Unvulcanized Rubber Research Articles

Wear-Resistant Elastomeric Composites Based on Unvulcanized Rubber Compound and Recycled Polytetrafluoroethylene

Advancements in industrial machinery and manufacturing equipment require more reliable and efficient polymer tribo-systems which operate in conditions associated with increasing machine speeds and a lack of cooling oil. The goal of the current research is to improve the tribological properties of elastomeric composites by adding a solid lubricant filler in the form of ultrafine polytetrafluoroethylene (PTFE) with the chemical formula [C2F4]n and recycled polytetrafluoroethylene (r-PTFE) powders. PTFE waste is recycled mechanically by abrasion. The elastomeric composites are prepared by mixing a nitrile butadiene rubber with a phenol-formaldehyde resin and PTFE powders in an extruder followed by rolling. The deformation-strength and tribological tests of r-PTFE elastomeric composites are conducted in comparison with the ultrafine PTFE composites. The latter is based on products of waste fluoropolymer processing using a radiation method. The deformation-strength test shows that the introduction of ultrafine PTFE and r-PTFE powder to the composite leads to a decrease in strength and elongation at break, which is associated with the poor compatibility of additives and the elastomeric matrix. The friction test indicates a decrease in the coefficient of friction of the composite material. It is determined that the 15 wt.% filler added in the elastomeric matrix leads to a reduction in the wear rate by 20%. The results obtained show the possibility of using ultrafine PTFE powder and r-PTFE for creating elastomeric composites with increased tribological properties. These research results are beneficial for rubber products used in many industries, mainly in mechanical engineering.

Optimization of Graphene infused Natural Rubber Sensing Film and Polydimethylsiloxane for Flexible Pressure Sensor

A flexible and stretchable pressure sensor offers significant benefits in human-computer interaction, healthcare, and tactile sensing in robots. We present a novel study optimising Polydimethylsiloxane (PDMS) and graphene-infused unvulcanised natural rubber sensing film to increase sensor sensitivity and dielectric permittivity. By optimising the PDMS thickness uniformity, NR-G film’s impedance and capacitance-pressure loading response, it is possible to enhance the pressure sensor's sensitivity across a wide pressure range, covering human finger motion. With our synthesized homogenous 5wt% of NRG composite, a capacitance value of 193pF was achieved when applying pressure of 150 kPa at a frequency of 0.5 Hz. Excellent sensitivity and dielectric permittivity of 0.020 kPa-1 and 109.1, respectively, which is ~ 6.5 folds higher than pure NR. PDMS thickness of 300μm with ±3% uniformity was achieved using 90s spin time and 200rpm spin speed. This optimisation of sensing material and substrate is important in developing wearable sensors having applications in soft robotics, health monitoring electronics, and soft human-machine interfaces.

Capillary non-Newtonian seepage model of unvulcanized rubber expressed by the four-parameter rheological flow

Micro-bubbles and pores in a tire, generated by the seepage process of rubber into steel cord, seriously degrade the safety of the tire in use. However, unclear seepage behavior of unvulcanized rubber while flowing into the interstice of steel cord makes it difficult to eliminate defects. Here, we studied the seepage behavior of unvulcanized rubber in a single capillary. When the four-parameter rheological flow was compared to the common shear rheological model, it was best suited to represent the rheological behavior of unvulcanized rubber because of its lowest variance. On this basis, the single capillary seepage equation of unvulcanized rubber was developed to interpret the relationship between the flow rate, process length, pressure, and pore diameter in a single capillary tube. And it was validated by the finite element analysis method with the four-parameter rheological equation as the material parameter; the accuracy of the single capillary seepage equation reached 99.95%. It lays a foundation for further exploring the seepage model under complex conditions such as variable aperture and multiple channels.

Prediction Formula Describing Viscoelasticity of Unvulcanized Rubber Compound Based on Time-Temperature Equivalent Superposition Principle

Fitting unvulcanized rubber compound’s (URC) dynamic viscoelasticity prediction formula and then constructing its mechanical constitutive model are of great significance for studying defect mechanisms in rubber products. However, it is difficult to measure the dynamic viscoelasticity of unvulcanized rubber at high and low frequencies due to its rapid relaxation property. This paper presents a convenient method to measure the dynamic viscoelasticity of unvulcanized rubber. The data of different temperatures at a fixed frequency are measured by dynamic thermomechanical analysis, and the master curve of unvulcanized rubber is obtained by using the time-temperature equivalent superposition principle, which is used to predict the modulus and stress at different temperatures as a function of frequency. The predicted moduli are in good agreement with experimental data when the strain is less than 10% and the applicable temperature range of the Williams–Landel–Ferry (WLF) equation, which indicates that the proposed method is a feasible way to study the dynamic viscoelasticity of unvulcanized rubber at different temperatures.

Investigation of rubber flow during tire shaping process by experiment and numerical simulations

AbstractTire plays an important role during driving as comes in direct contact with the road. A comprehensive understanding of the flowing behavior of unvulcanized rubber during the shaping process of tire is essential for the design of tire. The tread has grooves with complex shapes, which are formed by a mold during the tire shaping process. When tread rubber does not fill the mold properly, tire quality deteriorates crucially. We conducted an experiment and computer simulation to determine the flow of tread rubber in the mold. The comprehensive tire building and shaping processes are investigated through the finite element method. The material distribution of the tire obtained by simulation compares is in good agreement with that of the tire theoretical design. The maximum error of rubber components sizes between the simulation and test is 6.22%. The belt layer is the main force bearing component, and it has a directly influence on the rubber flow. The simulation results show that the belt cord force decrease with the cord laying angle from 24° to 30° and increase rapidly with the increase of the cord arrangement spacing.

Nonlinear viscoelastic behavior and their time-temperature superposition for filled styrene butadiene rubber compounds and vulcanizates

The nonlinear viscoelastic behavior of rubber composites is of great practical importance in their processing as well as the application. In this paper, nonlinear viscoelastic behavior for vulcanized and unvulcanized filled styrene butadiene rubbers (SBR), SBR/carbon black (CB) composites, were mainly investigated. Besides the conventional Payne effect, frequency (ω) sweep tests at different strains (linear and nonlinear viscoelastic regions) were performed to get more information about viscoelastic response, especially in nonlinear region that close to actual driving conditions. Conductivity synchronization test was also operated to explore the evolution of CB agglomerates. It reveals that the filler network structure recovers slowly but the rubber network recovers rapidly during an increasing and decreasing strain sweep cycle. At large strain, rheological parameters of vulcanizates change significantly with increasing ω. A pseudomaster curve based on the ω sweep at large strain and different temperature can be obtained both for compounds and vulcanizates, indicating that the time-temperature superposition is also applicable to the nonlinear viscoelastic behavior. Similar linear and nonlinear viscoelastic behaviors of filled vulcanizates to that of unfilled vulcanizates demonstrate the same mechanism of viscoelastic response. The loss modulus peak of filled vulcanizates primarily comes from the Rouse movement of rubber chains between crosslinking points. Under large strain, the strain amplication effect of particles hardly influence the characteristic relaxation time of Rouse movement between crosslinking points.

Structure-Property relationships in natural rubber representing several clonal varieties of Hevea Brasiliensis

In this study, the relationships between the structure of unvulcanized rubber and vulcanizate properties were investigated for the three natural rubber clones: RRIT251, PB235, and RRIM600. The highest tensile properties of rubber vulcanizates were achieved from the PB235 clone whereas the RRIM600 showed the lowest. The PB235 contained the largest average molecular weight (Mw) with the narrowest molecular mass distribution (MWD), whereas the least Mw was for RRIM600 with the broadest MWD. The highest protein contents were noticed in RRIM600 where the highest gel formation was found. In contrast, the PB235 showed the smallest amount of proteins and gel contents. Based on this finding, the results clearly suggested that the Mw represented as a key factor controlling the mechanical properties of vulcanizates. This was because the higher average Mw provide the greater active sites available for crosslinking reaction, while the protein content governed the gel formation in the unvulcanized rubber.

Study of waste rubber catalytic pyrolysis in a rotary kiln reactor with spent fluid-catalytic-cracking catalysts

The low utilization rate of waste rubber has caused serious environmental pollution problems. Catalytic pyrolysis is an effective method for ensuring the resource utilization of waste rubber. However, the high cost and nonrecyclability of the used catalysts complicate the utilization of this method in industrial applications. In this paper, the spent fluid-catalytic-cracking (FCC) catalysts were applied into pyrolysis of waste rubber, aiming to reduce the cost of catalytic pyrolysis of waste rubber. At the same time, the pyrolysis mechanisms of the spent FCC catalysts used in waste rubber were studied. Pyrolysis/catalytic pyrolysis experiments on single-rubber-type unvulcanized rubber, single-rubber-type vulcanized rubber, and tread compounds were performed in a self-developed industrial pilot plant. The experimental results showed that the pyrolysis oil yield of the spent FCC catalysts catalyzed pyrolysis of the waste rubber increased and the content of light aromatics in increased by more than 90 %, indicating that the spent FCC catalysts applied in waste rubber can improve the quality of pyrolysis products, increase production efficiency, and realize the collaborative high-value reuse of waste rubberand spent FCC catalysts.

Aerospace components made by Polymer material.

The aerospace and aviation industry have fasted growing industries on a global scale. Reliable aircraft demands many top rubber components. These rubber components must-have high performance and endurance properties, since they will be exposed to a range of extreme weather conditions, such as excessively hot or cold temperatures, and different types of oils and gases. Rubber products are becoming more famous because of their durability under extreme environmental conditions and cost-effectiveness. The rubber used for aircraft must be of high quality, and this factor is most important in the production of the necessary parts. To study the effect of all compounding ingredients while optimizing compound design and conforming to the various specification requirements and to study the effect of aging, generally, rubber is tested at three different stages viz. Unvulcanised rubber, vulcanized rubber, and finished product.

Influence of Non-Rubber Components on the Properties of Unvulcanized Natural Rubber from Different Clones.

Natural rubber from different Hevea braziliensis clones, namely RRIM600, RRIT251, PB235 and BPM24, exhibit unique properties. The influences of the various fresh natural rubber latex and cream concentrated latex on the non-rubber components related properties were studied. It was found that the fresh natural rubber latex exhibited differences in their particle size, which was attributed to the non-rubber and unique signature of clones which affect various properties. Meanwhile, the cream concentrated latex showed the protein contents, surface tension, and color of creamed latex to be lower than the fresh natural latex. However, TSC, DRC, viscosity, particle size and green strength of concentrated latex were found to be higher than the fresh natural latex. This is attributed to the incorporation of HEC molecules. Also, the rubber particle size distribution in the RRIM600 clone exhibited a large particle size and uniform distribution, showing good mechanical properties when compared to the other clones. Furthermore, the increased green strength in the RRIM600 clone can be attributed to the crystallization of the chain on straining and chain entanglement. These experimental results may provide benefits for manufacturing rubber products, which can be selected from a suitable clone.

Quantification of phenol-formaldehyde curing resin in unvulcanized rubber blend using Py-GC/MS supplemented by TG-IR analysis.

The curing bladder is the main element when producing a car tire. The tire curing bladder is a cylindrical bag concaved with a heat transfer medium, hot water, steam or gas during the vulcanization process. It is highly stressed due to the extremely high temperatures and pressures inside the pressing mold and it ensures the optimal process of vulcanization. Therefore, it is necessary to verify the quality of the tire curing bladder made of a suitable elastomer (rubber) blend. Analysis of rubber is an important technological operation in research and development in the automotive industry. The purpose of rubber blend analysis may be to confirm that the manufacturer or supplier owns or supplies a material according to the composition pattern, to clarify the cause of difficulties and failures during processing or to verify that the individual components of the rubber blend are correctly batched during technological operation “mixing”. Five analytical methods were used to determine the quality, presence and quantity of applied curing resin, specifically a combination of pyrolysis, gas chromatography and mass spectrometry and a combination of infrared spectroscopy and thermogravimetry. The concentration and percentage of the curing resin were determined from individual measurements and by comparing with reference samples (standards) from an industrial factory.

Hydrostatic compression tests, capillary rheometry tests, and extrusion tests performed on unvulcanized rubber confirm importance of compressibility for die swell — Arguments from dimensional analysis

This paper aims at elucidating which factors are effective in terms of influencing the die swell of unvulcanized rubber upon extrusion. To that end, compression, viscosity, and extrusion tests were performed on two types of ethylene–propylene–diene rubbers, while additional compression tests were performed on natural rubber. First, all three testing modalities were assessed separately, revealing that for the tested materials the compressibility is pressure-dependent; the viscosity is velocity-dependent; and the die swell is influenced by several, partly intertwined factors. In order to better understand the collected experimental data, we have employed the theoretical tool of dimensional analysis, showing that the compressibility of unvulcanized rubber is of great importance for the die swell. Surprisingly, the temperature dependence of the die swell turns out to be much less prominent than standardly assumed. Further key factors influencing the die swell concern the geometries of the die and of the canal.

Modeling and simulation for the swelling behavior of unvulcanized rubber during the calendering process

AbstractA comprehensive understanding of the swelling behavior of unvulcanized rubber during the calendering process is essential for the design of calendered products. In this work, the quasi‐static cyclic tensile experiments are carried out to investigate mechanical behaviors of unvulcanized rubber, including elasticity, inelasticity, and softening, as well as their strain‐rate dependences. Based on the obtained experimental results, a parallel network model consisting of a rate‐independent hyperelastic network and two rate‐dependent elastic‐viscoplastic networks is developed to characterize the constitutive behaviors of unvulcanized rubber. Then a steady‐state finite element method together with the constitutive model is proposed to explore the swelling behavior of unvulcanized rubber in the calendaring process. The divergence of thickness ratio between the simulation and experimental results is only 3.54%, which verifies the validity of the solution strategy. Besides, the effects of the calendar speeds and widths of unvulcanized rubber on swelling ratios are investigated. The numerical results show that the thickness/width swelling ratios increase/decrease rapidly with speeds from 1 m/min to 6 m/min, then tends to be stable at the speed of more than 6 m/min and widths hardly affect the variation laws of the swelling ratios with speeds.

Technology of Rubber Molding (Part2) —Rubber Behavior in the Processing Process—

In the mold vulcanization molding process, the unvulcanized rubber compound is filled into the sealed mold and under high pressure and temperature, it is transformed from the unvulcanized state into vulcanized rubber. The unvulcanized rubber compound is subjected to shear forces and associated thermal history during the processing process prior to vulcanization, which greatly affects its flowability and vulcanization behavior in the mold. In order to manufacture rubber products with excellent properties and functions, the flow behavior of the unvulcanized rubber compound in the mold must be analyzed and reflected in the compound composition of the rubber compound, rubber mold design, and vulcanization conditions. For this purpose, analysis of the flowability in the mold, pressure behavior, and visualization methods have been studied, but the behavior has not yet been clarified. In addition, improvement of flowability by compounding design is also being studied.

Influence of the Order of Incorporation of Sulfur in the Mechanical Properties of Vulcanized Nr Compounds

The objective of this work was to evaluate the influence of the order of sulfur addition on the mechanical properties of vulcanized natural rubber compounds. The addition of sulfur was carried out by two methodologies: (I) sulfur was added at the beginning of the mastication process, and (II) sulfur was added at the end of the mixing process. The compounds were obtained in open cylinder, and vulcanized in a press at 150°C. The vulcanization parameters were determined by rheometry, where as the mechanical properties were evaluated by testing samples for their tensile strength, tear strength, resilience, and Shore-A hardness. The dimensional stability of the vulcanized samples was also evaluated experimentally, by comparing specimens not heat-treated to those submitted to 100°C for 4 hours. Comparing the results of method (I) to method (II), the results, indicate that the addition of sulfur at the beginning of the mastication process (method I) yielded increases of 20 and 11% in tensile strength and tear strength, respectively, followed by a 9% increase in hardness, and 6% in resilience, without significant losses in maximum elongation. The dimensional stability test showed a reduction of 75% in the contraction for the vulcanized samples which had sulfur addition at the beginning of the mastication process of the unvulcanized NR rubber.

Fire performances of unvulcanized rubbers and influences of horizontal flowing melts

Fire performances of typical unvulcanized rubbers are investigated and the properties of rubbers and their flowing melts are characterized. If the horizontal melt flow is allowed the burning area increases by 75%–473% and proportionally the peak mass loss rate promotes by 55%–300%. When the rubber converts to its flowing melt the viscosity and heat of complete combustion reduce, and the total crosslink density increases, which might be ascribed to the curing, the curing reversion and the decomposition mechanism. Except for acrylonitrile-butadiene rubber both the Td,5% and the decomposition activation energy decrease. The pool fire development is related with the melt viscosity, the decomposition temperature and heat release rate (HRR) in the cone calorimeter. Low viscosity contributes to large pool area. High HRR and low decomposition temperature accelerate the extension of burning area.

A study of Rate of Temperature Change during Tire Curing Using Computational Fluid Dynamics

The most important procedure in tire manufacturing is curing. The purpose of the curing is to apply high pressure and temperature over a period of time to unvulcanised rubber so that the rubber is cured to the point of best material properties. In this research, fluid flow analysis was considered to understand airflow pattern in an autoclave for a better quality of the product. We present preliminary results of the temperature distribution of heat transfer in an autoclave using Computational Fluid Dynamics package, OpenFOAM. The turbulent model was verified by comparison with the experimental results to obtain an accurate heat transfer coefficient. It was found that the error was 12%. The results from the simulation and experiments are in good agreement. Consequently, this turbulent model can be used to determine the heat transfer coefficient to achieve a better and more efficient curing process.

Unvulcanized Rubber Tape Made from Natural Rubber and Synthetic Polyisoprene Modified with Rosin as a Tackifier

This presented work was to study mechanical and tack properties of unvulcanized rubber tapes made from STR 20 and IR 2200 with various amount of carbon black and rosin as reinforcing agent and tackifier, respectively. Mixing process of solid rubbers and all chemicals was carried out by two roll mill machine. All rubber compounds were subjected to increasing the stickiness by aging under hot air at 150°C for 3 hours. From the experiment, green strength of the sticky rubber tape mixed with carbon black and rosin showed higher than that of the commercial rubber tape. The formulation exhibited the highest tensile stress at 400% strain is STR 20 mixed with 15 and 5 phr of carbon black and rosin, respectively. Mooney viscosity of the rubber tape made from STR 20 and IR 2200 was also reduced with the higher content of rosin. Although Mooney viscosity of the adhesive rubber tape normally decreased after heating under hot air, its tack property investigeted by rolling ball test on the surface predominantly became increased. Moreover, Mooney viscosity of the rubber tape made from IR 2200 would be remarkably enhanced by blending with only 20% of STR 20.

The effect of non-rubber components on mechanical properties of TESPD silane coupling agent in silica-filled rubber compounds

Silica is reinforcing filler with high polarity, leading to the difficulty to get the homogenous mixing with a natural rubber (NR) compound, which normally becomes silica agglomeration. A silane coupling agent is applied in a silica-filled NR compound in order to enhance compatibility between silica and rubber. Moreover, non-rubber components, especially proteins, are believed to have competition with silane coupling agent during a silanization [1, 2]. In this work, the interaction between the silane coupling agent and silica-filled NR materials was investigated to show the components influencing in the filler-filler and filler-rubber interaction as well as mechanical properties. The rubber types with different non-rubber components such as fresh NR, deproteinized NR (DPNR) and polyisoprene rubber (IR), absence of non-rubber constituents were mixed with bis-triethoxysilylpropyl disulfide (TESPD) and silica by using an internal mixer at high temperature. Payne effect of the unvulcanised rubber samples were characterized to study silica dispersion, respectively. A swelling test was used to determined crosslink density in the rubber samples after a vulcanisation system. In addition, the effect of non-rubber components on mechanical properties of rubbers was investigated to find the relationship between the crosslink density and filler-rubber network.

PROCESSING–PROPERTY RELATIONSHIPS IN WHEAT PROTEIN–UNVULCANIZED ISOPRENE RUBBER COMPOSITES

ABSTRACT An optimized set of processing parameters was determined for trypsin hydrolyzed gliadin protein (THGd, from wheat) and unvulcanized synthetic isoprene rubber (IR) composite compounds. The compounding temperature, time, and shear dependency of the THGd:IR compounds were investigated with rheology, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). Individual protein aggregates measuring ∼64 × 280 nm, with a length-to-width aspect ratio of ∼4.3, were agglomerated within the IR matrix, as measured in SEM-EDX micrographs. A higher compounding temperature (T = 150 °C) was favorable for good protein aggregate dispersion and deagglomeration, which resulted in IR reinforcement, as demonstrated by up to a 65% increase in storage modulus (G′). The tan δ was lowered by the addition of the THGd protein to IR, indicating less mechanical energy was lost as heat in the composites. As the compounding speed, that is, shear rate, was increased from 30 to 60 rpm at constant temperature (T = 150 °C), the average agglomerate size and G′ were minimally affected, but the loss tangent (tan δ) was increased, indicating an increase in IR degradation with shear rate. By drying the THGd hydrolysate at a slower rate or to a greater solids content, the composite G′ was increased and tan δ was decreased. In the slow-dried THGd hydrolysate, protein aggregates were less resistant to breakup during processing, indicating that the protein preparation was an important processing parameter.