Organomodified montmorillonite as filler in natural and synthetic rubber

The filler action of dodecylamine (12C) intercalated montmorillonite (MNT) referred to as organomodified montmorillonite (12C-MNT) up to 4 wt % on natural rubber (NR) and styrene butadiene rubber (SBR) was studied and findings were compared with respect to the unmodified Na-MNT. X-ray analysis was used to calculate the interchain separation (R and R'), degree of crystallinity (X-c), and distortion factor (k). It is noted that R and R' showed the opposite trend, whereas X-c as well as k showed overall increasing trend with an increasing amount of 12C-MNT on both NR and SBR. For Na-MNT (1 wt %) filled NR and SBR, the corresponding magnitude of R and R ' and X-c showed nearly no change, whereas k, increased significantly. The crosslinking density (v(c)) does not show any significant changes in NR, whereas for SBR, it increases with increasing 12C-MNT as filler. Interestingly, in the case of 1 wt % pure Na-MNT used as filler for both NR and SBR, v(c) was lower compared to the virgin rubbers. Both swelling index (s(i)) and sol fraction (Q) do not show any significant variation for NR composites, whereas these decrease for SBR composites with increasing concentration of 12C-MNT filler. On the contrary, NR and SBR with 1 wt % of Na-MNT filler show greater magnitude of s(i) and Q corresponding to the pure ones. Measurements of mechanical properties showed a significant increase in tensile strength and elongation at break for NR-12C-MNT (4 wt %) when compared with either virgin NR. In addition, modulus at the elongation at 100 and 200% in general increases with increasing loading of 12C-MNT filler in NR. Similar observations were also noted in the case of SBR. Interestingly, when only pure Na-MNT is used as filler, the strength of NR and SBR decreases drastically. Scanning electron microscopic studies were also to used support the mechanical behavior of NR-12MNT and SBR-12CMNT composites. (C) 2004 Wiley Periodicals, Inc.