effb104b277ec.png"},{"id":89086704,"identity":"77c1320f-29a0-41b0-9194-ff23bd094530","added_by":"auto","created_at":"2025-08-14 14:09:06","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":221454,"visible":true,"origin":"","legend":"\u003cp\u003eFig. 10 \u0026nbsp;Promoting mechanism of (a)TD, (b)ETU and (c)3-Hp on rubber vulcanization.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-7015352/v1/2c339e7cbd8ecfb6017c818b.png"},{"id":98628739,"identity":"bc8cf04e-68cc-499a-a51a-2b1f83a58d35","added_by":"auto","created_at":"2025-12-19 17:12:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1941022,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7015352/v1/3271fafd-aa29-4847-99f4-fb492a0cf36c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Impact of Thioamide Derivative Composite Preservation System on Vulcanization of Natural Rubber","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eIn the current industrial context, the rubber sector holds a crucial position within the economy. Natural rubber (NR) products, renowned for their exceptional elasticity and durability, are extensively utilized across critical sectors such as automotive, structure, medical, and aviation [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e]. However, NR latex is inherently prone to microbial degradation and deterioration, necessitating effective preservation strategies [\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e]. Traditionally, ammonia has been employed for this purpose; however, its high volatility and irritating properties pose significant environmental and safety challenges to its use [\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e]. In response to this challenge, the industry has developed ammonia-free preservatives, such as hexahydroxyethyl homotriazine, benzisothiazolinone, and bismorpholine methane, among others [\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, factors such as the preservation effect, toxicity of preservatives, and production costs hinder the large-scale dissemination and application of these preservatives. Among these, the thioamide derivative composite preservative system (TDCPS) emerges as a promising alternative, exhibiting significant advantages in terms of safety, low toxicity, consistent quality, and cost-effectiveness. A key feature of TDCPS is its ability to significantly enhance the quality of NR latex while improving its physical and mechanical performance [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e]. The core component of the system is a thioamide derivative (TD), which is complemented by a minimal quantity of auxiliary additives. Analytical studies have revealed that TD is uniquely responsible for accelerating and enhancing vulcanization within TDCPS. This functionality is attributed to the synergistic interplay of thioamide and pyridine functional groups in its molecular structure. These groups not only facilitate efficient cross-linking but also optimize the kinetics and extent of vulcanization, ultimately contributing to the production of high-performance rubber materials with enhanced mechanical properties [\u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eNR, a primary raw material for rubber products, has long been the cornerstone of the rubber industry owing to its superior mechanical properties and environmental adaptability. Nevertheless, unprocessed NR exhibits certain constraints, notably low hardness and suboptimal abrasion resistance, restricting its use in high-performance applications [\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e]. Vulcanization, the process of creating a three-dimensional mesh structure between linear macromolecular chains, enhances these properties. This is achieved by introducing sulfur or other vulcanizing agents to the rubber, initiating a chemical reaction at a specified temperature. Post-vulcanization, rubber undergoes significant enhancements in its physical and mechanical attributes, rendering it suitable for high-performance applications [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e][\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e]. Within this process, the role of the vulcanization accelerator is pivotal [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]. Vulcanization accelerators expedite the vulcanization process, lower the required temperature, augment the mechanical characteristics of the vulcanized rubber, and decrease sulfur usage, thereby reducing costs. Additionally, they bolster the dynamic fatigue performance, abrasion resistance, and aging resilience of the vulcanized rubber. Consequently, judicious selection of vulcanization accelerators is paramount to elevating the quality of rubber products [\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eNR, a primary raw material for rubber products, has long been the cornerstone of the rubber industry owing to its superior mechanical properties and environmental adaptability. Nevertheless, unprocessed NR exhibits certain constraints, notably low hardness and suboptimal abrasion resistance, restricting its use in high-performance applications [\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e]. Vulcanization, which involves the formation of a three-dimensional mesh structure between linear macromolecular chains, enhances these properties. This is achieved by introducing sulfur or other vulcanizing agents into the rubber, initiating a chemical reaction at a specified temperature. Post-vulcanization, rubber undergoes significant enhancements in its physical and mechanical attributes, rendering it suitable for high-performance applications [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e]. The vulcanization accelerator plays a pivotal role in this process [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]. Vulcanization accelerators expedite the vulcanization process, lower the required temperature, augment the mechanical characteristics of vulcanized rubber, and decrease sulfur usage, thereby reducing costs. Additionally, they bolster the dynamic fatigue performance, abrasion resistance, and aging resilience of vulcanized rubber. Consequently, the judicious selection of vulcanization accelerators is paramount for improving the quality of rubber products [\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eVulcanization accelerators are chemicals that expedite the vulcanization reaction, thereby enhancing the physical attributes of vulcanized rubber. These accelerators not only reduce the vulcanization duration and lower the vulcanization temperature but also augment the aging and abrasion resistance of the resultant rubber. In the rubber industry, judicious selection and utilization of a vulcanization accelerator is paramount to elevating product quality. Currently, prevalent vulcanization accelerators in the market encompass hyposulfonamide, thiazole, and thiuram, each of which exhibits distinct characteristics and finds application in specific scenarios, offering unique advantages [\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e]. For instance, hyposulfonamide vulcanization accelerators possess commendable delayed-vulcanization properties, making them apt for an array of rubber products [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e], whereas thiazole accelerators are acclaimed for their rapid vulcanization capabilities, rendering them suitable for high-speed vulcanization processes [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]. Nevertheless, these conventional accelerators are not devoid of shortcomings; they may contain potentially hazardous substances and necessitate stringent operational conditions. With the expanding application of rubber products in extreme environments, there emerges an escalating demand for vulcanization accelerators capable of functioning proficiently under such challenging conditions [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003ePrevious studies have established that the enhancement of the mechanical properties of NR-vulcanized films via composite preservation systems is primarily governed by the concentration of thioamide derivatives (TD). Building on this foundation, this study aimed to identify the specific chemical groups within TD responsible for its vulcanization-promoting effects. To achieve this, four key compounds\u0026mdash;thioacetamide (TAA), thioketone accelerators (ETU), pyridine compounds, and TD \u0026mdash;were selected as model additives. Their influence on the vulcanization behavior of NR blends and the resulting physical and mechanical properties of the vulcanized rubbers were systematically evaluated [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e][\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e]. The experimental approach involved incorporating these four substances into fresh NR latex through a wet mixing process, followed by the production of raw rubber samples. The effects of each additive on the quality of raw rubber and the mechanical performance of the vulcanized products were characterized. This study specifically targeted the identification of key functional groups in TD that drive vulcanization enhancement and elucidated the underlying reaction mechanisms.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec2\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1 Materials\u003c/h2\u003e\n \u003cp\u003eNR latex was sourced from the Experimental Farm of the Chinese Academy of Tropical Agricultural Sciences in Hainan Province, China. Industrial-grade additives including TD, TAA, ETU, and 3-Hp (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) were procured from Shandong Yusuo Chemical Technology Co. TDCPS was prepared in the laboratory. Analytical grade tetrahydrofuran and ammonia (25% wt) were supplied by Guangdong Xilong Chemical Co., Ltd. Additional materials commonly used in the rubber industry, including ammonia, acetic acid, stearic acid, zinc oxide (ZnO), sulfur, and accelerator M accelerators, were employed in the experiments.\u003c/p\u003e\n \u003cp\u003eTable 1 \u0026nbsp;Chemical structure of four additives\u003c/p\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 20.0704%;\"\u003e\n \u003cp\u003eCategory\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20.0704%;\"\u003e\n \u003cp\u003eTD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.3662%;\"\u003e\n \u003cp\u003eTAA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21.1268%;\"\u003e\n \u003cp\u003eETU\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.3662%;\"\u003e\n \u003cp\u003e3-Hp\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 20.0704%;\"\u003e\n \u003cp\u003eChemical structure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 20.0704%;\"\u003e\n \u003cp\u003e\u003cimg width=\"80\" height=\"59\" src=\"data:image/emf;base64,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\" alt=\"image\"\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.3662%;\"\u003e\n \u003cp\u003e\u003cimg width=\"83\" height=\"72\" src=\"data:image/emf;base64,R0lGODlhfABsAHcAMSH+GlNvZnR3YXJlOiBNaWNyb3NvZnQgT2ZmaWNlACH5BAEAAAAALAIAAwB2AGUAhQAAAAAAAB4eHhISEhQUFBAQEBcXFxwcHCgoKDExMTs7OyAgICcnJzc3NzAwMCwsLCQkJDw8PDQ0NFFRUUJCQkpKSllZWVdXV0ZGRkxMTFVVVUBAQF1dXURERHd3d2ZmZmpqanNzc25ubmBgYIiIiAECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwECAwb/QIBwSCwaj8ikcslsEhEAinNKrVqvTkFiGMB6v+CwUFCEis/o9LAyULvf6MBgAq/bq4iAvHLv+5EKAVt/hIRdhYhqFkWHiY5gbEQTZo+VWBQBZG2WnJ2efQufolQMo6ZLBKeqSA1FraumBbCzAA5GpbSeH0e4uZwHRsC+nQ9FGMOdskWpyJUbR8fNj8pEBtKVF0UQ14/CRL3chNbL4Yh0Rq/lf9RD7Op90UO273/MQ7v0fuBC3vl1HEeK+bMzjoi7gW7SCXmGsE7Bdg3hKByiIeKbfvwsvslWTaObfec8onko5KBINfFOurHnaJETPpZCCtl3p5EQmEfyjCBis1AX/z49fRqhVEYOT0c9g/7piXMogE1CAuAjpODIVKFlkkBppLSmqJ8A+BDNKsSMzZ1oAaRdq7Yt27dto36tyqcCgrFD7soFYHOB37+AAwsePDjCXk9M8w4QcIhShS5SEXVF6hRA1ShmKLWZXEfB5SEJBkku0jQvgLF6KPO8aqjykE16jyLdEqhSadZkhLgUVdpUbpVuOAP/cjc2LZLD0WBMznyVyeZeGEI/83z6FYHWs3tCrr3KvO5eqoNvYnj8FfHmk3BMXyUU+yrc3yvJIH8K+vpEJuJHwnJ/Epr+GQFQgEnERyAA+h04RH8KDpGggss1uF6D31BIBWv1LZYHUcKB10sTJR+y9xsXN33YW3achZheikWM2N0HLEKxFXuTPVYGTqmhuBMRUKl42mHQ9cYVEx2KRMYij+3mI5DW0YEXXkZAZeFNFCo5JSaHBAEAOw==\" alt=\"image\"\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 21.1268%;\"\u003e\n \u003cp\u003e\u003cimg width=\"87\" height=\"79\" src=\"data:image/wmf;base64,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\" alt=\"image\"\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 19.3662%;\"\u003e\n \u003cp\u003e\u003cimg width=\"93\" height=\"72\" src=\"data:image/wmf;base64,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\" alt=\"image\"\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2 Methods\u003c/h2\u003e\n \u003cdiv id=\"Sec4\" class=\"Section3\"\u003e\n \u003ch2\u003e2.2.1 Preparation of NR raw rubber samples\u003c/h2\u003e\n \u003cp\u003eA certain amount of fresh latex was collected from the rubber plantation and preserved using 0.1% ammonia. Subsequently, according to the formula in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, the appropriate additives were added, mixed well, and left for 24 h. The appropriate amount of acid required to coagulate fresh latex was determined using the formula for calculating the amount of acid required for coagulation. After one day of standing, it was creased, dehydrated, and dried completely under hot air at 70\u0026deg;C to prepare raw latex samples (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eNR latex additive composition and dosage\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAdditives\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDosage/mmol∙L\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBlank\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTAA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eETU\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3-Hp\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\"\u003e\u003cstrong\u003eNote: The additives utilized were either aqueous solutions or colloidal suspensions, with the dosage indicating the optimal quantity of preservative employed for the preservation of natural latex.\u003c/strong\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\n \u003ch2\u003e2.2.2 Sample Preparation of Rubber Mixing and Vulcanization\u003c/h2\u003e\n \u003cp\u003eThe sample preparation adheres to the ACS I formula and mixing procedure as stipulated in GB/T 15340\u0026thinsp;\u0026minus;\u0026thinsp;1994. Natural raw rubber was mixed using an open kneader to obtain the rubber mixture. The vulcanization characteristics of this mixture were then examined using a rotorless vulcanizer at a set temperature of 143\u0026deg;C for 60 min. Subsequently, the mixed rubber was vulcanized using a plate vulcanizing machine, maintained at a temperature of 143\u0026deg;C. The vulcanization process was carried out for a positive vulcanization time of t\u003csub\u003e90\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;5 min, resulting in the formation of a vulcanized film.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\n \u003ch2\u003e2.2.3 Preparation of Test Sample for Rubber Mixing\u003c/h2\u003e\n \u003cp\u003eA pure rubber formulation was employed to produce 3.9 kilogram of compounded NR, which was subsequently divided into 13 equal 300 g portions. Subsequently, the additives were incorporated as per the specifications detailed in Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, ensuring thorough mixing. After allowing the mixture to rest for 12 hours, its vulcanization characteristics were examined. Subsequently, a vulcanized rubber film was fabricated to assess its physical and mechanical properties.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"left\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDosage of additives for compounded NR\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAdditives\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDosage/mmol∙L\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eblank\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.5, 5, 7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTAA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.5, 5, 7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eETU\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.5, 5, 7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3-Hp\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.5, 5, 7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n \u003ch2\u003e2.2.4 Testing of Raw Rubber\u003c/h2\u003e\n \u003cp\u003ePlasticity Initial Value (P\u003csub\u003e0\u003c/sub\u003e) and Plasticity Retention Rate (PRI): These were measured using a rapid plasticity meter, in accordance with the GB/T 3517\u0026thinsp;\u0026minus;\u0026thinsp;2014 and GB/T 3510\u0026thinsp;\u0026minus;\u0026thinsp;2006 standards.Menni Viscosity M\u003csub\u003eL\u003c/sub\u003e (1\u0026thinsp;+\u0026thinsp;4) at 100 ℃: This was tested using a Menni viscometer, following the GB/T 1232.1\u0026ndash;2016 standard. Nitrogen Content: The nitrogen content was measured using a Kjeldahl nitrogen tester, as prescribed by the GB/T 8088\u0026thinsp;\u0026minus;\u0026thinsp;2008 standard. A TENSOR 27 Fourier infrared spectroscopy tester was used for direct testing, with the detection range set at 4000\u0026thinsp;\u0026minus;\u0026thinsp;370 cm\u003csup\u003e-1\u003c/sup\u003e, a resolution of 4 cm\u003csup\u003e-1\u003c/sup\u003e, and 32 scans. The raw rubber sample was cut into small particles, and 10 mg of the sample was weighed and placed in a crucible for testing using an STA449 thermogravimetric analyzer. The test conditions included the use of nitrogen as the external atmosphere with a flow rate of 50 mL/min, high-purity nitrogen as the protective gas at a flow rate of 25 mL/min, a temperature range of 25\u0026ndash;600 ℃, and a heating rate of 10 K/min. The glass transition temperature of the dry gel film was determined using both the Differential Scanning Calorimetry (DSC) method, with a temperature range of -90-100 ℃ and a heating rate of 10 K/min, and the GPC gelation method, under similar conditions.Furthermore, the molecular weight size and distribution of the rubber were detected by GPC gel permeation chromatography. For this process, A 3 g of dry rubber was cut into small strips and soaked in an appropriate amount of tetrahydrofuran for one week until fully dissolved. The solution was then filtered using a needle filter and analyzed by gel permeation chromatography at 30\u0026deg;C.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n \u003ch2\u003e2.2.5 Determination of Mixing and Vulcanizing Rubber\u003c/h2\u003e\n \u003cp\u003eThe vulcanization speed of the rubber mix was determined using an MRL MD-3000A rotorless vulcanometer. Subsequently, the vulcanization characteristics of the mix were examined at 143 ℃ for 40 min using the same instrument. The tensile strength, elongation at break, and constant tensile stress of the vulcanized film were measured using an electronic universal testing machine. Tear strength was determined using the same machine. Specimens for the tensile strength and right-angled tests were prepared in accordance with ISO 527. The tests were conducted using an electronic universal testing machine. The tensile strength, elongation at break, and constant elongation stress were evaluated according to the guidelines of GB/T 528\u0026ndash;2009, while the tearing strength was assessed based on GB/T 528\u0026ndash;2008. Dumbbell and right-angle specimens required for these tests were prepared according to ISO 527. Finally, the stress-strain curves and relevant values of the samples were obtained using a universal electronic testing machine.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003e3.1 Impact of the Four Additives on the Vulcanization Characteristics and Physical and Mechanical Properties of the Compound Rubber\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n\u003cdiv class=\"Heading\"\u003e3.1.1 Influence of the Four Additives on the Vulcanization Characteristics of the Compound Rubber\u003c/div\u003e\n\u003cp\u003eFigures \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e depict the trends in the vulcanization characteristics of pure rubber formulations as the four additives were modified. The minimum torque (M\u003csub\u003eL\u003c/sub\u003e) value serves as an indicator of the viscosity or fluidity of the compound rubber at the onset of vulcanization; a lower M\u003csub\u003eL\u003c/sub\u003e value indicates superior processability. An increase in the maximum torque (M\u003csub\u003eH\u003c/sub\u003e) value results in an increased torque difference (M\u003csub\u003eH\u003c/sub\u003e-M\u003csub\u003eL\u003c/sub\u003e), which has direct implications for the hardness, elasticity, and other physical and mechanical attributes of the vulcanized rubber. This torque difference is a crucial metric for gauging the extent of hardening during vulcanization of the compound. A substantial torque difference typically signifies the commendable vulcanization responsiveness of the compound. Furthermore, vulcanization time provides insights into whether the additives accelerate or decelerate the vulcanization process.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(a) illustrates that as the dosage of the four different additives increases, the M\u003csub\u003eL\u003c/sub\u003e value initially declines, subsequently rises, and finally decreases again. This indicates that these four additives can effectively reduce the M\u003csub\u003eL\u003c/sub\u003e value of the rubber mix, thereby optimizing its processing performance. When comparing the M\u003csub\u003eL\u003c/sub\u003e values at the same additive content, the order was TAA\u0026thinsp;\u0026gt;\u0026thinsp;3-HP\u0026thinsp;\u0026gt;\u0026thinsp;TD\u0026thinsp;\u0026gt;\u0026thinsp;ETU. This suggests that under identical conditions, TAA exhibits the poorest processing performance, whereas ETU exhibits the best. Figures\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(b) and 2(c) reveal a consistent trend for M\u003csub\u003eH\u003c/sub\u003e and the M\u003csub\u003eH\u003c/sub\u003e-M\u003csub\u003eL\u003c/sub\u003e; that is, an increase in the content of the four additives leads to a corresponding increase in M\u003csub\u003eH\u003c/sub\u003e and M\u003csub\u003eH\u003c/sub\u003e-M\u003csub\u003eL\u003c/sub\u003e. Furthermore, at the same additive content, the lowest values of MH and M\u003csub\u003eH\u003c/sub\u003e-M\u003csub\u003eL\u003c/sub\u003e were observed for TAA, and the highest for TD. This demonstrates that TD has superior vulcanization responsiveness, significantly enhancing the properties of the material.\u003c/p\u003e\n\u003cp\u003eAs illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, TD exhibited the most pronounced effect on enhancing the vulcanization curve, characterized by the swiftest rise in the degree of vulcanization and peak torque value. Concurrently, an increase in TD dosage elevates the torque value and markedly reduces the vulcanization time, although all exhibit vulcanization reversion. Subsequently, 3-Hp notably promoted vulcanization, as evidenced by the accelerated vulcanization speed and heightened torque value, with the reversion of vulcanization phenomenon being less pronounced than that with TD. Conversely, ETU exerts a comparatively weaker promoting effect on the vulcanization of NR and may even diminish the vulcanization speed at lower dosages. Finally, TAA did not enhance the vulcanization of the compound and, to a certain extent, reduced the degree of vulcanization. Among the four additives, only the vulcanization time of the TD compounds was curtailed with increasing TD dosage, thereby significantly expediting the vulcanization process, whereas the other three additives exerted a lesser impact on vulcanization time.\u003c/p\u003e\n\u003ch2\u003e3.1.2 The Impact of Four Additives on the Physical and Mechanical Properties of Vulcanized Rubber\u003c/h2\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section3\"\u003eThe constant elongation stress of vulcanized rubber is intimately associated with its crosslink density. As illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, an increase in additive dosage, with the exception of TAA, results in varying degrees of enhancement in the constant elongation stress of vulcanized NR. Specifically, the samples of vulcanized rubber film treated with TD and 3-Hp exhibited a continuous rise in constant elongation stress as the additive dosage increased, demonstrating similar patterns of change. However, the rate and extent of improvement were notably more pronounced in the TD group. In contrast, the constant elongation stress for the vulcanized rubber in the ETU group showed an initial increase followed by a decrease, whereas the samples with TAA remained largely unchanged. Furthermore, it can be deduced that the enhancement in elongation provided by TD is primarily attributed to the pyridine group, with other groups offering significant auxiliary synergistic contributions.\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe physical and mechanical properties primarily encompass the tensile strength, elongation at break, tear strength, and hardness. As depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, the tensile strength of vulcanized NR experienced a marked increased significantly with increasing TD dosage. However, at lower dosages, 3-Hp also enhanced the tensile strength, but this effect plateaued when the dosage exceeded 5 mmol/Kg. Conversely, TAA and ETU exerted minimal influence on the tensile strength. The elongation at break for the vulcanized rubber demonstrated an initial increase, followed by a decrease as the TD dosage increased. The impact of TAA on these properties was marginal. An increasing 3-Hp dosage led to a consistent reduction in the elongation at break, whereas an increasing ETU dosage exhibited an initial decrease, followed by an increase. The tear strength of vulcanized NR consistently improved with increasing TD dosage, showing the most significant increase. The effect of 3-Hp dosage stabilized after a certain point, whereas an increased ETU dosage initially increased and then decreased. The influence of TAA on the tear strength was notably less pronounced. The hardness of the vulcanized rubber augmented with both TD and 3-Hp dosages, yet the increase with ETU displayed a pattern of initial growth, followed by a decrease. The role of TAA in altering the hardness was relatively minor in this study. The analysis indicates that the enhanced physical and mechanical properties of the materials post-TD addition are predominantly attributed to the pyridine group within TD, with the thioamide group providing supplementary contributions.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\n\u003cdiv class=\"Heading\"\u003e3.1.3 Result analysis of vulcanization characteristics and physical and mechanical properties\u003c/div\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cp\u003eThe variances in the properties of the four vulcanizing agents, TD, 3-HP, ETU, and TAA primarily arise from the impact of their distinct chemical structures on both the vulcanization reaction and the crosslinking network.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eThe thioamide in conjunction with the pyridine group facilitates the rapid release of sulfur radicals and coordinates Zn\u0026sup2;⁺, culminating in a pronounced cross-linking density and the briefest vulcanization time. This led to a marked enhancement in the constant tensile stress, tensile strength, and tear strength. However, the significant presence of polysulfide bonds (-Sₓ-) predisposes the material to easy fracture at elevated temperatures, compromising stability.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eIn the 3-HP compound, pyridine group coordination encourages cross-linking, while hydroxyl hydrogen bonding boosts network uniformity. However, the release of sulfur radicals was insufficient, resulting in a suboptimal crosslinking density and slower vulcanization process. The presence of short sulfur bonds (-S-/-S-S-) increases the brittleness and reduces the tear strength.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eETU is characterized by the rapid release of sulfur radicals from thione groups, resulting in the lowest initial viscosity. However, it lacks ligand groups and has a low crosslinking density. The network is dominated by short sulfur bonds, which contribute to medium tensile strength. However, it exhibits high energy dissipation under dynamic loading, resulting in high tear strength.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eThioamide activity exhibits inadequate activity owing to the deficient performance of thioamide groups. This led to an insufficient vulcanization reaction, resulting in the lowest crosslinking density. Consequently, vulcanization takes longer, and its properties closely resemble those of unvulcanized rubber.\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n\u003ch2\u003e3.2 Characteristics of NR Prepared by Wet Mixing with Four Additives\u003c/h2\u003e\n\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n\u003ch2\u003e3.2.1 Conventional Indicators of NR Raw Material\u003c/h2\u003e\nFresh latex was processed into raw NR through wet mixing with four distinct additives. Mooney viscosity is a critical parameter for evaluating the processing fluidity of rubber, as it indicates the shear characteristics of rubber during the mixing process. As shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, the raw rubber samples exhibited the highest Mooney viscosity upon the addition of ETU. Conversely, Mooney viscosity decreased with the incorporation of TAA, 3-HP, and TD. Plasticity provides insight into the malleability of rubber, and the retention of plasticity is a key index for assessing the stability of rubber. As shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, the initial plasticity value of the raw rubber displayed minimal variations upon the addition of the four additives. Notably, 3-HP and TAA reduced plasticity slightly. However, all four additives reduced the plasticity retention of raw rubber. Among them, ETU and 3-HP caused a more pronounced decline, whereas TD and TAA caused a relatively lesser decrease. Furthermore, alterations in nitrogen content could be attributed to either the inherent nitrogen in the additives or their potential to inhibit microbial degradation reactions, thereby preserving a higher protein content. Specifically, the elevated nitrogen content observed in the TD-enhanced raw rubber samples may be correlated with TD's potent antimicrobial and anti-mold properties of TD.\u003cbr /\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003ctable id=\"Tab4\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eConventional indexes of raw NR prepared by mixing fresh latex with the four additives\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eAdditives\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMooney viscosity\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eP\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ePRI/%\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eNitrogen content/%\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e71.57\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e34.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e86.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.407\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTD\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e68.74\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e35.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e82.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.478\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTAA\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e70.20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e33.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e83.14\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.466\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eETU\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e73.58\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e34.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e77.21\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.399\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3-Hp\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e69.62\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e32.1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e73.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.419\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\n\u003ch2\u003e3.2.2 The impact of various additives on the vulcanization properties of raw rubber.\u003c/h2\u003e\n\u003cp\u003eFigure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e and Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e present the vulcanization characteristics of pure rubber formulations derived from fresh latex processed via wet mixing with four distinct additives. Contrary to the trend depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(a), all four additives enhanced the Maximum Latent Hardness of the compounds. Notably, ETU and TD exhibited the most significant enhancement in the ML of the compounds. A strong correlation was observed between the Maximum Hardness and the difference between the Maximum Hardness and Maximum Latent Hardness of the compounds. The compounds into which 3-HP was incorporated demonstrated superior MH and M\u003csub\u003eH\u003c/sub\u003e-M\u003csub\u003eL\u003c/sub\u003e values, followed by TD. Meanwhile, ETU had a comparatively minor enhancing effect on MH and M\u003csub\u003eH\u003c/sub\u003e-M\u003csub\u003eL\u003c/sub\u003e values, whereas TAA reduced these values. With respect to vulcanization time, the samples containing 3-HP displayed the shortest duration and the fastest rate of vulcanization across all stages, followed by TD. Both ETU and TAA expedited the vulcanization process, albeit with relatively weaker effects.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab5\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eEffects of different additives on vulcanization characteristics of fresh latex prepared compound\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eAdditives\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eM\u003csub\u003eL\u003c/sub\u003e/dN∙m\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eM\u003csub\u003eH\u003c/sub\u003e/dN∙m\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eM\u003csub\u003eH\u003c/sub\u003e-M\u003csub\u003eL\u003c/sub\u003e/dN∙m\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003e10\u003c/sub\u003e/s\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003e50\u003c/sub\u003e/s\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003e90\u003c/sub\u003e/s\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.62\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e130\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e350\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1169\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTD\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.69\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e6.35\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5.66\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e91\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e226\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e826\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTAA\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.49\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.47\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4.98\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e142\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e367\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1192\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eETU\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.94\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5.33\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e117\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e313\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1097\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3-Hp\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.47\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e6.47\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e80\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e208\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e774\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\n\u003ch2\u003e3.2.3 Effects of different additives on the physical and mechanical properties of vulcanized rubber\u003c/h2\u003e\n\u003cp\u003eTable\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e presents the physical and mechanical properties of NR vulcanized from fresh latex using wet mixing with four additives. The quality of vulcanized rubber is determined by its physical and mechanical characteristics. Key metrics, such as constant tensile stress, tensile strength, elongation at break, tear strength, and hardness, are detailed. At 100%, 300%, and 500% elongations, the samples containing TD and 3-Hp displayed elevated tensile stresses, with 3-Hp achieving the highest values at each constant tensile stress, suggesting an enhanced load-bearing capacity. The constant tensile stress for the TAA samples diminished. For tensile strength, TD and 3-Hp samples exhibited values of 25.90 MPa and 26.49 MPa, respectively, while TAA samples showed 18.47 MPa, lower than that of the blank control group. The elongation at break remained consistent across the additives, with ETU showing the highest value at 902%. The highest tear strength was recorded for 3-Hp at 27.9 kN∙m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, followed by TD at 26.4 kN∙m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. While the ETU samples showed robust tear strength, the TAA samples showed notably lower strength. For hardness, TD and 3-Hp samples were stiffer, whereas ETU and TAA showed less variation. In conjunction with the previously discussed vulcanization characteristics and properties, the causes of these occurrences were analyzed as follows: TD exhibited superior performance in enhancing the mechanical properties through its pyridine group promoting vulcanization. TD creates cross-links in NR via covalent and hydrogen bonds, forming a network that increases the tensile strength. The TD improves the rubber properties by releasing reactive sulfur to form disulfide bonds, thereby increasing the crosslink density and interactions. This enhances the tensile strength and hardness while maintaining elongation through a uniform network distribution. The sulfur moiety strengthens the bonding by coordinating with the rubber double bond [\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e]. While 3-Hp's hydroxyl group improves the tensile strength via hydrogen bonding, it causes brittleness and uneven crosslinking. TAA's structural stability reduces vulcanization effectiveness. ETU and TD showed better network optimization than 3-Hp's strength-brittleness trade-off and TAA's inertness [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e]. ETU accelerates vulcanization by reducing the activation energy and forming polysulfide bonds. Although ETU cures faster than TD, its limited sulfur elongation restricts the tensile stress [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. TAA exhibited the weakest mechanical properties, confirming its poor vulcanization and hardness owing to reduced crosslinking and network formation [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab6\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eEffects of different additives on mechanical properties of vulcanized NR prepared from fresh latex\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eDetection index\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"5\" align=\"left\"\u003e\n\u003cp\u003eAdditives\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e-\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eTD\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eTAA\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eETU\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e3-Hp\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTensile stress at 100% elongation/MPa\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.59\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.68\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.55\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.70\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTensile stress at 300% elongation/MPa\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.21\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.50\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.14\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.31\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.57\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTensile stress at 500% elongation/MPa\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.49\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.29\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.34\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.80\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e3.55\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTensile strength/MPa\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e19.43\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e25.90\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e18.47\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e23.09\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e26.49\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eElongation at break/%\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e882.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e898.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e899.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e902.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e881.0\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTear strength/kN∙m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e26.4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e21.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e23.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e27.9\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eHardness/HA\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e33.3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e37.0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e32.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e34.8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e37.7\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section3\"\u003e\n\u003ch2\u003e3.2.4 Effects of different additives on the relative molecular weight size and distribution of raw NR\u003c/h2\u003e\n\u003cp\u003eThe molecular weight significantly influences the processing performance of rubber materials and the mechanical properties of the final product. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e and Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e present the relative molecular mass distribution and molecular weight detection results of raw NR prepared by wet mixing with the four additives, respectively. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, the relative molecular mass distributions of the additive-treated raw NR were not notably different from those of the control group, exhibiting a consistent bimodal distribution. The samples with 3-Hp showed differences in the distribution plots, with higher low-molecular-weight and lower high-molecular-weight fractions. Conversely, the TD-added samples showed minimal variation in the low-molecular-weight distribution compared to the 3-Hp samples, but their high-molecular-weight fractions were similarly reduced. The weight-average molecular weights of the raw NR with the four additives decreased compared to that of the control. TD showed an insignificant decline, whereas 3-HP displayed the most pronounced reduction. TAA led to a slight enhancement in the number-average molecular weight. However, these weights decreased with ETU and TD, with TD causing a greater decrease. The number-average molecular weight with 3-HP remained consistent with that of the control. The distribution coefficient increased due to TD but decreased with other additives, with 3-HP showing the sharpest decrease. These findings indicate that TD addition of TD increased the number of smaller molecular weight components. Concurrently, the molecular weight of the larger components increased, broadening the distribution and amplifying the molecular weight disparity among the rubber chains. With 3-HP introduction, smaller-molecular-weight components increased, larger molecules decreased, and the molecular weight distribution became more tightly clustered. These observations are consistent with the results shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eThe weight-average molecular weight of raw NR, derived from fresh latex via wet mixing with four additives, decreased compared to that of the control. TD showed an insignificant decline, whereas 3-Hp displayed the most substantial reduction. The incorporation of TAA marginally increased the number-average molecular weight. However, it diminished with the inclusion of both ETU and TD, with TD witnessing a sharper drop. Notably, the number-average molecular weights after 3-Hp addition aligned with those of the control group. The distribution coefficient increased upon TD addition but decreased with the other three additives, with 3-Hp causing the most pronounced reduction. After TD addition, the proportion of smaller-molecular-weight components increased, the molecular weight of the larger components increased, and the molecular weight distribution broadened. Conversely, after 3-Hp addition, there was a surge in smaller molecular weight components and a decrease in the count and molecular weight of larger molecules, leading to the tightest molecular weight distribution. These observations are consistent with the results shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab7\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 7\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eRelative molecular weight size and distribution coefficient of raw rubber with different additives\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eAdditives\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMn/10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMw/10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDistribution coefficient\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e13.02\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e236.52\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e18.17\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTD\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e11.35\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e235.96\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e20.79\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTAA\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e14.14\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e232.58\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e16.45\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eETU\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e12.48\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e221.26\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e17.72\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3-Hp\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e13.02\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e195.54\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e15.02\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec18\" class=\"Section3\"\u003e\n\u003ch2\u003e3.2.5 Effects of different additives on the preparation of infrared spectrum of NR\u003c/h2\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e shows the infrared spectrum of NR derived from fresh latex prepared via wet mixing with four distinct additives. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e, there are no noticeable shifts in the wave peaks of the infrared spectra of the five NR samples. Moreover, the intensities of these wave peaks did not exhibit significant changes. The characteristic peaks of all samples essentially fell within the same number of bands, and the overall infrared curve mappings were closely aligned, with minimal variance observed. The C\u0026thinsp;=\u0026thinsp;C double bond in the NR molecule corresponds to a wavenumber of 1645 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, accompanied by a bending vibration peak at 840 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The -CH\u003csub\u003e3\u003c/sub\u003e and -CH\u003csub\u003e2\u003c/sub\u003e groups exhibit wave numbers of 2959 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 2851 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively, with their bending vibration peaks manifesting near wave numbers of 1443 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1375 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Notably, the six profiles exhibited minor discrepancies in certain characteristic peaks, suggesting that the integration of the four molecules might not be optimal for the infrared profile. These slight variations in the characteristic peaks across the six profiles imply a marginal structural impact on NR after the addition of the four substances. Consequently, drawing definitive conclusions about their influence on the various properties of dried rubber films is challenging.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec19\" class=\"Section3\"\u003e\n\u003ch2\u003e3.2.6 Influence of different additives on the thermal stability of raw NR\u003c/h2\u003e\n\u003cp\u003eThe Thermogravimetric (TG) and Derivative Thermogravimetric (DTG) profiles of raw NR prepared from fresh latex with the four additives and their characteristic temperatures are presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e and Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e. The impact of the additives on NR's thermal stability of NR was assessed using the initial decomposition temperature (T\u003csub\u003e0\u003c/sub\u003e). Samples with TD and 3-Hp exhibited marginally higher onset decomposition temperatures, suggesting enhanced initial thermal stability. The TAA and ETU samples exhibited decomposition temperatures comparable to those of the blank samples, indicating a minimal effect on the initial thermal stability. For T\u003csub\u003e50\u003c/sub\u003e, 3-Hp recorded the highest value at 386.28\u0026deg;C, while TD displayed a lower T\u003csub\u003e50%\u003c/sub\u003e, indicating faster mid-period decomposition. Other additives minimally influenced the T\u003csub\u003e50%\u003c/sub\u003e. The peak decomposition temperature (Tp) varied with the additives, with TD showing the highest value at 382.00\u0026deg;C, followed by 3-HP, whereas TAA showed the lowest value. The final temperature (T\u003csub\u003ef\u003c/sub\u003e) for the TAA and ETU samples was marginally higher than that of the blanks, with minor differences between the 3-HP and control samples, whereas the TD was lower. While all additives elevated the initial decomposition temperature, TD showed inferior overall thermal stability, whereas the others demonstrated slightly enhanced stability compared to the controls. For TD, despite the pyridine group improving the initial stability, thioamide degradation and uneven crosslinking reduced the thermal stability later [\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e]. With 3-HP, hydrogen bonding and pyridine group synergy enhanced the molecular chain stability [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. TAA's low reactivity provided minimal thermal stability improvement.\u003csup\u003e32\u003c/sup\u003e ETU's early vulcanization due to rubber double bonds forms sulfur bonds, slightly improving the thermal stability [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"char\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab8\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 8\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eCharacteristic degradation temperature of NR latex dry films incorporating various additives\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003e0\u003c/sub\u003e/\u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003e50\u003c/sub\u003e/\u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003ep\u003c/sub\u003e/\u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eT\u003csub\u003ef\u003c/sub\u003e/\u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eBlank\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e353.62\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e385.35\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e377.31\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e415.17\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTD\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e354.69\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e383.58\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e382.00\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e411.98\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTAA\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e353.88\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e385.39\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e376.51\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e418.01\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eETU\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e353.98\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e385.70\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e377.85\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e416.20\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3-Hp\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e354.61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e386.28\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e380.08\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e415.97\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec20\" class=\"Section3\"\u003e\n\u003ch2\u003e3.2.7 Influence of different additives on RPA data of raw NR preparation\u003c/h2\u003e\n\u003cp\u003eThe analysis of G' (energy storage modulus) and tan \u0026delta; (loss factor) curves is crucial for understanding the dynamic mechanical properties of rubber materials. These curves provide insights into the elastic behavior and energy dissipation characteristics at varying frequencies and temperatures. As shown in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003eb, the incorporation of TD, 3-HP, and ETU enhanced the G' values across the test range. 3-HP showed the strongest effect, followed by TD, suggesting increased rubber rigidity due to the synergistic effect of TD and 3-HP, which promotes cross-linking and strengthens the network structure. Changes in the tan \u0026delta; curve indicate shifts in viscoelasticity. A peak shift to a higher temperature or frequency indicates an elevated glass transition temperature (Tg), indicating reduced flexibility and enhanced thermal stability. TAA minimally influences the G' and tan\u0026delta; of raw rubber samples. ETU slightly elevated G' and reduced tan\u0026delta;, which was similar to the TD effects. Samples with 3-HP showed the highest G' curve and lowest tan\u0026delta;. The causes are:\u003c/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cp\u003e3-HP: (1) Hydrogen bonding strengthens molecular chain interactions through reversible bonds between hydroxyl groups (-OH) and rubber chains, increasing crosslinking density and improving rigidity [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e]. (2) Pyridine groups coordinate with Zn\u003csup\u003e2+\u003c/sup\u003e (Zn(C5H5N)\u003csup\u003e2+\u003c/sup\u003e), optimizing the crosslinked network homogeneity and reducing energy dissipation [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e]. (3) Hydrogen bonding and ligand interactions form a stable crosslinking network, enhancing elastic storage and suppressing viscous dissipation.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eThioamide Derivatives (TD): (1) Thioamide enables cross-linking through sulfur radicals from R-C\u0026thinsp;=\u0026thinsp;S groups, accelerating sulfur cross-linking [\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e][\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. (2) Pyridine-Zn\u003csup\u003e2+\u003c/sup\u003e coordination increases network rigidity, although uneven crosslinking leads to incomplete chain movement restriction [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e]. (3) Thioamides may cause partial chain breaks during vulcanization, thereby increasing energy dissipation.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eThe properties of ethylene thiourea (ETU) are as follows: (1) Rapid crosslinking forms short sulfur bonds (-S- or -S-S-), creating a brittle network. (2) Short sulfur bonds break and reconnect during deformation, causing viscous dissipation [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. (3) High crosslink density trades off with network uniformity, limiting the optimization of the elastic response.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eThioacetamide (TAA): (1) Limited crosslinking: The thioamide group in TAA has low reactivity, preventing effective vulcanization and having a negligible impact on the crosslinked network. (2) Unrestricted Molecular Chain Movement: No cross-linking points are formed, maintaining the viscoelastic properties of the rubber (G' \u0026asymp; blank, tan\u0026delta;\u0026thinsp;\u0026asymp;\u0026thinsp;blank) [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTD promotes a uniformly high crosslink density by slowly releasing reactive sulfur and forming long sulfur bridges. This process fully extends the sulfur bonds, enhancing network stability with only a slight increase in the elongation at break [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]. In contrast, ETU accelerates vulcanization, generating dense short sulfur bonds that form a dense and flexible network. This resulted in an 8.9% increase in the tear strength, although the magnitude of tensile enhancement was lower than that of the TD direction [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. 3-Hp selective crosslinking leads to local overdensification and improves the tensile strength. However, hydrogen-bond-induced brittleness results in a 14.0% decrease in the tear strength [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e]. TAA, owing to its low reactivity, had no significant effect on the tensile strength. However, hydrogen bonding-induced brittleness results in a 14.0% decrease in the tear strength [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. The crosslink density positively enhanced the strength and hardness of the material. However, the tearing performance is dependent on the sulfur-bridge length and network homogeneity. The flexible structure of ETU is superior to the inhomogeneous distribution of 3-Hp, whereas TD balances high strength with moderate elongation. The mechanisms by which the three additives (TD, ETU, and 3-Hp) promoted NR vulcanization are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e. As depicted in this figure, all three components facilitated the crosslinking of rubber molecules, thereby significantly enhancing the mechanical properties of the rubber.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"4. CONCLUSION","content":"\u003cp\u003eThis study aimed to examine the key chemical groups of thioamide derivative (TD) present in the composite preservation system to amplify the vulcanization properties of NR. The distinct impacts of various additives, namely TD, TAA, ETU, and 3-Hp, on the preparation of NR blends and vulcanized rubber were meticulously analyzed. The findings revealed that TD significantly reduced the vulcanization time and exhibited potent vulcanization-promoting capabilities. Conversely, TAA exerted virtually no beneficial influence on vulcanization, whereas ETU and 3-Hp exhibited varying degrees of vulcanization promotion. Notably, the TD samples demonstrated an accelerated vulcanization speed and a heightened degree of vulcanization at increased dosages. In contrast, TAA's influence of TAA on the performance of vulcanized rubber was virtually imperceptible, and the effect of ETU was also relatively constrained.\u003c/p\u003e\u003cp\u003eThe raw rubber produced by incorporating TD into fresh latex via wet mixing exhibited a reduced number-average molecular weight and a broader molecular weight distribution. Similarly, the ETU sample displayed a diminished weight-average molecular weight with a relatively narrow molecular weight distribution coefficient. The 3-Hp sample also presented a decreased weight average molecular weight, and its molecular weight distribution coefficient was notably the lowest among the samples. The infrared spectroscopy results revealed consistent characteristic peaks across the five samples, with no marked migration or intensity variations, suggesting a minimal impact of the additives on the primary chain structure of NR. Notably, the raw rubber samples treated with TD and 3-Hp exhibited an elevated energy storage modulus (G'), indicating increased rigidity of the rubber molecules. Concurrently, their loss factor (tanδ) curves diminished, with the 3-Hp samples showing particularly low tanδ values.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eIn summary, the vulcanization promoted by TD is predominantly a synergistic result of the pyridine and thioamide groups. Consequently, the composite antibacterial and antifungal system, LS, not only markedly accelerated the vulcanization process and enhanced the degree of vulcanization of NR but also significantly improved the physical and mechanical properties of the vulcanized NR.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cdiv class=\"SimplePara\"\u003eNR\u003c/div\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cdiv class=\"SimplePara\"\u003eNatural rubber\u003c/div\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cdiv class=\"SimplePara\"\u003eTD\u003c/div\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cdiv class=\"SimplePara\"\u003eThioacetamide derivative\u003c/div\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cdiv class=\"SimplePara\"\u003eTAA\u003c/div\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cdiv class=\"SimplePara\"\u003eThioacetic acid\u003c/div\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cdiv class=\"SimplePara\"\u003eETU\u003c/div\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cdiv class=\"SimplePara\"\u003eThioketone accelerators\u003c/div\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cdiv class=\"SimplePara\"\u003e3-Hp\u003c/div\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cdiv class=\"SimplePara\"\u003e3-Hydroxypyridine\u003c/div\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cdiv class=\"SimplePara\"\u003eMv\u003c/div\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cdiv class=\"SimplePara\"\u003eMooney viscosity\u003c/div\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cdiv class=\"SimplePara\"\u003eM\u003csub\u003eL\u003c/sub\u003e\u003c/div\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cdiv class=\"SimplePara\"\u003eThe minimum torque\u003c/div\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cdiv class=\"SimplePara\"\u003eM\u003csub\u003eH\u003c/sub\u003e\u003c/div\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cdiv class=\"SimplePara\"\u003eThe highest maximum torque\u003c/div\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cdiv class=\"SimplePara\"\u003ephr\u003c/div\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cdiv class=\"SimplePara\"\u003eParts per hundred rubber\u003c/div\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003cbr/\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eLiguang Zhao: Conceptualization, Methodology, Writing\u0026mdash;original draft. Yiqun Liu: Methodology, Writing\u0026mdash;original draft preparation. Liyang Zhao: Validation. Yazhong Song: Project administration. Honghao Huang: Investigation, Methodology, Writing\u0026mdash;review and editing. Jianwei Li: Data curation, Project administration, Validation. Tuo Dai: Data curation, Validation. Minmin Chen: Formal analysis. Tao Zhao: Formal analysis, Project administration. Hongxing Gui: Methodology, Resources. Zhenxiang Xin: Investigation, Resources, Writing\u0026mdash;review and editing.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e\u003cp\u003eWe would like to thank the Ministry of Agriculture and Rural Affairs of China and the Department of Science and Technology of Hainan Province for their support. This reearch was supported by the National Key R\u0026amp;D Program of China (2024YFD2300903; 2022YFD2301201), the Agricultural Technology Experiment Demonstration and Service Support Project of the Ministry of Agriculture and Rural Affairs (XJSHT2-02-02), the Hainan Province Science and Technology Special Fund [ZDYF2024XDNY284], and Earmarked Fund for China Agriculture Research System [CARS-33-JG1].\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLoykulnant S, Kongkaew C, Chaikumpollert O, Sanguanthammarong P, Na Ubol P, Suchiva K (2011) Study of chitosan and its derivatives as preservatives for field natural rubber. Journal of Applied Polymer Science\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChaikumpollert O, Loykulnant S, Kongkaew C (2007) A novel preservative system for natural rubber latex. 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Polym Compos 41(4):1242\u0026ndash;1254\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Natural rubber, Preservation system, Vulcanization, Physical and mechanical properties","lastPublishedDoi":"10.21203/rs.3.rs-7015352/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7015352/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe thioacetamide derivative (TD)-composite preservation system (TDCPS) exhibits superior preservation effects on natural rubber (NR) latex and significantly enhances its vulcanization efficiency and mechanical properties. This study assessed TDCPS for NR, with a particular focus on its effects in promoting vulcanization. The TD containing both pyridine and thioamide groups was evaluated against other additives, namely thione accelerator ETU, pyridine 3-HP, and thioacetamide TAA. The results indicated that TD significantly reduced vulcanization time and enhanced efficiency, surpassing the moderate effects of ETU and 3-HP, as well as the minimal activity of TAA. Furthermore, TD and 3-HP demonstrated a synergistic effect in enhancing the properties of vulcanized NR, including elongation stress, tensile strength, tear resistance, and hardness, with TD achieving more rapid and complete vulcanization at higher dosages. Both TD and 3-HP increased the energy storage modulus of raw NR, thereby enhancing rigidity, while maintaining low loss factor values. The superior performance of TD is attributed to the synergistic interaction of its pyridine and thioamide groups, which optimize vulcanization kinetics and mechanical integrity. These findings underscore TD's potential as an efficient vulcanization promoter for NR.\u003c/p\u003e","manuscriptTitle":"Impact of Thioamide Derivative Composite Preservation System on Vulcanization of Natural Rubber","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-14 13:44:54","doi":"10.21203/rs.3.rs-7015352/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"632bc2c1-fd45-43b3-860e-0953d462393d","owner":[],"postedDate":"August 14th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-12-19T15:24:04+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-14 13:44:54","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7015352","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7015352","identity":"rs-7015352","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}