Effect of fillers in the binary systems containing TMTD–amidinothiourea and MBTS–amidinothiourea in NR vulcanization

In earlier studies,^1,2 we have shown that in MBTS–amidinothiourea and TMTD–amidinothiourea binary system of rubber vulcanization, amidinothiourea functions effectively as a secondary accelerator and improves the accelerator activity of these systems. These secondary accelerators enhance the physical properties of the vulcanizates and show better cure characteristics of the mixes compared to the reference systems studied. In this paper, we present the results of our study on the effect of various fillers in the sulfur vulcanization of natural rubber using amidinothiourea as the secondary accelerator. We have taken MBTS–amidinothiourea and TMTD–amidinothiourea binary accelerator systems and vulcanizates were prepared with carbon black, precipitated silica, and china clay as fillers. Different compositions of amidinothiourea were used in various mixes using standard recipes. Reference mixes were also studied. Curing characteristics of the mixes and various physical properties of the vulcanizates were evaluated. Optimum dosage of amidinothiourea required has also been derived. Among the different secondary accelerators tried including amidinothiourea, it may be stated generally that the more nucleophilic the secondary accelerator, the less the optimum cure times. This fact points to a nucleophilic reaction mechanism in the systems under review. In the evaluation of tensile and other physical properties of the vulcanizates, some of the systems containing amidinothiourea show better properties while others give comparable values with the reference mixes. Estimation of crosslink density also supports the above conclusion. © 1996 John Wiley & Sons, Inc.     

Studies on novel binary accelerator system in sulfur vulcanization of natural rubber

The synergistic activity of binary accelerator systems in rubber vulcanization is well known. Thiourea and its derivatives are important secondary accelerators in this context. It is suggested that thiourea containing binary systems of rubber vulcanization proceed by a nucleophilic reaction mechanism. Amidinothioureas (ATUs), which are derivatives of thiourea, have been investigated extensively as secondary accelerators. One of the aims of this study was to get further proof with regard to the theory of the nucleophilic reaction mechanism in such binary systems. In the present study phenyl substituted ATU was used as a secondary accelerator along with mercaptobenzothizyl disulfide, tetramethyl thiuram disulfide, or cyclohexyl benzthiazyl sulfenamide in the sulfur vulcanization of natural rubber. The results showed an appreciable reduction in the cure time for the mixes containing the ATU compared to the reference mixes. These results are indicative of a nucleophilic reaction mechanism in the vulcanization reaction under review. These vulcanizates also showed comparatively better tensile properties and good retention of these properties after aging. The optimum dosages of the secondary accelerator required for these vulcanization reactions were also derived. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1–8, 2001     

Studies on novel binary accelerator system in sulfur vulcanization of natural rubber

The synergistic activity of binary accelerator systems in rubber vulcanization is well known. Binary accelerator systems are being widely used in industry and are becoming increasingly popular because of the fact that such mixed systems can effectively prevent prevulcanization, permit the vulcanization to be carried out at a lower temperature in a shorter time, and produce a vulcanizate with superior mechanical properties compared to those of a stock cured with a single accelerator. Thiourea and its derivatives are important secondary accelerators in this context. It is suggested that thiourea containing binary accelerator systems cause rubber vulcanization to proceed by a nucleophilic reaction mechanism. In the present study 1‐phenyl‐5‐ortho, ‐meta, and ‐para‐tolyl derivatives of 2,4‐dithiobiurets, which are more nucleophilic than thiourea and vary in their nucleophilic reactivity, are used as secondary accelerators along with 2‐morpholinothiobenzothiazole in the vulcanization of natural rubber. The results show an appreciable reduction in the cure time for the mixes containing the dithiobiurets compared to the reference mix. These results are indicative of a nucleophilic reaction mechanism in the vulcanization reaction under consideration. These vulcanizates also demonstrate comparatively better tensile properties and good retention of these properties after aging. An attempt is also made to correlate the variation in physical properties to chemical crosslink formation in the various vulcanizates. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3173–3182, 2003     

A new secondary accelerator for the sulfur vulcanization of natural rubber latex and its effect on the rheological properties

The vulcanization of natural rubber (NR) latex can be effectively carried out at low temperatures by using binary accelerator systems containing thiourea (TU) as a secondary accelerator. It was reported that sulfur‐containing nucleophiles such as thiourea enable the primary accelerator to become effective even at low temperatures, indicating a nucleophilic reaction mechanism in such vulcanization reactions. In the present study, a derivative of thiourea [viz. aminoiminomethyl thiourea (AMT)], which is more nucleophilic than thiourea, is used as a secondary accelerator in the sulfur vulcanization of NR latex. One of the aims of this study was to give conclusive evidence for a nucleophilic reaction mechanism. The synergistic effect of the above thiourea derivative with primary accelerators such as tetramethylthiuram disulfide (TMTD), zinc diethyldithiocarbamate (ZDC), and cyclohexylbenzthiazyl sulfenamide (CBS) was studied at two different temperatures (viz. 100 and 120°C). These binary systems were found to be very effective in reducing the optimum cure time of the different mixes compared to control formulations containing TU. The optimum amount of the secondary accelerator required was also determined. Mechanical properties such as tensile strength and tear strength of the vulcanizates were also evaluated. Chemical characterization of the vulcanizates was carried out by determining the total crosslink density. Values of the cure characteristics evaluated support a nucleophilic reaction mechanism in these vulcanization reactions under review. The effect of this secondary accelerator on the rheological behavior of compounded latex is also studied and was found not to affect adversely. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2781–2789, 2004     

Effect of vulcanizing system on the crosslink density of nitrile rubber compounds

The synergistic activity of binary accelerator systems in rubber vulcanization is well known. Binary accelerator systems are being widely used in industry and are becoming increasingly popular because of the fact that such mixed systems can produce a vulcanizate with superior mechanical properties compared to those of stock cured with a single accelerator. The authors have studied the performance of a binary accelerator system based on cyclohexyl benzothiazole sulfenamide (CBS), tetramethyl thiuram disulphide (TMTD) in the sulfur vulcanization of nitrile rubber. The amount of sulfur and accelerator was varied to change the network crosslink density of vulcanizates. The observed mutual activity has been discussed based on the mechanical properties and crosslink density. The physical crosslink density of the various nitrile rubber mixes was estimated using the Kinetic Theory of Elasticity. The mechanical properties of the various rubber compounds were related to the corresponding crosslink density estimated for each compound. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2440–2445, 2005     

A new binary accelerator system for the sulfur vulcanization of natural rubber latex

Vulcanization of latex products are usually carried out at lower temperatures compared to dry rubber products. It has been suggested that, in latex vulcanization systems where thiourea is used as a secondary accelerator, it acts as a nucleophilic reagent facilitating the cleavage of the sulfur bonds in the primary accelerator like TMTD or CBS at lower temperature. But no conclusive proof is given to such a postulate. In the present study 1-phenyl-2,4-thiobiuret (DTB II) and 1,5-diphenyl-2,4-dithiobiuret (DTB III), which are more nucleophilic than thiourea and which vary in their nucleophilic reactivity, were studied as secondary accelerators along with tetramethyl thiuram disulphide (TMTD) and N-cyclohexylbenzothiazyl sulphenamide (CBS) in the vulcanization of natural rubber latex. These binary systems were found to be very effective in reducing the optimum vulcanization time. Also it was noted that 1-phenyl-2,4-dithiobiuret, which is more nucleophilic, is more reactive (as observed from the reduction in optimum cure time) as a secondary accelerator, indicating a nucleophilic reaction mechanism in the vulcanization reactions under review. The optimum dosages of the secondary accelerators required were derived. Physical properties like tensile strength, 300% modulus, and elongation at break of the latex vulcanizates were also studied. There is a definite advantage with respect to many of these properties for dithiobiuret systems compared to the systems containing TMTD alone or TMTD/thiourea. DTB III gives higher values in many of these physical properties than DTB II. Chemical characterization of the vulcanizates was also carried out to correlate the physical properties with the type of chemical crosslinks formed. © 1993 John Wiley & Sons, Inc.     

Synergic effect of N‐benzylimine aminothioformamide secondary accelerator during sulfur vulcanization of a styrene‐butadiene‐natural rubber blend

In this study we reported synergic activity of a novel secondary accelerator N‐Benzylimine aminothioformamide (BIAT) along with tetramethylthiuram disulfide (TMTD) in improving cure and mechanical properties of gum and filled mixes of Styrene‐Butadiene Rubber (SBR). The feasibility of application of BIAT in sulfur vulcanization of an ideal blend of SBR and natural rubber (NR) has also been investigated. The mechanical properties like t ensile strength, tear resistance, hardness, compression set, and abrasion loss were measured. Swelling values were also determined as a measure of crosslink densities of the vulcanizates. The binary accelerator system BIAT‐TMTD was found very effective in improving cure properties of the mixes of pure SBR and a 50/50 blend of SBR and NR.There was also found simultaneous improvement in mechanical properties of vulcanizates of both pure and blend. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

High temperature vulcanization of elastomers: 3. Network structure of efficiently vulcanized natural rubber mixes

The effect of vulcanization temperature (140–200°C) and time on the structures of pure gum natural rubber vulcanizates with two different N-cyclohexyl-2-benzothiazylsulphenamide (CBS): sulphur ratios (A, 3·5:1·5; B, 6·0:0·4 CBS/S) has been determined. Analyses of vulcanizates were carried out as reported in Part 2. Results show that both mixes are efficient in crosslinking, resulting in mainly monosulphidic crosslinks and relatively few modifications of the rubber chains. Raising the cure temperature from 140°C reduces the density of chemical crosslinks, particularly those of monosulphidic crosslinks, obtainable in the vulcanizates. This decrease in crosslink density has been shown to be irreversible with respect to cure temperature. The formation of intramolecular sulphidic groups and zinc sulphide increases with rising cure temperature, but this increase is small compared with that reported for the conventional CBS-accelerated system. The main difference between mixes A and B is that mix A yields a higher level of crosslinks and a major proportion of cyclic sulphides as main-chain modification. Negligible chain scission occurs during vulcanization at 140–200°C. These network results are interpreted mechanistically, and essential network features for obtaining good physical properties in high temperature vulcanizates are deduced.     

NR–EPDM covulcanization: A novel approach

Bis(diisopropyl)thiophosphoryl disulfide (DIPDIS) was used successfully as a novel coupling agent cum accelerator to co‐vulcanize the elastomer blend comprising highly unsaturated natural rubber (NR) and ethylene propylene diene rubber (EPDM) of low unsaturation content. The blend vulcanizates produced exhibit improved physical properties that can be further enhanced by implementing a two‐stage vulcanization technique, as well as by judicious selection of the NR‐to‐EPDM ratio. The results indicate coherency and homogeneity in the blend composition of two‐stage vulcanizates. The cure‐rate mismatch problem could thus be solved through the formation of rubber‐bound intermediates with a multifunctional rubber additive (i.e., DIPDIS), thereby restricting the curative migration from lower to highly unsaturated rubber. The blend morphology as revealed by SEM studies accounts for significant improvement in physical properties, particularly in two‐stage vulcanizates. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 800–808, 2001     

New binary accelerator systems for sulphur vulcanisation of styrene butadiene rubber

Abstract

It is suggested that binary systems of rubber vulcanisation containing thiourea proceed by a nucleophilic reaction mechanism. The exact mechanism of the chemical reactions involved when binary accelerator systems are used in rubber vulcanisation is not fully understood even now. It differs with the systems and the nature of the elastomer used. In the present work, a derivative of thiourea, N-amidino N'-phenyl thiourea (APT), was studied as a secondary accelerator along with tetramethyl thiuram disulphide (TMTD)/mercaptobenzothiazyl disulphide (MBTS) in the sulphur vulcanisation of styrene butadiene rubber. Thiourea binary systems were used as controls. The binary systems containing APT are very effective in reducing the optimum vulcanisation time. APT being more nucleophilic than thiourea, is more reactive here (as observed by the reduction in cure time). A nucleophilic reaction mechanism is indicated in the vulcanisation reaction under review. Different concentrations of APT were tried in various mixes using standard recipes, and reference mixes were also evaluated. The optimum dosage of APT required has been derived based on the cure characteristics of the mixes and the physical properties of the vulcanisates.     

Effect of bis(diisopropyl)thiophosphoryl disulfide on the covulcanization of styrene–butadiene rubber and ethylene–propylene–diene (monomer) blends

Covulcanization of elastomer blends constituting styrene–butadiene rubber (SBR) and ethylene–propylene–diene (monomer) rubber (EPDM) was successfully performed in the presence of reinforcing fillers like carbon black and silica by using a multifunctional rubber additive, bis(diisopropyl)thiophosphoryl disulfide (DIPDIS). The polarity of EPDM rubber was increased by a two‐stage vulcanization technique, which allowed the formation of rubber‐bound intermediates. In this way the migration of both curatives and reinforcing fillers in the EPDM–SBR blend could be controlled and cure rate mismatch could be minimized. The process significantly improved the physical properties of the blend vulcanizates. The phase morphology, as evident from the SEM micrographs, was indicative of the presence of a much more compact and coherent rubber matrix in the two‐stage vulcanizates. Different accelerator systems were studied to understand better the function and effectiveness of DIPDIS in developing homogeneity in the blends of dissimilar elastomers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1231–1242, 2004     

改性淀粉对炭黑填充丁苯橡胶/顺丁橡胶并用胶性能的影响

用改性淀粉替代部分炭黑填充丁苯橡胶(SBR)/顺丁橡胶(BR)并用胶,考察了改性淀粉用量及偶联剂种类对混炼胶硫化特性及硫化胶物理机械性能和动态力学性能的影响.结果表明,用改性淀粉替代部分炭黑可对SBR/BR混炼胶的硫化产生明显的延迟作用,但改性淀粉用量的变化对焦烧时间与正硫化时间影响不大;添加偶联剂KH-570或NDZ-201延迟了混炼胶的硫化过程,KH-550能大幅度地促进硫化作用,Si-69对于体系的硫化性能略有影响;随着改性淀粉用量的增加,SBR/BR硫化胶的拉伸性能、耐磨耗性均有所降低,但弹性、动态生热和滞后性能得到了明显改善,改性淀粉最佳用量为5～8份;各种偶联剂均可提高SBR/BR硫化胶的拉伸性能,硅烷偶联剂Si-69和KH-570对弹性和动态生热也略有改善,添加偶联剂KH-550改善了SBR/BR硫化胶的抗湿滑性能,但滞后性能变差,添加偶联剂KH-570或Si-69对SBR/BR硫化胶动态力学性能的影响较小,综合考虑,以添加偶联剂KH-570较好.     

Effect of Substituted Dithiobiurets—Tetramethyl Thiuram Disulfide (TMTD) Binary Accelerator Systems in the Vulcanization of NR-SBR Blends

1-Phenyl 2,4-dithiobiuret and 1,5-diphenyl 2,4-dithiobiuret were studied as secondary accelerators along with tetramethyl thiuram disulfide (TMTD) in the vulcanization of a blend of natural rubber (NR) and styrene-butadiene rubber (SBR). These binary systems were found to be very effective and reduced the optimum vulcanization time considerably. 1-Phenyl 2,4-dithiobiuret, which is more nucleophilic than 1,5-diphenyl 2,4-dithiobiuret, reduced the vulcanization time more, indicating a nucleophilic reaction mechanism in the vulcanization reactions under review. In both cases the optimum dosage of the secondary accelerator was derived. Physical properties such as modulus, tensile strength, elongation at break, hardness, compression set, heat buildup, resilience, etc., of the vulcanizates were studied before and after heat aging and compared with a reference mix. There is substantial increase in many of these properties compared with TMTD alone or with the reference mix. Chemical characterization of the vulcanizates was also carried out to correlate the physical properties with the type of chemical crosslinks formed in these systems.     

Nano ZnO as cure activator and reinforcing filler in natural rubber

Zinc oxide (ZnO) nanoparticles of size 20–90 nm and surface area 9.56 m²/g were synthesized from ZnCl₂ and Chitosan and characterized by X‐ray diffraction, high resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM). Natural rubber (NR) vulcanizates containing nano ZnO was prepared by mill mixing and characterized by SEM, energy dispersive X‐ray analysis (EDAX), and HRTEM. Cure characteristics, free volume studies, bound rubber, crosslink density, and dynamic mechanical properties were evaluated and compared with that of NR vulcanizate containing conventional micro ZnO. Considering the cure characteristics, it was found that NR vulcanizate with 0.5 phr (parts per 100 g rubber) of nano ZnO showed low values of optimum cure time (t₉₀) and very high cure rate index compared with 5 phr of conventional micro ZnO. The study shows that micro ZnO can be successfully replaced with nano ZnO for accelerated sulfur vulcanization process in NR, and preparation of vulcanizate containing nano ZnO with better properties as that of micro ZnO. The optimum dosage of nano ZnO as a cure activator in NR vulcanization was found to be 0.5 phr compared with conventional grade micro ZnO. This will lead to substantial cost reduction in the manufacture of rubber products and alleviate environmental pollution due to excess ZnO in rubber compounds. POLYM. ENG. SCI., 2013 © 2013 Society of Plastics Engineers     

Preparation and Characterization of Some NR and SBR Formulations Containing Different Modified Kaolinite

Kaolinite clay (KC) surface was modified with different surface modifiers such as methacrylic acid (MAA), polymethacrylic acid (PMAA1, mol wt 10,000) and polymethacrylic acid (PMAA2, mol wt 11,500). The adsorption isotherms of the above modifiers on the surface of KC were determined. The concentrations required for building up monolayer coverage of these modifiers on the surface of KC were determined from the adsorption isotherms. The optimum amount of modifier required for monolayer surface coverage on kaolinite was equal to 31 × 10^?5 mol/g for MAA, 35 × 10^?5 mol/gfor PMAA and 23.5 × 10^?5 mol/g for PMA. Different rubber mixes containing unmodified and modified KC were prepared. The rheometric characteristics of the rubber mixes and physico-mechanical properties of the rubber vulcanizates were measured. There was remarkable decrease in both the optimum cure time (tc₉₀) and scorch time (ts₂), following increase in the maximum torque of the SBR mixes by adding unmodified or modified KC. With the maximum torque increase, the values of both of the optimum cure time (tc₉₀) and scorch time (ts₂) decreases for the NR mixes by adding unmodified and modified KC. Also the mechanical properties of the investigated rubber vulcanizates as tensile strength and hardness were improved using unmodified KC and modified KC.     

环保型增塑剂腰果壳油对丁腈橡胶性能的影响

研究了腰果壳油(CNSL)用量对丁腈橡胶胶料的硫化特性和硫化胶性能的影响,并与使用邻苯二甲酸二辛酯和环氧大豆油作为增塑剂进行了对比。结果表明,在0～30份(质量)用量内,加入CNSL后胶料的焦烧时间和正硫化时间有所缩短。与加入相同用量的邻苯二甲酸二辛酯和环氧大豆油的胶料及硫化胶相比,使用CNSL的胶料在硫化曲线上的最小转矩和最大转矩以及硫化胶的硬度、定伸应力和耐ASTM1#标准油体积增加率较小;硫化胶的拉伸强度、撕裂强度、扯断伸长率和耐ASTM3#标准油体积增加率较大;硫化胶的耐热空气老化性能较好。     

促进剂对氯丁胶/反式-1,4-聚异戊二烯并用胶性能的影响

将促进剂TMTD、NA-22和DM用于氯丁橡胶（CR）和反式-1,4-聚异戍二烯（TPI）并用胶中,研究其对并用胶性能的影响。结果表明,与促进剂NA-22和DM相比,促进剂TMTD可以降低混炼胶的门尼粘度,提高胶料的流动性;缩短正硫化时间,有利于改善加工工艺,提高硫化效率。加入促进剂DM的胶料焦烧时间比较长,加工安全性提高,但正硫化时间过长,硫化效率低。加入促进剂TMTD的胶料拉伸强度、拉断伸长率、撕裂强度等物理机械性能优异,屈挠性能提高显著;耐老化性能略有下降。当促进剂TMTD的用量在1．0～1．3份时胶料的综合性能最好。     

Novel method for preparation of carboxylated nitrile rubber–natural rubber blends using bis(diisopropyl)thiophosphoryl polysulfides

Bis(diisopropyl)thiophosphoryl trisulfide (DIPTRI) and bis(diisopropyl)thiophosphoryl tetrasulfide (DIPTET) are successfully used as a novel coupling agent and accelerator, respectively, to covulcanize an elastomer blend comprising polar carboxylated nitrile rubber (XNBR) and nonpolar natural rubber (NR). These compounds are capable of forming a chemical link between these dissimilar rubbers to produce a technologically compatible blend as judged by a swelling experiment. The blend vulcanizates thus produced exhibit enhanced physical properties that can further be improved by adopting the two‐stage vulcanization technique and also by judicious selection of the NR:XNBR ratio. The blend morphology assessed by scanning electron microcroscopy micrographs accounts for significant improvement in the physical properties of the blend vulcanizates, particularly in two‐stage vulcanization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1725–1736, 2001     

Synthesis and effect of surface modified nano ZnO in natural rubber vulcanization

It is well known that surface of ZnO acts both as a reactant and a catalytic reaction template in rubber vulcanization by activating and bringing together reactants. The particles of accelerators, fatty acid, and sulfur diffuse through the polymer matrix and get adsorbed on the surface of ZnO, forming intermediate complexes. Hence dispersion of ZnO in the elastomer matrix is a determining parameter. Capping is one of the novel techniques for increasing ZnO‐stearic acid/accelerator interaction, thereby enhancing their activities. During the sol–gel precipitation of nano ZnO, if a suitable capping agent is added, agglomeration of ZnO particles gets reduced, leading to the formation of nano particles. Since only very few studies are found reported on synthesis of accelerator‐capped ZnO and its application in rubber vulcanization, attempts have been made in this study to synthesize our novel accelerator N‐benzylimine aminothioformamide (BIAT)‐capped‐stearic acid‐coated nano ZnO (ZOBS), and BIAT‐capped ZnO (ZOB) to investigate their effects in natural rubber (NR) vulcanization. Efforts have also been made to synthesize stearic acid‐coated nano zinc phosphate (ZPS) with an aim to find an alternative to conventional ZnO in vulcanization. Mechanical properties like tensile strength, tear resistance, abrasion resistance, and compression set were found out. Swelling values of the vulcanizates as a measure of crosslink densities were also determined. Optimum dosage of ZOBS and a combination of ZOB and ZPS were also derived and found that capped ZnO is superior in NR vulcanization to conventional ZnO in improving cure properties including scorch safety and mechanical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Studies on Cure Synergism. II,Effect of Diisopropyl Thiophosphoryl-N-Oxydiethylene Sulfenamide and Dibenzothiazyl Disulfide in the Vulcanization of NR

Thiazole sulfenamides as well as thiocarbamyl sulfenamides in the presence of dibenzothiazyl disulfide (MBTS) form synergistic combinations of rubber accelerators that provide technologically important rubber vulcanizates. The present investigation explores the feasibility of using thiophosphoryl sulfenamide with MBTS as a binary system of mutually activated accelerators in the vulcanization of rubber. The cure characteristics of the NR compound containing various proportions of diisopropyl thiophosphoryl-N-oxydiethylene sulfenamide (DIPTOS) and MBTS have been investigated keeping the total concentrations of the accelerators at 6 mmol per 100 rubber. The results indicated mutual activity of the mixed accelerators and significant enhancement of torque, modulus, and tensile strength of the resulting vulcanizates. The general character of the reaction of thiophosphoryl sulfenamide and MBTS has been established by replacing DIPTOS by diisopropylthiophosphoryl-N-cyclopentamethylene sulfenamide (DIPTCS), in the investigation. The mutual activity consequent upon the interaction of the accelerators can be demonstrated through isolation and identification of the reaction products formed in the early part of cure using the HPLC technique, which is also extremely helpful in explaining the cure behavior of the different stocks used in the investigation. The study reveals that diisopropylthiophosphoryl-2-benzothiazole disulfide (DIBDS), formed (in situ) as a result of interaction of DIPTOS and MBTS, plays an active part in improving the physical properties of NR vulcanizates. From the chemical analyses of the vulcanizates it is evident that the network structure obtained with the binary system of accelerators is highly rich in monosulfidic linkages that render the vulcanizates resistant to aging at 100°C.