Silica-filled Rubber Research Articles

Study of Styrene Butadiene Rubber Reinforced by Polybutadiene Liquid Rubber-Modified Silica.

The dispersion of silica in rubber systems and its interaction with rubber are two key factors in the preparation of rubber composites with excellent properties. In view of this, silica modified with terminal isocyanate-based polybutadiene liquid rubber (ITPB) is used to improve the dispersion effect of silica in rubber and enhance its interaction with the rubber matrix to improve the rubber's performance. The impact of different modification conditions on the dispersion of silica and the properties of modified silica-filled rubber composites were studied by changing the amount of ITPB and the modification method of silica, including blending and chemical grafting. The experimental results show that ITPB is successfully grafted onto silica, and the use of modified silica improves the cross-linking density of rubber, promotes the rate of rubber vulcanization, and overcomes the shortcomings of the delayed vulcanization of silica itself. When the ratio of ITPB liquid rubber to silica equals 1:20, the comprehensive performance of rubber is the best, the ITPB-modified silica has a better dispersion effect in rubber, and the rolling resistance is slightly improved, with tensile strength reaching 12.6 MPa. The material demonstrates excellent overall performance and holds promise for applications in the rail, automotive, and electrical fields.

TREATMENT FOR REMOVING ZN COMPOUNDS FROM SILICA-FILLED VULCANIZED RUBBER AND ANALYSIS OF SILICA AGGREGATE DISPERSION

ABSTRACT Treatment of silica-filled rubber vulcanizates with a diethyl ether/concentrated hydrochloric acid solution for 96 h at room temperature can remove most Zn compounds smaller than approximately 90 nm, which account for most of the residual ZnO, rubber-soluble Zn compounds and ZnS resulting from crosslinking reactions of by-products. However, a very small number of giant ZnO particles of a few micrometers in size remain after such treatment. In the silica-filled SBR matrix treated for 96 h, a significant increase in crosslink density and Young’s modulus was observed due to crosslinking reactions after HCl was removed from HCl-added rubber molecules. This increase in crosslink density was accompanied by an increase in the surrounding layer of bound rubber closest to the silica of the two bound rubber layers around it and a decrease in the rubber matrix of the same volume. It is inferred that there was little change in the aggregate structure of the silica due to these volume changes. Alternatively, ultra-small X-ray scattering measurements of the treated samples showed shoulders derived from silica aggregates and clear high-resolution X-ray computed microtomography (X-ray CT) images were obtained due to the removal of Zn compounds smaller than approximately 90 nm in size. The relationship between these shoulders and the size of silica aggregates obtained by X-ray CT imaging was qualitatively consistent, and it was not affected by the presence or absence of bis-(3-triethoxysilylpropyl) tetrasulfide and 1,3-diphenylguanidine, but was dependent on the rubber type. The distance between nearest neighbor particles of silica aggregates, determined by X-ray CT imaging, also depended on the types of rubber.

Property investigation of ready-to-use silica-filled rubber composites containing a curing agent prepared by a simple latex compounding method

A ready-to-use silica-filled rubber compound containing a curing agent was successfully prepared by a latex compounding method, followed by coagulation using a calcium chloride solution. This preparation technique provided a silica-filled compound with a small silica loss (ca. 1–5 % wt.). The rubber compounds were then subjected to various milling levels, ranging from 10 to 40 passes, prior to being tested for rheological and mechanical properties. The results reveal a reduction in compound viscosity with increasing milling levels. This may be attributed to the mastication effect (mostly dominant in the unfilled compounds) and the improved filler dispersion (particularly in the filled compounds). The magnitude of the Payne effect, an indicator of filler-filler interaction, of the heavily filled compounds (30–50 phr) was reduced by almost 50 % when the number of milling passes increased from 10 to 40 passes. The results suggest the improvement of silica dispersion with increasing the number of milling passes. Unfortunately, without a surface treatment of silica, the silica network was reformed when the rubber was subjected to high temperatures. This phenomenon was particularly obvious in the heavily filled compounds. Due to the improved silica dispersion in the highly filled compounds, increasing the milling pass from 10 to 40 passes resulted in noticeable increases in tensile strength (> 30 %) and elongation at break (> 30 %). Hardness, on the other hand, slightly decreased (10–15 %) with the increasing milling level. Overall, the silica-filled rubber compounds prepared by this technique had relatively high mechanical properties despite the absence of silane coupling agents. This technique can, therefore, be applied to prepare highly loaded silica-filled compounds without the need for expensive high-shear mixers.

Study on the nonlinear viscoelastic behavior of rubber composites filled with silica

Silica-filled rubber composites exhibit nonlinear viscoelastic behavior depending on filler dispersion and matrix interaction. This study investigated the effects of silane treatment on dynamic mechanical properties of precipitated and fumed silica-reinforced polybutadiene rubber composites. The silane coupling agent improved filler dispersion and interfacial adhesion as characterized by microscopy and bound rubber content. Payne effect measurements showed enhanced storage modulus and network stability for silanized composites due to better filler networking. Cyclic tensile loading displayed reduced stress-softening in treated composites attributable to minimized damage formation. Modeling using Kraus and damage mechanics approaches provided quantitative correlations between the microstructure and magnitude of nonlinear response. The results demonstrate that silane treatment optimizes the viscoelastic performance of silica-filled rubber composites.

Exploring Epoxy-Functionalized Polysulfide as a VOC-Free and Highly Effective Interfacial Modifier for Silica-Filled Rubber Composites

Exploring Epoxy-Functionalized Polysulfide as a VOC-Free and Highly Effective Interfacial Modifier for Silica-Filled Rubber Composites

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.

Fracture of V-notched natural rubber composites used in heavy-duty tire tread

Natural rubber-based composites have proven efficacy as candidate materials for heavy-duty tire tread. The mechanical properties of these composites depend on the type of filler and their loading; thus, a comparative investigation of material properties was carried out in this study for carbon black and silica-filled natural rubber composites. The mechanical properties of silica-filled rubber composites with silane loading of 16 wt% of silica were found to have optimum mechanical and fracture properties, but carbon black had better reinforcing efficacy after 300% elongation. The experimental investigations and finite element analysis show that the J-integral decreases with increasing crack opening angle. A decrement of 22% is observed in J-integral when crack opening angle varies from 300 to 600 for rubber composites with a pre-crack length of 5 mm. The geometry factor depended on the type of filler when the crack opening angle is increased for the composites having a large pre-crack length. We envisage that this study will be helpful for rectifying design faults of different rubber composites used in industrial applications, especially for passenger and heavy-duty tires.

Structural analyses of the bound rubber in silica-filled silicone rubber nanocomposites reveal mechanisms of filler-rubber interaction

Although the reinforcing effect of fumed silica on silicone rubber is always better than that of precipitated silica, their enhancement mechanism is still controversial due to the cognitive defects of the interface effect and filler network effect of polymer nanocomposites with the limited experimental study. Herein, significant entanglement network structure differences were revealed in the fumed and precipitated silica-filled phenyl silicone rubber by removing the physisorbed rubber gradually via 90 °C-ultrasonic solvent extraction method, which eventually obtained tightly bound rubber to explain filler-rubber interaction. The silica wrapped by tightly bound rubber was observed by SEM and TEM, where fumed silica is entangled with tightly bound rubber to robust dendritic structure, while precipitated silica is entangled with tightly bound rubber to the irregular agglomerate structure. Low-field 1H NMR confirmed that the mobility of the tightly bound rubber was significantly lower than loosely bound and free rubber. Furthermore, during the US treatment, the Si–O–Si infrared peaks of fumed silica-filled rubber exhibited "blueshift-redshift-blueshift" while the precipitated silica one only "blueshift" appears, which directly confirmed that different nanoporous structures of nanofiller induced diversity of filler-rubber entanglement network. The tightly bound rubber of precipitated silica (16.71%) was much more than that of fumed silica (3.72%) (40 phr). Although fumed silica adsorbs less tightly bound rubber than precipitated silica, the prominent nanofiller networks formed by fumed silica-rubber greatly enhanced the Payne effect and damping properties. This work can help to deeper understand the formation of the filler-rubber entanglement network and its contribution to the physical properties.

Inverse Vulcanization of Vinyltriethoxysilane: A Novel Interfacial Coupling Agent for Silica-Filled Rubber Composites

Sulfur-containing silane coupling agents (SSCAs) are widely incorporated into silica-filled rubber composites to improve silica dispersion and enhance interfacial adhesion, maximizing the potential of silica. However, SSCA synthesis involves multistep procedures and requires organic solvents. In addition, modifying rubber composites with SSCAs has persistent issues, such as low coupling efficiency and uncontrollable structure. Herein, we report the facile synthesis of alkoxysilyl-functionalized polysulfides (SPVs) with a tunable molecular structure (sulfur rank and alkoxysilyl fraction) via inverse vulcanization of vinyltriethoxysilane (VTES) with a copolymer of sulfur and styrene. SPVs serve as interfacial modifiers in silica-filled rubber composites by separately reacting with the silica and rubber chains. In particular, the multiple alkoxysilyl sites in the SPV chain increase the probability of silanization, yielding high coupling efficiency in the rubber composite. Although the molar content of alkoxysilyl groups in SPV1 (the mass feed ratio of VTES and copolymer is 1) is half of that in the most widely used small-molecules SSCAs of bis(3-triethoxysilylpropyl)tetrasulfide, stronger interfacial adhesion and better silica dispersion are achieved in SPV1-modified composites, which consequently lead to more improvements on the composite properties. In addition, the advantages of SPV1 as an interfacial modifier in improving the “magic triangle” properties of a practical tread composite have been demonstrated. More importantly, the effects of the SPV molecular structure on silica dispersion and interfacial adhesion have been investigated, providing the fundamentals for unraveling the coupling mechanism and guiding composite property regulation.

Use of naturally small molecule as an intelligent interfacial modifier for strengthening and toughening silica-filled rubber composite

The incorporation of interfacial modifiers into silica-filled rubber composite is necessary to optimize the composite properties because abundant silanol groups on silica surface make it essentially incompatible with non-polar rubbers. The modification of silica-filled composites with the commonly used silanes generally causes many constraints such as excessive silane dosage, high temperature compounding, volatile organic compound emission, and loss of toughness of the composite. In this contribution, we reported the use of naturally small molecule thioctic acid (TA) as an intelligent interfacial modifier for silica-filled styrene-butadiene rubber (SBR) composite. The carboxyl group of TA can interact with silica through hydrogen bonds, meanwhile the disulfide bond of TA can be cleaved to generate sulfur radicals and then couple with SBR macroradicals during compounding and curing, making TA a bridge between silica and SBR matrix. In the TA-modified composite, silica dispersion is greatly improved and hydrogen bond-mediated interface is constructed. When comparing with the most widely used bis-(γ-triethoxysilylpropyl)-tetrasulfide, TA-modified composites exhibit simultaneously improved strength, modulus, toughness and tear strength, which is on account of the reversible energy-dissipating mechanism of the hydrogen bond-mediated interfaces.

A spatio-temporal in-situ investigation of the Payne effect in silica-filled rubbers in Large Amplitude Oscillatory Extension

The present work deals with the structural and dynamic characteristics of a silica filler network within an industrial elastomeric composite with time-resolved Ultra-Small-Angle-X-ray Scattering (USAXS), collected for the first time in-situ under periodic uniaxial deformation. The in-situ configuration allows a unique correlation between the x-ray patterns highlighting the structure of the filler and the dynamic-mechanical stress-strain response that characterizes the full composite. A scattering model is applied to quantitatively identify the filler network evolution as a function of dynamic strain. To address the Payne effect and the underlying structural modifications correlated to intra- and inter-filler-aggregate effects, all rubbers were pre-conditioned to suppress stress-softening related to the Mullins effect. Sector-averaged scattering intensities along the parallel strain direction reveal a jamming/de-jamming transition between clusters. The dynamic stress response of the full composite shows onsets of non-linear behavior with contributions assigned to both filler and rubber phase separately. • Scattering analysis of silica-filled SBR elastomers. • Study of the Payne effect through in-situ combination of USAXS and DMA methods. • Relationship between structural and dynamic-mechanical properties. • Identification of jamming/de-jamming transition upon oscillatory deformation.

Catalyzed silanization by supporting ceria on silica towards rubber composites with improved mechanical properties

The silane modification in silica-filled rubber composites is essential to fulfil the potentials of silica. However, the silanization efficiency of silica generally remains unsatisfactory. Promoting silica silanization contributes to not only the improvements on composite properties, but also the reduction in volatile organic compound emissions during processing. In this work, we present a novel way to promote silica silanization in rubber composites by supporting ceria nanocrystals on silica surface. Specifically, silica supported with varied ceria nanocrystal loading is synthesized and used as a novel reinforcement for styrene-butadiene rubber. Model compound experiments demonstrate that the ceria on silica surface can effectively promote the silanization reaction based on its unique acid-base property. Due to the promoted silica silanization, silica dispersion is greatly improved and interfacial interaction is remarkably enhanced in the composites. Accordingly, the resulting composites filled with ceria-anchored silica exhibit desirable improvements on the tensile modulus and dynamic mechanical properties, which is conductive to tire application.

Preparation of Natural Rubber Composites with High Silica Contents Using a Wet Mixing Process.

A wet mixing process is proposed for filled rubber composites with a high silica loading to overcome the drawbacks of high energy consumption and workplace contamination of the conventional dry mixing process. Ball milling was adopted for preparing the silica dispersion because it has a simple structure, is easy to operate, and is a low-cost process that can be easily scaled up for industrial production. The response surface methodology was used to optimize the making of the silica dispersion. The optimum conditions for a well-dispersed silica suspension with the smallest silica particle size of 4.9 mm were an about 22% silica content and 62 h of ball milling. The effects of dry and wet mixing methods on the properties of silica-filled rubber composites were investigated in a broad range of silica levels from low to high loadings. The mixing method choice had little impact on the properties of rubber composites with low silica loadings. The silica-filled rubber demonstrated in this study, however, shows superior characteristics over the rubber composite prepared with conventional dry mixing, particularly with high silica loadings. When compared to silica-filled natural rubbers prepared by dry mixing (dry silica rubber, DSR), the wet mixing (for WSR) produced smaller silica aggregates with better dispersion. Due to the shorter heat history, the WSR exhibits superior curing characteristics such as a longer scorch time (2.2–3.3 min for WSR and 1.0–2.1 min for DSR) and curing time (4.1–4.5 min for WSR and 2.2–3.1 min for DSR). Additionally, the WSR has superior mechanical properties (hardness, modulus, tensile strength, and especially the elongation at break (420–680% for WSR and 360–620% DSR)) over the DSR. The rolling resistance of WSR is lower than that of DSR. However, the reversed trend on the wet skid resistance is observed.

Study on the Dynamics of Silica-filled Rubber Using X-ray Photon Correlation Spectroscopy

Study on the Dynamics of Silica-filled Rubber Using X-ray Photon Correlation Spectroscopy

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.

Visualization of chemical bonding in a silica-filled rubber nanocomposite using STEM-EELS

In nanocomposites, the adhesion between nanofillers and the polymeric matrix is key to the mechanical properties. The strength and spatial distribution of the adhesive layer around the nanofillers are important, particularly the presence of chemical bonding between the nanofillers and matrix. In this work, we studied a styrene-butadiene rubber composite filled with silica nanoparticles to visualize the spatial distribution of the adhesive layer. A silane coupling agent (SCA) was added to the nanocomposite for strong adhesion. The reaction involving the SCA on the silica surface was investigated by scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Si-L2,3 spectra of the silica-filled rubber nanocomposite without the SCA were the same around the nanofillers, whereas in the nanocomposite containing the SCA the spectra were position-dependent. The spectra were fitted with the intensity profiles of the Si-L2,3 spectra of silica and SCA by multiple linear least-squares fitting. The fitting coefficients of silica and SCA were used to map the spatial distribution of the chemical bonding between silica and rubber chains. Chemical bonding was observed around the silica nanoparticles but not in the SBR matrix region, providing direct evidence of the reinforcing mechanism in the silica-filled rubber nanocomposite.

Study on silica-based rubber composites with epoxidized natural rubber and solution styrene butadiene rubber

Carbon black has been replaced with silica as a reinforcing filler in tire tread compounds. This change has led to lower rolling resistance and improved hysteretic losses of so-called “green tires.” However, the dispersion of silica in the rubber matrix is an important issue due to the poor compatibility of hydrophilic silica with a hydrophobic rubber matrix. Recently, some rubbers with polar functional groups that can interact with silica have been studied to improve the interaction in silica-filled rubber composites. In this work, we fabricated the silica-filled rubber composites with solution styrene butadiene rubber (SSBR) and epoxidized natural rubber (ENR) and evaluated their properties in a silica-containing rubber formulation compared to conventional SBR and NR. The silica-embedded polar rubber matrix exhibits remarkable enhancement in the modulus, tensile strength, and abrasion properties due to an efficient dispersion of the silica and improvement of interfacial interactions with the rubber matrix. The polar rubber composite exhibits an enhanced dry and wet braking and improved rolling resistance due to the improved dispersion of the silica in the rubber matrix. These results show that rubber composites prepared with polar rubbers have great potential for tire engineering applications.

First Experiment of Spin Contrast Variation Small-Angle Neutron Scattering on the iMATERIA Instrument at J-PARC

Recently, we have developed a novel dynamic nuclear polarization (DNP) apparatus with a magnetic field of 7 T and a sample temperature of 1 K. High proton spin polarizations from −84% to 76%, for TEMPO doped polystyrene samples, have been demonstrated. This DNP apparatus satisfies the simultaneous requirement for quick and easy sample exchange and high DNP performance. On the iMATERIA (BL20) instrument at J-PARC, the first beam experiment using this DNP apparatus has been performed. For this experiment, the beamline was equipped with a supermirror polarizer. The stray magnetic field due to the superconducting magnet for DNP was also evaluated. The stray magnetic field plays an important role for in maintaining the neutron polarization during the transportation from the polarizer to the sample. The small-angle neutron scattering (SANS) profiles of silica-filled rubber under dynamically polarized conditions are presented. By applying our new analytical approach for SANS coherent scattering intensity, neutron polarization (PN) as a function of neutron wavelength was determined. Consequently, for the neutron wavelength, range from 4 Å to 10 Å, |PN| was sufficient for DNP-SANS studies.

EXPLORING THE SUITABILITY OF SOL-GEL–SYNTHESIZED NANO ZnO AS A CURE ACTIVATOR IN CARBON BLACK– AND SILICA-FILLED NR COMPOSITES

ABSTRACT Sol-gel–synthesized nano zinc oxide (ZnO) is introduced as a cure activator in carbon black (CB)– and silica-filled natural rubber (NR) composites. The performance of sol-gel–synthesized nano ZnO was systematically compared with conventional ZnO for various filled NR composites in terms of cure, mechanical, aging, and thermal properties. At a filler loading level of 40 parts per hundred parts of rubber (phr), only 1 phr nano ZnO provided a better cure rate index and tensile strength as compared with 5 phr conventional ZnO in CB-filled NR composites. On the other hand, at a 40 phr filler loading level, the cure and mechanical properties of the 1 phr nano ZnO cured NR/silica composite were comparable with the properties of the 5 phr conventional ZnO cured NR/silica composite. At the same filler loading level, both 1 phr nano ZnO and 5 phr conventional ZnO had a similar effect on the thermal stability of NR/CB and NR/silica composites. As a whole, 1 phr sol-gel–based nano ZnO could be used as an efficient cure activator instead of 5 phr conventional ZnO in CB- and silica-filled NR composites with successive reduction of ZnO level.