Silica Masterbatches Produced With Liquid Phase Mixing Part Iv. Volume Variation And Sem Observations Upon Stretching

The volume of vulcanizates changes slightly during stretching. Generally, dilatometry and hydrostatic weighing methods are used to measure volume change. Vacuole formation and polymer crystallization are the two main causes of the volume changes, and these are attributed to the separation of polymer from the filler surface and the alignment of polymer molecules, respectively. The relative volume change, Delta V/V, of four different vulcanizates based on a blend of SSBR (solution polymerized styrene-butadiene rubber) and BR (cis-polybutadiene rubber) has been plotted against elongation, epsilon. The relative volume change of an eco-visco-elastomer-composite (EVEC) compound produced by a continuous liquid phase mixing process was much less than that of a dry-mixed counterpart, especially after normalizing by stress, sigma. Scanning electron microscopy (SEM) was utilized to observe the emergence of vacuoles during stretching, and obtain information on their relative size and distribution without the need for replication or ion sputter coating. SEM images also showed that the dispersion of silica in EVEC is better and the number of vacuoles is much less than in the dry-mixed compounds, characterizing a "denser" vulcanizate.