Filled rubber compounds

Flow Singularities of Filled Rubber Compounds A Brief Overview.820... 

J.L. Leblanc and C. Barres, Bound Rubber A Key Factor in Understanding the Rheological Properties of Carbon Black Filled Rubber Compounds, Rub. Div. Mtg, ACS, Chicago, IL, April 13-16, 1999, p. 70. 

The interaction between two fillers particles can be investigated by measuring the Payne effect of a filled rubber compounds. In this measurement, dynamic properties are measured with strain sweep from a very small deformation to a high deformation. With the increased strain, the filler-filler network breaks and results in a lower storage modulus. This behavior is commonly known as the Payne effect... 

Chapman, A.V. Tinker, A.J. The effect of low molecular weight polybutadiene as processing aid on properties of silica-filled rubber compounds. Kautschuk Gummi K 2003, 56, 533. 

NOTE Plastic medical devices and/or containers may be depyrogenated by rinse processes, and/or high temperature moulding, and/or extrusion processes prior to filling. Rubber compound stoppers may be rendered pyrogen-free by multiple... 

Carbon-black-filled rubber compounds are usually produced on Banbury-type mixers, while conductive thermoplastics are preferably produced on twin-screw extruders. Unlike other filled compounds or polymer blends it is essential to adhere very precisely to the carbon-black concentration and the production parameters, since a very delicate balancing act is usually required to stay on the tight-rope of optimum composition and avoid falling into the pits of insufficient conductivity, inadequate mechanical properties or sharply increased viscosity. 

The attribution of the Payne effect to the filler network is strongly supported by the fact that carbon black pastes, made with carbon black and low molecular weight oils, present very similar G levels at very low shear strain (Payne, 1965). Obviously, when strain increases, G drops drastically for carbon black pastes and much more slowly for filled rubber compounds, because of the progressive desorption of elastomeric chains. 

The evolution of G and G" in the range of 0.1 to 0.5 strain amplitude is of major importance because this domain corresponds to the most common solicitations of filled rubber compounds, for example in tire tread applications [137]. 

Obviously, when strain increases, G drops drastically for carbon black pastes and much more slowly for filled rubber compounds, because of the progressive desorption of elastomeric chains. 

Combining silanes with silica led to high-performing silica-filled rubber compounds. Organofunctional silanes with polysulfane groups such as bis-(3-(triethoxysilyl)propyl)tetrasulfane (TESPT) and bis-(3-(triethoxysilyl)propyl)disulfane (TESPD) (Fig. 12) are utilized to improve dispersability of silica in the rubber matrix. 

Even though the final performances of the cured rubber compounds are very important, the process stability is also of great importance in manufacturing and cannot be neglected when choosing the silane structure. Figure 13 shows strain/modulus curves of three silica-filled rubber compounds using TESPT, TESPD, and mercaptopropyitriethoxysilane, respectively. 

In conclusion, it should be summarized that stearie is an important ingredient for rubber eompounds and blends. For almost 100 years it has eontinued to be the unique dispergator for carbon black filled rubber compounds. On the basis of measurements of the rheologieal properties of the rubber compounds and depending on the stearic acid in them, speeifying the optimal amount of the dispergator for the carbon black contained in the rubber... 

Dimitrov, R Sotirova, M Gegova, E. Electrical Conductivity -Criterion for Determination of the Optimum Time for Homogenization of Black-filled Rubber Compounds. Chem. Industry, 1971, Vol. 43, >fo2, 59 - 61 (in Bulgarian)... 

Zheleva D. An Attempt for Correlation between Mooney Viscosity and Rheological Properties of Filled Rubber Compounds. J. Chem. Technol. Metallurgy (UCTM), 2013, vol.48, JV23, 241 -246. 

H. D. Luginsland, J. Frohlich and A. Wehmeier, Influence of Different Silanes on the Reinforcement of Silica-filled Rubber Compounds, paper No. 59 presented at the ACS Meeting, Rhode Island/USA, April 24-27 Rhode Island/USA, 2001. 

A. Hasse, A. Wehmeier and H. D. Luginsland, Crosslinking and Reinforcement of Silica Silane-Filled Rubber Compounds, Rubber World Magazine s Electronic Publishing Division, Akron, Ohio, 2004. 

Micron-sized fillers, such as glass fibers, carbonfibers, carbon black, talc, and micronsized silica particles have been considered as conventional fillers. Polymer composites filled with conventional fillers have been widely investigated by both academic and industrial researchers. A wide spectrum of archival reports is available on how these fillers impact the properties. As expected, various fundamental issues of interest to nanocomposites research, such as the state of filler dispersion, filler-matrix interactions, and processing methods, have already been widely analyzed and documented in the context of conventional composites, especially those of carbon black and silica-filled rubber compounds [16], It is worth mentioning that carbon black (CB) could not be considered as a nanofiller. There appears to be a general tendency in contemporary literature to designate CB as a nanofiller - apparently derived from... 

AH, Z., Le, H.H., Ilisch, S., and Radusch, H.J. (2009) Morphology development in nanoclay filled rubber compounds and rubber blends detected by online measured electrical conductance. J. Mater. Sd., 44, 6427. 

Leblanc, J., A Molecular Explanation for the Origin of Bound Rubber in Carbon Black Filled Rubber Compounds J.Appl. Polym. Sci. 1997, 66, 2257-2268. 

With the advent of HDS, the ability to disperse silica to levels equal to that of carbon black is now possible for the creation of highly silica-filled rubber compounds. Thus, there has been a revolution in growing use of silica in place of carbon black in tires since the early 1990s, requiring growing use of specific coupling agents, whose number and chemistries have also expanded in this time period. A description of this class of rubber chemicals follows. 

To prepare filled rubber compounds and blends, rubbers were mixed with filler using an internal mixer. During the mixing time samples were taken out for further investigation. Used materials, formulations as well as mixing conditions will be given in details in each part later. 

The use of stearic acid as a modifier for silica and other fillers like CaCOs and Mg(OH)2 has been reported. The authors found that the presence of adsorbed stearic acid on the filler surface reduces the hydrophilicity of the silica surface and enhances the compatibility between filler and matrix, which may lead to an improvement in filler dispersion and the related mechanical performance of composites. Kosmalska et al also investigated the adsorption of DPG, ZnO and sulfur on the silica surface and reported that the bonding of DPG/ZnO and ZnO to silica causes a reduction in the surface energy of silica from 66 mN/m to 28.75 mN/m and 35.49 mN/m, respectively. A similar effect of ZnO on the surface tension of silica was also found by Laning et alP and Reuvekamp et al. The adsorption of that additive and its impact on the scorch time and reduction of the crosslink density in silica-filled rubber compounds have been frequently characterized. ... 

If heterogeneous polymer systems e.g. filled rubber compounds, are considered, then the volume fractions of ingredients further complicate the material functions, which must now be written as (restricted to the case of shear deformation) ... 

It has long been reported in literature [18, 19] that (carbon black) filled compounds are yield stress materials, i.e., when plotted versus the shear stress, the shear viscosity appears bounded by a critical shear stress Oc so that below it, no flow occurs (in other words, the viscosity goes to infinity as the shear stress decreases towards Oc). The right graph in Fig. 4 shows indeed that the shear viscosity q(o) increases, as the shear stress decreases, but one would hardly derive a bounding critical shear stress from such data. In other terms, that filled rubber compounds are essentially nonlinear viscoelastic materials is experimentally well demonstrated but that they are yield stress materials might be considered as a controversial subject. 

With either pure, unfilled elastomers or slightly filled rubber compounds (typically filler volume fraction lower than 10 %) however, a Unear viscoelastic region is observable within the experimental window of most dynamic rheometers providing the strain amplitude does not exceed 10—20 %. 

In principle, the time-temperature superposition principle applies only to materials that are said thermo-rheologically simple and therefore its use with filled rubber compounds should give poor results. As seen in Fig. 10, this is not the case and, in the author s experience, it is common observation that good mastercurves are obtained with many complex polymer materials through time-temperature superposition, providing experimental data are of quality. In this respect, closed-cavity rheometers offer obvious advantages over open-gap instruments. 

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