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The stress-strain behavior of rubber compounds is one of the key items to determine its application performance, and the different service conditions, especially the strain rate, have variable requirements for the performance of rubber compounds. The influence of tension strain rate on the stress-strain behavior of styrene butadiene rubber (SBR) vulcanizates filled with 3 kinds of carbon black was investigated from the point of view of rubber reinforcement. It was found that the stress at a given elongation of any SBR vulcanizate increases with increasing strain rate, and the more reinforcing the carbon black, the higher increment rate the stresses. For any given SBR vulcanizate, the stress increment rate decreases with the increase in strain. As the strain exceeds the critical points, such as 300%, the effect of strain rate on the rate of stress increase is becoming equivalent and independent of carbon black grades. From a filler reinforcement point of view, the tensile modulus of filled vulcanizates in the plateau region is governed by the surface activity of the carbon black. In quasi-static tension test, the networking of carbon black in vulcanizate will be gradually broken with increasing strain, which the break-up is predominantly controlled by strain rather than strain rate. [ABSTRACT FROM AUTHOR]

The development of advanced polymer nanocomposites requires a strong filler-polymer interfacial interaction and an optimal filler nanodispersion. The incorporation of the clays into a polymer matrix frequently does not improve the composite mechanical properties, owing to both poor dispersion and macroscopic particle dimensions. In this work, pristine and organically-modified sepiolites (Sep) were structurally modified by an acid treatment, which provides nano-sized sepiolite (NS-Sep) fibers with reduced particle size and increased silanol groups on the surface layer. NS-Sep fibers were used to prepare styrene-butadiene rubber nanocomposites with enhanced mechanical properties. Dynamic-mechanical analysis of clay polymer nanocomposites demonstrated that the NS-Sep fibers provided an excellent balance between reinforcing and hysteretic behavior, compared to the large-sized pristine Sep and isotropic silica. This was related to the enhanced interfacial chemical interaction between NS-Sep and rubber, as well as to the size and self-assembly of anisotropic nanofibers to form filler network structures, as supported by transmission electron microscopy analysis. The preparation of nanocomposites, based on Sep nanofibers obtained by a simple and versatile acid treatment, can thus be considered an alternative approach for the designing of advanced clay polymer nanocomposites. [ABSTRACT FROM AUTHOR]

This work, conceived as a second step in the development of high-performance damping materials suitable for seismic application, describes the preparation and characterization of complex natural rubber-based composites containing hybrid nano- and conventional fillers. The cluster-cluster aggregation model was used to assess the apparent filler networking energy. The values obtained suggested that the presence of the hybrid nanofiller strengthens the filler networking. The same model was used to understand the mechanisms of energy dissipation. The damping coefficient was found to be in the sought range between 10% and 20% (at 0.5 Hz and high shear strain). [ABSTRACT FROM AUTHOR]

In this paper some new aspects to the hybrid nano-filler networking in elastomer matrix under dynamic mechanical loading conditions and some new methods to reveal a hybrid nano-filler synergy are applied and discussed. Electron spin resonance (ESR) spectra of the multi-walled carbon nanotubes (MWCNT) present in the natural rubber (NR) based nanocomposites were investigated and the dependence of the double integral of resonance spectra on the amount of expanded organically modified montmorillonite (EOMt) present in the NR was established. Its decrease with an increasing amount of EOMt confirmed the synergy between these two nano-fillers. DMA temperature sweep measurements were performed and the cluster-cluster aggregation (CCA) model was used to assess the apparent filler networking energy. The obtained results suggest that the presence of the EOMt above a critical amount strengthens the hybrid-filler networking. In order to investigate how different ratios of these two nano-fillers influence the strain dependency of the storage modulus, strain sweep measurements were performed in tensile mode, and the CCA-model was used to describe the Payne effect. [ABSTRACT FROM AUTHOR]

Montmorillonite with dimethyl di(hydrogenatedtalloyl) ammonium as the compensating cation was added to a silica based elastomeric composite and the hybrid filler system led to reduction of filler networking phenomenon, better stability of elastic modulus with temperature, enhancement of stresses at all elongations, improvement of ultimate properties. This composite was based on a blend of natural rubber, poly(1,4- cis- isoprene) and poly(styrene- co -butadiene) from anionic polymerization and contained 70 parts per hundred rubber (phr) of silica. The organically modified clay (OC) was below the threshold required to establish an hybrid OC-silica filler network. Such threshold (about 7 phr) was estimated by preparing silica based nanocomposites containing various amounts of OC and determining shear storage and loss moduli as a function of strain amplitude. This work demonstrates that exfoliated OC favour lower dissipation of energy of silica based elastomeric composites under dynamic mechanical stresses and paves the way for further large scale applications. [ABSTRACT FROM AUTHOR]

This work describes the preparation and characterization of complex natural rubber (NR) based composites containing hybrid nano- and conventional fillers intended for base seismic application. Thorough rheometric and dynamic mechanical analyses in strain sweep mode at 2 Hz and 10 Hz (two frequencies laying in the range 0 - 15 Hz in which most of the earthquakes have the dominant frequencies) were performed on complex natural rubber (NR) based composites containing hybrid nanofiller (carbon nanotubes, expanded montmorillonite) and different amounts of conventional fillers like carbon black (CB) and silica. The rheometric studies showed that the influence of the combination of the different fillers on curing parameters is quite complex, but mainly the introduction of the fillers reduces the scorch and optimum cure time of the compounds. The dynamic mechanical analysis showed a pronounced non-linear strain dependence of the storage modulus and a remarkable increase of the loss factor tanδ for all composites, especially for those containing high CB content, compared to the NR-gum. To describe this strain-dependency of the storage modulus the cluster-cluster aggregation (CCA) model was used. The values of the fitting parameters ΔE'0, γc, and E'∞ calculated by this model show that they are affected by the type of the fillers present in the NR matrix and also by the applied frequency. [ABSTRACT FROM AUTHOR]

Abstract: Synergistic effects between a montmorillonite (Mt), modified with an organophilic ammonium as the compensating cation (OMt), and carbon black (CB) are reported in the literature. This work proposes the pronounced interaction between the organophilic ammonium cation and CB as a phenomenon at the origin of the synergism. A nanocomposite based on poly(1,4-cis-isoprene) containing both CB and OMt, formed in situ through the reaction between Mt and di(hydrogenated tallow)-dimethylammonium chloride (2HTCl), was prepared. Moreover, nanocomposites containing only CB in the presence and in the absence of 2HTCl were comparatively prepared and analysed. Synergism between OMt and CB was investigated by studying the filler networking process in the PI matrix through dynamic-mechanical tests and by assessing the nanocomposite structure by transmission electron microscopy analysis. It was found that 2HTCl promoted a pronounced enhancement of the non linear dynamic-mechanical behaviour of the nanocomposite material, with a much improved CB dispersion and a remarkable reduction of bound rubber. These effects were reduced in the presence of Mt, that involved the ammonium salt in the formation of OMt. The amount of 2HTCl required to achieve the largest non linear behaviour and the lowest bound rubber was calculated to correspond to a monolayer of the ammonium salt on the carbon black surface. [Copyright &y& Elsevier]

The specific role of filler networking of natural rubber compounds filled with carbon black N330 and modified carbon black (MCB) on viscoelastic properties and reinforcement was investigated. The MCB was prepared by adding special butadiene-vinylpyridine latex to N330. The effects of this filler surface treatment on the viscoelastic properties were systematically studied at equal filler loadings. The viscoelastic properties were assessed for both uncured and vulcanized compounds and were studied over a wide range of temperatures and strains. The results show that MCB can effectively enhance the filler-elastomer interaction and weaken the filler-filler interaction, thus improving the viscoelastic properties and reinforcement. [ABSTRACT FROM AUTHOR]

The effect of polymer-filler interaction on interphase dynamics between filler particles in elastomer nanocomposites and the mechanisms of rubber reinforcement by carbon black (CB) are investigated with different techniques. To determine how polymer-filler interface influences the properties of the system, CB black was modified with the ionic liquid (IL) 1-allyl-3-methylimidazolium chloride (AMIC) and mixed with different, more or less, polar elastomers. For typical diene-elastomers (EPDM, SBR), this modification leads to a decreased polymer-filler coupling strength due to the coverage of active sites at the CB surface by AMIC. This is demonstrated by evaluating the energy site distribution from static gas adsorption isotherms with the polymer analogues gas 1-Butene. However, an improvement of polymer filler coupling was determined in the case of saturated, polar rubbers (HNBR) due to attractive dipolar interactions between the polar units of the polymer and the strongly adsorbed IL at the CB surface. The different couplings affect the polymer-filler interphase dynamics between filler particles, which determines the properties of the filler network and filler-filler bonds. To describe the effect of CB surface modification quantitatively, the Dynamic Flocculation Model (DFM) has been used to calculate polymer- and filler-specific material parameters from cyclic stress-strain measurements. The fitted data deliver a coherent picture of filler-filler- and polymer-filler couplings showing a characteristic dependence on rubber polarity. A confirmation of the effect of surface modification on the strength of filler-filler bonds is obtained by nonequilibrium molecular dynamics (MD) simulations of bond rupture under tension. They also provide indications for a glassy-like behavior of strongly confined polymer layers between attractive walls. [ABSTRACT FROM AUTHOR]