The effects of certain recipe ingredients and mixing sequence on the rheology and processability of silica- and carbon black-filled tire compounds

The purpose of the work reported here was to study the Effects of curing ingredients, filler such as silica and its moisture content, mixing sequence, and mixing scheme on the rheology and the loss of processability of the tire compounds at different storage temperatures. Rheology was characterized over a wide range of shear rates. For the retardation of the development of pour processability during storage of the compound (assumed to be caused, at least in part, by filler particle reagglomeration and formation of bound rubber). the most effective ingredients are diphenylguanidine (DPG), polyethylene glycol (PEG) end cyclohexylbenzothiazolesulfenamide (CBS), the latter being even more effective if the storage temperature is not too high (e.g., lower than 70 degrees C). Two orders of mixing were considered: (i) Y-mixing (the mixing of a silica-filled masterbatch with a carbon black-filled masterbatch), and (ii) all-in-one mixing (the mixing of the rubbers and fillers all at the same time, in a single batch). We also observed that the Mooney peak (peak stress in low-strain-rate start-up flow) and extrudate roughness (indication of poor processability) increase much more slowly with storage time for the Y-mixed compound than it does for the all-in-one-mixed compounds. Also, a low moisture level in the silica leads to poor processability as does high-temperature heat treatment during the mixing stage.