Effect of Mixing Equipment Scale-up on the Rubber Compound Properties

Development of the rubber compounds is started commonly in laboratory scale. Bringing the compounding process to the production scale requires successful scale-up. Various scale-up approaches have been suggested in the literature, but the studies have mainly focused on carbon black reinforced rubber compounds. This thesis covers a study of effect of time-temperature-and power peak-based scale-up on the properties of a silica reinforced compound. Initial small- and large-scale mixing programs were compared. Mixing programs differed from feeding orders, temperature profiles, total amount of revolutions, and mixing times. The biggest differences were at the first stage of the mixing programs. Differences in the mixing programs resulted in differences in Mooney viscosities, mechanical properties, and dynamic mechanical properties. Mixing programs were unified to study the effect of the mixer size on the compound properties. Unifications were done first by unifying the feeding orders of the mixers and second by unifying the temperature profiles. Time-temperature based upscaling was studied in three different mixer sizes: small (1.5 l), medium (45 l), and large (320 l). Mixing programs of the small- and medium-scale mixers were modified the way that their time-temperature profiles corresponded to the time-temperature profile of the large-scale mixer. Targeted time-temperature profile was obtained by increasing the TCU temperatures and rotor speeds along the decreasing mixer size. Mixing program changes increased the total amount of revolutions and silanisation time. This was reflected to the compound properties. Mooney viscosity, ΔG*, and dynamic mechanical properties decreased by decreasing mixer size. Effect of the scale-up on the mechanical properties was not that clear. Anyhow, it was seen that Mod10 was significantly higher in case of the large-scale mixer, whereas Mod300/Mod100 was higher and elongation at break lower in the case of the small-scale mixer. Results suggested that the increase in the total revolutions and in silanisation times resulted in better dispersion and higher degree of silanisation, which furthermore caused differences in the properties of the compounds. Power peak-based upscaling was studied as an alternative to time-temperature-based upscaling. Mixing programs used in the time-temperature-based upscaling were modified so that the mixing time after passing the last power peak was constant in all the mixer sizes. Consequently, the mixing program was terminated the earlier the smaller was the mixer. The total amount of revolutions and silanisation times were more uniform between different mixer sizes than in the time-temperature based upscaling. Changes in the total amount of revolutions and silanisation times reflected to the compound properties. Mooney viscosity, ΔG*, dispersion, dynamic mechanical properties, and Mod300/Mod100 were more uniform than when the mixing process was upscaled based on the time-temperature profile. Power peak-based scale-up was seen as better option for mixing program scale-up than time-temperature-based scale-up