Bulk Rubber Research Articles

Effects of thermal aging on degradation mechanism of flame retardant‐filled ethylene–propylene–diene termonomer compounds

ABSTRACTEthylene–propylene–diene termonomer (EPDM) compounds filled with halogenated (Br and Cl) flame retardants (FRs) and Sb2O3 were prepared via melt mixing, and their thermal stability, weight loss, and elemental composition were investigated as a function of aging conditions (temperature: 120–380°C, period: ∼100 h, and atmosphere: nitrogen and air). The thermal aging was done with thermogravimetic analysis under both isothermal and nonisothermal conditions and a convection oven. Scanning electron microscopy–energy dispersive spectroscopy was used to study the surface morphology and elemental composition of the thermally aged FRs‐filled EPDM compounds. For a better precision of compositional analysis, a laser‐induced breakdown spectroscopy (LIBS) was employed in this study. The thermal degradation behavior of EPDM compounds containing halogenated FRs was strongly dependent on the aging atmosphere (N2 or air) and type of FRs. The weight loss of the EPDM compounds during thermal aging was found to be quite small in the temperature ranges below 190°C, while it was noticeable above the temperature. The LIBS technique can be an effective and promising analysis tools for analyzing the elemental components in a bulk rubber compound. Two possible mechanisms were proposed for the thermal degradation of the EPDM compounds containing brominated FR and Sb2O3. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41324.

Characterization of organoclay-networks modified low-temperature hydrogenated nitrile butadiene rubber composites

The low-temperature grade hydrogenated nitrile butadiene rubber (LTG-HNBR) composites with organoclays were successfully prepared for the purpose of using the clay-networks to improve bulk properties. In order to construct different clay-networks, three montmorillonite (MMT) modified by surfactants were added and then their dispersions and affinities in the rubber were compared. Transmission electron microscope and small-angle X-ray scattering results showed that 10 phr organoclays form partially exfoliated and intercalated structures in the matrix despite of modifier types. FTIR and particle analysis data display that increasing the number of alkyl tails of modifier molecules decreases the affinities of clays and their extent of intercalation in rubber whereas the special modifier with coupling agent enhances their compatibility with the bulk. The mechanical, oil resistance, and thermal properties of the composites are greatly reinforced by clay-networks which parallel their interactions. Importantly, the addition of clays barely changes glassy temperature (Tg) of rubber bulk, but it improves its low-temperature elasticity. Therefore, it is stressed that organoclay hybrid networks are very useful to modify low-temperature rubber. We believe that LTG-HNBR composites with organoclays may serve some applications of oil-sealing products. POLYM. COMPOS., 35:1306–1317, 2014. © 2013 Society of Plastics Engineers

Toughening of PA6 nanocomposites by reactive acrylonitrile–butadiene–styrene core–shell rubber particles

The effect of addition of organoclay and the reactive ABS‐g‐MA core‐shell particles on the mechanical properties and morphology of blends of polyamide (PA6) were reported. The reactive rubber particles with core‐shell structure were selected as modifier instead of conventional reactive bulk rubber. The microstructure of the ternary nanocomposites was characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Impact strength and stress–strain behavior of blends were measured as a function of organoclay content and core/shell ratio of ABS‐g‐MA. The organoclay plates affected the interfacial adhesion between polyamide and the core‐shell particles because of a shielding effect of organclay on the interacting of amine end groups of PA6 with the MA groups of ABS‐g‐MA. The poor dispersion behavior of ternary nanocomposites was observed when the core/shell ratio is 80/20, and with an increase of organoclay content, the core/shell dispersed phase size increased. Blends based on the maleated elastomer with the core/shell ratio 60/40 gave a more beneficial balance of toughness versus stiffness. POLYM. COMPOS., 35:864–871, 2014. © 2013 Society of Plastics Engineers

Local mechanical and dielectric behavior of the interacting polymer layer in silica nano-particles filled SBR by means of AFM-based methods

Filler-polymer interactions in reinforced rubbers are mainly governed by a thin layer of polymer around the filler particles. The dynamics of this layer has long been a matter of intense investigation. Some researchers suggest that this “interacting layer” is immobilized and possesses slower dynamics compared to the bulk, whereas some others consider it equally mobile. In this work, we address this problem by studying the macroscopic characteristics of reinforced rubber using Broadband Dielectric Spectroscopy (BDS) and by measuring its local dielectric behavior using a new AFM based approach: nano-dielectric spectroscopy. This new approach enables us to study the dielectric response of the interacting polymer layer and the bulk dynamics locally, with a spatial resolution of about 20–30 nm. The total amount of interacting polymer within the compounds was also obtained by analyzing the local mechanical properties. Both macro- and nano-measurements show no differences in the polymer local dynamics for the compounds here analyzed. We propose that, for our particular system, the interacting polymer layer shares the same local relaxation dynamics with the bulk rubber due to the presence of a flexible link between the polymer chains and the nanoparticles.

Crack propagation in pneumatic tires: Continuum mechanics and fracture mechanics approaches

In this paper, the fatigue life of pneumatic tires is investigated with particular focus on the phenomenon of belt separation. This phenomenon yields the propagation of fatigue cracks in the rubber separating the belts; not the separation of the rubber at the interfaces with the belts. Cracks at the belts edges are related among others to the high stress concentration due to the very different stiffness of the two materials. A steady-state rolling finite element model of the full tire is used to evaluate the stress and strain fields in the rubber at the edges of the belts. Suitable life predictors are defined and computed for the identification of the zones with a higher expectation of failure. For the evaluation of crack propagation in the bulk rubber material between different belts, in principle, two different approaches are employed associated with crack nucleation and crack growth. The two approaches are applied to the study of crack propagation in a truck tire and the results of different predictors are compared to crack propagation found in a real tire.

Characterization and Tribological Behaviour of Siloxane‐based Plasma Coatings on HNBR Rubber

AbstractA cold atmospheric pressure plasma jet (PlasmaSpot) was developed in our department and was successfully used to deposit siloxane‐based coatings on elastomer materials for tribological improvement. This paper reports on the deposition of a low‐friction atmospheric plasma coating on an HNBR sample using (3‐aminopropyl)triethoxysilane (APEO) as precursor. The chemical structure of the coating was examined with XPS and FTIR spectroscopy. Monitoring the top surface of the coating by optical microscopy showed 2–3 µm wide cracks appearing in the coating some days after deposition. Furthermore, a migration of waxes was seen from the bulk rubber through the cracks. The chemical nature of these products was revealed by FTIR analysis. Although these waxes act as lubricant and are added to the rubber for better processability, a tribological evaluation in a ball‐on‐disc test rig revealed that they did not contribute to the lower friction coefficient. A significant decrease of the friction coefficient was measured for the plasma coated HNBR sample compared to the untreated HNBR sample. magnified image

Migration of low molecular weight moiety at rubber–polyurethane interface: An ATR-IR spectroscopy study

In this study, a novel approach based on ATR-IR spectroscopy consisting in the combined use of two prisms of different nature and refraction index (germanium—about 1 μm depth and zinc selenide—about 3 μm depth) was proposed to study the polyurethane–rubber interface. More precisely, the migration of paraffin wax additive in as-received and MEK cleaned vulcanized styrene–butadiene rubber (SBR)–polyurethane coating interface was monitored. Polyurethane coating with thickness of about 2 μm was applied on the SBR rubber surface and the ATR-IR spectra were recorded in the polyurethane coating. Thus, the ATR-IR spectrum obtained with Ge prism analyzed only the polyurethane coating whereas the ATR-IR spectrum obtained with ZnSe analyzed both the polyurethane coating and the near surface SBR. The results obtained showed that the paraffin wax migrated from the SBR rubber bulk to the rubber–polyurethane interface, then diffused into the polyurethane and finally migrated to the polyurethane surface.

ゴム／亜鉛めっき鋼直接加硫接着系の耐水安定性

The adhesion degradation of rubber/galvanized-steel direct bonding system was accelerated by moisture. The route that moisture reached the rubber/galvanized-steel interface through, and improvement of stability of the adhesion system was studied.Following results were obtained. (1) The moisture does not penetrate through the rubber/metal interface, but through the rubber bulk phase. (2) Of the rubber components, emulsion-polymerized SBR shows the highest amount of moisture adsorption. So compounding solution-polymerized rubber as main material instead of emulsion-polymerized rubber, the adhesion stability under high moisture condition was remarkably improved.

Effect of temperature on the extent of migration of low molecular weight moieties to rubber surface

Vulcanized rubbers contain different low molecular weight additives in their formulation, including antiozonants, plasticizers, oils, etc. These moieties – mostly paraffin wax – often migrate to the surface causing a weak boundary layer of non-rubber contaminants which is deleterious for adhesion of rubber to adhesives (such as polyurethane and polychloroprene adhesives). One of the key steps in the manufacturing of rubber/adhesive joints is the reactivation, i.e. sudden heating of the thin adhesive layers on the substrates to be joined under infrared (IR) radiation to 80–90 °C for a few seconds to allow diffusion of the polymeric chains under pressure. This reactivation may cause the migration of low molecular weight additives to the rubber surface causing a lack of adhesion. The main aim of this study was to .identify the influence of the reactivation temperature (40 to 170 °C) on the surface properties of sulphur vulcanized styrene–butadiene rubber and determine the extent of the diffusion of paraffin wax and zinc stearate to the rubber surface. The changes produced on the rubber surface were measured immediately after reactivation treatment by ethylene glycol contact angle measurements, attenuated total reflectance infrared spectroscopy (ATR-IR) and scanning electron microscopy (SEM). Additionally, the weight loss of the rubber after reactivation at different temperatures was recorded. The reactivation of the rubber at different temperatures produced changes in the morphology and thickness of the paraffin wax layer on the surface. By heating at temperature close to that of the paraffin wax melting point, the paraffin wax migration was favoured and at the same time the crystals of paraffin wax on the rubber surface were melted. As a consequence a thicker and smoother film of melting paraffin wax was formed. By increasing the reactivation temperature, a partial removal of paraffin wax was produced and the thickness of the paraffin wax film on the rubber surface was reduced. For reactivation temperatures below 90 °C, the higher the temperature, the lower the weight loss of the rubber, because the increase in the surface area of the melted paraffin wax layer that prevented migration from the rubber bulk. However, for reactivation temperature higher than 90 °C, the weight loss of the rubber increased with the reactivation temperature and this was likely due to sublimation of the paraffin wax on the rubber surface. Besides, even after reactivation at 170 °C, a thin film of paraffin wax always remained on the rubber surface as was evidenced by contact angle measurements. On the other hand, a critical reactivation temperature at 90–100 °C existed at which the migration of zinc stearate to the paraffin wax layer on the rubber surface was favoured.

Study on Slicing for Soft Composite Materials by Cutting Method

Soft composite materials are used for a functional film for a thermal interface material. The surface of this functional film must be flatter and thinner, and contacting fillers to have a better thermal conductivity. Cutting would meet these requirements to slice such soft materials. Soft composite materials consisting of acrylic rubber bulk and graphite fillers were prepared and sliced into films (1mm thickness) as thermal interface materials by developed cutting method. Measurements of curl radius and cutting forces were conducted on the orthogonal cutting experiments. It was found that the following three strategies were effective for reducing curl of chip and cutting force : (1) higher operating temperature, (2) slower cutting speed, and (3) larger tool rake angle. This result suggested a useful method for the effective slicing by controlling the cutting conditions.

The dynamic response of isolated polybutadiene chains undergoing thermal retraction from extended conformations

All-atom molecular dynamic simulations were performed on isolated polybutadiene chains to study the retraction velocity of a free end of an idealized network chain from extended conformations due to thermal collisions. We compare the snap-back velocity calculated from these simulations with experimental measurements on bulk rubber samples. Over a range of chain lengths, extension ratios and temperatures, we find that the average retraction velocity of a free end seen in the simulations is about two orders of magnitude less than the experimental value.

Wet sliding friction of elastomer compounds on a rough surface under varied lubrication conditions

‘Green’ tire bearing tread rubber reinforced with precipitated silica can exhibit improved wet traction performance. The underlying mechanism is currently not well understood. To improve our capability of rational material design for enhanced driving safety, wet sliding friction for various rubber compounds is tested on a Portland cement concrete surface under varied lubrication conditions. The wetting liquid is either ethanol or water, and the initial amount of liquid on the concrete surface is adjusted. Sliding friction is detected to alter with lubrication condition. Under ethanol lubrication, the sliding friction is markedly lower than that under water lubrication. Additionally the benefit in wet traction from silica is significantly diminished or eliminated in ethanol. Such observations cannot be rationalized with simple considerations of rubber bulk viscoelasticity, liquid viscosity, cavitation, or capillary effect. We believe that these observations strongly indicate the significance of interfacial interactions in determining the wet sliding friction of elastomer compounds. The potential relevance of capillary porosity in concrete and Marangoni drying effect to wet traction is also introduced.

Second Plateau Observed in Solutions of Gum Rubbers Containing Gels

Viscoelastic behavior of solutions of rubbers containing macro‐gel and micro‐gel were examined. Macro‐gel is a giant molecule of the rubber having many long branches. Micro‐gel is also a giant molecule but a cross‐linked particle. The sample of macro‐gel was butadiene‐acrylonitrile copolymer (NBR) and the solvent was a plasticizer, dibutylphthalate (DBP). The latter was polyethylacrylate (ACM) in diethylphthalate (DEP). Both rubbers contained about 70% gel, which swelled in the solvent. The rubber concentration was 20%, 10%, and 5%. The frequency range was from 10−2 to 102 rad/s. Measurements were made at room temperature. At 20% and 10% concentration, the storage modulus, G′, and the loss modulus, G″, had the following relation; with NBR‐DBP, G′ was slightly lower than G″ and with ACM‐DEP they were about equal. The gels in the former solution had a degree of swelling lower than did those in the latter. The behavior persisted over the entire range of the frequency. The swollen gel particles are touching each other or almost so. At 5% concentration G′ and G″ curves showed shapes similar to those of the rubber plateau. However, the concentration is much too low to expect to see the rubber plateau. The plateau appears to be the manifestation of the deformation of the gel particle. While the bulk rubber behavior is distinctly different between macro‐gel–containing and micro‐gel–containing rubber, the gel type is not distinguished in the behavior of the semi dilute solution.

Sealing is at the origin of rubber slipping on wet roads

Loss of braking power and rubber skidding on a wet road is still an open physics problem, as neither the hydrodynamic effects nor the loss of surface adhesion that are sometimes blamed really manage to explain the 20-30% observed loss of low-speed tyre-road friction. Here we report a novel mechanism based on sealing of water-filled substrate pools by the rubber. The sealed-in water effectively smoothens the substrate, thus reducing the viscoelastic dissipation in bulk rubber induced by surface asperities-well established as a major friction contribution. Starting with the measured spectrum of asperities one can calculate the water-smoothened spectrum and from that the predicted friction reduction, which is of the correct magnitude. The theory is directly supported by fresh tyre-asphalt friction data.

Processing guayule for latex and bulk rubber

The production of latex or bulk rubber from guayule has been pursued at various times since guayule rubber ceased being an article of commerce more than 60 years ago. Hypo-allergenic guayule latex has been prepared in 25–50-kg laboratory batches. Dilute latex was first washed from ground shrub and then concentrated by a combination of multi-stage centrifugation and creaming steps. This material was used to fabricate prototype medical products. A total of 8.8 t of dry guayule rubber was produced by simultaneous extraction of rubber and resin with a mixed organic solvent, followed by fractionation of the polymer stream. This material was tested in aircraft and light truck tires. At present, those seeking to process guayule must be prepared to meet several challenges: increasing the bulk viscosity of the rubber polymer, reducing the level of entrained resin and assuring oxidative and thermal stability. From this standpoint, latex process development remains in its early stages, whereas processing guayule for bulk rubber has been more thoroughly and successfully evaluated.

QENS investigation of filled rubbers

The polymer segmental dynamics is investigated in a series of silica-filled rubbers. The presence of inert fillers in polymers greatly affects the mechanical and physical performance of the final materials. For example, silica has been proposed as a reinforcing agent of elastomers in tire production. Results from quasielastic neutron scattering and Dynamic Mechanical Thermal Analysis (DMTA) measurements are presented on styrene–ran-butadiene rubber filled with silica. A clear indication is obtained of the existence of a bimodal dynamics, which can be rationalized in terms of the relaxation of bulk rubber and the much slower relaxation of the rubber adsorbed on the filler surface.

Effect of MAH Modified Carbon Black Prepared by Solid State Grafting in situ on the Adhesion Between Nylon 66 Cords and Natural Rubber and Dynamic Mechanical Properties of the Vulcanizates

Abstract Effect of maleic anhydride (MAH) modified carbon black prepared by solid state grafting in situ on the adhesion between nylon 66 cords and natural rubber was investigated by H pull out and flat belts-determination of ply adhesion test, and scanning electron microscopy (SEM). The results, which are cords bulk failure and rubber bulk failure in the two tests for unaged and aged samples employing MAH modified carbon black respectively, shown that good adhesion between cords and rubber interfaces is formed for the samples and kept in the two tests. This indicates that MAH modified carbon black can effectively enhance RFL dipped nylon 66 cords to natural rubber adhesion. In our viewpoint, the reason of the results is that active reaction groups introduced onto the carbon black surface by modification reacted with RFL; hence, integration effect was formed between dipped RFL nylon 66 cords and natural rubber interfaces. DMA results show that the modification of carbon black with MAH can effectively lower the rolling resistance of natural rubber vulcanizates. Mechanical property studies indicate carbon black modified with MAH is beneficial to keep higher tensile strength and elongation, especially for the aged vulcanizates.

Estimation of rubber sliding friction from asperity interaction modeling

Interaction between a soft rubber asperity and its hard counterpart is traced with the help of a finite element computation. The analysis is aimed to estimate the influence of adhesion between rubber and rigid surfaces and the energy losses arising from the deformation of rubber bulk to the sliding resistance. At the contact zone, interfacial bonds are formed due to adhesion and their resistance to sliding is represented by the shear strength of the contact interface. In the rubber bulk, the hysteresis loss is calculated using an appropriate model of the viscoelastic mechanical behavior of rubber for large strains. Dependence of friction on sliding speeds and temperature is hence detected. Influence of surface roughness and contact pressure on friction is also examined.

Adhesion improvement of SBR rubber by treatment with trichloroisocyanuric acid solutions in different esters

Ethyl, propyl and butyl acetates (EA, PA, BA, respectively) were used as solvents for trichloroisocyanuric acid (TCI) to chlorinate styrene–butadiene rubber (SBR). Characterization of the treated surfaces was carried out using ATR-IR spectroscopy, scanning electron microscopy (SEM), and contact angle measurements. Stress-strain measurements were also carried out to determine the mechanical properties of the treated rubber. Adhesion properties were studied using a polyurethane adhesive and the failed surfaces obtained after performing T-peel tests were analyzed in order to precisely locate the joint failure. The results showed that the solvent is a key factor in the effectiveness of the chlorination of R2 rubber. The solvents with slower evaporation rate led to more pronounced modifications on the R2 rubber surface. But these solvents could favour the migration of wax from the bulk rubber to the surface creating a weak antiadherent layer that prevented adhesion. The increase in TCI percentage in the chlorinating solution produced more marked modifications on the R2 rubber surface, avoiding the migration of wax. The solvent in the chlorinating solution also affects the effectiveness of the zinc stearate elimination from the R1 rubber surface; however, good adhesion was obtained even though this compound was not completely removed, indicating that the presence of zinc stearate in the rubber formulation did not produce a detrimental effect in the adhesion of SBRs.

Weak boundary layers on vulcanized styrene–butadiene rubber treated with sulfuric acid

A synthetic vulcanized styrene-butadiene rubber (R2) was used in this study. The presence of paraffin wax and zinc stearate in the rubber composition prevented the adhesion of R2 rubber to solvent-based polyester-urethane adhesive. To increase the adhesion properties of R2 rubber, a surface treatment with sulfuric acid (cyclization) was applied, and the length of the immersion in sulfuric acid and the time between the immersion time and the neutralization were varied. The treated R2 rubber surfaces were characterized using ATR-IR spectroscopy, contact angle measurements (water, ethanediol), and scanning electron microscopy (SEM). The mechanical properties of the treated rubber were obtained from stress-strain experiments. The joint strength was obtained from the T-peel test on treated R2 rubber/polyurethane adhesive joints. Due to the penetration of the sulfuric acid into the R2 rubber bulk, the mechanical properties decreased. The treatment with sulfuric acid produced several chemical modifications on the rubber surface: sulfonation of the butadiene and the creation of C C and C O bonds. Furthermore, the surface treatment of the R2 rubber with sulfuric acid removes paraffin wax from the rubber surface, which had a beneficial effect on adhesion to the polyurethane adhesive. To remove the wax layer, the surface was wiped with petroleum ether solvent after treating the R2 rubber with sulfuric acid. However, in some experiments a progressive migration of wax from the R2 rubber bulk to the surface with time happened. The migration of wax was prevented by increasing the immersion time in H2SO4 by more than 5 min.