Predicting the processability of silica-reinforced rubber compounds : Focus on extrusion behaviour

Rubber compounds must be processed sufficiently well in extrusion in order to produce high-quality tire components. However, due to the complex rheology of rubber compounds, they do not always process as desired in extrusion, which can result in poor-quality products. This thesis investigated which properties affect the processability of rubber compounds and which laboratory methods can be used to measure these properties. Once the properties affecting the processability have been identified and suitable laboratory methods for measuring them have been found, it will be easier to predict the extrusion behaviour of rubber compounds in advance. The study, conducted in collaboration with Nokian Tyres, examined the prediction of the processability of silica-reinforced rubber compounds, with a focus on the extrusion process. Laboratory measurements were performed on five silica rubber compounds (Compound 1-5), and the results were compared with the data obtained from production extrusion, which corresponded to the actual extrusion behaviour of the samples. The extrusion data obtained from production showed that there were clear differences in the processability of the samples. Compound 3 was the most processable, while Compound 5 was the least processable. According to the study, the complex viscosity and storage shear modulus results of the frequency sweep test performed with the Rubber Process Analyser (RPA) correlated well with the production extrusion data when the results were examined within a specific frequency range. Higher complex viscosity values were associated with higher storage shear modulus values, which means greater resistance to material flow. This, in turn, impairs the processability of the material in extrusion. In addition, the study identified methods that are not suitable for predicting the processability of silica compounds as such.