Efficient Vulcanization System Research Articles

Revealing phase-specific properties of elastomeric blends and their molecular structure at the nanoscale by AFM

Immiscible elastomeric blends are of interest for a variety of technical applications, in which the optimization of material properties and performance are influenced by the result of co-vulcanization. The differential solubility of curing additives used during the vulcanization process, such as sulfur or accelerators, can lead to different concentrations and vulcanization rates in each elastomer depending on their composition. Therefore, the comprehension of the phase-specific effects of curatives in the blend is desirable. In this work, two different atomic force microscopy (AFM) approaches are explored: Amplitude Modulated – Frequency Modulated (AM-FM) and AFM-IR, for the characterization of the phase-specific nanomechanical properties and molecular structure, respectively. These methods are applied to the analysis of polyisoprene/polybutadiene (PI/BR) blends, focusing on the study of the effects of a conventional and an efficient vulcanization system. AFM-IR mappings at the nanoscale provide images of the morphology based on the molecular structure of the phases and complementary information on the effects of the variation of the sulfur/accelerator ratio through the observation of changes of the trans/cis ratio at the nanoscale. The variations of viscoelastic properties revealed by quantitative nanomechanical mappings are associated with the cross-link density evolution in the samples as a function of variation of curatives in the compound and are observed to follow the same trend as molecular structure changes observed by AFM-IR.

Mechanical properties of rubber vulcanizates containing Ethylene Propylene Diene Rubber waste at different types of vulcanization system

Ethylene Propylene Diene Rubber (EPDM) waste filled Natural Rubber (NR) that cured by using conventional vulcanization (CV), semi-efficient vulcanization (semi-EV) and efficient vulcanization (EV) system was successfully compounded by an internal mixer. The ratio of sulphur and accelerator is different for each vulcanization system, that finally affect the vulcanizate properties due to the different structural features of an accelerated sulphur vulcanizate of NR. 60 phr of pulverized EPDM waste was incorporated into 40 phr of NR in each vulcanization system. Studies about the usage of abundantly available EPDM waste as a potential filler is essential towards green environment and minimize landfill area in future. It is found that the cured rubber with CV system has the best properties due to high degree of crosslinking of polysulphidic crosslink. Tensile properties and abrasion resistance of the rubber compound indicated its mechanical properties were investigated. Density and hardness test were also done to study its physical properties. For tensile strength, CV system has 14% increment from EV system because of a stress-relieving mechanism that exhibited in this vulcanization system. As for tensile modulus, M500 for CV system shown 29% increment than EV system. As a result of the decreased chain flexibility caused by the increased crosslinking density in the CV system, the elongation at break of the vulcanizate is the lowest (174 mm) when compared to the EV system (336 mm). CV system shown highest Abrasion resistance index (ARI) i.e. 1820%. This indicate that very small amount of mass loss obtained for the CV cured rubber during the testing. CV system gives highest density and hardness values i.e. 1.0747 g/cm3 and 52.5 Shore A, respectively. Thus, the results indicated that NR containing EPDM waste cured by CV system is able to be utilized in the development of rubber compound with a compromise property.

Influence of the curing system on the physical-mechanical, dynamic properties, and aging resistance of ethylene–propylene–diene monomer formulations for applications at high temperatures

The effects of three curing systems on rheometric, morphological, physical-mechanical, thermal, and dynamic properties of ethylene–propylene–diene monomer (EPDM) composites was investigated. The influence of thermo-oxidative aging on crosslink density and physical-mechanical properties was studied. Based on a standard composition for application at high temperatures, EPDM formulations with semi-efficient vulcanization systems (ES), efficient vulcanization systems (ED), and peroxide curing systems (EP) were prepared. Experimental results indicated that EPDM compounds cured with efficient vulcanization systems exhibit the highest scorch time with an intermediate maximum torque value at 150°C. The filler dispersion in the elastomeric matrix was greater than 94%; however, the ED formulation showed a more pronounced decrease, with the increase in deformation indicating a greater filler–filler interaction. In comparison with those cured with peroxide and semi-efficient systems, EPDM formulations cured with an efficient system presented better thermal resistance and the crosslink density was sufficient to maintain the mechanical integrity, leading to an intermediate hardness value, tensile strength, modulus, and greater elongation at breaking. In summary, the results indicated that the efficient curing system was the most appropriate to be used in the envelope’s manufacture, due to the better performance of the mechanical properties associated with the better resistance to thermal aging.

Influence of n-ZnO Morphology on Sulfur Crosslinking and Properties of Styrene-Butadiene Rubber Vulcanizates.

This paper examines the influence of the morphology of zinc oxide nanoparticles (n-ZnO) on the activation energy, vulcanization parameters, crosslink density, crosslink structure, and mechanical properties in the extension of the sulfur vulcanizates of styrene-butadiene rubber (SBR). Scanning electron microscopy was used to determine the particle size distribution and morphology, whereas the specific surface area (SSA) and squalene wettability of the n-ZnO nanoparticles were adequately evaluated using the Brunauer–Emmet–Teller (BET) equation and tensiometry. The n-ZnO were then added to the SBR in conventional (CV) or efficient (EV) vulcanization systems. The vulcametric curves were plotted, from which the cure rate index (CRI) rate of the vulcanization and the activation energy were calculated. The influence on the mechanical properties of the SBR vulcanizates was stronger in the case of the EV curing system than when the CV curing system was used. Of the vulcanizates produced in the EV curing system, the best performance was detected for n-ZnO particles with a hybrid morphology (flat-ended rod-like particles on a “cauliflower” base) and high SSA. Vulcanizates produced using the CV curing system showed slightly better mechanical properties after the addition of nanoparticles with a “cauliflower” morphology than when the rod-like type were used, irrespective of their SSA. In general, nanoparticles with a rod-like structure reduced the activation energy and increased the speed of vulcanization, whereas the cauliflower type slowed the rate of the process and the vulcanizates required a higher activation energy, especially when using the EV system. The crosslink structures were also more clearly modified, as manifested by a reduction in the polysulfidic crosslink content, especially when n-ZnO activators with a rod-like morphology were applied.

Reinforcing Behaviors of Sulfur-Containing Silane Coupling Agent in Natural Rubber-Based Magnetorheological Elastomers with Various Vulcanization Systems.

Magnetorheological elastomers (MRE) is known as an intelligent material constituted of a rubber matrix as well as soft magnetic particles. Silane coupling agents are used to raise the interplay between the inorganic particles and rubber matrix. Silane coupling agent, bis-[-3-(trimethylsilyl propyl)tetra sulfide] (Si69), was picked for comparison of its reinforcing efficiency in the MRE with various vulcanization systems: a conventional (CV), semi-efficient (semi-EV), and efficient (EV) vulcanization system. The outcome illustrated that not only was there improved Si69 surface hydrophobicity of the magnetic particles, but also enhanced Si69 in the interplay between the rubber matrix and magnetic particles. On one hand, the saturated induced magnetic modulus and zero magnetic field modulus of MRE was increased in the vulcanization system, and the loss factor was reduced after the magnetic particles were modified by Si69. On the other hand, the effect of Si69 on the MRE depended on the vulcanization system. The Si69 provided better enhancements in the EV system due to effects of the sulfur contribution of Si69.

Payne effect of thermo-oxidatively aged isoprene rubber vulcanizates

While many works focus on aging mechanisms and mechanical performances of aged vulcanizates, rare is performed to investigate the influences of aging induced network variation on the Payne effect and energy dissipation. Herein the influence of thermo-oxidative aging on Payne effect of isoprene rubber (IR) gum vulcanized with conventional vulcanization (CV) and efficient vulcanization (EV) systems at similar crosslinking densities was investigated, in order to disclose the roles of the crosslink types and therefore the thermo-oxidative degradation on the Payne effect. The results indicate that the crosslink structure and thus the Payne effect are highly susceptible to the thermo-oxidative aging. The aging induced degradation is more severe in CV than that in EV systems, which greatly improves the dissipation of accompanying the Payne effect. This work is helpful for understanding the contribution of network structure to the Payne effect for design rubber materials with optimized aging and dynamic properties.

Study of rubber composites between natural rubber and Mahogany Shell Powder (MHSP) and potential for pavement block

This research was aimed to study the feasibility of using mahogany fruit shell powder as filler in rubber and investigated in properties of obtained vulcanized rubber. As mahogany fruit shell contains 75.61% holocellulose, 13.54% lignin and 11.02% extractives [1]. Hence the fruit shell should be able to act as reinforcement in rubber materials [2]. In this study, mahogany fruit shell was milled into small particles with the particle size of approximately 60 micrometres follow by ASTM D 422 - Standard Test Method for Particle-Size Analysis of Soils. The particle was characterized for their thermal stability. The morphology of mahogany fruit shell powder, MHSP, was flake like particle and can be used as reinforcement fillers in natural rubber. As NR is generally sensitive to O2 thus ethylene propylene diene monomer, EPDM, would be laminated on the top of NR/MHSP composites. The rubbers were formulated with efficient vulcanization system and contain 10, 20, 30, 40 and 50 phr of MHSP. The rubber compounds were characterized for cure characteristic parameter such as scorch time, cure time, minimum and maximum torque. Rubber vulcanizates were prepared using compression molding and characterized for their morphology, mechanical properties, thermal degradation, hardness and weathering resistance. In order to improve environment stability and abrasion resistance of the NR/MHSP composites, EPDM/MHSP were prepared and laminated on NR/MHSP and vulcanized. The laminated vulcanizated composites possessed the properties follow Thai Industrial Standard for rubber paving blocks could be obtained. The results also showed that NR filled with 50 phr of MHSP in NR and in EPDM gave the properties follow the standard and has high potential for outdoor rubber paving block.

Design of Elastomeric Bridge Bearing Pad Compound Formula Based on Hydrogenated Natural Rubber

Laminated elastomeric bearing pad which is commonly produced by natural or chloroprene rubber is functioned as isolation system in bridge or flyover structures. In the research, hydrogenated natural rubber (HNR) was evaluated its feasibility to be used as base elastomer on steel-laminated bearing pad production by designing rubber compound formula. The compounding procedures of HNR applied various vulcanization system and carbon black filler types. The physical and mechanical tests result showed that only hardness parameter could fill the standar quality requirement of commercial elastomeric bearing pad as stated in AASHTO M251 in the range of 50 "“ 70 Shore A scale. The tensile property and compression set value of the HNR vulcanizates were under the requirement. This was due to low rubber-filler interaction and rigidity of crosslink network. The low interaction was more evident with increasing carbon filler particle size. By adjusting semi efficient vulcanization system and used N220 as carbon filler in designing compound formula,HNR was regarded as alternative promosing base elastomer for elastomeric bridge bearing pad manufacture. Nevertheless, it was necessary to improve the procedure to achieve better tesile property and compression set parameter.

Study of crosslink structure and dynamic mechanical properties of magnetorheological elastomer: Effect of vulcanization system

Magnetorheological elastomers are a kind of intelligent and smart materials which are mainly composed of rubbery polymers and soft magnetic particles. The role of various vulcanization systems on the crosslink structures, curing properties, and dynamic mechanical properties of natural rubber–based magnetorheological elastomer was investigated. Conventional, semi-efficient, and efficient vulcanization systems were used and compared. It was found that the content of polysulfide linkages decreased and the monosulfide linkages increased when the vulcanization system was changed from conventional to semi-efficient and efficient vulcanization systems, respectively. The crosslink density has the same tendency with the content of polysulfide linkages. In all vulcanization systems, the zero-field modulus, magnetic-induced modulus, controllability of damping, and the degree of the influence of Payne effect of the samples had an increasing trend when the crosslink density decreased. Evidence from micrographs of scanning electron microscope showed that this was because the particle chains in the low crosslink density composites were longer and more aligned. As the proportion of monosulfide linkages increased, the value of the loss factor increased and the modulus of the composites was more affected by the increasing frequency.

Effect of Different Vulcanizing Systems on SMR-L/Waste Latex Compound Blends

Abstract Natural rubber (NR) is widely used in the industry to produce various products. It requires excellent physical, mechanical and thermal properties to prolong its performance for indoor and outdoor applications. Different sulphur vulcanization systems such as conventional vulcanization (CV), semi-efficient vulcanization (SEV) and efficient vulcanization (EV) systems have different sulphur intake thus give different cross-link density (CLD) and subsequently end properties of the NR vulcanizate. To conserve natural resources, industrial waste such as waste latex compound (WLC) can be utilized to form rubber-rubber blend with the NR. In this study, the effect of different vulcanizing system on the properties of SMR-L/WLC blend was investigated. By comparing the properties of 75:25 SMR-L/WLC blend with 100:0 SMR-L/WLC blend, the effect of WLC loading was also studied. Generally, 100:0 and 75:25 SMR-L/WLC blend with CV system has the best physical and mechanical properties in tensile strength, elongation at break, M100, M300 and hardness. This is due to higher polysulphidic cross-links in CV system which facilitate structural networks rearrangement. This enable the test specimens to withstand higher force. For heat retention properties, both blends showed EV system has better heat retention properties. EV system consists of mainly monosulphidic cross-links with higher thermal stability because the monosulphidic bond is stronger than the polysulphidic bond. The loading of WLC has affect the end properties of rubber vulcanizate. In general, WLC improved the physical and mechanical of vulcanizate but may improve or deteriorate the heat retention. WLC is partially vulcanized rubber thus, presence of WLC lead to higher crosslink density. However, during heat ageing test, the structural changes of the blend vulcanizate results in lesser changes in M100 and M300 but more changes in tensile strength and elongation at break. As conclusion, there is an optimum rubber vulcanizate properties need to be obtained by either using different sulphur vulcanization system or the WLC to have a balance in physical, mechanical and thermal properties.

Tuning of accelerator and curing system in devulcanized green natural rubber compounds

These days sustainable ecosystem warrants cleaner, safer and easier mobility of resources in a production cycle. In a response of such call, in this present work, sulphur crosslinked natural rubber (NR) is successfully devulcanized using bis(3-triethoxysilyl propyl) tetrasulfide (TESPT) - a dual function disulfide chemical. It is observed that the mono-, di- and poly sulfide crosslinks, those determine the final performance of the composites, can be controlled by using various chemicals like N-cyclohexyl-benzothiazyl-sulphenamide (CBS), tetramethylthiuram disulfide (TMTD), 2-mercaptobenzothiazol (MBT) and N-tert-butyl-2-benzothiazyl-sulphonamide (TBBS). Subsequently different vulcanizing systems like conventional, efficient and semi efficient vulcanization systems were also studied. Furthermore, in the optimization of vulcanizing system, semi-EV showed the highest mechanical properties compared to that of the CV and EV system. The study shows a unique correlation between the crosslink density, (mono-, di- and polysulfide) and the mole % uptake of the solvent with time. It also shows the dependence of the fraction of immobilized polymer chain and the segmental dynamics of the composites on the crosslink density.

“NITROSAMINE SAFE” THIURAM DISULFIDE

ABSTRACT An investigation into the technological performance of a new nitrosamine safe thiuram disulfide, tetraisononylthiuramdisulfide (TINTD), in natural rubber was undertaken. Initially, TINTD was synthesized from di(3,5,5-trimethylhexyl)amine. It was then demonstrated to function as a sulfur donor, a primary accelerator, and as a secondary accelerator when combined with sulfenamides. These investigations found that the long-branched alkyl chain on the nitrogen of TINTD and of its vulcanization breakdown product zinc diisononyldithiocarbamate (ZDNC) makes both chemical species very soluble in the elastomer. This high solubility of TINTD and ZDNC in the rubber makes TINTD highly attractive for use in soluble efficient vulcanization systems. In addition, the nature of the long-branched alkyl chain means that the formation of carcinogenic N-nitrosamine is difficult, and if formed, it is toxicologically much less hazardous in terms of both acute toxicity and metabolic activity. Thus, concerns of accelerator toxicity, irritant dermatitis from thiuram and dithiocarbamate, and type IV allergy may be reduced or totally eliminated. The curing efficiency of various thiuram disulfides was also investigated as a function of alkyl chain length and the degree of chain branching. The cure performance was found to be determined by both chain length and chain branching.

CURE CHARACTERISTICS OF DEVULCANIZED RUBBER:THE ISSUE OF LOW SCORCH

ABSTRACT We investigate the reasons behind the observed low scorch during the revulcanization of devulcanized rubber. Mechanically devulcanized carbon black filled natural rubber vulcanizates originally cured by conventional vulcanization (CV), semiefficient vulcanization (semi EV), efficient vulcanization (EV), and peroxide systems as well as buffing dust obtained from pre-cured tread with known formulation were used. Revulcanization of these devulcanized samples using sulfur/sulfonamide system led to the following observations; irrespective of the type of sulfur cure system used for the initial vulcanization of the rubber, (i) the devulcanized samples cured without pre-vulcanization induction time and (ii) devulcanized samples prepared from peroxide vulcanized rubber cured with scorch safety. Based on the earlier reports that solvent extraction of devulcanized rubber did not improve the scorch time during revulcanization, the role of zinc bound non-extractable moieties was investigated using devulcanized rubber prepared from activator-free vulcanizates, which disproved the role of such moieties. This confirmed that the scorch reducing moieties should be attached to the rubber main chain, which can be unreacted crosslink precursors and cyclic sulfides left after the initial accelerated sulfur vulcanization of the original sample. The ability of pre-vulcanization inhibitor to induce scorch safety when devulcanized rubber is revulcanized as such, without adding any virgin rubber, proved that mercaptobenzothiazole (MBT) generated from crosslink precursors is the cause of low scorch. Acetone extracted devulcanized rubber samples prepared from tetramethyl thiuramdisulfide (TMTD) cured natural rubber, which does not follow the MBT pathway when revulcanized, cured with scorch safety, which further proved the role of MBT. Based on the previous reports and our results, it is obvious that powdering of rubber vulcanizate and devulcanization processes have no role on the low process safety of these materials, but it is inherent to the initial accelerated sulfur vulcanization chemistry undergone by these materials.

Studies on natural rubber containing kaolin modified with hexamethylenediamine derivative of phosphorylated cashew nut shell liquid prepolymer

Kaolin was modified with a solution of phosphorylated cashew nut shell liquid prepolymer (PCNSL) containing hexamethylenediamine (HMDA). The organomodified kaolin was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and infrared spectroscopy (FTIR). Processability characteristics and physico-mechanical properties of natural rubber (NR) compositions of conventional vulcanization (CV), semi efficient vulcanization (SEV) and efficient vulcanization (EV) systems containing 6phr (parts per hundred rubber) of the HMDA-PCNSL modified kaolin and unmodified kaolin have been studied. Compositions containing the organomodified kaolin showed improved cure characteristics and vulcanizate properties such as hardness, tensile strength, tear strength, abrasion resistance and thermal stability along with lower heat build-up and compression set which could be advantageous for applications such as tire treads.

Effect of ENR Contents on Cure Characteristic and Properties of NR/ENR/EVA Foam

This research studied foaming of natural rubber (NR), epoxidized natural rubber (ENR) and ethylene vinyl acetate copolymer (EVA) blends vulcanizate. The contents of NR/ENR/EVA investigated were 60/10/30, 70/10/20, 50/20/30 and 60/20/20 to keep NR based to 70 and 80 % by weight whereas EVA contents were 20 and 30 % by weight. ENR used in this research was ENR 50. The content of ENR was varied as 10 and 20 % by weight with restpect to total polymer content. The Efficient vulcanization and peroxide systems were used for rubber vulcanization in order to cure both rubber and EVA. Oxydibenzenesulfonyl hydrazide (EW or OBSH) was used as foaming agent. The results showed that rubber blends with 20% ENR tended to show better compatibilization between NR and EVA. The viscosity of rubber blend which indicated by minumum torque was increased with the content of ENR. Cell size of rubber blends foam containing ENR 20 % showed rather normal distribution than ENR 10%. Foam with high content of NR based rubber showed slightly higher density than the other systems. Tensile properties of rubber blends foam were dependent upon NR based contents and compatibility between NR and EVA. Rubber blends foam with high ENR content showed higher specific secant modulus. The specific tensile strength and elongation at break were slightly inferior. The specific tear resistance of the rubber foam was independent on compatibility. High EVA content reduced both specific compressive modulus and compressive strength of the foam. For the foam that contained EVA domain showed permanent deformation and hence high in compression set. Compatibilized rubber blend foams and the foam with high EVA possessed low ball rebound resilience.

EFFECT OF DEVULCANIZATION ON CROSSLINK DENSITY AND CROSSLINK DISTRIBUTION OF CARBON BLACK FILLED NATURAL RUBBER VULCANIZATES

ABSTRACTCarbon black filled natural rubber (NR) vulcanizates were devulcanized at ambient temperature in a two roll mill. The effect of cure system, that is, conventional vulcanization (CV), semiefficient vulcanization (semi EV), and efficient vulcanization (EV) systems, used for vulcanization of the original sample, on the efficiency of devulcanization was studied. The efficiency of devulcanization expressed as percentage devulcanization of the samples calculated from residual crosslink density measurements was correlated with the sol fraction of the devulcanized samples based on Horikx analysis. Using chemical probe analysis, we determined (i) the crosslink distribution pattern of the original sample, (ii) the extent to which the different types of crosslinks—that is, polysulfidic, disulfidic, and monosulfidic crosslinks—have been debonded or broken during the shearing process in the two roll mill, and (iii) the pattern of bond formation during revulcanization. Mechanical shearing predominantly breaks the majority crosslink type (polysulfidic crosslinks in CV and semi EV cure systems and disulfidic crosslinks in EV samples). Irrespective of the significant reduction in total crosslink density in all three sets of samples, chain shortening reactions similar to the post-crosslinking chemical reactions at curing temperatures also occur during mechanical shear at ambient conditions, which increased the absolute value of monosulfidic links in CV and semi EV systems. However, in the devulcanized EV system, the absolute value of polysulfidic crosslinks increased, which might be due to the re-crosslinking of the cleaved bonds. All the devulcanized samples were revulcanized, and the mechanical and morphological properties were analyzed. The percentage retention of the vulcanizate properties after revulcanization of the devulcanized samples correlated very well with efficiency of devulcanization.

Karakteristik termogravimetri dan kinetika dekomposisi EPDM dengan bahan pengisi carbon black

The thermal characteristics of a material are important to learn in order to know the thermal stability of the materials. Ethylene propylene diene monomer (EPDM) is a synthetic rubber that is widely used in industry due to its resistance to aging, ozone, and chemicals. The kinetic parameters and thermal decomposition of vulcanized EPDM were studied using thermogravimetric method with various vulcanization systems (efficient, semi-efficient, and conventional vulcanization system) and various carbon black (CB) as filler (50, 60, and 70 phr). Decomposition consist of two stages; the oxidation of EPDM and volatile matter loss then decomposition of EPDM. Kinetic parameters of the thermal decomposition were approximated by the Coats Redfern equation. Activation energy and decomposed mass increases with decreasing content of CB. Vulcanized EPDM with CB as filler has fairly good resistance against thermal decomposition. The decomposition process can be viewed in detail in this paper. Keywords: EPDM, thermal decomposition, kinetic, thermogravimetric, carbon black.

Mechanical and rheometric properties of gilsonite/carbon black/natural rubber compounds cured using conventional and efficient vulcanization systems

The effect of adding gilsonite micrometric particles on the properties of N330 carbon black (CB) reinforced natural rubber (NR) compounds was investigated. Formulations with 30/0, 22.5/7.5, 15/15, 7.5/22.5 and 0/30 parts per hundred of rubber (phr) of CB/gilsonite were used, comparing the effect of conventional and efficient vulcanization systems. Gilsonite was characterized by X-ray fluorescence (XRF), thermogravimetric analysis (TGA), elemental analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Tension, uniaxial compression, compression-set, abrasion resistance and dielectric strength tests were carried out on specimens that were moulded using the optimal curing time measured by oscillating disc rheometry (ODR). Abrasion wear resistance, and mechanical and rheometric properties varied with the CB/gilsonite content and on the vulcanization system. It was found that gilsonite facilitated the incorporation of carbon black during mixing, diminished the reversion during rheometric tests of compounds with efficient vulcanization cure systems and increased the dielectric strength. Some gilsonite/CB/NR compounds showed similar rheometric properties, compressive modulus and wear resistance to CB/NR compounds, which evidenced the use of gilsonite as an available filler for NR-based materials.

Design and manufacturing of new elastomeric composites: Mechanical properties, chemical and physical analysis

Abstract Filler-reinforced vulcanized rubber and its blends have been used for engineering applications for over a century. Traditional applications include tires, seals, bushings, and engine mounts. The rubbers for tire manufacturing must have high elasticity, good frictional properties and high load bearing capacity. Conforming to these needs, rubbers are vulcanized by various materials such as sulphur, carbon black, accelerators, and retardants under different conditions. The reactivity of sulphur vulcanization and physical properties of the final product are affected by the chemical structure, molecular weight, and conformation of the base elastomers. The aim of this study is to investigate the influence of accelerator-vulcanizing agent system and the vulcanization temperature on the mechanical and aging properties of vulcanizates based on natural rubber/Polybutadiene rubber (NR/BR) composites. Two ratios of accelerator to sulphur were used for the preparation of the composites also known as conventional vulcanization system (CV), where the quantity of sulphur is more and efficient vulcanization system (EV), where the quantity of accelerator is more. This preliminary study will allow optimization of the composition/processing conditions to improve the mechanical properties and resistance to damage. NR/BR based composites at different vulcanization temperatures and using different curing systems were manufactured. Tensile strength, elongation at break, tensile modulus at 100% (M100) and at 300% (M300) deformation hardness (Shore A) of the composites were determined. Scanning electron microscopy was used to study the microstructure of the fracture surfaces. The main findings are that CV gives more reliable results for multi-purpose applications. Effective vulcanization system is suitable for application in areas where good aging resistance is needed and also in applications where low deformations are expected. Vulcanization temperature does not play significant role although most of the results are in favor of the lower temperature (140 °C).

The Influence of Chemical Compounds on the Sulfur K-Edge X-Ray Absorption near Edge Spectrum of the Vulcanized Rubber

The vulcanized styrene-butadiene rubber (SBR) was studied using X-ray absorption near edge spectroscopy (XANES). The effect of the sulfur containing molecules left over in the sample on the precision of the sulfur K-edge XANES spectrum was focused. The six rubber compounds used here were vulcanized with different curing systems including convention, semi-efficiency and efficiency. For each compound, the measurements were preformed on two different samples which were the untreated and treated chloroform samples. The results showed when compounds were cured with conventional or semi-efficient vulcanization system, the XANES spectra between the untreated and treated sample was changed with very high sulfur to accelerator ratio. On the other hand, the tremendous dissimilarity was observed when compounds were cured with the efficient vulcanization system. Thus the sample treatment was necessary when using XANES to identify sulfur crosslink.