Elemental mapping in natural rubber latex films by electron energy loss spectroscopy associated with transmission electron microscopy.

Element distribution maps from Hevea brasiliensis natural rubber latex thin films were obtained, by electron energy-loss spectroscopic imaging in a low-energy (80 kV) transmission electron microscope. C, N, O, P, Na, Ca, Mg, Al, Si, and S maps are presented for latex fractionated by centrifugation, either followed by dialysis or not. Most elements forming non-carbon compounds are concentrated in small, electron-dense spots surrounded by a carbon-rich matrix of polymer, thus showing that the rubber is filled with small particles compatible with the polyisoprene matrix. Ca distribution is unique, since it closely parallels the C distribution, evidencing an important role for -COO(-)-Ca2+-COO- ionic bridges in the structure of natural rubber.