Sulfur Vulcanization Research Articles

Diphenylguanidine combined with high molecular weight polyacrylonitrile precursor for high-conductivity and high-sulfur-loading cathode of lithium-sulfur battery

Sulfurized polyacrylonitrile (SPAN) cathode have high discharge specific capacity, close to 100 % coulombic efficiency and excellent cycle stability, which is regarded as a very promising cathode material in lithium-sulfur batteries. However, polyacrylonitrile as vulcanization precursor have a great influence on the performance of SPAN. Therefore, the effects of different molecular weight polyacrylonitrile precursors while diphenylguanidine as vulcanization accelerator on the performance of SPAN cathodes are reported for the first time. Considering that diphenylguanidine as vulcanization accelerator can significantly increase the sulfur loading of SPAN. Prepared SPAN-1000k cathode by an ultra-high molecular weight polyacrylonitrile precursor (Mw = 1000k) has a sulfur-loading of up to 54.5 %. Surprisingly, a 22 % increase in conductivity resulting in a remarkable discharge capacity of 830 mAh gcomposite−1 at a high rate of 1C (0.7 A/g). This work demonstrates that diphenylguanidine as vulcanization accelerator prepared ultra-high molecular weight SPAN cathode can greatly improve sulfur loading and conductivity, and exhibit excellent electrochemical performance at a high rate.

Enhanced wastewater bioremediation by a sulfur-based copolymer as scaffold for microalgae immobilization (AlgaPol)

In recent years, there has been an increasing concern related to the contamination of aqueous ecosystems by heavy metals, highlighting the need to improve the current techniques for remediation. This work intends to address the problem of removing heavy metals from waterbodies by combining two complementary methodologies: adsorption to a copolymer synthesized by inverse vulcanization of sulfur and vegetable oils and phytoremediation by the microalga Chlorella sorokiniana to enhance the metal adsorption. After studying the tolerance and growth of Chlorella sorokiniana in the presence of the copolymer, the adsorption of highly concentrated Cd2+ (50 mg L−1) by the copolymer and microalgae on their own and the combined immobilized system (AlgaPol) was compared. Additionally, adsorption studies have been performed on mixtures of the heavy metals Cd2+ and Cu2+ at a concentration of 8 mg L−1 each. AlgaPol biofilm is able to remove these metals from the growth medium by more than 90%. The excellent metal adsorption capacity of this biofilm can be kinetically described by a pseudo-second-order model.

Inverse vulcanization of elemental sulfur catalyzed by trialkyl amines

Under eco-friendly trialkyl amine catalysis, facile and fast low-temperature inverse vulcanization of elemental sulfur using unreactive crosslinkers is enabled.

New ways of processing and application of the croton fraction of waste from the production of JSC “Navoiazot”

The purpose of this work is to study the interaction of the croton fraction with amides – urea and thiourea and to develop technologies for obtaining accelerators for vulcanization of rubbers for the rubber industry.

Gas pyrolysis resin as a plasticizer for composite elastomer materials

The aim of the study is to study the effect of gas pyrolysis resin on the properties of elastomeric composite materials. It has been established that in the presence of it in the thiuram vulcanizing system, the relative rate of vulcanization of styrene-butadiene rubber increases, the time to reach the optimum vulcanization decreases, but the degree of vulcanization decreases, proportional to the maximum torque, and when using a sulfur vulcanizing system, it activates the vulcanization process, which is facilitated by the presence in its composition of active functional groups (-OH, -COOH, etc.). It is shown that the tensile strength and relative elongation of the vulcanizates increase, while the elasticity remains at an average level.

Выбор ускорителей вулканизации для резин на основе эпихлоргидринового каучука

The effect of vulcanization accelerators on the structure and properties of rubbers based on Hydrin T6000 epichlorohydrin rubber has been studied. Mercaptobenzthiazole (MBT) in the amount of 1.5 pts.wt., tetramethylthiuram disulfide (TMTD) — 0.5 – 1.5 pst.wt. were used as accelerators and N,N’-diphenylguanidine (DPG) — 0.5 – 1.5 pst.wt., which represent a triple system of accelerators. The choice of accelerators is based on the possibility of obtaining a vulcanization spatial structure of different sulfide content: thiuram group accelerators promote the formation of mono-, disulfide bonds; guanidine — polysulfide bonds, and thiazole groups — from carbon-carbon to polysulfide with varying degrees of sulfide. According to the results of the study of physical and mechanical properties, the determination of the parameters of the spatial grid and the study of the dynamic behavior of rubber, differences were revealed due to the formation of a spatial structure with different types of cross-links and density. It is shown that rubber containing 1.5 pst. wt. MBT, 0.5 pst. wt. DFG and 0.5 – 1.0 pst.wt. TMTD due to the manifestation of a synergistic effect on the formation of a vulcanization network of a certain density and the ratio of poly-, di- and monosulfide cross-links. Thus, the use of a group of accelerators with different functional effects makes it possible to obtain vulcanizates with an optimal set of technological and operational properties.

Interface Coupling in Rubber/Carbon Black Composites toward Superior Energy-Saving Capability Enabled by Amino-Functionalized Polysulfide

Natural rubber/carbon black (NR/CB) composites have found indispensable application in aircraft tires. Interfacial modification of NR/CB composites for acquiring uniform CB dispersion and strong interfacial adhesion is a persistent and challenging theme, as it is a prerequisite to improve comprehensive mechanical properties and decrease energy loss of the composites under dynamic deformations. In this work, we reported the use of an amino-functionalized polysulfide (PDAS) synthesized by inverse vulcanization of sulfur and m-phenylenediamine as a novel interfacial modifier in NR/CB composites. Specifically, the amino of PDAS can react with the carboxyl groups on the CB surface, meanwhile the polysulfide chains of PDAS can react with rubber chains, enabling the crosslinking of NR and establishment of a molecular bridge between NR and CB. The influences of PDAS dosages on CB dispersion and interfacial adhesion are revealed, and their correlations with composite properties are discussed. Compared with the unmodified counterpart, CB dispersion is greatly improved and interfacial adhesion is significantly enhanced in the PDAS-modified composite having an identical crosslink density, leading to remarkably decreased hysteresis loss. In addition, PDAS can significantly resist thermal-oxidative aging of the composites due to its radical scavenging activity.

Photoinduced inverse vulcanization.

The inverse vulcanization (IV) of elemental sulfur to generate sulfur-rich functional polymers has attracted much recent attention. However, the harsh reaction conditions required, even with metal catalysts, constrains the range of feasible crosslinkers. We report here a photoinduced IV that enables reaction at ambient temperatures, greatly broadening the scope for both substrates and products. These conditions enable volatile and gaseous alkenes and alkynes to be used in IV, leading to sustainable alternatives for environmentally harmful plastics that were hitherto inaccessible. Density functional theory calculations reveal different energy barriers for thermal, catalytic and photoinduced IV processes. This protocol circumvents the long curing times that are common in IV, generates no H2S by-products, and produces high-molecular-weight polymers (up to 460,000 g mol-1) with almost 100% atom economy. This photoinduced IV strategy advances both the fundamental chemistry of IV and its potential industrial application to generate materials from waste feedstocks.

Physical Properties and Biodegradability Evaluation of Vulcanized Epoxidized Natural Rubber/Thermoplastic Potato Starch Blends.

The sustainable material-thermoplastic potato starch (TPS)-was blended with modified natural rubber-epoxidized natural rubber (ENR). The poor mechanical properties of the ENR/TPS blends limited the application. Sulfur vulcanization is a common and economical method to improve the mechanical properties in the rubber industry. To fully understand the relationship between vulcanization systems and ENR/TPS blends and the sustainability of the developed material, the effects of a vulcanization accelerator (N-cyclohexylbenzothiazole-2-sulphenamide (CBS), 2-mercaptobenzothiazole (MBT), N-tert-butylbenzothiazole-2-sulphenamide (TBBS)) and a system type (conventional vulcanization (CV), semi-efficient vulcanization (SEV) and efficient vulcanization (EV)) on curing characteristics, mechanical and thermal properties, water absorption and biodegradability were systematically evaluated. The results indicate that vulcanization significantly improves the mechanical properties of ENR/TPS blends. The performance optimization of the CBS-CV vulcanization system is the best for improving the mechanical properties and reducing the water absorption. The CBS-CV curing system makes ENR/TPS less biodegradable (12-56% of mass loss) than other accelerators and systems. TBBS-CV makes the material more biodegradable (18-66% of mass loss). The low rubber content enables the rapid biodegradation of the vulcanized blend. This has implications for research on sustainable materials. The material can be applied for eco-friendly packaging and agricultural films, etc. The investigation on performance by using common accelerators and systems provides ideas for industries and research.

Preparation of high‐performance deproteinized natural rubber/chitosan composite films via a green and sulfur‐free method

AbstractTo solve the environment and health issues arose from the sulfur vulcanization, a facile and completely eco‐friendly method of latex‐assembly and in situ cross‐linking is developed to prepare fully bio‐based and high‐performance rubber films. The films are featured by a “reinforced concrete” structure composed of dynamically cross‐linked chitosan framework and unvulcanized deproteinized natural rubber (DPNR) matrix. The self‐assembly of DPNR latex particles and chitosan, as well as the in situ cross‐linking of chitosan in the film forming process are confirmed by transmission electron microscope and dynamic light scattering. As green rubbers without vulcanization, the as‐designed composite films possess excellent mechanic properties comparable to those of the sulfur vulcanized DPNR film, whose tensile strength and toughness reach 15.2 MPa and 77.6 MJ m−3 respectively. Moreover, the films exhibited appropriate permeability to moisture and achievable reprocessing, which have potential applications in wearable devices.

Turning abundant waste sulfur to polymers for manufacturing: Exploiting role of organic crosslinkers and benign catalysts

Abundant source of sulfur produced as byproduct of refineries demands sustainable valorization solutions. Use of organic crosslinkers and benign catalysts to polymerize sulfur for use in manufacturing offers a sustainable value-added application. This paper introduces MgO as an effective benign catalyst and oleic acid as an organic crosslinker for inverse vulcanization of sulfur. We further compare efficacy of MgO with other metal catalysts (ZnO and CaO) using molecular modeling and laboratory experiments. ZnO is commonly used in elastomeric formulations; however, industries try hard to keep the ZnO level low because of its environmental impact, particularly on aquatic organisms, and for economic reasons. Our rheological characterization shows the inverse vulcanization is enhanced when MgO is present as evidenced by the increase of viscosity of sulfur-oleic acid blends by 94 % relative to the blend without catalyst and 39 % relative to the blend with ZnO catalyst. Based on our quantum-based molecular modeling, using density functional theory (DFT), coordination complexes of Mg oleate (Mg (RCOO)2), made from the reaction between oleic acid and MgO, are energetically better stabilized compared to Zn or Ca oleate. Stronger interactions in Mg oleate, leading to the more stabilized coordination complexes, could be a reason for higher viscosity for MgO/sulfur-oleic acid compared to ZnO/sulfur-oleic acid. In complexes of sulfur and metal oleate, regardless of the electronic nature of sulfur chains (ionic or radical form), coordination complexes containing MgO show binding energies that are higher than those of Zn complexes and notably higher than those of Ca complexes, indicating capability of Mg substitution in Zn oleate compounds as catalysts. Studying the addition reactions of sulfur radicals to oleic acid and the formation of CS bonds, using DFT modeling, shows the superiority of allylic (CHCHĊH) sites of oleic acid over olefinic (CC) sites in reactions of sulfur radicals. Compared to sulfur radicals, sulfur chains in ionic character provide higher binding energies with metal oleates because of the electrostatic interactions between the positively charged metal and negative sulfur atoms. The study outcomes support sustainability and resource conservation in chemical manufacturing and petroleum refining industry.

Supramolecular Design Strategy of a Water-Soluble Diphenylguanidine-Cyclodextrin Polymer Inclusion Complex.

Diphenylguanidine (DPG) is a widely used secondary accelerator for the vulcanization of natural rubber (NR) latex. However, its low water solubility and high toxicity limit its use in high-end NR products. In this study, a water-soluble inclusion complex of DPG and a β-cyclodextrin polymer (β-CDP), termed DPG-β-CDP, was prepared through supramolecular interactions and characterized using Fourier-transform infrared spectroscopy, 1H NMR, scanning electron microscopy, and UV-vis spectroscopy techniques. In comparison with that of DPG, the water solubility of DPG-β-CDP was greatly enhanced because of the water-soluble host molecule. The molar ratio of DPG to the CD unit in β-CDP was determined to be 1:1. At 25 °C, the binding constant of DPG-β-CDP was found to be 9.2 × 105 L/mol by UV-vis spectroscopy. The proposed method for forming inclusion complexes with high potential for use as water-soluble vulcanization accelerators is promising.

Microstructure-properties of dynamically vulcanized mengkuang leaf fibre/ethylene vinyl acetate/natural rubber thermoplastic elastomer composites

Thermoplastic elastomer composites based on ethylene vinyl acetate (EVA), natural rubber (NR), and Mengkuang leaf fibre were prepared using the sulfur and peroxide vulcanization systems. Different curing systems and fibre loadings affecting the processing torque, tensile, thermal, and morphology of the composites were investigated. Addition of Mengkuang leaf fibre resulted in poor fibre dispersion and agglomeration in the matrix, which may have affected the efficiency of stress transfer and thus could explain a decline in tensile and thermal properties. Composites with dynamic vulcanization showed a rougher surface that might be due to the presence of crosslinking, which requires more force to fail. The increase in stabilization torque for the composites with dynamic vulcanization was observed due to the addition of curing agents, which implies some changes at the molecular level due to crosslinking. Tensile properties of Mengkuang leaf fibre filled EVA/NR composites indicated that the tensile strength, elongation at break, and Young’s modulus of the peroxide cure system were higher than the sulfur cure system and unvulcanised composites. The sulphur cure system showed better resistance towards thermal degradation compared to the peroxide cure system. This was attributed to dicumyl peroxide (DCP), which degrades the polymer chain or the composites at high temperature.

Simulating vulcanization process during tire production to explore sulfur migration during pyrolysis

This paper systematically investigated sulfur transformation during pyrolysis of waste tires by simulating vulcanization process. Three formulas with rubbers, carbon black, ZnO, and typical vulcanization accelerators were prepared by vulcanization and compounded process as simulated tires. Stepwise temperature programmed pyrolysis was conducted in thermogravimetric analyzer and fixed bed reactor. Vulcanization promoted the weight loss rate for thermal degradation of vulcanized rubbers at 300–400 °C, but weakened it at 400–500 °C. The addition of vulcanization accelerators made these effects even more pronounced. Accordingly, more pyrolytic oil was obtained at 300–400 °C for vulcanized rubbers which should contribute to the partial destruction of polymer chains by vulcanization. Besides, vulcanized rubbers attained higher proportion of aromatics but less cyclenes than compounded rubbers. Vulcanized rubbers with ethyl ziram accelerator inhibited H2S release, while vulcanized rubbers with N-tert-Butyl-2-benzothiazolesulfenamide inhibited the formation of CH3SH. The detailed sulfur compounds in gas, oil, and solid char were analyzed. Vulcanization seemed to exhibit positive effect on sulfur transformation in pyrolytic products, i.e., higher retention rate in pyrolytic char but lower proportion ratio in gas. Sulfurization promoted the conversion of thiophene sulfur to inorganic sulfur and sulfides found in pyrolytic char was only ZnS.

Quantum-chemical modeling of reactions initiating sulfuric vulcanization of isoprene rubber

The quantum-chemical method of the density functional DFT B3LYP / 6-311G ** have been used for calculation of thermodynamic functions and changes in the total electronic energy during the initiation of sulfur vulcanization of isoprene rubber using the N - cyclohexyl - 2 benzthiazolyl sulfenamide accelerator in the presence of atmospheric oxygen. Since sulfur, in the process of vulcanization of rubber compounds, is in a larger amount in a dissolved state, unlike oxygen, it is concluded that in the presence of sulfur, the formation of a valid vulcanization agent (DAV) will occur, and oxidation will occur to a lesser extent. When comparing the values of the reaction energy with the addition of the S8 molecule, it was found that sulfur in the accelerator radical acceptance reactions is a more active acceptor than oxygen in similar reactions. The effect of the number of sulfur atoms on the activity of the radicals of the sulfidating complex arising upon the acceptance of sulfur by the radicals formed during the decay of the accelerator is analyzed. It was found that the cyclohexyl radicals of the accelerator are the most active, however, in subsequent reactions of DAV with rubber, the radicals of DAV obtained with the participation of benzthiazolyl fragments are more active. The study of the effect of the number of atoms on the energies of the reactions of the formation of persulfhydryl suspensions shows that the primary suspensions are most likely to contain 8 sulfur atoms formed in reactions involving biradicals formed during the decay of the eight-membered ring of a sulfur molecule

Nuclear magnetic resonance structural characterization of sulfur‐derived copolymers from inverse vulcanization. Part 1: Styrene

AbstractOrganosulfur polymers prepared via the inverse vulcanization of elemental sulfur with olefinic comonomers represent a new class of high‐chalcogenide content organic/inorganic macromolecules. Extensive reporting on new synthetic advances and materials derived from the inverse vulcanization process have been explored in the past decade. However, detailed structural analysis of these sulfur copolymers have not been rigorously conducted, due to the poor solubility of many of these materials, coupled with the numerous side‐reactions that result in complex microstructures from these synthetic methods. In the current report, we revisit analysis of the solution 13C NMR spectral data for poly(S‐r‐Sty) and identify for the first time previously unidentified carbon peaks that offer new insights into a corrected repeating unit structure of this sulfur copolymer.

Influence of Mixed Sulfur and Peroxide Curing Systems on Cross‐Linking and Properties of Rubber Compounds Based on EPDM

AbstractIn this work, sulfur vulcanization system, peroxide vulcanization system, and combined sulfur and peroxide curing systems are applied for cross‐linking of rubber compounds based on ethylene propylene diene monomer rubber. The goal is to investigate the influence of curing system composition on cross‐linking and properties of rubber formulations. The combination of both vulcanization systems in cross‐linking of rubbers combines the pattern of carbon–carbon linkages and sulfidic bridges, which gives the real presumption to modify physical–mechanical properties of final vulcanizates. The results reveal that the combination of vulcanization systems affects the curing characteristics, cross‐link density as well as physical–mechanical properties of tested materials. In comparison with vulcanizates cured only with sulfur or peroxide system, rubber compounds cross‐linked with mixed sulfur and peroxide curing systems exhibite higher tensile strength and elongation at break.

Electrosynthesis of tetrabenzylthiuram disulfide via flow reactors

• Advanced flow electrosynthesis method of TBzTD is developed. • Main factors influenced the electrosynthesis reaction are carefully discussed. • The scaling-up of flow reactor via increasing electrode area is exhibited. • Circulation of aqueous solution is accomplished for high atomic economy. Tetrabenzylthiuram disulfide (TBzTD) is an environmentally friendly vulcanization accelerator, which has attracted much attention in recent years. In contrast to traditional synthesis technologies, which create stoichiometric sodium sulfate or sodium chloride waste salts, we carefully studied an electrosynthesis method of TBzTD based on flow reactors, which prevented the generation of salt. Two reactors with different electrode areas were used to implement the electrochemical oxidative coupling reaction of sodium dibenzyl dithiocarbamates, and effects of potential, current, electrode material, electrode distance, flow rate, concentration, and temperature on the yield and space time yield of TBzTD were carefully investigated. Almost 100% Faraday efficiency of the reaction was obtained at relatively optimized reaction condition and the highest yield of TBzTD reached 86%. Although the yield of TBzTD did not reach 100% in the electrosynthesis reaction, the circulation of aqueous phase demonstrated by a membrane separator assisted flow reaction system helped to accomplish fully conversion of initial amine and carbon disulfide and atomic economic synthesis of TBzTD.

Multi-functionalization of Al2O3 nanoparticles for enhancing thermal conductivity of epoxy natural rubber composites

The poor interfacial compatibility between inorganic thermally conductive nanoparticles and organic polymeric matrix largely limits the improvement of thermal conductivity (λ) of composites. In this study, poly(catechol-polyamine) (PCPA) and bis-(γ-triethoxysilylpropyl)-tetrasulfide (Si69) were used to multi-functionalize alumina (Al2O3) nanoparticles (denoted as Al2O3-PCPA-Si69) to improve the interfacial compatibility and prepare effective thermally conductive epoxy natural rubber (ENR) composites. The non-covalent PCPA modification protected the inner thermal characteristics of Al2O3 nanoparticles and the Si69 with vulcanization accelerator structure provided strong covalent bond between Al2O3 filler and rubber chains during vulcanization. Owing to the constructed thermally conductive pathways and decreased interfacial resistance, the λ of ENR composite reached 0.3773 W (mK)−1 at Al2O3-PCPA-Si69 nanoparticles content of 30 vol%, which is 270 % of the pure ENR (0.1400 W (mK)−1). The multi-functionalization of Al2O3 nanoparticles is highly efficient and cost effective, which can be expanded in other thermally conductive fillers to make them attractive candidate for insulating electronic field.

Thermally Activable Bistetrazoles for Elastomers Crosslinking.

Sulfur vulcanization is the most used method for curing of natural and synthetic rubbers. The crosslinking degree achieved is usually controlled by adding proper quantities of accelerants, activators, co-activators, retardants, and inhibitors, and influences the hardness, elasticity, hysteresis of elastomers and, consequently, the properties and behavior of the materials that incorporate them. Despite the fine tuning pursued over the years, sulfur crosslinking is still difficult to control both in terms of degree and homogeneity of cross-link. Addition of thermally activable bifunctional reagents able to crosslink the polymer matrix through covalent bonds could be a strategy to modulate and control finely the reticulation grade of elastomers. Tetrazoles can form highly reactive nitrilimines by thermal treatment at appropriate temperature, which can react with the vinyl double bonds present in the rubber. In this work a set of bis-tetrazoles were synthesized and those with the right activation temperatures were used for the curing of styrene-butadiene rubber, acting both as single crosslinkers and together with classic sulfur-based ones. The addition of bistetrazoles simplified and made more efficient the compounding process, allowing to prolong the mixing until optimum dispersion and homogeneity were obtained. Moreover, they led to an improvement in the hysteretic properties of the compound and to the reduction of the non-linearity of the dynamic behavior (Payne effect).