Silica-filled Rubber Compounds Research Articles

Modeling the rheological behavior of silica filled rubber compounds

The rheological behavior of styrene–butadiene rubber (SBR) compounds filled with silica is investigated as a function of silica volume fraction. To predict the mechanical response, a continuum model for entangled polymer melts filled with nanoparticles is herein introduced. This model is capable of describing the rheological response in both the linear and nonlinear viscoelastic regimes in the context of non-equilibrium thermodynamics to guarantee its thermodynamic admissibility. The constitutive model describes the polymer nanocomposite melts at a mesoscopic level of description by considering the conformation tensor between successive entanglement points, and the orientation tensor for the, in general, spheroidal nanoparticles that describes their average orientation. Evolution equations are developed for nanoparticles with an arbitrary shape but are eventually specified to the case of spherical ones. The multimode version of the new constitutive model provides a very accurate prediction of the rheological behavior of the processability range of SBR/silica nanocomposites. Thus, the new model is a tool able to provide answers to the several difficulties that rubber-producing manufacturers face when processing rubber compounds.

Optimized End Functionality of Silane-Terminated Liquid Butadiene Rubber for Silica-Filled Rubber Compounds.

As the world is shifting from internal combustion engine vehicles to electric vehicles in response to environmental pollution, the tire industry has been conducting research on tire performance to meet the requirements of electric vehicles. In this experiment, functionalized liquid butadiene rubber (F-LqBR) with triethoxysilyl groups at both ends was introduced into a silica-filled rubber compound as a substitute for treated distillate aromatic extract (TDAE) oil, and comparative evaluation was conducted according to the number of triethoxysilyl groups. The results showed that F-LqBRs improved silica dispersion in the rubber matrix through the formation of chemical bonds between silanol groups and the base rubber, and reduced rolling resistance by limiting chain end mobility and improving filler-rubber interaction. However, when the number of triethoxysilyl groups in F-LqBR was increased from two to four, self-condensation increased, the reactivity of the silanol groups decreased, and the improvement of properties was reduced. As a result, the optimized end functionality of triethoxysilyl groups for F-LqBR in silica-filled rubber compound was two. The 2-Azo-LqBR with the optimized functionality showed an improvement of 10% in rolling resistance, 16% in snow traction, and 17% in abrasion resistance when 10 phr of TDAE oil was substituted.

Influence of functionalized S–SBR on silica–filled rubber compound properties

Styrene–butadiene–Rubber, SBR, is most often used in tread compounds in order to improve the Rolling Resistance (RR). The functionalized SBRs are used to increase the polymer–filler interaction in the compound to improve RR. In this study, the effect of different types of functional groups in SBR was investigated. Several types of functionalized S–SBR’s were synthesized by anionic polymerization: (i) SBR with an amine group at one end of the polymer chain, (ii) SBR with an alkoxy silane group at one end (iii) SBR with an amine group at one end and an alkoxy silane group at the other end of the polymer chain. A model reaction of silanization was conducted in a solvent to estimate how the amine functional group affects the silanization. Silica filled compounds were prepared with these SBR types. Payne effect and bound rubber measurement were done. The model silanization reaction of TESPT (Bis(triethoxysilylpropyl)tetrasulfide) with silica in the presence of amine shows that a higher amount of ethanol (EtOH) is released from TESPT compared to the amine free system. This result indicates that the silanization reaction can be accelerated by the presence of an amine functional group at the SBR polymer chain used in silica–filled compounds. The amine functionalized SBR and the alkoxy silane functionalized SBR show less Payne effect of the compounds which indicates that both functional groups can decrease the filler–filler interaction. More chemical bound rubber was obtained in branched SBRs compared to the corresponding linear SBRs. A branched polymer chain has a higher molecular weight compared to the linear type. Therefore, when one branched polymer chain reacts with silica or creates a silica–silane–polymer bond, more bound rubber can be obtained for the branched than for the linear type. The compound of the SBR with the alkoxy–silane functional group shows lower tan δ compared to the non–functionalized SBR and the amine functionalized SBR compounds. The influence of the type of functionalization of the SBR on tan δ at 70 °C was more significant in branched SBRs than in linear SBRs, due to the before–mentioned effect of the functional group on silanization and bound rubber.

Effect of the Functional Group Position in Functionalized Liquid Butadiene Rubbers Used as Processing Aids on the Properties of Silica-Filled Rubber Compounds.

Recently, research conducted on tread compounds with liquid butadiene rubber (LqBR) have been conducted in the tire industry. In particular, the introduction of functional groups into LqBRs is expected to lower hysteresis loss caused by the free chain ends of LqBR. To study this, LqBRs with functional groups at different positions were synthesized. The occurrences of in-chain and chain-end functionalization of functionalized LqBRs (F-LqBRs) were confirmed, the microstructure and functionalization efficiency of F-LqBRs were calculated through the characterizations. This novel functionalization technology was beneficial not only to immobilizing the free chain ends of LqBRs to the surfaces of silica to decrease the number of free chain ends, but also chemically bonding the LqBR chains on the base polymer through a crosslinking reaction to enhance the filler-rubber interaction. The effects of the functional group position and number of the free chain ends on the physical properties and hysteresis of the compounds were investigated by partially replacing the treated distillate aromatic extract (TDAE) oil with LqBR in silica-filled rubber compounds. The results showed that compounds that had applied DF-LqBR with both end functionalization performed better, including improving the silica dispersion, higher extraction resistance, and lower rolling resistance, than other F-LqBRs compounds.

Properties of silica-filled rubber compounds vs. epoxidized oil content and degree of epoxidation

Epoxidized vegetable oils are well-known as biobased, sustainable additives for polymers. However, relatively little work has been done to explore their effects on silica-filled rubber composites in depth. In order to address this knowledge gap, high purity epoxidized soybean (Glycine max (L.) Merr.) oils with varying levels of epoxidation were synthesized and compounded with a model silica-filled styrene-butadiene rubber formulation. The green properties, process characteristics, and cured properties (quasi-static and dynamic mechanical characteristics) of the resultant compounds were then assessed. A ∼7 % decrease in mixing energy was observed with the inclusion of ∼0.8 vol% of 100 % epoxidized soybean oil. Changes in cure kinetics and dynamic mechanical properties were observed as a function of epoxy group concentration. The changes in dynamic mechanical properties are explained in terms of changes in silica dispersion state as a consequence of epoxidized soybean oil addition.

Dispersion and vulcanization characteristics of nitrile rubber reinforced with N,N‐dimethylacetamide/lithium chloride treated silica

AbstractN,N‐Dimethylacetamide/lithium chloride (DMAc/LiCl) treated silica is used as a reinforcing filler in nitrile rubber (NBR). Effect of the treatment on aggregate morphology and dispersion of silica in the matrix is investigated using XPS, SEM, and AFM. Binding energy levels of O1s and Si2p electrons in DMAc/LiCl treated silica have shifted significantly from 532.49 to 530.98 eV and 103.19 to 101.33 eV respectively. SEM observations have revealed a reduction in the agglomerate size of silica‐a desirable feature for realizing better processing properties of silica filled rubber compounds. Data from AFM observations have also shown better dispersion of DMAc/LiCl treated silica. Mooney viscosity of masterbatches, measured at 100°C over a period of 7 days, has not exhibited any storage hardening which is an indication of easier processability. At 125°C, Mooney data exhibited a reduction in scorch time as a function of DMAc/LiCl concentration. However, MDR data at 160°C have not shown much changes in the scorch time while NBR with high nitrile content exhibited longer cure times. Higher crosslink density of vulcanizates indicate that DMAc/LiCl treatment of silica could effectively reduce filler‐filler interactions and networking in silica filled rubber compounds thereby enabling mixing and processing operations energy efficient.

Effect of Vinyl Group Content of the Functionalized Liquid Butadiene Rubber as a Processing Aid on the Properties of Silica Filled Rubber Compounds

Effect of Vinyl Group Content of the Functionalized Liquid Butadiene Rubber as a Processing Aid on the Properties of Silica Filled Rubber Compounds

Silane-modified low molecular weight ‘liquid’ polymers in sulfur cured mixtures of styrene-butadiene copolymers and silica

Silane coupling agents are used in silica filled rubber compounds to increase the filer-polymer interactions and to lower the filler-filer interactions. In addition, silane functionalized polymers can be used. Special types of polymers are low molecular weight ‘liquid’ polymers. The goal of this paper is to obtain more understanding about the uses and effects of these low molecular weight ‘liquid’ polymers in combination with silanes and other compound components. Three different silane coupling agents and six different low molecular weight ‘liquid’ polymers were selected, evaluated and comparatively introduced in mixtures of a SSBR/silica compound. The Payne effect was measured to evaluate the strain dependence of the mixtures. It was used to evaluate the filler-filler interactions and estimate the micro dispersion. This provides information about the interactions and the building of additional networks that comprises the low molecular weight ‘liquid’ polymer together with the silica, silane and main polymer. Results of dynamic mechanical analysis are discussed. The microstructures and silane-functionalizations show clear dependences on the glass transition temperatures, loss moduli and tan δ values.

On the various roles of 1,3-DIPHENYL Guanidine in silica/silane reinforced sbr/br blends

The aim of this study was to evaluate the various roles of 1,3-DiPhenyl Guanidine (DPG) in silica-reinforced rubber compounds. Two roles of DPG are well known to be: adsorption onto silica surface to reduce the acidic sites and second to boost the silanization reaction as secondary accelerator. However, these two roles are in a way conflicting. When DPG molecules occupy the reactive silanol sites on silica by adsorption, then the access of silane molecules needed for silica-rubber coupling is blocked. Therefore, it may be assumed that there is another role DPG plays in silica filled rubber compounds. In order to evaluate another role which can reconcile these contradictory functions of DPG, a series of rubber compound mixings was performed with different DPG concentrations in the masterbatch and final stages. Additionally, a series of model reaction experiments has been done in combination with other ingredients, such as zinc oxide and stearic acid. According to the results a new role of DPG is observed: DPG possibly reacts with the silane coupling agent bis-(triethoxysilylpropyl)tetrasulfide (TESPT) and releases sulfur during the mixing process, which enhances filler-polymer coupling, but reduces cure rate and crosslink density.

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.

The Effect of Silanization Temperature and Time on the Marching Modulus of Silica-Filled Tire Tread Compounds.

Marching modulus phenomena are often observed in silica-reinforced solution styrene–butadiene rubber/butadiene rubber (S-SBR/BR) tire tread compounds. When such a situation happens, it is difficult to determine the optimum curing time, and as a consequence the physical properties of the rubber vulcanizates may vary. Previous studies have demonstrated that the curing behavior of silica compounds is related to the degree of silanization. For the present work, the effect of silanization temperature and time on the marching modulus of silica-filled rubber was evaluated. The correlations between these mixing parameters and their effect on the factors that have a strong relation with marching modulus intensity (MMI) were investigated: the amount of bound rubber, the filler flocculation rate (FFR), and the filler–polymer coupling rate (CR). The MMI was monitored by measuring the vulcanization rheograms using a rubber process analyzer (RPA) at small (approximately 7%) and large (approximately 42%) strain in order to discriminate the effects of filler–filler and filler–polymer interactions on the marching modulus of silica-filled rubber compounds. The results were interpreted via the correlation between these factors and their effect on the MMI. A higher temperature and a longer silanization time led to a better degree of silanization, in order of decreasing influence.

EFFECTS OF SILANE AGENTS AND CURING TEMPERATURES ON VULCANIZATE STRUCTURES

ABSTRACT Silane coupling agents are commonly used in silica-filled rubber compounds to hydrophobize the silica surface and improve filler–rubber interaction. The coupling agent bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT) is the most widely used coupling agent. The tetrasulfide is more reactive than the disulfide in bis[3-(triethoxysilyl)propyl]disulfide (TESPD) due to its low decomposition energy, resulting in more coupling reaction with rubber molecules. Meanwhile, vulcanization temperature affects chemical networks. Polysulfide is vulnerable to heat, so it can be easily broken to form shorter crosslinks. Compounds with TESPD or TESPT were vulcanized at 160 and 180 °C. In addition to the decomposition, the reactivity of the silanes was confirmed from the cure characteristics of the compounds without the curatives. TESPD could also cause a coupling reaction without the curatives such as TESPT known to release free sulfur. By analyzing vulcanizate structures, total crosslink density was separated into chemical crosslink density and filler–rubber networks. Applying TESPT or vulcanizing at 180 °C increased the filler–rubber networks, and the higher vulcanization temperature decreased the chemical crosslink density. By correlating physical properties, effects of the vulcanizate structures on performance of tread compounds were investigated. The filler–rubber interaction was dominant for wet traction and mechanical properties in tensile test. The chemical crosslink density affected rolling resistance.

THE ORIGIN OF MARCHING MODULUS OF SILICA-FILLED TIRE TREAD COMPOUNDS

ABSTRACTSilica-reinforced S-SBR/BR tire tread compounds often show characteristic vulcanization profiles that do not exhibit a distinct maximum in the cure curve nor a plateau profile within acceptable time scales (marching modulus). In such a situation, it is difficult to determine the optimum curing time, and as a consequence, the physical properties of the rubber compounds may vary. Previous studies stated that the curing behavior of silica-filled rubber compounds is related to the degree of filler dispersion, the silanization, and the filler–polymer coupling reaction, as well as to the donation of free sulfur from the silane coupling agent. Such results imply that these are the key factors for minimization of the marching modulus. Various silane coupling agents with different sulfur ranks and functionalities were mixed at varied silanization temperatures. The correlation between these factors and their effect on the marching modulus intensity (MMI) were investigated. The MMI was monitored by measuring the vulcanization rheograms using a rubber process analyzer at small (approximately 7%) and large (approximately 42%) strains to discriminate the effects of filler–filler and filler–polymer interactions on the marching modulus of the silica-filled rubber compounds. Both factors have an intricate influence on the marching modulus, determined by the degree of filler–filler interaction and the coupling agent.

Kinetic behavior of the reaction between silica and epoxidized liquid rubber

The use of epoxidized rubber as compatibilizer in silica-filled rubber compounds has been proposed in literature. However, the investigation of the reaction kinetics between the epoxy groups and the hydroxyl groups at the silica surface is not yet described. It is a difficult task, mainly because of the high dilution of the system due the difficulty of incorporating high levels of silica in a matrix containing epoxidized rubbers of high molecular weight. In this work, a mixture of precipitated silica and an epoxidized liquid rubber (EpLHPB) was prepared and the reaction between silanols and epoxy groups was followed by DSC under isothermal conditions, at 150, 160 and 170 °C. An autocatalytic data treatment was applied to determine the kinetic parameters of the reaction. Furthermore, it was possible to estimate the amount of epoxy groups required for the saturation of the external surface of the silica, resulting in 5.4 epoxy groups/nm2.

The Development of Sulphur-Functional Silanes as Coupling Agents in Silica-Reinforced Rubber Compounds. Their Historical Development over Several Decades

Where silica is used as an active filler in rubber vulcanisates, a bifunctional silane has to be added to achieve the full reinforcement potential in almost all cases. Sulphur vulcanisation is the crosslinking method of choice in many fields of application, particularly because of the outstanding dynamic properties of the resulting parts. Since sulphur-functional silanes are able to participate directly in sulphur vulcanisation, this substance class has become the preferred coupling agent for the sulphur-based vulcanisation of silica-filled rubber compounds. This paper outlines in four stages the history of sulphur-silane development over the last few decades.

Improvement of Filler-Rubber Interaction by Grafting of Acrylamide onto Saponified Natural Rubber under Ultraviolet Radiation as a Continuous Process

Silica and carbon black have been widely used as the main reinforcing fillers for improving the properties of natural rubber (NR). In a silica-filled rubber compound, it is known that the low compatibility between NR and silica affects the mechanical properties of rubber products. In order to overcome this drawback, the functionalized saponified NR (FSPNR) was carried out by grafting acrylamide (AM) onto the saponified NR (SPNR) under UV radiation as a continuous process. An increasing in the bound rubber content and Mooney viscosity was found as an increasing AM content. Storage modulus at low strain amplitude of the silica-filled FSPNR was lower than that of the raw NR. In addition, SEM micrographs showed the good dispersion of silica in FSPNR. These confirmatory evidences indicate the improvement of rubber-filler interaction and the reduction of filler-filler interaction by functionalization under UV radiation.

Influence of Mixing Procedure on Properties of Silica Filled Epoxidised Natural Rubber Compounds

Since the introduction of the so-called Green Tyre concept, in the early 90ies, the use of silica as reinforcing fillers has spread and grown worldwide. The general advantages of silica as reinforcing filler over carbon black filler are better rolling resistance by achieving at least equal wet traction while tread wear should not be adversely affected. One way to obtain both low rolling resistance and high wet traction is indeed, to use precipitated silica together with solution polymers in tyre treads. The benefits of reinforcement by silane coupled silicas, in certain blends of solution styrene –butadiene rubber (SBR) and butadiene rubber (BR), were recognized by major tyre manufacturer. However, the use of silica compounds entails considerable disadvantages in terms of raw material costs and processability (before vulcanization). These difficulties include higher compound Mooney Viscosity (ML1+4) that increases upon storage, short scorch time and environmental problems related to alcohol evolution. The high viscosity and poor processability in silica filled rubber compounds are believed to be associated with silica reaggregation (self aggregation) after rubber compounding. The study has been made of the effect of increased mixing stage and dispersion agent in rubber on uncured properties of the Silica Filled Epoxidised Natural Rubber Compounds. In this experiment, two orders of mixing were considered (1) Two Stages Mixing and (2) Three Stages Mixing. Results showed that filler dispersion, Mooney Viscosity and Payne Effect was influenced by the degree of mixing. The incorporation of dispersion agents in the compounds also resultant in the similar manner. It is believed that the dispersion agent could coat the silica surfaces as they are being broken down during the mixing and then stabilize the dispersed structure by stearically preventing silica reagglomeration.

Mechanical and Dynamic Properties of Silica-Filled Rubber Compounds

Natural rubber compound using different silicas, including unmodified silica, admicellar-modified silica and silica with silane coupling agent, were studied. The properties including cure characteristics, mechanical properties and dynamic properties were examined with the comparison of three compounds. The results show that cure characteristics of admicellar silica/rubber compound (Ad-Si/R) was shorter than those of unmodified silica/rubber compound (Un-Si/R) and silane coupling silica/rubber compound (Sil-Si/R). Mechanical properties of Ad-Si/R and Sil-Si/R were better than those of Un-Si/R. In addition, wet grip and rolling resistance analyzed from tan δ (5 Hz) at 0°C and 60°C, respectively, by DMA were found that the wet grip of Ad-Si/R was the best, whereas the rolling resistance of Sil-Si/R was the best, in the comparison.

Influence of Water and Filler Content on the Dielectric Response of Silica-Filled Rubber Compounds

We present in this work a systematic study to analyze the influence of water and filler content on the dielectric response of silica-filled rubber compounds. For nanoparticle-filled polymers an additional dielectric process is usually observed in the loss dielectric spectra at frequencies lower than the alpha (α) or segmental relaxation. This process has generated some controversy in the literature due to the different (sometimes contradictory) interpretations given to explain its physical origin. We demonstrate, by means of dielectric spectroscopy in combination with thermal analysis, that this low-frequency process is compatible with a MWS process enhanced by the presence of water molecules at the silica surface. We show that the frequency of the maximum for this process is strongly affected by the amount of water attached to the silica particles. The dielectric response of the MWS process is rationalized by means of a simple interlayer model (IL). In addition, we also study the influence of water and f...

Flocculation in Silica Reinforced Rubber Compounds

Abstract Flocculation plays an important role in reinforcement of silica filled rubber compounds, even if coupling agents are applied. It is well known that silica tends to flocculate during the early stages of vulcanization, when no dense rubber network has been formed yet. In the present study, flocculation was monitored by following the change in storage modulus at low strain, the so-called Payne effect, using a RPA2000 dynamic mechanical tester. The kinetic parameters: the rate constant and the activation energy of the silica flocculation were calculated according to the well-known Arrhenius equation. On basis of the value of the activation energy obtained for flocculation, it can be concluded that the silica flocculation is a purely physical phenomenon. Bound rubber measurements were also done in order to estimate the interfacial interaction layer between silica and polymer resulting from the coupling agent. The silica flocculation rate decreases with increasing interfacial interaction layer on the silica surface. This indicates that the decrease of the flocculation rate is due to the shielding effect of the coupling agent. It is argued that the attractive flux from forces related to polarity differences between the silica and the rubber is the determining factor for silica flocculation.