## 4 Discussion  
The replacement of an equivalent amount of oil by resin in the CB-filled compounds, combined with the high temperature above the softening point of the resin generated during mixing, results in similar end torques. In the CB/SI- and SI-systems, the addition of resins imparts lower mixing torque than in the control (Figure 4). The temperature of silanization for both, the CB/SI- and SI-filled compound, was maintained at 150 \({}^{\circ}\)C, well above the softening points of the resins. Thus, the resins easily penetrate into the rubber matrix, decrease the intermolecular forces and facilitate filler incorporation and distribution into the rubber matrix. The amount of resin is equal to the amount of oil in the CB-filled compound, hence no significant difference in MV is observed depending on the addition of oil or resin. In CB/SI- and SI-filled compounds, the controls contain no oil, therefore they impart high MV (Figure 5). The silanization temperature of CB/SI- and SI materials was maintained at 150 \({}^{\circ}\)C, and at this temperature the resins were in liquid, viscous form. Therefore, they could easily penetrate between the polymer chains. The presence of low molecular weight molecules such as resins pushes the polymer chains apart and reduces the intermolecular force between rubber molecules, which increases the free volume and facilitates better filler dispersion, decreasing the MV. The results of MV (Figure 5) are in line with the results of the mixing curves: lower end torques for lower MV (Figure 4). The incorporation of the higher molecular weight resins instead of oil increases the cohesive strength, thus increases the force needed for separation (Figure 7a). CB-C shows a higher separation distance than CB-TP and CB-C9 (Figure 7b). This may be because both CB-C and the carcass compound contain CB and oil. The surface energies of these two materials will not differ much, thus readily promoting contact and inter-diffusion when brought into contact. The separation distance increases because these compounds are more sticky; however, the force needed for separation is low due to poor cohesive strength of the compound due to the oil. The separation distance of compounds containing resins in both, the CB/SI- and SI-filled systems, is the same as their respective controls. This is most probably due to the fact that all compounds containing silica with or without resins have to overcome the surface energy difference with the carcass material containing CB and oil. In order for the contact area to increase, for interdiffusion and for bonding between the two surfaces to take place, the material must overcome this surface energy barrier. Compounds which have different compositions might need more time, higher pressure or temperature to overcome the surface energy difference. The rheometer minimum torque S\({}_{\text{min}}\) bears a relation to the mixing torque at the end of the mixing process and the MV, as can be seen by comparison with the data presented in Figure 5. The maximum rheometer torque S\({}_{\text{max}}\) or better the torque difference S\({}_{\text{max}}\)-S\({}_{\text{min}}\) is often quoted as a measure for crosslink density. However, this is not quite right as the intrinsic viscoelastic rigidity of the compounds, determined by filler-filler and preferred filler-polymer interactions also contribute to the S\({}_{\text{max}}\). Thus, the lower the S\({}_{\text{min}}\) to start with, the lower the S\({}_{\text{max}}\) at equal crosslink density (Figure 8). The contributions of crosslink density and intrinsic viscoelastic rigidity cannot be separated in these curves. The S\({}_{\text{max}}\)-S\({}_{\text{min}}\) generally increases in the series of CB \(<\) CB/SI \(<\) SI, irrespective of whether the controls are compared or the TP or C9 variants. Furthermore, the TP and C9 compounds generally show a reduced S\({}_{\text{max}}\)-S\({}_{\text{min}}\) versus their controls (Table 7).