Influence of mixing procedures and mica addition on properties of NR/BR vulcanizates. I

Elastomeric compositions of natural rubber (NR) and polybutadiene rubber (BR) in a 1 : 1 ratio (w/w), with mica in the range 0-30 phr, were investigated. For all compositions the same formulation was used but two different additives incorporation sequences were followed. The results of the tests showed that the mechanical performance is sequence-dependent, as the two elastomers have very different rheometric characteristics. It was also observed that mica, when present in amounts of 20 and 30 phr, improves the mechanical properties. Scanning electron microscopy (SEM) permitted the observation of the fracture behavior of each composition, and dynamic mechanical thermal analysis (DMTA) suggested different migration tendencies of the additives in each phase, thus corroborating the differences found for the mechanical properties. (C) 2004 Wiley Periodicals, Inc.