Defining Key Factors in Carbon Black-Filled NR/BR Compounds for Balancing Aircraft Tire Tread Properties

Abstract

Carbon black (CB) is the most common reinforcing filler used in aircraft tire tread formulations. For CB-reinforced natural rubber/butadiene rubber (NR/BR) compounds, material and processing parameters are important factors that need to be controlled, as they can influence both, processing as well as the vulcanizate properties. It is essential to investigate and optimize the key elements, in order to achieve the target properties, while maintaining an acceptable trade-off for other characteristics. In the present study, the type of BR, mixer temperature, rotor speed, and filler mixing time were selected as input factors. A complete design of experiments (DOE) process was performed that comprised the following—two-level full factorial setup for initial screening, response surface method (RSM) for optimization, and confirmation runs for validation. This evaluation procedure was used to study the impact of factors and their interactions on the properties of CB-filled NR/BR compounds. From the DOE optimization which was later confirmed by the DOE validation, high rotor speed and long filler mixing time were the most significant factors in improving the Mooney viscosity, modulus at 300% elongation, hysteresis (tan delta), as well as in reducing the filler–filler interaction (Payne effect). In the case of tensile strength (TS) and abrasion resistance index (ARI), high rotor speed and long filler mixing time had an adverse effect, thus, causing a deterioration of these properties. Therefore, it is recommended to decrease the filler mixing time when combining it with high rotor speed.