Syed K. Mowdood

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 poor 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) and cyclohexylbenzothiazolesulfenamide (CBS), the latter being even more effective if the storage temperature is not too high (e.g., lower than 70 °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.

Laser Mass Spectral Investigations of Rubber Compound Surface Species

Abstract Laser desorption mass spectrometry has proven a uniquely useful technique for the direct characterization of rubber-compound surface species. Mass spectra were obtained for intact molecular ions (M+) of organic chemical rubber additives such as the aromatic processing oil, and the aromatic antiozonant and antioxidants incorporated to protect the rubber. Molecular-weight information from the molecular ions and structural information from the fragmentation ions could be obtained without interference from the fragmentation peaks of the rubber backbone. Rubber compounding ingredients were also characterized by LDMS techniques. Differences in the structure of two carbon blacks were apparent, based upon the relative intensities of the various peaks present such as the significantly higher m/z 26 peak thought to be due to CN− compared to the m/z 24 peak thought to be due to C2−, and the peaks resulting from the presence of hydrogen atom(s) on the carbon clusters for the high NSA and DBPA black. Laser an...