We start with the control system of carbon black only. The effect
on the rubber (NBR) is very similar to that of silica, but very
different from that of PALF. Carbon black affects the stress at low
strain only slightly (see Fig. 2(b) and Fig. 4(a)). The effect becomes
more and more apparent at increasing strains. Consequently, the
greatest effect on stress is seen at the failure point. The tensile
strength of carbon black filled NBR seems to approach a limit after
addition of 20 phr (Fig. 5) while tear strengths increases with
increasing carbon black content (Fig. 9). Elongation at break is not
very much altered (Fig. 6).