Rubber bound

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  

7 number of adsorbed segments per primary mass average molecule (the so-called adsorption index) 

Specific bound rubber, L, is another factor, Ifequcntly used in comparative studies  

It is a very convenient factor because it allows the amount of bound rubber and the available active surface to be related. 

In laboratory practice, a small sample of rubber is extracted with solvent (usually toluene) at room temperature for a specified period of time (1 week) and the percentage of bound rubber, Rb, is calculated from the equation  

There are several reactions postulated as being important in bound rubber besides physical adsorption. For example, mastication under shear causes degradation of organic polymer molecules with the formation of free radicals (Casale and Porter, 1971 Watson, 1955)  

The percentage of bound rubber increases with increasing unsaturation of the polymer. 

Attention is called to the following (1) The size of the carbon black particles is comparable to the size of the dispersed phase in the block-copolymer thermoplastic elastomers, and (2) the physical bonding/grafting combination between the rubber and the filler functionally resembles the 

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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... 

Although many interface models have been given so far, they are too qualitative and we can hardly connect them to the mechanics and mechanism of carbon black reinforcement of rubbers. On the other hand, many kinds of theories have also been proposed to explain the phenomena, but most of them deal only with a part of the phenomena and they could not totally answer the above four questions. The author has proposed a new interface model and theory to understand the mechanics and mechanism of carbon black reinforcement of rubbers based on the finite element method (FEM) stress analysis of the filled system, in journals and a book. In the new model and theory, the importance of carbon gel (bound rubber) in carbon black reinforcement of rubbers is emphasized repeatedly. Actually, it is not too much to say that the existence of bound rubber and its changeable and deformable characters depending on the magnitude of extension are the essence of carbon black reinforcement of rubbers. 

The new interface model and the concept for the carbon black reinforcement proposed by the author fundamentally combine the structure of the carbon gel (bound mbber) with the mechanical behavior of the filled system, based on the stress analysis (FEM). As shown in Figure 18.6, the new model has a double-layer stmcture of bound rubber, consisting of the inner polymer layer of the glassy state (glassy hard or GH layer) and the outer polymer layer (sticky hard or SH layer). Molecular motion is strictly constrained in the GH layer and considerably constrained in the SH layer compared with unfilled rubber vulcanizate. Figure 18.7 is the more detailed representation to show molecular packing in both layers according to their molecular mobility estimated from the pulsed-NMR measurement. 

It is not too much to say that the existence of bound rubber (SH layer) and its changeable and deformable characters depending on the magnitude of extension are the essence of carbon black reinforcement of rubbers. 

It is an unfortunate fact that several preexisting theories have tried to explain complicated mechanical phenomena of CB-reinforced rubbery materials but they have not been so successful." " However, a recent report might have a capability of explaining them collectively," when the author accepted the existence of the component whose molecular mobility is different from that of matrix mbber component in addition to the existence of well-known bound rubber component. The report described that this new component might be the most important factor to determine the reinforcement. These mbber components have been verified by spin-spin relaxation time 2 by pulsed nuclear magnetic resonance (NMR) technique, ° while the information obtained by NMR is qualitative and averaged over the sample and, therefore, lacking in the spatial... 

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. 

Most elastomers require reinforcing fillers to function effectively, and NMR has been used to characterize the structures of such composites as well. Examples are the adsorption of chains onto filler surfaces [275], the immobilization of these chains into "bound rubber" [276], and the imaging of the filler itself [277]. 

Bromo-2-nitropropane-l,3-diol, latex auxiliary. Bound Rubber... 

Bound rubber in an unvulcanised carbon black-rubber mix. It results from the production of free radicals in the mastication of rubber these radicals attach themselves chemically to the particles of carbon black and form a proportion of carbon gel which is insoluble in the usual rubber solvents. 

Chemically, a colloidal solution which has set to a jelly. The term has a special significance in rubber technology. See Bound Rubber, Carbon Gel. 

C. J. Carman We did try to look at the bound rubber. It turns out that there still is too much motion in such rubber to get cross polarization. You can see it by bound rubber measurements. On the time scale of this experiment it does not contribute to the spectrum. 

C. J. Carman Let me answer this way. We know there is bound rubber present using standard techniques. I have yet to see the bound rubber with the C NMR technique, is what I am saying. Area measurements of high resolution spectra do not give numbers for bound rubber that coincide with standard measurements. For this reason I am not convinced I have ever seen it with NMR. 

The dynamic response of polydimethylsiloxane (PDMS) reinforced with fused silica with and without surface treatment has been discussed in terms of interactions between the filler and polymer [54]. Since bound rubber measurements showed that PDMS chains were strongly attached to the silica surface, agglomeration due to direct contact between silica aggregates was considered an unlikely explanation for the marked increase in storage modulus seen with increasing filler content at low strains. Instead three types of flller-polymer-flller association were proposed which would cause agglomeration, as depicted in Fig. 15. 

The original coupling agents, which were called promotors, were used to ensure a good bond between rubber and the carbon black filler. These promotors increase the tensile strength, modulus, and the bound rubber (the insoluble mixture of filler and rubber) content of rubber. Although natural rubber is soluble in benzene, it becomes less soluble when carbon black or amorphous silica is added. 

Another attempt by Tricas et al. to modify the surface of carbon black was by the plasma polymerization of acrylic acid [34]. Treatment with acrylic acid made carbon black hydrophilic. Plasma-coated carbon black was mixed with natural rubber and showed increased filler-filler interaction. The bound rubber content was reduced after the surface treatment of the filler. The authors also concluded that the surface of the carbon black was completely covered by the plasma polymer film, preventing the carbon black surface from playing any role in the polymer matrix. 

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. 

Figure 18 shows the bound rubber content of samples filled with untreated silica, plasma-treated silicas, and silane-modified silica, as representative of the filler-polymer interactions. Samples SPTh and SPA show the highest bound rubber contents, and the ST the lowest value. The SPPy sample shows a bound rubber content slightly lower than that of SU. 

Fig. 18 Bound rubber content of untreated silica, PA-, PPy-, and PTh-silicas, and silane-modified silica in S-SBR...

In Fig. 23, the bound rubber values are shown of S-SBR/EPDM-blend samples filled with untreated silica, plasma-coated silicas, and silane-modified silica. The plasma-treated silicas show in all cases a significantly higher bound rubber content... 

The higher amounts of bound rubber for all samples filled with plasma-treated silica demonstrate an improved filler-polymer interaction between the plasma-treated silica and the polymers in the blend compared to untreated and silane-treated silica. The highest filler-polymer interaction for the PPy-silica can be due to the best compatibilization effect of PPy-silica with both polymers in the blend, as... 

For silica in SBR, a polyacetylene coating gives the lowest filler-filler interaction, a good filler-polymer interaction, and the best dispersion compared to untreated and the other plasma-treated samples. However, for the stress-strain properties, the polythiophene-treated sample gives the best results. This shows the importance of sulfur moieties on the surface of the filler, which form a secondary network in the cured materials. In the blend of S-SBR and EPDM rubbers, the situation is less conclusive. The Payne effect, the bound rubber, and... 

After a screening of the different parameters available for the characterization of reinforcing fillers, the nature of filler-elastomer interactions is examined (occluded and bound rubber). 

The latter can be of two types, either purely mechanical, and be associated with the occlusion of rubber into carbon black aggregates (occluded rubber), are more complex and involve physical and chemical interactions, they will then be related to bound rubber. 

Figure 10. Sketch of polymer chains in an elastomer constrained in the vicinity of a reinforcing filler particle. The constrained chains are arbitrarily shown by the heavier lines, and are referred to in the elastomer literature as bound rubber [233, 236-238].

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