Silica-filled Rubber Research Articles

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.

Hierarchical Scattering Function for Silica-Filled Rubbers under Deformation: Effect of the Initial Cluster Distribution

In this study, the evolution of the scattering function of silica-filled styrene-butadiene copolymer rubbers (SBRs) under a continuous uniaxial strain cycle is investigated in situ with a complemen...

Effects of TESPT-Silane Coupling Agent on Torque Properties and Degree of Filler Dispersion of Silica Filled Natural Rubber and Epoxidized Natural Rubbers Compounds

The effect of the addition of a bis(triethoxysilylpropyl) tetra sulphide or TESPT-silane coupling agent on torque properties and degree of filler dispersion of silica-filled compounds of natural rubber (NR), epoxidized natural rubbers with 25% mole of epoxidation (ENR 25) and epoxidized natural rubbers with 50% mole of epoxidation (ENR 50) were investigated. All the rubbers were filled by silica filler at a fixed loading (30.0 parts per hundred rubber, phr) and the TESPT was added to each silica-filled rubbers compounds at 1.0phr. It was found that TESPT affected the torque properties of all the silica-filled rubbers compounds. The TESPT decreased the minimum torque of NR system but increased the minimum torque of ENRs systems and maximum and torque differences of the all rubbers systems. The minimum torque was decreased from 0.61 to 0.53 dN.m for NR; were increased from 0.23 to 0.49 dN.m for ENR 25 and from 0.07 to 0.34 dN.m for ENR 50.It was also found that the TESPT acted as an internal plasticizer for NR which improved the degree of silica dispersion. Presumably, for the ENRs, the TESPT acted as an additional cross linker with a more pronouncedly which poorer the degree of silica dispersion.

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.

Effects of Alkalinity of Ionic Liquid on Catalyzed Silanization in Rubber/Silica Composites

The silane coupling agent has been used for ages to improve the performance of silica-filled rubber composites. To improve the degree of silanization of silica, ionic liquids (ILs) as a catalyst ar...

Evolution of Payne effect of silica-filled natural rubber in curing process

Vulcanisation is the key process for determining the final properties of elastomers due to the relationship between curing condition and viscoelastic behaviour. This study focuses on the variations in the dynamic behaviour of silica-filled natural rubber caused by crosslinking. The rubber samples with different degrees of curing (DOC) are prepared by thermal quenching during the crosslinking process. The strain sweep mode is used to study the Payne effect. The Kraus model is used to fit the test data. The relationship between the parameters of Kraus model and DOC is obtained at small strain (< 10%). The storage modulus at small strain amplitudes (usually < 0.01%) $$ G^{\prime}_{ 0} $$ is proportional to DOC; however, the storage modulus at large strain amplitudes $$ G^{\prime}_{\infty } $$ has small changes with DOC. The characteristic value of the strain amplitude $$ \gamma_{\text{C}} $$ shifts to large strain and the maximum loss modulus $$ G^{\prime\prime}_{\text{m}} $$ decreases with the increase of DOC. In addition, a deviation between Kraus model and experiment is observed when the strain is larger than 10%, and the loss modulus increases with the increase of strain amplitude. The deviation decreases when DOC increases. The mechanism for this deviation is discussed and the interaction between silica filler and rubber chain might be responsible for the observed deviation.

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.

TEM observation of silane coupling agent in silica-filled rubber tyre compound

The microdispersion of silica in filled elastomer vulcanisates was evaluated by transmission electron microscopy (TEM)—network visualisation analysis. In this study, the silica is modified with a wide range of coupling and non-coupling silanes. The silica-filled elastomer samples were microtomed using a glass knife. The resulting TEM micrographs were interpreted and characterised based on aggregates with a cross-sectional area larger than 100 nm2. The study showed that silica surface modification has reduced the silica aggregate size by approximately 30–40% compared to an untreated silica-filled elastomer vulcanisate. The TEM micrographs showed evidence of coupling between silica and the elastomer phase and demonstrated a good estimation of silica microdispersion in the elastomer phase. This study has shown that the presence of different surface functionalities has an effect on the silica microdispersion.

Some factors affecting the flex life of polybutadiene rubber vulcanisate

Flex life of three different grades of polybutadiene rubber (BR) with highly linear chains, linear chains and long-branched chains was measured. The rubbers were reinforced with a precipitated silica nanofiller, the surface of which had been pre-treated with sulphur-bearing bis(3-triethoxysilylpropyl-)-tetrasulphane (TESPT) coupling agent. The rubbers were cured by reacting the sulphur in TESPT with the rubber chains to produce vulcanisates. The mechanical properties of the rubber vulcanisates such as tensile strength, Young’s modulus, elongation at break, stored energy density at break and tear energy were subsequently determined. The flex life of the rubber vulcanisates was also measured at a constant maximum strain amplitude and a test frequency of 3.17 Hz at ambient temperature. Additionally, the flex life of some unfilled rubber vulcanisates of similar Mooney viscosities cured with elemental sulphur was also measured. For the silica-filled rubber vulcanisate, the rubber with the highly linear chains had the longest flex life and the one with long-branched chains, the shortest flex life. It seemed that a correlation between the flex life and the molecular chains structure might exist despite the crosslink density of the rubber vulcanisates being different and the compounds having silica in them. For the unfilled rubber vulcanisates, the rubber with highly linear chains had the longest flex life and the one with linear chains the shortest flex life. Therefore, it was concluded that the flex life of the rubber vulcanisate was determined, to a large extent, by the molecular chains structure of the raw rubber, irrespective of whether the rubber had reinforcing silica filler, different crosslink densities and different initial viscosities or not. A similar trend was also observed for some of the mechanical properties. For example, the elongation at break was lower and Young’s modulus higher for the silica-filled rubber vulcanisates with long-branched chains than those measured for the silica-filled rubber vulcanisate with highly linear chains.

Influence of Graphene Nanoplatelets on Silica-Filled Natural Rubber Composites: Dispersion Mixing and Effect on Thermal Stability, Rheological and Mechanical Properties

In this study, graphene nanoplatelets C750 (GnPs-C750) was introduced to silica-filled natural rubber composites (NR/SiO2/GnPs) by simple latex mixing process and coagulation following conventional vulcanization process to investigate the outstanding properties compared to individuals. The SiO2 and GnPs contents were fixed at 40 and 2 parts per hundred of rubber (phr), respectively. The results showed that in the presence of GnPs in SiO2-filled natural rubber composites, the thermal stability of the composite was improved. Meanwhile, the rheological properties including minimum torque and maximum torque were increased and cure characteristics including scorch time and optimum cure time were decreased related to cure rate index was greater than SiO2 individual. The influence of GnPs on the mechanical properties was investigated. The results showed that it was not significantly changed in mechanical properties.

Low-molecular-weight styrene–butadiene copolymers (L-SSBR) as processing aids used for silica-filled rubber: Synthesis, functionalization and application

Three different types of low-molecular-weight solution styrene-butadiene rubbers (L-SSBRs) were synthesized by anionic polymerization. Two of them were end-capped with methoxy (M-L-SSBR) and ethoxy (E-L-SSBR) functional groups, respectively, while the other was terminated with alcohol (L-SSBR). The content of functional groups was estimated on the basis of gel permeation chromatography and proton nuclear magnetic resonance analysis. The influence of L-SSBR on the properties of silica-filled SSBR as an alternative for the plasticizing oil was investigated in tyre tread formulation. L-SSBRs of high vinyl content were used in place of part of oil for preparation of compound K1 enriched with linear (L-SSBR) and compound K2 and K3 enriched with two star-like liquid rubbers modified, respectively, with methoxy (M-L-SSBR) and ethoxy (E-L-SSBR) functional groups. Although particular attention was paid to the effect of polar groups on the silica dispersions, cure characteristic, compound viscosity and mechanical properties were also analyzed. Rubber with only treated distillate aromatic extract was used (K5) as the reference.

Entrapped Styrene Butadiene Polymer Chains by Sol-Gel-Derived Silica Nanoparticles with Hierarchical Raspberry Structures.

A sol-gel transformation of liquid silica precursor to solid silica particles was carried out in a one-pot synthesis way, where a solution of styrene butadiene elastomer was present. The composites, thus produced, offered remarkable improvements of mechanical and dynamic mechanical performances compared to precipitated silica. The morphological analysis reveals that the alkoxy-based silica particles resemble a raspberry structure when the synthesis of the silica was carried out in the presence of polymer molecules and represent a much more open silica-network structure. However, in the absence of the polymer, the morphology of the silica particles is found to be different. It is envisaged that the special morphology of the in situ synthesized silica particles contributes to the superior reinforcement effects, which are associated with a strong silica-rubber interaction by rubber chains trapped inside the raspberry-like silica aggregates. Therefore, the interfaces are characterized in detail by low-field solid-state 1H NMR spectroscopy, 29Si solid-state NMR spectroscopy, and energy-dispersive X-ray spectroscopy. Low-field 1H NMR-based double-quantum experiments provide a quantitative information about the cross-link density of the silica-filled rubber composites and about the influence of silane coupling agent on the chemical cross-link density of the network and correlates well with equilibrium swelling measurements. The special microstructure of the alkoxy-based silica was found to be associated with the interaction between alkoxy-based silica and rubber chains as a consequence of particle growth in the presence of rubber chains.

Structural Analysis of Silica-filled Rubber Under Cyclic Deformation Using Time-resolved Ultra-small Angle X-ray Scattering

Structural Analysis of Silica-filled Rubber Under Cyclic Deformation Using Time-resolved Ultra-small Angle X-ray Scattering

Effect of organosilane agents on the vulcanizate structure and physical properties of silica-filled solution styrene butadiene rubber compounds

Physical properties of rubber compounds are affected by the filler-rubber interaction, filler dispersion in the rubber matrix, and crosslink structure formed during vulcanization. Organosilane agents are essentially used in silica-rubber compounds to inhibit the formation of silica agglomerates and increase the formation of silica-rubber networks. Generally, organosilane agents have an alkoxysilyl alkyl sulfide structure and are classified into silane coupling and covering agents depending upon the presence of sulfur. Coupling agents have a sulfur moiety and serve as a sulfur donor during the vulcanization process, thus increasing the formation of filler-rubber and chemical crosslink networks. On the other hand, covering agents promote the hydrophobation of silica surfaces, decreasing the adsorption loss of vulcanization additives, which increases the formation of chemical crosslink networks. This implies that organosilane agents can affect the vulcanizate structure, which causes a variation in the properties of silica compounds. Therefore, in this study, the effect of coupling (bis(3-triethoxysilylpropyl)disulfide (TESPD) and bis(3-triethoxysilylpropyl)tetrasulfide (TESPT)) agents and a covering (triethoxy(octyl)silane) agent on the vulcanizate structure and properties of silica compounds was investigated and compared. In the comparative study of coupling and covering agents, the influence of sulfur donors on the formation of vulcanizate structures was investigated. In the case of the coupling agents, the effect of sulfur rank on the vulcanizate structure and properties of silica-rubber compounds was quantitatively analyzed through various characterization techniques.

EFFECTS OF SILANE COUPLING AGENTS ON STRUCTURE AND PROPERTIES OF SILICA-FILLED SILICONE RUBBER/STYRENE BUTADIENE RUBBER COMPOSITES

ABSTRACT Two silane coupling agents, bis-(γ-triethoxysilylpropyl)-tetrasulfide (Si69) and vinyltriethoxysilane (A151), were selected to investigate their effects on structure and properties of silica-filled methyl vinyl silicone rubber (VMQ)/emulsion styrene butadiene rubber (ESBR) composites. The filler–rubber interactions were investigated via bound rubber content and solid-state 1H low-field nuclear magnetic resonance (NMR) spectroscopy, and the mass ratio of VMQ and ESBR in the rubber–filler gel was investigated by thermogravimetric analysis (TGA). The results revealed that VMQ showed a better compatibility with silica than ESBR. Compared with the A151 composite, the composite with Si69 showed the higher content of ESBR in rubber–filler gel, which resulted in the higher bound rubber content and the weaker Payne effect, and it also exhibited higher tensile strength, higher tear strength, better wear resistance, and lower hardness. However, the presence of Si69 reduced the crosslink efficiency of ESBR and completely inhibited the crosslinking of VMQ, which caused the composite to show higher tan δ value at 60 °C than the A151 composite.

Correlation of silane grafting density with rheological properties of silica filled rubber: Coupling of flow and temperature

The structure and rheological properties of butadiene rubber / silica / silane nanocomposites were investigated in this paper. The structure of the nanocomposites was characterized by NMR analysis which allowed the quantification of silane grafting rates. A time temperature equivalence parameter was defined as a unique mixing conditions parameter taking into consideration both temperature and mixing speed. A direct law between grafting rates and mixing conditions was found. Rheological properties were characterized by creep and elongation measurements, and the influence of mixing speed and temperature on these properties was determined. A competition between grafting and breaking mechanisms on elastic entities, respectively promoted by the increase of temperature and of speed, was highlighted. Therefore this paper shows correlations between temperature and speed process conditions, the mixture’s structure and its rheological properties. Thanks to these results, a model of the structure of the silica-filled rubber was proposed; unusual rheological properties stem from the formation of clusters of connected aggregates by way of grafted rubber.

Dependence of nonlinear elasticity on filler size in composite polymer systems

Nanosized filler particles enhance the mechanical properties of polymer composites in a size-dependent fashion. This is puzzling, because classical elasticity is inherently scale-free, and models for the elasticity of composite systems never predict a filler-size dependence. Here, we study the industrially important system of silica-filled rubbers, together with a well-characterized model-filled crosslinked gel and show that at high filler content both the linear and nonlinear elastic properties of these systems exhibit a unique scaling proportional to the cube of the volume fraction divided by the particle size. This remarkable behavior makes it possible to predict the full mechanical response of particle-filled rubbers for small but finite deformations based solely on the rheology of the matrix and the size and modulus of the filler particles.

Observation of Silica-filled Rubber Using Simultaneous Measurement of Time-resolved Ultra-small Angle X-ray Scattering and Viscoelastic Properties

Observation of Silica-filled Rubber Using Simultaneous Measurement of Time-resolved Ultra-small Angle X-ray Scattering and Viscoelastic Properties

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.