Dual Filler System Research Articles

Synergistic behavior of dual filler system (n‐Si3N4/COOH‐MWCNT) on the mechanical, tribological, curing, and corrosion characteristics of epoxy hybrid nanocomposites

AbstractEpoxy hybrid nanocomposites reinforced with silicon nitride nanoparticles (SiN) and carboxylic acid‐modified multiwalled carbon nanotubes (COOH‐MWCNT) were prepared by hand layup. These hybrid nanocomposites have not undergone thorough investigation in the fields of mechanical, tribological, and corrosion‐resistant characteristics. The 0.25/0.5 SiN/MWCNT hybrid nanocomposite displayed improvement in elongation by 190% and fracture toughness by 360%. The effect of dual filler system on the wear and friction properties of the composite was investigated. The influence of silicon nitride and hybrid fillers the curing characteristics of epoxy was examined using Fourier transform infrared spectroscopy (FTIR). From differential scanning calorimetry (DSC), it was found that the use of dual fillers in the epoxy system reduced the residual heat of reaction and curing time by 15%. In a highly corrosive environment (3.5% NaCl), TAFEL polarization showed that 0.5/0.5 SiN/MWCNT epoxy hybrid coating on mild steel (MS) increased protection against corrosion by 30%. The dispersion of nanofillers and their interactions were verified using high‐resolution transmission electron microscopy (HR‐TEM). The morphology of the fracture, wear, and corroded surfaces were examined by field emission scanning electron microscopy (FE‐SEM). SiN manifested a synergistic effect with MWCNTs making it a superior reinforcement at very low content.

Interplay of regio-selectively modified dendritic silica particles with styrene-butadiene rubber: The route towards better tires with lower rolling-resistance and higher grip

The current study presents for the very first time to our knowledge the synthesis, characterization, and application of regio-selectively modified dendritic silica particles (RMDS) in tire rubber composites. So far, no study has ever reported mesoporous silica bringing greater mechanical properties than small fractal precipitated silica. With mechanical testing (DMA, tensile strength) and advanced imaging (TEM-EDS, HIM-SIMS, micro-CT), it was demonstrated that dendritic particles enable superior mechanical reinforcement of rubber-based nanocomposites without any drawback as usually reported with fractal fillers. On one side, their modified porous surface mimics the porous aggregates formed by classic fillers, enabling the rubber chains to permeate the pores and closely interact with the particles. On the other side, unlike fractal fillers, RMDS consist of single particles instead of aggregates, and therefore do not suffer as much from the Payne effect and irreversible dislocations under mechanical solicitations. Also, the excellent dispersibility of RMDS allows to combine them with small amount of fractal filler. Dual filler composite shows superior mechanical performances versus materials using one filler family, leading to higher reinforcement, better traction and rolling resistance indicators. The use of porous particles as “unbreakable” fillers for rubber with a small amount of fractal silica as additive fillers paves the way for novel reinforcing dual-filler systems to be used in disruptive tires technology.

THERMALLY CONDUCTIVE DURABLE STRAIN SENSORS FOR NEXT-GENERATION INTELLIGENT TIRES FROM NATURAL RUBBER NANOCOMPOSITES

ABSTRACT A substantial knowledge gap persists in the material development of smart tires for future self-driving automobiles, which can increase both the vehicles' performance as well as the safety of the passengers. Due to the very high stiffness of conventional strain sensors compared to the softer rubber compound used as the tire tread material, an inaccurate representation of tire deformation characteristics is anticipated. Here, a comprehensive characterization of the electrical conduction and strain sensing behavior of a natural rubber (NR)-based commercial tire tread composite combining the reinforcement of a carbon black-conductive nanofiber dual filler system was carried out for the very first time. The incorporation of as low as 2 wt.% of carbon nanotubes (CNT) and graphite nanofibers (GNF) could increase the electrical conductivity of the control compound by two orders of magnitude compared to the control compound. The gauge factor observed was much higher than the value reported for metallic or polyvinylidene difluoride (PVDF) based stain sensors developed for this application. A 25% enhancement in thermal conductivity was also observed. Thus, the developed composites have the potential to be used as in situ strain sensors so that the problems of debonding and heating differences in the sensor–rubber interfaces in tires can be avoided in future.

Nanofiber‐Carbon black dual filler reinforced sustainable high‐performance Natural Rubber nanocomposites

AbstractIn the present work, uncured and cured properties of high‐performance, sustainable Natural Rubber nanocomposites developed by leveraging the unique synergy between carbon black and fibrous nanofillers such as silicon carbide, carbon nanotubes, and aramid nanofibers were investigated. Reinforcement in these composites was analyzed using the properties of the unvulcanized compounds, which were then correlated with those of the vulcanized compounds. A 50% increment was recorded for the bound rubber content of the nanocomposites, which resulted in tremendous improvements in the reinforcement index and tensile strength of the unvulcanized nanocomposites. In contrast, the die swell index came down compared with the control compound. The formation of a percolating network due to the presence of high aspect ratio fibers resulted in a higher Payne effect in hybrid nanocomposites, which was confirmed from the scanning and transmission electron microscopy. The 100% modulus, 300% modulus, and tensile strength of the unvulcanized nanocomposites recorded an improvement of 80, 121, and 450%, respectively, by the incorporation of nanofibers. The molecular aspects of reinforcement were elucidated from theoretical calculations using Mooney–Rivlin plots. It was presumed that the improved reinforcing efficiency of the nanofibers resulted from restricted mobility of elastomer chains due to the presence of the dual filler system.

Improved mechanical and rheological behavior of nitrile rubber reinforced with multi-walled carbon nanotubes and carbon black dual-filler system

The use of carbon nanotubes at low content in the production of rubber nanocomposites has already been proven promising, leading to significant improvements in overall mechanical properties of these materials. The addition of dual-filler systems in rubber compounds can be advantageous, leading to synergistic improvements. In this work, the effect of dual-filler system containing carbon black and multi-walled carbon nanotubes on mechanical and rheological properties of nitrile rubber matrices was evaluated. Increasing nanotube content has been proven effective in optimizing mechanical performance of nitriles. Based on a 40 phr carbon black reference compound, the dual-filler system containing 10 phr of nanotubes and 40 phr of carbon black presented noticeable results in tear and tensile strenght, hardness, besides higher stress relaxation. Formation of agglomerates are highlighted herein as a point of caution.

Excavating the unique synergism of nanofibers and carbon black in Natural rubber based tire tread composition

AbstractThe article portrays the synergistic reinforcement of new generation nanofillers such as silicon carbide nanofibers (SiCs), carbon nanotubes (CNTs), and graphite nanofibers (GNFs) when used along with carbon black (CB) in a typical tire tread composition. The unique synergism in these composites, which were fabricated by a liquid phase mixing method, was reflected in their enhanced failure resistance and dynamic mechanical properties. At 4 phr loading of the nanofiber, the tensile strength, tear strength, modulus at 300% elongation, storage modulus, rolling resistance, and abrasion resistance were improved by 29, 45, 36, 110, 15, and 14%, respectively. The role of nanofibers in the development of a hybrid microstructure was investigated by scanning and transmission electron microscopy. Tribological characteristics were studied using a Laboratory Abrasion Tester (LAT 100), and the abrasion loss of the samples was correlated with energy dissipation occurring during the process. The fatigue properties indicated the ability of the CB‐nanofiber dual filler system to arrest crack growth. The study also serves to establish a correlation between the wear loss and fatigue properties of the hybrid nanocomposites containing different fibrous nanofillers. A mechanism of reinforcement by hybrid fillers is proposed.

Decoupling the Contributions of ZnO and Silica in the Characterization of Industrially-Mixed Filled Rubbers by Combining Small Angle Neutron and X-Ray Scattering.

Scattering techniques with neutrons and X-rays are powerful methods for the investigation of the hierarchical structure of reinforcing fillers in rubber matrices. However, when using only X-ray scattering, the independent determination of the filler response itself sometimes remains an issue because of a strong parasitic contribution of the ZnO catalyst and activator in the vulcanization process. Microscopic characterization of filler-rubber mixtures even with only catalytic amounts of ZnO is, therefore, inevitably complex. Here, we present a study of silica aggregates dispersed in an SBR rubber in the presence of the catalyst and show that accurate partial structure factors of both components can be determined separately from the combination of the two scattering probes, neutrons, and X-rays. A unique separation of the silica filler scattering function devoid of parasitic catalyst scattering becomes possible. From the combined analysis, the catalyst contribution is determined as well and results to be prominent in the correction scheme. The experimental nano-structure of the ZnO after the mixing process as the by-product of the scattering decomposition was found also to be affected by the presence or absence of silica in the rubber mixture, correlated with the shear forces in the mixing and milling processes during sample preparation. The presented method is well suited for studies of novel dual filler systems.

BETTER BALANCE OF SILICA-REINFORCED NATURAL RUBBER TIRE TREAD COMPOUND PROPERTIES BY THE USE OF MONTMORILLONITE WITH OPTIMUM SURFACE MODIFIER CONTENT

ABSTRACT Reinforcement of silica in tire tread compounds is known to reduce hysteresis or energy loss, which leads to a production of energy-saving tires. Even though silica–silane technology has been well established, further development to enhance its performance is still needed. One of the approaches is to use hybrid or dual filler. The use of silica-organomodified montmorillonite (MMT) dual filler in the reinforcement of natural rubber (NR) truck tire tread compounds is investigated. The NR-MMT master batches were prepared by using the in situ organomodified and latex compounding method. Because the surface-modifying agent or surfactant is a key factor in determining the level of MMT dispersion in the rubber matrix, the effect of quaternary amine salt (Q) contents on mechanical and dynamic properties of NR tread compounds reinforced by silica-MMT was studied. The results revealed that MMT and Q can effectively reduce the filler–filler interaction and complex viscosity owing to a good dispersion of MMT and silica in the NR matrix and Q, which acts as a dispersing agent in addition to the silane coupling agent used in the compound, leading to improvement in tensile, abrasion resistance, and dynamic mechanical properties with an increasing amount of Q. Furthermore, at the optimum content of the surfactant used (36 wt%), the silica-MMT–reinforced NR exhibited improved tensile strength (+4%), wet grip, and rolling resistance, respectively, as indicated by loss tangent at 0 °C (+6%) and 60 °C (−15%), while maintaining a modulus at 300% strain and abrasion resistance as compared with the silica-NR reference compound. Such a dual-filler system demonstrates its potential use for tire treads with better performance.

Cyclic uniaxial stress-strain test and rheological behavior of carbon black/metakaolin dual-filler system used in nitrile rubber compounds

Abstract Dual-filler systems may promote synergetic effects to mechanical properties in rubber compounds. The use of metakaolin (M) and carbon black (C) in nitrile rubber (NBR) compounds was studied with respect to rheological and non-obvious mechanical tests. The reaction order of the curing process was not influenced by the filler system, however, carbon black presented a slowdown effect in the vulcanization process. Cyclic uniaxial tests indicated that stress softening was observed even for unfilled compound; however, notably only-carbon black filled compound experienced the highest values for decrease in stress softening after second cycle. Although the polymer chains alone are the main driving force of hysteresis, it was more negatively affected by carbon black than by metakaolin. Moreover, dual filler composites experienced balanced results for stress softening, and other properties as Payne effect and complex viscosity.

Role of hydrogen in affecting the growth trend of CNT on micron spherical silica gel

Grafting CNTs onto substrates such as fibres and microparticles offers an alternative approach to tackle the issues associated with dispersion in a composite matrix, as well as additional benefits (hybrid effects) provided by these dual-filler systems. One approach to obtain such hybrid systems is the direct growth of nanotubes on the supporting fibre or particles. Previous study has shown that the CNTs would grow on the silica microparticles with the morphology closely related to the operating conditions such as temperature and time. However, the role of hydrogen in affecting the tube’s morphology was not explored before. The particles were synthesized via chemical vapour deposition (CVD) method. Spherical silica gel with 40 − 75 μm diameter was used as the substrate. Toluene and ferrocene were used as the hydrocarbon and catalyst source, respectively. The reaction time was kept for four hours while the temperature was maintained at 850°C. The FESEM and TEM investigation proved that the flow hydrogen during reaction caused a tremendous difference in the outer diameter of the synthesized CNTs. Relatively thin CNT was observed under 50 ml/min of hydrogen flow compared to the particles synthesized without hydrogen. Raman spectroscopy of the CNTs revealed three bands; the disorder-induced D mode (∼1321 cm−1), the tangential G mode (∼1570 cm−1) and second order G′ mode (∼2642 cm−1). Raman analysis shows that the synthesized CNTs exhibited all these peaks, confirming the existence of CNTs. As G peak is more intense than D peak for all samples synthesized under hydrogen flow, it can be concluded that CNTs synthesized is indeed of high quality. It can be confirmed that hydrogen plays an important role in influencing the morphology of the synthesized tubes.

Processability Behaviour of Dual Filler Systems Reinforced Epoxised Natural Rubber

Rheological studies of polymers are of great importance in optimizing the processing conditions and in designing processing equipments like injection molding machines, extruders, and dies required for various products. Melt rheological studies give us valuable viscosity data that will be helpful in optimizing the processing conditions. Parameters like melt viscosity as a function of shear rate or shear stress and temperature have become more and more important. Previous study indicated that the flow behaviour of the compound depends on the filler loading. Lesser elastic torque was found with compound containing lower filler content as compared to higher filler content. In this work, effect of dual filler, based on Carbon Black / Silica filled Epoxidised Natural Rubber (ENR) compound was investigated. A total of 80phr of filler content based on passenger tyre tread formulation was used in the experiment. The compounds were prepared by melt mixing in tangential type of an internal mixer. The rheological and the processability properties of the compounds were determined using three different testing instruments namely Capillary Rheometer, Mooney viscometer and Rubber Process Analyzer (RPA). A variation of shear rates (ranging from low to high) was performed, in order to better reflect the actual processing condition in rubber manufacturing. It was found that ENR mix with ratio silica to carbon black 70:10 exhibited the best flow behaviour and processability properties as compared to control and other mixes.

The effect of coupling agents on silicate-based nanofillers/carbon black dual filler systems on the properties of a natural rubber/butadiene rubber compound

Nanofillers have been introduced a few years ago, but their application in elastomers is still a challenge. With the existing rubber processing equipment and constraints of rubber mixing, dispersion of nanofillers is difficult. The processability and performance of compounds containing plate- or tube-like silicates in a blend with conventional fillers, such as carbon black (CB), are investigated, and the effect of surface modification of the nanofillers is studied. Processing is facilitated by the replacement of CB by the nanofillers, but curing efficiency is reduced. The dispersion of the fillers is improved with the addition of nanofillers. The dynamic properties of the cured composite material are affected, giving the composite material lower hysteresis, while the mechanical properties are merely affected by the addition of nanofillers. Additionally, the filler–polymer interaction is increased. The addition of a compatibilizing and coupling agent, a silane, has only a minor effect and does not improve processing and properties significantly for these combined filler systems.

PREDICTION OF ROLLING RESISTANCE FOR TRUCK BUS RADIAL TIRES WITH NANOCOMPOSITE BASED TREAD COMPOUNDS USING FINITE ELEMENT SIMULATION

ABSTRACT Tire rolling resistance (RR) is a key performance index in the tire industry that addresses environmental concerns. Reduction of tire rolling resistance is a critical part of lowering fuel consumption, which could be achieved by changing both design and compound formulation. The major challenge is availability of a suitable software code to evaluate RR of tires using nonlinear viscoelastic properties of rubber. We developed a rolling resistance code and used it to predict rolling resistance of truck bus radial tires with nanocomposite based tread compounds. The energy dissipation in the tire is evaluated using the product of elastic strain energy and loss tangent of materials through post-processing using the rolling resistance code developed in this work. The elastic strain energy is obtained through steady state rolling simulation of tires using commercial software. The loss tangent versus strains at two reference temperatures is measured in the laboratory using a dynamic mechanical thermal analyzer. A temperature equation is developed to incorporate the effect of temperature on loss energy. Good correlation of rolling resistance is observed between simulation and experimental results. Nanocomposites used in this study are prepared based on natural rubber and polybutadiene rubber blends with either organoclay and carbon black or organoclay and silica dual filler system. Carboxylated nitrile rubber, a polar rubber, is used as a compatibilizer to facilitate the clay dispersion in the rubber matrix. Compared with general carbon black or silica tread compounds, substantial improvement of rolling resistance is predicted by finite element simulation with nanocomposite based tread compounds containing dual fillers.

Dual Filler Effect of Compatibilized Pure and Oil Extended Ethylene Propylene Diene Monomer Nanocomposites

Pure and oil extended ethylene propylene diene monomer nanocomposites were prepared using suitable compatibilizer. Since ethylene propylene diene monomer (EPDM) is non-polar, incorporation of organically modified nanoclay may not lead to better dispersion in the rubber matrix. Hence a polar rubber like epoxidized natural rubber (ENR) can be used as a compatibilizer for dispersing nanoclay in the EPDM matrix. ENR - organically modified nanoclay composites (EC) were prepared by solution mixing. The nanoclay used in this study is Cloisite 20A. ENR-nanoclay composites were incorporated in EPDM and oil-extended EPDM (OE-EPDM) matrices along with carbon black. The morphological studies prove that the nanoclay platelets get intercalated in ENR. Low loading of EC in EPDM and OE-EPDM matrices enhances the dispersion of nanoclay forming partially exfoliated platelets. Curing study shows improvement in torque and faster cure time for the compatibilized EPDM and OE-EPDM nanocomposites containing dual filler system compared to pure and single filler (carbon black) containing rubber compounds. Dynamic mechanical thermal analysis shows high storage modulus and lesser damping characteristics for the dual fillers containing EPDM and OE-EPDM compounds. The same compounds show tremendous improvement in mechanical properties. Scanning electron microscopic (SEM) images of tensile fractured single and dual filler containing rubber specimens show rough and tortuous path of fracture, which may be due to physical interaction between filler and rubber.

The Effects of Silica/Carbon Black Ratio on the Dynamic Properties of the Tread compounds in Truck Tires

NR is the major constituent in the rubber compound used for the tread on the truck tires. A general compound formulation of the tire tread includes NR and BR as polymer base and carbon black as the reinforcing filler, and curative components. In this paper the effects of dual filler system (carbon black and precipitated silica) on the dynamic properties of tire treat has been studied. The results show by increasing of precipitated silica, significant improvement was observed in fatigue resistance, rolling resistance and heat buildup of the tire. Tensile strength and modulus and wet grip of tire tread decrease with increasing of silica in rubber compound formulation.

Development of compatibilized SBR and EPR nanocomposites containing dual filler system

The study described in this paper is an analysis of the role of a compatibilizer for dispersing organically modified nanoclay in styrene butadiene rubber (SBR) and ethylene propylene rubber (EPR) matrices. The normal mixing of non-polar rubbers and organically modified nanoclay may not lead to improved distribution of the nanofiller in the rubbery matrix. Hence, a polar rubber such as epoxidized natural rubber (ENR) can be used as a compatibilizer for dispersing nanoclay in the non-polar rubber matrices. ENR–organically modified nanoclay composites (EC) were prepared by solution mixing. The nanoclay used in this study is Cloisite 20A. The obtained ENR–nanoclay composites were incorporated in SBR and EPR matrices along with carbon black. The morphological studies proved the intercalation of nanoclay platelets in ENR and further incorporation of EC in SBR and EPR matrices leads to partial exfoliation of nanoclay platelets. A curing study demonstrated faster scorch time, cure time and increased maximum torque for the compatibilized SBR and EPR nanocomposites containing a dual filler system compared to the control. Dynamic mechanical thermal analysis showed increase in storage modulus for the SBR and EPR compounds containing dual fillers compared to rubber compounds containing pure and single filler. The same compounds show substantial improvement in mechanical properties. The tensile fractured surface of the rubber compounds containing single and dual filler observed by scanning electron microscopy, (SEM) showed highly rough and irregular fracture paths, which proved the physical interaction between filler and rubber.

Production of carbon black/silica composite particles by adsorption of poly(vinyl pyrrolidone)

To reinforce the mechanical and electrical properties of materials, carbon black has been widely used as a filler in polymer industry because of its excellent properties such as heat, chemical, and weathering resistance, lightweight, electroconductivity, and low thermal expansion.1,2 The dispersibility of carbon black is important to show such abilities in organic solvents and polymer matrices. Therefore, many researches have been reported that the dispersibility of carbon black in solvents and polymer matrices is remarkably improved by grafting of polymers on the surface of carbon black.3,4 Silica offers a unique combination of tear strength, abrasion resistance, and aging resistance compared to carbon black.5 In tire treads, silica yields a lower rolling resistance at an equal wear resistance and wet grip than carbon black.6 Therefore, the use of a dual filler system separately composed of carbon black and silica in polymer matrices can give the benefits from each component.7 To the best of our knowledge, carbon black/silica hybrid composite particles have not prepared to date.