Tire Tread Reinforcement with Short Aramid Fibers

Tensile testing on short fiber reinforced composites is helping to identify the advantages and disadvantages of different rubber compound

Factors Influencing Reinforcement of NR and EPDM Rubbers with Short Aramid Fibers

Among short fiber reinforced composites, those with rubbery matrices have gained great importance due to the advantages they have in processing and low cost, coupled with high strength. These composites combine the elastic behavior of rubbers with strength and stiffness of fibers. Reinforcement with short fibers offers additional features such as design flexibility, high modulus, tear strength, etc. The degree of reinforcement depends on parameters such as: the nature of the rubber matrix, the type of fibers, the concentration and orientation of fibers, fiber to rubber adhesion (generation of a strong interface), fiber length and aspect ratio of the fibers. In this research aramid fibers have been chosen because of their significantly higher modulus and strength, compared to other commercial fibers. Compounds based on NR and EPDM are prepared. Short aramid fibers with different kinds of surface treatments, standard finish and RFL-coating result in different rubber-fiber interfaces. The reinforcing effect of these short aramid fibers is characterized by mechanical and viscoelastic experiments, and by studying the fracture surfaces with microscopic techniques

Reinforcement of natural rubber by precipitated silica: the influence of processing temperature

The thermal history and in particular the mixing dump temperature is a parameter of paramount importance in mixing rubber and silica with a silane coupling agent in order to achieve proper silanization of silica and to avoid premature scorch reactions. In this work, the influence of mixing dump temperature on the performance of silica reinforced Natural Rubber (NR) is investigated. The investigation also includes the effect of non-rubber constituents, primarily proteins in NR, by using deproteinized Natural Rubber (DPNR) and synthetic polyisoprene (IR). The vulcanization properties and rubber-to-filler interactions of silica reinforced NR in presence and absence of a silane coupling agent are highlighted. With increasing mixing dump temperature, the silanization reaction between silica and silane coupling agent proceeds further. At sufficiently high dump temperature, filler-filler interactions in the NR-silica compounds are reduced and silica-rubber interaction improved as evidenced by a drop in the Payne effect and increment in chemically bound rubber. It is demonstrated that NR and IR compounds mixed till above the optimum dump temperature exhibit cure reversion and reduction in tensile properties. On the other hand, DPNR-silica vulcanizates show slightly more constant physical properties

Comparative investigation of the de-vulcanization parameters of tire rubbers

The optimal process conditions for a high ratio of de-vulcanization to\ud polymer degradation have been investigated for tire rubbers: SBR, BR, NR and CIIR. These polymers all show their own particular breakdown characteristics. The temperature dependence of the breakdown mechanism was investigated by measuring sol fractions and crosslink densities. For SBR and BR, the highest reduction in crosslink density was found at a temperature of 220°C, together with a moderate increase in sol content. According to the Horikx theory, which correlates sol fraction and decrease in crosslink density, this is the result of a high degree of crosslink scission. Higher process temperatures result in a lower decrease in crosslink density due to recombination of active chain fragments. NR and CIIR show different behaviour. Breakdown of NR in this temperature range results in an almost complete destruction of the polymer network; crosslink density is reduced to almost zero and the sol fraction is close to 100%. The same result is found for CIIR at higher temperatures.\ud Although different rubbers react via other de-vulcanization mechanisms, the best devulcanization conditions for whole passenger car tire material are optimized

The challenges of silica-silane reinforcement of natural rubber

In recent years, highly-dispersible silica has become the preferred alternative to carbon-black as reinforcing filler for low rolling-resistance tires. However, the application of this filler system is so far limited to passenger car tires, as their treads contain styrene butadiene rubber (SBR). In contrast to this, truck tires are mainly made from natural rubber (NR); this is the main application of the currently used 11 million tons of natural rubber. unfortunately, the combination of NR with silica and a coupling agent remains a challenge. Natural rubber is a durable, natural resource, but has the disadvantage of containing a variety of non-rubber components such as proteins. An in-rubber study of the interaction of silica with proteins present in natural rubber shows that the latter compete with the coupling agent during the silanization reaction; the presence of proteins makes the silane less efficient for improving dispersion and fillerpolymer coupling, and thus negatively influences the final properties of the rubber material. Furthermore, the protein\ud content influences the rheological properties as well as filler-filler and filler-polymer interactions. Stress strain properties also vary with protein content, as do dynamic properties. With high amounts of proteins present in NR, the interactions between proteins and silica are able to disrupt the silica-silica network and improve silica dispersion. High amounts of proteins reduce the thermal sensitivity of the filler-polymer network formation. The effect of proteins is most pronounced when no silane is used; however, proteins are not able to replace a coupling agent. In order to achieve a good balance of properties, the presence of a coupling agent is essential. Keywords: silica, silane, natural rubber, protein, rolling resistance

Contact mechanics and friction for transversely isotropic viscoelastic materials

Transversely isotropic materials are an unique group of materials whose properties are the same along two of the principal axes of a Cartesian coordinate system. Various natural and artificial materials behave effectively as transversely isotropic elastic solids. Several materials can be classified as transversely isotropic materials including crystals, rocks, piezoelectrics, some biological tissues such as muscles, skin, cartilage tissue or brainstem and fibrous composites. In this study, the theory of contact mechanics developed by Persson is extended in such a way that it can model the contact and friction of a transversely isotropic viscoelastic solid in contact with a rigid rough surface. Numerical results show that anisotropy should be taken into account when dealing with transversely isotropic materials. The hysteresis friction between a transversely isotropic viscoelastic rubber, reinforced unidirectionally by fibers and two rough counter surfaces are measured by a pin-on-disk setup. The experimental results validate the theory

Rezepturoptimierung für kieselsäureverstärkte Naturkautschukmischungen

The rubber formulation plays a significant role in the properties of NR compounds filled with silica. In this work, the influences of various silicas, silane coupling agents and diphenylguanidine (DPG) on the properties of compounds and vulcanizates, i. e. cure characteristics, Mooney viscosity, flocculation kinetics, bound rubber content, Payne effect, tan δ at 60 °C, tensile and tear properties are investigated. The results demonstrate that compound viscosity and curing behavior, as well as vulcanizate properties of the silica-filled NR are much improved by incorporating silane coupling agents. Bis-triethoxysilylpropyltetrasulfide (TESPT) clearly gives better overall properties than the disulfide-based silane (TESPD), except for scorch safety. DPG acts as a synergist to sulfenamide primary accelerators, as well as activator for the silanization reaction. Highly dispersible (HD) silicas can significantly enhance the degree of dispersion, and so lead to higher filler-rubber interaction. As a consequence, the HD silicas provide better dynamic and mechanical properties for filled NR vulcanizates compared to conventional (CV) counterparts. The optimal quantities of both, silane coupling agent and DPG, required in the formulation are correlated to the cetyl trimethylammonium bromide (CTAB) specific surface area of the silicas. Furthermore, the results reveal that the silica structure as characterized by the dibutylphthalate (DBP) adsorption also strongly influences the reinforcing efficienc