Bound rubber Compounds

Previous studies have demonstrated that QDI improves the formation of bound rubber. From the previous discussion of free-radical chemistry, the formation of bound mbber in butadiene elastomer compounds would be expected to occur at a higher rate than in NR. 

The compounds containing QDI (red lines) exhibit much lower viscosity than either the control compound (yellow hnes) or the compound containing the peptizer (blue hnes). The increase in the viscosity as high discharge temperatures are reached is attributed to an increase in bound rubber... 

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. 

Calcined clays are hard clays which have been heat treated to remove the combined water. The removal of any surface bound entity from the clay particles improves the capacity to improve the electrical resistance of rubber compounds. Calcinated clays also reduce compound water... 

Silica used as a filler for rubbers is silicon dioxide, with particle sizes in the range of 10-40 nm. The silica has a chemically bound water content of 25% with an additional level of 4-6% of adsorbed water. The surface of silica is strongly polar in nature, centring around the hydroxyl groups bound to the surface of the silica particles. In a similar fashion, other chemical groups can be adsorbed onto the filler surface. This adsorption strongly influences silica s behaviour within rubber compounds. The groups found on the surface of silicas are principally siloxanes, silanol and reaction products of the latter with various hydrous oxides. It is possible to modify the surface of the silica to improve its compatibility with a variety of rubbers. 

Bound rubber - The bound rubber content was measured with toluene as solvent [48,49]. The nonvulcanized samples (0.2 g) were cut into small pieces and put into a steel-wire basket of very fine mesh, which was immersed in 100 mL of toluene at room temperature for 72 h. The solvent was renewed after 24 h. The extracts were collected and left for 24 h in air and 24 h in vacuo at 105°C to evaporate the solvent. The amount of bound rubber (BdR) is expressed as the percentage of the total polymer content in the compound. 

The first is an EPDM fraction which is loosely bound to the carbon black due to adsorption interactions. This loosely bound rubber has numerous adsorption network junctions, similar to those in bound rubber. The second EPDM fraction, consisting of extractable rubber, contains a relatively small number of adsorption network junctions and can apparently be extracted from the compounds. The fraction of loosely bound EPDM chains determined with the aid of NMR increases with an increase in the maximum possible EPDM-carbon black contact area per unit volume of the elastomer, regardless the type of carbon black used, and is relatively close to the content of bound rubber [62]. 

Bound rubber is the fraction of polymer which is not extracted by a good solvent from a rubber-filler mix. It is a measure of rubber reinforcement as well as of filler activity towards the rubber. This concept was introduced in 1925 by Twiss. Although, the traditional term bound rubber is commonly used for rubber compounds, the concept can also be applied to other macromolecular materials. The amount of bound rubber is given by the following equations ... 

Diamine salts of fatty acids are used as multifunctional additives in natural rubber compounds filled with carbon black.They affect the elastomer-carbon black interface. With an increased concentration of multifunctional additive, the concentration of bound rubber decreases but dispersion of carbon black is improved. In silica filled rubber, multifunctional additive also improves the dispersion of silica, but in addition, it decreases the negative influence of silica filler on vulcanization rate. 

Rubber-bound intermediate compounds R-Sy-X, giving in turn ... 

Lablanc, J.L. and Hardy, P., Evolution of bound rubber during the storage of uncured compounds, Kautschuk-Gummi-Kunststoffe, AA, 1119-1124, 1991. 

Bound rubber determination is also applied to silica compounds, even if the numerous possible interactions naturally limit the interpretation of the values [127,128]. 

The basic requirement for the rubber compound is that it will meet the customer s requirements in terms of physical properties and service life. In reality it is necessary to look beyond these bounds. The manufacturer must consider a number of aspects before committing to produce any item. 

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. 

The filler localization experimentally determined by the use of our wetting concept is correlated to the wetting behaviour of rubber as follows the more the filler surface is wetted by a rubber phase, the more the filler is included and distributed in this phase. When filler is mixed with a single rubber, for instance SBR, a part of the rubber chains will be bonded to the active centres, which are available on the filler surface. If the rubber is extracted from the filled uncured rubber compound with a suitable solvent, the rubber molecules bound on the filler surface remain in the rubber-filler gel. In our concept, we are interested in the fraction of rubber in this rubber-filler gel. The wetting... 

The mass mi corresponds to the rubber compound before extracting, and it is the sum of the mass of the bonded rubber part Rf the mass of the soluble rubber part and filler, m2 is the mass of the rubber-filler gel, which is the sum of the bonded rubber part and filler, is the mass concentration of filler in the single rubber mixture or binary blends. 1 is the mixing time in an internal mixer. The difference between the terms rubber layer L and bound rubber, which has been commonly used in rubber technology, was discussed in our previous work. To understand the physical background of the rubber layer L, we correlated the wetting behaviour determined from our extraction experiment with the infiltration behaviour reported in the literature." In a capillary flow of a Newtonian fluid in a small gap between two parallel plates, the position x of the liquid-air interface at time t is given by Equation (6.27) ... 

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. 

Leblanc J. A molecular explanation for the origin of bound rubber in carbon black filled rubber compounds. J Appl Polym Sci 1997 66 2257-68. 

Some of the critical properties associated with SBRs that can relate to their performance in a rubber compound are the Mooney viscosity (ASTM D1646), which crudely relates to its average molecular weight, and the percent bound styrene contained in the polymer. Higher bound styrene can increase tire traction but decrease tire rolling resistance. The most common percent bound styrene level is 23.5%. 

ATH is a relatively inexpensive flame retardant and flller used by the rubber industry. ATH possesses bound water, which is released at higher temperatures to promote a degree of flame retardancy. It can release as much as 34% of its weight as water at elevated temperatures. To be effective, ATH must be used at signiflcantly high concentrations in a rubber compound. ATH grades used in rubber must have sufficiently fine particle size, so as not to degrade the cured physical properties of the rubber compounds. 

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