Triethoxysilylpropyl Tetrasulfide Research Articles

MODIFICATION OF MIXTURES BASED ON ETHYLENEPROPYLENE RUBBER AND SILICON ACID FILLER

The aim of the work was to study the effect of bis-(triethoxysilylpropyl)-tetrasulfide (TESPT) mixed with carbon black N330 in a ratio of 1:1, as a technical product OFS 6945 on the structure and properties of rubber mixtures and rubbers based on ethylene propylene rubber of the brand Vistalon 2504N and silica filler (KKN) of the brand Rosil-175, taken at a dosage of 30 wt. h. per 100 wt.h. rubber. The content of TESPT was 0.035, 0.050 and 0.070 mmol / 100 g of rubber. A group of vulcanizing agents included sulphur, thiuram, captax, zinc oxide and technical stearin. Rubber mixtures were prepared on rollers Lb 320 160/160. Organosilane was injected into rubber at the same time as Rosil-175. The homogeneity of the filler distribution in the finished mixtures was evaluated based on the results of testing samples on the RPA-2000 vibrorheometer. Vulcanization characteristics were determined using an MDR-2000 device. The structure of mixtures and rubbers was studied by the method of equal swelling of samples in toluene. It is shown that with the increasing content of TESPT, the proportion of bound rubber in a three-component mixture of the rubber – filler – organosilane increases due to the formation of interfacial connections. The uniformity of distribution of silica fillers in rubber matrix also increases. Workability of the mixtures on roller equipment improves. The rate of cross-linking in the core period and the degree of cross-linking of macromolecules at the same time curing increase as well. As a result, the elastic-strength properties of rubbers determined in the static test mode are improved, the best complex of which is provided with an organosilane content of 0.050 mmol/100 g of rubber.

Potential Eco-friendly Application of Sugarcane Bagasse Ash in the Rubber Industry

Inorganic fillers (mainly obtained from residue recycling/reuse operations) have been widely used as an alternative reinforcement in polymer composites to replace commercial silica. In this study, we analyze the interaction between Sugarcane Bagasse Ash (SCBA) and natural rubber using Bis[3-(triethoxysilyl)propyl] Tetrasulfide (TESPT) as the silane coupling agent and Tetramethylthiuram Disulfide (TMTD) as the curing alternative system. Based on the results, we were able to validate their influence on the physical properties of the obtained composites. In particular, the coupling agent used in this study led to an improved interaction between SCBA and the polymer matrix, which was corroborated by the resulting mechanical response (stress–strain tests) and DMA (tensile strength) characterizations. Therefore, these findings encourage further research to explore a process at the industrial level to reuse SCBA waste and, thus, contribute to the protection of the environment.

Surface modification of oxidized carbon fibers by grafting bis(triethoxysilylpropyl) tetrasulfide (TESPT) and rubber sizing agent : Application to short carbon fibers/SBR composites

Bis(triethoxysilylpropyl) tetrasulfide (TESPT) with ethoxysilyl and tetrasulfide groups were grafted successfully on the oxidized short carbon fibers (CF) surface in order to create a strong continuous network between short CF and styrene butadiene rubber (SBR). The Hummer's method has been used for initial surface modification of short CF by solution oxidation (CF-OH) to establish hydroxyl groups required for the grafting process. Furthermore, a novel “rubber sizing agent” on the surface of short CF was applied by solution of SBR for the first time (CF-OH-g-TESPT-SBR). The surface of the modified short CF analyzed using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM) micrographs to confirm the oxidation, grafting of TESPT and rubber sizing agent onto the CF surface. Then the SBR reinforced with different loading of modified short CF composites were compounded in a two-roll mill. The highest value of electrical conductivity and thermal properties was achieved at 5 phr modified short CF in SBR composite. Tear strength was increased to 24.5% in the transverse direction of the modified short CF. This has agreement with the results of surface morphology of fracture and weight loss of the composites by SEM and TGA, respectively.

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.

Material identification for improving the strength of silica/SBR interface using MD simulations.

Comprehensive molecular dynamics simulations are conducted to identify material modifications which can improve strength and reduce hysteresis losses at the nanointerfaces formed between silica, silane coupling agent (SCA) and styrene-butadiene rubber (SBR), all of which are important ingredients of green tyres. Improving strength and reducing hysteresis losses at such interfaces are expected to reduce rolling resistance (RR), consequently lowering greenhouse emissions. Various modifications considered in this work include a variety of SBR blends, several SCA and surface occupancies of SCA on the silica surface. To tackle a large number of combinations possible and identify modifications which may improve the nature of the interfaces, a hierarchical computational framework is developed. The reduced sample space of such material modifications may be more amenable to comprehensive and computationally or experimentally expensive studies. It was found that some amino-based SCA in combination with certain blends of SBR can improve the interfaces strength and lower hysteresis losses, when compared to the commonly used bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT), which is a sulphur-based SCA.

Contribution of filler–filler interaction and filler aspect ratio in rubber reinforcement by silica and mica

The reinforcement degree offered by silica as a spherical filler with low aspect ratio and high filler–filler interaction was compared with mica as a platelet filler with higher aspect ratio and lower filler–filler interaction. By replacing half of the carbon black with silica or mica in a typical formulation, rubber composites were prepared and their properties were evaluated under two conditions: In the first one, the impact of increasing the amount of a chemical surface modifier, namely silane TESPT (bis triethoxysilylpropyl tetrasulfide), was investigated and in the second one, the increasing amount of a physical modifier namely DPG (diphenyl guanidine) on the performance of the two fillers was explored. The resulting composites were subjected to physico-mechanical experiments including the bound rubber, tensile test, and the dynamic mechanical thermal analysis (DMTA). Results indicated that the greater amount of filler–filler interaction resulting from the higher SiO2 and hydroxyl content in silica has a dominating role over the aspect ratio of mica which is then led to a remarkable difference in their bound rubber. However, the mica-containing composites were capable of competing with silica when the DPG was used. Nevertheless, the compound only containing carbon black with 19.7 MPa of tensile strength and 24.4 kgf/cm of tear strength showed the best mechanical properties among other fillers, and by replacing 30 phr carbon black, these properties decreased approximately 15 ± 3%. Based on DMTA findings, promising data were obtained for the mica-reinforced rubbers with regard to the tire application.

Enhanced interfacial and mechanical performance of styrene-butadiene rubber/silica composites compatibilized by soybean oil derived silanized plasticization

Silanized plasticizer (SP) was chemically derived and synthesized from soybean oil (SBO) co-vulcanized with bis-(3-(triethoxysilyl)-propyl) tetrasulfide (TESPT) by using the sulfur-accelerated curing system. SP extended styrene-butadiene rubber (SBR)/silica composites have been studied for their improved filler dispersion through coupling interaction at the SBR/silica interface. The effect of SP on cross-link density, thermal, static and dynamic mechanical properties of SBR composites related to the tire performance, were investigated. The results revealed that SP enhanced tensile strength, modulus, and hardness of the composites due to an improved matrix-filler interaction together with an excellent control over oil migration. Further improvement was observed for SP with increasing TESPT content, what was related to the increase in cross-linking density, and bound rubber content of the composite materials. Morphology and reduced Payne effect confirmed the silica particles have an even dispersion throughout the SBR matrix. The dynamic curves indicated the highest efficacy for wet and dry traction performances of SP extended SBR composites comparing to unmodified reference sample. This research provided the effect of SP as a novel reactive bio-plasticizer to improve the performance of SBR/silica composites for green tire manufacture, while being eco-friendly.

Solving “magic triangle” of tread rubber composites with phosphonium-modified petroleum resin

The wet traction, rolling resistance and abrasion resistance have rarely been improved simultaneously in tread rubbers, which is regarded as “magic triangle” in tire industry. Recently, we have demonstrated that phosphoniums are effective in lowering rolling resistance of tread via catalyzing the interfacial silanization. In addition, incorporating the C5/C9-based petroleum resin into tread formulation is a well-established technology toward high wet traction. Accordingly, we aim to solve the “magic triangle” dilemma by using phosphonium-modified petroleum resin (PSR), which is prepared through a two-step reaction. PSR is incorporated into the silica-filled styrene-butadiene rubber (SBR) composites with bis [3-(triethoxysilyl)propyl] tetrasulfide (TESPT). Due to the electrostatic interaction between PSR and silica, the dispersion of silica is improved. Moreover, PSR exhibits catalytic effect on the interfacial silanization, leading to the improvement of interfacial interactions. With incorporation of 2 phr of PSR, the tan δ at 0 °C and abrasion loss of the rubber composite are increased by 19% and decreased by 28%, respectively, which suggests that the wet traction and abrasion resistance are increased. The tan δ at 60 °C of the rubber composite is decreased by 14%, indicating that the rolling resistance is decreased. In addition, the overall excellent “magic triangle” performance of a typical tread rubber is also demonstrated by incorporating PSR, indicating that PSR has great potential in practical applications. We envisage that this study provides a new solution for high-performance tread rubber for green tires.

Poly(lactic acid)-based Composites Incorporated with Spent Coffee Ground and Tea Leave for Food Packaging Application: A Waste to Wealth

Polymer composites of polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT) incorporated with spent coffee grounds (SCG) and tea leave (TL) were prepared by two-roll mill mixer. 4,4-methylene diphenyl diisocyanate (MDI), toluene 2,4-diisocyanate (TDI), and bis[3-(triethoxysilyl) propyl] tetrasulfide (TESPT) were used as coupling agents. The influences of coupling agent types, coupling agent content, and weight ratios of polymer to filler on the mechanical properties, melt flow index, and overall migration (OM) of the composites were studied. The results showed that MDI and TDI had better performance compared to TESPT for both tensile and elongation at break. The tensile strength and elongation at break of PLA+PBAT/SCG composites with weight ratio of polymer to filler = 70/30 increased from 19.6 MPa to ∼23.0 to 25.0 MPa, and 6.6 to ∼10.0%, respectively when using these coupling agents (MDI and TDI) of 3 g/100 g polymers. Moreover, the addition of MDI and TDI greatly increased the viscosity of the melted composites (4-fold), while TESPT made the viscosity decrease. However, the mechanical properties of the composites decreased drastically with increasing SCG proportion. Compared to PLA+PBAT/SCG, interfacial adhesion of PLA+PBAT/TL was higher confirming by tensile strength and SEM images. However, there was no significant difference between PLA+PBAT/TL and PLA+PBAT/SCG composites in terms of elongation at break, impact strength and melt flow index. The OM of PLA+PBAT/SCG and PLA+PBAT/TL composites with coupling agents were in the range of ∼0.03–0.28 mg/dm2 when using 3% acetic acid and 10% ethanol as food simulants, which not excess the migration limit (10 mg/dm2) according to Food Contact Materials EU No. 10/2011 legislation. It means that they might be safe for use as food contact materials for packaging and containers.

An innovative approach to utilize waste silica fume from zirconia industry to prepare high performance natural rubber composites for multi-functional applications

Silica fume (SF) is silica-rich amorphous waste by-product obtained during zirconium silicate electrofusion process. The key objective of the study was to determine the efficiency of SF as a reinforcing filler in Natural Rubber (NR) compounds vis a vis the conventional filler, high abrasion furnace (HAF) black. Inter-particle distance and particle size distribution analysis from Transmission Electron Microscopy exhibited homogeneous dispersion of filler in hybrid composite (NR SF20/HAF30) with Bis[3-(triethoxysilyl)propyl] tetrasulfide (TESPT). NR composite with 20 phr SF loading improved modulus by 107%, tensile strength by 12%, and tear strength by 28% over gum NR. Hybrid composite showed 111% increase in modulus than NR SF20 composite. Theoretical modelling of Young's modulus with volume fraction of filler quite fit with Guth-Gold equation. Hybrid composite with TESPT showed 72% reduction in heat build-up compared to NR HAF50 composite. Thermal stability improved by 6 °C and rolling resistance reduced by 64% for hybrid TESPT composite compared to NR HAF50 composite. Constrained region in NR composites obtained from dynamic mechanical analysis showed improved rubber-filler interaction in hybrid TESPT composite. Hence, this work not only provides a new approach to utilize industrial waste but also provides for a high performance NR composite at low cost.

Estimation of silica flocculation in SBR/BR compounds reinforced with different silica contents from their rheocurves

ABSTRACTThe rheocurves of silica‐filled styrene–butadiene/polybutadiene rubber (SBR/BR) compounds containing 3‐octadecyltriethoxy silane (OTES) and bis‐[triethoxysilylpropyl]tetrasulfide (TESPT) were investigated to examine the effects of silica content and silanes on silica flocculation during mixing and cure. SBR/BR compounds without curatives were also prepared to infer the effect of cure on silica flocculation. The maximum torque of the compounds could be deconvoluted to individual source torques such as silica flocculation during mixing and cure, crosslinking of rubber, and coupling between rubber and silica by assuming the independence of silica flocculation from cure and coupling. Torque due to silica flocculation increased with the silica content of the SBR/BR compounds, but its effect was significantly reduced by the addition of OTES or TESPT. TESPT suppressed silica flocculation and facilitated coupling, thus yielding enhanced tensile properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48559.

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.

Physiochemical characterization of soybean oil derived silanized factice and its interaction with styrene butadiene rubber/silica composite

Abstract Soybean oil-based silanized factice (SF) was prepared and its compatibility with styrene butadiene rubber (SBR)/silica composite was evaluated. Characterization of SF, obtained by the inter-mixing of soybean oil (SBO), sulfur and bis-(3-(triethoxysilyl)-propyl) tetrasulfide (TESPT) with curing additives, was investigated and compared with the controlled factice (CF) which does not possess any TESPT. Free sulfur and acetone extract values of the SF were studied with varying TESPT content and optimum values were recorded. Structural differences were elucidated by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), where disappearance of peaks at 3010 cm−1 and 1650 cm−1 belonging to the stretching vibrations of the olefinic bonds in SBO, occurred with the formation of SF. The results were further confirmed by1H NMR spectroscopy where the signals corresponding to the vinylic and allylic protons were chemically shifted to 5.3 ppm and 2.8 ppm, respectively. Thermal changes were demonstrated with varying TESPT content. The morphology of the SF was elucidated by optical microscopy and scanning electron microscopy (SEM), which showed the fine structure following the addition of TESPT. Together with plasticization, the SF exhibited an excellent improvement in tensile strength compared with the SBR/silica composite due to the presence of interfacial interactions. This work proposes an approach to the preparation and characterization of bio-oil derived polymers for rubber composites.

Enhanced wettability and adhesion of carbon fibers with polyimide resin interfaces via grafted modified SiO2 nanoparticles

ABSTRACTFunctionalized modified SiO2 was prepared by a mild and simple dip coating method, and a layer of functionalized modified SiO2 coating was introduced onto the carbon fiber surfaces not only to improve the surface wettability and activity of carbon fiber, but also strengthen the interphase of the carbon fiber/polyimide composite. The successful functionalization of SiO2 by bis[3-(triethoxysilyl)propyl] tetrasulfide (TESPT) silane was confirmed. Moreover, a uniform coating with well-dispersed particles on a carbon fiber surface was achieved with a 1.0 wt% addition of TESPT-modified SiO2 (TESPT@SiO2) particles. Under this condition it was observed that the interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) augmentation was 26.37% and 38.27%, respectively, in comparison with carbon fiber composite coated only with polyimide resin. The functionalized modified SiO2 coating could effectively heal the surface defects of fiber, and the fiber tensile strength increased by more than 10.61%. This study provides a scalable, simple, and cost effective method of simultaneously increasing the interfacial strength of composites.

Tensile Properties and Dynamic Mechanical Behaviour of Natural Rubber Compound Filled with Rice Husk Silica Produced via Solvent-Thermal Extraction Method

This study highlighted the effect of incorporation of rice husk silica (RHS) on the tensile properties and dynamic mechanical behaviour of natural rubber (NR) compounds. High purity RHS was synthesised by solvent-thermal extraction method, which was inspired by TAPPI T204 cm-97 and TAPPI T264 cm-97 standards with some modifications. The extraction method had successfully produced RHS with 99.9% of silica content and surface area of 234.25 m2/g. The incorporation of RHS in NR showed increment in tensile properties compared to unfilled NR. Further improvement was recorded by surface modification of RHS with 1 wt. % bis (triethoxysilylpropyl) tetrasulfide (TESPT). The modification of RHS with TESPT increased the rubber-filler interaction between RHS and NR matrix, hence enhancing the strength-related properties. The modified RHS-NR also recorded highest storage modulus, and the presence of RHS in the NR compound had slightly shifted the glass transition temperature (Tg) to a higher value. This confirmed that the strong rubber-filler interaction had increased the rigidity of the compounds and restricted the mobility of the rubber chains.

Implications of the Use of Silica as Active Filler in Passenger Car Tire Compounds on Their Recycling Options.

Tires are an important vehicle component, as car handling, safety and fuel economy depend for a major part on the tire composition and construction. As a consequence, tires are improved continuously. The most prominent improvement in the recent past was the use of a silica-silane filler system in passenger car tread compounds, instead of traditionally used carbon black. For recycling and re-use of end-of-life car tire rubber one of the most promising recycling methods is devulcanization: re-plasticizing the vulcanized rubber by selectively breaking the sulfur bridges between the polymer molecules. In the present paper, the influence of silica, which is present in the passenger car tires granulate, on both devulcanization and subsequent revulcanization, is investigated. In a step-wise approach it is shown that the presence of silica influences both devulcanization and revulcanization. The best tensile strength of the revulcanizate, using a carbon-black-based revulcanization formulation, was 5 MPa. This could be improved to 6.5 MPa by using 2.8 phr of 1,3-DiPhenylGuanidine (DPG) in the revulcanization formulation. After addition of a silanization step during revulcanization by adding 3.2 phr bis[3-(TriEthoxySilyl)Propyl] Tetrasulfide (TESPT), a silane, to the formulation, the tensile strength of the revulcanizate was further improved to 8 MPa. With these results it is shown that the silica in the granulate can be used to improve the revulcanization properties. To check the benefits of using pure tire tread material for the devulcanization and subsequent revulcanization, of both a carbon black and a silica-based virgin tread compound, it is shown that a tensile strength of the revulcanizate of 13 MPa can be reached. This shows the potential of devulcanized rubber when the various tire components are separated before whole car tire material is granulated as the beginning of the recycling.

Mechanical, thermal, morphological, and curing properties of geopolymer filled natural rubber composites

ABSTRACTThe main objective of this work was to investigate influence of natural rubber (NR) types on mechanical, thermal, morphological, and curing properties together with relaxation behavior of geopolymer filled NR composites with and without bis(triethoxysilylpropyl) tetrasulfide (TESPT) silane coupling agent. Three alternative types of NR: unmodified NR, and epoxidized NR with 25 (ENR‐25) or 50 mol % epoxide (ENR‐50) were exploited. Rubber compounds filled with GP particles were prepared in an internal mixer at 60 °C and 130–150 °C for the ones with and without TESPT, respectively. It was found that incorporation of GP significantly affected cure characteristics and mechanical properties of the rubber composites. That is, decreasing cure time was observed from 11.6, 3.2, and 7.0 min in gum NR, ENR‐25, and ENR‐50 to 6.9, 2.1, and 5.0 min in NR/GP, ENR‐25/GP, and ENR‐50/GP compounds, respectively. Furthermore, the ENR‐25/GP and ENR‐50/GP composites showed finely dispersed GP particles which indicate high filler–rubber interactions. The in situ silanization with TESPT in rubber composites enhanced the mechanical properties of NR/GP and ENR‐25/GP composites but no such enhancement was found in the ENR‐50/GP composite. This matched the observations of Payne effect, maximum tan δ, and stress relaxation properties of the composites. We found that the ENR‐25/GP composites exhibited the best overall properties. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47346.

The influences of silane coupling agents on rheological properties of bentonite/nitrile butadiene rubber nanocomposites during curing process

In the present work, the influences of different silane coupling agents (SCA) on the rheological behaviors of Bent/NBR nanocomposites during the curing process were investigated. The nanocomposites were prepared with a green method which is simple and free of organic solvents. The dispersion state and filler–polymer interfaces were analyzed with XRD, TEM, and SEM while rheological behaviors of the nanocomposites were explored with a rubber processing analyzer (RPA). (3‐Mercaptopropyl)trimethoxysilane (MPTMS) and bis[3‐(triethoxysilyl)propyl] tetrasulfide (TESPT) both improved the dispersion state of bentonite in the matrixes significantly. MPTMS increased the crosslinking density by forming single sulfur bonds while TESPT worked as a plasticizer and delayed the formation of crosslinking during curing process. [3‐(2‐Aminoethylamino)propyl]triethoxysilane (AEAPTMS) led to reversible filler–rubber interactions, which was the main reason for the low elastic torque of the vulcanized nanocomposites. J. VINYL ADDIT. TECHNOL., 25:236–242, 2019. © 2018 Society of Plastics Engineers

HYBRID SILANE TECHNOLOGY IN SILICA-REINFORCED TREAD COMPOUND

ABSTRACT The use of a silane coupling agent in silica-reinforced tread can effectively improve silica dispersion in the rubber matrix and strengthen the interfacial interaction between the rubber and filler; this is beneficial to the enhancement of tire grip under wet conditions and reduces tire rolling resistance. The monofunctional silane n-octyltriethoxysilane (OTES) can react with the silanol group of the silica surface and hence improve silica dispersion. It can also suppress silica reaggregation during tire processing. Two hybrid silanes, OTES and 3-mercaptopropylethoxy-bis(tridecyl-pentaethoxy-siloxane) (Si747) or OTES and bis(triethoxysilylpropyl)tetrasulfide (TESPT), were filled in silica-reinforced tread compounds. The effect of the two hybrid silanes on the silica was investigated via Fourier transform infrared spectroscopy and thermogravimetric analysis. The processing ability of the silica-filled compounds and the performance of the vulcanizates were also investigated. Our experimental results show that OTES is able to further react with the silica following reaction between the TESPT and silica and that it should be added when the molar amount of TESPT or Si747 is constant, to prevent reduction of the cross-link density. Furthermore, the addition of OTES can extend the scorch time, especially in Si747 and OTES compounds. In addition, OTES can improve silica dispersion and only has a slightly negative effect on the physical properties of vulcanizates.

Exploring the comparative effect of silane coupling agents with different functional groups on the cure, mechanical and thermal properties of nano-alumina (Al2O3)-based natural rubber (NR) compounds

The surface of sol–gel-synthesized nano-alumina (Al2O3) was modified by three types of silane coupling agents with different specific functionalities, namely 3-aminopropyltriethoxysilane (APTES), triethoxy(octyl)silane (OCTEOS) and bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT). The aim of the present study was to explore the effect of both unmodified and surface-modified nano-Al2O3 on the cure characteristics, mechanical properties, cross-link density and thermal stability of natural rubber (NR) nanocomposites. Results revealed that silane coupling agents were very effective to enhance maximum rheometric torque (R∞) and mechanical properties like modulus and tensile strength of nano-Al2O3-based NR nanocomposites. APTES offered higher value of cure rate index for NR compounds as compared to two other silane coupling agents. Among three silane coupling agents, TESPT provided highest improvement in the mechanical properties of NR/nano-Al2O3 composites. This might be explained by considering excellent improvement in the cross-link density of NR compounds in the presence of TESPT-treated nano-Al2O3. The incorporation of both TESPT- and OCTEOS-modified nano-Al2O3 into the NR matrix markedly improved the thermal stability of NR composites. Moreover, bi-functional silane TESPT not only increased the hydrophobicity of nano-Al2O3, but also improved the probability of sulfur cross-linking during cure process of NR compounds.