The raw materials were mixed for 10 minutes at 50 °C and a rotor speed of 50 rpm in a Haake Rheomix 600p (Thermo Scientific, Germany) lab-scale internal mixer to a fill factor of 0.7. The mixed compounds were cross-linked into 2 mm thick plates on a hydraulic press based on their 90 % curing times (t90) of 4, 8, and 22 minutes for NR, SBR, and the blend, respectively, obtained according to DIN 53529 on an Elastograph MDR (Göttfert, Germany) moving-die rheometer. For comparative studies, pristine polymers with similar thermal histories were also prepared.