Vulcanization kinetics and reversion behavior of natural rubber/styrene-butadiene rubber blend filled with nanodiamond – the role of sulfur curing system

Sulfur and Peroxide Vulcanization of the Blends Based on Styrene-Butadiene Rubber, Ethylene-Propylene-Diene Monomer Rubber and Their Combinations

Rubber blends based on styrene-butadiene rubber, ethylene-propylene-diene monomer rubber and a combination of both rubbers were cured with different sulfur and peroxide curing systems. In sulfur curing systems, two type of accelerators, namely tetramethylthiuram disulfide, N-cyclohexyl-2-benzothiazole sulfenamide, and combinations of both accelerators were used. In peroxide curing systems, dicumyl peroxide, and a combination of dicumyl peroxide with zinc diacrylate or zinc dimethacrylate, respectively, were applied. The work was aimed at investigating the effect of curing systems composition as well as the type of rubber or rubber combinations on the curing process, cross-link density and physical-mechanical properties of vulcanizates. The dynamic mechanical properties of the selected vulcanizates were examined too. The results revealed a correlation between the cross-link density and physical-mechanical properties. Similarly, there was a certain correlation between the cross-linking degree and glass transition temperature. The tensile strength of vulcanizates based on rubber combinations was higher when compared to that based on pure rubbers, which points out the fact that in rubber combinations, not only are the features of both elastomers combined, but improvement in the tensile characteristics can also be achieved. When compared to vulcanizates cured with dicumyl peroxide, materials cured with a sulfur system exhibited higher tensile strength. With the application of co-agents in peroxide vulcanization, the tensile strength overcame the tensile behavior of sulfur-cured vulcanizates.

A Novel Approach for Simulation and Optimization of Rubber Vulcanization

The kinetic model, encompassing the curing and reversion phenomena of the NR/SBR rubber vulcanization process, was developed by means of the finite element method simultaneously with heat transfer equations, including heat generation due to curing reactions. The vulcanization simulation was conducted for three spheres of different diameters (1, 5 and 10 cm) and two rubber wheels, one of which was a commercial product of the rubber industry. The proposed advanced simulation model, based on products’ two-dimensional axisymmetry, includes cooling after vulcanization, during which the crosslinking reactions continue to take place as a result of the products’ heated interiors. As a criterion for removing the product from the mold, an average vulcanization degree of 0.9 was set, whereby, during cooling, the vulcanization degree increases, due to crosslinking reactions. Based on the minimal difference between the maximal and minimal vulcanization degrees, which did not exceed a value of 0.0142, the optimal process parameters for each product were determined, achieving homogeneity and obtaining high-quality rubber products, while simultaneously ensuring a more efficient vulcanization process and enhanced cost effectiveness for the rubber industry.

Preparation and Characterization of Acrylonitrile Butadiene Rubber Reinforced with Bio-Hydroxyapatite from Fish Scale

This work aims to enhance the mechanical properties, oil resistance, and thermal properties of acrylonitrile butadiene rubber (NBR) by using the Nile tilapia fish scales as a filler and using bis(triethoxysilylpropyl)tetrasulfide (TESPT) as a coupling agent (CA). The prepared fish scale particles (FSp) are B-type hydroxyapatite and the particle shape is rod-like. The filled NBR with FSp at 10 phr increased tensile strength up to 180% (4.56 ± 0.48 MPa), reduced oil absorption up to 155%, and increased the decomposition temperature up to 4 °C, relative to the unfilled NBR. The addition of CA into filled NBR with FSp at 10 phr increased tensile strength up to 123% (5.62 ± 0.42 MPa) and percentage of elongation at break up to 122% relative to the filled NBR with FSp at 10 phr. This work demonstrated that the prepared FSp from the Nile tilapia fish scales can be used as a reinforcement filler to enhance the NBR properties for use in many high-performance applications.

Rubber Rail Pad Reinforced by Modified Silica Using GPTMS and Sulfenamide Accelerator

The interaction between silica and rubber is very important for the production of high performance rubber. Silica surface modification with silane is a general method that aims to enhance the reinforcement efficiency of silica. In this study, a new surface modification of silica with silane and the chemical reaction with sulfenamide accelerator were investigated. The (gamma-glycidoxypropyl) trimethoxysilane (GPTMS) was used as a silane. The N-cyclohexyl-2-benzothiazole sulfenamide (CBS) and N-tert-butyl-2-benzothiazole sulfenamide (TBBS) were used as sulfenamide accelerators. The FTIR spectra results indicate that the GPTMS and sulfenamide accelerators (CBS and TBBS) could successfully form on the silica surface. The new modification is capable of significantly enhancing the reinforcement efficiency; more than the conventional silica surface modification by GPTMS (m-silica). In particular, modifying silica with GPTMS and TBBS (m-silica-TBBS) is capable of increasing the crosslink density and mechanical properties more efficiently than modified silica with GPTMS and CBS (m-silica-CBS), m-silica, silica (unmodified), and unfilled natural rubber. This is due to the presence of GPTMS, which plays an important role in increasing the chemical cross-linking in the rubber chain, while TBBS, as a sulfenamide accelerator, provides a high accelerator to sulfur ratio, which is able to give a more efficient vulcanization. With the reinforcement of a rubber rail pad with silica surface modification, the results indicate that the increment of m-silica-TBBS loading could reduce the deformation percentage of the rubber rail pad more than m-silica and m-silica loading. This is mainly due to the static spring improvement, which results in a stiffer material.

Nanodiamond—Carbon Black Hybrid Filler System for Demanding Applications of Natural Rubber—Butadiene Rubber Composite

The objective of the study was to investigate the effect of the partial replacement of carbon black (CB) by nanodiamonds (NDs) on the vulcanization, mechanical and dynamic properties of a natural rubber—butadiene rubber compound, a typical elastomer compound found in several applications (the tire and mining industry, for example). A studied hybrid filler system resulted in a 28% increase in tensile strength and 29% increase in 300% modulus at low ND loadings even though the total weight fraction of the filler system was kept constant at 25 parts per hundred rubber. The hybrid filler system improved dispersion of both fillers as was proven by scanning electron microscopy and the Payne effect study. In addition, the replacement of 2.5 and 5 phr CB by NDs resulted in 62% improvement in wear resistance. The DMA study showed that a certain ND-CB filler combination has a positive effect on tire properties such as wet grip and rolling resistance.

Poly (Lactic Acid)/Ground Tire Rubber Blends Using Peroxide Vulcanization

Poly (Lactic Acid) (PLA)/Ground Tire Rubber (GTR) blends using Dicumyl peroxide (DCP) as a crosslinking agent were prepared with the following aims: propose a new route to recycle wastes rubber from the automotive industry and improve the toughness and impact strength of the inherently brittle bio-based PLA. The GTR were subjected to two types of grinding process (cryo- and dry ambient grinding). Swelling measurements revealed the grinding to be associated with a mechanical damage of the rubber chains, independently on the type of grinding or on the GTR size (from <400 µm to <63 µm). Moreover, the finest GTR contains the largest amount of reinforcing elements (carbon black, clay) that can be advantageously used in PLA/GTR blends. Indeed, the use of the finest cryo-grinded GTR in the presence of DCP showed the least decrease of the tensile strength (−30%); maintenance of the tensile modulus and the largest improvement of the strain at break (+80%), energy at break (+60%) and impact strength (+90%) as compared to the neat PLA. The results were attributed to the good dispersion of both fine GTR and clay particles into the PLA matrix. Moreover, a possible re-crosslinking of the GTR particles and/or co-crosslinking at PLA/GTR interface in presence of DCP is expected to contribute to such improved ductility and impact strength.

Modeling the optimal rubber composition using industrial waste

Due to the complex composition of the rubber compound, the optimization of the formulation for its preparation is a complex process. The experiments required to determine the optimal composition are a multi-step process that requires time and money. The purpose of this article is to use the method of mathematical modeling to determine the optimal composition of a rubber compound with the addition of industrial waste. Sulfur of the Tengiz deposit and metallurgical production slags were used as industrial waste. The Protodyakonov equation was used to derive the generalized equation and check its adequacy. The escaped equations were used to prepare the rubber compound. The process of vulcanization of the mixture with and without the addition of waste was carried out. The kinetics of vulcanization of the optimized mixture has been studied. The optimized composite provides higher minimum and maximum torque levels, shorter initiation times and optimal cure times compared to a blend without additive. Tensile tests have shown that the composition of the rubber compound, selected by the method of mathematical modeling, is not inferior to the standard formulation. The computational model for determining the optimal composition of the rubber compound can be used for research and applied purposes in various industries related to rubber.

The Influence of Curing Systems on the Cure Characteristics and Physical Properties of Styrene-Butadiene Elastomer

The goal of this work is to study the influence of different curing systems on the cure characteristics and performance of styrene–butadiene elastomer (SBR) filled with carbon black or nanosized silica. A multifunctional additive for rubber compounds, namely Activ8, was applied as an additional activator and accelerator to increase the efficiency of sulfur vulcanization and to reduce the content of zinc oxide elastomers cured in the presence of 2-mercaptobenzothizole or 1,3-diphenylguanidine as a primary accelerator. The influence of the curing system composition on the crosslink density and physical properties of SBR vulcanizates, such as mechanical properties, thermal stability, and resistance to thermo-oxidative aging, is also reported. Activ8 effectively supports the vulcanization of SBR compounds, especially filled with nanosized silica. It reduces the optimal vulcanization time of SBR compounds and increases the crosslink density of the vulcanizates. Moreover, vulcanizates with Activ8 exhibit higher tensile strength and better damping properties than elastomer with zinc oxide. Activ8 allows the amount of ZnO to be reduced by 40% without detrimental effects on the crosslink density and mechanical performance compared to the vulcanizates conventionally crosslinked with ZnO. This is an important ecological goal since ZnO is classified as being toxic to aquatic species.

A functional modified graphene oxide/nanodiamond/nano zinc oxide composite for excellent vulcanization properties of natural rubber

A modified graphene oxide/nanodiamond/nanozinc oxide (MGO/ND/nanoZnO) functional hybrid filler is designed and prepared to improve the vulcanization efficiency of a rubber composite and to reduce the use of ZnO. ND was grafted onto graphite oxide with the aid of 4,4'-methylene diphenyl diisocyanate (MDI). NanoZnO, with high surface activity, was then loaded onto the MGO/ND complex through the wet chemical method, in order to synthesize the MGO/ND/nanoZnO functional hybrid filler. Rubber composites were prepared using the rubber latex composite method and their vulcanization behaviors were investigated. Our results show that the MGO/ND/nanoZnO functional hybrid filler can remarkably improve the vulcanization behaviors of the rubber composite. Compared with that of pure natural rubber (NR), the vulcanization activation energy of the rubber composite was reduced by approximately 16%. Moreover, the vulcanization efficiency can be improved by 63% (i.e., the optimum cure time is shortened from the original 405 s to 150 s) after the same amount of traditional ZnO was replaced by the functional hybrid filler loaded with 1 wt% nanoZnO. The prepared MGO/ND/nanoZnO functional hybrid filler thus provides a promising alternative to improve the vulcanization efficiency of rubber composites.

Poly(acrylonitrile-co-butadiene) as polymeric crosslinking accelerator for sulphur network formation

The major controlling factors that determine the various mechanical properties of an elastomer system are type of chemical crosslinking and crosslink density of the polymer network. In this study, a catalytic amount of acrylonitrile butadiene copolymer (NBR) was used as a co-accelerator for the curing of polybutadiene (BR) elastomer. After the addition of this copolymer along with other conventional sulphur ingredients in polybutadiene compounds, a clear and distinct effect on the curing and other physical characteristics was noticed. The crosslinking density of BR was increased, as evidenced by rheometric properties, solid-state NMR and swelling studies. The vulcanization kinetics study revealed a substantial lowering of the activation energy of the sulphur crosslinking process when acrylonitrile butadiene copolymer was used in the formulation. The compounds were also prepared in the presence of carbon black and silica, and it was found that in the carbon black filled system the catalytic effect of the NBR was eminent. The effect was not only reflected in the mechanical performance but also the low-temperature crystallization behavior of BR systems was altered.

Correlation between the Crosslink Characteristics and Mechanical Properties of Natural Rubber Compound via Accelerators and Reinforcement

The extreme elasticity and reversible deformability of rubber, which is one of the most versatile polymers in modern society, is dependent on several factors, including the processing conditions, curing system, and types of additives used. Since the rubber's mechanical properties are influenced by the existing structural crosslinks, their correlation with the crosslink characteristics of rubber was investigated using the equilibrium swelling theory of the Flory-Rehner equation and the rubber-filler interaction theory of the Kraus equation. Herein, we examined whether the accelerator and reinforcement agent quantitatively contributed to chemical cross-linkages and rubber-filler interaction. In conclusion, the accelerator content supported the chemically crosslinked structures of the monosulfides and the disulfides in natural rubber (NR). Additionally, these results demonstrated that the mechanical properties and the thermal resistance of NR were dependent on the crosslink characteristics. The findings of this study provide an insight into the development and application of NR products for the mechanical optimization of rubber-based products.

Polymer/nanodiamond composites - a comprehensive review from synthesis and fabrication to properties and applications

Nanodiamond (ND) is an allotrope of carbon nanomaterials which exhibits many outstanding physical, mechanical, thermal, optical and biocompatibility characteristics. Meanwhile, ND particles possess unique spherical shape containing diamond-like structure at the core with graphitic carbon outer shell which intuitively contains many oxygen-containing functional groups at the outer surface. Such superior properties and unique structural morphology of NDs are essentially attractive to develop polymer composites with multifunctional properties. However, despite a long history from the discovery of NDs, which is dated back to the1960s, this nanoparticle has been less explored in the field of polymer (nano)composites compared with other carbon nanomaterials, e.g. carbon nanotube (CNT) and graphene. However, open literature indicates that research works in the field of polymer/ND (PND) composites have gained great momentum in the past half a decade. The present article provides a comprehensive review on recent achievements in ND based polymer composites. This review covers a very broad aspect from the synthesis, purification and functionalization of NDs to dispersion, preparation and fabrication of polymer/ND (PND) composites with a look in their recent applications for both structural and functional basis. Therefore, the review would be useful to pave the way for researchers to take some advancing steps in this respect.

Colloids of detonation nanodiamond particles for advanced applications

Nanodiamond (ND) is one of the most attractive allotropic modification of carbon due to their unique physical and chemical properties. In the present review the current state of science and technology in the field of NDs is analyzed. ND can be used in various application and in different form e.g. as a dispersion phase in suspension, as a filler in composites, etc., so the sedimentation stability of ND in different media are under scrutiny. Thus, theoretical aspects of ND suspension coagulation mechanisms and the methods avoiding it were considered. The dependence of rheological behavior on particles modification was discussed as well. Various methods for the preparation and modification of NDs to obtain particles of various sizes on a nanometer scale with different physicochemical properties were reviewed. The area of practical application for NDs was considered on the example of polymer composites. The various manufacturing methods, mechanical properties and medical aspects for thermosetting, thermoplastic and elastomer ND composites were summarized.

Functionalized Halloysite Nanotubes⁻Silica Hybrid for Enhanced Curing and Mechanical Properties of Elastomers

Vulcanization and reinforcement are critical factors in governing the ultimate practical applications of elastomer composites. Here we achieved a simultaneous improvement of curing and mechanical properties of elastomer composites by the incorporation of a functionalized halloysite nanotubes–silica hybrid (HS-s-M). Typically, HS-s-M was synthesized by 2-mercapto benzothiazole (M) immobilized on the surface of halloysite nanotubes–silica hybrid (HS). It was found that the HS-s-M uniformly dispersed in the styrene-butadiene rubber (SBR) matrix, offering more opportunity for M molecules to communicate with rubber. In addition, the physical loss of accelerator M from migration and volatilization was efficiently suspended. Therefore, SBR/HS-s-M composites showed a lower curing activation energy and a higher crosslinking density than SBR/HS composites. Moreover, a stronger interfacial interaction between HS-s-M and SBR was formed by the cross-linking reaction, giving a positive contribution to the eventual mechanical properties. The possible vulcanization and reinforcement mechanisms of SBR/HS-s-M composites were also analyzed in detail.

In the Search for Sustainable Processing in Compounds Containing Recycled Natural Rubber: The Role of the Reversion Process

The production of consumption goods made of elastomers is increasing day by day, producing large amounts of vulcanized/cured residues which constitute a serious socio-environmental problem. An option for companies that produce elastomeric residues is their incorporation in the formulations, by producing polymeric blends with ground waste elastomers. Therefore, this work aims to prepare polymeric blends composed of raw natural rubber (NR)/ground waste NR in different concentrations. The influence of vulcanization reversion as result of additional heating during compression molding on the mechanical properties of the blends was analyzed, and the relationship among vulcanization characteristics, dynamic-mechanical, morphology and mechanical properties of blends was also determined.

Sensor-Based Real-Time Detection in Vulcanization Control Using Machine Learning and Pattern Clustering

Recent paradigm shifts in manufacturing have resulted from the need for a smart manufacturing environment. In this study, we developed a model to detect anomalous signs in advance and embedded it in an existing programmable logic controller system. For this, we investigated the innovation process for smart manufacturing in the domain of synthetic rubber and its vulcanization process, as well as a real-time sensing technology. The results indicate that only analysis of the pattern of input variables can lead to significant results without the generation of target variables through manual testing of chemical properties. We have also made a practical contribution to the realization of a smart manufacturing environment by building cloud-based infrastructure and models for the pre-detection of defects.

Preparation and characterization of silicone rubber with high modulus via tension spring-type crosslinking

“Tension spring-type crosslinking” for improving the modulus of silicone rubber.

Isoconversional Kinetics of Polymers: The Decade Past

This article surveys the decade of progress accomplished in the application of isoconversional methods to thermally stimulated processes in polymers. The processes of interest include: crystallization and melting of polymers, gelation of polymer solutions and gel melting, denaturation (unfolding) of proteins, glass transition, polymerization and crosslinking (curing), and thermal and thermo-oxidative degradation. Special attention is paid to the kinetics of polymeric nanomaterials. The article discusses basic principles for understanding the variations in the activation energy and emphasizes the possibility of using models for linking such variations to the parameters of individual kinetic steps. It is stressed that many kinetic effects are not linked to a change in the activation energy alone and may arise from changes in the preexponential factor and reaction model. Also noted is that some isoconversional methods are inapplicable to processes taking place on cooling and cannot be used to study such processes as the melt crystallization.

Preparation and characterization of silicone rubber cured via catalyst-free aza-Michael reaction

A novel silicone rubber of high strength and stable dimension was cured via catalyst-free aza-Michael reaction.