Impact of filler surface modification on large scale mechanics of styrene butadiene/silica rubber composites

摘要

In material science of elastomers the influence of nanoscale and nanostructured filler particles is of utmost significance for the performance of innovative rubber products, i.e., passenger car tires with ultralow rolling resistance but high wet-grip performance. A better understanding of the physical characteristics of the filler-rubber interface and the filler-rubber interphase as well is necessary to improve the overall macroscopic properties of these elastomeric nanocomposites. Therefore, the surface energies and polarities of filler particles with different modified surfaces were measured by a modified Wilhelmy technique. In all cases the rubber matrix consisted of a solution - styrene butadiene copolymers, filled with 20 or 40 phr pyrogenic or precipitated silica grades with different surface modifications by silanes, and a carbon black sample as reference. A moving die rheometer was employed to observe the filler flocculation at elevated temperatures (160 °C) in rubber mixtures containing no curatives. A significant influence of the surface energy of the filler was noticed: the flocculation tendency increased with increasing difference in work of adhesion between filler and rubber. In dynamic mechanical measurements the influence of the filler/filler and the filler/polymer interactions were studied in cured S-SBR samples. Amplitude sweep experiments were carried out to investigate the temperature dependent nonlinear characteristics of the elastic and viscous moduli, which is commonly associated with a progressive breakdown of the filler network at higher strain amplitudes (Payne effect). Static measurements and relaxations test were accomplished by large scale strain experiments. A structural-phenomenological modeling of the long strain mechanical properties of these rubber compounds was done: the "layered fiber model". This new model is based on the hypothesis that during deformation of the composites the polymer chains slipped off from the polymer interphase around the filler particles into the gaps between aggregates, where high-strength polymer fibers in an uniaxially oriented state are formed. We find new interesting correlations between the physicochemical properties of the filler/polymer interface and the macroscopic mechanical properties of the elastomeric materials.