Vulcanization Of Elastomers Research Articles

Automated identification of kinetics model in elastomer vulcanization using a rheometer MDR and Rubber-K pattern recognition software

This research developed a novel tool for the automatic characterization of elastomers during vulcanization. For this task, robust algorithms for digital image processing and pattern recognition related to curing kinetics were generated and integrated into Rubber-K software. Rheometer tests were performed under ASTM D2084 standard. Experimental data are imported in portable document format and fit the models established by Kamal-Ryan and Isayev-Deng, using a system of first-order ordinary differential equations. During the fitting of the experimental data, the reduced gradient method is used to minimize the error in the objective function. The models used in the algorithms allow higher accuracy and numerical stability compared to similar applications. Rubber-K software provides relevant information to the user during the injection molding parameterization process, allowing production optimization and significantly reducing non-conforming parts. In order to validate the results and accuracy of Rubber-K software, it was compared with data published by other software developers and similar models, whose findings confirm the power and applicability of the software.

Computer simulation of the flow of a thermoplastic elastomer vulcanizate melt through an axisymmetric extrusion die using an augmented Navier’s slip equation

Computer simulation of the flow of a thermoplastic elastomer vulcanizate melt through an axisymmetric extrusion die using an augmented Navier’s slip equation

Effects of polyamide elastomer on the morphology, crosslink density, mechanical, and oil‐resistant properties of acrylonitrile‐butadiene rubber/polyamide elastomer vulcanizates

AbstractPolyamide elastomer (PAE) is a novel material which may improve the performances of acrylonitrile‐butadiene rubber (NBR). This work uses equilibrium swelling and rheological apparatus to study the effects of the PAE content on the overall crosslink densities of NBR/PAE vulcanizate. The presence of PAE significantly increased the overall crosslink density. During the aging stage, the overall crosslink density first increased and then decreased with increasing aging temperature from 25 to 150°C. There was a linear relationship between the tensile strength with the overall crosslink density of the NBR/PAE vulcanizate. Oil resistance of the NBR/PAE vulcanizate was improved with increasing PAE content.

The Influence of Freeze-Dried Alcohol-Water Extracts from Common Yarrow (Achillea millefolium L.) and German Chamomile (Matricaria chamomilla L.) on the Properties of Elastomer Vulcanizates

This research work aimed to investigate the properties of freeze-dried extracts from Matricaria chamomilla L. and Achillea millefolium L. and to perform a characterization of their impact on the natural rubber-based vulcanizates. First, extracts were prepared in three different solvents at selected volume ratios: water (100), water-methanol (50/50), and water-ethanol (50/50). Next, the freeze-drying of extracts was established and then obtained bio-additives were introduced to the rubber mixtures. Freeze-dried extracts were investigated by UV-VIS diffuse reflectance spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Near-Infrared spectroscopy (NIR) and thermogravimetric analysis (TGA). Antioxidant activity and total phenolic content (TPC) were also defined. Rubber mixtures were examined in a rheometer and after vulcanization they were subjected to accelerated simulated aging by UV radiation and thermo-oxidative aging. To determine the resistance of vulcanizates to the degradation processes, the study of cross-linking density (equilibrium swelling method), mechanical properties (tensile strength, elongation at break) and color change were conducted. Performed studies proved the antioxidant activity of freeze-dried extracts caused by the high content of polyphenols and their beneficial influence on the properties of elastomer vulcanizates.

Antioxidant and Anti-Aging Activity of Freeze-Dried Alcohol-Water Extracts from Common Nettle (Urtica dioica L.) and Peppermint (Mentha piperita L.) in Elastomer Vulcanizates.

The research article aimed to examine the antioxidant nature of freeze–dried extracts from Urtica dioica L. and Mentha piperita L. and to present a deep characterization of their influence on the properties of natural rubber–based vulcanizates before and after simulated aging processes. Natural extracts were prepared in three solvent systems at selected volume ratios: water (100), methanol–water (50/50), ethanol–water (50/50), which were further lyophilized and used as additive to natural rubber mixtures. Freeze–dried materials were investigated by UV–VIS diffuse reflectance spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), thermal stability by thermogravimetric analysis (TGA). Antioxidant activity and total phenolic content (TPC) were also examined. Prepared samples were subjected to accelerated simulated degradation processes by using ultraviolet and thermo-oxidative aging. Vulcanizates resistance to degradation effects was determined by the study of cross-linking density (equilibrium swelling method), mechanical properties (tensile strength, elongation at break) and color change in comparison with the results of the reference samples. The research showed that analyzed extracts are characterized by a high content of polyphenols and antioxidant activity, thus have a protective influence on elastomer vulcanizates against damaging effects of aging processes, which consequently extends the lifetime of materials.

Cyclic Compression Testing of Three Elastomer Types-A Thermoplastic Vulcanizate Elastomer, a Liquid Silicone Rubber and Two Ethylene-Propylene-Diene Rubbers.

Thermoplastic elastomer vulcanizate (TPV) and liquid silicone rubber (LSR) are replacement candidates for ethylene-propylene-diene rubbers (EPDM), as they offer the possibility for two-component injection moulding. In this study, these material types were compared side by side in cyclic compression tests. The materials were also characterized to provide details on the formulations. Compared to the rubbers, the TPV had higher compression set (after a given cycle) and hysteresis loss, and a stronger Mullins effect. This is due to the thermoplastic matrix in the TPV. The LSR had lower compression set (after a given cycle) than the EPDM, but stronger Mullins effect and higher relative hysteresis loss. These differences between the LSR and the EPDM are likely due to differences in polymer network structure and type of filler. Methods for quantifying the Mullins effect are proposed, and correlations between a Mullins index and parameters such as compression set are discussed. The EPDMs showed a distinct trend in compression set, relative hysteresis loss and relaxed stress fraction vs. strain amplitude; these entities were almost independent of strain amplitude in the range 15–35%, while they increased in this range for the TPV and the LSR. The difference between the compression set values of the LSR and the EPDM decreased with increasing strain amplitude and increasing strain recovery time.

Vulcanization of Elastomers with Quinol Ethers of P-Benzoquinone Dioxime

The article discusses the synthesis and development of the direction of vulcanization of elastomers with quinol esters of p-benzoquinone dioxime. The concept of a critical temperature Tcr which denotes noticeability of the vulcanization process of unsaturated rubbers (with k=1×10-6, s-1) is introduced. Noted the increased vulcanizational activity of quinol esters of p-quinone dioxime after nitrosoarenes addition. The reactional ability of nitrosoarenes is proportional to estimated charge value on the oxygen of the nitroso group, with lgk= 11,3+49,7 qO. Quinol esters of p-quinone dioxime are proposed to create three-dimensional rubber paintings and prints.

Relationships of tensile strength with crosslink density for the high‐carbon black‐filledEPDMcompounds with various softeners

AbstractEquilibrium swelling and rheological tests were adopted to systematically investigate the effects of softener type and dosage on the crosslink densities. The results turned out that the chemical crosslink density could be distinguished from the physical crosslink density by comparing the results of equilibrium swelling and rheological tests. The liquid butadiene (LB) as a softener leads to the greatest reduction in crosslink density, followed by polyethylene wax (PW) and paraffinic oil (PO). The tensile strength decreases with increasing PO content while shows peak values with increase of LB and PW contents. The dependencies of chemical crosslink density on the aging time under 150°C are quite different for the three softeners, which can be expected from the double crosslinking networks consisting of small softener and large main crosslinking networks. Further investigation has been performed to correlate the tensile strength with chemical crosslink density of ethylene propylene diene monomer elastomer vulcanizates. Three different linear relationships can be obtained for the softeners independent of the aging time. It can now be expected from this study that the role of some new softeners in rubber compounds is not only confined to plasticization but also forms crosslinking networks in the peroxide‐cured rubbers.

Natural rubber/natural rubber reclaim nanocomposites: Role of functional nanoparticles, mixing sequences and coupling agents

Elastomer vulcanizates based on natural rubber (NR), NR reclaim (NRR) and layered silicates were compounded in an internal mixer and cured on a two-roll mill. Cure characteristics and mechanical properties of samples based on 50NR/50NRR reinforced with Cloisite 20A, Cloisite 30B and Nanolin DK1 were compared to those of conventional NR/NRR/kaolin microcomposites. Due to the light/soft nature of organoclays suppressing the friction forces, the minimum torque values decreased in the presence of organoclays, whereas the crosslink density, evidenced by the difference between the maximum and minimum torque values, increased in all samples and scorch times shortened by 37% to a minimum in the presence of Nanolin alkaline/catalytic role in the cure reaction. Fatigue resistance improved by about 10% benefiting the crack tips blunting/energy consuming hysteresis mechanisms motivated by the organoclays among which Nanolin DK1 provides the most efficient dispersion/distribution of nanolayers by faster intragallery crosslinking reactions that pushes the stacks apart. Higher states of dispersion in this sample would also promote strain-induced crystallization under deformation responsible for the improvements seen in the modulus and elongation-at-break. Two-step mixing sequence further improved the compound performance due to the dispersion state progress confirmed by X-ray diffraction and transmission electron microscopy (20% in fatigue resistance and 53% in tensile modulus). In-situ compatibilization through bis(triethoxysilylpropyl)tetrasulfide bi-functional silane coupling agent also promoted modulus and fatigue resistance. However, a prolonged scorch time was observed due tothe blinded NR cure-reactive sites as well as steric hindrance of large functional groups in the presence of this coupling agent.

Anti-Oxidative Activity of Alcohol-Water Extracts from Field Horsetail (Equisteum arvense) in Elastomer Vulcanizates Subjected to Accelerated Aging Processes.

The article aimed to highlight the antioxidant potential of natural extracts obtained from Equisteum arvense in elastomer vulcanizatec made of natural rubber. Horsetail extracts were prepared using four solvent systems at different volume ratios: methanol–water (50/50 and 70/30) and ethanol–water (50/50 and 70/30), which were then lyophilized and added to the polymer matrix. A deep characterization of the obtained bio-additives was performed. The obtained vulcanizates were subjected to various aging processes: thermo-oxidative, ultraviolet and solar. Then, the resistance and susceptibility of vulcanizates to selected processes of accelerated, simulated degradation were determined based on the changes in the spatial structure (network nodes), material strength and physical properties (color). The research showed the presence of polyphenols in the extracts of horsetail, which resulted in their high anti-oxidative activity. Moreover, the extracts were able to absorb UV radiation. As a consequence, they were active additives that protected rubber vulcanizates against the damaging effects of the aging processes, securing their functional properties. Samples containing natural extracts were characterized by better stability of: mechanical strength parameters, the increase in cross-linking density and color changes after simulating aging processes in comparison with the control sample.

Experimental Study on Heat Dissipative Ability in Recycled Thermoplastic Vulcanizate and Reclaimed Rubber Composites

In our time with the growing cooling demand in electronics and energy industries, new thermally conductive materials are in high demand. Thermal gasket and thermal interface materials (TIM) are applications acquiring the characteristics of the thermally conductive materials. They are used to offer bonding strength and efficient heat dissipation for heat dissipating device applications. These materials are inserted between two components in order to increase the thermal coupling between them. Elastomeric materials are promising as the thermal gasket and TIM. They are, however, limited for thermal conductivity causing a thermal insulator behaviour. In this framework, the major challenge is to create suitable elastomeric composites for enhancing thermal conductivity, whereas remaining a good elastic behavior. This article presents the effects of thermally conductive fillers (aluminum nitrile and zinc oxide) on thermal properties and flexibility of recycled thermoplastic elastomer vulcanizate composites and reclaimed rubber composites, while the analysis of composite morphology is scrutinized. The objective of this research is to perceive the characteristics of recycled elastomeric composites in order to deduce a fundamental notion to develop the gaskets or TIMs from recycled materials. New flexible composites are capable to provide approximately 0.4 W/m-K of thermal conductivity. The result indicates that the composites are conceivable to be applied for thermally conductive tape or adhesive applications which required the thermal conductivity in the range of 0.4-0.5 W/m-K.

Surface Energy Mapping of Modified Silica Using IGC Technique at Finite Dilution.

The reinforcing silica filler, which can be more than 40% of an elastomer composite, plays a key role to achieve the desired mechanical properties in elastomer vulcanizates. However, the highly hydrophilic nature of silica surface causes silica particle aggregation. It remained a challenge for many tire manufacturers when using silica-filled elastomer compounds. Here, the silica surface energy changes when the surface is modified with coupling or noncoupling silanes; coupling silanes can covalently bond the silica to the elastomers. The surface energy of silica was determined using inverse gas chromatography (IGC) at finite dilution (FD-IGC) and found to be reduced by up to 50% when the silica surface was silanized. The spatial distribution of silica aggregates within the tire matrix is determined by transmission electron microscopy (TEM) and a direct correlation between aggregate size (silica microdispersion) and work of cohesion from IGC is reported, highlighting surface energy and work of cohesion being excellent indicators of the degree of dispersion of silica aggregates.

Comparative study among TMTD, TBzTD, and ZBEC accelerators in isobutylene‐isoprene elastomer vulcanization

ABSTRACTAccelerators such as tetramethylthiuram disulfide (TMTD) are responsible for releasing nitrosamines, considered carcinogenic by international organizations. Tetrabenzylthiuram disulfide (TBzTD) and zinc dibenzyldithiocarbamate (ZBEC) are indicated as substituents of TMTD for not releasing noxious nitrosamines. Thus, the objective of this work was to compare the use of TMTD, TBzTD, and ZBEC accelerators in the production of isobutylene‐isoprene rubber compounds. It was evaluated the effect of TBzTD/mercaptobenzothiazole and ZBEC/N‐cyclohexyl‐2‐benzothiazolesulfenamide pairs in the rheological properties and the first pair achieved better results. Subsequently, it was evaluated compounds containing TBzTD and ZBEC accelerators separately. The experimental design data of the obtained maximum torque were correlated by an interpolation method (thin‐plate spline interpolation method). Physical–mechanical and thermodynamic measurements showed a decrease in the mechanical properties of TBzTD and ZBEC compounds. Thermogravimetric analysis did not indicate thermal differences between the compounds, Fourier transform infrared and swelling degree analyses corroborated the difference found in the crosslink densities of the compounds. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48965.

Mechanical and Thermal Properties of Green Thermoplastic Elastomer Vulcanizate Nanocomposites Based on Poly (vinyl chloride) and Nitrile Butadiene Rubber Containing Organoclay and Rice Straw Natural Fibers

Green thermoplastic elastomer vulcanizates (GTPV) nanocomposites using poly (vinyl chloride) (PVC) and nitrile butadiene rubber (NBR) containing 5 wt% Cloisite 30B as an organoclay and various concentrations of rice straw natural fibers were made by melt mixing process and compression molding. The effect of used organoclay and various loadings of rice straw was monitored through using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), tensile tests and rheological measurements. The morphological investigations revealed that the GTPV nanocomposites reinforced by rice straw natural fiber show a more rough fracture surfaces indicated the existence of some interactions between the natural fiber and polymer matrix. Thermal decomposition measurements revealed a higher thermal stability for GTPV nanocomposites containing higher rice straw natural fibers. The tensile test analysis suggested that there is an optimum value for the weight fraction of rice straw to enhance the Young’s modulus and tensile strength of the prepared GTPV nanocomposites up to 9 MPa and 35 MPa, respectively. The effect of rice straw loading on the Young’s modulus of the PVC/NBR/organoclay GTPV nanocomposites was predicted through using the parallel and series equations of modified Ji’s model. The results show that the theoretical model can precisely predict the variation of Young’s modulus with respect to the rice straw loading.

Enhancement of mechanical, thermal and morphological properties of compatibilized graphene reinforced dynamically vulcanized thermoplastic elastomer vulcanizates based on polyethylene and reclaimed rubber

The effect of graphene nanoplatelets (GnPs) introduction into the compatibilized multiphase polymer systems such as dynamically vulcanized thermoplastic elastomers (TPVs) based on linear low density polyethylene (LLDPE) and reclaimed rubber (RR) was explored through using the experimental and theoretical analysis. The nanocomposites were prepared by using traditional melt mixing method and characterized by various experimental measurements including transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), Dynamic mechanical thermal analysis (DMTA), tensile test and rheological measurements. The morphological investigations of prepared TPV nanocomposites show the considerable effect of GnPs on the size reduction of rubber droplets. The DSC measurements indicated the role of GnPs as an effective nucleating agent in the TPV nanocomposites. The results of TGA measurements show that the GnPs can cause a higher thermal stability in LLDPE/RR TPVs especially in the presence of a maleated polyethylene (MA-PE) as a compatibilizer. The mechanical properties exploration of TPV nanocomposites represents the considerable effect of GnPs on the increasing of Young's modulus. The analytical stiffness analysis through using Christensen-Lo model with emphasizing the effect of interphase region could precisely predict the effect of various GnPs loading on the Young's modulus. Fabrication of an industrial applicable TPV nanocomposites with enhanced mechanical, thermal and morphological properties could be achieved by using both the proper loadings of GnPs and compatibilizer.

Terpene-Based Sustainable Elastomers: Vulcanization and Reinforcement Characteristics

Allured by the quest to fabricate sustainable elastomers having tangible applications, the present work reports the study of vulcanization and reinforcement characteristics of several sustainable elastomers derived from β-myrcene—a naturally occurring “waste” monoterpene from plant. The elastomers were synthesized by the environmentally benign and industrially robust emulsion polymerization method. Conventional elastomer processing techniques were employed for the compounding and vulcanization of the synthesized elastomers. The vulcanization characteristics of the synthesized sustainable elastomers are similar to natural rubber. Polymer microstructure, molecular weight, and type and amount of comonomer influence the curing characteristics and physico-mechanical properties of the elastomer vulcanizates. An attempt has been made to elucidate the plausible network structure of the polymyrcene vulcanizate. Because of wide range of polarity, these sustainable elastomers could also aid in dispersion of function...

Evaluation of Effect of Various Nanofillers on Technological Properties of NBR/NR Blend Vulcanized Using BIAT-CBS System

Owing to processing ease and resistance to oils and chemicals, NBR is widely used in many industries. But since neat NBR has only poor tensile properties, it is better to use suitable blends of NR and NBR after incorporating appropriate nanoingredients before vulcanization. It is well established that nanoparticles can be easily dispersed in a more uniform pattern in polymer matrix, thereby enhancing the technological properties of the elastomer vulcanizate. Since there are no systematic comparative studies on technological properties of NBR/NR blend containing different nanoingredients, efforts have been made in this study to investigate cure and technological properties like tensile properties, tear resistance, compression set, hardness, abrasion loss and swelling value of NBR/NR (80/20) blend vulcanizates containing stearic acid-coated nano-zinc oxide (ZOS), nano-BIAT, nano-silicate-coated CaCO3, PEO-coated calcium silicate, and surface-modified carbon nanotubes (CNT). XRD and electron microscopy have been used for morphological analysis. The nano ingredients were effective in enhancing the technological properties of the vulcanizates. Among the nanofillers, modified CNT was found to impart superior properties to NBR/NR blend due to more intercalation.

Dynamic optimization of the vulcanization of EPDM elastomers by short waves infrared technologies

This article deals with the optimization of superficial vulcanization of elastomers by infrared heating. This mode of heating notably used in automotive industry is particularly attractive in the transformation processes of extruded elastomers. The use of infrared emitters working in the short waves range offers the possibility to apply to the surface of the product a great heat flux with a weak thermal inertia. Moreover, the energy directly transmitted is easily adjustable. Consequently, it is necessary to correctly evaluate the energy contribution.In this paper, the incident infrared irradiation and the process time enabling to reach a desired vulcanization profile in the product thickness is estimated off-line by an optimal command method. This estimation is based on the exploitation of a model including both the heat transfer and the vulcanization reaction. The tests are performed with EPDM based elastomer plane plates (8mm thickness).

Nanosized Mineral Oxides Modified with Unsaturated Acids as Coagents for Peroxide Vulcanization

The activity of nanosized calcium and magnesium oxides as coagents in peroxide vulcanization of hydrogenated acrylonitrile- butadiene elastomer (HNBR) was studied. The surface of mineral oxides was modified with unsaturated acids (allylmalonic, citronellic, and sorbic) to ensure the activity in elastomer vulcanization. The effect of coagents on the cross-linking density and mechanical properties of vulcanizates was discussed. Modified nanosized calcium and magnesium oxide seemed to be active as coagents and caused the formation of additional labile ionic clusters in elastomer networks. Their application decreased the optimal vulcanization time of rubber compounds and improved the cross-link density and tensile strength of vulcanizates, which is very important from technological point of view.

Study on peroxide vulcanization thermodynamics of ethylene–vinyl acetate copolymer rubber using 2,2,6,6,‐tetramethylpiperidinyloxyl nitroxide

AbstractA step forward in the understanding of rubber vulcanization with organic peroxides is provided by combining a proper arrangement between polymer, vulcanizing agent and cure conditions. For this purpose, an ethylene–vinyl acetate copolymer with a high content of vinyl acetate (70 mol%) was used since a fully saturated polymer backbone allows its vulcanization via peroxide. For the range of conditions analysed here, it is shown that the predominant process taking place is crosslinking via radical recombination, minimizing or even avoiding undesirable secondary reactions such us polymer degradation. Once conditions had been optimized, peroxide vulcanization was analysed in more depth in the presence of 2,2,6,6‐tetramethylpiperidinyloxyl, which is a mediating stable free radical commonly used in controlled radical polymerization. Consequently, it was possible to differentiate the termination reaction from the initiation and propagation steps, allowing the determination of the enthalpy of formed C–C crosslinks as measured using calorimetry. It was possible to isolate and determine the contribution of the crosslinking pathway from the global vulcanization reaction by means of calorimetric methods at optimum conditions. In fact, this simple methodology could be an important tool for understanding in detail the complex peroxide vulcanization of elastomers since reactions involved in this process determine the final network structure, and thus the final elastic properties of these compounds.