Rubber Vulcanization Accelerators Research Articles

Adverse effect of TWPs on soil fungi and the contribution of benzothiazole rubber additives

Tire wear particles (TWPs) pollution is widely present in soil, especially in areas severely affected by traffic. Herein, regular variation of fungal biomass with TWPs was found in soils with different distances from the highway. In addition, the concentrations of benzothiazole compounds (BTHs), an important class of rubber vulcanization accelerators, were found to be positively correlated to the TWPs abundance. Sixty days' soil microcosm experiments were conducted to further confirm the adverse effect of TWPs and BTHs on soil fungi. TWPs spiking at 1000 mg/kg, a detectable level in the roadside, resulted in significant reduction of biomass and significant changes of soil fungal community structure, with Eurotium and Polyporales being the sensitive species. BTH+ 2-hydroxybenzothiazole (OHBT) (the dominant BTHs in soil) spiking at 200 ng/kg, the dose equivalent to 1000 mg/kg TWPs pollution, also caused a similar magnitude of soil fungal biomass reduction. Adonis demonstrated no significant difference of fungal community structure between TWPs and BTH+OHBT spiked soil, suggesting the adverse effect of TWPs on soil fungi may be explained by the act of BTHs. Pure culture using the representative soil fungi Eurotium and Polyporales also confirmed that BTHs were the main contributors to the adverse effect of TWPs on soil fungi.

Tracing the odor source of crumb rubber modified asphalt emissions and evaluating the deodorization effect of attapulgite

Crumb rubber modified asphalt (CRMA) is widely used in road construction due to its excellent performance. However, it generates significant odorous gases during paving. To analyze the odor contribution, both untreated crumb rubber and desulfurized rubber were involved in this study to prepare CRMA and desulfurized rubber modified asphalt (DRMA). Attapulgite was selected as an emission reduction agent to reduce the odorous emissions released from CRMA and DRMA. An indoor fume collection system and gas chromatography-mass spectrometry (GC-MS) analysis were used to trace the odor source and quantify the odorous emissions. A comprehensive olfactory thresholds database for CRMA emissions was further established to evaluate the odor level of various rubberized asphalt binders by using three-point comparative odor bag method, along with known olfactory thresholds of certain compounds reported in the literature. Dynamic shear rheometer (DSR), multiple stress creep recovery (MSCR), bending beam rheometer (BBR) and Brookfield viscosity tests were used to analyze the effect of attapulgite on rheological properties of CRMA and DRMA. Results indicated that odor emission rate of CRMA containing 1 %, 3 %, and 5 % attapulgite was decreased by 42.62 %, 63.29 %, and 71.06 %, respectively. Benzothiazole, derived from tire rubber vulcanization accelerator, can be reduced by 60.25 % with 1 % attapulgite, demonstrating excellent performance in terms of reducing target odor emissions. Although DRMA has a lower emission rate than that of conventional CRMA, the addition of 1 % attapulgite can further reduce the odor emission rate of DRMA by 37.92 %. The addition of attapulgite has less impact on the overall performance of CRMA and DRMA. Besides, it was found that attapulgite can reduce the viscosity of rubberized asphalt binders, which is beneficial for rubberized asphalt mixture paving and compaction. Considering odor reduction, performance, and economic factors, the optimal attapulgite content was determined to be 5 % for CRMA and 1 % for DRMA. This approach successfully reduces odorous emissions while maintaining the desirable properties of CRMA, making it a viable solution for environmentally friendly road construction.

Sodium dimethyl dithiocarbamate, as a capable heavy metal chelating agent: Production and applications

Sodium dimethyl dithiocarbamate (SDDC) is a universal heavy metal precipitant/chelating agent, which is widely used in the treatment of heavy metals in industrial wastewater and fly ash from waste incineration. It can be utilized as a heavy metal precipitant, fungicide, agricultural insecticide, rubber vulcanization accelerator, styrene-butadiene rubber polymerization terminator, polymerization inhibitor, mineral processing reagent, etc. This review article focuses on the research of the production and application of SDDC in heavy metal chelation. The following three benefits of using SDDC as a heavy metal chelating agent are: (1) it can chelate with various heavy metal ions at room temperature to generate insoluble chelate salts and precipitates, which can be easily removed; (2) SDDC can perform chelation reaction with varies heavy metal ions at the same time; (3) as a heavy metal chelating agent, SDDC is simple to use and low costs, which is significantly better than other heavy metal chelating agents and precipitants. This review paper presents novel ideas for the performance enhancement based on SDDC in removing heavy metals and is a prospect for the research, development, production, and applications of SDDC.

Indirect Electrocatalysis S─N/S─S Bond Construction by Robust Polyoxometalate Based Foams.

Indirect electrocatalytic conversion of cheap organic raw materials via the activation of S─H and N─H bonds into the value-added S─N/S─S bonds chemicals for industrial rubber production is a promising strategy to realize the atomic economic reaction, during which the kinetic inhibition that is associated with the electron transfer at the electrode/electrolyte interface in traditional direct electrocatalysis can be eliminated to achieve higher performance. In this work, a series of di-copper-substituted phosphotungstatebased foams (PW10 Cu2 @CMC) are fabricated with tunable loadings (17 to 44wt%), which can be successfully applied in indirect electrocatalytic syntheses of sulfenamides and disulfides. Specifically, the optimal PW10 Cu2 @CMC (44wt%) exhibits excellent electrocatalytic performance for the construction of S─N/S─S bonds (yields up to 99%) coupling with the efficient production of H2 (≈50µmolg-1 h-1 ). Remarkably, it enables the scale-up production (≈14.4g in a batch experiment) and the obtained products can serve as rubber vulcanization accelerators with superior properties to traditional industrial rubber additives in real industrial processes. This powerful catalysis system that can simultaneously produce rubber vulcanization accelerator and H2 may inaugurate a new electrocatalytic avenue to explore polyoxometalate-based foam catalysts in electrocatalysis field.

MoS2-Catalyzed Aerobic Synthesis of Tetraethylthiuram Disulfide in Batch and Continuous Flow

Abstract:Tetraethylthiuram disulfide (TETD) is one of the most important thiuram-class rubber vulcanization accelerators and a ‘star molecule’ in other areas. The development of a mild, efficient, low-cost, safe, and sustainable approach to produce TETD is extremely desirable. Here, we developed a much-improved route to synthesize TETD using MoS2 as the catalyst and ethanol as the solvent. A packed-bed microflow strategy was implemented to accelerate the catalytic process. TETD was obtained with an excellent yield and purity within a short residence time. Besides, this continuous process did not generate any waste salts, rendering it a sustainable method for producing thiuram-type compounds.

FUNCTIONALIZED SILICA AS AN ECO-FRIENDLY VULCANIZATION ACCELERATOR TO ENHANCE THE INTERFACIAL INTERACTION IN NR/SILICA COMPOSITES

ABSTRACT Xanthate is a class of non-toxic, rapid, and eco-friendly rubber vulcanization accelerator, but it is seldom used in the rubber industry because of its poor thermostability and ease of decomposition. To overcome these drawbacks, silica supported sodium isobutyl xanthate (silica-s-SIBX) was prepared by chemically bonding SIBX onto the silica surface. After loading, the initial degradation temperature (T0), maximum degradation temperature (Tp), and final decomposition temperature (Tf) of silica-s-SIBX were increased by 85.8, 118.9, and 146.9 °C, respectively. Meanwhile, silica-s-SIBX could not only improve the dispersion of fillers in the rubber but also enhance the interfacial interaction between silica and the rubber matrix. Therefore, it may offer new scientific and technological opportunities for preparation of green additives in the rubber industry.

Novel Architecture of ZnO Nanobundles Grown on Porous Silica as High Performance Vulcanization Accelerators that Reinforce Rubber Composites

A novel functional rubber vulcanization accelerator, petal-like ZnO nanobundles grown on porous silica (ZnO-g-SiO2), was fabricated via a facile and environmentally friendly process. The zinc sourc...

Processes for synthesis of altax

Literature analysis was focused on the existing processes for synthesis of altax (2,2’-dibenzothiazolyldisulfide) as an important rubber vulcanization accelerator. Oxidation of mercaptobenzothiazole (captax) with various oxidants such as oxygen in the presence of catalysts, hydrogen peroxide etc., as well as electrochemical oxidation was shown to be the primary way to altax. The data from literature were the basis to develop a low-tonnage technology for synthesis of altax; the technology was developed at the Boreskov Institute of Catalysis and tested using a pilot setup at the Volgograd Department of BIC.

Vulcanization accelerator functionalized nanosilica: Effect on the reinforcement behavior of SSBR/BR

The application of nanosilica in high performance tire highly depends on its uniform dispersion in rubber matrix. A series of dispersible nanosilica (denoted as DNS) modified by diphenyl guanidine (denoted as DPG, a vulcanization accelerator) were synthesized by liquid phase in situ surface chemical modification. The structure of the as‐obtained DNS‐DPG fillers was investigated in relation to Fourier transform infrared spectrometric analysis, thermogravimetric analysis, dynamic light scattering test, and transmission electron microscopic observation. It was found that the rubber vulcanization accelerator DPG was successfully grafted onto the surface of nanosilica, thereby effectively preventing the silica nanoparticles from agglomeration and significantly reducing the average particle size. The reinforcing effect of the DPG‐modified DNS nano‐fillers for the solution polymerized styrene butadiene rubber/butadiene rubber (denoted as SSBR/BR) was dependent on the fraction of the modifier DPG; in particular, when the amount of modifier DPG is 135.25 mmol/kg (denoted as DNS‐DPG‐3), silica exhibited very homogeneous dispersion in the SSBR/BR matrix, which contributed to significantly enhancing the filler‐rubber compatibility. As a result, SSBR/BR/DNS‐DPG‐3 nanocomposite exhibited the best mechanical properties, integrated high abrasion resistance and low rolling resistance. The modified silica not only possessed the effect of accelerating the crosslinking reaction, but also showed the reinforcing effect. This could make it feasible for SSBR/BR/DNS‐DPG nanocomposite to find promising application in green tire tread. POLYM. ENG. SCI., 59:1270–1278 2019. © 2019 Society of Plastics Engineers

Fall Creek Monitoring Station: Highly Resolved Temporal Sampling to Prioritize the Identification of Nontarget Micropollutants in a Small Stream.

The goal of this research was to comprehensively characterize the occurrence and temporal dynamics of target and nontarget micropollutants in a small stream. We established the Fall Creek Monitoring Station in March 2017 and collected daily composite samples for one year. We measured water samples by means of high-resolution mass spectrometry and developed and optimized a postacquisition data processing workflow to screen for 162 target micropollutants and group all mass spectral (MS) features into temporal profiles. We used hierarchical clustering analysis to prioritize nontarget MS features based their similarity to target micropollutant profiles and developed a high-throughput pipeline to elucidate the structures of prioritized nontarget MS features. Our analyses resulted in the identification of 31 target micropollutants and 59 nontarget micropollutants with varying levels of confidence. Temporal profiles of the 90 identified micropollutants revealed unexpected concentration-discharge relationships that depended on the source of the micropollutant and hydrological features of the watershed. Several of the nontarget micropollutants have not been previously reported including pharmaceutical metabolites, rubber vulcanization accelerators, plasticizers, and flame retardants. Our data provide novel insights on the temporal dynamics of micropollutant occurrence in small streams. Further, our approach to nontarget analysis is general and not restricted to highly resolved temporal data acquisitions or samples collected from surface water systems.

Simulation of Structure, Molecular Orbitals, Electron Density and Reactivity Aspects of Rubber Vulcanization Accelerator 2-Mercaptobenzothiazole by Density Functional Theory

Simulation of Structure, Molecular Orbitals, Electron Density and Reactivity Aspects of Rubber Vulcanization Accelerator 2-Mercaptobenzothiazole by Density Functional Theory

Hydrogenation of tar residue derived from the synthesis of rubber vulcanization accelerator 2‐mercaptobenzothiazole

AbstractA large amount of hazardous tar residue is produced during the synthesis of rubber vulcanization accelerator 2‐mercaptobenzothiazole (MBT). In this study, pyrite (FeS2) was used as catalyst for the hydrogenation of the tar residue under different conditions. Optimal hydrogenation conditions were as follows: 270 °C under an H2 pressure of 4.5 MPa for 8 h under a catalyst loading of 2%. MBT presented in tar residue is converted to benzothiazole (BT) by a high yielding hydrogenation in 86.9% yield based on the initial amount of BT with a small quantity aniline also produced as side product. This work provides a framework for possible ways to treat the toxic tar residue formed in the industrial synthesis of BT through the hydrogenation procedure established in this study. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.

One-step approach to reduce and modify graphene oxide via vulcanization accelerator and its application for elastomer reinforcement

An efficient and rapid one-step approach to prepare organically modified graphene from graphene oxide (GO) by using nontoxic rubber vulcanization accelerator N-cyclohexyl-2-benzothiazolesulfenamide (CZ) as reducing and modifying agent was presented. CZ was highly effective in reducing graphene oxide in a short time (1h) under a mild condition (70°C). Meanwhile, the reduced graphene decorated with 20wt% CZ molecules exhibited a good solubility in organic solvents, which significantly reduced the irreversible graphene agglomerates and improve the compatibility between graphene and elastomer. Consequently, elastomer composites with CZ reduced and modified GO possessed a combination of high tensile strength and large extensibility, showing 82% and 21% increases respectively, in comparison with elastomer composites with hydrazine hydrate reduced GO containing equivalent filler and CZ content. One-step reaction, short reaction time, mild reaction conditions and high-efficiency make the approach of using rubber additives a promising strategy for the eco-friendly production of graphene and may uncover an extensive family of building blocks for constructing high performance elastomer/graphene composites.

Novel Ionic Liquids as Accelerators for the Sulfur Vulcanization of Butadiene–Styrene Elastomer Composites

The aim of this work was to study the activity of novel benzalkonium and ammonium ionic liquids with 2-mercaptobenzothiazolate as accelerators in the sulfur vulcanization of butadiene–styrene elastomer (SBR). In this Article, the effect of the ionic liquids on the vulcanization kinetics of the rubber compounds, the cross-link density, and the mechanical properties of the vulcanizates, as well as their resistance to thermal and UV aging, was studied. The application of novel ionic liquids allowed for the elimination of N-cyclohexyl-2-benzothiazolesulfenamide from SBR compounds and for the considerable reduction of the amount of 2-mercaptobenzothiazole present in rubber products. Synthesized salts seem to be good substitutes for standard accelerators in the sulfur vulcanization of SBR rubber, without the observation of any detrimental effects on the vulcanization process, the physical properties, or the thermal stability of the obtained vulcanizates.

Homolytic SS Bond Dissociation of 11 Bis(thiocarbonyl)disulfides R‐C(S)SSC(S)R and Prediction of A Novel Rubber Vulcanization Accelerator

The structures and energetics of eight substituted bis(thiocarbonyl)disulfides (RCS(2))(2), their associated radicals RCS(2)(*), and their coordination compounds with a lithium cation have been studied at the G3X(MP2) level of theory for R = H, Me, F, Cl, OMe, SMe, NMe(2), and PMe(2). The effects of substituents on the dissociation of (RCS(2))(2) to RCS(2)(*) were analyzed using isodesmic stabilization reactions. Electron-donating groups with an unshared pair of electrons have a pronounced stabilization effect on both (RCS(2))(2) and RCS(2)(*). The S-S bond dissociation enthalpy of tetramethylthiuram disulfide (TMTD, R = NMe(2)) is the lowest in the above series (155 kJ mol(-1)), attributed to the particular stability of the formed Me(2)NCS(2)(*) radical. Both (RCS(2))(2) and the fragmented radicals RCS(2)(*) form stable chelate complexes with a Li(+) cation. The S-S homolytic bond cleavage in (RCS(2))(2) is facilitated by the reaction [Li(RCS(2))(2)](+)+Li(+)-->2 [Li(RCS(2))](*+). Three other substituted bis(thiocarbonyl) disulfides with the unconventional substituents R = OSF(5), Gu(1), and Gu(2) have been explored to find suitable alternative rubber vulcanization accelerators. Bis(thiocarbonyl)disulfide with a guanidine-type substituent, (Gu(1)CS(2))(2), is predicted to be an effective accelerator in sulfur vulcanization of rubber. Compared to TMTD, (Gu(1)CS(2))(2) is calculated to have a lower bond dissociation enthalpy and smaller associated barrier for the S-S homolysis.

Synthesis, spectroscopic characterization and vulcanization activity of a new compound containing the anion bis(4-methylphenylsulfonyldithiocarbimato)zincate(II)

A new compound of the formula: (Bu 4N) 2[Zn(4-CH 3C 6H 4SO 2N CS 2) 2] (Bu 4N = tetrabutylammonium cation) was obtained by the reaction of CH 3C 6H 4SO 2N CS 2K 2 · 2H 2O with zinc(II) acetate dihydrate and tetrabutylammonium bromide in dimethylformamide. The elemental analyses of C, H, N and Zn are consistent with the proposed formula. The IR data point to the formation of a zinc(II)–bis(dithiocarbimato) complex. The 1H NMR and 13C NMR spectra showed the expected signals for the tetrabutylammonium cation and the dithiocarbimato moiety. This compound was evaluated as for the vulcanization activity and compared to the commercial accelerators CBS, MBTS and TMTD. These studies showed that the zinc(II)–ditiocarbimates are a new class of rubber vulcanization accelerators, worth of further investigation.

FTIR, Raman spectra and ab initio calculations of 2-mercaptobenzothiazole

FTIR and Raman spectra of a rubber vulcanization accelerator, 2-mercaptobenzothiazole (MBT), were recorded in the solid phase. The harmonic vibrational wavenumbers, for both the toutomeric forms of MBT, as well as for its dimeric complex, have been calculated, using ab initio RHF and density functional B3LYP methods invoking different basis sets upto RHF/6-31G** and B3LYP/6-31G** and the results were compared with the experimental values. Conformational studies have been also carried out regarding its toutomeric monomer forms and its dimer form. With all the basis sets the thione form of MBT (II) is predicted to be more stable than thiol form (I) and dimeric conformation (III) is predicted to be more stable with monomeric conformations (I) and (II). Vibrational assignments have been made, and it has been found that the calculated normal mode frequencies of dimeric conformation (III) are required for the analysis of IR and Raman bands of the MBT. The predicted shift in NH− stretching vibration towards the lower wave number side with the B3LYP/6-31G** calculations for the most stable dimer form (III), is in better agreement with experimental results. The intermolecular sulfur-nitrogen distance in N H···S hydrogen bond was found to be 3.35 Å from these calculations, is also in agreement to the experimental value.

Survey of sulfur‐containing rubber accelerator levels in latex and nitrile exam gloves

2-Mercaptobenzothiazole and zinc dialkyldithiocarbamates are commonly used sulfur-containing rubber vulcanization accelerators known to cause allergic contact dermatitis. Exposure to these agents occurs through clothing such as undergarments and shoes, latex medical devices and latex and nitrile gloves. A simple, inexpensive screening method for total sulfur accelerator and a high performance liquid chromatographic speciation method were developed in the present study. These methods were applied to screen and quantify the sulfur accelerator content from 38 brands of 'off-the-shelf' latex and nitrile gloves obtained from commercial vendors. It was found that accelerator levels ranged from not detectable to 7.35 mg/g in the gloves analysed. Brands were found to contain single and multiple accelerator species within the glove. Powdered gloves had significantly higher accelerator levels than powder-free gloves from the same manufacturer; however, these chemical accelerators do not preferentially partition to the powder. The present analytical methodology is suitable for both manufacturing quality validation purposes, as well as for accelerator allergy research.

Amidino Thiourea as a Secondary Accelerator in the Sulphur Vulcanization of Natural Rubber Containing Fillers

As a part of our study on the mechanism of vulcanization we investigated a number of thiourea derivatives as secondary accelerators in the sulphur vulcanization of natural rubber. In the present study, the accelerator activity of a new binary accelerator system containing unsubstituted amidinothiourea viz. aminoiminomethyl thiourea (ATU) along with different primary accelerators has been examined. Different fillers like carbon black, silica and china clay are incorporated in these mixes under review. Various compositions of ATU are examined for the above vulcanization study. The optimum concentration of this secondary accelerator in different systems has also been derived. The mixes are examined for different cure characteristics and the vulcanizates are evaluated for their physical properties. In order to study the effect of the secondary accelerator on the temperature of vulcanization, these mixes are cured and evaluated at two different temperatures, viz. 120o and at 150oC. The correlation between physical properties and chemical cross links in the different vulcanizates is also examined by determining the cross link density values of the vulcanizates. These binary systems are found to be effective in the filled systems studied. The optimum cure time has been found to be reduced considerably by this secondary accelerator. At the lower temperature i.e., at 120°C, the reduction in cure time is found to be more significant with increase in the concentration of ATU especially when compared with systems containing thiourea. ATU being more nucleophilic than thiourea this points to a nucleophilic reaction mechanism in these vulcanization reactions. The tensile properties of the vulcanizates from these systems are better/comparable to those of the reference mixes. There is favourable increase in many of the physical properties like hardness, compression set, abrasion loss, tear strength etc. The crosslink density values evaluated also support the above conclusions. The non-toxic nature of ATU, which is used in pharmaceutical applications, is an added advantage in this context.

Quantitative determination of dithiocarbamates in human plasma, serum, erythrocytes and urine: pharmacokinetics of broccoli sprout isothiocyanates in humans

Background: Humans are exposed to substantial quantities of isothiocyanates and glucosinolates from vegetables. Since dietary isothiocyanates are widely regarded as potentially important chemoprotectors against cancer, reliable methods for measuring the plasma and tissue pharmacokinetics of isothiocyanates and their dithiocarbamate metabolites are essential for defining dosing regimens. Methods: Isothiocyanates (ITC) and dithiocarbamates (DTC) react quantitatively with 1,2-benzenedithiol to produce 1,3-benzodithiole-2-thione that can be quantified spectroscopically. Although this cyclocondensation reaction has been highly useful for analyzing plant material and urine samples, the determination of DTC/ITC (the total quantity of DTC and ITC components in a sample that react in the cyclocondensation reaction) in blood and tissues has been hampered by their low levels and the high concentrations of proteins that interfere with the cyclocondensation reaction. The protein content of blood and tissues was reduced by the precipitation with polyethylene glycol (PEG) or ultrafiltration, and the sensitivity of the method was increased substantially by the solid phase extraction of the cyclocondensation product. Results: Pharmacokinetic measurements were made in four human volunteers who received single doses of about 200 μmol of broccoli sprout isothiocyanates (largely sulforaphane, with lesser amounts of iberin and erucin). Isothiocyanates were absorbed rapidly, reached peak concentrations of 0.943–2.27 μmol/l in plasma, serum and erythrocytes at 1 h after feeding and declined with first-order kinetics (half-life of 1.77±0.13 h). The cumulative excretion at 8 h was 58.3±2.8% of the dose. Clearance was 369±53 ml/min, indicating active renal tubular secretion. Conclusion: A sensitive and specific method for quantifying DTC levels in human plasma, serum, and erythrocytes has been devised. Determinations of ITC/DTC levels are important because: (i) dietary isothiocyanates are of potential value in reducing the risk of cancer, and (ii) humans are extensively exposed to DTC as fungicides, insecticides, pesticides and rubber vulcanization accelerators.